Split (1)

train · 28.6k rows

id stringlengths 11 24	title stringlengths 1 59	context stringlengths 151 10k	language stringclasses 2 values	answer_text stringlengths 1 239 ⌀	answer_start float64 0 2.66k ⌀	__index_level_0__ int64 0 191k	question listlengths 1 30	negative_samples listlengths 1 30
5a6bb9624eec6b001a80a538	Myocardial_infarction	People with an acute coronary syndrome where no ST elevation is demonstrated (non-ST elevation ACS or NSTEACS) are treated with aspirin. Clopidogrel is added in many cases, particularly if the risk of cardiovascular events is felt to be high and early PCI is being considered. Depending on whether early PCI is planned, a factor Xa inhibitor or a potentiator of antithrombin (fondaparinux or low molecular weight heparin respectively) may be added. In very high-risk scenarios, inhibitors of the platelet glycoprotein αIIbβ3a receptor such as eptifibatide or tirofiban may be used.	en	null	null	190,556	[ "When is clopidogrel removed?", "What is NSTEACS an abbreviation for?", "Clopidogrel is a form of what inhibitor?", "What inhibitors are used in low-risk scenarios?", "Eptifibatide has what kind of molecular weight?" ]	[ [ "Verdigris is made by placing a plate or blade of copper, brass or bronze, slightly warmed, into a vat of fermenting wine, leaving it there for several weeks, and then scraping off and drying the green powder that forms on the metal. The process of making verdigris was described in ancient times by Pliny. It was used by the Romans in the murals of Pompeii, and in Celtic medieval manuscripts as early as the 5th century AD. It produced a blue-green which no other pigment could imitate, but it had drawbacks; it was unstable, it could not resist dampness, it did not mix well with other colors, it could ruin other colors with which it came into contact., and it was toxic. Leonardo da Vinci, in his treatise on painting, warned artists not to use it. It was widely used in miniature paintings in Europe and Persia in the 16th and 17th centuries. Its use largely ended in the late 19th century, when it was replaced by the safer and more stable chrome green. Viridian, also called chrome green, is a pigment made with chromium oxide dihydrate, was patented in 1859. It became popular with painters, since, unlike other synthetic greens, it was stable and not toxic. Vincent van Gogh used it, along with Prussian blue, to create a dark blue sky with a greenish tint in his painting Cafe terrace at night.", "천연두는 종두가 실시된 후, 1977년 소말리아의 마지막 환자를 끝으로 WHO가 공식적으로 박멸한 것으로 선언한 바이러스 전염병이다. 옛날 조선에서는 ‘마마’, ‘두창’이라고 불리었으며, 1879년에 지석영이 이를 퇴치하기 위해 종두를 처음으로 주사하였다. ‘백신’의 보급으로 완전히 박멸된 첫 번째 전염병이다. 두창은 발열, 수포, 농포성의 병적인 피부 변화를 특징으로 하는 급성 질환으로, 두창 바이러스에 의해 발생한다. 사망률이 매우 높은 감염질환으로, 한 때 우리나라를 포함하여 전세계 전체 사망 원인의 10%를 차지하기도 하였다. 1979년에 전 세계적으로 두창은 사라진 질병으로 선언되었고, 현재까지 자연적인 질병의 발생은 보고된 바가 없다. 1980년 이후로 대한민국의 모든 의과대학에서도 배우지 않는다. 두창은 천연두 혹은 우두에 걸리면 예방이 되나, 우두 백신을 맞아 예방할 수 있다. 그러나 현재는 그 백신을 쓰지않는다.그러나 두창 바이러스가 생물 테러무기로 이용될 가능성이 알려지면서 최근 다시 관심이 모이고 있는 질환이다. 현재 천연두 바이러스를 연구하기 위해 남긴 실험용 샘플을 완전 폐기할 것인가 말 것인가를 두고 논란 중이다. 연구를 위해 샘플을 남겨두자는 측과 혹시라도 다시 밖으로 유출되어 문제를 일으킬 수도 있다는 주장이 맞서고 있다. 일부 국가에서는 천연두 바이러스를 생화학 무기에 이용하기 위해 연구중이라는 소문도 있었다. 흔히 말하는 곰보 자국을 남기는 질병이며, 치사율이 95%로 매우 높았다.", "태어나서부터 첫 월경까지의 시간 중에 여성할례를 받게 되지만 대부분 4-8세에 여성성기절제술을 받게 된다. 여성 성기의 절제 순서의 실제 방법은 인종 집단과 도시 그리고 농촌지역 등에 따라 다양한 절차들이 있다. 사회 경제적 상태에 따라서도 다르게 나타난다.도시 지역에서는 병원에서도 이루어지며 전문의들이 담당하기도 하지만 이 시술은 주로 나이 많은 여성이나 조산자, 산파들이 행한다. 마취 없이 시술되는 경우가 많다.소녀들의 비명 소리가 들리지 않도록, 할례 의식은 동 트기 직전에 거행된다. 소녀들은 나이든 여자들에 의해 움직일 수 없게 평평한 곳에 눕혀져 시술을 받게 된다.도구는 사용 전후에 소독되지 않는 경우가 많으며 면도날, 칼, 가위, 깨진 유리 조각, 날카로운 돌 등이 도구로 사용된다. 어떤 지역에서는 이빨을 사용하기도 한다.특히 봉쇄술의 경우에는 아카시아 나무의 가시로 살에 구멍을 여러 개 뚫어 그 구멍을 희고 질긴 실로 꿰맨다. 여성 성기 절제 시술이 끝나면 다리를 움직이지 못하도록 발목에서 골반까지 천으로 꽁꽁 묶어 놓는다.상처가 어느 정도 회복이 될 때까지 집에서 떨어져 작은 움막에서 지내게 된다. 상처가 아물 때까지 다리는 계속 묶여 있게 된다. 이 절차는 소녀에게 여러 부작용을 가져오며 죽음을 초래하기도 한다. 또한 사망하지 않는다 하더라도 다량의 출혈, 패혈증, 파상풍, 쇼크, 고통, 감염, 요폐(Urine retention), 인근 조직의 상처 등이 생기며 HIV의 잠재적인 감염통로가 될 수 있다.", "이통의 조절은 항생제 사용과 더불어 주된 약물 치료로, 아세트아미노펜이나 이부프로펜을 주로 사용한다. 또 고막에 벤조카인 마취 이용액을 사용할 수도 있으며, 통증과 세균 배양을 목적으로 고막절개를 시행하기도 한다. 고막 절개 후 또는 고막의 천공으로 이루가 있을 때는 국소 항생제 이용액이 도움이 된다. 고막의 발적, 팽륜이 있고, 계속해서 심한 이통이나 두통, 고열이 있을 때, 유아가 뇌전증 발작을 할 때 고막 절개를 하면 증상을 급속히 호전시킬 수 있으며, 레이저 고막 절개가 안전한 방법으로 사용된다. 전신 상태가 불량하거나 항생제 치료에 반응이 없을 때, 두개 내 합병증이 있을 때는 고막 절개 또는 고막 천자(穿刺)를 통해 세균배양검사와 항생제 감수성 검사를 시행하여 적절한 항생제를 선택하여 치료하는 것이 필수적이다." ], [ "남 네바다 지역 교통위원회(Regional Transportation Commission of Southern Nevada: RTC )에서 관리하는 RTC 트랜싯(Transit) 버스는 총49개의 노선으로 라스베이거스 주변 지역의 대중교통 서비스를 하고 있다. 대부분의 노선 운행은 아침 5:30 a.m.부터 밤 1:30 a.m.까지지만 일부 노선은 24시간 운행한다. 관광객이 가장 많이 다니는 스트립(Strip)과 다운타운을 다니는 버스로 듀스(Deuce) 버스와 준 급행 SDX버스가 있다. 듀스버스는 2층버스이고 노선이 스트립과 다운타운 두곳을 다니는 이유로 \"2\"자를 강조해서 듀스(Deuce) 버스라고 이름지었다. SDX버스는 같은 노선이면서 정거장을 줄여서 준급행(Express)으로 운영하는 버스인데 스트립과 다운타운의 첫글자를 따서 이름을 SDX(Strip Downtown Express)라고 지었다. 이 버스는 버스표를 점검하는 사람이 없이 전적으로 승객이 자율적으로 표를 산것으로 믿고 운행한다. 두 버스 모두 매 15분 간격으로 운행한다. 이 버스는 다른 버스와 달리 일회승차권을 쓰지않고 시간별로 계산하는 방식을 쓰고 있다. 요금은 2시간 동안 사용하는 표가 $6이며 24시간 쓸수 있는 표는 $8이다. 위의 두 버스외에 어떤 다른 일반 RTC트랜싯 버스라도 정해진 시간 이내에는 반복해서 승차할 수 있다.", "Working closely in conjunction with the definition of the Near East provided by the State Department is the Near East South Asia Center for Strategic Studies (NESA), an educational institution of the United States Department of Defense. It teaches courses and holds seminars and workshops for government officials and military officers who will work or are working within its region. As the name indicates, that region is a combination of State Department regions; however, NESA is careful to identify the State Department region. As its Near East is not different from the State Department's it does not appear in the table. Its name, however, is not entirely accurate. For example, its region includes Mauritania, a member of the State Department's Africa (Sub-Sahara).", "Under these complex circumstances regional names are less useful. They are more historical than an accurate gauge of operations. The Directorate of Intelligence, one of four directorates into which the CIA is divided, includes the Office of Near Eastern and South Asian Analysis (NESA). Its duties are defined as \"support on Middle Eastern and North African countries, as well as on the South Asian nations of India, Pakistan, and Afghanistan.\" The total range of countries is in fact the same as the State Department's Near East, but the names do not correspond. The Near East of the NESA is the same as the Middle East defined in the CIA-published on-line resource, The World Factbook. Its list of countries is limited by the Red Sea, comprises the entire eastern coast of the Mediterranean, including Israel, Turkey, the small nations of the Caucasus, Iran and the states of the Arabian Peninsula.", "유럽의 융합과학은 CTEKS로 불린다. 이는 유럽의 지식사회를 위한 융합과학의 줄임말로 나노과학, 생명과학, 정보과학, 인지과학, 사회과학, 인류학, 철학, 지리학, 환경과학, 거시-미시세계의 보다 폭넓은 융합을 다룬다. 특히, 유럽공동체의 융합과학은 미국이 제시한 NBIC 융합과학기술에 사회과학적인 측면을 더하였으며 이러한 면을 강조한다. 즉, 지리학, 환경과학, 철학 등 사회 과학기술을 추가하여 융합과학기술의 개념을 더 확장시켰다. 앞으로 미래 사회는 사회학, 동물생태학, 언어학, 경제학, 정치학, 조직행동학과 같은 사회적인 측면과 테크놀로지디자인과학, 인간공학, 생물공학과 같은 공학적인 측면이 더욱 더 강조될 것으로 보인다." ], [ "조현병 치료제 중 일본 오츠카제약이 개발한 아리피프라졸(aripiprazole) 성분의 도파민 부분 효능제인 '아빌리파이'가 체중 증가 및 추체 외로 장애 등 운동 및 대사 장애의 부작용이 적은 효과적인 조현병 치료제로, 조현병(정신분열병)을 비롯한 양극성 장애의 급성 조증에도 효과를 나타내어 정신 질환의 광범위한 치료가 가능하다. 아리피프라졸을 비롯한 그 외에도 영국 아스트라제네카사의 조현병 치료제 '쎄로켈 XR(푸마르산 쿠에티아핀 서방형 제제)'(푸마르산 쿠에티아핀, quetiapine extended-release)도 성인의 우울증 치료를 위한 주요 우울 장애 치료의 부가 요법제로 승인을 얻었다. 이 외에도 올란자핀(olanzapine), 아미설프라이드(amisulpride), 지프라시돈(ziprasidone) 제제 등이 우울 증상의 부가 요법제로 쓰일 수 있다.", "비정형적 제제가 상당한 체중 증가, 당뇨 및 대사 증후군등 추체 외로계 장애의 위험을 증가시키는 것과 관련되어 있는 반면 정형적 제제는 추체외로 증상(EPS)을 야기할 확률이 높다. 영국 아스트라제네카사의 조현병 치료제 '쎄로켈(푸마르산 쿠에티아핀)'이나 일본 오츠카사의 조현병 치료제 '아빌리파이(아리피프라졸)' 등 일부 비정형적 제제는 정형적 제제인 페르페나진에 비해 자살 위험성이 내재되어 있으므로, 성인의 우을증 치료를 위한 주요 우울 장애 치료의 부가 요법제로 승인되어, 자살 목적 등 과량 투여의 위험을 막기 위해 최소량부터 처방 하도록 경고 하고 있지만, 클로자핀은 자살위험성이 가장 낮은 약물이다. 가장 최근에 출시된 약물 중, 3세대 비정형 조현병 치료제인 아리피프라졸(아빌리파이)은 일본 오츠카사가 개발한 도파민 부분 효능제로, 조현병의 양성 및 음성 증상을 동시에 개선시켜 주는 효과가 있지만, 심각한 신경학적 장애인 신경이완제 악성 증후군을 발생시킬 가능성이 낮은지는 명확하지 않다.", "In the 2010s, American jurisdictions have experienced a shortage of lethal injection drugs, due to anti-death penalty advocacy and low production volume. Hospira, the only U.S. manufacturer of sodium thiopental, stopped making the drug in 2011. The European Union has outlawed the export of any product that could be used in an execution; this has prevented executioners from using EU-manufactured anesthetics like propofol which are needed for general medical purposes. Another alternative, pentobarbital, is also only manufactured in the European Union, which has caused the Danish producer to restrict distribution to U.S. government customers.", "사용된 CNS(중추 신경계) 의약품 중에서 향정신성 불면증 치료제인 '스틸녹스(졸피뎀)'는 4200개 사용되었다. 육군 중에서 1군과 2군, 그리고 해군과 공군은 불면증 치료제 사용 실적이 전혀 없었고 3군은 알 수 없는 불면증 치료제 사용이 나왔다. 향정신성의약품이란 마약류관리법에 따라 마약, 대마와 함께 '마약류'로 분류되며, 인간의 중추신경계에 작용하는 것으로서 오용 또는 남용할 경우 인체에 현저한 위해가 있다고 인정되는 의약품이다. 식약처는 '스틸녹스(졸피뎀)'를 복용하면, 우울증 환자의 자살 충동, 환각, 괴기한 행동 등의 부작용이 나타날 수 있다고 경고하고 있다. '스틸녹스(졸피뎀)'는 오남용 등 우려의 소지가 있는 불면증 치료제로, 신중하게 사용해야 할 마약류관리에 관한 법률에 따른 향정신성의약품인 것이다." ], [ "A 2009 Cochrane review concluded that thiazide antihypertensive drugs reduce the risk of death (RR 0.89), stroke (RR 0.63), coronary heart disease (RR 0.84), and cardiovascular events (RR 0.70) in people with high blood pressure. In the ensuring years other classes of antihypertensive drug were developed and found wide acceptance in combination therapy, including loop diuretics (Lasix/furosemide, Hoechst Pharmaceuticals, 1963), beta blockers (ICI Pharmaceuticals, 1964) ACE inhibitors, and angiotensin receptor blockers. ACE inhibitors reduce the risk of new onset kidney disease [RR 0.71] and death [RR 0.84] in diabetic patients, irrespective of whether they have hypertension.", "신경독소는 활동전위를 차단하는 물질로, 자연계에 존재하기도 하고 합성되기도 한다. 복어의 테트로도톡신과 와편모충류에 속하는 적조 Gonyaulax속의 색시톡신은 전압 민감성 나트륨 채널을 저해하여 활동전위를 차단한다. 아프리카산 독사 맘바의 덴드로톡신도 전압 민감성 칼륨 채널을 차단한다. 이온 채널의 저해제는 특정한 이온 채널을 차단하여 다른 채널의 역할을 따로 연구하는 데에 쓰인다. 이온 채널을 친화성 크로마토그래피로 분리 정제할 때에도 유용하다. 저해제는 효과적인 신경독소로 작용할 수도 있어 화학 무기로 쓰일 가능성이 있다. 곤충의 이온 채널을 표적으로 삼는 신경독소는 효율적인 살충제이다. 합성 퍼메트린(permethrin)은 활동전위에 관여하는 나트륨 채널의 활성을 연장시킨다. 곤충의 이온 채널은 사람의 것과 충분히 다르기 때문에 사람에게 부작용은 거의 없다. 다른 신경독소 중에는 시냅스, 특히 신경근육 이음부에서 활동전위가 전달되는 것을 방해하는 것도 있다.", "Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects. Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints.", "Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen should be used in those with low oxygen levels or shortness of breath. In ST elevation MIs treatments which attempt to restore blood flow to the heart are typically recommended and include angioplasty, where the arteries are pushed open, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use angioplasty in those at high risk. In people with blockages of multiple coronary arteries and diabetes, bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers, and statins, are typically recommended." ], [ "해달은 해양 포유류로서는 가장 작은 종 중 하나이지만, 족제비과 동물 중에서는 가장 무거운 축에 든다. 수컷 해달의 체중은 22 킬로그램 ~ 45 킬로그램(49 파운드 ~ 99 파운드) 정도이며, 신장은 1.2 미터 ~ 1.55 미터(3 피트 10 인치 ~ 4 피트 10 인치) 정도인데, 체중 54 킬로그램(120 파운드)까지 나가는 표본이 기록된 바 있다. 암컷은 그것보다 작아서, 체중은 14 킬로그램 ~ 33 킬로그램(31 파운드 ~ 73 파운드), 신장 1.0 미터 ~ 1.4 미터(3 피트 3 인치 ~ 4 피트 7 인치) 정도이다. 해달의 음경골은 수컷의 경우 매우 크고 묵직하며 위쪽으로 굽어 있다. 그 길이는 150 밀리미터(5.9 인치), 음경골 뿌리는 15 밀리미터(0.59 인치) 정도이다.", "Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 7000100794000000000♠1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note 1] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.", "한편 세월호에 얼마 전까지 근무했던 기관사는 먼저 선박이 회전을 할 때 균형을 잡아주는 선박 양 측면의 스태빌라이저가 결함이 있었다고 증언하였다. 스태빌라이저는 선박 측면에 날개 모양의 형태로, 선체의 안과 밖을 반복적으로 왕복한다. 급회전 시 이 스태빌라이저가 작동하지 않으면 배가 기울어져 버린다. 그런데 여기에는 전제조건이 있는데, 화물의 과적재이다. 이에 대해 청해진해운 측은 과적재가 아니라고 주장했지만 JTBC는 이를 다음과 같이 반박한다. 세월호의 전체 중량은 6,825톤인데, 이것은 선박 자체, 화물, 승객, 연료 등의 무게를 모두 더한 수치다(만재배수톤수). 이 무게를 넘어서게 되면 과적이 돼 출항을 할 수 없는 것이 원칙이다. 세월호 배 자체의 무게는 3,031톤, 선사 측이 밝힌 화물과 승객 무게는 3,638톤이다. 모두 더하면 6,825톤을 넘지 않아 문제가 되지 않는 것으로 보이지만, 배의 연료와 평형수 등의 무게가 누락돼 있다는 것이다. 세월호 연료로 쓰인 벙커C유와 내부 발전용인 경유를 환산한 무게는 약 160톤으로 이를 더하면, 6,825톤을 넘어선다는 것이다. 윤종희 한국해양대 교수는 \"모든 것을 실은 상태에서 거기 화물도 있고, 연료·물·선용품 음식 등 이런 거 다 있지 않습니까. 그런 종류도 다 포함돼요.\"라고 밝혔다. 이 부분에 대해서는 청해진해운 측은 답변을 하지 않았다.", "Dietary fiber is a carbohydrate that is incompletely absorbed in humans and in some animals. Like all carbohydrates, when it is metabolized it can produce four Calories (kilocalories) of energy per gram. However, in most circumstances it accounts for less than that because of its limited absorption and digestibility. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer which is indigestible as humans do not have the required enzymes to disassemble it. There are two subcategories: soluble and insoluble fiber. Whole grains, fruits (especially plums, prunes, and figs), and vegetables are good sources of dietary fiber. There are many health benefits of a high-fiber diet. Dietary fiber helps reduce the chance of gastrointestinal problems such as constipation and diarrhea by increasing the weight and size of stool and softening it. Insoluble fiber, found in whole wheat flour, nuts and vegetables, especially stimulates peristalsis – the rhythmic muscular contractions of the intestines, which move digesta along the digestive tract. Soluble fiber, found in oats, peas, beans, and many fruits, dissolves in water in the intestinal tract to produce a gel that slows the movement of food through the intestines. This may help lower blood glucose levels because it can slow the absorption of sugar. Additionally, fiber, perhaps especially that from whole grains, is thought to possibly help lessen insulin spikes, and therefore reduce the risk of type 2 diabetes. The link between increased fiber consumption and a decreased risk of colorectal cancer is still uncertain." ] ]
5a6bb9f34eec6b001a80a54c	Myocardial_infarction	Cardiac rehabilitation benefits many who have experienced myocardial infarction, even if there has been substantial heart damage and resultant left ventricular failure; ideally other medical conditions that could interfere with participation should be managed optimally. It should start soon after discharge from hospital. The program may include lifestyle advice, exercise, social support, as well as recommendations about driving, flying, sport participation, stress management, and sexual intercourse.	en	null	null	190,561	[ "Cardiac rehabilitation is not an option under what circumstances?", "Cardiac rehabilitation often recommends ceasing what activities?", "What should start immediately upon registering at the hospital?", "When are other medical conditions address?" ]	[ [ "At common law, in general, a myocardial infarction is a disease, but may sometimes be an injury. This can create coverage issues in administration of no-fault insurance schemes such as workers' compensation. In general, a heart attack is not covered; however, it may be a work-related injury if it results, for example, from unusual emotional stress or unusual exertion. In addition, in some jurisdictions, heart attacks suffered by persons in particular occupations such as police officers may be classified as line-of-duty injuries by statute or policy. In some countries or states, a person having suffered from an MI may be prevented from participating in activity that puts other people's lives at risk, for example driving a car or flying an airplane.", "The main treatment for MI with ECG evidence of ST elevation (STEMI) include thrombolysis and percutaneous coronary intervention. Primary percutaneous coronary intervention (PCI) is the treatment of choice for STEMI if it can be performed in a timely manner. If PCI cannot be performed within 90 to 120 minutes then thrombolysis, preferably within 30 minutes of arrival to hospital, is recommended. If a person has had symptoms for 12 to 24 hours evidence for thrombolysis is less and if they have had symptoms for more than 24 hours it is not recommended.", "Complications may occur immediately following the heart attack (in the acute phase), or may need time to develop (a chronic problem). Acute complications may include heart failure if the damaged heart is no longer able to pump blood adequately around the body; aneurysm of the left ventricle myocardium; ventricular septal rupture or free wall rupture; mitral regurgitation, in particular if the infarction causes dysfunction of the papillary muscle; Dressler's syndrome; and abnormal heart rhythms, such as ventricular fibrillation, ventricular tachycardia, atrial fibrillation, and heart block. Longer-term complications include heart failure, atrial fibrillation, and an increased risk of a second MI.", "Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen should be used in those with low oxygen levels or shortness of breath. In ST elevation MIs treatments which attempt to restore blood flow to the heart are typically recommended and include angioplasty, where the arteries are pushed open, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use angioplasty in those at high risk. In people with blockages of multiple coronary arteries and diabetes, bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers, and statins, are typically recommended." ], [ "Exercise can trigger bronchoconstriction both in people with or without asthma. It occurs in most people with asthma and up to 20% of people without asthma. Exercise-induced bronchoconstriction is common in professional athletes. The highest rates are among cyclists (up to 45%), swimmers, and cross-country skiers. While it may occur with any weather conditions it is more common when it is dry and cold. Inhaled beta2-agonists do not appear to improve athletic performance among those without asthma however oral doses may improve endurance and strength.", "Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen should be used in those with low oxygen levels or shortness of breath. In ST elevation MIs treatments which attempt to restore blood flow to the heart are typically recommended and include angioplasty, where the arteries are pushed open, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use angioplasty in those at high risk. In people with blockages of multiple coronary arteries and diabetes, bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers, and statins, are typically recommended.", "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Bloodstream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary arteries, it leads to MI (necrosis of downstream myocardium). It is estimated that one billion cardiac cells are lost in a typical MI." ], [ "The main treatment for MI with ECG evidence of ST elevation (STEMI) include thrombolysis and percutaneous coronary intervention. Primary percutaneous coronary intervention (PCI) is the treatment of choice for STEMI if it can be performed in a timely manner. If PCI cannot be performed within 90 to 120 minutes then thrombolysis, preferably within 30 minutes of arrival to hospital, is recommended. If a person has had symptoms for 12 to 24 hours evidence for thrombolysis is less and if they have had symptoms for more than 24 hours it is not recommended.", "Infection begins when an organism successfully enters the body, grows and multiplies. This is referred to as colonization. Most humans are not easily infected. Those who are weak, sick, malnourished, have cancer or are diabetic have increased susceptibility to chronic or persistent infections. Individuals who have a suppressed immune system are particularly susceptible to opportunistic infections. Entrance to the host at host-pathogen interface, generally occurs through the mucosa in orifices like the oral cavity, nose, eyes, genitalia, anus, or the microbe can enter through open wounds. While a few organisms can grow at the initial site of entry, many migrate and cause systemic infection in different organs. Some pathogens grow within the host cells (intracellular) whereas others grow freely in bodily fluids.", "1904년 9월 23일에 미국인 사업가 루이스 세브란스(영어: Louis H. Severance 루이스 H. 세버런스, 1838년 ~ 1913년)의 후원을 받아서 숭례문 밖 복숭아골(현재 서울역 앞 연세재단 빌딩 일대)에 병원을 신축하면서 기증자의 이름을 따서 세브란스 기념 병원(Severance Memorial Hospital)으로 명칭을 변경하였으며, 의학 교육 기관인 세브란스 의학전문학교를 설립하였다. 1908년 6월 4일에 제1회 졸업생 7명에게는 대한제국 내부 위생국으로부터 의료 활동을 할 수 있는 최초의 의사면허증인 의술개업인허장이 발급되었다. 1909년에 교명을 ‘사립 세브란스 의학교’, 1913년 4월에는 ‘사립 세브란스 연합의학교’로 각각 변경하였으며, 1917년 5월 14일에 ‘세브란스 연합의학전문학교’로 발전하였으나, 1942년 6월에 일본의 강요로 교명을 ‘아사히 의학전문학교’(旭醫學專門學校)로 변경하였다. 해방 이후 1945년 11월에 세브란스 의학전문학교로 환원되고, 1947년 7월에 문교부로부터 6년제의 세브란스 의과대학으로 인가를 얻었다. 1955년 3월에 연희대학교와 통합을 결정하였고, 5월에 서울특별시 서대문구 신촌동에 병원 건물을 착공하면서 1962년에 세브란스 병원을 신촌으로 이전하였다. 한편, 1906년 9월에 쉴즈(영어: Miss Esther L. Shields 미스 에스터 L. 실즈)가 세브란스 병원에 간호원 양성전문기관으로 간호학교를 설치하면서 1910년에 최초의 간호원을 배출하는 계기가 되었으며, 1968년에는 연세대학교 간호대학으로 승격하였다.", "When a USB device is first connected to a USB host, the USB device enumeration process is started. The enumeration starts by sending a reset signal to the USB device. The data rate of the USB device is determined during the reset signaling. After reset, the USB device's information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices." ], [ "Other researchers point out that finding a difference in disease prevalence between two socially defined groups does not necessarily imply genetic causation of the difference. They suggest that medical practices should maintain their focus on the individual rather than an individual's membership to any group. They argue that overemphasizing genetic contributions to health disparities carries various risks such as reinforcing stereotypes, promoting racism or ignoring the contribution of non-genetic factors to health disparities. International epidemiological data show that living conditions rather than race make the biggest difference in health outcomes even for diseases that have \"race-specific\" treatments. Some studies have found that patients are reluctant to accept racial categorization in medical practice.", "Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's quality of life and general functioning. Psychological factors such as social support, hypnotic suggestion, excitement, or distraction can significantly affect pain's intensity or unpleasantness. In some arguments put forth in physician-assisted suicide or euthanasia debates, pain has been used as an argument to permit terminally ill patients to end their lives.", "The medical treatment of infectious diseases falls into the medical field of Infectious Disease and in some cases the study of propagation pertains to the field of Epidemiology. Generally, infections are initially diagnosed by primary care physicians or internal medicine specialists. For example, an \"uncomplicated\" pneumonia will generally be treated by the internist or the pulmonologist (lung physician). The work of the infectious diseases specialist therefore entails working with both patients and general practitioners, as well as laboratory scientists, immunologists, bacteriologists and other specialists.", "A number of other health conditions occur more frequently in those with asthma, including gastro-esophageal reflux disease (GERD), rhinosinusitis, and obstructive sleep apnea. Psychological disorders are also more common, with anxiety disorders occurring in between 16–52% and mood disorders in 14–41%. However, it is not known if asthma causes psychological problems or if psychological problems lead to asthma. Those with asthma, especially if it is poorly controlled, are at high risk for radiocontrast reactions." ] ]
5a6bba8a4eec6b001a80a554	Myocardial_infarction	Some risk factors for death include age, hemodynamic parameters (such as heart failure, cardiac arrest on admission, systolic blood pressure, or Killip class of two or greater), ST-segment deviation, diabetes, serum creatinine, peripheral vascular disease, and elevation of cardiac markers. Assessment of left ventricular ejection fraction may increase the predictive power. Prognosis is worse if a mechanical complication such as papillary muscle or myocardial free wall rupture occurs. Morbidity and mortality from myocardial infarction has improved over the years due to better treatment.	en	null	null	190,565	[ "How many classes of ST-segmentation are there?", "Prognosis improves after what complication?", "What has decreased over the years?", "What are some examples of ST-segment deviation?", "What are risk factors called?" ]	[ [ "For a person to qualify as having a STEMI, in addition to reported angina, the ECG must show new ST elevation in two or more adjacent ECG leads. This must be greater than 2 mm (0.2 mV) for males and greater than 1.5 mm (0.15 mV) in females if in leads V2 and V3 or greater than 1 mm (0.1 mV) if it is in other ECG leads. A left bundle branch block that is believed to be new used to be considered the same as ST elevation; however, this is no longer the case. In early STEMIs there may just be peaked T waves with ST elevation developing later.", "Discrete transistors are individually packaged transistors. Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package (currently only for large integrated circuits). It has solder \"balls\" on the underside in place of leads. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power rating.", "1970년대 독일 막스 플랑크 연구소 산하 과학기술시대의 삶의 조건 연구소에서 활동했던 사회학자 게르노트 뵈머, 볼프강 반 덴 데일 볼프강 크론 등도 신생연구분야의 형성에 관한 이론을 내놓았다. 연구소가 있던 도시 이름을 따서 슈타른베르크 학파라고도 불린 이들은 토마스 쿤의 패러다임 이론과 임레 라카토슈의 연구 프로그램 이론을 차용하여 새로운 연구분야가 형성되는 과정을 3단계로 구분하였다. 패러다임 이전단계에서는 체계적인 이론이나 법칙, 연구방법이 없기 때문에 학문의 정체성이 희미하다. 이 단계에서는 외부적 요인이 학문의 발전을 이끄는 원동력이 될 수 있는데, 예를 들어 1850년대 농업 생산성을 높이고자 하는 움직임은 농업화학의 발전을 촉진하였다. 이후 학문 체계가 구체화되면서 연구분야는 패러다임 단계에 들어선다. 이 단계에서 연구자들은 패러다임에 기반하여 질문을 만들고 해결을 하려고 노력한다. 패러다임이 연구분야 발전의 원동력이 되면서 외부의 요인은 점차 감소한다. 만약 학문이 완전히 성숙하면 패러다임은 더 이상 연구의 원동력이 되지 못하는데 이것을 패러다임 이후단계라고 한다. 이 단계에서 학문의 발전방향은 사회나 다른 학문의 요구에 맞춰 변화한다. 특히 슈타른베르크 학파들은 외부 요인이 연구 원동력이 되며, 학문이 나아갈 길을 제시하는 현상을 지향성(Finalization)이라 칭하였다.", "There are generally four recognized levels of tests: unit testing, integration testing, component interface testing, and system testing. Tests are frequently grouped by where they are added in the software development process, or by the level of specificity of the test. The main levels during the development process as defined by the SWEBOK guide are unit-, integration-, and system testing that are distinguished by the test target without implying a specific process model. Other test levels are classified by the testing objective." ], [ "Complications may occur immediately following the heart attack (in the acute phase), or may need time to develop (a chronic problem). Acute complications may include heart failure if the damaged heart is no longer able to pump blood adequately around the body; aneurysm of the left ventricle myocardium; ventricular septal rupture or free wall rupture; mitral regurgitation, in particular if the infarction causes dysfunction of the papillary muscle; Dressler's syndrome; and abnormal heart rhythms, such as ventricular fibrillation, ventricular tachycardia, atrial fibrillation, and heart block. Longer-term complications include heart failure, atrial fibrillation, and an increased risk of a second MI.", "The prognosis for asthma is generally good, especially for children with mild disease. Mortality has decreased over the last few decades due to better recognition and improvement in care. Globally it causes moderate or severe disability in 19.4 million people as of 2004 (16 million of which are in low and middle income countries). Of asthma diagnosed during childhood, half of cases will no longer carry the diagnosis after a decade. Airway remodeling is observed, but it is unknown whether these represent harmful or beneficial changes. Early treatment with corticosteroids seems to prevent or ameliorates a decline in lung function.", "Other supportive evidence includes: a ≥20% difference in peak expiratory flow rate on at least three days in a week for at least two weeks, a ≥20% improvement of peak flow following treatment with either salbutamol, inhaled corticosteroids or prednisone, or a ≥20% decrease in peak flow following exposure to a trigger. Testing peak expiratory flow is more variable than spirometry, however, and thus not recommended for routine diagnosis. It may be useful for daily self-monitoring in those with moderate to severe disease and for checking the effectiveness of new medications. It may also be helpful in guiding treatment in those with acute exacerbations.", "People with an acute coronary syndrome where no ST elevation is demonstrated (non-ST elevation ACS or NSTEACS) are treated with aspirin. Clopidogrel is added in many cases, particularly if the risk of cardiovascular events is felt to be high and early PCI is being considered. Depending on whether early PCI is planned, a factor Xa inhibitor or a potentiator of antithrombin (fondaparinux or low molecular weight heparin respectively) may be added. In very high-risk scenarios, inhibitors of the platelet glycoprotein αIIbβ3a receptor such as eptifibatide or tirofiban may be used." ], [ "The number of pubs in the UK has declined year on year, at least since 1982. Various reasons are put forward for this, such as the failure of some establishments to keep up with customer requirements. Others claim the smoking ban of 2007, intense competition from gastro-pubs, the availability of cheap alcohol in supermarkets or the general economic climate are either to blame, or are factors in the decline. Changes in demographics may be an additional factor.", "From the second half of the 20th century on parties which continued to rely on donations or membership subscriptions ran into mounting problems. Along with the increased scrutiny of donations there has been a long-term decline in party memberships in most western democracies which itself places more strains on funding. For example, in the United Kingdom and Australia membership of the two main parties in 2006 is less than an 1/8 of what it was in 1950, despite significant increases in population over that period.", "From the 1980s, mainstream sensibilities were reasserted and serialization became less common as the number of comics magazines decreased and many comics began to be published directly as albums. Smaller publishers such as L'Association that published longer works in non-traditional formats by auteur-istic creators also became common. Since the 1990s, mergers resulted in fewer large publishers, while smaller publishers proliferated. Sales overall continued to grow despite the trend towards a shrinking print market.", "In more recent years, however, many country pubs have either closed down, or have been converted to establishments intent on providing seating facilities for the consumption of food, rather than a venue for members of the local community meeting and convivially drinking." ], [ "For a person to qualify as having a STEMI, in addition to reported angina, the ECG must show new ST elevation in two or more adjacent ECG leads. This must be greater than 2 mm (0.2 mV) for males and greater than 1.5 mm (0.15 mV) in females if in leads V2 and V3 or greater than 1 mm (0.1 mV) if it is in other ECG leads. A left bundle branch block that is believed to be new used to be considered the same as ST elevation; however, this is no longer the case. In early STEMIs there may just be peaked T waves with ST elevation developing later.", "Wright himself believed that values >0.25 represent very great genetic variation and that an FST of 0.15–0.25 represented great variation. However, about 5% of human variation occurs between populations within continents, therefore FST values between continental groups of humans (or races) of as low as 0.1 (or possibly lower) have been found in some studies, suggesting more moderate levels of genetic variation. Graves (1996) has countered that FST should not be used as a marker of subspecies status, as the statistic is used to measure the degree of differentiation between populations, although see also Wright (1978).", "The population geneticist Sewall Wright developed one way of measuring genetic differences between populations known as the Fixation index, which is often abbreviated to FST. This statistic is often used in taxonomy to compare differences between any two given populations by measuring the genetic differences among and between populations for individual genes, or for many genes simultaneously. It is often stated that the fixation index for humans is about 0.15. This translates to an estimated 85% of the variation measured in the overall human population is found within individuals of the same population, and about 15% of the variation occurs between populations. These estimates imply that any two individuals from different populations are almost as likely to be more similar to each other than either is to a member of their own group. Richard Lewontin, who affirmed these ratios, thus concluded neither \"race\" nor \"subspecies\" were appropriate or useful ways to describe human populations. However, others have noticed that group variation was relatively similar to the variation observed in other mammalian species.", "Discrete transistors are individually packaged transistors. Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package (currently only for large integrated circuits). It has solder \"balls\" on the underside in place of leads. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power rating." ], [ "Current Governor of the Reserve Bank of India Raghuram Rajan had predicted the crisis in 2005 when he became chief economist at the International Monetary Fund.In 2005, at a celebration honouring Alan Greenspan, who was about to retire as chairman of the US Federal Reserve, Rajan delivered a controversial paper that was critical of the financial sector. In that paper, \"Has Financial Development Made the World Riskier?\", Rajan \"argued that disaster might loom.\" Rajan argued that financial sector managers were encouraged to \"take risks that generate severe adverse consequences with small probability but, in return, offer generous compensation the rest of the time. These risks are known as tail risks. But perhaps the most important concern is whether banks will be able to provide liquidity to financial markets so that if the tail risk does materialise, financial positions can be unwound and losses allocated so that the consequences to the real economy are minimised.\"", "The pricing of risk refers to the incremental compensation required by investors for taking on additional risk, which may be measured by interest rates or fees. Several scholars have argued that a lack of transparency about banks' risk exposures prevented markets from correctly pricing risk before the crisis, enabled the mortgage market to grow larger than it otherwise would have, and made the financial crisis far more disruptive than it would have been if risk levels had been disclosed in a straightforward, readily understandable format.", "This boom in innovative financial products went hand in hand with more complexity. It multiplied the number of actors connected to a single mortgage (including mortgage brokers, specialized originators, the securitizers and their due diligence firms, managing agents and trading desks, and finally investors, insurances and providers of repo funding). With increasing distance from the underlying asset these actors relied more and more on indirect information (including FICO scores on creditworthiness, appraisals and due diligence checks by third party organizations, and most importantly the computer models of rating agencies and risk management desks). Instead of spreading risk this provided the ground for fraudulent acts, misjudgments and finally market collapse. In 2005 a group of computer scientists built a computational model for the mechanism of biased ratings produced by rating agencies, which turned out to be adequate to what actually happened in 2006–2008.[citation needed]", "Because most injuries sustained by adolescents are related to risky behavior (car crashes, alcohol, unprotected sex), a great deal of research has been done on the cognitive and emotional processes underlying adolescent risk-taking. In addressing this question, it is important to distinguish whether adolescents are more likely to engage in risky behaviors (prevalence), whether they make risk-related decisions similarly or differently than adults (cognitive processing perspective), or whether they use the same processes but value different things and thus arrive at different conclusions. The behavioral decision-making theory proposes that adolescents and adults both weigh the potential rewards and consequences of an action. However, research has shown that adolescents seem to give more weight to rewards, particularly social rewards, than do adults." ] ]
