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magnetic resonance imaging

(Encyclopedia)magnetic resonance imaging (MRI), noninvasive diagnostic technique that uses nuclear magnetic resonance to produce cross-sectional images of organs and other internal body structures. The patient lies...

mandorla

(Encyclopedia)mandorla mänˈdôrlä [key], [Ital.,=almond], a medieval Christian artistic convention by which an oval or almond-shaped area or series of lines surrounds a deity, most commonly Jesus. The mandorla i...

thresher shark

(Encyclopedia)thresher shark, long-tailed, warm-water shark, genus Alopias. The upper fork of its tail is slender and sickle-shaped and is about equal in length to the rest of the body. This shark uses its tail str...

RISC processor

(Encyclopedia)RISC processor [Reduced Instruction Set Computer], computer arithmetic-logic unit that uses a minimal instruction set, emphasizing the instructions used most often and optimizing them for the fastest ...

citric acid

(Encyclopedia)citric acid or 2-hydroxy-1,2,3-propanetricarboxylic acid, HO2CCH2C(OH)(CO2H)CH2CO2H, an organic carboxylic acid containing three carboxyl groups; it is a solid at room temperature, melts at 153℃, an...

defibrillator

(Encyclopedia)defibrillator, device that delivers an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances (arrhythmias). The shock changes a fibrillation to an organized r...

Delany, Samuel R.

(Encyclopedia)Delany, Samuel R. (Samuel Ray Delany, Jr.), 1942–, African-American wrtier, b. Harlem, New York City. Delany uses science fiction, fantasy, and memoir to explore sexual identity, race, language, and...

graphite

(Encyclopedia)graphite grăfˈīt [key], an allotropic form of carbon, known also as plumbago and black lead. It is dark gray or black, crystalline (often in the form of slippery scales), greasy, and soft, with a m...

varicose vein

(Encyclopedia)varicose vein, superficial vessel that is abnormally lengthened, twisted, or dilated, seen most often on the legs and thighs. Varicose veins develop spontaneously, and are usually attributed to a here...

radiochemistry

(Encyclopedia)radiochemistry, chemistry of radioactive substances (see radioactivity). Radioactive isotopes are very useful as tracers to study the mechanisms of complex organic reactions, since even minute amounts...