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| 熔点 |
熔点熔點是晶体將其物態由固態轉變（熔化）為液態的过程中固液共存状态的溫度。進行相反動作（即由液態轉為固態）的溫度，稱之為凝固点（也称冰点），晶体的凝固点和熔点相同。一般的，非晶体并没有固定的熔点和凝固点。與沸點不同的是，熔點受壓力的影響很小。
参见
- 沸点
- 三态点
category:熱力學
category:溫度
ja:融点
ko:녹는점
th:จุดหลอมเหลว
晶体
晶体是原子或分子按照一定的周期性在空间排列形成的固体。
- 晶体的分布非常广泛，自然界的固体物质中，绝大多数是晶体。气体、液体和非晶物质在一定的合适条件下也可以转变成晶体。
- 晶体内部原子或分子排列的三维空间周期性结构，是晶体最基本的、最本质的特征，并使晶体具有下面的通性：
- #均匀性，即晶体内部各处宏观性质相同；
- #各向异性，即晶体中不同的方向上性质不同；
- #能自发形成多面体外形；
- #有确定的、明显的熔点；
- #有特定的对称性；
- #能对X射线和电子束产生衍射效应等。
category:固体物理学
category:化學
固体固体是物质存在的一种状态。与液体和气体相比固体有比较固定的体积和形状、质地比较坚硬。
通过其组成部分之间的相互作用固体的特性可以与组成它的粒子的特性有很大的区别。研究固体的物理科学叫做固体物理学。
一般来说，一个物体要达到一定的大小才能被称为固体，但对这个大小没有明确的规定。一般来说固体是宏观物体，除一些特殊的低温物理学的现象如超导现象、超液现象外固体作为一个整体不显示量子力学的现象。
Category:自然科学
Category:凝聚态物理学
Category:固体物理学
ja:固体
ko:고체
ms:Pepejal
simple:Solid
液体液体是物质存在的一种状态，有比较固定的体积而没有固定的形状，可流动的。增溫或減壓一般能使液體氣化，成爲氣體，例如將水加溫成水蒸氣。加壓或减溫一般能使液體固化，成爲固體，例如將水减溫成冰。然而，仅加压并不能使所有气体液化，如氧，氢，氦等。
Category:凝聚态物理学
ja:液体
ko:액체
ms:Cecair
simple:Liquid
溫度温度是表征物体冷热程度的物理量。温度只能通过物体随温度变化的某些特性来间接测量，而用来量度物体温度数值的标尺叫温标。它规定了温度的读数起点（零点）和测量温度的基本单位。目前国际上用得较多的温标有华氏温标、摄氏温标、热力学温标和国际实用温标。
温度是物体内分子间平均动能的一种表现形式。
大气层中气体的温度是气温，是天气学常用名词。
category:温度
ja:温度
ko:온도
th:อุณหภูมิ
壓力
壓力是一個物理的概念，定義為物質於每一單位面積所承受的力。符號為P國際單位為帕司卡(Pascale, Pa);1Pa=1kgm-1s-1。
公式
一物體所承受的壓力P可以利用以下公式表示:
:, F為該物體所承受的力;A為該物體的面積
單位
國際單位。1 Pa= 1 kgm-1s-1。
大氣壓力(atmospheric pressure, atm) 亦為常用的壓力單位，1atm約為一般情況下空氣氣壓。1atm 約為 101kPa。atm 常用於計算氣體之氣壓。
mmHg亦為壓力單位，常用於量度血壓。
category:力學
Warfarin potassium
Warfarin (also known under the brand names of Coumadin® and Marevan®) is an anticoagulant medication that is administered orally. It is used for the prophylaxis of thrombosis and embolism in many disorders. Its activity has to be monitored by frequent blood testing for the international normalized ratio (INR).
Warfarin was originally developed as a rat poison, and is still widely used as such, although warfarin-resistant rats are becoming more common.
Mechanism of action
Normally, vitamin K is converted to vitamin K epoxide in the liver. This epoxide is then reduced by the enzyme epoxide reductase. The reduced form of vitamin K epoxide is necessary for the synthesis of many coagulation factors (II, VII, IX and X, as well as protein C and protein S). Warfarin inhibits the enzyme epoxide reductase in the liver, thereby inhibiting coagulation.
Uses
Medical use
Warfarin is given to people with an excessive tendency for thrombosis. This can prevent growth or embolism (spread) of a thrombus. Common indications for warfarin use are atrial fibrillation, artificial heart valves, deep venous thrombosis and pulmonary embolism.
Therapeutic drug monitoring is required, as warfarin has a very narrow therapeutic index, which means the levels in the blood that are effective are close to the levels that cause bleeding. Dosing of warfarin is further complicated by the fact that it is known to interact with many other medications and other chemicals which may be present in appreciable quantities in food (including caffeine and ascorbic acid). These interactions range from enhancing warfarin's anticoagulation effect to reducing the effect of warfarin.
As a result, it is easy to over- or under-coagulate the patient. Warfarin's effects must be closely monitored: this is done by using the INR. Initially, checking may be as often as twice a week; the intervals can be lengthened if the patient manages stable therapeutic INR levels on a stable warfarin dose.
When initiating warfarin therapy ("warfarinisation"), the doctor will generally decide how strong the anticoagulant therapy needs to be. A common target INR level is 2.0-3.0, though it varies from case to case.
The new oral anticoagulant ximelagatran (Exanta®) does not require INR monitoring, and was expected to replace warfarin to a large degree when introduced; however, it has run into approval problems and currently (2005) it is not clear if or when it will ever become available for general use.