5a6bbb724eec6b001a80a55e	Myocardial_infarction	Complications may occur immediately following the heart attack (in the acute phase), or may need time to develop (a chronic problem). Acute complications may include heart failure if the damaged heart is no longer able to pump blood adequately around the body; aneurysm of the left ventricle myocardium; ventricular septal rupture or free wall rupture; mitral regurgitation, in particular if the infarction causes dysfunction of the papillary muscle; Dressler's syndrome; and abnormal heart rhythms, such as ventricular fibrillation, ventricular tachycardia, atrial fibrillation, and heart block. Longer-term complications include heart failure, atrial fibrillation, and an increased risk of a second MI.	en	null	null	190,570	[ "What is Dressler's syndrome?", "What does an aneurysm of the left ventricle lead to?", "What does mitral regurgitation cause?", "Atrial fibrillation can only be what kind of problem?" ]	[ [ "치매나 백혈병, 당뇨, 파킨슨병과 같은 난치병들 중에는 세포의 변이나 사멸로 인한 질병이 대다수이다. 이러한 퇴행성 질병의 경우 세포 치료법을 이용해여 치료하는 경우가 많다.[6] 특이점주의자들에 따르면 줄기세포 연구와 같은 세포 연구는 생명 공학 연구의 일부분이며 유전자 DNA 지도를 완벽하게 구조화할 수 있다면 세포분화 치료 혹은 세포복제 치료를 통해 환자 자신의 DNA를 지니고 텔로미어가 연장된 세포를 공급할 수 있을 것이라고 본다. 예컨데 현재 당뇨병 치료에 쓰이는 거부반응 제어제가 위험한 부작용을 일으킬 가능성이 있는 반면 이러한 세포 치료는 부작용 가능성을 급격히 낮출 수 있다. 이러한 세포 치료는 단순히 난치병의 치료에만 그치는 것이 아니라, 교차분화 기술을 이용한 새로운 신체 기관으로의 교체를 가능하게 한다.", "일반적인 증상으로 외부 현실을 제대로 인식하지 못하여 부조화된 환각, 망상, 환영, 환청 등을 경험하고 대인 관계에서 지나친 긴장감 혹은 타인의 시각에 대한 무관심, 기이한 행동을 보인다. 언어 관련 장애나 기분장애 등 역시 동반되기도 한다. 이로 인해 사회활동과 가족관계를 악화시키는 대표적인 정신질환이다. 이 질환은 조발성치매라는 이름으로도 불리었으나 치매와는 연관이 없음이 밝혀졌다. 조현병의 과거 명칭인 정신분열병의 어감이 부정적 편견을 가져왔었기 때문에 정신건강의학회는 이 병을 언어 순화 차원에서 조현병으로 개칭하였다. 참고로, 일본의 경우 조현병을 '통합실조증'으로 개명해 부르고 있다. 하지만 통합실조증은 영양실조에서처럼 '실조'라는 단어가 주는 또 다른 부정적 측면 때문에 환자 가족들의 반대가 큰 편이다. 대한민국의 장애인 복지법엔 우울장애, 반복성 우울장애, 양극성 정동장애(조울증)과 함께 정신장애로 인정된다.", "The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.", "알츠하이머병(Alzheimer's disease (AD)=Alzheimer disease)은 치매의 가장 흔한 형태이며 75%의 치매 환자가 알츠하이머병이다. 현대 의학에서는 치료할 수 없는 질병으로, 시간이 지날수록 증상이 악화되며 결과적으로 죽음에 이른다. 1906년 독일의 정신과 의사인 알로이스 알츠하이머(Alois Alzheimer)에 의해 알려졌다. 대부분의 경우 알츠하이머병은 65세가 넘어 발병하지만, 드물게 그 이전에 발병할 수 있다. 미국에서는 65~74세 인구의 약 3%, 75~84세 인구의 약 19%, 85세 이상 인구의 50%가 이 병을 앓고 있다. 한국에서는 최근 한 농촌 지역을 중심으로 한 연구 보고에 의하면, 농촌 지역 60세 이상의 인구에서 약 21%가 치매 양상을 보이고, 이 중 63%가 알츠하이머형 치매인 것으로 보고되고 있다. 2006년 전 세계 26.6만명이 가진 질병이다. 2050년에는 85명중 1명꼴로 발병될 것으로 예측된다." ], [ "Shortness of breath occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis (an excessive form of sweating), weakness, light-headedness, nausea, vomiting, and palpitations. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system, which occurs in response to pain and the blood flow abnormalities that result from dysfunction of the heart muscle. Loss of consciousness (due to inadequate blood flow to the brain and cardiogenic shock) and sudden death (frequently due to the development of ventricular fibrillation) can occur in MIs.", "If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the occluded coronary artery die (chiefly through necrosis) and do not grow back. A collagen scar forms in their place. Recent studies indicate that another form of cell death, apoptosis, also plays a role in the process of tissue damage following an MI. As a result, the person's heart will be permanently damaged. This myocardial scarring also puts the person at risk for potentially life-threatening abnormal heart rhythms (arrhythmias), and may result in the formation of a ventricular aneurysm that can rupture with catastrophic consequences.", "Injured heart tissue conducts electrical impulses more slowly than normal heart tissue. The difference in conduction velocity between injured and uninjured tissue can trigger re-entry or a feedback loop that is believed to be the cause of many lethal arrhythmias. The most serious of these arrhythmias is ventricular fibrillation (V-Fib/VF), an extremely fast and chaotic heart rhythm that is the leading cause of sudden cardiac death. Another life-threatening arrhythmia is ventricular tachycardia (V-tach/VT), which can cause sudden cardiac death. However, VT usually results in rapid heart rates that prevent the heart from pumping blood effectively. Cardiac output and blood pressure may fall to dangerous levels, which can lead to further coronary ischemia and extension of the infarct.", "Some risk factors for death include age, hemodynamic parameters (such as heart failure, cardiac arrest on admission, systolic blood pressure, or Killip class of two or greater), ST-segment deviation, diabetes, serum creatinine, peripheral vascular disease, and elevation of cardiac markers. Assessment of left ventricular ejection fraction may increase the predictive power. Prognosis is worse if a mechanical complication such as papillary muscle or myocardial free wall rupture occurs. Morbidity and mortality from myocardial infarction has improved over the years due to better treatment." ], [ "Inflammatory diarrhea occurs when there is damage to the mucosal lining or brush border, which leads to a passive loss of protein-rich fluids and a decreased ability to absorb these lost fluids. Features of all three of the other types of diarrhea[clarification needed] can be found in this type of diarrhea. It can be caused by bacterial infections, viral infections, parasitic infections, or autoimmune problems such as inflammatory bowel diseases. It can also be caused by tuberculosis, colon cancer, and enteritis.[citation needed]", "Osmotic diarrhea occurs when too much water is drawn into the bowels. If a person drinks solutions with excessive sugar or excessive salt, these can draw water from the body into the bowel and cause osmotic diarrhea. Osmotic diarrhea can also be the result of maldigestion (e.g., pancreatic disease or Coeliac disease), in which the nutrients are left in the lumen to pull in water. Or it can be caused by osmotic laxatives (which work to alleviate constipation by drawing water into the bowels). In healthy individuals, too much magnesium or vitamin C or undigested lactose can produce osmotic diarrhea and distention of the bowel. A person who has lactose intolerance can have difficulty absorbing lactose after an extraordinarily high intake of dairy products. In persons who have fructose malabsorption, excess fructose intake can also cause diarrhea. High-fructose foods that also have a high glucose content are more absorbable and less likely to cause diarrhea. Sugar alcohols such as sorbitol (often found in sugar-free foods) are difficult for the body to absorb and, in large amounts, may lead to osmotic diarrhea. In most of these cases, osmotic diarrhea stops when offending agent (e.g. milk, sorbitol) is stopped.", "Shortness of breath occurs when the damage to the heart limits the output of the left ventricle, causing left ventricular failure and consequent pulmonary edema. Other symptoms include diaphoresis (an excessive form of sweating), weakness, light-headedness, nausea, vomiting, and palpitations. These symptoms are likely induced by a massive surge of catecholamines from the sympathetic nervous system, which occurs in response to pain and the blood flow abnormalities that result from dysfunction of the heart muscle. Loss of consciousness (due to inadequate blood flow to the brain and cardiogenic shock) and sudden death (frequently due to the development of ventricular fibrillation) can occur in MIs.", "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest." ], [ "Injured heart tissue conducts electrical impulses more slowly than normal heart tissue. The difference in conduction velocity between injured and uninjured tissue can trigger re-entry or a feedback loop that is believed to be the cause of many lethal arrhythmias. The most serious of these arrhythmias is ventricular fibrillation (V-Fib/VF), an extremely fast and chaotic heart rhythm that is the leading cause of sudden cardiac death. Another life-threatening arrhythmia is ventricular tachycardia (V-tach/VT), which can cause sudden cardiac death. However, VT usually results in rapid heart rates that prevent the heart from pumping blood effectively. Cardiac output and blood pressure may fall to dangerous levels, which can lead to further coronary ischemia and extension of the infarct.", "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Bloodstream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary arteries, it leads to MI (necrosis of downstream myocardium). It is estimated that one billion cardiac cells are lost in a typical MI.", "At common law, in general, a myocardial infarction is a disease, but may sometimes be an injury. This can create coverage issues in administration of no-fault insurance schemes such as workers' compensation. In general, a heart attack is not covered; however, it may be a work-related injury if it results, for example, from unusual emotional stress or unusual exertion. In addition, in some jurisdictions, heart attacks suffered by persons in particular occupations such as police officers may be classified as line-of-duty injuries by statute or policy. In some countries or states, a person having suffered from an MI may be prevented from participating in activity that puts other people's lives at risk, for example driving a car or flying an airplane." ] ]
5a6bbc0f4eec6b001a80a566	Myocardial_infarction	In contrast, IHD is becoming a more common cause of death in the developing world. For example, in India, IHD had become the leading cause of death by 2004, accounting for 1.46 million deaths (14% of total deaths) and deaths due to IHD were expected to double during 1985–2015. Globally, disability adjusted life years (DALYs) lost to ischemic heart disease are predicted to account for 5.5% of total DALYs in 2030, making it the second-most-important cause of disability (after unipolar depressive disorder), as well as the leading cause of death by this date.	en	null	null	190,574	[ "What percentage of deaths does unipolar depressive disorder cause?", "How many people died from IHD from 1985-2015?", "What is the worldwide leading cause of death?", "What percentage of deaths will IHD be responsible for in 2030?", "When did IHD begin to be a bigger problem in the developing word?" ]	[ [ "The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.", "알츠하이머병(Alzheimer's disease (AD)=Alzheimer disease)은 치매의 가장 흔한 형태이며 75%의 치매 환자가 알츠하이머병이다. 현대 의학에서는 치료할 수 없는 질병으로, 시간이 지날수록 증상이 악화되며 결과적으로 죽음에 이른다. 1906년 독일의 정신과 의사인 알로이스 알츠하이머(Alois Alzheimer)에 의해 알려졌다. 대부분의 경우 알츠하이머병은 65세가 넘어 발병하지만, 드물게 그 이전에 발병할 수 있다. 미국에서는 65~74세 인구의 약 3%, 75~84세 인구의 약 19%, 85세 이상 인구의 50%가 이 병을 앓고 있다. 한국에서는 최근 한 농촌 지역을 중심으로 한 연구 보고에 의하면, 농촌 지역 60세 이상의 인구에서 약 21%가 치매 양상을 보이고, 이 중 63%가 알츠하이머형 치매인 것으로 보고되고 있다. 2006년 전 세계 26.6만명이 가진 질병이다. 2050년에는 85명중 1명꼴로 발병될 것으로 예측된다.", "Similar to the other Eur-A countries, most Portuguese die from noncommunicable diseases. Mortality from cardiovascular diseases (CVD) is higher than in the eurozone, but its two main components, ischaemic heart disease and cerebrovascular disease, display inverse trends compared with the Eur-A, with cerebrovascular disease being the single biggest killer in Portugal (17%). Portuguese people die 12% less often from cancer than in the Eur-A, but mortality is not declining as rapidly as in the Eur-A. Cancer is more frequent among children as well as among women younger than 44 years. Although lung cancer (slowly increasing among women) and breast cancer (decreasing rapidly) are scarcer, cancer of the cervix and the prostate are more frequent. Portugal has the highest mortality rate for diabetes in the Eur-A, with a sharp increase since the 1980s.", "The main active ingredient of beer is alcohol, and therefore, the health effects of alcohol apply to beer. Consumption of small quantities of alcohol (less than one drink in women and two in men) is associated with a decreased risk of cardiac disease, stroke and diabetes mellitus. The long term health effects of continuous, moderate or heavy alcohol consumption include the risk of developing alcoholism and alcoholic liver disease. A total of 3.3 million deaths (5.9% of all deaths) are believed to be due to alcohol. Alcoholism often reduces a person's life expectancy by around ten years. Alcohol use is the third leading cause of early death in the United States." ], [ "On 7 January 2015, two French Muslim extremists attacked the Paris headquarters of Charlie Hebdo and killed thirteen people, and on 9 January, a third terrorist killed four hostages during an attack at a Jewish grocery store at Porte de Vincennes. On 11 January an estimated 1.5 million people marched in Paris–along with international political leaders–to show solidarity against terrorism and in defence of freedom of speech. Ten months later, 13 November 2015, came a series of coordinated terrorist attacks in Paris and Saint-Denis claimed by the 'Islamic state' organisation ISIL ('Daesh', ISIS); 130 people were killed by gunfire and bombs, and more than 350 were injured. Seven of the attackers killed themselves and others by setting off their explosive vests. On the morning of 18 November three suspected terrorists, including alleged planner of the attacks Abdelhamid Abaaoud, were killed in a shootout with police in the Paris suburb of Saint-Denis. President Hollande declared France to be in a three-month state of emergency.", "The World Health Organization declared TB a \"global health emergency\" in 1993, and in 2006, the Stop TB Partnership developed a Global Plan to Stop Tuberculosis that aims to save 14 million lives between its launch and 2015. A number of targets they have set are not likely to be achieved by 2015, mostly due to the increase in HIV-associated tuberculosis and the emergence of multiple drug-resistant tuberculosis. A tuberculosis classification system developed by the American Thoracic Society is used primarily in public health programs.", "The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.", "The 2015 Human Development Report by the United Nations Development Program was released on December 14, 2015, and calculates HDI values based on estimates for 2014. Below is the list of the \"very high human development\" countries:" ], [ "The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.", "Tuberculosis is the second-most common cause of death from infectious disease (after those due to HIV/AIDS). The total number of tuberculosis cases has been decreasing since 2005, while new cases have decreased since 2002. China has achieved particularly dramatic progress, with about an 80% reduction in its TB mortality rate between 1990 and 2010. The number of new cases has declined by 17% between 2004–2014. Tuberculosis is more common in developing countries; about 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5–10% of the US population test positive. Hopes of totally controlling the disease have been dramatically dampened because of a number of factors, including the difficulty of developing an effective vaccine, the expensive and time-consuming diagnostic process, the necessity of many months of treatment, the increase in HIV-associated tuberculosis, and the emergence of drug-resistant cases in the 1980s.", "As of 2011, 235–330 million people worldwide are affected by asthma, and approximately 250,000–345,000 people die per year from the disease. Rates vary between countries with prevalences between 1 and 18%. It is more common in developed than developing countries. One thus sees lower rates in Asia, Eastern Europe and Africa. Within developed countries it is more common in those who are economically disadvantaged while in contrast in developing countries it is more common in the affluent. The reason for these differences is not well known. Low and middle income countries make up more than 80% of the mortality.", "약이 만들어지면서 많은 백신과 치료는 사람들이 가장 많이 시달린 질병(흑사병, 매독, 발진티푸스, 클로레라, 말라리아)을 위해 사용되었다. 그러나, 질병의 유기체의 혁명이 빨르기 때문에, 백신으로도 많은 질병에 의한 완전한 면역체계를 갖추기에는 어려움이 있었다. 백신 없이는 세계는 전염성이 짙은 질병에 취약했을 것이다. 이처럼 질병의 혁명은 현시대에서 가장 위협이 되는 존재이다. 예를 들면, 가장 최신인 \"돼지 인플루엔자\" 또는 H1N1은 원래의 감기에서 진화된 새로운 변종이다. 본토에서 기초로 한 몇세기에 걸친 아시안 플루로 알려졌다. 1918년에서 1920년까지, 세계1차대전은 유행병으로 50-100만명의 사람들을 죽였고, 미국같은 경우는 50만명만 남겨두기도 했다. H1N1은 조류, 돼지류와 사람 플루 부분으로 부분적으로 나뉘어져 진화하였다." ], [ "The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.", "참여연대는 이에 대해 \"OECD 회원국의 건강보험 보장비율이 평균 81%인 것에 견줘 보장율 목표 70%는 적정한 수치로 보기 어렵다\"며 \"2012년 대통령 선거에서 문재인 후보의 공약이었던 병원비 본인부담금 100만 원 상한제를 실시해야 한다\"고 밝혔다. 김태년 더불어민주당 정책위의장은 \"핵심은 건강보험 하나만 있으면 아픈데도 돈이 없어서 치료를 못 받는 일은 더 이상 없도록 하겠다는 것\"이라며 \"의료비 증가의 주된 원인이자 민간 실손보험 가입의 주요원인인 비급여 문제를 바로 잡을 것\"이라고 밝혔다. 또한 \"노인·여성·아동·장애인 등 취약계층에 대한 지원을 늘리고, 본인부담 상한제와 재난적 의료비 지원제도를 강화해 저소득층의 의료비 부담을 줄이겠다\"고 덧붙였다. 반면, 김광림 자유한국당 정책위의장은 \"재원 대책이 두루뭉실해 5년 뒤가 보이지 않는다\"며 \"13페이지의 건보 대책 발표문에 지원 내용은 깨알같이 많은데 재원대책은 3분의 1 뿐\"이라고 비판했다. 김 의장은 \"모든 병을 정부의 의료보험으로 급여화하겠다는 것은 찬성이지만, 의사들이 제대로 된 수가를 받을 수 있도록 해주지 않고 통제하면 3만 개의 병원 중 3분의 1은 5년 뒤 문을 닫게 될 것\"이라고 덧붙였다. 이에 문재인은 10일 수석·보좌관 회의를 주재하면서 \"새 정부의 복지 확대 정책에 대해 세금 폭탄이나 건보료 폭탄 또는 막대한 재정적자 없이 가능할 것인가 궁금해하는 국민이 많다\"며 \"기획재정부와 충분히 협의해 재원대책을 꼼꼼히 검토했고, 올 하반기부터 2022년까지 단계적으로 시행하도록 설계해 현실적으로 건전 재정을 유지하면서 감달할 수 있는 최선을 선택한 것\"이라고 직접 반박에 나섰다.", "The Human Development Index (HDI) is a composite statistic of life expectancy, education, and income per capita indicators, which are used to rank countries into four tiers of human development. A country scores higher HDI when the life expectancy at birth is longer, the education period is longer, and the income per capita is higher. The HDI was developed by the Pakistani economist Mahbub ul Haq, often framed in terms of whether people are able to \"be\" and \"do\" desirable things in their life, and was published by the United Nations Development Programme.", "The 2010 Human Development Report introduced an Inequality-adjusted Human Development Index (IHDI). While the simple HDI remains useful, it stated that \"the IHDI is the actual level of human development (accounting for inequality),\" and \"the HDI can be viewed as an index of 'potential' human development (or the maximum IHDI that could be achieved if there were no inequality).\"" ], [ "In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, the world already having split into two camps, 25/50 Hz and 30/60 Hz, largely due to the differences in mains frequency. The IWP11/6 working party considered many views and throughout the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.", "The 2010 Human Development Report introduced an Inequality-adjusted Human Development Index (IHDI). While the simple HDI remains useful, it stated that \"the IHDI is the actual level of human development (accounting for inequality),\" and \"the HDI can be viewed as an index of 'potential' human development (or the maximum IHDI that could be achieved if there were no inequality).\"", "The Human Development Index (HDI) is a composite statistic of life expectancy, education, and income per capita indicators, which are used to rank countries into four tiers of human development. A country scores higher HDI when the life expectancy at birth is longer, the education period is longer, and the income per capita is higher. The HDI was developed by the Pakistani economist Mahbub ul Haq, often framed in terms of whether people are able to \"be\" and \"do\" desirable things in their life, and was published by the United Nations Development Programme.", "The 2010 Human Development Report was the first to calculate an Inequality-adjusted Human Development Index (IHDI), which factors in inequalities in the three basic dimensions of human development (income, life expectancy, and education). Below is a list of countries in the top quartile by IHDI:" ] ]
5a6bbd284eec6b001a80a57a	Myocardial_infarction	At common law, in general, a myocardial infarction is a disease, but may sometimes be an injury. This can create coverage issues in administration of no-fault insurance schemes such as workers' compensation. In general, a heart attack is not covered; however, it may be a work-related injury if it results, for example, from unusual emotional stress or unusual exertion. In addition, in some jurisdictions, heart attacks suffered by persons in particular occupations such as police officers may be classified as line-of-duty injuries by statute or policy. In some countries or states, a person having suffered from an MI may be prevented from participating in activity that puts other people's lives at risk, for example driving a car or flying an airplane.	en	null	null	190,579	[ "What is a myocardial infarction is always considered to be?", "What occupation cannot have a heart attack classified as work-related?", "What typically covers an MI?", "When is an MI not considered a work-related injury?", "What generally treats MI as an injury?" ]	[ [ "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Bloodstream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary arteries, it leads to MI (necrosis of downstream myocardium). It is estimated that one billion cardiac cells are lost in a typical MI.", "The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous. Chest pain is the most common symptom of acute MI and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia (a lack of blood and hence oxygen supply) of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen, where it may mimic heartburn. Levine's sign, in which a person localizes the chest pain by clenching their fists over their sternum, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed it had a poor positive predictive value.", "Myocardial infarction in the setting of plaque results from underlying atherosclerosis. Inflammation is known to be an important step in the process of atherosclerotic plaque formation. C-reactive protein (CRP) is a sensitive but nonspecific marker for inflammation. Elevated CRP blood levels, especially measured with high-sensitivity assays, can predict the risk of MI, as well as stroke and development of diabetes. Moreover, some drugs for MI might also reduce CRP levels. The use of high-sensitivity CRP assays as a means of screening the general population is advised against, but it may be used optionally at the physician's discretion in those who already present with other risk factors or known coronary artery disease. Whether CRP plays a direct role in atherosclerosis remains uncertain." ], [ "대부분의 외근직 소방공무원의 근무형태는 2조 맞교대로, 주 84시간을 근무한다. 이는 대한민국의 법정근로시간인 1주 40시간을 두배 이상 초과하고 있다. 이는 소방공무원의 사기저하를 불러올 수 있으며 이에 따라 소방공무원들이 3교대를 주장하는 근거가 된다. 또한 외상 후 스트레스 장애의 치료에 대한 지원도 거의 없으며, 총 정원 3만 7894명 중에 2만 1376명이 직업병을 갖고 있거나 직업병을 갖고 있는 것으로 의심받고 있다. 확실히 직업병을 가진 소방관은 14.3%였다. 그러나 공상을 신청할 경우 인사상의 불이익 때문에 부상을 입은 88%의 소방관이 공상을 신청하지 못했으며, 직무연관성으로 인해 백혈병이나 혈액암이 발병해도 공무원연금공단에서는 공상을 인정하지 않고 있으며, 2008년에 대법원이 직무연관성을 인정했음에도 이후의 공상 신청에서 불승인 판정을 내고 있다.", "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Asthma as a result of (or worsened by) workplace exposures, is a commonly reported occupational disease. Many cases however are not reported or recognized as such. It is estimated that 5–25% of asthma cases in adults are work–related. A few hundred different agents have been implicated with the most common being: isocyanates, grain and wood dust, colophony, soldering flux, latex, animals, and aldehydes. The employment associated with the highest risk of problems include: those who spray paint, bakers and those who process food, nurses, chemical workers, those who work with animals, welders, hairdressers and timber workers.", "이러한 8체질별 특징은 직업과도 밀접하게 관련된다.[25] 심폐의 발성능력을 발휘하는 방송 아나운서와 소프라노와 지휘자, 항해 선장 그리고 건축설계사와 대목장 등의 금음체질, 성대마술사로 불리는 성우와 요들러, 좁은 공간 우주선 갭슐에 잘 적응하는 우주인, 그래픽 디자이너 또는 인쇄공으로서 전문소양을 보이는 금양체질, 교육사업팀의 정서적 적응이 완벽하며 마술가의 기질이 탁월한 목양체질, 사실탐구의 집중력이 고도로 발달하는 고고학의 목음체질, 분주하게 오가며 다양한 사람들을 만나고 영업하는 토양체질, 실물디자인과 정보산업의 탁월한 중추를 이루는 토음체질, 관상학자와 번화장 그리고 커피샾의 바리스타에 독보적인 수음체질, 프로게이머와 전기노동자의 수양체질 등의 단편적 특성들은 모두 체질의 장부강약의 조화에서 우러나오는 기량이다. 이 외에도 체질적 기량의 실력을 최고도로 발휘할 수 있는 요소들은 보다 구체적인 분류를 통해 연결된다. 일반적인 개성으로서 유사한 정도에서는 체질적 구별이 모호하지만 올림픽 대회 우승과 같이 최고의 기량이 드러나는 것은 반드시 체질에 따른다. 악기를 다루는 데에서도 금음체질의 가볍고 길게 부는 플루트와 목음체질이 힘주어 부는 색소폰은 체질적 바탕에서 발휘된다. 큰북과 작은북을 누구나 두드릴 수 있지만 빠른 손목의 힘을 낼 수 있는 토양체질이 아니면 수월하게 다루기 힘든 것도 체질적 기량이 받쳐주어야 하기 때문이다. 이러한 분류는 체질판별이라는 보다 진보된 방식의 분류에 의해 시도되어야 한다. 이러한 분류가 검증의 절차를 필요로 하지만 보편적 정서를 거스르지 않는다. 체질적인 합리적 구분이 이런 경향을 예측가능케 한다. 임상적 결과를 축적하면서 앞으로 보다 세밀하게 밝혀내야 할 8체질의학의 대중적 과제이다. 이 과제는 역으로 성립할 수 있다. 즉 기량과 특징을 통해 역으로 체질을 알아내 것이다. 과학의 시대에 여러 요소들을 종합하여 체질망이라는 이름으로 구축함으로써 한의학적 역사적 근거를 보다 간결하고 일관성있는 과학적 근거로 바꾸는 작업이 필요하다. 체질의학의 최대 과제인 판별을 과학적 자료에 대입하여 누구라도 쉽게 알아내는 방법은 체질의 유전법칙과 개인별 체질적 기량 그리고 질병의 체질 상관성을 명백하게 밝혀내는 것이다." ], [ "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol intake, among others. The mechanism of an MI often involves the complete blockage of a coronary artery caused by a rupture of an atherosclerotic plaque. MIs are less commonly caused by coronary artery spasms, which may be due to cocaine, significant emotional stress, and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests, and coronary angiography. An ECG may confirm an ST elevation MI if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB.", "Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Bloodstream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary arteries, it leads to MI (necrosis of downstream myocardium). It is estimated that one billion cardiac cells are lost in a typical MI.", "At least one quarter of all MIs are silent, without chest pain or other symptoms. These cases can be discovered later on electrocardiograms, using blood enzyme tests, or at autopsy without a prior history of related complaints. Estimates of the prevalence of silent MIs vary between 22 and 64%. A silent course is more common in the elderly, in people with diabetes mellitus and after heart transplantation, probably because the donor heart is not fully innervated by the nervous system of the recipient. In people with diabetes, differences in pain threshold, autonomic neuropathy, and psychological factors have been cited as possible explanations for the lack of symptoms." ], [ "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol intake, among others. The mechanism of an MI often involves the complete blockage of a coronary artery caused by a rupture of an atherosclerotic plaque. MIs are less commonly caused by coronary artery spasms, which may be due to cocaine, significant emotional stress, and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests, and coronary angiography. An ECG may confirm an ST elevation MI if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB.", "Tobacco smoking (including secondhand smoke) and short-term exposure to air pollution such as carbon monoxide, nitrogen dioxide, and sulfur dioxide (but not ozone) have been associated with MI. Other factors that increase the risk of MI and are associated with worse outcomes after an MI include lack of physical activity and psychosocial factors including low socioeconomic status, social isolation, and negative emotions. Shift work is also associated with a higher risk of MI. Acute and prolonged intake of high quantities of alcoholic drinks (3-4 or more) increase the risk of a heart attack.", "Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Bloodstream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary arteries, it leads to MI (necrosis of downstream myocardium). It is estimated that one billion cardiac cells are lost in a typical MI." ], [ "Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.", "Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen should be used in those with low oxygen levels or shortness of breath. In ST elevation MIs treatments which attempt to restore blood flow to the heart are typically recommended and include angioplasty, where the arteries are pushed open, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use angioplasty in those at high risk. In people with blockages of multiple coronary arteries and diabetes, bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers, and statins, are typically recommended.", "The onset of symptoms in myocardial infarction (MI) is usually gradual, over several minutes, and rarely instantaneous. Chest pain is the most common symptom of acute MI and is often described as a sensation of tightness, pressure, or squeezing. Chest pain due to ischemia (a lack of blood and hence oxygen supply) of the heart muscle is termed angina pectoris. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen, where it may mimic heartburn. Levine's sign, in which a person localizes the chest pain by clenching their fists over their sternum, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed it had a poor positive predictive value.", "Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol intake, among others. The mechanism of an MI often involves the complete blockage of a coronary artery caused by a rupture of an atherosclerotic plaque. MIs are less commonly caused by coronary artery spasms, which may be due to cocaine, significant emotional stress, and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests, and coronary angiography. An ECG may confirm an ST elevation MI if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB." ] ]
5a7db48670df9f001a87505f	Matter	Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.	en	null	null	190,584	[ "What did the term matter include after the 20th century?", "What are atoms composed of?", "What are two examples of matter?", "What can an object's mass not come from?", "Matter is currently considered to be what kind of concept?" ]	[ [ "There is an entire literature concerning the \"structure of matter\", ranging from the \"electrical structure\" in the early 20th century, to the more recent \"quark structure of matter\", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics.[further explanation needed] In this connection, physicists speak of matter fields, and speak of particles as \"quantum excitations of a mode of the matter field\". And here is a quote from de Sabbata and Gasperini: \"With the word \"matter\" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields).\"[further explanation needed]", "Some critics express the opinion that it is only from the mid-19th century, and especially in the 20th century, that the score began to hold such a high significance. Previously, improvisation (in preludes, cadenzas and ornaments), rhythmic flexibility (e.g., tempo rubato), improvisatory deviation from the score and oral tradition of playing was integral to the style. Yet in the 20th century, this oral tradition and passing on of stylistic features within classical music disappeared. Instead, musicians tend to use just the score to play music. Yet, even with the score providing the key elements of the music, there is considerable controversy about how to perform the works. Some of this controversy relates to the fact that this score-centric approach has led to performances that emphasize metrically strict block-rhythms (just as the music is notated in the score).", "The concept of matter has changed in response to new scientific discoveries. Thus materialism has no definite content independent of the particular theory of matter on which it is based. According to Noam Chomsky, any property can be considered material, if one defines matter such that it has that property.", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality." ], [ "Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine. This occurs normally only during prolonged starvation.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "Vaiśeṣika metaphysical premises are founded on a form of atomism, that the reality is composed of four substances (earth, water, air, fire). Each of these four are of two types: atomic (paramāṇu) and composite. An atom is, according to Vaiśeṣika scholars, that which is indestructible (anitya), indivisible, and has a special kind of dimension, called “small” (aṇu). A composite, in this philosophy, is defined to be anything which is divisible into atoms. Whatever human beings perceive is composite, while atoms are invisible. The Vaiśeṣikas stated that size, form, truths and everything that human beings experience as a whole is a function of atoms, their number and their spatial arrangements, their guṇa (quality), karma (activity), sāmānya (commonness), viśeṣa (particularity) and amavāya (inherence, inseparable connectedness of everything).", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter." ], [ "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes)." ], [ "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object)." ], [ "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Modern philosophical materialists extend the definition of other scientifically observable entities such as energy, forces, and the curvature of space. However philosophers such as Mary Midgley suggest that the concept of \"matter\" is elusive and poorly defined.", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "The concept of matter has changed in response to new scientific discoveries. Thus materialism has no definite content independent of the particular theory of matter on which it is based. According to Noam Chomsky, any property can be considered material, if one defines matter such that it has that property." ] ]
5a7db5c270df9f001a875069	Matter	All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered "point particles" with no effective size or volume. Nevertheless, quarks and leptons together make up "ordinary matter", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.	en	null	null	190,589	[ "What orbits around electrons?", "What are protons and neutrons made out of?", "All particles with rest mass have what kind of volume?", "What cannot contribute to effective volume?", "What kind of size or volume do point particles have?" ]	[ [ "The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as \"orbiting\" the proton in analogy to the Earth's orbit of the Sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.", "Neptune's orbit has a profound impact on the region directly beyond it, known as the Kuiper belt. The Kuiper belt is a ring of small icy worlds, similar to the asteroid belt but far larger, extending from Neptune's orbit at 30 AU out to about 55 AU from the Sun. Much in the same way that Jupiter's gravity dominates the asteroid belt, shaping its structure, so Neptune's gravity dominates the Kuiper belt. Over the age of the Solar System, certain regions of the Kuiper belt became destabilised by Neptune's gravity, creating gaps in the Kuiper belt's structure. The region between 40 and 42 AU is an example.", "Neptune is the eighth and farthest known planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Among the giant planets in the Solar System, Neptune is the most dense. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune.[c] Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 astronomical units (4.50×109 km). Named after the Roman god of the sea, its astronomical symbol is ♆, a stylised version of the god Neptune's trident.", "유로파의 궤도는 근처 다른 위성들이 미치는 중력 때문에 약간 찌그러져 있는데 이는 유로파의 목성 직하점이 평균 위치 근처에서 왔다갔다 하게 만든다. 유로파가 목성에 가까이 오면 목성으로부터 멀리 있을 때보다 중력이 강해져 유로파의 모양을 변형시키고, 유로파가 목성으로부터 먼 지점으로 이동하면 중력이 약해져서 유로파가 다시 원래 모습으로 되돌아가게 된다. 이러한 운동이 표면을 쥐어짜며 조석 가속 현상을 만든다. 유로파의 궤도 이심률은 이오와의 궤도 공명으로 유지된다. 따라서, 이 유로파의 조석 가속은 유로파의 내부가 움직이면서 마찰열을 만들어, 바다가 얼지 않게 하는 에너지를 만든다. 이 에너지의 궁극적인 발생 원인은 이오가 공전하기 때문이다. 목성 주위를 돌 때, 이오가 목성으로부터 에너지를 받고, 그 에너지를 유로파와 가니메데로 보내기 때문이다." ], [ "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components." ], [ "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).", "Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the \"matter\" status of \"massless particles\" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]", "The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average. According to modern understanding, even if all matter could be removed from a volume, it would still not be \"empty\" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays, neutrinos, and other phenomena in quantum physics. In the electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of matter." ], [ "Fluids cannot generally be pulled, so a vacuum cannot be created by suction. Suction can spread and dilute a vacuum by letting a higher pressure push fluids into it, but the vacuum has to be created first before suction can occur. The easiest way to create an artificial vacuum is to expand the volume of a container. For example, the diaphragm muscle expands the chest cavity, which causes the volume of the lungs to increase. This expansion reduces the pressure and creates a partial vacuum, which is soon filled by air pushed in by atmospheric pressure.", "The maximum energy is a function of dielectric volume, permittivity, and dielectric strength. Changing the plate area and the separation between the plates while maintaining the same volume causes no change of the maximum amount of energy that the capacitor can store, so long as the distance between plates remains much smaller than both the length and width of the plates. In addition, these equations assume that the electric field is entirely concentrated in the dielectric between the plates. In reality there are fringing fields outside the dielectric, for example between the sides of the capacitor plates, which will increase the effective capacitance of the capacitor. This is sometimes called parasitic capacitance. For some simple capacitor geometries this additional capacitance term can be calculated analytically. It becomes negligibly small when the ratios of plate width to separation and length to separation are large.", "공기주입은 선체 내에 공기호스를 주입하여, 혹시 모를 선내 생존자들의 생존시간을 늘리는 역할과 부력을 유지하는 역할을 할 수 있다. 물체가 물 위에 뜨기 위해서는 중력에 상응하는 부력이 작용해야 하기 때문이다. 공기는 부력을 증가시켜줄 수 있다. 따라서 일종의 부력주머니인 리프트백과 공기주입을 정부는 추진하였다. 그러나 이러한 조치에 대하여, 알파잠수기술공사 이종인 대표는 이해가 잘 안된다고 논평했다. 공기주입은 사람이 있을 만한 곳에 해야 함에도, 제일 상갑판인 조타실에 공기주입을 했다는 주장이다. 또한, 조타실의 구조적 특성을 근거로 공기가 주입되어 다른 쪽으로 공기가 퍼져 에어포켓을 형성할 가능성에 대해서도 부정했다. 그는 오히려 공기주입은 일단 조사 후, 식당 등 사람이 살아 있을 확률이 있는 곳에 해야 한다고 지적했다. 또, 18일 진행된 정부의 리프트백 설치 양상이 단지 배가 거기 있다고 표시하는 어떤 풍선처럼 돼 있을 뿐, 어떤 부력을 작용하는 효과를 보여주지 못하고 있다고 평가했다.", "The above explanation is merely a simple introduction to vacuum pumping, and is not representative of the entire range of pumps in use. Many variations of the positive displacement pump have been developed, and many other pump designs rely on fundamentally different principles. Momentum transfer pumps, which bear some similarities to dynamic pumps used at higher pressures, can achieve much higher quality vacuums than positive displacement pumps. Entrapment pumps can capture gases in a solid or absorbed state, often with no moving parts, no seals and no vibration. None of these pumps are universal; each type has important performance limitations. They all share a difficulty in pumping low molecular weight gases, especially hydrogen, helium, and neon." ], [ "수성은 지구형 행성 중 하나로, 표면은 암석으로 이루어져 있다. 수성은 태양계 행성들 중 가장 반지름이 작은 행성으로, 구체적인 크기는 2439.7 km이다. 특히, 태양계 내 위성 중, 가니메데나 타이탄은 수성보다 반지름이 크다(그러나 수성은 이들보다는 더 무겁다). 수성은 질량의 70 %는 금속, 나머지 30 %는 규산염 물질로 이루어져 있다. 수성의 밀도는 지구의 5.515 g/cm³다음으로 큰 5.427 g/cm³이다. 그러나 지구는 자체 중력의 영향으로 내부 물질이 더 조밀하게 뭉쳐 있기 때문에, 압축되지 않은 조건에서 비교할 경우 수성의 밀도는 5.3 g/cm³으로 지구의 4.4 g/cm³보다 크다. 이를 통해 실질적으로 수성이 태양계 행성들 중 가장 밀도가 큰 천체임을 알 수 있다.", "In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter (such as plasmas, superfluids, supersolids, Bose–Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of thermodynamics. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details).", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Stars, planets, and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 6998320000000000000♠3.2×10−2 Pa at 100 kilometres (62 mi) of altitude, the Kármán line, which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar winds, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre." ] ]
