| attenuation factor | <radiobiology> A measure of the opacity of a layer of material for radiation transversing it, the ratio of the incident intensity to the transmitted intensity. It is equal to Io/I, where Io and I are the intensities of the incident and emergent radiation, respectively. In the usual sense of exponential absorption (I = Ioe- m x), the attenuation factor is e- m x, where x is the thickness of the material and m is the absorption coefficient. (16 Dec 1997) |
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| attenuation | <radiobiology> Process by which a beam of radiation is reduced in intensity when passing through material - combination of absorption and scattering processes, leading to a decrease in flux density of beam when projected through matter. (16 Dec 1997) |
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| attenuation coefficient | 1. <radiobiology> Compton: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing as a result of Compton effect interactions. 2. Linear: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing due to all absorption and scattering processes. 3. Pair Production: That fractional decrease in the intensity of a beam of ionising radiation due to pair production in a medium through which it passes. 4. Photoelectric Effect: That fractional decrease in the intensity of a beam of ionising radiation due to photoelectric effect in a medium through which it passes. (16 Dec 1997) |
| attenuation compensation | In ultrasonography, an increase in receiver gain with time to compensate for loss in echo amplitude with depth, usually due to attenuation. Synonym: attenuation compensation, depth compensation, time compensation gain, time-compensated gain, time-varied gain control, time-varied gain. (05 Mar 2000) |
| mass attenuation coefficient | <physics> The mass attenuation coefficient, u/p, of a material for uncharged ionising particles is the quotient of DN/N by pdl, where DN/N is the fraction of particles that experience interactions in traversing a distance dl in a material of density p. (16 Dec 1997) |
| accelerator factor | <chemical> Heat- and storage-labile plasma glycoprotein which accelerates the conversion of prothrombin to thrombin in blood coagulation. Factor v accomplishes this by forming a complex with factor xa, phospholipid, and calcium (prothrombinase complex). Deficiency of factor v leads to owren's disease. Chemical name: Blood-coagulation factor V (12 Dec 1998) |
| acetate replacement factor | <biochemistry> 1,2 dithiolane 3 valeric acid. Regarded as a coenzyme in the oxoglutarate dehydrogenase complex of the citric acid cycle. Involved generally in oxidative decarboxylations of _ keto acids. A growth factor for some organisms. (18 Nov 1997) |
| adrenal weight factor | A postulated substance of adenohypophysial origin responsible for maintenance of the weight of the adrenal cortex. (05 Mar 2000) |
| adrenocorticotropic releasing factor | Hormone produced by hypothalamus that causes pituitary to secrete adrenocorticotropic hormone. (05 Mar 2000) |
| a-factor | <molecular biology> A protein which is found in the bacterial genus Streptomyces that helps start the production of streptomycin and the process of morphological differentiation. It is used in biotechnology to induce these functions in mutant strains of Streptomyces that cannot produce it themselves. (09 Feb 1998) |
| angiogenesis factor | Substance causing proliferation of new blood vessels. It is found in tissues with high metabolic requirements, such as the retina, and in certain cancers. The factor is also released by hypoxic macrophages at the edges or outer surfaces of wounds and initiates revascularization in wound healing. (12 Dec 1998) |
| animal protein factor | <biochemistry> Member of the water soluble B vitamin group, important in the proper function of the nervous system and important in proper carbohydrate, protein and fat metabolism. (27 Sep 1997) |
| antialopecia factor | A member of the vitamin B complex necessary for growth of yeast and of mice, absence from the diet causes hair loss and dermatitis in mice. (27 Sep 1997) |
| antianaemic factor | <biochemistry> Member of the water soluble B vitamin group, important in the proper function of the nervous system and important in proper carbohydrate, protein and fat metabolism. (27 Sep 1997) |
| antiberiberi factor | Synonym: thiamin. (05 Mar 2000) |
| anti-black-tongue factor | A precursor of NAD, that is a product of the oxidation of nicotine. (18 Nov 1997) |