| radioactive decay | <physics> The process by which a spontaneous change in nuclear state takes place. This process is accompanied by the emission of energy in various specific combinations of electromagnetic and corpuscular radiation and neutrinos. (16 Dec 1997) |
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| decay | To pass gradually from a sound, prosperous, or perfect state, to one of imperfection, adversity, or dissolution; to waste away; to decline; to fail; to become weak, corrupt, or disintegrated; to rot; to perish; as, a tree decays; fortunes decay; hopes decay. "Ill fares the land, to hastening ills a prey, Where wealth accumulates and men decay." (Goldsmith) Origin: OF. Decaeir, dechaer, decheoir, F. Dechoir, to decline, fall, become less; L. De- + cadere to fall. See Chance. 1. Gradual failure of health, strength, soundness, prosperity, or of any species of excellence or perfection; tendency toward dissolution or extinction; corruption; rottenness; decline; deterioration; as, the decay of the body; the decay of virtue; the decay of the Roman empire; a castle in decay. "Perhaps my God, though he be far before, May turn, and take me by the hand, and more - May strengthen my decays." (Herbert) "His [Johnson's] failure was not to be ascribed to intellectual decay." (Macaulay) "Which has caused the decay of the consonants to follow somewhat different laws." (James Byrne) 2. Destruction; death. 3. Cause of decay. "He that plots to be the only figure among ciphers, is the decay of the whole age." (Bacon) Synonym: Decline, consumption. See Decline. Source: Websters Dictionary (01 Mar 1998) |
| decay accelerating factor | <biochemistry, protein> Plasma protein that regulates complement cascade by blocking the formation of the C3bBb complex (the C3 convertase of the alternate pathway). Widely distributed in tissues but deficient in paroxysmal nocturnal haemoglobinuria. (18 Nov 1997) |
| decay constant | <physics, radiobiology> The fraction of the amount of a radionuclide that undergoes transition per unit time. Formally: Lamda=dP/dt Where dP is the probability of a given nucleus undergoing spontaneous nuclear transition in the time interval dt. (16 Dec 1997) |
| decay modes | <radiobiology> Different pathways for decay of radioactive nuclei. The decay modes for a given unstable state can include beta emission (negative = electron, positive = positron), electron capture, alpha emission, fission, and gamma emission. (13 Nov 1997) |
| decay theory | A theory of forgetting based on the premise that an engram or memory trace dissipates progressively with time during the interval when it is not activated. (05 Mar 2000) |
| tone decay test | The sounding of a continuous tone at threshold for 1 min; if the intensity must be increased by more than 5 dB for continued perception, it may be a sign of retrocochlear damage. (05 Mar 2000) |
| exponential decay | <epidemiology> A decline in which the rate of decay is always proportional to the amount of material remaining; the constant of proportionality is the rate constant. (05 Dec 1998) |
| free induction decay | In magnetic resonance imaging, the decay curve that is detected by the radiofrequency coil after the application of an excitation pulse, without additional pulses (free). (05 Mar 2000) |
| superior dental branches of superior dental plexus | Branches passing from the superior dental plexus to the roots of the teeth of the upper jaw. Synonym: rami dentales superiores plexus dentalis superioris. (05 Mar 2000) |
| inferior dental branches of inferior dental plexus | Branches passing from the inferior dental plexus to the roots of the teeth of the lower jaw. Synonym: rami dentales inferiores plexus dentalis inferioris. (05 Mar 2000) |
| acid etching, dental | Pretreatment of tooth surfaces with etching agents, usually phosphoric acid, to increase the adhesion of various resin systems. (12 Dec 1998) |
| american dental association | Professional society representing the field of dentistry. (12 Dec 1998) |
| anterior superior dental arteries | Origin, infraorbital artery within intraorbital canal; distribution, via anterior alveolar canals to upper incisors and canine teeth, mucus membrane of maxillary sinus. Synonym: arteriae alveolares superiores anteriores, anterior superior dental arteries. (05 Mar 2000) |
| apical dental foramen | The opening at the apex of the root of a tooth that gives passage to the nerve and blood vessels. Synonym: foramen apicis dentis, apical dental foramen, root foramen. (05 Mar 2000) |