5a7db6b770df9f001a875073	Matter	Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).	en	null	null	190,594	[ "How many forms of solids are there?", "What theory states that matter can exist in four states?", "Who suggested the Bose-Einstein theory?", "What new form of plasma did Democritus discover?", "How long have scientists focused on an elementary-particle view?" ]	[ [ "In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter (such as plasmas, superfluids, supersolids, Bose–Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of thermodynamics. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details).", "Although the elements usually must be soluble in the liquid state, they may not always be soluble in the solid state. If the metals remain soluble when solid, the alloy forms a solid solution, becoming a homogeneous structure consisting of identical crystals, called a phase. If the mixture cools and the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases. However, in other alloys, the insoluble elements may not separate until after crystallization occurs. These alloys are called intermetallic alloys because, if cooled very quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents. As time passes, the atoms of these supersaturated alloys separate within the crystals, forming intermetallic phases that serve to reinforce the crystals internally.", "Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known, but only one binary aluminium hydride. Binary indium hydride has not yet been identified, although larger complexes exist.", "The vast majority of living organisms encode their genes in long strands of DNA (deoxyribonucleic acid). DNA consists of a chain made from four types of nucleotide subunits, each composed of: a five-carbon sugar (2'-deoxyribose), a phosphate group, and one of the four bases adenine, cytosine, guanine, and thymine.:2.1" ], [ "Vaiśeṣika metaphysical premises are founded on a form of atomism, that the reality is composed of four substances (earth, water, air, fire). Each of these four are of two types: atomic (paramāṇu) and composite. An atom is, according to Vaiśeṣika scholars, that which is indestructible (anitya), indivisible, and has a special kind of dimension, called “small” (aṇu). A composite, in this philosophy, is defined to be anything which is divisible into atoms. Whatever human beings perceive is composite, while atoms are invisible. The Vaiśeṣikas stated that size, form, truths and everything that human beings experience as a whole is a function of atoms, their number and their spatial arrangements, their guṇa (quality), karma (activity), sāmānya (commonness), viśeṣa (particularity) and amavāya (inherence, inseparable connectedness of everything).", "The nature and definition of matter - like other key concepts in science and philosophy - have occasioned much debate. Is there a single kind of matter (hyle) which everything is made of, or multiple kinds? Is matter a continuous substance capable of expressing multiple forms (hylomorphism), or a number of discrete, unchanging constituents (atomism)? Does it have intrinsic properties (substance theory), or is it lacking them (prima materia)?", "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.", "Thomas Davidson taught a philosophy called \"apeirotheism\", a \"form of pluralistic idealism...coupled with a stern ethical rigorism\" which he defined as \"a theory of Gods infinite in number.\" The theory was indebted to Aristotle's pluralism and his concepts of Soul, the rational, living aspect of a living substance which cannot exist apart from the body because it is not a substance but an essence, and nous, rational thought, reflection and understanding. Although a perennial source of controversy, Aristotle arguably views the latter as both eternal and immaterial in nature, as exemplified in his theology of unmoved movers. Identifying Aristotle's God with rational thought, Davidson argued, contrary to Aristotle, that just as the soul cannot exist apart from the body, God cannot exist apart from the world." ], [ "Albert Einstein proposed that the laws of physics should be based on the principle of relativity. This principle holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames. This theory was motivated by Maxwell's equations, which show that electromagnetic waves propagate in a vacuum at the speed of light. However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate.", "The beginning of the 20th century brought the start of a revolution in physics. The long-held theories of Newton were shown not to be correct in all circumstances. Beginning in 1900, Max Planck, Albert Einstein, Niels Bohr and others developed quantum theories to explain various anomalous experimental results, by introducing discrete energy levels. Not only did quantum mechanics show that the laws of motion did not hold on small scales, but even more disturbingly, the theory of general relativity, proposed by Einstein in 1915, showed that the fixed background of spacetime, on which both Newtonian mechanics and special relativity depended, could not exist. In 1925, Werner Heisenberg and Erwin Schrödinger formulated quantum mechanics, which explained the preceding quantum theories. The observation by Edwin Hubble in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the Big Bang theory by Georges Lemaître.", "20세기 초반은 물리학 분야에서 혁명과도 같은 시기였다. 20세기 들어, 오랜 기간동안 정상과학으로 여겨졌던 뉴턴의 이론들은 사물현상에 합치하지 아니한다는 사실이 밝혀지게 되었다. 1900년대 초반, 플랑크, 아인슈타인, 보어 등의 연구자들은 에너지의 이산(離散) 준위에 의한 특별한 현상을 설명하는 양자역학을 제안하였다. 작은 규모에서의 운동법칙을 설명하는 양자역학 뿐만 아니라, 1915년에 아인슈타인이 일반 상대성 이론을 제안하였다. 이 이론은 뉴턴의 고전역학과 특수 상대성 이론이 전제하고 있던 시공간의 개념에 대한 절대적인 기준이 존재할 수 없다는 내용을 담고 있는 것이다. 1925년에, 하이젠베르크와 슈뢰딩거는 양자에 대한 가설을 설명하는 양자역학을 수식화하였다. 1929년, 허블은 관측을 통해 은하의 후퇴를 은하의 거리와 연관시키는 연구를 통해 은하 후퇴의 속도를 밝혀냈으며, 이를 통해 가모프는 우주의 확대에 대한 이해를 이끌어 내었다. 곧이어 르메트르는 우주 확대에 대한 이해를 체계화하는 빅뱅이론을 제시하였다.", "From November 17, 1947 to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in the United States performed experiments and observed that when two gold point contacts were applied to a crystal of germanium, a signal was produced with the output power greater than the input. Solid State Physics Group leader William Shockley saw the potential in this, and over the next few months worked to greatly expand the knowledge of semiconductors. The term transistor was coined by John R. Pierce as a contraction of the term transresistance. According to Lillian Hoddeson and Vicki Daitch, authors of a biography of John Bardeen, Shockley had proposed that Bell Labs' first patent for a transistor should be based on the field-effect and that he be named as the inventor. Having unearthed Lilienfeld’s patents that went into obscurity years earlier, lawyers at Bell Labs advised against Shockley's proposal because the idea of a field-effect transistor that used an electric field as a \"grid\" was not new. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor. In acknowledgement of this accomplishment, Shockley, Bardeen, and Brattain were jointly awarded the 1956 Nobel Prize in Physics \"for their researches on semiconductors and their discovery of the transistor effect.\"" ], [ "Ancient Greek philosophers like Thales, Anaxagoras (ca. 500 BC – 428 BC), Epicurus and Democritus prefigure later materialists. The Latin poem De Rerum Natura by Lucretius (ca. 99 BC – ca. 55 BC) reflects the mechanistic philosophy of Democritus and Epicurus. According to this view, all that exists is matter and void, and all phenomena result from different motions and conglomerations of base material particles called \"atoms\" (literally: \"indivisibles\"). De Rerum Natura provides mechanistic explanations for phenomena such as erosion, evaporation, wind, and sound. Famous principles like \"nothing can touch body but body\" first appeared in the works of Lucretius. Democritus and Epicurus however did not hold to a monist ontology since they held to the ontological separation of matter and space i.e. space being \"another kind\" of being, indicating that the definition of \"materialism\" is wider than given scope for in this article.", "The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide. Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium). He named the newly discovered element after the planet Uranus, (named after the primordial Greek god of the sky), which had been discovered eight years earlier by William Herschel.", "The pre-Socratics were among the first recorded speculators about the underlying nature of the visible world. Thales (c. 624 BC–c. 546 BC) regarded water as the fundamental material of the world. Anaximander (c. 610 BC–c. 546 BC) posited that the basic material was wholly characterless or limitless: the Infinite (apeiron). Anaximenes (flourished 585 BC, d. 528 BC) posited that the basic stuff was pneuma or air. Heraclitus (c. 535–c. 475 BC) seems to say the basic element is fire, though perhaps he means that all is change. Empedocles (c. 490–430 BC) spoke of four elements of which everything was made: earth, water, air, and fire. Meanwhile, Parmenides argued that change does not exist, and Democritus argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy called atomism. All of these notions had deep philosophical problems.", "1895년 11월 8일 늦은 오후, 뢴트겐은 그의 생각을 시험해보기로 했다. 그는 조심스럽게 레나르트의 진공관의 것과 유사한 마분지 덮개를 만들었다. 그는 히토르프-크룩스 진공관을 마분지로 덮고 전극을 정자기 전하를 발생시키는 룸코르프 유도코일(Ruhmkorf induction coil)에 연결했다. 그의 생각을 시험하기 위한 바륨-시안화백금산염(barium platinocyanide) 스크린을 설치하기 전에, 뢴트겐은 마분지 막의 불투명도(opacity)를 확인하기 위해 방을 어둡게 했다. 그가 룸코르프 코일의 전하를 진공관을 통해 흘려보내는 동안 덮개가 빛을 막았다고 생각하고 실험의 다른 단계를 준비하기 위해 돌아섰다. 그 때, 뢴트겐은 진공관에서 몇 피트쯤 떨어진 벤치에서 희미한 발광이 있는 것을 알아차렸다. 당연히 그는 여러 번 방전을 시켜보았고, 매번 발광이 일어나는 것을 확인했다. 그는 그 빛이 나중에 쓰려고 둔 바륨-시안화백금산염 스크린이 있는 곳에서 온 것임을 발견했다. 그는 그것이 새로운 종류의 광선일 것이라고 추측했다. 11월 8일은 금요일이었고, 그는 주말동안 실험을 반복하고 논문을 작성할 수 있었다. 그 다음 주에 그는 실험실에서 먹고 자면서, 그 원인을 규명할 수 없다는 뜻에서 X선이라고 임시로 이름붙인 새로운 광선의 특징들을 연구하였다. 물체들은 어느 정도 차이를 보이지만 이 '새로운 광선'을 투과시킨다는 사실을 알아냈다. 또 엑스레이가 사진건판을 감광시키며, 반사하거나 굴절하지 않는다는 것, 자기장 속에서도 굽어지지 않는다는 것, 음극선이 유리벽이나 반대편 양극에 부딪칠 때 이 빛이 나온다는 것 등을 알아냈다." ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "The photoelectric effect is the emission of electrons (called \"photoelectrons\") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real.", "Einstein showed in his thought experiments that people travelling at different speeds, while agreeing on cause and effect, measure different time separations between events, and can even observe different chronological orderings between non-causally related events. Though these effects are typically minute in the human experience, the effect becomes much more pronounced for objects moving at speeds approaching the speed of light. Many subatomic particles exist for only a fixed fraction of a second in a lab relatively at rest, but some that travel close to the speed of light can be measured to travel farther and survive much longer than expected (a muon is one example). According to the special theory of relativity, in the high-speed particle's frame of reference, it exists, on the average, for a standard amount of time known as its mean lifetime, and the distance it travels in that time is zero, because its velocity is zero. Relative to a frame of reference at rest, time seems to \"slow down\" for the particle. Relative to the high-speed particle, distances seem to shorten. Einstein showed how both temporal and spatial dimensions can be altered (or \"warped\") by high-speed motion.", "일반상대론의 가장 중요한 측면은 우주 전체에 적용될 수 있다는 점이다. 핵심은, 매우 거대한 규모에서는 우리 우주는 매우 단순한 선상에 만들어진 것처럼 보인다. 현재의 모든 관측들은 모든 우주의 구조가 평균적으로 봤을 때 관찰자의 위치나 관찰 방향과 무관하게 근사적으로 동일하다는 점을 시사한다. 즉 우주는 근사적으로 균질하며 등방하다. 이렇게 비교적 단순한 우주는 아인슈타인 방정식의 단순해로써 나타내질 수 있다. 오늘날의 물리우주론 모형들은 이러한 일반상대론의 단순해에 우주의 질량 내용물들을 기술하는 다른 분야, 예컨대 열역학, 핵물리학, 입자물리학 등을 조합하여 만들어진 것이다. 물리우주론 모형들에 따르면 현재의 우리 우주는 약 140억 년 전의 극도의 고밀도 고온 상태, 즉 대폭발로부터 시작되어 그 이후 팽창을 계속하고 있다." ] ]
5a7db77770df9f001a87507d	Matter	Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.	en	null	null	190,599	[ "What is considered the same as matter?", "What does special relativity show mass can do?", "What can be created or destroyed?", "What changes during the transformation of matter?", "What does not change in an open system?" ]	[ [ "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ], [ "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "Energy gives rise to weight when it is trapped in a system with zero momentum, where it can be weighed. It is also equivalent to mass, and this mass is always associated with it. Mass is also equivalent to a certain amount of energy, and likewise always appears associated with it, as described in mass-energy equivalence. The formula E = mc², derived by Albert Einstein (1905) quantifies the relationship between rest-mass and rest-energy within the concept of special relativity. In different theoretical frameworks, similar formulas were derived by J. J. Thomson (1881), Henri Poincaré (1900), Friedrich Hasenöhrl (1904) and others (see Mass-energy equivalence#History for further information).", "아인슈타인은 일반 상대성 이론을 수립한 후 시공간의 구조에 대해 관측 가증한 몇 가지 특별한 예측을 발표하였다. 그 중에 하나는 빛이 중력장에 의해 휠 수 있다는 것이다. 일반 상대성 이론에 따르면 강력한 중력장은 시공간 자체를 변형시키기 때문에 빛 자체로서는 직진한다고 하더라도 제3의 관찰자 입장에서 보았을 때 진행 경로가 곡선일 수 있는 것이다. 예를 들어 블랙홀과 같은 매우 큰 중력장은 배경에 있는 천체에서 나온 빛의 진행에 영향을 주어 제3의 관찰자가 보기에 마치 렌즈를 통해 보는 것처럼 천체의 상(像)이 여러 개로 보일 수 있다. 이를 중력 렌즈라고 한다. 아서 에딩턴은 1919년 개기 일식 때 실제로 중력 렌즈 현상을 관측하여 이를 입증하였다.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object)." ], [ "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "According to the Omnipotence paradox or 'Paradox of the Stone', can God create a stone so heavy that he cannot lift it? Either he can or he can’t. If he can’t, the argument goes, then there is something that he cannot do, namely create the stone, and therefore he is not omnipotent. If he can, it continues, then there is also something that he cannot do, namely lift the stone, and therefore he is not omnipotent. Either way, then, God is not omnipotent. A being that is not omnipotent, though, is not God, according to many theological models. Such a God, therefore, does not exist. Several answers to this paradox have been proposed.", "헌법의 개정은 헌법의 변천과 구분된다(이에 대해서는 뒤에 서술). 또한 헌법의 개정은 헌법의 경우에 반하는 조치를 취하는 헌법의 침훼(侵毁, 독일어: Verfassungsdurchbrechung)와 구분되며(헌법의 침훼는 물론 위헌이다), 혁명 등으로 말미암아 헌법 제정 권력까지도 배제되는 헌법의 파괴 또는 파기(破棄, Verfassungsvernichtung)와도 구분된다. 그뿐만 아니라 기존의 헌법만 배제될 뿐, 헌법 제정 권력은 변경되지 않는 헌법의 폐제(廢除) 또는 폐지(廢止, Verfassungsbeseitigung)와 특정 조항의 효력이 일시적으로 상실되는 헌법의 정지(Verfassungssuspension)와 구분된다.", "It must be emphasized, however, that an entity is not merely a sum of its relations, but also a valuation of them and reaction to them. For Whitehead, creativity is the absolute principle of existence, and every entity (whether it is a human being, a tree, or an electron) has some degree of novelty in how it responds to other entities, and is not fully determined by causal or mechanistic laws. Of course, most entities do not have consciousness. As a human being's actions cannot always be predicted, the same can be said of where a tree's roots will grow, or how an electron will move, or whether it will rain tomorrow. Moreover, inability to predict an electron's movement (for instance) is not due to faulty understanding or inadequate technology; rather, the fundamental creativity/freedom of all entities means that there will always remain phenomena that are unpredictable." ], [ "In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter (such as plasmas, superfluids, supersolids, Bose–Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of thermodynamics. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details).", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes)." ], [ "For \"closed systems\" with no external source or sink of energy, the first law of thermodynamics states that a system's energy is constant unless energy is transferred in or out by mechanical work or heat, and that no energy is lost in transfer. This means that it is impossible to create or destroy energy. While heat can always be fully converted into work in a reversible isothermal expansion of an ideal gas, for cyclic processes of practical interest in heat engines the second law of thermodynamics states that the system doing work always loses some energy as waste heat. This creates a limit to the amount of heat energy that can do work in a cyclic process, a limit called the available energy. Mechanical and other forms of energy can be transformed in the other direction into thermal energy without such limitations. The total energy of a system can be calculated by adding up all forms of energy in the system.", "IBM announced it will launch its new software, called \"Open Client Offering\" which is to run on Linux, Microsoft Windows and Apple's Mac OS X. The company states that its new product allows businesses to offer employees a choice of using the same software on Windows and its alternatives. This means that \"Open Client Offering\" is to cut costs of managing whether to use Linux or Apple relative to Windows. There will be no necessity for companies to pay Microsoft for its licenses for operating systems since the operating systems will no longer rely on software which is Windows-based. One alternative to Microsoft's office document formats is the Open Document Format software, whose development IBM supports. It is going to be used for several tasks like: word processing, presentations, along with collaboration with Lotus Notes, instant messaging and blog tools as well as an Internet Explorer competitor – the Mozilla Firefox web browser. IBM plans to install Open Client on 5% of its desktop PCs. The Linux offering has been made available as the IBM Client for Smart Work product on the Ubuntu and Red Hat Enterprise Linux platforms.", "According to conservation of energy, energy can neither be created (produced) nor destroyed by itself. It can only be transformed. The total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. Energy is subject to a strict global conservation law; that is, whenever one measures (or calculates) the total energy of a system of particles whose interactions do not depend explicitly on time, it is found that the total energy of the system always remains constant.", "In November 2014, the Bill and Melinda Gates Foundation announced that they are adopting an open access (OA) policy for publications and data, \"to enable the unrestricted access and reuse of all peer-reviewed published research funded by the foundation, including any underlying data sets\". This move has been widely applauded by those who are working in the area of capacity building and knowledge sharing.[citation needed] Its terms have been called the most stringent among similar OA policies. As of January 1, 2015 their Open Access policy is effective for all new agreements." ] ]
5a7db7f770df9f001a875087	Matter	Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word "matter". Scientifically, the term "mass" is well-defined, but "matter" is not. Sometimes in the field of physics "matter" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.	en	null	null	190,604	[ "What is always used the same way across fields?", "What is poorly defined besides matter?", "What does matter do in chemistry that it does not do in physics?", "What is the combination of mass and matter called in chemistry?", "What speed does matter travel at in physics?" ]	[ [ "The Canadian football field is 150 yards (137 m) long and 65 yards (59 m) wide with end zones 20 yards (18 m) deep, and goal lines 110 yards (101 m) apart. At each goal line is a set of 40-foot-high (12 m) goalposts, which consist of two uprights joined by an 18 1⁄2-foot-long (5.6 m) crossbar which is 10 feet (3 m) above the goal line. The goalposts may be H-shaped (both posts fixed in the ground) although in the higher-calibre competitions the tuning-fork design (supported by a single curved post behind the goal line, so that each post starts 10 feet (3 m) above the ground) is preferred. The sides of the field are marked by white sidelines, the goal line is marked in white, and white lines are drawn laterally across the field every 5 yards (4.6 m) from the goal line. These lateral lines are called \"yard lines\" and often marked with the distance in yards from and an arrow pointed toward the nearest goal line. In previous decades, arrows were not used and every yard line was usually marked with the distance to the goal line, including the goal line itself which was marked with a \"0\"; in most stadiums today, the 10-, 20-, 30-, 40-, and 50-yard lines are marked with numbers, with the goal line sometimes being marked with a \"G\". The centre (55-yard) line usually is marked with a \"C\". \"Hash marks\" are painted in white, parallel to the yardage lines, at 1 yard (0.9 m) intervals, 24 yards (21.9 m) from the sidelines. On fields that have a surrounding running track, such as Commonwealth Stadium, Molson Stadium, and many universities, the end zones are often cut off in the corners to accommodate the track. In 2014, Edmonton placed turf over the track to create full end zones. This was particularly common among U.S.-based teams during the CFL's American expansion, where few American stadiums were able to accommodate the much longer and noticeably wider CFL field.", "The development of a three-field rotation system for planting crops[AA] increased the usage of land from one half in use each year under the old two-field system to two-thirds under the new system, with a consequent increase in production. The development of the heavy plough allowed heavier soils to be farmed more efficiently, aided by the spread of the horse collar, which led to the use of draught horses in place of oxen. Horses are faster than oxen and require less pasture, factors that aided the implementation of the three-field system.", "As the Laws were formulated in England, and were initially administered solely by the four British football associations within IFAB, the standard dimensions of a football pitch were originally expressed in imperial units. The Laws now express dimensions with approximate metric equivalents (followed by traditional units in brackets), though use of imperial units remains popular in English-speaking countries with a relatively recent history of metrication (or only partial metrication), such as Britain.", "Migratory birds may use two electromagnetic tools to find their destinations: one that is entirely innate and another that relies on experience. A young bird on its first migration flies in the correct direction according to the Earth's magnetic field, but does not know how far the journey will be. It does this through a radical pair mechanism whereby chemical reactions in special photo pigments sensitive to long wavelengths are affected by the field. Although this only works during daylight hours, it does not use the position of the sun in any way. At this stage the bird is in the position of a boy scout with a compass but no map, until it grows accustomed to the journey and can put its other capabilities to use. With experience it learns various landmarks and this \"mapping\" is done by magnetites in the trigeminal system, which tell the bird how strong the field is. Because birds migrate between northern and southern regions, the magnetic field strengths at different latitudes let it interpret the radical pair mechanism more accurately and let it know when it has reached its destination. There is a neural connection between the eye and \"Cluster N\", the part of the forebrain that is active during migrational orientation, suggesting that birds may actually be able to see the magnetic field of the earth." ], [ "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "Modern philosophical materialists extend the definition of other scientifically observable entities such as energy, forces, and the curvature of space. However philosophers such as Mary Midgley suggest that the concept of \"matter\" is elusive and poorly defined.", "The term \"matter\" is used throughout physics in a bewildering variety of contexts: for example, one refers to \"condensed matter physics\", \"elementary matter\", \"partonic\" matter, \"dark\" matter, \"anti\"-matter, \"strange\" matter, and \"nuclear\" matter. In discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter (Gk. common matter). It is fair to say that in physics, there is no broad consensus as to a general definition of matter, and the term \"matter\" usually is used in conjunction with a specifying modifier." ], [ "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below)." ], [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ], [ "Einstein showed in his thought experiments that people travelling at different speeds, while agreeing on cause and effect, measure different time separations between events, and can even observe different chronological orderings between non-causally related events. Though these effects are typically minute in the human experience, the effect becomes much more pronounced for objects moving at speeds approaching the speed of light. Many subatomic particles exist for only a fixed fraction of a second in a lab relatively at rest, but some that travel close to the speed of light can be measured to travel farther and survive much longer than expected (a muon is one example). According to the special theory of relativity, in the high-speed particle's frame of reference, it exists, on the average, for a standard amount of time known as its mean lifetime, and the distance it travels in that time is zero, because its velocity is zero. Relative to a frame of reference at rest, time seems to \"slow down\" for the particle. Relative to the high-speed particle, distances seem to shorten. Einstein showed how both temporal and spatial dimensions can be altered (or \"warped\") by high-speed motion.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Albert Einstein proposed that the laws of physics should be based on the principle of relativity. This principle holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames. This theory was motivated by Maxwell's equations, which show that electromagnetic waves propagate in a vacuum at the speed of light. However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate.", "Neptune's weather is characterised by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s (2,200 km/h; 1,300 mph)—nearly reaching supersonic flow. More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20 m/s in the easterly direction to 325 m/s westward. At the cloud tops, the prevailing winds range in speed from 400 m/s along the equator to 250 m/s at the poles. Most of the winds on Neptune move in a direction opposite the planet's rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is thought to be a \"skin effect\" and not due to any deeper atmospheric processes. At 70° S latitude, a high-speed jet travels at a speed of 300 m/s." ] ]
5a7db89470df9f001a875091	Matter	In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. "Matter" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.	en	null	null	190,609	[ "What type of quantity is mass?", "One can add the rest masses of particles in a system to get what?", "What can the energy-momentum tensor not do?", "What does gravity contribute to in a system?", "What field does not view matter as a contributor to energy-momentum?" ]	[ [ "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter (such as plasmas, superfluids, supersolids, Bose–Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of thermodynamics. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details).", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality." ], [ "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).", "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]", "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter." ], [ "In general relativity, a vanishing stress-energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does not mean that the curvature of space-time is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and gravitational waves (technically, these phenomena are the components of the Weyl tensor). The black hole (with zero electric charge) is an elegant example of a region completely \"filled\" with vacuum, but still showing a strong curvature.", "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as \"orbiting\" the proton in analogy to the Earth's orbit of the Sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics." ], [ "The single most revealing property of wood as an indicator of wood quality is specific gravity (Timell 1986), as both pulp yield and lumber strength are determined by it. Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water; density is the ratio of a mass of a quantity of a substance to the volume of that quantity and is expressed in mass per unit substance, e.g., grams per millilitre (g/cm3 or g/ml). The terms are essentially equivalent as long as the metric system is used. Upon drying, wood shrinks and its density increases. Minimum values are associated with green (water-saturated) wood and are referred to as basic specific gravity (Timell 1986).", "케플러는 우주를 종교적인 관점으로, 태양이 하나님 아버지의 상징이며 태양계 기동력의 원천이라고 생각했다. 실제로 케플러는 《자석에 관해서》(1600년)에 나온 지구의 자기적에 대한 윌리엄 길버트의 이론과 광학에 유추하여 자신의 연구를 이끌어 냈다. 케플러는 행성이 태양에 가깝고 멀리 갈수록 운동이 빨라지고 느려지기 때문에 움직이는 힘(또는 움직이는 생명) 이 태양에 의해 퍼져나가며, 멀어질수록 약화된다고 생각했다. 이 가정은 천문학적 체계를 부활시킬 수학적 관계를 담고 있었던 것으로 보인다. 그는 원일점과 지구와 화성의 근일점 측정에 바탕하여 행성의 운동 비율은 태양까지의 거리에 반비례한다는 법칙을 알아냈다. 궤도 주기를 통해 이 관계를 입증했지만, 이는 대규모의 계산을 필요로 했다. 이 작업을 단순화하기 위해 1602년 말에 케플러는 기하학적 관점에서 계산을 다음과 같이 재공식화했다. “행성과 태양을 연결하는 가상적인 선분이 같은 시간 동안 쓸고 지나가는 면적은 행성과 태양 사이 거리에 관계없이 항상 같다.” 이것이 제2 법칙, 면적속도 일정의 법칙이었다.", "This principle is vitally important to understanding the behaviour of a quantity closely related to energy, called entropy. Entropy is a measure of evenness of a distribution of energy between parts of a system. When an isolated system is given more degrees of freedom (i.e., given new available energy states that are the same as existing states), then total energy spreads over all available degrees equally without distinction between \"new\" and \"old\" degrees. This mathematical result is called the second law of thermodynamics.", "실용적 적용에 있어 대단히 탁월하게 유용한 사례는 범지구위치결정시스템(GPS)을 비롯한 위성항법시스템들이다. 위성항법시스템들은 항법(위치의 결정)과 계시(시간의 결정)라는 두 가지 업무를 매우 높은 정밀도로 수행한다. 이러한 시스템들은 두 개의 원자시계로 이루어져 있다. 원자시계 하나는 지구 주위를 공전하는 궤도상의 인공위성에 탑재되어 있고, 나머지 하나는 대조군으로서 지구 표면에 장치되어 있다. 일반상대론의 예측에 따르면 두 시계는 운동이 다르기 때문에(이 효과는 특수상대론에서 이미 예측된 바이다) 그리고 지구의 중력장 안에서 점하고 있는 위치가 다르기 때문에 시간에 차이가 발생할 것이다. 시스템의 정확도를 유지하기 위해서는 인공위성에 탑재된 시계가 상대론적 요인을 고려하거나 또는 평가 알고리즘을 통한 요인을 사용하여 좀더 느리게 가게 해야 한다. 다시 말하면, 위성항법시스템의 정확도 시험(특히 협정세계시의 정의를 내리기 위한 매우 철저한 측정 등)은 상대론적 예측의 타당성을 검증하는 시험이기도 한 것이다." ], [ "One challenge to the traditional concept of matter as tangible \"stuff\" came with the rise of field physics in the 19th century. Relativity shows that matter and energy (including the spatially distributed energy of fields) are interchangeable. This enables the ontological view that energy is prima materia and matter is one of its forms. On the other hand, the Standard Model of Particle physics uses quantum field theory to describe all interactions. On this view it could be said that fields are prima materia and the energy is a property of the field.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality." ] ]
5a7db92970df9f001a87509b	Matter	The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]	en	null	null	190,614	[ "What type of radiation does not contribute mass?", "What is another name for electromagnetic radiation?", "What is another name for isolated kinetic energy of massive particles?" ]	[ [ "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics." ], [ "Prior to Einstein's paper, electromagnetic radiation such as visible light was considered to behave as a wave: hence the use of the terms \"frequency\" and \"wavelength\" to characterise different types of radiation. The energy transferred by a wave in a given time is called its intensity. The light from a theatre spotlight is more intense than the light from a domestic lightbulb; that is to say that the spotlight gives out more energy per unit time and per unit space(and hence consumes more electricity) than the ordinary bulb, even though the colour of the light might be very similar. Other waves, such as sound or the waves crashing against a seafront, also have their own intensity. However, the energy account of the photoelectric effect didn't seem to agree with the wave description of light.", "Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the \"thumb in the direction of the propagation\" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.", "Heat is energy in transit that flows due to temperature difference. Unlike heat transmitted by thermal conduction or thermal convection, thermal radiation can propagate through a vacuum. Thermal radiation is characterized by a particular spectrum of many wavelengths that is associated with emission from an object, due to the vibration of its molecules at a given temperature. Thermal radiation can be emitted from objects at any wavelength, and at very high temperatures such radiations are associated with spectra far above the infrared, extending into visible, ultraviolet, and even X-ray regions (i.e., the solar corona). Thus, the popular association of infrared radiation with thermal radiation is only a coincidence based on typical (comparatively low) temperatures often found near the surface of planet Earth.", "In the last years of the nineteenth century, Planck was investigating the problem of black-body radiation first posed by Kirchhoff some forty years earlier. It is well known that hot objects glow, and that hotter objects glow brighter than cooler ones. The electromagnetic field obeys laws of motion similarly to a mass on a spring, and can come to thermal equilibrium with hot atoms. The hot object in equilibrium with light absorbs just as much light as it emits. If the object is black, meaning it absorbs all the light that hits it, then its thermal light emission is maximized." ], [ "Energy transformations in the universe over time are characterized by various kinds of potential energy that has been available since the Big Bang later being \"released\" (transformed to more active types of energy such as kinetic or radiant energy) when a triggering mechanism is available. Familiar examples of such processes include nuclear decay, in which energy is released that was originally \"stored\" in heavy isotopes (such as uranium and thorium), by nucleosynthesis, a process ultimately using the gravitational potential energy released from the gravitational collapse of supernovae, to store energy in the creation of these heavy elements before they were incorporated into the solar system and the Earth. This energy is triggered and released in nuclear fission bombs or in civil nuclear power generation. Similarly, in the case of a chemical explosion, chemical potential energy is transformed to kinetic energy and thermal energy in a very short time. Yet another example is that of a pendulum. At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum. At its lowest point the kinetic energy is at maximum and is equal to the decrease of potential energy. If one (unrealistically) assumes that there is no friction or other losses, the conversion of energy between these processes would be perfect, and the pendulum would continue swinging forever.", "Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the \"matter\" status of \"massless particles\" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]", "The total energy of a system can be subdivided and classified in various ways. For example, classical mechanics distinguishes between kinetic energy, which is determined by an object's movement through space, and potential energy, which is a function of the position of an object within a field. It may also be convenient to distinguish gravitational energy, thermal energy, several types of nuclear energy (which utilize potentials from the nuclear force and the weak force), electric energy (from the electric field), and magnetic energy (from the magnetic field), among others. Many of these classifications overlap; for instance, thermal energy usually consists partly of kinetic and partly of potential energy.", "Some types of energy are a varying mix of both potential and kinetic energy. An example is mechanical energy which is the sum of (usually macroscopic) kinetic and potential energy in a system. Elastic energy in materials is also dependent upon electrical potential energy (among atoms and molecules), as is chemical energy, which is stored and released from a reservoir of electrical potential energy between electrons, and the molecules or atomic nuclei that attract them.[need quotation to verify].The list is also not necessarily complete. Whenever physical scientists discover that a certain phenomenon appears to violate the law of energy conservation, new forms are typically added that account for the discrepancy." ] ]
5a7dbca870df9f001a8750b5	Matter	A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only "rest mass" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the "invariant mass" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).	en	null	null	190,617	[ "How many difficulties are there in defining mass?", "What is invariant mass equivalent to?", "What type of systems is rest mass applied to?", "Invariant mass cannot be weighed when a system has no what?", "Kinetic energy cannot add what kind of mass to a system?" ]	[ [ "Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the \"matter\" status of \"massless particles\" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "There are both practical and theoretical difficulties in determining h. The practical difficulties can be illustrated by the fact that the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another. The most likely reason is that the measurement uncertainty for one (or both) of the methods has been estimated too low – it is (or they are) not as precise as is currently believed – but for the time being there is no indication which method is at fault.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects." ], [ "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "In classical physics, an inertial reference frame is one in which an object that experiences no forces does not accelerate. In general relativity, an inertial frame of reference is one that is following a geodesic of space-time. An object that moves against a geodesic experiences a force. An object in free fall does not experience a force, because it is following a geodesic. An object standing on the earth, however, will experience a force, as it is being held against the geodesic by the surface of the planet. In light of this, the bucket of water rotating in empty space will experience a force because it rotates with respect to the geodesic. The water will become concave, not because it is rotating with respect to the distant stars, but because it is rotating with respect to the geodesic.", "In the classical case, the invariance, or symmetry, group and the covariance group coincide, but, interestingly enough, they part ways in relativistic physics. The symmetry group of the general theory of relativity includes all differentiable transformations, i.e., all properties of an object are dynamical, in other words there are no absolute objects. The formulations of the general theory of relativity, unlike those of classical mechanics, do not share a standard, i.e., there is no single formulation paired with transformations. As such the covariance group of the general theory of relativity is just the covariance group of every theory." ], [ "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "Energy gives rise to weight when it is trapped in a system with zero momentum, where it can be weighed. It is also equivalent to mass, and this mass is always associated with it. Mass is also equivalent to a certain amount of energy, and likewise always appears associated with it, as described in mass-energy equivalence. The formula E = mc², derived by Albert Einstein (1905) quantifies the relationship between rest-mass and rest-energy within the concept of special relativity. In different theoretical frameworks, similar formulas were derived by J. J. Thomson (1881), Henri Poincaré (1900), Friedrich Hasenöhrl (1904) and others (see Mass-energy equivalence#History for further information).", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or interseasonal durations. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements." ], [ "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the \"matter\" status of \"massless particles\" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]", "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter." ], [ "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.", "Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the \"matter\" status of \"massless particles\" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]", "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]" ] ]
