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melting point

(Encyclopedia)melting point, temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific tem...

norepinephrine

(Encyclopedia)norepinephrine nôrˌĕpīnĕfˈrən [key], a neurotransmitter in the catecholamine family that mediates chemical communication in the sympathetic nervous system, a branch of the autonomic nervous sys...

luminescence

(Encyclopedia)luminescence, general term applied to all forms of cool light, i.e., light emitted by sources other than a hot, incandescent body, such as a blackbody radiator. Luminescence is caused by the movement ...

Kelvin, William Thomson, 1st Baron

(Encyclopedia)Kelvin, William Thomson, 1st Baron, 1824–1907, British mathematician and physicist, b. Belfast. He was professor of natural philosophy at the Univ. of Glasgow (1846–99). He is known especially for...

liquid air

(Encyclopedia)liquid air, ordinary air that has been liquefied by compression and cooling to extremely low temperatures (see liquefaction). Its commercial preparation involves purification by washing to remove solu...

Aristide, Jean-Bertrand

(Encyclopedia)Aristide, Jean-Bertrand zhänˈ bĕrträndˈ äˌrēstēdˈ [key], 1953–, president of Haiti (1991, 1994–96, 2001–4). A radical Catholic priest who defended liberation theology, he worked among ...

Karadžić, Radovan

(Encyclopedia)Karadžić, Radovan räˈdōvän käˈräjĭch [key], 1945–, Bosnian Serb physician, author, and political leader, b. Savnik, Montenegro, Yugoslavia. The son of a Serb nationalist and World War II r...

placebo

(Encyclopedia)placebo pləsēˈbō [key], inert substance given instead of a potent drug. Placebo medications are sometimes prescribed when a drug is not really needed or when one would not be appropriate because t...

caffeine

(Encyclopedia)caffeine kăfēnˈ [key], odorless, slightly bitter alkaloid found in coffee, tea, kola nuts (see cola), ilex plants (the source of the Latin American drink maté), and, in small amounts, in cocoa (se...

vibration

(Encyclopedia)vibration, in physics, commonly an oscillatory motion—a movement first in one direction and then back again in the opposite direction. It is exhibited, for example, by a swinging pendulum, by the pr...