Pesticide use
Warfarin is used as a rodenticide for controlling rats and mice in residential, industrial, and agricultural areas. It is both odorless and tasteless. It is effective when mixed with food bait, because the rodents will return to the bait and continue to feed over a period of days, until a lethal dose is accumulated (considered to be 1 mg/Kg/day over four to five days). It may also be mixed with talc and used as a tracking powder, which accumulates on the animal's skin and fur, and is subsequently consumed during grooming. The use as rat poison is now declining because many rat populations have developed resistance to warfarin.
Source
Warfarin is a derivative of coumarin, a chemical found naturally in many plants, notably woodruff (Galium odoratum, Rubiaceae), and at lower levels in licorice, lavender and various other species.
Advantages and disadvantages
lavender
Pharmacokinetics and antagonism
Warfarin is slower acting than the common anticoagulant heparin, though it has a number of advantages. Heparin must be given by injection, while warfarin is available orally. Warfarin has a long half-life and need only be given once a day. As well as these problems, heparin can also cause thrombocytopenia (a decrease in platelet levels), which may cause bleeding. For these main reasons, hospitalised patients are usually given heparin initially, and are then moved on to warfarin.
Heparin can be antagonised with protamine sulfate, while warfarin can be reversed with vitamin K.
Side effects
Side effects can include gastrointestinal bleeding and the feared (but rare) complication of warfarin necrosis, which occurs mainly in patients with a deficiency of protein C. Protein C is an innate anticoagulant, and as warfarin further decreases protein C levels by inhibiting vitamin K, it can lead to massive thrombosis with necrosis and gangrene of limbs. Its natural counterpart, purpura fulminans, occurs in children who are homozygous for protein C mutations. The patient's general tendency to bruise and bleed is raised somewhat, and incidents involving bleeding and its complications - especially when the INR has drifted too high - are not uncommon. Most bleeds are not serious, but a very small proportion develops a cerebral hemorrhage or a gastrointestinal bleed, both of which need urgent medical attention.
Interactions and contraindications
There are many drug-drug interactions with warfarin, and its metabolism varies greatly between patients. This makes finding the correct dosage difficult, and accentuates the need of monitoring; when initiating a medication that is known to interact with warfarin (e.g. amiodarone), INR checks are increased or dosages adjusted until a new ideal dosage is found.
In 2004 it was reported that cranberry juice could potentiate warfarin, and UK patients on warfarin were advised to avoid cranberry juice until the exact mechanism was understood.
Warfarin cannot be given to pregnant women, especially in the first trimester, as it is a teratogen (it causes deformations of the face and bones). During the third trimester, antepartum hemorrhage can occur. Instead of warfarin, low molecular weight heparin is generally used.
Rigorous use of alcohol is also known to effect the metabolism of warfarin, although moderate drinking usually has little or no effect on the INR value. Patients suffering from liver damage or alcoholism are usually treated with heparin injections instead.
Overdose
Symptoms of overdose or side effect (see above) include hemoptysis, excessive bruising, bleeding from nose or gums, or blood in urine or stool. If an overdose of warfarin occurs (revealed by bleeding and/or a high INR), the effects can be reversed by administering a vitamin K injection, or (in case of severe bleeding) prothrombin complex or fresh frozen plasma infusion to replace coagulation proteins. A mildly elevated INR in a patient who is not bleeding may be corrected with oral vitamin K.
History
The early 1920s saw the outbreak of a previously unrecognized disease of cattle in the northern United States and Canada. Cattle would die of uncontrollable bleeding from very minor injuries, or sometimes drop dead of internal hemorrhage with no external signs of injury. In 1922, Frank Schofield, a Canadian veterinarian, determined that the cattle were ingesting a toxin from moldy silage made from sweet clover that functioned as a potent anticoagulant.
The identity of the anticoagulant substance in moldy sweet clover remained a mystery until 1940 when Karl Link and Harold Campbell, chemists working at the University of Wisconsin, determined that it was the coumarin derivative 4-hydroxycoumarin. Over the next few years, numerous similar chemicals were found to have the same anticoagulant properties. The first of these to be widely commericialized was dicoumarol, patented in 1941. Link continued working on developing more potent coumarin-based anticoagulants for use as rodent poisons, resulting in warfarin in 1948. (The name warfarin stems from the acronym WARF, for Wisconsin Alumni Research Foundation + the ending -arin indicating its link with coumarin. The attribution, sometimes quoted as fact even by doctors, to Wisconsin Anti-Rat Federation is folklore.) Warfarin was first registered for use as a rodenticide in the US in 1952.
After an incident in 1951, where a naval enlisted man unsuccessfully attempted suicide with warfarin and recovered fully, studies began in the use of warfarin as a therapeutic anticoagulant. It was found to be generally superior to dicoumarol, and in 1954 was approved for medical use in humans.
Other coumarins
In some countries, other coumarins are used instead of warfarin, such as acenocoumarol and phenprocoumon. These have a shorter (acenocoumarol) or longer (phenprocoumon) half-life, and are not completely interchangeable with warfarin.
Notes
- [http://www.mca.gov.uk/ourwork/monitorsafequalmed/currentproblems/currentproblems_oct04.pdf "Current Problems in Pharmacovigilance" (pdf file)] October 2004 - has cranberry juice caution, p. 10
External links
- [http://ace.orst.edu/cgi-bin/mfs/01/pips/warfarin.htm Warfarin pesticide profile] from US Department of Agriculture
- [http://www.chemsoc.org/exemplarchem/entries/2002/hook/warfarin.htm Warfarin factsheet] from the Royal Society of Chemistry
Category:Anticoagulants
Category:Rodenticides
ja:ワルファリン
th:วาร์ฟาริน
wycieczki szkolne Dorota Rabczewska metal firma mieszne filmy
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