| exponential | Pertaining to exponents; involving variable exponents; as, an exponential expression; exponential calculus; an exponential function. Exponential curve, a curve whose nature is defined by means of an exponential equation. Exponential equation, an equation which contains an exponential quantity, or in which the unknown quantity enters as an exponent. <mathematics> Exponential quantity, a quantity whose exponent is unknown or variable, as a^x. Exponential series, a series derived from the development of exponential equations or quantities. Origin: Cf. F. Exponentiel. Source: Websters Dictionary (01 Mar 1998) |
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| 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) |
| exponential distribution | The time until failure of a process at constant hazard. (05 Mar 2000) |
| exponential growth | <biology> A rate of growth of an organism, a part of an organism, or a population of organisms which, when graphed, produces an exponential or logarithmic curve. Such a rate occurs, for example: during the exponential growth phase, when a population of bacterial (or other) cells divide at a constant rate so that the total number of cells doubles with each division. (09 Oct 1997) |
| 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) |
| 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) |
| 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) |
| 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) |