5a7dc20570df9f001a875117	Matter	Since such mass (kinetic energies of particles, the energy of trapped electromagnetic radiation and stored potential energy of repulsive fields) is measured as part of the mass of ordinary matter in complex systems, the "matter" status of "massless particles" and fields of force becomes unclear in such systems. These problems contribute to the lack of a rigorous definition of matter in science, although mass is easier to define as the total stress–energy above (this is also what is weighed on a scale, and what is the source of gravity).[citation needed]	en	null	null	190,622	[ "What is electromagnetic radiation stored in?", "The mass of kinetic energy particles is not considered part of what?", "What tends to be clear in complex systems?", "What field has a clear definition of matter?", "Mass is harder to define as being what?" ]	[ [ "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]", "A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e. an insulator that can store energy by becoming polarized). The conductors can be thin films, foils or sintered beads of metal or conductive electrolyte, etc. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.", "The majority of eukaryotic genes are stored on a set of large, linear chromosomes. The chromosomes are packed within the nucleus in complex with storage proteins called histones to form a unit called a nucleosome. DNA packaged and condensed in this way is called chromatin.:4.2 The manner in which DNA is stored on the histones, as well as chemical modifications of the histone itself, regulate whether a particular region of DNA is accessible for gene expression. In addition to genes, eukaryotic chromosomes contain sequences involved in ensuring that the DNA is copied without degradation of end regions and sorted into daughter cells during cell division: replication origins, telomeres and the centromere.:4.2 Replication origins are the sequence regions where DNA replication is initiated to make two copies of the chromosome. Telomeres are long stretches of repetitive sequence that cap the ends of the linear chromosomes and prevent degradation of coding and regulatory regions during DNA replication. The length of the telomeres decreases each time the genome is replicated and has been implicated in the aging process. The centromere is required for binding spindle fibres to separate sister chromatids into daughter cells during cell division.:18.2", "In a slower process, radioactive decay of atoms in the core of the Earth releases heat. This thermal energy drives plate tectonics and may lift mountains, via orogenesis. This slow lifting represents a kind of gravitational potential energy storage of the thermal energy, which may be later released to active kinetic energy in landslides, after a triggering event. Earthquakes also release stored elastic potential energy in rocks, a store that has been produced ultimately from the same radioactive heat sources. Thus, according to present understanding, familiar events such as landslides and earthquakes release energy that has been stored as potential energy in the Earth's gravitational field or elastic strain (mechanical potential energy) in rocks. Prior to this, they represent release of energy that has been stored in heavy atoms since the collapse of long-destroyed supernova stars created these atoms." ], [ "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.", "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ], [ "A computer will solve problems in exactly the way it is programmed to, without regard to efficiency, alternative solutions, possible shortcuts, or possible errors in the code. Computer programs that learn and adapt are part of the emerging field of artificial intelligence and machine learning.", "It would appear that living organisms are remarkably inefficient (in the physical sense) in their use of the energy they receive (chemical energy or radiation), and it is true that most real machines manage higher efficiencies. In growing organisms the energy that is converted to heat serves a vital purpose, as it allows the organism tissue to be highly ordered with regard to the molecules it is built from. The second law of thermodynamics states that energy (and matter) tends to become more evenly spread out across the universe: to concentrate energy (or matter) in one specific place, it is necessary to spread out a greater amount of energy (as heat) across the remainder of the universe (\"the surroundings\").[note 3] Simpler organisms can achieve higher energy efficiencies than more complex ones, but the complex organisms can occupy ecological niches that are not available to their simpler brethren. The conversion of a portion of the chemical energy to heat at each step in a metabolic pathway is the physical reason behind the pyramid of biomass observed in ecology: to take just the first step in the food chain, of the estimated 124.7 Pg/a of carbon that is fixed by photosynthesis, 64.3 Pg/a (52%) are used for the metabolism of green plants, i.e. reconverted into carbon dioxide and heat.", "Mathematicians often strive for a complete classification (or list) of a mathematical notion. In the context of finite groups, this aim leads to difficult mathematics. According to Lagrange's theorem, finite groups of order p, a prime number, are necessarily cyclic (abelian) groups Zp. Groups of order p2 can also be shown to be abelian, a statement which does not generalize to order p3, as the non-abelian group D4 of order 8 = 23 above shows. Computer algebra systems can be used to list small groups, but there is no classification of all finite groups.q[›] An intermediate step is the classification of finite simple groups.r[›] A nontrivial group is called simple if its only normal subgroups are the trivial group and the group itself.s[›] The Jordan–Hölder theorem exhibits finite simple groups as the building blocks for all finite groups. Listing all finite simple groups was a major achievement in contemporary group theory. 1998 Fields Medal winner Richard Borcherds succeeded in proving the monstrous moonshine conjectures, a surprising and deep relation between the largest finite simple sporadic group—the \"monster group\"—and certain modular functions, a piece of classical complex analysis, and string theory, a theory supposed to unify the description of many physical phenomena.", "In mathematics, a group is an algebraic structure consisting of a set of elements equipped with an operation that combines any two elements to form a third element. The operation satisfies four conditions called the group axioms, namely closure, associativity, identity and invertibility. One of the most familiar examples of a group is the set of integers together with the addition operation, but the abstract formalization of the group axioms, detached as it is from the concrete nature of any particular group and its operation, applies much more widely. It allows entities with highly diverse mathematical origins in abstract algebra and beyond to be handled in a flexible way while retaining their essential structural aspects. The ubiquity of groups in numerous areas within and outside mathematics makes them a central organizing principle of contemporary mathematics." ], [ "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "There is an entire literature concerning the \"structure of matter\", ranging from the \"electrical structure\" in the early 20th century, to the more recent \"quark structure of matter\", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics.[further explanation needed] In this connection, physicists speak of matter fields, and speak of particles as \"quantum excitations of a mode of the matter field\". And here is a quote from de Sabbata and Gasperini: \"With the word \"matter\" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields).\"[further explanation needed]", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below)." ], [ "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object).", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "In the context of relativity, mass is not an additive quantity, in the sense that one can add the rest masses of particles in a system to get the total rest mass of the system. Thus, in relativity usually a more general view is that it is not the sum of rest masses, but the energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. \"Matter\" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology. In this view, light and other massless particles and fields are part of matter.", "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter." ] ]
5a7dc2b470df9f001a87512b	Matter	A definition of "matter" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent "particles" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).	en	null	null	190,627	[ "What is made out of negatively charged protons?", "What type of charge do atoms have?", "This definition does not include what type of matter?", "What is located in a sea of protons?", "What are made up of leptons?" ]	[ [ "Oxidation of hydrogen removes its electron and gives H+, which contains no electrons and a nucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central to discussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptors.", "A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to them. However, the term 'proton' is sometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to other species in this fashion, and as such is denoted \"H+\" without any implication that any single protons exist freely as a species.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "64Zn, the most abundant isotope of zinc, is very susceptible to neutron activation, being transmuted into the highly radioactive 65Zn, which has a half-life of 244 days and produces intense gamma radiation. Because of this, Zinc Oxide used in nuclear reactors as an anti-corrosion agent is depleted of 64Zn before use, this is called depleted zinc oxide. For the same reason, zinc has been proposed as a salting material for nuclear weapons (cobalt is another, better-known salting material). A jacket of isotopically enriched 64Zn would be irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, forming a large amount of 65Zn significantly increasing the radioactivity of the weapon's fallout. Such a weapon is not known to have ever been built, tested, or used. 65Zn is also used as a tracer to study how alloys that contain zinc wear out, or the path and the role of zinc in organisms." ], [ "The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent compounds with most non-metallic elements, most of the hydrogen on Earth exists in molecular forms such as in the form of water or organic compounds. Hydrogen plays a particularly important role in acid–base reactions as many acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) when it is known as a hydride, or as a positively charged (i.e., cation) species denoted by the symbol H+. The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex species than that would suggest. As the only neutral atom for which the Schrödinger equation can be solved analytically, study of the energetics and bonding of the hydrogen atom has played a key role in the development of quantum mechanics.", "Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-white metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable (with half-lives of the six naturally known isotopes, uranium-233 to uranium-238, varying between 69 years and 4.5 billion years). The most common isotopes of uranium are uranium-238 (which has 146 neutrons and accounts for almost 99.3% of the uranium found in nature) and uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found naturally). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.", "Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 7000100794000000000♠1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note 1] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.", "Because of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. Furthermore, the corresponding simplicity of the hydrogen molecule and the corresponding cation H+\n2 allowed fuller understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s." ], [ "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy." ], [ "A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to them. However, the term 'proton' is sometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to other species in this fashion, and as such is denoted \"H+\" without any implication that any single protons exist freely as a species.", "The mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane. As is customary in planetary science, this mixture is referred to as icy even though it is a hot, dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean. The mantle may consist of a layer of ionic water in which the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice. At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones. Very-high-pressure experiments at the Lawrence Livermore National Laboratory suggest that the base of the mantle may comprise an ocean of liquid carbon with floating solid 'diamonds'.", "A molecular form called protonated molecular hydrogen (H+\n3) is found in the interstellar medium, where it is generated by ionization of molecular hydrogen from cosmic rays. This charged ion has also been observed in the upper atmosphere of the planet Jupiter. The ion is relatively stable in the environment of outer space due to the low temperature and density. H+\n3 is one of the most abundant ions in the Universe, and it plays a notable role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H3 can only exist in an excited form and is unstable. By contrast, the positive hydrogen molecular ion (H+\n2) is a rare molecule in the universe.", "Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4." ], [ "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles." ] ]
5a7dc3ae70df9f001a875135	Matter	Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)	en	null	null	190,632	[ "What is the most famous electron?", "What are quarks made from?", "Who determined that electrons were leptons?", "How many generation particles are there?", "What type of fermions are protons and neutrons?" ]	[ [ "Although exotic on Earth, one of the most common ions in the universe is the H+\n3 ion, known as protonated molecular hydrogen or the trihydrogen cation.", "Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 7000100794000000000♠1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note 1] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.", "Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-white metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable (with half-lives of the six naturally known isotopes, uranium-233 to uranium-238, varying between 69 years and 4.5 billion years). The most common isotopes of uranium are uranium-238 (which has 146 neutrons and accounts for almost 99.3% of the uranium found in nature) and uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found naturally). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter." ], [ "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks. It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars).", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below)." ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "1세대의 전하를 띠는 렙톤인, 전자는 19세기의 여러 과학자들에 의해 이론적으로 제안되었고, 1897년에 J.J.Tomson과 그의 동료인 여러 영국 물리학자들이 발견했다. 그 후 전자 1930년 Wolfgang Pauli가 베타 붕괴 현상 이전과 이후의 에너지, 운동량, 각운동량이 보존되지 않는다는 실험 결과에 아직 발견되지 않은 입자가 숨어 있을 것이라 추론했으며, 그 숨어 있는 입자를 중성미자(neutrino)라고 명명했다. 여담으로 당시에는 전자 중성미자라고 따로 명명되지 않은 이유는 전자 이외의 전하를 띠는 렙톤이 제안되지 않아서 렙톤이라는 개념조차 없었던 시대였기 때문이다. 전자 중성미자는 1956년 Clyde Cowan과 Frederick Reines이 훗날 ‘Cowan-Reines 중성미자 실험’라 명명된 실험을 통하여 처음 발견했다.", "1세대의 전하를 띠는 렙톤 전자는 19세기의 여러 과학자들에 의해 이론적으로 제안되었고, 1897년에 톰슨이 발견했다. 뮤온은 1936년에 앤더슨이 발견했으나, 발견 당시에는 메존으로 잘못 분류했었다. 그러나 실험을 통해, 새로 발견한 뮤온이 메존의 성질을 띠기보다는 전자에 가까운 성질을 띤다는 사실을 알아냈다. 1947년에서야 전자와 같이 행동하는 입자들을 ‘렙톤’이라 이름 붙여주며, 뮤온을 렙톤에 포함시켰다. 전자 중성미자는 1930년 파울리가 입자의 베타 붕괴 현상을 설명하기 위해, 이론적으로 처음 제안했다. 전자 중성미자는 1956년 카원과 라이너스가 훗날 ‘카원-라이너스 중성미자 실험’라 명명된 실험을 통하여 처음 발견했다. 뮤온 중성미자는 1962년 레더먼, 슈워츠, 스타인버거가 발견했다. 타우온은 1974년과 1977년 사이에 스탠퍼드 선형 가속기 센터와 로런스 버클리 국립 연구소에서 연구한 마틴 루이스 펄과 그의 동료들이 발견했다. 타우 중성미자는 2000년 7월 페르미 국립 가속기 연구소의 DONUT Collaboration이 발견했다고 발표했다.", "The photoelectric effect is the emission of electrons (called \"photoelectrons\") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real." ], [ "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "The duplication and transmission of genetic material from one generation of cells to the next is the basis for molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parents' cells. In asexually reproducing organisms, the offspring will be a genetic copy or clone of the parent organism. In sexually reproducing organisms, a specialized form of cell division called meiosis produces cells called gametes or germ cells that are haploid, or contain only one copy of each gene.:20.2 The gametes produced by females are called eggs or ova, and those produced by males are called sperm. Two gametes fuse to form a diploid fertilized egg, a single cell that has two sets of genes, with one copy of each gene from the mother and one from the father.:20", "The growth, development, and reproduction of organisms relies on cell division, or the process by which a single cell divides into two usually identical daughter cells. This requires first making a duplicate copy of every gene in the genome in a process called DNA replication.:5.2 The copies are made by specialized enzymes known as DNA polymerases, which \"read\" one strand of the double-helical DNA, known as the template strand, and synthesize a new complementary strand. Because the DNA double helix is held together by base pairing, the sequence of one strand completely specifies the sequence of its complement; hence only one strand needs to be read by the enzyme to produce a faithful copy. The process of DNA replication is semiconservative; that is, the copy of the genome inherited by each daughter cell contains one original and one newly synthesized strand of DNA.:5.2" ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays (electrons or positrons from the elements produced; see beta particle). The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ausonium and hesperium, respectively. The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann in Hahn's laboratory in Berlin. Lise Meitner and her nephew, the physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process \"nuclear fission\". Soon after, Fermi hypothesized that the fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of the rare uranium isotope uranium-235. Further work found that the far more common uranium-238 isotope can be transmuted into plutonium, which, like uranium-235, is also fissile by thermal neutrons. These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power." ] ]
5a7dc46e70df9f001a875147	Matter	The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the "mass" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.	en	null	null	190,637	[ "What are atoms and molecules elementary forms of?", "What holds building blocks together?", "What is the mass of a proton?", "What binds an atom together?", "Most of the mass of binding energy is due to what?" ]	[ [ "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine. This occurs normally only during prolonged starvation.", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ], [ "Building first evolved out of the dynamics between needs (shelter, security, worship, etc.) and means (available building materials and attendant skills). As human cultures developed and knowledge began to be formalized through oral traditions and practices, building became a craft, and \"architecture\" is the name given to the most highly formalized and respected versions of that craft.", "보통 시스템 구조 및 동작을 제어하고 분석하는데 많이 쓰인다. 각 장치, 예를 들면 자동차에서는 모터 및 기어 등이 블록이 되고 아파트에서는 각 층과 기둥 및 구조물들이 블록이 되는 것이다. 이때 장치 사이에 적용되는 물리적인 관계식들이 블록을 잇는 선이 된다. 이러한 블록들은 결국 입력에서 출력까지 이어지게 되는데 이를 통해 시스템의 구조를 간단하게 정리할 수 있다. .즉 블록 다이어그램을 사용하면 복잡한 물리적인 인과관계들이 어떻게 전달되는지 쉽게 파악할 수 있다. 동시에 이를 제어하려면 어떤 요소를 조정해야 하는지까지도 쉽게 찾을 수 있으므로 간단한 숙제문제에서부터 권위있는 연구 논문까지 광범위하게 쓰이는 시스템 표현 방법 중 하나이다.", "Building Partnerships is described as airmen interacting with international airmen and other relevant actors to develop, guide, and sustain relationships for mutual benefit and security. Building Partnerships is about interacting with others and is therefore an inherently inter-personal and cross-cultural undertaking. Through both words and deeds, the majority of interaction is devoted to building trust-based relationships for mutual benefit. It includes both foreign partners as well as domestic partners and emphasizes collaboration with foreign governments, militaries and populations as well as US government departments, agencies, industry, and NGOs. To better facilitate partnering efforts, Airmen should be competent in the relevant language, region, and culture.", "Architecture (Latin architectura, from the Greek ἀρχιτέκτων arkhitekton \"architect\", from ἀρχι- \"chief\" and τέκτων \"builder\") is both the process and the product of planning, designing, and constructing buildings and other physical structures. Architectural works, in the material form of buildings, are often perceived as cultural symbols and as works of art. Historical civilizations are often identified with their surviving architectural achievements." ], [ "Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 7000100794000000000♠1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note 1] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.", "The gyromagnetic ratio γ is the constant of proportionality between the frequency ν of nuclear magnetic resonance (or electron paramagnetic resonance for electrons) and the applied magnetic field B: ν = γB. It is difficult to measure gyromagnetic ratios precisely because of the difficulties in precisely measuring B, but the value for protons in water at 7002298150000000000♠25 °C is known to better than one part per million. The protons are said to be \"shielded\" from the applied magnetic field by the electrons in the water molecule, the same effect that gives rise to chemical shift in NMR spectroscopy, and this is indicated by a prime on the symbol for the gyromagnetic ratio, γ′p. The gyromagnetic ratio is related to the shielded proton magnetic moment μ′p, the spin number I (I = 1⁄2 for protons) and the reduced Planck constant.", "There are a number of proposals to redefine certain of the SI base units in terms of fundamental physical constants. This has already been done for the metre, which is defined in terms of a fixed value of the speed of light. The most urgent unit on the list for redefinition is the kilogram, whose value has been fixed for all science (since 1889) by the mass of a small cylinder of platinum–iridium alloy kept in a vault just outside Paris. While nobody knows if the mass of the International Prototype Kilogram has changed since 1889 – the value 1 kg of its mass expressed in kilograms is by definition unchanged and therein lies one of the problems – it is known that over such a timescale the many similar Pt–Ir alloy cylinders kept in national laboratories around the world, have changed their relative mass by several tens of parts per million, however carefully they are stored, and the more so the more they have been taken out and used as mass standards. A change of several tens of micrograms in one kilogram is equivalent to the current uncertainty in the value of the Planck constant in SI units.", "Neptune's mass of 1.0243×1026 kg, is intermediate between Earth and the larger gas giants: it is 17 times that of Earth but just 1/19th that of Jupiter.[d] Its gravity at 1 bar is 11.15 m/s2, 1.14 times the surface gravity of Earth, and surpassed only by Jupiter. Neptune's equatorial radius of 24,764 km is nearly four times that of Earth. Neptune, like Uranus, is an ice giant, a subclass of giant planet, due to their smaller size and higher concentrations of volatiles relative to Jupiter and Saturn. In the search for extrasolar planets, Neptune has been used as a metonym: discovered bodies of similar mass are often referred to as \"Neptunes\", just as scientists refer to various extrasolar bodies as \"Jupiters\"." ], [ "Because of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. Furthermore, the corresponding simplicity of the hydrogen molecule and the corresponding cation H+\n2 allowed fuller understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.", "When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each element in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent. This is called a substitutional alloy. Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms. With the interstitial mechanism, one atom is usually much smaller than the other, so cannot successfully replace an atom in the crystals of the base metal. The smaller atoms become trapped in the spaces between the atoms in the crystal matrix, called the interstices. This is referred to as an interstitial alloy. Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are replaced with nickel and chromium atoms.", "Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine. This occurs normally only during prolonged starvation.", "Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction and the CNO cycle nuclear fusion." ], [ "Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction and the CNO cycle nuclear fusion.", "In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e−E/kT – that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation.The activation energy necessary for a chemical reaction can be in the form of thermal energy.", "In cosmology and astronomy the phenomena of stars, nova, supernova, quasars and gamma-ray bursts are the universe's highest-output energy transformations of matter. All stellar phenomena (including solar activity) are driven by various kinds of energy transformations. Energy in such transformations is either from gravitational collapse of matter (usually molecular hydrogen) into various classes of astronomical objects (stars, black holes, etc.), or from nuclear fusion (of lighter elements, primarily hydrogen). The nuclear fusion of hydrogen in the Sun also releases another store of potential energy which was created at the time of the Big Bang. At that time, according to theory, space expanded and the universe cooled too rapidly for hydrogen to completely fuse into heavier elements. This meant that hydrogen represents a store of potential energy that can be released by fusion. Such a fusion process is triggered by heat and pressure generated from gravitational collapse of hydrogen clouds when they produce stars, and some of the fusion energy is then transformed into sunlight.", "In biology, energy is an attribute of all biological systems from the biosphere to the smallest living organism. Within an organism it is responsible for growth and development of a biological cell or an organelle of a biological organism. Energy is thus often said to be stored by cells in the structures of molecules of substances such as carbohydrates (including sugars), lipids, and proteins, which release energy when reacted with oxygen in respiration. In human terms, the human equivalent (H-e) (Human energy conversion) indicates, for a given amount of energy expenditure, the relative quantity of energy needed for human metabolism, assuming an average human energy expenditure of 12,500 kJ per day and a basal metabolic rate of 80 watts. For example, if our bodies run (on average) at 80 watts, then a light bulb running at 100 watts is running at 1.25 human equivalents (100 ÷ 80) i.e. 1.25 H-e. For a difficult task of only a few seconds' duration, a person can put out thousands of watts, many times the 746 watts in one official horsepower. For tasks lasting a few minutes, a fit human can generate perhaps 1,000 watts. For an activity that must be sustained for an hour, output drops to around 300; for an activity kept up all day, 150 watts is about the maximum. The human equivalent assists understanding of energy flows in physical and biological systems by expressing energy units in human terms: it provides a \"feel\" for the use of a given amount of energy." ] ]
5a7dc51370df9f001a87515b	Matter	The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.	en	null	null	190,642	[ "What model has two generations?", "Which generation has the up and down muon and muon neutrino?", "What type of particles are tau and tau neutrino?", "What generation has charm and strange muon?", "How many electrons are there in the generations?" ]	[ [ "A new approach to avoiding overhead wires is taken by the \"second generation\" tram/streetcar system in Bordeaux, France (entry into service of the first line in December 2003; original system discontinued in 1958) with its APS (alimentation par sol – ground current feed). This involves a third rail which is flush with the surface like the tops of the running rails. The circuit is divided into segments with each segment energized in turn by sensors from the car as it passes over it, the remainder of the third rail remaining \"dead\". Since each energized segment is completely covered by the lengthy articulated cars, and goes dead before being \"uncovered\" by the passage of the vehicle, there is no danger to pedestrians. This system has also been adopted in some sections of the new tram systems in Reims, France (opened 2011) and Angers, France (also opened 2011). Proposals are in place for a number of other new services including Dubai, UAE; Barcelona, Spain; Florence, Italy; Marseille, France; Gold Coast, Australia; Washington, D.C., U.S.A.; Brasília, Brazil and Tours, France.", "Two major hardware revisions of the Xbox 360 have succeeded the original models; the Xbox 360 S (also referred to as the \"Slim\") replaced the original \"Elite\" and \"Arcade\" models in 2010. The S model carries a smaller, streamlined appearance with an angular case, and utilizes a redesigned motherboard designed to alleviate the hardware and overheating issues experienced by prior models. It also includes a proprietary port for use with the Kinect sensor. The Xbox 360 E, a further streamlined variation of the 360 S with a two-tone rectangular case inspired by Xbox One, was released in 2013. In addition to its revised aesthetics, Xbox 360 E also has one fewer USB port and no longer supports S/PDIF.", "The duplication and transmission of genetic material from one generation of cells to the next is the basis for molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parents' cells. In asexually reproducing organisms, the offspring will be a genetic copy or clone of the parent organism. In sexually reproducing organisms, a specialized form of cell division called meiosis produces cells called gametes or germ cells that are haploid, or contain only one copy of each gene.:20.2 The gametes produced by females are called eggs or ova, and those produced by males are called sperm. Two gametes fuse to form a diploid fertilized egg, a single cell that has two sets of genes, with one copy of each gene from the mother and one from the father.:20", "Launched worldwide across 2005–2006, the Xbox 360 was initially in short supply in many regions, including North America and Europe. The earliest versions of the console suffered from a high failure rate, indicated by the so-called \"Red Ring of Death\", necessitating an extension of the device's warranty period. Microsoft released two redesigned models of the console: the Xbox 360 S in 2010, and the Xbox 360 E in 2013. As of June 2014, 84 million Xbox 360 consoles have been sold worldwide, making it the sixth-highest-selling video game console in history, and the highest-selling console made by an American company. Although not the best-selling console of its generation, the Xbox 360 was deemed by TechRadar to be the most influential through its emphasis on digital media distribution and multiplayer gaming on Xbox Live. The Xbox 360's successor, the Xbox One, was released on November 22, 2013. Microsoft has stated they plan to support the Xbox 360 until 2016. The Xbox One is also backwards compatible with the Xbox 360." ], [ "1세대의 전하를 띠는 렙톤 전자는 19세기의 여러 과학자들에 의해 이론적으로 제안되었고, 1897년에 톰슨이 발견했다. 뮤온은 1936년에 앤더슨이 발견했으나, 발견 당시에는 메존으로 잘못 분류했었다. 그러나 실험을 통해, 새로 발견한 뮤온이 메존의 성질을 띠기보다는 전자에 가까운 성질을 띤다는 사실을 알아냈다. 1947년에서야 전자와 같이 행동하는 입자들을 ‘렙톤’이라 이름 붙여주며, 뮤온을 렙톤에 포함시켰다. 전자 중성미자는 1930년 파울리가 입자의 베타 붕괴 현상을 설명하기 위해, 이론적으로 처음 제안했다. 전자 중성미자는 1956년 카원과 라이너스가 훗날 ‘카원-라이너스 중성미자 실험’라 명명된 실험을 통하여 처음 발견했다. 뮤온 중성미자는 1962년 레더먼, 슈워츠, 스타인버거가 발견했다. 타우온은 1974년과 1977년 사이에 스탠퍼드 선형 가속기 센터와 로런스 버클리 국립 연구소에서 연구한 마틴 루이스 펄과 그의 동료들이 발견했다. 타우 중성미자는 2000년 7월 페르미 국립 가속기 연구소의 DONUT Collaboration이 발견했다고 발표했다.", "1943년 W. W. 모건과 P. C. 키넌이 항성분류법을 개정하였고, 이걸 모건과 키넌의 이름을 따서 모건-키넌 분류, 또는 MK 분류라고 한다. MK 분류는 항성 각각에게 분광형(하버드 분류법에 기초한) 및 광도등급을 배정했다. 하버드 분류법은 수소선의 세기에 따라 별들에게 서로 다른 글자들을 배정했는데(그때는 아직 스펙트럼과 온도 사이의 관계가 밝혀지기 전이었다), 항성의 온도에 따른 정렬을 한 뒤 중복되는 것들을 제거하고 나자 푸른색에서 붉은색으로, 즉 파장이 짧은 순서로 O, B, A, F, G, K, M이라는 분광형들이 정립되었다. 광도등급은 광도가 큰 것을 I로 시작해서 어두워지는 순으로 V까지 분류했다. 주계열 위의 항성들은 광도등급 V에 해당한다.", "1세대의 전하를 띠는 렙톤인, 전자는 19세기의 여러 과학자들에 의해 이론적으로 제안되었고, 1897년에 J.J.Tomson과 그의 동료인 여러 영국 물리학자들이 발견했다. 그 후 전자 1930년 Wolfgang Pauli가 베타 붕괴 현상 이전과 이후의 에너지, 운동량, 각운동량이 보존되지 않는다는 실험 결과에 아직 발견되지 않은 입자가 숨어 있을 것이라 추론했으며, 그 숨어 있는 입자를 중성미자(neutrino)라고 명명했다. 여담으로 당시에는 전자 중성미자라고 따로 명명되지 않은 이유는 전자 이외의 전하를 띠는 렙톤이 제안되지 않아서 렙톤이라는 개념조차 없었던 시대였기 때문이다. 전자 중성미자는 1956년 Clyde Cowan과 Frederick Reines이 훗날 ‘Cowan-Reines 중성미자 실험’라 명명된 실험을 통하여 처음 발견했다.", "The London Underground in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails. On the London Underground, a top-contact third rail is beside the track, energized at +420v DC, and a top-contact fourth rail is located centrally between the running rails at −210v DC, which combine to provide a traction voltage of 630v DC. London Underground is now upgrading its fourth rail system to 750v DC with a positive conductor rail energised to +500v DC and a negative conductor rail energised to -250v DC. However, many older sections in tunnels are still energised to 630v DC. The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary or a third rail." ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)" ], [ "뮤는 안정된 능력치와 기술머신과 비전머신으로부터 어떤 기술이라도 습득할 수 있는 능력을 가지고 있기에, 포켓몬스터 적녹에서 최고의 포켓몬 중 하나로 인정받고 있다. '피카츄의 세계 모험: 포켓몬의 흥망' 에 등장하는 것과 같은 허구의 캐릭터가 아동에 미치는 영향에 대한 연구에 따르면, 귀여운 캐릭터를 선호하는 경향이 있는 저연령대의 여자 아동들에게 뮤의 인기가 높았다. 이에 비해, 뮤와 정반대의 성향으로 묘사되고 있는 뮤츠의 경우 거칠거나 무서운 캐릭터에 매력을 느끼는 경향이 강한 고연령대 남자들에게 인기가 있었다. Media and the Make-believe Worlds of Children 에서도 유사한 비교가 나온다. 이 책은 뮤를 어린아이 같고 다정하며, 힘과 귀여움이 공존하는 캐릭터로 묘사하고 있으며 뮤와 뮤츠를 비교하는 것이 캐릭터의 매력 포인트를 짚어내는 역할의 중요함을 강조한다. IGN는 뮤를 뮤츠, 후딘, 아쿠스타와 함께 아주 좋은 에스퍼 타입 포켓몬으로 꼽았다. 그들은 뮤츠가 어떠한 기술머신, 비전머신, 포켓몬 기술 훈련 아이템을 사용할 수 있는 능력이 있다는 점을 들어 예측할 수 없는 포켓몬이며, 뮤츠와 어울리는 경쟁자라고 불렀다.", "The Slovenian countryside displays a variety of disguised groups and individual characters among which the most popular and characteristic is the Kurent (plural: Kurenti), a monstrous and demon-like, but fluffy figure. The most significant festival is held in Ptuj (see: Kurentovanje). Its special feature are the Kurents themselves, magical creatures from another world, who visit major events throughout the country, trying to banish the winter and announce spring's arrival, fertility, and new life with noise and dancing. The origin of the Kurent is a mystery, and not much is known of the times, beliefs, or purposes connected with its first appearance. The origin of the name itself is obscure.", "The fourth Digimon series, which began airing on April 7, 2002, radically departs from the previous three by focusing on a new and very different kind of evolution, Spirit Evolution, in which the human characters use their D-Tectors (this series' Digivice) to transform themselves into special Digimon called Legendary Warriors, detracting from the customary formula of having digital partners. After receiving unusual phone messages from Ophanimon (one of the three ruling Digimon alongside Seraphimon and Cherubimon) Takuya Kanbara, Koji Minamoto, Junpei Shibayama, Zoe Orimoto, Tommy Himi, and Koichi Kimura go to a subway station and take a train to the Digital World. Summoned by Ophanimon, the Digidestined realize that they must find the ten legendary spirits and stop the forces of Cherubimon from physically destroying the Digital World. After finding the ten spirits of the Legendary Warriors and defeating Mercurymon, Grumblemon, Ranamon, and Arbormon, they finally end up fighting Cherubimon hoping to foil his effort to dominate the Digital World. After the defeat of Cherubimon, the Digidestined find they must face an even greater challenge as they try to stop the Royal Knights—Dynasmon and Crusadermon—from destroying the Digital World and using the collected data to revive the original ruler of the Digital World: the tyrannical Lucemon. Ultimately the Digidestined fail in preventing Lucemon from reawakening but they do manage to prevent him from escaping into the Real World. In the final battle, all of the legendary spirits the digidestined have collected thus far merge and create Susanoomon. With this new form, the digidestined are able to effectively defeat Lucemon and save the Digital World. In general, Frontier has a much lighter tone than that of Tamers, yet remains darker than Adventure and Adventure 02.", "Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks. It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars)." ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "The duplication and transmission of genetic material from one generation of cells to the next is the basis for molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parents' cells. In asexually reproducing organisms, the offspring will be a genetic copy or clone of the parent organism. In sexually reproducing organisms, a specialized form of cell division called meiosis produces cells called gametes or germ cells that are haploid, or contain only one copy of each gene.:20.2 The gametes produced by females are called eggs or ova, and those produced by males are called sperm. Two gametes fuse to form a diploid fertilized egg, a single cell that has two sets of genes, with one copy of each gene from the mother and one from the father.:20", "Although several companies each produce over a billion individually packaged (known as discrete) transistors every year, the vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs). \"About 60 million transistors were built in 2002… for [each] man, woman, and child on Earth.\"", "Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-white metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable (with half-lives of the six naturally known isotopes, uranium-233 to uranium-238, varying between 69 years and 4.5 billion years). The most common isotopes of uranium are uranium-238 (which has 146 neutrons and accounts for almost 99.3% of the uranium found in nature) and uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found naturally). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite." ] ]
