| AAGP | American Academy of General Practice; American Association for Geriatric Psychiatry |
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| ACOP | American College of Osteopathic Pediatricians; approved code of practice |
| AGPA | American Group Practice Association; American Group Psychotherapy Association |
| APN | acute pyelonephritis; advanced practice nurse; average peak noise |
| CPGs | clinical practice guidelines |
| Abbe theory of image formation | <optics, physics> Abbe's theory is based on the fact that a non-self-luminous particle, which is illuminated by an extraneous source, gives rise to diffracted light rays, in addition to the dioptric pencil. He stated that to form a good microscopical image as many of the diffracted rays as possible should be intercepted by the objective. With closely ruled lines, his theory is easily demonstrated by observing the back lens of the objective, for here the diffracted rays can be observed directly if the aperture diaphragm is closed. It can be shown that, when the illumination is arranged to exclude the diffracted images, resolution is lost. (11 Mar 1998) |
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| adsorption theory of narcosis | That a drug becomes concentrated at the surface of the cell as a result of adsorption, and thus alters permeability and metabolism. (05 Mar 2000) |
| Altmann's theory | A theory that protoplasm consists of granular particles (called bioblasts) that are clustered and enclosed in indifferent matter. (05 Mar 2000) |
| Arrhenius-Madsen theory | That the reaction of an antigen with its antibody is a reversible reaction, the equilibrium being determined according to the law of mass action by the concentrations of the reacting substances. (05 Mar 2000) |
| atomic theory | That chemical compounds are formed by the union of atoms in certain definite proportions; in its modern form, first advanced in 1803 by John Dalton. (05 Mar 2000) |
| Baeyer's theory | That carbon bonds are set at fixed angles (109 |
| balance theory | In social psychology, a theory which assumes that steady and unsteady states can be specified for cognitive units, such as an individual and his or her attitudes or acts, and that such units tend to seek steady states (balance); e.g., balance exists when both parts of a unit are evaluated the same, but disequilibrium arises when both parts are not evaluated the same, which causes either cognitive reevaluation of the parts or their segregation. See: cognitive dissonance theory, consistency principle. (05 Mar 2000) |
| beta-oxidation-condensation theory | <biochemistry> That the two carbon fragments split from the fatty acid molecule by beta-oxidation are converted to acetic acid and then condensed to acetoacetic acid. (05 Mar 2000) |
| Bohr's theory | That spectrum lines are produced 1) by the quantised emission of radiant energy when electrons drop from an orbit of a higher to one of a lower energy level, or 2) by absorption of radiation when an electron rises from a lower to a higher energy level. (05 Mar 2000) |
| Bordeau theory | That each organ of the body manufactured a specific humor which it secreted into the bloodstream. (05 Mar 2000) |
| Bowman's theory | That the urine is formed by passive filtration through the glomeruli and secretion by the epithelium of the tubules, the water and salts being separated from the plasma in the former situation, the urea and other urinary constituents in the latter. Parts of this theory are now known to be wrong. (05 Mar 2000) |
| Bronsted theory | That an acid is a substance, charged or uncharged, liberating hydrogen ions in solution, and that a base is a substance that removes them from solution (e.g., NH4+, CH3COOH, and HSO4- are acids; NH3, CH3COO-, and SO4- are bases); useful in the concept of weak electrolytes and buffers. Compare: Bronsted acid, Bronsted base. (05 Mar 2000) |
| Cannon-Bard theory | The view that the feeling aspect of emotion and the pattern of emotional behaviour are controlled by the hypothalamus. (05 Mar 2000) |
| Cannon's theory | A theory of the emotions, advanced by W.B. Cannon, that animal and human organisms respond to emergency situations by increased sympathetic nervous system activity including an increased catecholamine production with associated increases in blood pressure, heart and respiratory rates, and skeletal muscle blood flow. See: relaxation response. Synonym: Cannon's theory. (05 Mar 2000) |
| game theory | A mathematical theory that deals with action in a conflict situation as if it were a game in which each player seeks to maximise his opponent's losses. (12 Dec 1998) |