| drift wave | <radiobiology> Oscillations in a magnetically-confined plasma arising in the presence of density gradients (such as at the plasma's surface). These resemble the waves that propagate at the interface of two fluids with different density in a gravitational field. (09 Oct 1997) |
|---|
| antigenic drift | <immunology> A change that occurs on the molecular level to effect a change in the antigenicity of a bacteria or virus. Antigenic drift occurs naturally and more rapidly in certain viruses (for example HIV). It is antigenic drift which complicates the development of an effective HIV (AIDS) vaccine. (27 Sep 1997) |
|---|---|
| genetic drift | <genetics> The random change of the occurance of a particular gene in a population, genetic drift is thought to be one cause of speciation when a group oforganisms is separated from its parent population. (09 Oct 1997) |
| pure random drift | That which has random components only with an average value of zero and no systematic effects. Brownian movement in a still container shows pure random drift but in the Mississippi shows a steady downstream tendency. (05 Mar 2000) |
| drift | Collectively, stream invertebrates (almost wholly the aquatic larval stages of insects) that voluntarily or accidentally leave the substrate to move or float with the current, as well as terrestrial invertebrates that drop into the stream. Also, any detrital material transported in the water current. (09 Oct 1997) |
| drift cyclotron loss cone instabilities | (DCLC) This is an electrostatic microinstability (frequencies at harmonics of the ion cyclotron frequency) which is of major concern in small mirror devices. Mode is driven by radial gradients in the electron density, and causes loss of ions due to non-conservation of magnetic moment (see adiabatic invariant) as they interact with the mode, and are dispersed in velocity space into the loss cone. Stabilisation is accomplished by increasing the plasma size and by partially filling the loss cone with a continuous extermal warm plasma stream. (09 Oct 1997) |
| drift feeder | Fish and other predators that forage on invertebrates drifting on the water surface or in the water column. (09 Oct 1997) |
| drift line | An accumulation of water-carried debris along a contour or at the base of vegetation that provides direct evidence of prior inundation and often indicates the directional flow of flood waters. (09 Oct 1997) |
| drift motion | <radiobiology> Ordinarily particles placed in a magnetic field will simply orbit in circles, but if the magnetic field is not uniform, or curves, or there is an electrical field perpendicular to the magnetic field, or another force is applied perpendicular to the magnetic field, then the guiding centres of the particle orbits will drift (generally perpendicular to the magnetic field and to the applied force). (09 Oct 1997) |
| drift movements | Slow ocular movements of greater amplitude than flicks, occurring during ocular fixation. Synonym: drift movements. (05 Mar 2000) |
| drift pumping | <radiobiology> A process that removes ions trapped in a thermal barrier using radial transport induced by an externally-applied radiofrequency field tuned to resonate with the azimuthal drift frequency. (09 Oct 1997) |
| drift surface | <radiobiology> Surface on which the guiding centre of a particle is constrained to move, due to the effects of the laws of adiabatic invariance on its drift motion. (09 Oct 1997) |
| drift velocity | <radiobiology> Characteristic velocity at which the centre of a particle's orbit (guiding centre) drifts when drift motion (see above) occurs. (09 Oct 1997) |
| acid wave | A temporary increase in the acidity of the urine occurring during fasting. Synonym: acid wave. (05 Mar 2000) |
| alkaline wave | A period of urinary neutrality or even alkalinity after meals due to withdrawal of hydrogen ion for the purpose of secretion of the highly acid gastric juice. Synonym: alkaline wave. (05 Mar 2000) |
| alpha wave | Brain waves in the encephalogram which have a frequency of 8 to 13 per second. They are typical of the normal person awake and in a quiet resting state, and occur principally in the occipital region. (12 Dec 1998) |