5a7dc5b470df9f001a875165	Matter	Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy.	en	null	null	190,647	[ "What is dark energy composed of?", "What probe saw white dwarf stars?", "What percentage of the universe are black holes?", "What percentage of the universe can be seen by telescope?", "What type of light accounts for 72% of the universe?" ]	[ [ "According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the \"matter\" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.", "In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of the early universe and the big bang theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. The commonly accepted view is that most of the dark matter is non-baryonic in nature. As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles, which are not Standard Model particles, but relics formed at very high energies in the early phase of the universe and still floating about.", "Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction and the CNO cycle nuclear fusion.", "In cosmology and astronomy the phenomena of stars, nova, supernova, quasars and gamma-ray bursts are the universe's highest-output energy transformations of matter. All stellar phenomena (including solar activity) are driven by various kinds of energy transformations. Energy in such transformations is either from gravitational collapse of matter (usually molecular hydrogen) into various classes of astronomical objects (stars, black holes, etc.), or from nuclear fusion (of lighter elements, primarily hydrogen). The nuclear fusion of hydrogen in the Sun also releases another store of potential energy which was created at the time of the Big Bang. At that time, according to theory, space expanded and the universe cooled too rapidly for hydrogen to completely fuse into heavier elements. This meant that hydrogen represents a store of potential energy that can be released by fusion. Such a fusion process is triggered by heat and pressure generated from gravitational collapse of hydrogen clouds when they produce stars, and some of the fusion energy is then transformed into sunlight." ], [ "외계 행성을 발견했다는 주장은 19세기부터 있었다. 대표적으로 쌍성 뱀주인자리 70에 행성이 있다는 주장을 꼽을 수 있다. 1855년에 영국 동인도 회사의 마드라스 천문대에 근무하던 제이콥은 쌍성 궤도의 불규칙함이 행성 존재로부터 나오는 결과라고 주장했다. 1890년대에는 시카고 대학교 및 미국 해군 천문대 소속인 토머스 시는 뱀주인자리 70의 공전궤도의 변칙성은 항성을 36년 주기로 도는, 눈에 보이지 않는 천체가 있기 때문이라고 주장했다. 그러나 포레스트 레이 몰턴은 세 개 천체로 이루어진 계는 매우 불안정하다는, 토머스 시의 주장을 공격하는 논문을 발표했다. 1950년대에서 1960년대에 걸쳐 스와스모어 대학교의 페터 반 데 캄프는 바너드 별 주위에 행성이 존재한다는 주장을 여러 차례에 걸쳐 내놓았다. 현재 천문학자들은 초기 외계 행성을 발견했다는 주장 모두를 관측자들의 착오로 간주하고 있다.", "The boreholes on Funafuti, at the site now called Darwin's Drill, are the result of drilling conducted by the Royal Society of London for the purpose of investigating the formation of coral reefs to determine whether traces of shallow water organisms could be found at depth in the coral of Pacific atolls. This investigation followed the work on The Structure and Distribution of Coral Reefs conducted by Charles Darwin in the Pacific. Drilling occurred in 1896, 1897 and 1898. Professor Edgeworth David of the University of Sydney was a member of the 1896 \"Funafuti Coral Reef Boring Expedition of the Royal Society\", under Professor William Sollas and lead the expedition in 1897. Photographers on these trips recorded people, communities, and scenes at Funafuti.", "1988년에 캐나다의 천문학자인 브루스 캠벨과 G. A. H. 워커, 스티븐슨 양은 항성 세페우스자리 감마 주위를 도는 행성이 있다고 주장했다. 이들의 발견은 추가 검증을 통해 그 존재가 논문으로 출판된 최초 사례였다. 캠벨 일행은 행성을 발견했다는 사실을 조심스럽게 발표했으나 이들의 시선속도 관측자료는 감마별을 행성 한 개가 돌고 있음을 증명하고 있었다. 다만 캠벨의 관측 자료 일부는 당시 관측장비 성능의 한계점 근처에 있었기 때문에 천문학자들은 이후 수 년 동안 이 발견 및 다른 비슷한 관측들에 대하여 냉소적인 반응을 보였다. 행성이 분명한 천체 몇몇도 갈색 왜성(항성과 행성 중간 정도 질량을 지닌 천체)으로 여겨졌다. 1990년 세페우스자리 감마를 도는 행성이 존재함을 입증하는 추가 논문들이 발표되었으나 1992년 추가로 발표된 논문은 다시금 심각한 논란을 불러왔다. 결국 2003년 개선된 관측 장비의 성능 및 기술에 힘입어 세페우스자리 감마를 도는 행성의 존재는 검증되었다.", "1610년의 첫 번째 달에 갈릴레오 갈릴레이는 강력한 기능을 지닌 신형 망원경을 이용, 목성의 주위를 돌고 있는 4개의 위성 가니메데, 칼리스토, 이오, 유로파를 발견하였다. 갈릴레오는 《시데레우스 눈치우스》(Sidereus Nuncius;〈별세계의 사자〉라는 뜻)를 출판하면서 자기 관측 결과의 신빙성을 강화하기 위해 케플러의 자문을 구하였다. 케플러는 《별의 메신저와의 대화》(Dissertatio cum Nuncio Sidereo)를 통해 매우 열심히 대답해 주었다. 그는 갈릴레오의 관측을 보증하였고, 갈릴레오의 발견이 뜻하고 암시하는 바와 망원경 이용의 추측 범위를 우주론과 점성술 뿐만 아니라 천문학과 광학에까지 확대하자고 제안하였다. 그 해가 지나고, 케플러는 달을 망원경을 이용하여 독자적으로 관측, 《목성의 위성에 대한 해설》(Narratio de Jovis Satellitibus)을 출판하여 갈릴레오의 이론에 힘을 보탰다. 그러나 갈릴레오는 《신천문학》에 대해 아무런 반응도 보이지 않았고, 케플러는 실망하였다. 당시 천문학자들은 목성의 위성들이 실제 존재하는 것이 아니라 망원경이 만들어낸 허상에 불과하다고 공격했다. 갈릴레오는 케플러의 보증으로 자신을 겨냥한 이런 비판들을 모두 꺾어 버릴 수 있었지만, 케플러는 고맙다는 인사말 한마디도 들을 수 없었다. 그럼에도 케플러는 갈릴레오의 무례에 불만을 표시하지 않았고, 갈릴레오는 천문학 이론의 개혁을 이룬 케플러의 업적에 아무런 관심도 기울이지 않았다" ], [ "블랙홀(black hole)은 강력한 밀도와 중력으로 인해 입자나 전자기 복사, 빛을 포함한 그 무엇도 빠져나올 수 없는 시공간 영역이다. 일반상대론은 충분히 밀집된 질량이 시공을 뒤틀어 블랙홀을 형성할 수 있음을 예측한다. 블랙홀로부터의 탈출이 불가능해지는 경계를 사건의 지평선이라고 한다. 어떤 물체가 사건의 지평선을 넘어갈 경우, 그 물체에게는 파멸적 영향이 가해지겠지만, 바깥 관찰자에게는 속도가 점점 느려져 그 경계에 영원히 닿지 않는 것처럼 보인다. 블랙홀은 빛을 반사하지 않기에 이상적 흑체처럼 행동한다. 또한 휘어진 시공간의 양자장론에 따르면 사건의 지평선은 블랙홀의 질량에 반비례하는 온도를 가진 흑체와 같은 스펙트럼의 열복사를 방출하며, 이를 호킹 복사라고 한다. 항성질량 블랙홀의 경우 이 온도가 수십억분의 1 켈빈 수준이기에 그 열복사를 관측하는 것은 본질적으로 불가능하다.", "According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the \"matter\" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.", "블랙홀의 괴이한 성질들을 생각해 보면, 이런 기이한 천체가 과연 실존하는 것인지, 그저 아인슈타인 방정식의 해를 이끌어내는 과정에서 도출된 비정상적 결과물에 지나지 않는 것이 아닌지 의문을 가질 법도 하다. 심지어 아인슈타인 본인마저 붕괴하는 입자의 각운동량으로 인해 그 운동이 특정 반경에서 안정화될것이기에 블랙홀은 존재할 수 없다는 잘못된 판단을 한 바 있다. 이 때문에 일반상대론 학계는 오랜 세월동안 아인슈타인의 견해와 배치되는 결과들을 모두 평가절하하였다. 그러나 일부 소장파는 블랙홀이 물리적 천체로서 실재한다는 견해를 고수하였고, 1960년대 말엽이 되면 학계 대부분이 사건의 지평선 형성을 가로막는 장애물이 없다는 데 동의하기에 이른다.", "블랙홀의 안을 들여다볼 수는 없지만, 블랙홀이 다른 물질과 상호작용하는 것을 통해 그 성질을 알아낼 수 있다. 블랙홀 위로 낙하한 물질은 강착원반을 형성하고, 원반은 마찰열로 인해 뜨거워져 열복사로 빛난다. 우주에서 가장 밝은 천체인 퀘이사는 이러한 과정을 통해 만들어진다. 블랙홀 주위를 공전하는 다른 항성이 있을 경우, 그 궤도를 통해 블랙홀의 질량과 위치를 비정할 수 있다. 이러한 관측을 통해 중성자별을 비롯한 다른 유사 천체들을 제외함으로써 천문학자들은 블랙홀 후보들이 포함된 쌍성계를 셀 수 없이 많이 발견해냈고, 우리은하 중심 방향에 존재하는 전파원 궁수자리 A*가 4백 3십만 M☉의 초대질량 블랙홀임을 밝혔다." ], [ "The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected atmospheric windows. This limitation can be partially alleviated by placing the telescope observatory at a high altitude, or by carrying the telescope aloft with a balloon or an aircraft. Space telescopes do not suffer from this handicap, and so outer space is considered the ideal location for infrared astronomy.", "According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the \"matter\" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.", "Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining known 14 moons were located telescopically until the 20th century. The planet's distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989. The advent of Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar.", "초신성을 제외하면 인류가 알고 있는 별의 대부분은 우리 은하 내 국부 은하군 및 우리 은하 내 관측이 가능한 부분들(성표에서 다루고 있다.)에 속해 있다. 그러나 지구에서 1억 광년 정도 떨어진 곳에 있는 처녀자리 은하단 내 M100의 별 몇몇이 관측되기도 했다. 현재 망원경 수준으로 국부 초은하단 내 성단과 수억 광년 떨어진 곳에 있는 국부 은하군 내 개개의 별을 관측하는 것은 가능하다.(세페이드 변광성 참조). 그러나 국부 초은하단 너머에 있는 별 및 성단을 낱낱이 보는 것은 불가능하다. 그러나 최근 10억 광년 정도 떨어진 거리에 있는 거대 성단을 촬영하는 데 성공했다. 이 성단은 수백 개에서 수천 개의 별이 뭉쳐 있다. 이 성단은 이전에 관측되었던 가장 먼 성단보다 열 배 먼 곳에 있다." ], [ "According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the \"matter\" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.", "Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction and the CNO cycle nuclear fusion.", "Infrared radiation is popularly known as \"heat radiation\"[citation needed], but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths. Visible light or ultraviolet-emitting lasers can char paper and incandescently hot objects emit visible radiation. Objects at room temperature will emit radiation concentrated mostly in the 8 to 25 µm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see black body and Wien's displacement law).", "In cosmology and astronomy the phenomena of stars, nova, supernova, quasars and gamma-ray bursts are the universe's highest-output energy transformations of matter. All stellar phenomena (including solar activity) are driven by various kinds of energy transformations. Energy in such transformations is either from gravitational collapse of matter (usually molecular hydrogen) into various classes of astronomical objects (stars, black holes, etc.), or from nuclear fusion (of lighter elements, primarily hydrogen). The nuclear fusion of hydrogen in the Sun also releases another store of potential energy which was created at the time of the Big Bang. At that time, according to theory, space expanded and the universe cooled too rapidly for hydrogen to completely fuse into heavier elements. This meant that hydrogen represents a store of potential energy that can be released by fusion. Such a fusion process is triggered by heat and pressure generated from gravitational collapse of hydrogen clouds when they produce stars, and some of the fusion energy is then transformed into sunlight." ] ]
5a7dcb3b70df9f001a87518d	Matter	In physics, degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero. The Pauli exclusion principle requires that only two fermions can occupy a quantum state, one spin-up and the other spin-down. Hence, at zero temperature, the fermions fill up sufficient levels to accommodate all the available fermions—and in the case of many fermions, the maximum kinetic energy (called the Fermi energy) and the pressure of the gas becomes very large, and depends on the number of fermions rather than the temperature, unlike normal states of matter.	en	null	null	190,652	[ "What is the name of the principle for the ground state of gas?", "What depends on the temperature at absolute zero?", "What is the minimum kinetic energy called?", "What shrinks to accommodate fermions?", "What is the pressure of the gas called?" ]	[ [ "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "The first law of thermodynamics asserts that energy (but not necessarily thermodynamic free energy) is always conserved and that heat flow is a form of energy transfer. For homogeneous systems, with a well-defined temperature and pressure, a commonly used corollary of the first law is that, for a system subject only to pressure forces and heat transfer (e.g., a cylinder-full of gas) without chemical changes, the differential change in the internal energy of the system (with a gain in energy signified by a positive quantity) is given as", "1775년 5월 26일 라부아지에는 공기의 성분 중 특정 성분이 생물의 호흡과 관련되어있다는 사실을 발견하고 이를 '생명의 공기'라고 이름을 붙였다. (사실 이 공기는 산소로, 셸레와 프리스틀리에 의해서 이미 발견되어있었다.) 1777년에 제출한 논문인 Mémoire sur la combustion en général에서 라부아지에는 모든 산은 공기 내의 특정 성분에 의해서 생성된다고 주장하였고, 이를 principe oxygine이라고 명명하였다. 이는 그리스어로 '산을 생성하는 것'이라는 뜻으로, 산소의 어원이 되었다. (principe oxygine 역시 산소와 같은 물질이나 라부아지에는 처음에 이를 알지 못하였다.) 추가적인 연구를 통해서 라부아지에는 설탕과 principe oxygine이 반응하면 옥살산이 생성되는 등 여러 물질과 반응하여 산을 생성한다는 사실을 알게 되었다. 현대의 시각으로 보았을 때 이 이론은 염화 수소 등 산소를 포함하지 않은 산에 관해서는 들어맞지 않으나, 산소산을 설명하기 적합하다.", "Stars, planets, and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 6998320000000000000♠3.2×10−2 Pa at 100 kilometres (62 mi) of altitude, the Kármán line, which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar winds, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre." ], [ "Antarctica is the coldest of Earth's continents. The coldest natural temperature ever recorded on Earth was −89.2 °C (−128.6 °F) at the Soviet (now Russian) Vostok Station in Antarctica on 21 July 1983. For comparison, this is 10.7 °C (20 °F) colder than subliming dry ice at one atmosphere of partial pressure, but since CO2 only makes up 0.039% of air, temperatures of less than −150 °C (−238 °F) would be needed to produce dry ice snow in Antarctica. Antarctica is a frozen desert with little precipitation; the South Pole itself receives less than 10 cm (4 in) per year, on average. Temperatures reach a minimum of between −80 °C (−112 °F) and −89.2 °C (−128.6 °F) in the interior in winter and reach a maximum of between 5 °C (41 °F) and 15 °C (59 °F) near the coast in summer. Sunburn is often a health issue as the snow surface reflects almost all of the ultraviolet light falling on it. Given the latitude, long periods of constant darkness or constant sunlight create climates unfamiliar to human beings in much of the rest of the world.", "Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Antarctica is considered a desert, with annual precipitation of only 200 mm (8 in) along the coast and far less inland. The temperature in Antarctica has reached −89.2 °C (−128.6 °F), though the average for the third quarter (the coldest part of the year) is −63 °C (−81 °F). There are no permanent human residents, but anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Organisms native to Antarctica include many types of algae, bacteria, fungi, plants, protista, and certain animals, such as mites, nematodes, penguins, seals and tardigrades. Vegetation, where it occurs, is tundra.", "얼음은 자연그대로의 것일 수도 있지만, 일반적으로 냉동 플랜트를 이용해 동결한다. 얕은 물받이 바닥에 세로로 고정시킨 수많은 파이프를 통해 염수 용액을 펌핑하는 방식이다. 대다수 컬링 클럽에는 아이스 메이커가 있으며, 주로 얼음을 관리하는 역할을 한다. 중요한 컬링 챔피언십에서는 얼음 유지가 매우 중요하다. 브리어나 여타 국내외 챔피언십과 같은 대규모 이벤트는 일반적으로 아이스 메이커에게 어려운 과제를 안겨주는 경기장에서 개최된다. 아이스 메이커는 쉴 세 없이 이어지는 경기에 적합한 빙판을 담보하기 위해 기온과 습도 수준을 계속 모니터링하고 조정해야 한다. 개별 얼음 시트마다 표면 온도를 모니터링하기 위해 여러 센서가 내장되어 있으며 (습기를 모니터링하기 위해) 관람 구역과 (압축 공기 공급 및 순환 온도를 모니터링하기 위해) 압축 공기 통제실에는 탐침이 설치되는 것이 보통이다. 얼음의 표면은 23 °F (−5 °C) 정도의 온도가 유지된다.", "Humans and animals exposed to vacuum will lose consciousness after a few seconds and die of hypoxia within minutes, but the symptoms are not nearly as graphic as commonly depicted in media and popular culture. The reduction in pressure lowers the temperature at which blood and other body fluids boil, but the elastic pressure of blood vessels ensures that this boiling point remains above the internal body temperature of 37 °C. Although the blood will not boil, the formation of gas bubbles in bodily fluids at reduced pressures, known as ebullism, is still a concern. The gas may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Swelling and ebullism can be restrained by containment in a flight suit. Shuttle astronauts wore a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 2 kPa (15 Torr). Rapid boiling will cool the skin and create frost, particularly in the mouth, but this is not a significant hazard." ], [ "The total energy of a system can be subdivided and classified in various ways. For example, classical mechanics distinguishes between kinetic energy, which is determined by an object's movement through space, and potential energy, which is a function of the position of an object within a field. It may also be convenient to distinguish gravitational energy, thermal energy, several types of nuclear energy (which utilize potentials from the nuclear force and the weak force), electric energy (from the electric field), and magnetic energy (from the magnetic field), among others. Many of these classifications overlap; for instance, thermal energy usually consists partly of kinetic and partly of potential energy.", "First recognized in 1900 by Max Planck, it was originally the proportionality constant between the minimal increment of energy, E, of a hypothetical electrically charged oscillator in a cavity that contained black body radiation, and the frequency, f, of its associated electromagnetic wave. In 1905 the value E, the minimal energy increment of a hypothetical oscillator, was theoretically associated by Einstein with a \"quantum\" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle, as opposed to an electromagnetic wave. It was eventually called the photon.", "In biology, energy is an attribute of all biological systems from the biosphere to the smallest living organism. Within an organism it is responsible for growth and development of a biological cell or an organelle of a biological organism. Energy is thus often said to be stored by cells in the structures of molecules of substances such as carbohydrates (including sugars), lipids, and proteins, which release energy when reacted with oxygen in respiration. In human terms, the human equivalent (H-e) (Human energy conversion) indicates, for a given amount of energy expenditure, the relative quantity of energy needed for human metabolism, assuming an average human energy expenditure of 12,500 kJ per day and a basal metabolic rate of 80 watts. For example, if our bodies run (on average) at 80 watts, then a light bulb running at 100 watts is running at 1.25 human equivalents (100 ÷ 80) i.e. 1.25 H-e. For a difficult task of only a few seconds' duration, a person can put out thousands of watts, many times the 746 watts in one official horsepower. For tasks lasting a few minutes, a fit human can generate perhaps 1,000 watts. For an activity that must be sustained for an hour, output drops to around 300; for an activity kept up all day, 150 watts is about the maximum. The human equivalent assists understanding of energy flows in physical and biological systems by expressing energy units in human terms: it provides a \"feel\" for the use of a given amount of energy.", "In the late 17th century, Gottfried Leibniz proposed the idea of the Latin: vis viva, or living force, which defined as the product of the mass of an object and its velocity squared; he believed that total vis viva was conserved. To account for slowing due to friction, Leibniz theorized that thermal energy consisted of the random motion of the constituent parts of matter, a view shared by Isaac Newton, although it would be more than a century until this was generally accepted. The modern analog of this property, kinetic energy, differs from vis viva only by a factor of two." ], [ "One adaptation helping both predators and prey avoid detection is camouflage, a form of crypsis where species have an appearance that helps them blend into the background. Camouflage consists of not only color but also shape and pattern. The background upon which the organism is seen can be both its environment (e.g., the praying mantis to the right resembling dead leaves) or other organisms (e.g., zebras' stripes blend in with each other in a herd, making it difficult for lions to focus on a single target). The more convincing camouflage is, the more likely it is that the organism will go unseen.", "Among the other phyla, the Ctenophora and the Cnidaria, which includes sea anemones, corals, and jellyfish, are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. Both have distinct tissues, but they are not organized into organs. There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. The tiny placozoans are similar, but they do not have a permanent digestive chamber.", "Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses. A marsupial has a short gestation period, typically shorter than its estrous cycle, and gives birth to an undeveloped newborn that then undergoes further development; in many species, this takes place within a pouch-like sac, the marsupium, located in the front of the mother's abdomen. This is the plesyomorphic condition among viviparous mammals; the presence of epipubic bones in all non-placental mammals prevents the expansion of the torso needed for full pregnancy. Even non-placental eutherians probably reproduced this way.", "While the majority of flowers are perfect or hermaphrodite (having both pollen and ovule producing parts in the same flower structure), flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization. Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot easily transfer pollen to the pistil (receptive part of the carpel). Homomorphic flowers may employ a biochemical (physiological) mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers." ], [ "Stars, planets, and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 6998320000000000000♠3.2×10−2 Pa at 100 kilometres (62 mi) of altitude, the Kármán line, which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar winds, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre.", "This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa, 20 atm or 600 inHg). This is because high-pressure H\n2 is the most marketable product and Pressure Swing Adsorption (PSA) purification systems work better at higher pressures. The product mixture is known as \"synthesis gas\" because it is often used directly for the production of methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly optimized technology is the formation of coke or carbon:", "The SI unit of pressure is the pascal (symbol Pa), but vacuum is often measured in torrs, named for Torricelli, an early Italian physicist (1608–1647). A torr is equal to the displacement of a millimeter of mercury (mmHg) in a manometer with 1 torr equaling 133.3223684 pascals above absolute zero pressure. Vacuum is often also measured on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres. Low vacuum is often measured in millimeters of mercury (mmHg) or pascals (Pa) below standard atmospheric pressure. \"Below atmospheric\" means that the absolute pressure is equal to the current atmospheric pressure.", "The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure, but a complete characterization requires further parameters, such as temperature and chemical composition. One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~6997100000000000000♠1×10−3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. The Crookes radiometer turns when the MFP is larger than the size of the vanes." ] ]
5a7dccd270df9f001a8751a9	Matter	Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks. It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars).	en	null	null	190,657	[ "What is quark matter usually thought of as?", "What is nuclear matter similar to?", "At low density, what is expected of strange matter?", "What kind of core does nuclear matter occur in?", "What has Strange matter been definitely proven to occur as?" ]	[ [ "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC)." ], [ "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large." ], [ "In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of the early universe and the big bang theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. The commonly accepted view is that most of the dark matter is non-baryonic in nature. As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles, which are not Standard Model particles, but relics formed at very high energies in the early phase of the universe and still floating about.", "While outer space provides the most rarefied example of a naturally occurring partial vacuum, the heavens were originally thought to be seamlessly filled by a rigid indestructible material called aether. Borrowing somewhat from the pneuma of Stoic physics, aether came to be regarded as the rarefied air from which it took its name, (see Aether (mythology)). Early theories of light posited a ubiquitous terrestrial and celestial medium through which light propagated. Additionally, the concept informed Isaac Newton's explanations of both refraction and of radiant heat. 19th century experiments into this luminiferous aether attempted to detect a minute drag on the Earth's orbit. While the Earth does, in fact, move through a relatively dense medium in comparison to that of interstellar space, the drag is so minuscule that it could not be detected. In 1912, astronomer Henry Pickering commented: \"While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there\".", "충돌에 의해 뿜어져 나온 물질에서 예상 외로 먼지와 작은 얼음이 많이 뿜어져 나온 초기 결과는 놀라웠다. 혜성 구조가 배제 물질의 느슨한 조합으로 이루어졌다는 이론만이 이 결과와 만족스럽게 일치했다. 또한, 물질들은 예상보다 더 미세했는데, 과학자들은 혜성의 구성물을 모래보다는 활석 가루와 비슷하다고 비교했다. 또한 충돌의 여파를 분광기로 측정하면서 점토, 탄산염, 나트륨과 결정형 규산염이 발견되었다. 점토와 탄산염은 일반적으로 형성될 때 물이 필요하고 나트륨은 우주에서는 드문 원소이다. 이 관측은 혜성 내부는 75%가 빈 공간이고, 눈 같은 것으로 혜성의 표면이 덮여 있다는 것을 보여주었다. 천문학자들은 이것이 유일한 경우인지 아니면 다른 곳에서도 그런지와, 다른 혜성에는 태양계 형성 초기의 광물이 있을지를 알기 위하여 다른 혜성들을 탐사하는 계획에 관심을 표현했다.", "Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy." ], [ "Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor control rods (see nuclear reactor physics for a description of this process of reactor control).", "The majority of eukaryotic genes are stored on a set of large, linear chromosomes. The chromosomes are packed within the nucleus in complex with storage proteins called histones to form a unit called a nucleosome. DNA packaged and condensed in this way is called chromatin.:4.2 The manner in which DNA is stored on the histones, as well as chemical modifications of the histone itself, regulate whether a particular region of DNA is accessible for gene expression. In addition to genes, eukaryotic chromosomes contain sequences involved in ensuring that the DNA is copied without degradation of end regions and sorted into daughter cells during cell division: replication origins, telomeres and the centromere.:4.2 Replication origins are the sequence regions where DNA replication is initiated to make two copies of the chromosome. Telomeres are long stretches of repetitive sequence that cap the ends of the linear chromosomes and prevent degradation of coding and regulatory regions during DNA replication. The length of the telomeres decreases each time the genome is replicated and has been implicated in the aging process. The centromere is required for binding spindle fibres to separate sister chromatids into daughter cells during cell division.:18.2", "핵융합은 두 개의 원자가 합쳐져 새로운 물질을 만들 때 질량이 손실되어 에너지가 방출되는 것을 말한다. 비슷한 원리로 원자력이라고 불리는 핵분열 반응은 무거운 원자가 외부 자극에 의해 분열하게 될 때 질량손실이 일어나게 되어 아인슈타인의 상대성 원리 공식에 따라 에너지를 방출한다. 예를 들면 현재 한국에서 가동 중인 핵분열 원자력 발전소에서는 우라늄을 분해하여 전기를 얻고 있다. 핵융합 반응을 가장 쉽게 볼 수 있는 것은 태양이다. 태양이 불타고 있는 이유는 태양 내부에서 수소, 헬륨이 서로 핵융합 반응을 하고 있기 때문이다. 이 과정을 통해 태양은 초당 4조W의 100조배에 달하는 에너지를 방출하고 있다. 이런 핵융합 반응은 중수소와 삼중수소의 반응, 중수소와 중수소의 반응, 중수소와 헬륨의 반응, 중수소와 리튬의 반응 등 여러 가지 형태로 나타날 수 있다. 이 중 핵융합 발전을 위해 가능한 연료로는 지구 상에서 누구나 쉽게 얻을 수 있어야 하며 핵융합 반응이 쉽게 일어날 수 있어야 한다는 조건이 있어야 한다. 이를 만족하는 연료로 현재는 중수소와 삼중수소의 반응이 핵융합 반응으로 추대되고 있다. 왜냐하면 중수소는 바닷물에서 아주 쉽고 저렴하게 구할 수 있으며 삼중수소 또한 바닷물에서 구한 리튬을 통해 쉽게 만들 수 있기 때문이다. 이런 핵융합 반응이 일어나기 위해서는 두 가지 중요한 기술이 필요하다. 첫 번째 기술은 플라즈마를 1억도씨 이상으로 가열하는 기술이고 두 번째는 이런 초고온 플라즈마를 핵융합 장치에 가두는 기술이 필요하다.", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter." ], [ "In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of the early universe and the big bang theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. The commonly accepted view is that most of the dark matter is non-baryonic in nature. As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles, which are not Standard Model particles, but relics formed at very high energies in the early phase of the universe and still floating about.", "2013년 호주 연방과학원은 2007년 파크스 천문대를 통해 관측된 전파가 기원 불명의 전파로 확인됐다고 밝혔다. 분석한 결과 10초 간격으로 1밀리초(1/1000초) 동안 4번에 걸쳐 다른 방향에서 관측됐으며, 거리는 지구로부터 약 110억 광년 거리에서 온 것이다. 특히 감마선에서 엑스선이 함께 관측되지 않았다는 점에서 일반적으로 감마선폭발 때나 블랙홀 충돌, 증발 때 관측되는 것과는 다른 신호이다. 이에 대해 SETI의 라비르 바탈 박사는 “기계적 결함이나 우주에서 온 무의미한 광학 잡음일 수도 있지만 외계 문명이 보낸 메시지일 가능성도 있다. 중요한 것은 단 한 번도 이 같은 신호가 관측된 적이 없었다는 점이다.\"라고 말하였다. 이 관측 결과는 2013년 7월 5일자 사이언스지에 발표됐다.", "Some modern day physicists and science writers—such as Paul Davies and John Gribbin—have argued that materialism has been disproven by certain scientific findings in physics, such as quantum mechanics and chaos theory. In 1991, Gribbin and Davies released their book The Matter Myth, the first chapter of which, \"The Death of Materialism\", contained the following passage:", "While outer space provides the most rarefied example of a naturally occurring partial vacuum, the heavens were originally thought to be seamlessly filled by a rigid indestructible material called aether. Borrowing somewhat from the pneuma of Stoic physics, aether came to be regarded as the rarefied air from which it took its name, (see Aether (mythology)). Early theories of light posited a ubiquitous terrestrial and celestial medium through which light propagated. Additionally, the concept informed Isaac Newton's explanations of both refraction and of radiant heat. 19th century experiments into this luminiferous aether attempted to detect a minute drag on the Earth's orbit. While the Earth does, in fact, move through a relatively dense medium in comparison to that of interstellar space, the drag is so minuscule that it could not be detected. In 1912, astronomer Henry Pickering commented: \"While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there\"." ] ]
5a7dcd9270df9f001a8751bd	Matter	In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter (such as plasmas, superfluids, supersolids, Bose–Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of thermodynamics. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details).	en	null	null	190,662	[ "What are phases known as?", "What is a phase not dependent on?", "How many phases are there total?", "What are examples of paramagnetic phases?", "What field studies nanomaterials?" ]	[ [ "Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase, a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The second phase of growth is the log phase, also known as the logarithmic or exponential phase. The log phase is marked by rapid exponential growth. The rate at which cells grow during this phase is known as the growth rate (k), and the time it takes the cells to double is known as the generation time (g). During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth is the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport. The final phase is the death phase where the bacteria run out of nutrients and die.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Different phases of digestion take place including: the cephalic phase , gastric phase, and intestinal phase. The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin. The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine. The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.", "For instance, a phased array consists of two or more simple antennas which are connected together through an electrical network. This often involves a number of parallel dipole antennas with a certain spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can operate as a \"broadside array\" (directional normal to a line connecting the elements) or as an \"end-fire array\" (directional along the line connecting the elements). Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical." ], [ "감각 뉴런처럼 외부 자극에 대하여 활동전위를 일으키는 것과는 달리, 아무런 자극 없이 발화하는 흥분성 세포가 있다. 이들은 규칙적인 속도로 축삭 언덕에서 자발적으로 탈분극하여 시계처럼 작용한다. 이 세포의 전압 변화를 박동조율기 전위라고 한다. 심장의 굴심방결절에 있는 심장 박동조율기 세포가 이에 속한다. 박동조율기 전위는 자연적인 리듬을 가지고 있지만 외부 자극에 의해 조절될 수도 있다. 예를 들어 심박수는 약물이나 교감 및 부교감신경에 의해 변화한다. 외부 자극은 세포가 반복적으로 발화하도록 하는 것이 아니라 자연적으로 발화하는 시간을 조절한다. 발화 빈도는 복잡하게 조절되고, 돌발적인 활동전위 패턴(bursting)을 만들기도 한다.", "가장 널리 연구되는 전압 의존성 이온 채널은 빠른 신경 전도에 관련된 나트륨 채널이다. 나트륨 채널과 활동전위의 생물물리학적 연구로 노벨상을 수상한 앨런 로이드 호지킨(Alan Hodgkin)과 앤드루 헉슬리Andrew Huxley)의 이름을 따 나트륨 채널을 호지킨-헉슬리 나트륨 채널이라고도 부르고, 더욱 단순하게는 NaV 채널(V는 전압을 의미)이라고 부른다. NaV 채널은 불활성형(deactivated state), 활성형(activated state), 차단형(inactivated state) 등 세 가지 상태로 존재할 수 있다. 채널은 활성형 상태일 때 나트륨 이온에 대해서만 투과성이 있다. 막 전위가 낮을 때 채널은 대부분의 시간 동안 불활성형(닫힌형) 형으로 존재한다. 막 전위가 특정 수준 이상으로 올라가면 채널이 활성형(열린형)으로 전이될 확률이 증가하고, 막 전위가 높을수록 확률은 더 커진다. 채널이 활성화되고 나면 차단형(닫힌형)으로 변화하고, 그 상태로 일정 시간 유지된다. 막 전위가 다시 낮아지면 채널은 불활성형(닫힌형)으로 돌아간다. 결론적으로 활동전위 동안 채널이 거치는 주기는 불활성형 → 활성형 → 차단형 → 불활성형 순이다. 이 순서는 채널 전체를 기준으로 평균적인 행동이고, 이론적으로 각각의 채널은 한 시점에서 전이 상태가 모두 다를 수 있다. 다만 채널이 차단형에서 곧바로 활성형으로 바뀌는 것은 거의 일어나지 않는다. 차단형에 있는 채널은 불활성형으로 되돌아갈 때까지 불응기(무반응성, refractory)를 거친다.", "FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage. For enhancement mode, the channel is off at zero bias, and a gate potential can \"enhance\" the conduction. For the depletion mode, the channel is on at zero bias, and a gate potential (of the opposite polarity) can \"deplete\" the channel, reducing conduction. For either mode, a more positive gate voltage corresponds to a higher current for n-channel devices and a lower current for p-channel devices. Nearly all JFETs are depletion-mode because the diode junctions would forward bias and conduct if they were enhancement-mode devices; most IGFETs are enhancement-mode types.", "Phase-two mode can only be activated by a key switch located inside the elevator on the centralized control panel. This mode was created for firefighters so that they may rescue people from a burning building. The phase-two key switch located on the COP has three positions: off, on, and hold. By turning phase two on, the firefighter enables the car to move. However, like independent-service mode, the car will not respond to a car call unless the firefighter manually pushes and holds the door close button. Once the elevator gets to the desired floor it will not open its doors unless the firefighter holds the door open button. This is in case the floor is burning and the firefighter can feel the heat and knows not to open the door. The firefighter must hold door open until the door is completely opened. If for any reason the firefighter wishes to leave the elevator, they will use the hold position on the key switch to make sure the elevator remains at that floor. If the firefighter wishes to return to the recall floor, they simply turn the key off and close the doors." ], [ "Different phases of digestion take place including: the cephalic phase , gastric phase, and intestinal phase. The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin. The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine. The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.", "Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase, a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The second phase of growth is the log phase, also known as the logarithmic or exponential phase. The log phase is marked by rapid exponential growth. The rate at which cells grow during this phase is known as the growth rate (k), and the time it takes the cells to double is known as the generation time (g). During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth is the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport. The final phase is the death phase where the bacteria run out of nutrients and die.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Holometabolism, or complete metamorphosis, is where the insect changes in four stages, an egg or embryo, a larva, a pupa and the adult or imago. In these species, an egg hatches to produce a larva, which is generally worm-like in form. This worm-like form can be one of several varieties: eruciform (caterpillar-like), scarabaeiform (grub-like), campodeiform (elongated, flattened and active), elateriform (wireworm-like) or vermiform (maggot-like). The larva grows and eventually becomes a pupa, a stage marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin.:151 Insects undergo considerable change in form during the pupal stage, and emerge as adults. Butterflies are a well-known example of insects that undergo complete metamorphosis, although most insects use this life cycle. Some insects have evolved this system to hypermetamorphosis." ], [ "Likewise, group theory helps predict the changes in physical properties that occur when a material undergoes a phase transition, for example, from a cubic to a tetrahedral crystalline form. An example is ferroelectric materials, where the change from a paraelectric to a ferroelectric state occurs at the Curie temperature and is related to a change from the high-symmetry paraelectric state to the lower symmetry ferroelectic state, accompanied by a so-called soft phonon mode, a vibrational lattice mode that goes to zero frequency at the transition.", "In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed \"q-glass\") could be grown from the melt. This phase is the first phase, or \"primary phase,\" to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.", "The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.", "Energy transformations in the universe over time are characterized by various kinds of potential energy that has been available since the Big Bang later being \"released\" (transformed to more active types of energy such as kinetic or radiant energy) when a triggering mechanism is available. Familiar examples of such processes include nuclear decay, in which energy is released that was originally \"stored\" in heavy isotopes (such as uranium and thorium), by nucleosynthesis, a process ultimately using the gravitational potential energy released from the gravitational collapse of supernovae, to store energy in the creation of these heavy elements before they were incorporated into the solar system and the Earth. This energy is triggered and released in nuclear fission bombs or in civil nuclear power generation. Similarly, in the case of a chemical explosion, chemical potential energy is transformed to kinetic energy and thermal energy in a very short time. Yet another example is that of a pendulum. At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum. At its lowest point the kinetic energy is at maximum and is equal to the decrease of potential energy. If one (unrealistically) assumes that there is no friction or other losses, the conversion of energy between these processes would be perfect, and the pendulum would continue swinging forever." ], [ "Northwestern is home to the Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern Institute for Complex Systems, Nanoscale Science and Engineering Center, Materials Research Center, Institute for Policy Research, International Institute for Nanotechnology, Center for Catalysis and Surface Science, Buffet Center for International and Comparative Studies, the Initiative for Sustainability and Energy at Northwestern and the Argonne/Northwestern Solar Energy Research Center and other centers for interdisciplinary research.", "1950년대 후반, 허버트 멘젤 등이 과학자들의 의사소통 방식에 대한 연구를 시작하였다. 처음에는 머턴의 과학사회학과 무관하게 진행하였지만, 의사소통이 새로운 학문을 형성하는데 중요함을 알게 되면서 두 연구분야는 융합하였다. 이 분야의 대표적 저서는 다이애나 크레인의 《보이지 않는 대학 Invisible College》과 니콜라스 멀린스의 논문 《생물학자들 간의 사회적 연결망 Social Networks Among Biological Scientists》등이 있다. 그 외에도 요셉 벤다비드나 독일의 학자들도 새로운 연구분야가 형성되는 과정을 연구하였다. 그러나 제시된 모형의 대부분은 학자들이 연구의 소재로 삼은 사례에 대해서만 맞아떨어졌다. 예를 들어 영국의 사회학자 마이클 멀케이와 데이비드 엣지는 저서 《천문학의 재탄생 (과학, 문화와 사회) Astronomy Transformed (Science, Culture & Society)》에서 전파천문학의 발전과정이 기존에 제시된 모형들과 맞지 않음을 보였다. 최근에는 신생 연구분야의 탄생과정을 설명할 수 있는 간단하고 일반적인 이론은 없다는 견해가 대세를 차지한다.", "이러한 추세는 세계 각국의 과학기술 정책 변화와 과학 재단의 변화를 일으켰다. 미국 국립 과학재단이 나노 과학자들을 중심으로 미래 과학기술의 틀을 모색할 초기 단계에서 융합의 개념에 도달하였다. 미국에서는 일차적으로 'GRIN'(유전학(Genetic), 로보틱스(Robotics), 정보과학(Information Science), 나노공학(Nano technology))의 틀을 제시하였다. 이후 2001년 말에 유전학이 생명공학으로 범위가 확장되었고 로보틱스가 정보과학에 포함이 되었다. 또 그 후 인지과학이 추가되어서 마침내 2002년 NBIC(나노공학(Nano technology), 생명공학(Biotechnology), 정보과학(Information Science), 인지과학(Cognitive Science)) 융합과학기술의 틀이 완정되었다.", "The university employs 3,401 full-time faculty members across its eleven schools, including 18 members of the National Academy of Sciences, 65 members of the American Academy of Arts and Sciences, 19 members of the National Academy of Engineering, and 6 members of the Institute of Medicine. Notable faculty include 2010 Nobel Prize–winning economist Dale T. Mortensen; nano-scientist Chad Mirkin; Tony Award-winning director Mary Zimmerman; management expert Philip Kotler; King Faisal International Prize in Science recipient Sir Fraser Stoddart; Steppenwolf Theatre director Anna Shapiro; sexual psychologist J. Michael Bailey; Holocaust denier Arthur Butz; Federalist Society co-founder Steven Calabresi; former Weatherman Bernardine Rae Dohrn; ethnographer Gary Alan Fine; Pulitzer Prize–winning historian Garry Wills; American Academy of Arts and Sciences fellow Monica Olvera de la Cruz and MacArthur Fellowship recipients Stuart Dybek, and Jennifer Richeson. Notable former faculty include political advisor David Axelrod, artist Ed Paschke, writer Charles Newman, Nobel Prize–winning chemist John Pople, and military sociologist and \"don't ask, don't tell\" author Charles Moskos." ] ]
5a7dcf1970df9f001a8751e1	Matter	In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.	en	null	null	190,667	[ "What is composed of antimatter?", "What happens when two antiparticles collide?", "What are particle-antiparticle pairs that are not high-energy called?", "What kind of energy do particle-antiparticle pairs have more of than they had originally?", "Who discovered quantum chemistry?" ]	[ [ "Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay, lightning or cosmic rays). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, and whether other places are almost entirely antimatter instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called the charge parity (or CP symmetry) violation. CP symmetry violation can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.", "The term \"matter\" is used throughout physics in a bewildering variety of contexts: for example, one refers to \"condensed matter physics\", \"elementary matter\", \"partonic\" matter, \"dark\" matter, \"anti\"-matter, \"strange\" matter, and \"nuclear\" matter. In discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter (Gk. common matter). It is fair to say that in physics, there is no broad consensus as to a general definition of matter, and the term \"matter\" usually is used in conjunction with a specifying modifier." ], [ "Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay, lightning or cosmic rays). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "LIGO 합동연구진은 2015년 9월 14일 지구에서 13억 광년 떨어진 질량 약 30 M☉의 블랙홀 두 개가 서로 충돌하여 질량 60 M☉의 단일 블랙홀로 융합될 때 발생한 중력파를 검출함으로써 최초로 중력파 관측에 성공했다고 2016년 2월 11일 발표했다. 연구원들 중 한 명 이상이 이 사건을 블랙홀을 직접적으로 감지한 최초의 사례라고 규정했다. LIGO의 중력파 검출 성공은 최초의 중력파 관측일 뿐 아니라 블랙홀 쌍성계가 서로 융합하는 것이 최초로 관측된 사례이기도 하다. 융합되기 직전 두 천체 사이의 거리는 불과 350 킬로미터였으며, 두 천체가 모두 블랙홀이라는 것 외에는 질량이 30 M☉인 두 개의 천체가 이렇게 가까이 접근할 수 있었음에 대한 타당한 설명이 없다. 검출된 중력파의 특징은 융합된 이후에는 블랙홀이 안정화되면서 중력파가 급속히 감쇠하는 등, 두 블랙홀 사이의 융합으로 인해 발생할 중력파의 이론적 예상과 정확히 일치했다. 이 검출은 블랙홀의 존재가 예상되는 강력한 중력장 환경에서 일반상대론이 검증된 현재까지 가장 강력한 사례로서, 일반상대론의 예측과 배치되는 증거는 전혀 발견되지 않았다. 또한 질량 25 M☉ 이상의 항성질량 블랙홀이 자연계에서 형성될 수 있다는 첫 증거이기도 하다.", "2005년 7월 4일 협정 세계시 08시 00분에 있었던 이후 여파 브리핑에서, 1차 처리된 사진은 원래 있던 충돌구가 찍혔다는 것을 보였다. NASA의 과학자들은 충돌기가 부딪혀서 생긴 충돌구를 잘 확인할 수 없었지만, 이후에 폭 100m에 깊이 30m인 충돌구가 발견되었다. 충돌 과정의 공동 연구자 중 한 명인 루시 맥파든은 이렇게 말했다: \"우리는 첫 번째 임무인 '밝은 먼지 구름'은 관찰했지만, 두 번째 임무인 '충돌구'를 보는 것은 기대하지 않았습니다. 그러나 그것 또한 예기치 못한 발견을 하는 과학의 재미 중 하나죠.\"스위프트 감마선 망원경의 관측 자료를 분석한 결과, 충돌 이후 13일 동안 혜성에서 계속 먼지 구름이 뿜어져 나옴을 확인했다. 물 5백만 킬로그램과 10만~25만 킬로그램의 먼지가 충돌 시 우주로 사라졌다." ], [ "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4.", "1977년에 이휘소는 스티븐 와인버그와 함께 〈무거운 뉴트리노 질량의 우주론적 최소 경계치〉라는 제목의 논문을 발표하였다. 이 논문에서 그들은 초기 우주 팽창의 흔적으로 쌍소멸을 통해 이윽고 다른 입자로 바뀌는, 충분히 무거우며 또한 안정적인 입자가 남아있다면 그들의 상호작용의 세기는 최소한 2GeV일 것이라고 예상하였다. 여기에서 이들이 다룬 입자는 윔프이다. 윔프의 질량이 작아질수록 그 쌍소멸 반응 단면적의 크기도 작아져야 하는데, 이는 대략 ≈ m / M 정도이다. 여기서 m은 윔프의 질량이며, M은 Z보존의 질량이다. 이것은 초기 우주에서 풍부하게 생산된 윔프들 중 가벼운 윔프는 무거운 윔프보다 보다 일찍 상호작용을 그만둔, 즉 우주의 온도가 보다 더 높았을 때에 상호작용을 그만둔 윔프라는 것을 의미한다. 이휘소와 스티븐 와인버그의 계산에 의하면, 윔프의 질량이 ~ 2 GeV보다도 가볍다면 그 흔적의 밀도는 우주의 스케일을 뛰어넘는, 즉 있을 수 없는 값을 갖게 된다. 윔프의 질량이 더이상 작아질 수 없는 이 경계를 리-와인버그 경계라고 한다." ], [ "중력파의 간접적 효과는 몇몇 쌍성계를 관측하면서 이미 검출된 바 있다. 문제의 쌍성계들은 계를 구성하는 두 항성이 서로서로에 대해 공전하며, 그 결과 서서히 에너지를 잃으면서 그 에너지를 중력파로 발산한다. 태양 같은 보통의 별들은 이렇게 잃는 에너지가 너무 작아서 검출할 수 없으나, 1974년 PSR1913+16이라는 펄서 쌍성계에서 이러한 에너지가 발견되었다. 펄서 쌍성계는 쌍성의 구성 항성 둘 중 한쪽이 펄서이다. 펄서는 극도로 밀도가 높은 밀집성으로, 중성자별의 일종이다. 중성자별이 방출하는 중력파는 보통 항성의 그것보다 훨씬 강하다. 또한 펄서는 양극으로 좁은 전자기파 빔을 발산한다. 펄서가 자전하면서 빔은 지구 방향도 한바퀴 쓸어가게 되고, 그러면 지구에서는 일정한 전파 맥동의 형태로 그 빛줄기가 관찰된다. 마치 등대의 램프가 계속 켜진 채로 회전하는 것이 먼 바다의 배가 보기에는 불이 깜빡거리는 것처럼 보이는 것과 같다. 이 전파 맥동의 간격은 극도로 일정하여, 매우 정확한 \"시계\"로서 기능한다. 이 펄서 맥동은 쌍성계의 공전주기를 알아낼 때도 사용될 수 있으며, 또한 펄서 바로 주위의 시공간의 왜곡에 매우 민감하게 반응한다.", "플루토늄-238은 어쩌면 핵반응로에서는 우라늄-235보다 더 효율적인 동위 원소가 될 수 있다. 왜냐하면 플루토늄-238은 우라늄-235보다 더욱 작은 임계 질량을 가지고 있지만 핵분열 연쇄 반응이 조종 막대에 의해 멈출 때까지 끊임없이 붕괴하여 많은 양의 열 에너지를 생산하기 때문이다.(0.56 W/g) 이것의 용도는 한정적인데, 왜냐하면 플루토늄-238의 높은 가격 때문이다.(1g당 약 1,100,000원) 이 동위 원소는 우주에서 인공 위성과 우주 정거장에서 열전퇴 기능과 물을 증류하는 기능에 쓰인다. 또한 갈릴레오와 아폴로 우주선 (예: 아폴로 14호)에서도 킬로그램 정도의 무게인 산화플루토늄-238로 히터를 작동시켰다; 또한 이 열은 열전퇴와 함께 전기로 바뀌기도 한다. 플루토늄-238의 붕괴에서는 거의 해롭지 않은 알파 입자를 방사하고, 감마선 조사를 동반하지 않는다. 그러므로, 이 동위 원소는(~160 mg) 원자력 심장페이스메이커의 에너지원에 사용된다. 원자력 심장페이스메이커에서의 에너지는 일반 배터리보다 5배 더 길다.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e−E/kT – that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation.The activation energy necessary for a chemical reaction can be in the form of thermal energy." ], [ "Modern chemistry emerged from the sixteenth through the eighteenth centuries through the material practices and theories promoted by alchemy, medicine, manufacturing and mining. A decisive moment came when 'chymistry' was distinguished from alchemy by Robert Boyle in his work The Sceptical Chymist, in 1661; although the alchemical tradition continued for some time after his work. Other important steps included the gravimetric experimental practices of medical chemists like William Cullen, Joseph Black, Torbern Bergman and Pierre Macquer and through the work of Antoine Lavoisier (Father of Modern Chemistry) on oxygen and the law of conservation of mass, which refuted phlogiston theory. The theory that all matter is made of atoms, which are the smallest constituents of matter that cannot be broken down without losing the basic chemical and physical properties of that matter, was provided by John Dalton in 1803, although the question took a hundred years to settle as proven. Dalton also formulated the law of mass relationships. In 1869, Dmitri Mendeleev composed his periodic table of elements on the basis of Dalton's discoveries.", "Richard Phillips Feynman (/ˈfaɪnmən/; May 11, 1918 – February 15, 1988) was an American theoretical physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics for which he proposed the parton model. For his contributions to the development of quantum electrodynamics, Feynman, jointly with Julian Schwinger and Sin-Itiro Tomonaga, received the Nobel Prize in Physics in 1965. He developed a widely used pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, which later became known as Feynman diagrams. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World he was ranked as one of the ten greatest physicists of all time.", "근대 화학은 보일의 저서 《회의적 화학자(The Sceptical Chymist)》에서 연금술과 화학이 구별된 데에서부터 시작한다. 이 책이 출간될 1600년대 중반까지만 해도 컬런(W. Cullen), 블랙, 베리만, 마케(P. Macquer)과 같은 약리화학자들에 의해 질량측정 실험과 같은 연금술적 실험이 계속되고 있었다. 현대 화학의 대부라 불리는 라부아지에는 그의 산소에 대한 이론과 질량 보존의 법칙을 바탕으로 플로지스톤설이 잘못되었음을 증명하고 이를 폐기하였다. 1803년에는 돌턴이 모든 물질은 파괴되지 아니하며 물리화학적 성질을 잃지 아니하는 가장 작은 요소인 원자로 이루어져있다는 이론을 제기하였다. 돌턴은 이 이론에서 부분 압력의 법칙을 수식화하였다. 1869년에는 멘델레예프가 돌턴의 발견을 기초로하여 주기율표를 완성하였다.", "앙투안로랑 드 라부아지에(프랑스어: Antoine-Laurent de Lavoisier, 1743년 8월 26일 ~ 1794년 5월 8일)는 프랑스의 화학자이다. 근대 화학의 아버지라 불린다. 대한민국에서는 짧게 줄여 '라부아지에'라고도 표기한다. 그는 뛰어난 실험자였으며, 화학 이외의 다른 방면에서도 뛰어난 능력을 발휘하여 여러 공직에 있기도 하였다. 연소에 관한 새로운 이론을 주장하여 플로지스톤설을 폐기하면서 화학을 크게 발전시켰고, 산화 과정에서 산소의 작용, 산화나 호흡 간의 정량적인 유사점 등을 발견하기도 하였다. 또한 화학 반응에서 질량 보존의 법칙을 확립하였으며 원소와 화합물을 구분하여 근대 화합물 명명법의 기초를 마련하였다. 화학에 정량적인 방법을 처음으로 도입한 학자 중 한 명이기도 하다." ] ]
5a7dcf8e70df9f001a8751ff	Matter	Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay, lightning or cosmic rays). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.	en	null	null	190,672	[ "Where is antimatter found naturally in large quantities?", "What does antimatter annihilate?", "Where is ordinary matter created?", "What is an example of an antiparticle?", "Large quantities of what can be created for testing?" ]	[ [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, and whether other places are almost entirely antimatter instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called the charge parity (or CP symmetry) violation. CP symmetry violation can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.", "As cellular metabolism/energy production requires oxygen, potentially damaging (e.g., mutation causing) compounds known as free radicals can form. Most of these are oxidizers (i.e., acceptors of electrons) and some react very strongly. For the continued normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds. Recently, some researchers suggested an interesting theory of evolution of dietary antioxidants. Some are produced by the human body with adequate precursors (glutathione, Vitamin C), and those the body cannot produce may only be obtained in the diet via direct sources (Vitamin C in humans, Vitamin A, Vitamin K) or produced by the body from other compounds (Beta-carotene converted to Vitamin A by the body, Vitamin D synthesized from cholesterol by sunlight). Phytochemicals (Section Below) and their subgroup, polyphenols, make up the majority of antioxidants; about 4,000 are known. Different antioxidants are now known to function in a cooperative network. For example, Vitamin C can reactivate free radical-containing glutathione or Vitamin E by accepting the free radical itself. Some antioxidants are more effective than others at neutralizing different free radicals. Some cannot neutralize certain free radicals. Some cannot be present in certain areas of free radical development (Vitamin A is fat-soluble and protects fat areas, Vitamin C is water-soluble and protects those areas). When interacting with a free radical, some antioxidants produce a different free radical compound that is less dangerous or more dangerous than the previous compound. Having a variety of antioxidants allows any byproducts to be safely dealt with by more efficient antioxidants in neutralizing a free radical's butterfly effect.", "Before the early 20th century, treatments for infections were based primarily on medicinal folklore. Mixtures with antimicrobial properties that were used in treatments of infections were described over 2000 years ago. Many ancient cultures, including the ancient Egyptians and ancient Greeks, used specially selected mold and plant materials and extracts to treat infections. More recent observations made in the laboratory of antibiosis between microorganisms led to the discovery of natural antibacterials produced by microorganisms. Louis Pasteur observed, \"if we could intervene in the antagonism observed between some bacteria, it would offer perhaps the greatest hopes for therapeutics\". The term 'antibiosis', meaning \"against life\", was introduced by the French bacteriologist Jean Paul Vuillemin as a descriptive name of the phenomenon exhibited by these early antibacterial drugs. Antibiosis was first described in 1877 in bacteria when Louis Pasteur and Robert Koch observed that an airborne bacillus could inhibit the growth of Bacillus anthracis. These drugs were later renamed antibiotics by Selman Waksman, an American microbiologist, in 1942. Synthetic antibiotic chemotherapy as a science and development of antibacterials began in Germany with Paul Ehrlich in the late 1880s. Ehrlich noted certain dyes would color human, animal, or bacterial cells, whereas others did not. He then proposed the idea that it might be possible to create chemicals that would act as a selective drug that would bind to and kill bacteria without harming the human host. After screening hundreds of dyes against various organisms, in 1907, he discovered a medicinally useful drug, the synthetic antibacterial salvarsan now called arsphenamine." ], [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.", "There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, and whether other places are almost entirely antimatter instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called the charge parity (or CP symmetry) violation. CP symmetry violation can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.", "Amensalism is the type of relationship that exists where one species is inhibited or completely obliterated and one is unaffected. This type of symbiosis is relatively uncommon in rudimentary reference texts, but is omnipresent in the natural world.[citation needed] There are two types of amensalism, competition and antibiosis. Competition is where a larger or stronger organisms deprives a smaller or weaker one from a resource. Antibiosis occurs when one organism is damaged or killed by another through a chemical secretion. An example of competition is a sapling growing under the shadow of a mature tree. The mature tree can begin to rob the sapling of necessary sunlight and, if the mature tree is very large, it can take up rainwater and deplete soil nutrients. Throughout the process the mature tree is unaffected. Indeed, if the sapling dies, the mature tree gains nutrients from the decaying sapling. Note that these nutrients become available because of the sapling's decomposition, rather than from the living sapling, which would be a case of parasitism.[citation needed] An example of antibiosis is Juglans nigra (black walnut), secreting juglone, a substance which destroys many herbaceous plants within its root zone." ], [ "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks. It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars)." ], [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "Amensalism is the type of relationship that exists where one species is inhibited or completely obliterated and one is unaffected. This type of symbiosis is relatively uncommon in rudimentary reference texts, but is omnipresent in the natural world.[citation needed] There are two types of amensalism, competition and antibiosis. Competition is where a larger or stronger organisms deprives a smaller or weaker one from a resource. Antibiosis occurs when one organism is damaged or killed by another through a chemical secretion. An example of competition is a sapling growing under the shadow of a mature tree. The mature tree can begin to rob the sapling of necessary sunlight and, if the mature tree is very large, it can take up rainwater and deplete soil nutrients. Throughout the process the mature tree is unaffected. Indeed, if the sapling dies, the mature tree gains nutrients from the decaying sapling. Note that these nutrients become available because of the sapling's decomposition, rather than from the living sapling, which would be a case of parasitism.[citation needed] An example of antibiosis is Juglans nigra (black walnut), secreting juglone, a substance which destroys many herbaceous plants within its root zone.", "With advances in medicinal chemistry, most modern antibacterials are semisynthetic modifications of various natural compounds. These include, for example, the beta-lactam antibiotics, which include the penicillins (produced by fungi in the genus Penicillium), the cephalosporins, and the carbapenems. Compounds that are still isolated from living organisms are the aminoglycosides, whereas other antibacterials—for example, the sulfonamides, the quinolones, and the oxazolidinones—are produced solely by chemical synthesis. Many antibacterial compounds are relatively small molecules with a molecular weight of less than 2000 atomic mass units.[citation needed]", "Bacteriophages are viruses that infect bacteria. Many types of bacteriophage exist, some simply infect and lyse their host bacteria, while others insert into the bacterial chromosome. A bacteriophage can contain genes that contribute to its host's phenotype: for example, in the evolution of Escherichia coli O157:H7 and Clostridium botulinum, the toxin genes in an integrated phage converted a harmless ancestral bacterium into a lethal pathogen. Bacteria resist phage infection through restriction modification systems that degrade foreign DNA, and a system that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact with in the past, which allows them to block virus replication through a form of RNA interference. This CRISPR system provides bacteria with acquired immunity to infection." ], [ "Software developers can't test everything, but they can use combinatorial test design to identify the minimum number of tests needed to get the coverage they want. Combinatorial test design enables users to get greater test coverage with fewer tests. Whether they are looking for speed or test depth, they can use combinatorial test design methods to build structured variation into their test cases. Note that \"coverage\", as used here, is referring to combinatorial coverage, not requirements coverage.", "Load testing is primarily concerned with testing that the system can continue to operate under a specific load, whether that be large quantities of data or a large number of users. This is generally referred to as software scalability. The related load testing activity of when performed as a non-functional activity is often referred to as endurance testing. Volume testing is a way to test software functions even when certain components (for example a file or database) increase radically in size. Stress testing is a way to test reliability under unexpected or rare workloads. Stability testing (often referred to as load or endurance testing) checks to see if the software can continuously function well in or above an acceptable period.", "A fundamental problem with software testing is that testing under all combinations of inputs and preconditions (initial state) is not feasible, even with a simple product.:17-18 This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, non-functional dimensions of quality (how it is supposed to be versus what it is supposed to do)—usability, scalability, performance, compatibility, reliability—can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.", "In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed \"splat cooling\" by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become \"locked into\" a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys." ] ]
5a7de5f270df9f001a8752c3	Matter	There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, and whether other places are almost entirely antimatter instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called the charge parity (or CP symmetry) violation. CP symmetry violation can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.	en	null	null	190,677	[ "What is the disappearance of matter linked to?", "When was there more antimatter than matter?", "What problem has physics solved?", "Where is the Standard Model found?", "What field of study speculates about science fiction?" ]	[ [ "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "Some modern day physicists and science writers—such as Paul Davies and John Gribbin—have argued that materialism has been disproven by certain scientific findings in physics, such as quantum mechanics and chaos theory. In 1991, Gribbin and Davies released their book The Matter Myth, the first chapter of which, \"The Death of Materialism\", contained the following passage:", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "For example, consider electron–positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. This is a reversible process – the inverse process is called pair creation – in which the rest mass of particles is created from energy of two (or more) annihilating photons. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction." ], [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay, lightning or cosmic rays). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Ancient Greek philosophers like Thales, Anaxagoras (ca. 500 BC – 428 BC), Epicurus and Democritus prefigure later materialists. The Latin poem De Rerum Natura by Lucretius (ca. 99 BC – ca. 55 BC) reflects the mechanistic philosophy of Democritus and Epicurus. According to this view, all that exists is matter and void, and all phenomena result from different motions and conglomerations of base material particles called \"atoms\" (literally: \"indivisibles\"). De Rerum Natura provides mechanistic explanations for phenomena such as erosion, evaporation, wind, and sound. Famous principles like \"nothing can touch body but body\" first appeared in the works of Lucretius. Democritus and Epicurus however did not hold to a monist ontology since they held to the ontological separation of matter and space i.e. space being \"another kind\" of being, indicating that the definition of \"materialism\" is wider than given scope for in this article." ], [ "Replacing the classical physics in use since the end of the scientific revolution, modern physics arose in the early 20th century with the advent of quantum physics, substituting mathematical studies for experimental studies and examining equations to build a theoretical structure.[citation needed] The old quantum theory was a collection of results which predate modern quantum mechanics, but were never complete or self-consistent. The collection of heuristic prescriptions for quantum mechanics were the first corrections to classical mechanics. Outside the realm of quantum physics, the various aether theories in classical physics, which supposed a \"fifth element\" such as the Luminiferous aether, were nullified by the Michelson-Morley experiment—an attempt to detect the motion of earth through the aether. In biology, Darwinism gained acceptance, promoting the concept of adaptation in the theory of natural selection. The fields of geology, astronomy and psychology also made strides and gained new insights. In medicine, there were advances in medical theory and treatments.", "The black-body problem was revisited in 1905, when Rayleigh and Jeans (on the one hand) and Einstein (on the other hand) independently proved that classical electromagnetism could never account for the observed spectrum. These proofs are commonly known as the \"ultraviolet catastrophe\", a name coined by Paul Ehrenfest in 1911. They contributed greatly (along with Einstein's work on the photoelectric effect) to convincing physicists that Planck's postulate of quantized energy levels was more than a mere mathematical formalism. The very first Solvay Conference in 1911 was devoted to \"the theory of radiation and quanta\". Max Planck received the 1918 Nobel Prize in Physics \"in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta\".", "The beginning of the 20th century brought the start of a revolution in physics. The long-held theories of Newton were shown not to be correct in all circumstances. Beginning in 1900, Max Planck, Albert Einstein, Niels Bohr and others developed quantum theories to explain various anomalous experimental results, by introducing discrete energy levels. Not only did quantum mechanics show that the laws of motion did not hold on small scales, but even more disturbingly, the theory of general relativity, proposed by Einstein in 1915, showed that the fixed background of spacetime, on which both Newtonian mechanics and special relativity depended, could not exist. In 1925, Werner Heisenberg and Erwin Schrödinger formulated quantum mechanics, which explained the preceding quantum theories. The observation by Edwin Hubble in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the Big Bang theory by Georges Lemaître.", "In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Eventually following Stoic physics in this instance, scholars from the 14th century onward increasingly departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion widely acknowledged by the 17th century, which helped to segregate natural and theological concerns." ], [ "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "In a simple model, often referred to as the transmission model or standard view of communication, information or content (e.g. a message in natural language) is sent in some form (as spoken language) from an emisor/ sender/ encoder to a destination/ receiver/ decoder. This common conception of communication simply views communication as a means of sending and receiving information. The strengths of this model are simplicity, generality, and quantifiability. Claude Shannon and Warren Weaver structured this model based on the following elements:", "A standard dialect (also known as a standardized dialect or \"standard language\") is a dialect that is supported by institutions. Such institutional support may include government recognition or designation; presentation as being the \"correct\" form of a language in schools; published grammars, dictionaries, and textbooks that set forth a correct spoken and written form; and an extensive formal literature that employs that dialect (prose, poetry, non-fiction, etc.). There may be multiple standard dialects associated with a single language. For example, Standard American English, Standard British English, Standard Canadian English, Standard Indian English, Standard Australian English, and Standard Philippine English may all be said to be standard dialects of the English language.", "Standard Catalan, virtually accepted by all speakers, is mostly based on Eastern Catalan, which is the most widely used dialect. Nevertheless, the standards of Valencia and the Balearics admit alternative forms, mostly traditional ones, which are not current in eastern Catalonia." ], [ "가상현실에 대한 철학적 논의가 본격화되기 이전부터 가상현실은 SF영화나 문학작품, 기술 분야에서 다양한 이름으로 명명되며 사람들에게 인식되었다. 닐 스티븐슨의 사이버 펑크 소설 스노우 크래쉬(1991)에서 명명된 '메타버스(Metaverse)'와 윌리엄 깁슨의 소설 뉴로맨서(1984)에서 ‘사이버스페이스(cyberspace)'가 그 예이다. 그러나 컴퓨터 기술의 지속적 발달로 인해 가상현실 시스템이 실제로 인간의 삶 속에서 영향력을 발휘하고, 현대인의 삶의 무대가 가상의 공간으로까지 확장됨에 따라 가상현실에 대한 적극적인 철학적 논의와 고찰의 필요성이 대두되었다. 가상현실에 대한 철학적 논의는 '가상현실'에서 가상, 즉 '버추얼(virtual)'의 개념 자체에 대한 것도 있고, 인간 감각의 한계 및 가상현실 기술의 특성과 관련하여 존재론적인 고찰, 실재성과 공간성 개념에 대한 논의들도 활발히 제기되고 있다. 가상현실에 대한 철학적으로 고찰한 서적으로 마이클 하임(Michael Heim)의 가상현실의 철학적 의미(1993)가 있다. 또, 가상현실에 대한 직접적 논의를 다루고 있지는 않지만 '가상성'과 관련하여 장 보드리야르(Jean baudrillard)의 시뮬라시옹이 유명하다. 가상현실에 대한 철학적 사유를 자극하는 영화로는 매트릭스, 토탈리콜, 공각기동대 등이 있다.", "Genre fiction also showed it could question reality in its 20th century forms, in spite of its fixed formulas, through the enquiries of the skeptical detective and the alternative realities of science fiction. The separation of \"mainstream\" and \"genre\" forms (including journalism) continued to blur during the period up to our own times. William Burroughs, in his early works, and Hunter S. Thompson expanded documentary reporting into strong subjective statements after the second World War, and post-modern critics have disparaged the idea of objective realism in general.", "Much of the study of the history of science has been devoted to answering questions about what science is, how it functions, and whether it exhibits large-scale patterns and trends. The sociology of science in particular has focused on the ways in which scientists work, looking closely at the ways in which they \"produce\" and \"construct\" scientific knowledge. Since the 1960s, a common trend in science studies (the study of the sociology and history of science) has been to emphasize the \"human component\" of scientific knowledge, and to de-emphasize the view that scientific data are self-evident, value-free, and context-free. The field of Science and Technology Studies, an area that overlaps and often informs historical studies of science, focuses on the social context of science in both contemporary and historical periods.", "Further studies, e.g. Jerome Ravetz 1971 Scientific Knowledge and its Social Problems referred to the role of the scientific community, as a social construct, in accepting or rejecting (objective) scientific knowledge. The Science wars of the 1990 were about the influence of especially French philosophers, which denied the objectivity of science in general or seemed to do so. They described as well differences between the idealized model of a pure science and the actual scientific practice; while scientism, a revival of the positivism approach, saw in precise measurement and rigorous calculation the basis for finally settling enduring metaphysical and moral controversies. However, more recently some of the leading critical theorists have recognized that their postmodern deconstructions have at times been counter-productive, and are providing intellectual ammunition for reactionary interests. Bruno Latour noted that \"dangerous extremists are using the very same argument of social construction to destroy hard-won evidence that could save our lives. Was I wrong to participate in the invention of this field known as science studies? Is it enough to say that we did not really mean what we meant?\"" ] ]
5a7de6bf70df9f001a8752d7	Matter	In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of the early universe and the big bang theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. The commonly accepted view is that most of the dark matter is non-baryonic in nature. As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles, which are not Standard Model particles, but relics formed at very high energies in the early phase of the universe and still floating about.	en	null	null	190,682	[ "What does dark matter emit to make it visible?", "What effect on other matter allows electromagnetic radiation to be visible?", "What is baryonic in nature?", "What does dark matter form?", "Supersymmetric particles are part of what Model?" ]	[ [ "Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy.", "Infrared radiation is popularly known as \"heat radiation\"[citation needed], but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths. Visible light or ultraviolet-emitting lasers can char paper and incandescently hot objects emit visible radiation. Objects at room temperature will emit radiation concentrated mostly in the 8 to 25 µm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see black body and Wien's displacement law).", "블랙홀의 안을 들여다볼 수는 없지만, 블랙홀이 다른 물질과 상호작용하는 것을 통해 그 성질을 알아낼 수 있다. 블랙홀 위로 낙하한 물질은 강착원반을 형성하고, 원반은 마찰열로 인해 뜨거워져 열복사로 빛난다. 우주에서 가장 밝은 천체인 퀘이사는 이러한 과정을 통해 만들어진다. 블랙홀 주위를 공전하는 다른 항성이 있을 경우, 그 궤도를 통해 블랙홀의 질량과 위치를 비정할 수 있다. 이러한 관측을 통해 중성자별을 비롯한 다른 유사 천체들을 제외함으로써 천문학자들은 블랙홀 후보들이 포함된 쌍성계를 셀 수 없이 많이 발견해냈고, 우리은하 중심 방향에 존재하는 전파원 궁수자리 A*가 4백 3십만 M☉의 초대질량 블랙홀임을 밝혔다.", "Infrared is used in night vision equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of ambient light photons into electrons that are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to augment the available ambient light for conversion by night vision devices, increasing in-the-dark visibility without actually using a visible light source." ], [ "The reason for this is that in this definition, electromagnetic radiation (such as light) as well as the energy of electromagnetic fields contributes to the mass of systems, and therefore appears to add matter to them. For example, light radiation (or thermal radiation) trapped inside a box would contribute to the mass of the box, as would any kind of energy inside the box, including the kinetic energy of particles held by the box. Nevertheless, isolated individual particles of light (photons) and the isolated kinetic energy of massive particles, are normally not considered to be matter.[citation needed]", "Infrared radiation is popularly known as \"heat radiation\"[citation needed], but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths. Visible light or ultraviolet-emitting lasers can char paper and incandescently hot objects emit visible radiation. Objects at room temperature will emit radiation concentrated mostly in the 8 to 25 µm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see black body and Wien's displacement law).", "The photoelectric effect is the emission of electrons (called \"photoelectrons\") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real.", "Prior to Einstein's paper, electromagnetic radiation such as visible light was considered to behave as a wave: hence the use of the terms \"frequency\" and \"wavelength\" to characterise different types of radiation. The energy transferred by a wave in a given time is called its intensity. The light from a theatre spotlight is more intense than the light from a domestic lightbulb; that is to say that the spotlight gives out more energy per unit time and per unit space(and hence consumes more electricity) than the ordinary bulb, even though the colour of the light might be very similar. Other waves, such as sound or the waves crashing against a seafront, also have their own intensity. However, the energy account of the photoelectric effect didn't seem to agree with the wave description of light." ], [ "Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy.", "Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements. Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernovae. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics.", "Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 7000100794000000000♠1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note 1] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.", "Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4." ], [ "Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 23% is dark matter, and about 72% is dark energy.", "Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks. It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars).", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below)." ], [ "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the \"matter\" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.", "From his diagrams of a small number of particles interacting in spacetime, Feynman could then model all of physics in terms of the spins of those particles and the range of coupling of the fundamental forces. Feynman attempted an explanation of the strong interactions governing nucleons scattering called the parton model. The parton model emerged as a complement to the quark model developed by his Caltech colleague Murray Gell-Mann. The relationship between the two models was murky; Gell-Mann referred to Feynman's partons derisively as \"put-ons\". In the mid-1960s, physicists believed that quarks were just a bookkeeping device for symmetry numbers, not real particles, as the statistics of the Omega-minus particle, if it were interpreted as three identical strange quarks bound together, seemed impossible if quarks were real. The Stanford linear accelerator deep inelastic scattering experiments of the late 1960s showed, analogously to Ernest Rutherford's experiment of scattering alpha particles on gold nuclei in 1911, that nucleons (protons and neutrons) contained point-like particles that scattered electrons. It was natural to identify these with quarks, but Feynman's parton model attempted to interpret the experimental data in a way that did not introduce additional hypotheses. For example, the data showed that some 45% of the energy momentum was carried by electrically-neutral particles in the nucleon. These electrically-neutral particles are now seen to be the gluons that carry the forces between the quarks and carry also the three-valued color quantum number that solves the Omega-minus problem. Feynman did not dispute the quark model; for example, when the fifth quark was discovered in 1977, Feynman immediately pointed out to his students that the discovery implied the existence of a sixth quark, which was discovered in the decade after his death.", "Richard Phillips Feynman (/ˈfaɪnmən/; May 11, 1918 – February 15, 1988) was an American theoretical physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics for which he proposed the parton model. For his contributions to the development of quantum electrodynamics, Feynman, jointly with Julian Schwinger and Sin-Itiro Tomonaga, received the Nobel Prize in Physics in 1965. He developed a widely used pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, which later became known as Feynman diagrams. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World he was ranked as one of the ten greatest physicists of all time." ] ]
5a7de78370df9f001a8752e1	Matter	The pre-Socratics were among the first recorded speculators about the underlying nature of the visible world. Thales (c. 624 BC–c. 546 BC) regarded water as the fundamental material of the world. Anaximander (c. 610 BC–c. 546 BC) posited that the basic material was wholly characterless or limitless: the Infinite (apeiron). Anaximenes (flourished 585 BC, d. 528 BC) posited that the basic stuff was pneuma or air. Heraclitus (c. 535–c. 475 BC) seems to say the basic element is fire, though perhaps he means that all is change. Empedocles (c. 490–430 BC) spoke of four elements of which everything was made: earth, water, air, and fire. Meanwhile, Parmenides argued that change does not exist, and Democritus argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy called atomism. All of these notions had deep philosophical problems.	en	null	null	190,687	[ "When did Socratics live?", "What did Parmenides believe was the fundamental material of the world?", "What is the name for the philosophical problems of understanding the nature of the world?", "How many elements did Democritus name?", "What did Parmenides say everything was made of?" ]	[ [ "The earliest Greek philosophers, known as the pre-Socratics, provided competing answers to the question found in the myths of their neighbors: \"How did the ordered cosmos in which we live come to be?\" The pre-Socratic philosopher Thales (640-546 BC), dubbed the \"father of science\", was the first to postulate non-supernatural explanations for natural phenomena, for example, that land floats on water and that earthquakes are caused by the agitation of the water upon which the land floats, rather than the god Poseidon. Thales' student Pythagoras of Samos founded the Pythagorean school, which investigated mathematics for its own sake, and was the first to postulate that the Earth is spherical in shape. Leucippus (5th century BC) introduced atomism, the theory that all matter is made of indivisible, imperishable units called atoms. This was greatly expanded by his pupil Democritus.", "6th-century BCE pre-Socratic Greek philosophers Thales of Miletus and Xenophanes of Colophon were the first in the region to attempt to explain the world in terms of human reason rather than myth and tradition, thus can be said to be the first Greek humanists. Thales questioned the notion of anthropomorphic gods and Xenophanes refused to recognise the gods of his time and reserved the divine for the principle of unity in the universe. These Ionian Greeks were the first thinkers to assert that nature is available to be studied separately from the supernatural realm. Anaxagoras brought philosophy and the spirit of rational inquiry from Ionia to Athens. Pericles, the leader of Athens during the period of its greatest glory was an admirer of Anaxagoras. Other influential pre-Socratics or rational philosophers include Protagoras (like Anaxagoras a friend of Pericles), known for his famous dictum \"man is the measure of all things\" and Democritus, who proposed that matter was composed of atoms. Little of the written work of these early philosophers survives and they are known mainly from fragments and quotations in other writers, principally Plato and Aristotle. The historian Thucydides, noted for his scientific and rational approach to history, is also much admired by later humanists. In the 3rd century BCE, Epicurus became known for his concise phrasing of the problem of evil, lack of belief in the afterlife, and human-centred approaches to achieving eudaimonia. He was also the first Greek philosopher to admit women to his school as a rule.", "어거스틴의 신학방법론은 Credo ut intelligam(신앙은 찾고 지성은 이해한다)이다. 믿음으로 시작하고 이성으로 이해하는 방식이다. 플라톤주의, 신플라톤주의을 올바르게 활용하여 성경적 신학을 이루어었다.어거스틴의 신학방법론은 져스틴의 방법과 터툴리안의 방법을 결합하고 종합했다.저스틴은 소크라테스와 플라톤도 기독교인이라고 주장한다.플라톤과 소크라테스가 기독교인이라는 말은 모든 지식, 지성은 로고스에서 비롯되었다는 것이다. 모세의 지식이든, 플라톤, 소크라테스의 지식이든 로고스는 만세 전부터 계셨다. 태초부터 계신 로고스가 모든 지식을 파생시켰는데, 그 로고스가 육체로 태어났다는 주장이다. 그 주장에 반기를 든 사람이 터툴리안이다.그 는 '예루살렘과 아테네가 기독교와 무슨 상관이 있느뇨'라고 외쳤다. 이와같이 어거스틴은 이성적인 관점은 저스틴에게 신앙적인 관점은 터툴리안으로 부터 영향을 받아 변증법적 종합을 통하여 그의 신학방법론을 만들었다.[1]", "The Sanskrit grammatical tradition, Vyākaraṇa, one of the six Vedangas, began in the late Vedic period and culminated in the Aṣṭādhyāyī of Pāṇini, which consists of 3990 sutras (ca. fifth century BCE). About a century after Pāṇini (around 400 BCE), Kātyāyana composed Vārtikas on the Pāṇini sũtras. Patanjali, who lived three centuries after Pāṇini, wrote the Mahābhāṣya, the \"Great Commentary\" on the Aṣṭādhyāyī and Vārtikas. Because of these three ancient Vyākaraṇins (grammarians), this grammar is called Trimuni Vyākarana. To understand the meaning of the sutras, Jayaditya and Vāmana wrote a commentary, the Kāsikā, in 600 CE. Pāṇinian grammar is based on 14 Shiva sutras (aphorisms), where the whole mātrika (alphabet) is abbreviated. This abbreviation is called the Pratyāhara." ], [ "In Hellenistic Egypt, the mathematician Euclid laid down the foundations of mathematical rigor and introduced the concepts of definition, axiom, theorem and proof still in use today in his Elements, considered the most influential textbook ever written. Archimedes, considered one of the greatest mathematicians of all time, is credited with using the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of Pi. He is also known in physics for laying the foundations of hydrostatics, statics, and the explanation of the principle of the lever.", "Hellenistic Geometers such as Archimedes (c. 287 – 212 BC), Apollonius of Perga (c. 262 – c. 190 BC), and Euclid (c. 325 – 265 BC), whose Elements became the most important textbook in mathematics until the 19th century, built upon the work of the Hellenic era Pythagoreans. Euclid developed proofs for the Pythagorean Theorem, for the infinitude of primes, and worked on the ﬁve Platonic solids. Eratosthenes used his knowledge of geometry to measure the circumference of the Earth. His calculation was remarkably accurate. He was also the first to calculate the tilt of the Earth's axis (again with remarkable accuracy). Additionally, he may have accurately calculated the distance from the Earth to the Sun and invented the leap day. Known as the \"Father of Geography \", Eratosthenes also created the first map of the world incorporating parallels and meridians, based on the available geographical knowledge of the era.", "The Vaiśeṣika philosophy is a naturalist school; it is a form of atomism in natural philosophy. It postulated that all objects in the physical universe are reducible to paramāṇu (atoms), and one's experiences are derived from the interplay of substance (a function of atoms, their number and their spatial arrangements), quality, activity, commonness, particularity and inherence. Knowledge and liberation was achievable by complete understanding of the world of experience, according to Vaiśeṣika school . The Vaiśeṣika darśana is credited to Kaṇāda Kaśyapa from the second half of the first millennium BCE. The foundational text, the Vaiśeṣika Sūtra, opens as follows,", "Vaiśeṣika metaphysical premises are founded on a form of atomism, that the reality is composed of four substances (earth, water, air, fire). Each of these four are of two types: atomic (paramāṇu) and composite. An atom is, according to Vaiśeṣika scholars, that which is indestructible (anitya), indivisible, and has a special kind of dimension, called “small” (aṇu). A composite, in this philosophy, is defined to be anything which is divisible into atoms. Whatever human beings perceive is composite, while atoms are invisible. The Vaiśeṣikas stated that size, form, truths and everything that human beings experience as a whole is a function of atoms, their number and their spatial arrangements, their guṇa (quality), karma (activity), sāmānya (commonness), viśeṣa (particularity) and amavāya (inherence, inseparable connectedness of everything)." ], [ "In Classical Antiquity, the inquiry into the workings of the universe took place both in investigations aimed at such practical goals as establishing a reliable calendar or determining how to cure a variety of illnesses and in those abstract investigations known as natural philosophy. The ancient people who are considered the first scientists may have thought of themselves as natural philosophers, as practitioners of a skilled profession (for example, physicians), or as followers of a religious tradition (for example, temple healers).", "Anthropology is a global discipline where humanities, social, and natural sciences are forced to confront one another. Anthropology builds upon knowledge from natural sciences, including the discoveries about the origin and evolution of Homo sapiens, human physical traits, human behavior, the variations among different groups of humans, how the evolutionary past of Homo sapiens has influenced its social organization and culture, and from social sciences, including the organization of human social and cultural relations, institutions, social conflicts, etc. Early anthropology originated in Classical Greece and Persia and studied and tried to understand observable cultural diversity. As such, anthropology has been central in the development of several new (late 20th century) interdisciplinary fields such as cognitive science, global studies, and various ethnic studies.", "Despite the large number of philosophical schools and subtle nuances between many, all philosophies are said to fall into one of two primary categories, which are defined in contrast to each other: Idealism, and materialism.[a] The basic proposition of these two categories pertains to the nature of reality, and the primary distinction between them is the way they answer two fundamental questions: \"what does reality consist of?\" and \"how does it originate?\" To idealists, spirit or mind or the objects of mind (ideas) are primary, and matter secondary. To materialists, matter is primary, and mind or spirit or ideas are secondary, the product of matter acting upon matter.", "Subsequently, Plato and Aristotle produced the first systematic discussions of natural philosophy, which did much to shape later investigations of nature. Their development of deductive reasoning was of particular importance and usefulness to later scientific inquiry. Plato founded the Platonic Academy in 387 BC, whose motto was \"Let none unversed in geometry enter here\", and turned out many notable philosophers. Plato's student Aristotle introduced empiricism and the notion that universal truths can be arrived at via observation and induction, thereby laying the foundations of the scientific method. Aristotle also produced many biological writings that were empirical in nature, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, classified more than 540 animal species, and dissected at least 50. Aristotle's writings profoundly influenced subsequent Islamic and European scholarship, though they were eventually superseded in the Scientific Revolution." ], [ "Ancient Greek philosophers like Thales, Anaxagoras (ca. 500 BC – 428 BC), Epicurus and Democritus prefigure later materialists. The Latin poem De Rerum Natura by Lucretius (ca. 99 BC – ca. 55 BC) reflects the mechanistic philosophy of Democritus and Epicurus. According to this view, all that exists is matter and void, and all phenomena result from different motions and conglomerations of base material particles called \"atoms\" (literally: \"indivisibles\"). De Rerum Natura provides mechanistic explanations for phenomena such as erosion, evaporation, wind, and sound. Famous principles like \"nothing can touch body but body\" first appeared in the works of Lucretius. Democritus and Epicurus however did not hold to a monist ontology since they held to the ontological separation of matter and space i.e. space being \"another kind\" of being, indicating that the definition of \"materialism\" is wider than given scope for in this article.", "In Ancient Greece, green and blue were sometimes considered the same color, and the same word sometimes described the color of the sea and the color of trees. The philosopher Democritus described two different greens; cloron, or pale green, and prasinon, or leek green. Aristotle considered that green was located midway between black, symbolizing the earth, and white, symbolizing water. However, green was not counted among of the four classic colors of Greek painting; red, yellow, black and white, and is rarely found in Greek art.", "The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide. Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium). He named the newly discovered element after the planet Uranus, (named after the primordial Greek god of the sky), which had been discovered eight years earlier by William Herschel.", "Early philosophers were divided as to whether the seat of the soul lies in the brain or heart. Aristotle favored the heart, and thought that the function of the brain was merely to cool the blood. Democritus, the inventor of the atomic theory of matter, argued for a three-part soul, with intellect in the head, emotion in the heart, and lust near the liver. Hippocrates, the \"father of medicine\", came down unequivocally in favor of the brain. In his treatise on epilepsy he wrote:" ], [ "Impermanence (Pāli: anicca) expresses the Buddhist notion that all compounded or conditioned phenomena (all things and experiences) are inconstant, unsteady, and impermanent. Everything we can experience through our senses is made up of parts, and its existence is dependent on external conditions. Everything is in constant flux, and so conditions and the thing itself are constantly changing. Things are constantly coming into being, and ceasing to be. Since nothing lasts, there is no inherent or fixed nature to any object or experience. According to the doctrine of impermanence, life embodies this flux in the aging process, the cycle of rebirth (saṃsāra), and in any experience of loss. The doctrine asserts that because things are impermanent, attachment to them is futile and leads to suffering (dukkha).", "Vaiśeṣika metaphysical premises are founded on a form of atomism, that the reality is composed of four substances (earth, water, air, fire). Each of these four are of two types: atomic (paramāṇu) and composite. An atom is, according to Vaiśeṣika scholars, that which is indestructible (anitya), indivisible, and has a special kind of dimension, called “small” (aṇu). A composite, in this philosophy, is defined to be anything which is divisible into atoms. Whatever human beings perceive is composite, while atoms are invisible. The Vaiśeṣikas stated that size, form, truths and everything that human beings experience as a whole is a function of atoms, their number and their spatial arrangements, their guṇa (quality), karma (activity), sāmānya (commonness), viśeṣa (particularity) and amavāya (inherence, inseparable connectedness of everything).", "In Hellenistic Egypt, the mathematician Euclid laid down the foundations of mathematical rigor and introduced the concepts of definition, axiom, theorem and proof still in use today in his Elements, considered the most influential textbook ever written. Archimedes, considered one of the greatest mathematicians of all time, is credited with using the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of Pi. He is also known in physics for laying the foundations of hydrostatics, statics, and the explanation of the principle of the lever.", "There were guilds of dyers who specialized in red in Venice and other large Europeans cities. The Rubia plant was used to make the most common dye; it produced an orange-red or brick red color used to dye the clothes of merchants and artisans. For the wealthy, the dye used was Kermes, made from a tiny scale insect which fed on the branches and leaves of the oak tree. For those with even more money there was Polish Cochineal; also known as Kermes vermilio or \"Blood of Saint John\", which was made from a related insect, the Margodes polonicus. It made a more vivid red than ordinary Kermes. The finest and most expensive variety of red made from insects was the \"Kermes\" of Armenia (Armenian cochineal, also known as Persian kirmiz), made by collecting and crushing Porphyophora hamelii, an insect which lived on the roots and stems of certain grasses. The pigment and dye merchants of Venice imported and sold all of these products and also manufactured their own color, called Venetian red, which was considered the most expensive and finest red in Europe. Its secret ingredient was arsenic, which brightened the color." ] ]
5a7de83a70df9f001a8752eb	Matter	For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a "principle") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).	en	null	null	190,692	[ "What exists independently?", "Who said matter had actuality in and of itself?", "Aristotle said parts have existence outside of what?", "What does grass turn the horse into?" ]	[ [ "The Necessary exists 'due-to-Its-Self', and has no quiddity/essence (mahiyya) other than existence (wujud). Furthermore, It is 'One' (wahid ahad) since there cannot be more than one 'Necessary-Existent-due-to-Itself' without differentia (fasl) to distinguish them from each other. Yet, to require differentia entails that they exist 'due-to-themselves' as well as 'due to what is other than themselves'; and this is contradictory. However, if no differentia distinguishes them from each other, then there is no sense in which these 'Existents' are not one and the same. Avicenna adds that the 'Necessary-Existent-due-to-Itself' has no genus (jins), nor a definition (hadd), nor a counterpart (nadd), nor an opposite (did), and is detached (bari) from matter (madda), quality (kayf), quantity (kam), place (ayn), situation (wad), and time (waqt).", "In theism, God is the creator and sustainer of the universe, while in deism, God is the creator, but not the sustainer, of the universe. Monotheism is the belief in the existence of one God or in the oneness of God. In pantheism, God is the universe itself. In atheism, God is not believed to exist, while God is deemed unknown or unknowable within the context of agnosticism. God has also been conceived as being incorporeal (immaterial), a personal being, the source of all moral obligation, and the \"greatest conceivable existent\". Many notable philosophers have developed arguments for and against the existence of God.", "Avicenna's consideration of the essence-attributes question may be elucidated in terms of his ontological analysis of the modalities of being; namely impossibility, contingency, and necessity. Avicenna argued that the impossible being is that which cannot exist, while the contingent in itself (mumkin bi-dhatihi) has the potentiality to be or not to be without entailing a contradiction. When actualized, the contingent becomes a 'necessary existent due to what is other than itself' (wajib al-wujud bi-ghayrihi). Thus, contingency-in-itself is potential beingness that could eventually be actualized by an external cause other than itself. The metaphysical structures of necessity and contingency are different. Necessary being due to itself (wajib al-wujud bi-dhatihi) is true in itself, while the contingent being is 'false in itself' and 'true due to something else other than itself'. The necessary is the source of its own being without borrowed existence. It is what always exists.", "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself." ], [ "Arthur Schopenhauer (1788-1860) wrote that \"...materialism is the philosophy of the subject who forgets to take account of himself\". He claimed that an observing subject can only know material objects through the mediation of the brain and its particular organization. That is, the brain itself is the \"determiner\" of how material objects will be experienced or perceived:", "Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his \"Rules of Reasoning in Philosophy\", Newton lists the universal qualities of matter as \"extension, hardness, impenetrability, mobility, and inertia\". Similarly in Optics he conjectures that God created matter as \"solid, massy, hard, impenetrable, movable particles\", which were \"...even so very hard as never to wear or break in pieces\". The \"primary\" properties of matter were amenable to mathematical description, unlike \"secondary\" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities.", "In contrast, Joseph Smith, the founder of the Latter Day Saint movement, taught: \"There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes; We cannot see it; but when our bodies are purified we shall see that it is all matter.\" This spirit element has always existed; it is co-eternal with God. It is also called \"intelligence\" or \"the light of truth\", which like all observable matter \"was not created or made, neither indeed can be\". Members of the Church of Jesus Christ of Latter-day Saints view the revelations of Joseph Smith as a restoration of original Christian doctrine, which they believe post-apostolic theologians began to corrupt in the centuries after Christ. The writings of many[quantify] of these theologians indicate a clear influence of Greek metaphysical philosophies such as Neoplatonism, which characterized divinity as an utterly simple, immaterial, formless, substance/essence (ousia) that transcended all that was physical. Despite strong opposition from many Christians, this metaphysical depiction of God eventually became incorporated into the doctrine of the Christian church, displacing the original Judeo-Christian concept of a physical, corporeal God who created humans in His image and likeness.", "The concept of matter has changed in response to new scientific discoveries. Thus materialism has no definite content independent of the particular theory of matter on which it is based. According to Noam Chomsky, any property can be considered material, if one defines matter such that it has that property." ], [ "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.", "Aristotle's explanation of how this was possible was not strictly empiricist in a modern sense, but rather based on his theory of potentiality and actuality, and experience of sense perceptions still requires the help of the active nous. These notions contrasted with Platonic notions of the human mind as an entity that pre-existed somewhere in the heavens, before being sent down to join a body on Earth (see Plato's Phaedo and Apology, as well as others). Aristotle was considered to give a more important position to sense perception than Plato, and commentators in the Middle Ages summarized one of his positions as \"nihil in intellectu nisi prius fuerit in sensu\" (Latin for \"nothing in the intellect without first being in the senses\").", "Historically, there has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato, even the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, itself, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite literally nothing at all, which cannot rightly be said to exist. Aristotle believed that no void could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void.", "Thomas Davidson taught a philosophy called \"apeirotheism\", a \"form of pluralistic idealism...coupled with a stern ethical rigorism\" which he defined as \"a theory of Gods infinite in number.\" The theory was indebted to Aristotle's pluralism and his concepts of Soul, the rational, living aspect of a living substance which cannot exist apart from the body because it is not a substance but an essence, and nous, rational thought, reflection and understanding. Although a perennial source of controversy, Aristotle arguably views the latter as both eternal and immaterial in nature, as exemplified in his theology of unmoved movers. Identifying Aristotle's God with rational thought, Davidson argued, contrary to Aristotle, that just as the soul cannot exist apart from the body, God cannot exist apart from the world." ], [ "The development of a three-field rotation system for planting crops[AA] increased the usage of land from one half in use each year under the old two-field system to two-thirds under the new system, with a consequent increase in production. The development of the heavy plough allowed heavier soils to be farmed more efficiently, aided by the spread of the horse collar, which led to the use of draught horses in place of oxen. Horses are faster than oxen and require less pasture, factors that aided the implementation of the three-field system.", "A typical pommel horse exercise involves both single leg and double leg work. Single leg skills are generally found in the form of scissors, an element often done on the pommels. Double leg work however, is the main staple of this event. The gymnast swings both legs in a circular motion (clockwise or counterclockwise depending on preference) and performs such skills on all parts of the apparatus. To make the exercise more challenging, gymnasts will often include variations on a typical circling skill by turning (moores and spindles) or by straddling their legs (Flares). Routines end when the gymnast performs a dismount, either by swinging his body over the horse, or landing after a handstand. This requires back muscles to do any sort of skill. From handstands being easy to back or front flips being a little difficult.", "Farming had been a traditional occupation for centuries, although it became less dominant in the 20th century with the advent of tourism. Grazing and pasture land are limited because of the steep and rocky topography of the Alps. In mid-June cows are moved to the highest pastures close to the snowline, where they are watched by herdsmen who stay in the high altitudes often living in stone huts or wooden barns during the summers. Villagers celebrate the day the cows are herded up to the pastures and again when they return in mid-September. The Alpanschluss or Désalpes (\"coming down from the alps\") is celebrated by decorating the cows with garlands and enormous cowbells while the farmers dress in traditional costumes.", "The Spanish Empire and other Europeans brought horses to the Americas. Some of these animals escaped and began to breed and increase their numbers in the wild. The re-introduction of the horse, extinct in the Americas for over 7500 years, had a profound impact on Native American culture in the Great Plains of North America and of Patagonia in South America. By domesticating horses, some tribes had great success: horses enabled them to expand their territories, exchange more goods with neighboring tribes, and more easily capture game, especially bison." ] ]
5a7de93570df9f001a8752f3	Matter	For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.	en	null	null	190,696	[ "What philosophy did Aristotle describe?", "What did Aristotle define as distinct from matter?", "How did Aristotle elevate matter?", "What activity does locomotion have?", "How does Descartes use matter and the formal/forming principle?" ]	[ [ "Subsequently, Plato and Aristotle produced the first systematic discussions of natural philosophy, which did much to shape later investigations of nature. Their development of deductive reasoning was of particular importance and usefulness to later scientific inquiry. Plato founded the Platonic Academy in 387 BC, whose motto was \"Let none unversed in geometry enter here\", and turned out many notable philosophers. Plato's student Aristotle introduced empiricism and the notion that universal truths can be arrived at via observation and induction, thereby laying the foundations of the scientific method. Aristotle also produced many biological writings that were empirical in nature, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, classified more than 540 animal species, and dissected at least 50. Aristotle's writings profoundly influenced subsequent Islamic and European scholarship, though they were eventually superseded in the Scientific Revolution.", "Aristotle of Stagira, the most important disciple of Plato, shared with his teacher the title of the greatest philosopher of antiquity. But while Plato had sought to elucidate and explain things from the supra-sensual standpoint of the forms, his pupil preferred to start from the facts given us by experience. Except from these three most significant Greek philosophers other known schools of Greek philosophy from other founders during ancient times were Stoicism, Epicureanism, Skepticism and Neoplatonism.", "Thomas Davidson taught a philosophy called \"apeirotheism\", a \"form of pluralistic idealism...coupled with a stern ethical rigorism\" which he defined as \"a theory of Gods infinite in number.\" The theory was indebted to Aristotle's pluralism and his concepts of Soul, the rational, living aspect of a living substance which cannot exist apart from the body because it is not a substance but an essence, and nous, rational thought, reflection and understanding. Although a perennial source of controversy, Aristotle arguably views the latter as both eternal and immaterial in nature, as exemplified in his theology of unmoved movers. Identifying Aristotle's God with rational thought, Davidson argued, contrary to Aristotle, that just as the soul cannot exist apart from the body, God cannot exist apart from the world.", "Aristotle's explanation of how this was possible was not strictly empiricist in a modern sense, but rather based on his theory of potentiality and actuality, and experience of sense perceptions still requires the help of the active nous. These notions contrasted with Platonic notions of the human mind as an entity that pre-existed somewhere in the heavens, before being sent down to join a body on Earth (see Plato's Phaedo and Apology, as well as others). Aristotle was considered to give a more important position to sense perception than Plato, and commentators in the Middle Ages summarized one of his positions as \"nihil in intellectu nisi prius fuerit in sensu\" (Latin for \"nothing in the intellect without first being in the senses\")." ], [ "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).", "Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his \"Rules of Reasoning in Philosophy\", Newton lists the universal qualities of matter as \"extension, hardness, impenetrability, mobility, and inertia\". Similarly in Optics he conjectures that God created matter as \"solid, massy, hard, impenetrable, movable particles\", which were \"...even so very hard as never to wear or break in pieces\". The \"primary\" properties of matter were amenable to mathematical description, unlike \"secondary\" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities.", "Thomas Davidson taught a philosophy called \"apeirotheism\", a \"form of pluralistic idealism...coupled with a stern ethical rigorism\" which he defined as \"a theory of Gods infinite in number.\" The theory was indebted to Aristotle's pluralism and his concepts of Soul, the rational, living aspect of a living substance which cannot exist apart from the body because it is not a substance but an essence, and nous, rational thought, reflection and understanding. Although a perennial source of controversy, Aristotle arguably views the latter as both eternal and immaterial in nature, as exemplified in his theology of unmoved movers. Identifying Aristotle's God with rational thought, Davidson argued, contrary to Aristotle, that just as the soul cannot exist apart from the body, God cannot exist apart from the world.", "Aristotle's explanation of how this was possible was not strictly empiricist in a modern sense, but rather based on his theory of potentiality and actuality, and experience of sense perceptions still requires the help of the active nous. These notions contrasted with Platonic notions of the human mind as an entity that pre-existed somewhere in the heavens, before being sent down to join a body on Earth (see Plato's Phaedo and Apology, as well as others). Aristotle was considered to give a more important position to sense perception than Plato, and commentators in the Middle Ages summarized one of his positions as \"nihil in intellectu nisi prius fuerit in sensu\" (Latin for \"nothing in the intellect without first being in the senses\")." ], [ "Aristotle's explanation of how this was possible was not strictly empiricist in a modern sense, but rather based on his theory of potentiality and actuality, and experience of sense perceptions still requires the help of the active nous. These notions contrasted with Platonic notions of the human mind as an entity that pre-existed somewhere in the heavens, before being sent down to join a body on Earth (see Plato's Phaedo and Apology, as well as others). Aristotle was considered to give a more important position to sense perception than Plato, and commentators in the Middle Ages summarized one of his positions as \"nihil in intellectu nisi prius fuerit in sensu\" (Latin for \"nothing in the intellect without first being in the senses\").", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).", "Subsequently, Plato and Aristotle produced the first systematic discussions of natural philosophy, which did much to shape later investigations of nature. Their development of deductive reasoning was of particular importance and usefulness to later scientific inquiry. Plato founded the Platonic Academy in 387 BC, whose motto was \"Let none unversed in geometry enter here\", and turned out many notable philosophers. Plato's student Aristotle introduced empiricism and the notion that universal truths can be arrived at via observation and induction, thereby laying the foundations of the scientific method. Aristotle also produced many biological writings that were empirical in nature, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, classified more than 540 animal species, and dissected at least 50. Aristotle's writings profoundly influenced subsequent Islamic and European scholarship, though they were eventually superseded in the Scientific Revolution.", "Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his \"Rules of Reasoning in Philosophy\", Newton lists the universal qualities of matter as \"extension, hardness, impenetrability, mobility, and inertia\". Similarly in Optics he conjectures that God created matter as \"solid, massy, hard, impenetrable, movable particles\", which were \"...even so very hard as never to wear or break in pieces\". The \"primary\" properties of matter were amenable to mathematical description, unlike \"secondary\" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities." ], [ "Modern electrification systems take AC energy from a power grid which is delivered to a locomotive and converted to a DC voltage to be used by traction motors. These motors may either be DC motors which directly use the DC or they may be 3-phase AC motors which require further conversion of the DC to 3-phase AC (using power electronics). Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive. Where should this conversion take place and at what voltage and current (AC or DC) should the power flow to the locomotive? And how does all this relate to energy-efficiency? Both the transmission and conversion of electric energy involve losses: ohmic losses in wires and power electronics, magnetic field losses in transformers and smoothing reactors (inductors). Power conversion for a DC system takes place mainly in a railway substation where large, heavy, and more efficient hardware can be used as compared to an AC system where conversion takes place aboard the locomotive where space is limited and losses are significantly higher. Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for.", "A typical pommel horse exercise involves both single leg and double leg work. Single leg skills are generally found in the form of scissors, an element often done on the pommels. Double leg work however, is the main staple of this event. The gymnast swings both legs in a circular motion (clockwise or counterclockwise depending on preference) and performs such skills on all parts of the apparatus. To make the exercise more challenging, gymnasts will often include variations on a typical circling skill by turning (moores and spindles) or by straddling their legs (Flares). Routines end when the gymnast performs a dismount, either by swinging his body over the horse, or landing after a handstand. This requires back muscles to do any sort of skill. From handstands being easy to back or front flips being a little difficult.", "Cockroaches are among the fastest insect runners and, at full speed, adopt a bipedal run to reach a high velocity in proportion to their body size. As cockroaches move very quickly, they need to be video recorded at several hundred frames per second to reveal their gait. More sedate locomotion is seen in the stick insects or walking sticks (Phasmatodea). A few insects have evolved to walk on the surface of the water, especially members of the Gerridae family, commonly known as water striders. A few species of ocean-skaters in the genus Halobates even live on the surface of open oceans, a habitat that has few insect species.", "Gymnastics is a sport involving the performance of exercises requiring strength, flexibility, balance and control. Internationally, all events are governed by the Fédération Internationale de Gymnastique (FIG). Each country has its own national governing body (BIW) affiliated to FIG. Competitive artistic gymnastics is the best known of the gymnastic events. It typically involves the women's events of vault, uneven bars, balance beam, and floor exercise. Men's events are floor exercise, pommel horse, still rings, vault, parallel bars, and the high bar. Gymnastics evolved from exercises used by the ancient Greeks that included skills for mounting and dismounting a horse, and from circus performance skills." ], [ "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes).", "Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his \"Rules of Reasoning in Philosophy\", Newton lists the universal qualities of matter as \"extension, hardness, impenetrability, mobility, and inertia\". Similarly in Optics he conjectures that God created matter as \"solid, massy, hard, impenetrable, movable particles\", which were \"...even so very hard as never to wear or break in pieces\". The \"primary\" properties of matter were amenable to mathematical description, unlike \"secondary\" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities.", "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. With the acquiescence of Cartesian mechanical philosophy to the \"brute fact\" of action at a distance, and at length, its successful reification by force fields and ever more sophisticated geometric structure, the anachronism of empty space widened until \"a seething ferment\" of quantum activity in the 20th century filled the vacuum with a virtual pleroma." ] ]
5a7de9b570df9f001a875308	Matter	Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his "Rules of Reasoning in Philosophy", Newton lists the universal qualities of matter as "extension, hardness, impenetrability, mobility, and inertia". Similarly in Optics he conjectures that God created matter as "solid, massy, hard, impenetrable, movable particles", which were "...even so very hard as never to wear or break in pieces". The "primary" properties of matter were amenable to mathematical description, unlike "secondary" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities.	en	null	null	190,702	[ "What did Descartes write?", "What did Newton reject that Descartes did not?", "What did Descartes say were the universal qualities of matter?", "Both primary and secondary properties are suited to what form of description?" ]	[ [ "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.", "Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. With the acquiescence of Cartesian mechanical philosophy to the \"brute fact\" of action at a distance, and at length, its successful reification by force fields and ever more sophisticated geometric structure, the anachronism of empty space widened until \"a seething ferment\" of quantum activity in the 20th century filled the vacuum with a virtual pleroma.", "In 1644, René Descartes theorized that pain was a disturbance that passed down along nerve fibers until the disturbance reached the brain, a development that transformed the perception of pain from a spiritual, mystical experience to a physical, mechanical sensation[citation needed]. Descartes's work, along with Avicenna's, prefigured the 19th-century development of specificity theory. Specificity theory saw pain as \"a specific sensation, with its own sensory apparatus independent of touch and other senses\". Another theory that came to prominence in the 18th and 19th centuries was intensive theory, which conceived of pain not as a unique sensory modality, but an emotional state produced by stronger than normal stimuli such as intense light, pressure or temperature. By the mid-1890s, specificity was backed mostly by physiologists and physicians, and the intensive theory was mostly backed by psychologists. However, after a series of clinical observations by Henry Head and experiments by Max von Frey, the psychologists migrated to specificity almost en masse, and by century's end, most textbooks on physiology and psychology were presenting pain specificity as fact.", "The most influential publication of the Enlightenment was the Encyclopédie, compiled by Denis Diderot and (until 1759) by Jean le Rond d'Alembert and a team of 150 scientists and philosophers. It was published between 1751 and 1772 in thirty-five volumes, and spread the ideas of the Enlightenment across Europe and beyond. Other landmark publications were the Dictionnaire philosophique (Philosophical Dictionary, 1764) and Letters on the English (1733) written by Voltaire; Rousseau's Discourse on Inequality (1754) and The Social Contract (1762); and Montesquieu's Spirit of the Laws (1748). The ideas of the Enlightenment played a major role in inspiring the French Revolution, which began in 1789. After the Revolution, the Enlightenment was followed by an opposing intellectual movement known as Romanticism." ], [ "Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. With the acquiescence of Cartesian mechanical philosophy to the \"brute fact\" of action at a distance, and at length, its successful reification by force fields and ever more sophisticated geometric structure, the anachronism of empty space widened until \"a seething ferment\" of quantum activity in the 20th century filled the vacuum with a virtual pleroma.", "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.", "There were two distinct lines of Enlightenment thought: the radical enlightenment, inspired by the philosophy of Spinoza, advocating democracy, individual liberty, freedom of expression, and eradication of religious authority; and a second, more moderate variety, supported by René Descartes, John Locke, Christian Wolff, Isaac Newton and others, which sought accommodation between reform and the traditional systems of power and faith. Both lines of thought were opposed by the conservative Counter-Enlightenment.", "Friedrich Nietzsche argued that Kant commits an agnostic tautology and does not offer a satisfactory answer as to the source of a philosophical right to such-or-other metaphysical claims; he ridicules his pride in tackling \"the most difficult thing that could ever be undertaken on behalf of metaphysics.\" The famous \"thing-in-itself\" was called a product of philosophical habit, which seeks to introduce a grammatical subject: because wherever there is cognition, there must be a thing that is cognized and allegedly it must be added to ontology as a being (whereas, to Nietzsche, only the world as ever changing appearances can be assumed). Yet he attacks the idealism of Schopenhauer and Descartes with an argument similar to Kant's critique of the latter (see above)." ], [ "For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies: this is the mechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance. They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary principles that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a potential independent existence), but Descartes elevates matter to an actual independent thing in itself.", "The pre-Socratics were among the first recorded speculators about the underlying nature of the visible world. Thales (c. 624 BC–c. 546 BC) regarded water as the fundamental material of the world. Anaximander (c. 610 BC–c. 546 BC) posited that the basic material was wholly characterless or limitless: the Infinite (apeiron). Anaximenes (flourished 585 BC, d. 528 BC) posited that the basic stuff was pneuma or air. Heraclitus (c. 535–c. 475 BC) seems to say the basic element is fire, though perhaps he means that all is change. Empedocles (c. 490–430 BC) spoke of four elements of which everything was made: earth, water, air, and fire. Meanwhile, Parmenides argued that change does not exist, and Democritus argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy called atomism. All of these notions had deep philosophical problems.", "Ancient Greek philosophers like Thales, Anaxagoras (ca. 500 BC – 428 BC), Epicurus and Democritus prefigure later materialists. The Latin poem De Rerum Natura by Lucretius (ca. 99 BC – ca. 55 BC) reflects the mechanistic philosophy of Democritus and Epicurus. According to this view, all that exists is matter and void, and all phenomena result from different motions and conglomerations of base material particles called \"atoms\" (literally: \"indivisibles\"). De Rerum Natura provides mechanistic explanations for phenomena such as erosion, evaporation, wind, and sound. Famous principles like \"nothing can touch body but body\" first appeared in the works of Lucretius. Democritus and Epicurus however did not hold to a monist ontology since they held to the ontological separation of matter and space i.e. space being \"another kind\" of being, indicating that the definition of \"materialism\" is wider than given scope for in this article.", "Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. With the acquiescence of Cartesian mechanical philosophy to the \"brute fact\" of action at a distance, and at length, its successful reification by force fields and ever more sophisticated geometric structure, the anachronism of empty space widened until \"a seething ferment\" of quantum activity in the 20th century filled the vacuum with a virtual pleroma." ], [ "In response to the early-to-mid-17th century \"continental rationalism\" John Locke (1632–1704) proposed in An Essay Concerning Human Understanding (1689) a very influential view wherein the only knowledge humans can have is a posteriori, i.e., based upon experience. Locke is famously attributed with holding the proposition that the human mind is a tabula rasa, a \"blank tablet\", in Locke's words \"white paper\", on which the experiences derived from sense impressions as a person's life proceeds are written. There are two sources of our ideas: sensation and reflection. In both cases, a distinction is made between simple and complex ideas. The former are unanalysable, and are broken down into primary and secondary qualities. Primary qualities are essential for the object in question to be what it is. Without specific primary qualities, an object would not be what it is. For example, an apple is an apple because of the arrangement of its atomic structure. If an apple was structured differently, it would cease to be an apple. Secondary qualities are the sensory information we can perceive from its primary qualities. For example, an apple can be perceived in various colours, sizes, and textures but it is still identified as an apple. Therefore, its primary qualities dictate what the object essentially is, while its secondary qualities define its attributes. Complex ideas combine simple ones, and divide into substances, modes, and relations. According to Locke, our knowledge of things is a perception of ideas that are in accordance or discordance with each other, which is very different from the quest for certainty of Descartes.", "Despite the large number of philosophical schools and subtle nuances between many, all philosophies are said to fall into one of two primary categories, which are defined in contrast to each other: Idealism, and materialism.[a] The basic proposition of these two categories pertains to the nature of reality, and the primary distinction between them is the way they answer two fundamental questions: \"what does reality consist of?\" and \"how does it originate?\" To idealists, spirit or mind or the objects of mind (ideas) are primary, and matter secondary. To materialists, matter is primary, and mind or spirit or ideas are secondary, the product of matter acting upon matter.", "Changes in secondary sex characteristics include every change that is not directly related to sexual reproduction. In males, these changes involve appearance of pubic, facial, and body hair, deepening of the voice, roughening of the skin around the upper arms and thighs, and increased development of the sweat glands. In females, secondary sex changes involve elevation of the breasts, widening of the hips, development of pubic and underarm hair, widening of the areolae, and elevation of the nipples. The changes in secondary sex characteristics that take place during puberty are often referred to in terms of five Tanner stages, named after the British pediatrician who devised the categorization system.", "Declarative memory can be further sub-divided into semantic memory, concerning principles and facts taken independent of context; and episodic memory, concerning information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract knowledge about the world, such as \"Paris is the capital of France\". Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time. Episodic memories often reflect the \"firsts\" in life such as a first kiss, first day of school or first time winning a championship. These are key events in one's life that can be remembered clearly. Autobiographical memory - memory for particular events within one's own life - is generally viewed as either equivalent to, or a subset of, episodic memory. Visual memory is part of memory preserving some characteristics of our senses pertaining to visual experience. One is able to place in memory information that resembles objects, places, animals or people in sort of a mental image. Visual memory can result in priming and it is assumed some kind of perceptual representational system underlies this phenomenon.[citation needed]" ] ]
5a7dea8870df9f001a875311	Matter	There is an entire literature concerning the "structure of matter", ranging from the "electrical structure" in the early 20th century, to the more recent "quark structure of matter", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics.[further explanation needed] In this connection, physicists speak of matter fields, and speak of particles as "quantum excitations of a mode of the matter field". And here is a quote from de Sabbata and Gasperini: "With the word "matter" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields)."[further explanation needed]	en	null	null	190,706	[ "When did de Sabbata and Gasperini write?", "What theory came after the quark structure of matter?", "Understanding electrical structure has lead to important advances in what field?", "Who described particles as quantum excitations?", "What theory uses spinor fields?" ]	[ [ "이탈리아 요리에 대해 최초의 저술을 남긴 사람은 그리스계 시칠리아 사람인 아케스트라투스이다. 기원전 4세기에 지금의 시라쿠사 지역에 살던 그는 “계절에 맞는 최상의 재료”를 사용하는 것에 대한 시를 남겼다. 그는 또한 향신료나 허브, 양념 따위를 사용한 음식과 그 중요성, 생선 요리 등에 대해 서술했다. 특정 양념이나 향신료가 지나쳐서는 안 된다는 것 또한 집필 내용에 포함됐지만 470가지의 요리법을 담은 책인 《데 레 코퀴나리아》(De re coquinaria《요리에 관하여》)를 출판하면서 이런 형태의 요리는 역사 속으로 사라졌다. 이 책은 생선의 비린내나 특정 재료의 맛을 숨기면서 다른 맛을 낼 수 있는 소스에 대해서 서술해 놓았다. 로마 사람들은 그리스 최고의 제빵사를 고용해서 빵을 만들었고 가장 뛰어난 재료로 알려져 있던 페코리니(pecorini)를 시칠리아에서 수입해 왔다고 한다. 로마인은 염소를 사육해 육식을 함과 동시에 여러 가지 식물도 재배한 것으로 알려져 있다.", "19세기에는 이탈리아 초대 국왕의 요리사이던 조반니 비알라르디가 《현대 요리법에 대한 저서》(A Treatise of Modern Cookery and Patisserie)를 내놓으면서 가정에서도 쉽게 만들 수 있는 요리를 다루었다. 그가 소개한 요리법은 감자를 이용한 12가지의 요리 등 여러 요리였는데 그 중 하나가 “제노바식 캐폰 마그로”('Genoese Cappon Magro)로 제노바에서는 아직도 흔하다. 1829년에는 지오반니 펠리스 루라스키(Giovanni Felice Luraschi)가 Il Nuovo Cuoco Milanese Economico에서 레몬이나 안초비를 곁들인 콩팥 요리와 밀라노식 요리법을 소개했다. 1871년 지안 바티스타(Gian Battista)와 지오반니 라토(Giovanni Ratto)는 《제노바의 요리》(La Cucina Genovese)에서 리구리아 지방 요리를 다루면서 페스토(Pesto) 요리를 처음으로 소개했다. 《라 쿠시나 테오리코 프라티카》(La Cucina Teorico-Pratica)는 카발칸티(Cavalcanti)가 쓴 책으로서 토마토를 넣은 파스타 요리를 최초로 설명한 저서이다. 이탈리아 근대 요리의 결정체로 손꼽히는 책은 펠레그리노 아르투시가 써서 1891년에 초판이 발행된 《올바른 식사법과 조리법》(La scienza in cucina e l'arte di mangiare bene)으로서 이탈리아 전역에서 널리 수용됐다. 주로 지금의 에밀리아로마냐 주와 토스카나 주의 요리를 다루었는데, 그곳은 그가 태어나 살았던 곳이었다.", "1662년 만토바 공국의 요리사였던 바르톨미오 스테파니(Bartolomeo Stefani)가 《뛰어난 요리의 예술》(L'Arte di Ben Cucinare)을 출판했다. 그는 이탈리아 요리에 대한 전문 서적을 출판한 마지막 근세인이자 일반 음식을 주제로 집필한 최초의 사람이기도 했다. 그는 만토바 공국의 찰스 3세가 스웨덴의 크리스티나에게 대접한 만찬의 준비 모습과 관련해 나이프를 비롯한 숟가락, 유리잔, 접시, 큰 그릇을 놓는 법과 그 사용법을 모두 설명해 놓았다. 사발 대신에 냅킨도 사용했다. 이 시대의 또 다른 책 《갈라테오》(Galatheo)는 지오반니 델라 카사(Giovanni della Casa)가 지은 책으로 여기서는 웨이터(scalci)가 손님들에게 식사를 준비하면서 어떻게 행동하는지 설명했다. 일종의 식사 예절 교육에 대해 많이 서술했는데 웨이터들은 머리나 신체를 긁어서는 안 되고 침을 뱉거나 코를 풀거나 재채기를 하는 것도 금지됐으며, 냅킨으로 땀을 닦거나 손가락을 빨면서 식사를 하는 것도 추하다고 했다.", "카를 마리아 폰 베버(1786-1826)는 베토벤이 사망하기 1년 전에 이미 그의 일생을 마쳤으나 슈베르트보다도 훨씬 후기형에 속하는 낭만적 작곡가라 하겠다. 피아노곡·오페라·가곡·교회음악 등에서 상당히 많은 작품을 남겼으며, 1820년에 작곡되고 다음해 베를린에서 처음으로 공연된 오페라 <마탄의 사수>는 역사적으로 획기적인 의미를 지녔다. 그리고 5년 전에 같은 장소에서 공연된 E. T. A. 호프만의 <운디네>를 베버는 \"어느 시대에도 결코 우리에게 줄 수 없었던 가장 정신적인 것으로 충만한 작품의 하나\"라고 평하였으나, 호프만이나 슈포르의 작품이 아니라 바로 <마탄의 사수>가 획기적이라는 이유는 보다 개성적으로 강한 베버의 음악적 재능에 있다. 줄거리는 괴테도 지적했듯이 약간 유치하나, 장면을 진행시키는 멜로디나 훌륭한 관현악법 속에 독일 숲의 신비적인 분위기나 등장인물의 심리 등이 선명하게 떠오르고 있다. 여기서 호프만풍의 낭만적인 영역은 직접적으로는 전개되지 않는다. 그 대신에 나중의 '낭만파 음악'이라 불리는 개념의 기초가 이룩되었던 것이다. 베버는 또한 독일 징슈필의 형식에 따른 <마탄의 사수>에서 한걸음 더 나아가 완전한 오페라 형식으로 독일 낭만주의적인 오페라 세리아의 작곡을 원했으나 결국 <오이뤼안테>나 <오베론>은 <마탄의 사수> 영역을 넘어서지는 못했다." ], [ "Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma. For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).", "A definition of \"matter\" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of, meaning anything made of positively charged protons, neutral neutrons, and negatively charged electrons. This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example white dwarf matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent \"particles\" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields (gluons) that bind them together (see Quarks and leptons definition below).", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "From his diagrams of a small number of particles interacting in spacetime, Feynman could then model all of physics in terms of the spins of those particles and the range of coupling of the fundamental forces. Feynman attempted an explanation of the strong interactions governing nucleons scattering called the parton model. The parton model emerged as a complement to the quark model developed by his Caltech colleague Murray Gell-Mann. The relationship between the two models was murky; Gell-Mann referred to Feynman's partons derisively as \"put-ons\". In the mid-1960s, physicists believed that quarks were just a bookkeeping device for symmetry numbers, not real particles, as the statistics of the Omega-minus particle, if it were interpreted as three identical strange quarks bound together, seemed impossible if quarks were real. The Stanford linear accelerator deep inelastic scattering experiments of the late 1960s showed, analogously to Ernest Rutherford's experiment of scattering alpha particles on gold nuclei in 1911, that nucleons (protons and neutrons) contained point-like particles that scattered electrons. It was natural to identify these with quarks, but Feynman's parton model attempted to interpret the experimental data in a way that did not introduce additional hypotheses. For example, the data showed that some 45% of the energy momentum was carried by electrically-neutral particles in the nucleon. These electrically-neutral particles are now seen to be the gluons that carry the forces between the quarks and carry also the three-valued color quantum number that solves the Omega-minus problem. Feynman did not dispute the quark model; for example, when the fifth quark was discovered in 1977, Feynman immediately pointed out to his students that the discovery implied the existence of a sixth quark, which was discovered in the decade after his death." ], [ "The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. First conceived by Julius Lilienfeld in 1926 and practically implemented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.", "Because of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. Furthermore, the corresponding simplicity of the hydrogen molecule and the corresponding cation H+\n2 allowed fuller understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.", "Over time, electric lighting became ubiquitous in developed countries. Segmented sleep patterns disappeared, improved nighttime lighting made more activities possible at night, and more street lights reduced urban crime.", "In the 21st century, these trends have continued, and several new approaches have come into prominence, including multielectrode recording, which allows the activity of many brain cells to be recorded all at the same time; genetic engineering, which allows molecular components of the brain to be altered experimentally; genomics, which allows variations in brain structure to be correlated with variations in DNA properties and neuroimaging." ], [ "Richard Phillips Feynman (/ˈfaɪnmən/; May 11, 1918 – February 15, 1988) was an American theoretical physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics for which he proposed the parton model. For his contributions to the development of quantum electrodynamics, Feynman, jointly with Julian Schwinger and Sin-Itiro Tomonaga, received the Nobel Prize in Physics in 1965. He developed a widely used pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, which later became known as Feynman diagrams. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World he was ranked as one of the ten greatest physicists of all time.", "First recognized in 1900 by Max Planck, it was originally the proportionality constant between the minimal increment of energy, E, of a hypothetical electrically charged oscillator in a cavity that contained black body radiation, and the frequency, f, of its associated electromagnetic wave. In 1905 the value E, the minimal energy increment of a hypothetical oscillator, was theoretically associated by Einstein with a \"quantum\" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle, as opposed to an electromagnetic wave. It was eventually called the photon.", "The photoelectric effect is the emission of electrons (called \"photoelectrons\") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real.", "Quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states. There are two types of schemes for QD excitation. One uses photo excitation with a primary light source LED (typically blue or UV LEDs are used). The other is direct electrical excitation first demonstrated by Alivisatos et al." ], [ "Lie groups are of fundamental importance in modern physics: Noether's theorem links continuous symmetries to conserved quantities. Rotation, as well as translations in space and time are basic symmetries of the laws of mechanics. They can, for instance, be used to construct simple models—imposing, say, axial symmetry on a situation will typically lead to significant simplification in the equations one needs to solve to provide a physical description.v[›] Another example are the Lorentz transformations, which relate measurements of time and velocity of two observers in motion relative to each other. They can be deduced in a purely group-theoretical way, by expressing the transformations as a rotational symmetry of Minkowski space. The latter serves—in the absence of significant gravitation—as a model of space time in special relativity. The full symmetry group of Minkowski space, i.e. including translations, is known as the Poincaré group. By the above, it plays a pivotal role in special relativity and, by implication, for quantum field theories. Symmetries that vary with location are central to the modern description of physical interactions with the help of gauge theory.", "20세기 후반 이후 진화생물학의 연구 분야는 여러 방향으로 확산되었다. 로널드 피셔 등에 의해 시작된 집단유전학은 진화의 작동 기제에 대한 보다 세밀한 이론을 제시하고 있다. 집단유전학이 제시한 유전자 부동은 오늘날 진화를 이해하는 필수적인 개념이 되었으며, 하디 와인버그 평형은 생물 종의 유지와 분화의 요인을 탁월하게 설명하는 이론을 제시한다. 한편 수평적 유전자 이동의 발견은 생물 진화의 계통도를 완전히 바꾸어 놓았다. 오늘날의 진화 계통도는 다윈이 제시했던 생명의 나무를 폐기하고 다양한 생물의 유전자들이 얽힌 그물 모습으로 변했다. 기무라 모토는 유전적 부동을 진화의 중요한 요인으로 파악하는 중립 진화 이론을 제시하였다.", "카시미르 효과의 원인은 공간에서 각각 서로 양자화 전자기장과같은 다양한 기본 장의 상태인 양자장론으로 설명된다. 간단하게 보면, 물리에서의 “장”은 마치 공간이 서로 연결된 진동하는 공과 끈으로 차있다고 생각되며, 장의 세기는 공이 있는 지점에서의 변위로 시각화할 수 있다. 장에서의 진동은 전파되며 문제 안의 특정 장을 위해 적절한 파동 방정식의 지배를 받는다. 양자장론의 정준양자화는 공과 끈의 조합이 양자화되는 것을 요구하며, 공간 안의 각 지점에서 장의 세기는 양자화된다. 가장 낮은 준위에서 공간의 각 지점의 장은 양자 조화 진동자이며, 이것의 양자화로 각 지점마다 양자 조화 진동자를 두게 된다. 장의 들뜸은 입자물리학의 기본입자와 같다. 그러나 진공일지라도 대단히 복잡한 구조가 존재하며, 양자장론의 모든 계산은 이 진공 모형과 관련이 있도록 만들어진다.", "After the success of quantum electrodynamics, Feynman turned to quantum gravity. By analogy with the photon, which has spin 1, he investigated the consequences of a free massless spin 2 field, and derived the Einstein field equation of general relativity, but little more. The computational device that Feynman discovered then for gravity, \"ghosts\", which are \"particles\" in the interior of his diagrams that have the \"wrong\" connection between spin and statistics, have proved invaluable in explaining the quantum particle behavior of the Yang–Mills theories, for example, QCD and the electro-weak theory." ] ]
5a7deb7170df9f001a87531b	Matter	In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.	en	null	null	190,711	[ "What field of physics began in the 19th century?", "What do atoms form?", "What are quarks divided into?", "Leptons are made up of what?", "We now know that quarks and leptons are not what?" ]	[ [ "The Romantic Movement of the early 19th century reshaped science by opening up new pursuits unexpected in the classical approaches of the Enlightenment. Major breakthroughs came in biology, especially in Darwin's theory of evolution, as well as physics (electromagnetism), mathematics (non-Euclidean geometry, group theory) and chemistry (organic chemistry). The decline of Romanticism occurred because a new movement, Positivism, began to take hold of the ideals of the intellectuals after 1840 and lasted until about 1880.", "Replacing the classical physics in use since the end of the scientific revolution, modern physics arose in the early 20th century with the advent of quantum physics, substituting mathematical studies for experimental studies and examining equations to build a theoretical structure.[citation needed] The old quantum theory was a collection of results which predate modern quantum mechanics, but were never complete or self-consistent. The collection of heuristic prescriptions for quantum mechanics were the first corrections to classical mechanics. Outside the realm of quantum physics, the various aether theories in classical physics, which supposed a \"fifth element\" such as the Luminiferous aether, were nullified by the Michelson-Morley experiment—an attempt to detect the motion of earth through the aether. In biology, Darwinism gained acceptance, promoting the concept of adaptation in the theory of natural selection. The fields of geology, astronomy and psychology also made strides and gained new insights. In medicine, there were advances in medical theory and treatments.", "One challenge to the traditional concept of matter as tangible \"stuff\" came with the rise of field physics in the 19th century. Relativity shows that matter and energy (including the spatially distributed energy of fields) are interchangeable. This enables the ontological view that energy is prima materia and matter is one of its forms. On the other hand, the Standard Model of Particle physics uses quantum field theory to describe all interactions. On this view it could be said that fields are prima materia and the energy is a property of the field.", "Midway through the 19th century, the focus of geology shifted from description and classification to attempts to understand how the surface of the Earth had changed. The first comprehensive theories of mountain building were proposed during this period, as were the first modern theories of earthquakes and volcanoes. Louis Agassiz and others established the reality of continent-covering ice ages, and \"fluvialists\" like Andrew Crombie Ramsay argued that river valleys were formed, over millions of years by the rivers that flow through them. After the discovery of radioactivity, radiometric dating methods were developed, starting in the 20th century. Alfred Wegener's theory of \"continental drift\" was widely dismissed when he proposed it in the 1910s, but new data gathered in the 1950s and 1960s led to the theory of plate tectonics, which provided a plausible mechanism for it. Plate tectonics also provided a unified explanation for a wide range of seemingly unrelated geological phenomena. Since 1970 it has served as the unifying principle in geology." ], [ "Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine. This occurs normally only during prolonged starvation.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each element in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent. This is called a substitutional alloy. Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms. With the interstitial mechanism, one atom is usually much smaller than the other, so cannot successfully replace an atom in the crystals of the base metal. The smaller atoms become trapped in the spaces between the atoms in the crystal matrix, called the interstices. This is referred to as an interstitial alloy. Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are replaced with nickel and chromium atoms." ], [ "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)" ], [ "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ], [ "These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter." ] ]
5a7e05ef70df9f001a875425	Matter	These quarks and leptons interact through four fundamental forces: gravity, electromagnetism, weak interactions, and strong interactions. The Standard Model of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by classical physics (see quantum gravity and graviton). Interactions between quarks and leptons are the result of an exchange of force-carrying particles (such as photons) between quarks and leptons. The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy). Force carriers are usually not considered matter: the carriers of the electric force (photons) possess energy (see Planck relation) and the carriers of the weak force (W and Z bosons) are massive, but neither are considered matter either. However, while these particles are not considered matter, they do contribute to the total mass of atoms, subatomic particles, and all systems that contain them.	en	null	null	190,716	[ "How many quarks and leptons are there?", "What model satisfactorily explains gravity?", "Interactions between quarks and leptons are the exchange of what?", "Mass and energy can always be compared to what?", "What relation explains the carriers of the electric force?" ]	[ [ "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles.", "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components." ], [ "From his diagrams of a small number of particles interacting in spacetime, Feynman could then model all of physics in terms of the spins of those particles and the range of coupling of the fundamental forces. Feynman attempted an explanation of the strong interactions governing nucleons scattering called the parton model. The parton model emerged as a complement to the quark model developed by his Caltech colleague Murray Gell-Mann. The relationship between the two models was murky; Gell-Mann referred to Feynman's partons derisively as \"put-ons\". In the mid-1960s, physicists believed that quarks were just a bookkeeping device for symmetry numbers, not real particles, as the statistics of the Omega-minus particle, if it were interpreted as three identical strange quarks bound together, seemed impossible if quarks were real. The Stanford linear accelerator deep inelastic scattering experiments of the late 1960s showed, analogously to Ernest Rutherford's experiment of scattering alpha particles on gold nuclei in 1911, that nucleons (protons and neutrons) contained point-like particles that scattered electrons. It was natural to identify these with quarks, but Feynman's parton model attempted to interpret the experimental data in a way that did not introduce additional hypotheses. For example, the data showed that some 45% of the energy momentum was carried by electrically-neutral particles in the nucleon. These electrically-neutral particles are now seen to be the gluons that carry the forces between the quarks and carry also the three-valued color quantum number that solves the Omega-minus problem. Feynman did not dispute the quark model; for example, when the fifth quark was discovered in 1977, Feynman immediately pointed out to his students that the discovery implied the existence of a sixth quark, which was discovered in the decade after his death.", "프톨레마이오스는 그 이전의 플라톤, 아리스토텔레스 등으로부터 이어져오던 천동설에 그 때의 유효한 데이터를 바탕으로 수정된 지구중심 모델을 제안했다. 당시 바빌로니아 천문학자들은 천체의 운동을 설명하는 데 있어 수학적인 방법을 사용하였고, 히파르코스같은 그리스의 천문학자들은 기하학적 모델을 사용하였다. 프톨레마이오스는 그 사고방법과 관측 자료들은 히파르코스의 학설을 이어받았으나 독자적인 수학적 방법을 채용하였다. 그의 지구중심 모델은 저서 《알마게스트》(Almagest)를 통해서 확인할 수 있는데 여기에 나타난 우주의 모습은 주전원설 구조체계에 피타고라스의 등속원운동과 아폴로니우스의 주전원을 결합한 것이다. 그는 고대부터 지구 중심설에 반하는 두 가지 데이터인 행성의 밝기 문제와 역행운동을 설명하기 위해서 주전원, 대원, 이심같은 개념을 좀 더 확장시켰다. 이전의 개념은 이심원은 이심을 중심으로 하는(지구는 중심에서 벗어나 있으며 천구의 중심이다.) 거대한 원이고, 주전원은 중심이 이심원의 원주를 따라 회전하는 작은 원이다. 태양과 달, 그리고 다른 행성들은 각각의 주전원의 원주를 따라 움직인다. 하지만 이 이론만으로는 모든 행성들의 관측된 현상을 완전히 설명할 수 없었기 때문에 프톨레마이오스는 여기에 동시심(equant)의 개념을 더 도입했다. 그는 행성의 주전원의 중심이 동시심이라고 부르는 점을 중심으로 일정한 속도로 원운동을 하고 있다고 가정했다. - 이러한 가정은 동시심에서는 주전원의 중심이 일정하게 운동하지만 이심원에 대해서는 일정하지 않을 것이라는 것을 말해준다. 이것은 천체의 운동을 더욱 정확하게 설명할 수 있는 장치를 마련해 주었지만 동시에 등속원운동이라는 아리스토텔레스의 교리도 무너지게 되었다. - 동시심은 가상점으로서 이심원의 지름 위에 있으나 이심을 기준으로 할 때는 지구의 반대쪽에 있는 점이다. 즉 이심은 지구와 동시심의 중간에 있게 된다. 이러한 가정에 의해 그는 관측된 많은 행성운동을 더 잘 설명할 수 있었다.", "In 1687, Isaac Newton published the Principia Mathematica, detailing two comprehensive and successful physical theories: Newton's laws of motion, which led to classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. The behavior of electricity and magnetism was studied by Faraday, Ohm, and others during the early 19th century. These studies led to the unification of the two phenomena into a single theory of electromagnetism, by James Clerk Maxwell (known as Maxwell's equations).", "The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as \"orbiting\" the proton in analogy to the Earth's orbit of the Sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies." ], [ "In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms. Today, we know that even protons and neutrons are not indivisible, they can be divided into quarks, while electrons are part of a particle family called leptons. Both quarks and leptons are elementary particles, and are currently seen as being the fundamental constituents of matter.", "The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the \"mass\" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon is approximately 7001125000000000000♠12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately 7002938000000000000♠938 MeV/c2). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.", "Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: ordinary matter is anything that is made of the same things that atoms and molecules are made of. (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons, and neutrons are made of quarks, this definition in turn leads to the definition of matter as being quarks and leptons, which are the two types of elementary fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino. (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.)", "The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the up and down quarks, the electron and the electron neutrino; the second includes the charm and strange quarks, the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino. The most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than elementary particles." ], [ "Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.", "Energy gives rise to weight when it is trapped in a system with zero momentum, where it can be weighed. It is also equivalent to mass, and this mass is always associated with it. Mass is also equivalent to a certain amount of energy, and likewise always appears associated with it, as described in mass-energy equivalence. The formula E = mc², derived by Albert Einstein (1905) quantifies the relationship between rest-mass and rest-energy within the concept of special relativity. In different theoretical frameworks, similar formulas were derived by J. J. Thomson (1881), Henri Poincaré (1900), Friedrich Hasenöhrl (1904) and others (see Mass-energy equivalence#History for further information).", "Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems. However, because mass (like energy) can neither be created nor destroyed, the quantity of mass and the quantity of energy remain the same during a transformation of matter (which represents a certain amount of energy) into non-material (i.e., non-matter) energy. This is also true in the reverse transformation of energy into matter.", "A source of definition difficulty in relativity arises from two definitions of mass in common use, one of which is formally equivalent to total energy (and is thus observer dependent), and the other of which is referred to as rest mass or invariant mass and is independent of the observer. Only \"rest mass\" is loosely equated with matter (since it can be weighed). Invariant mass is usually applied in physics to unbound systems of particles. However, energies which contribute to the \"invariant mass\" may be weighed also in special circumstances, such as when a system that has invariant mass is confined and has no net momentum (as in the box example above). Thus, a photon with no mass may (confusingly) still add mass to a system in which it is trapped. The same is true of the kinetic energy of particles, which by definition is not part of their rest mass, but which does add rest mass to systems in which these particles reside (an example is the mass added by the motion of gas molecules of a bottle of gas, or by the thermal energy of any hot object)." ], [ "Since the armature windings of a direct-current or universal motor are moving through a magnetic field, they have a voltage induced in them. This voltage tends to oppose the motor supply voltage and so is called \"back electromotive force (emf)\". The voltage is proportional to the running speed of the motor. The back emf of the motor, plus the voltage drop across the winding internal resistance and brushes, must equal the voltage at the brushes. This provides the fundamental mechanism of speed regulation in a DC motor. If the mechanical load increases, the motor slows down; a lower back emf results, and more current is drawn from the supply. This increased current provides the additional torque to balance the new load.", "The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as \"orbiting\" the proton in analogy to the Earth's orbit of the Sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.", "When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of the capacitor, a displacement current can flow.", "Energy gives rise to weight when it is trapped in a system with zero momentum, where it can be weighed. It is also equivalent to mass, and this mass is always associated with it. Mass is also equivalent to a certain amount of energy, and likewise always appears associated with it, as described in mass-energy equivalence. The formula E = mc², derived by Albert Einstein (1905) quantifies the relationship between rest-mass and rest-energy within the concept of special relativity. In different theoretical frameworks, similar formulas were derived by J. J. Thomson (1881), Henri Poincaré (1900), Friedrich Hasenöhrl (1904) and others (see Mass-energy equivalence#History for further information)." ] ]
5a7e070b70df9f001a875439	Matter	The term "matter" is used throughout physics in a bewildering variety of contexts: for example, one refers to "condensed matter physics", "elementary matter", "partonic" matter, "dark" matter, "anti"-matter, "strange" matter, and "nuclear" matter. In discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter (Gk. common matter). It is fair to say that in physics, there is no broad consensus as to a general definition of matter, and the term "matter" usually is used in conjunction with a specifying modifier.	en	null	null	190,721	[ "Physics has broadly agreed on the definition of what?", "Who coined the term partonic matter?", "What is another name for anti-matter?", "Matter usually does not need to be used in conjunction with what?", "What field of study has a variety of unusual contexts?" ]	[ [ "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "Albert Einstein proposed that the laws of physics should be based on the principle of relativity. This principle holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames. This theory was motivated by Maxwell's equations, which show that electromagnetic waves propagate in a vacuum at the speed of light. However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate.", "일반상대론의 가장 중요한 측면은 우주 전체에 적용될 수 있다는 점이다. 핵심은, 매우 거대한 규모에서는 우리 우주는 매우 단순한 선상에 만들어진 것처럼 보인다. 현재의 모든 관측들은 모든 우주의 구조가 평균적으로 봤을 때 관찰자의 위치나 관찰 방향과 무관하게 근사적으로 동일하다는 점을 시사한다. 즉 우주는 근사적으로 균질하며 등방하다. 이렇게 비교적 단순한 우주는 아인슈타인 방정식의 단순해로써 나타내질 수 있다. 오늘날의 물리우주론 모형들은 이러한 일반상대론의 단순해에 우주의 질량 내용물들을 기술하는 다른 분야, 예컨대 열역학, 핵물리학, 입자물리학 등을 조합하여 만들어진 것이다. 물리우주론 모형들에 따르면 현재의 우리 우주는 약 140억 년 전의 극도의 고밀도 고온 상태, 즉 대폭발로부터 시작되어 그 이후 팽창을 계속하고 있다.", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality." ], [ "Arthur Schopenhauer (1788-1860) wrote that \"...materialism is the philosophy of the subject who forgets to take account of himself\". He claimed that an observing subject can only know material objects through the mediation of the brain and its particular organization. That is, the brain itself is the \"determiner\" of how material objects will be experienced or perceived:", "Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilisation process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, which used the term gemmule to describe hypothetical particles that would mix during reproduction. Although Mendel's work was largely unrecognized after its first publication in 1866, it was 'rediscovered' in 1900 by three European scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak, who claimed to have reached similar conclusions in their own research.", "There is an entire literature concerning the \"structure of matter\", ranging from the \"electrical structure\" in the early 20th century, to the more recent \"quark structure of matter\", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics.[further explanation needed] In this connection, physicists speak of matter fields, and speak of particles as \"quantum excitations of a mode of the matter field\". And here is a quote from de Sabbata and Gasperini: \"With the word \"matter\" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields).\"[further explanation needed]", "Isaac Newton (1643–1727) inherited Descartes' mechanical conception of matter. In the third of his \"Rules of Reasoning in Philosophy\", Newton lists the universal qualities of matter as \"extension, hardness, impenetrability, mobility, and inertia\". Similarly in Optics he conjectures that God created matter as \"solid, massy, hard, impenetrable, movable particles\", which were \"...even so very hard as never to wear or break in pieces\". The \"primary\" properties of matter were amenable to mathematical description, unlike \"secondary\" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities." ], [ "In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.", "Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay, lightning or cosmic rays). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.", "There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, and whether other places are almost entirely antimatter instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called the charge parity (or CP symmetry) violation. CP symmetry violation can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.", "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality." ], [ "Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass and matter. As such, there is no single universally agreed scientific meaning of the word \"matter\". Scientifically, the term \"mass\" is well-defined, but \"matter\" is not. Sometimes in the field of physics \"matter\" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality.", "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.", "All the objects from everyday life that we can bump into, touch or squeeze are composed of atoms. This atomic matter is in turn made up of interacting subatomic particles—usually a nucleus of protons and neutrons, and a cloud of orbiting electrons. Typically, science considers these composite particles matter because they have both rest mass and volume. By contrast, massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered \"point particles\" with no effective size or volume. Nevertheless, quarks and leptons together make up \"ordinary matter\", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.", "For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as atoms), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a substance), but exists interdependently (i.e., as a \"principle\") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only receive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence in a whole (otherwise they would be independent wholes)." ], [ "This meagre statistic expanded in the 20th century to comprise anthropology departments in the majority of the world's higher educational institutions, many thousands in number. Anthropology has diversified from a few major subdivisions to dozens more. Practical anthropology, the use of anthropological knowledge and technique to solve specific problems, has arrived; for example, the presence of buried victims might stimulate the use of a forensic archaeologist to recreate the final scene. Organization has reached global level. For example, the World Council of Anthropological Associations (WCAA), \"a network of national, regional and international associations that aims to promote worldwide communication and cooperation in anthropology\", currently contains members from about three dozen nations.", "Environmental anthropology is a sub-specialty within the field of anthropology that takes an active role in examining the relationships between humans and their environment across space and time. The contemporary perspective of environmental anthropology, and arguably at least the backdrop, if not the focus of most of the ethnographies and cultural fieldworks of today, is political ecology. Many characterize this new perspective as more informed with culture, politics and power, globalization, localized issues, and more. The focus and data interpretation is often used for arguments for/against or creation of policy, and to prevent corporate exploitation and damage of land. Often, the observer has become an active part of the struggle either directly (organizing, participation) or indirectly (articles, documentaries, books, ethnographies). Such is the case with environmental justice advocate Melissa Checker and her relationship with the people of Hyde Park.", "A genre that greatly rose in importance was that of scientific literature. Natural history in particular became increasingly popular among the upper classes. Works of natural history include René-Antoine Ferchault de Réaumur's Histoire naturelle des insectes and Jacques Gautier d'Agoty's La Myologie complète, ou description de tous les muscles du corps humain (1746). Outside ancien régime France, natural history was an important part of medicine and industry, encompassing the fields of botany, zoology, meteorology, hydrology and mineralogy. Students in Enlightenment universities and academies were taught these subjects to prepare them for careers as diverse as medicine and theology. As shown by M D Eddy, natural history in this context was a very middle class pursuit and operated as a fertile trading zone for the interdisciplinary exchange of diverse scientific ideas.", "과학 분야에서는 직접· 간접적 교류가 없는 학자들이 동일한 연구를 독립적으로 수행하는 현상이 자주 발생한다. 이러한 현상은 중복 발견이라 불리며, 많은 역사학자들과 사회학자들의 관심대상이었다. 예를 들어 19세기 영국의 역사학자 토마스 매콜리는 미적분학을 독자적으로 발견한 영국의 뉴턴과 독일의 라이프니츠를 연구한 후, 당시의 사회적 상황이 미적분학을 개발할 수 밖에 없는 환경을 만들었다고 생각하였다. 즉, 뉴턴이나 라이프니츠가 아니라도 누군가가 미적분학을 비슷한 시기에 개발했으리라는 것이다. 이와 비슷하게 20세기 미국의 사회학자 윌리엄 오그번과 도로시 토마스는 지식이 축적되고 사회가 발전함에 따라 연구자들은 어쩔 수 없이 특정한 문제들에 주목하게 된다고 언급하였다. 머턴은 좀 더 나아가서 \"과학적 성과는 원칙적으로 중복 발견이며, 표면적으로는 단독 발견처럼 생각되는 것도 예외가 아니다\"라고 이야기하면서 다양한 역사적 사례를 논거로 제시한다. 그는 중복 발견을 여러가지 형태로 분류하기도 하였는데, 미발표 연구를 나중에 다른 학자가 독립적으로 수행하는 경우· 논문이 발표되기는 하였지만 묻혀있다가 다른 사람의 연구로 빛을 보는 경우· 거의 같은 시기에 중복 발견이 이뤄져서 모두가 논문을 발표하거나 한 쪽이 소식을 미리 듣고 포기하는 경우 등 다양하다." ] ]

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