| 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) |
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| 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) |
| 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) |
| 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) |
| 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) |
| random | 1. Force; violence. "For courageously the two kings newly fought with great random and force." (E. Hall) 2. A roving motion; course without definite direction; want of direction, rule, or method; hazard; chance; commonly used in the phrase at random, that is, without a settled point of direction; at hazard. "Counsels, when they fly At random, sometimes hit most happily." (Herrick) "O, many a shaft, at random sent, Finds mark the archer little meant !" (Sir W. Scott) 3. Distance to which a missile is cast; range; reach; as, the random of a rifle ball. 4. <chemical> The direction of a rake-vein. Origin: OE. Randon, OF. Randon force, violence, rapidity, a randon, de randon, violently, suddenly, rapidly, prob. Of German origin; cf. G. Rand edge, border, OHG. Rant shield, edge of a shield, akin to E. Rand, n. See Rand. Going at random or by chance; done or made at hazard, or without settled direction, aim, or purpose; hazarded without previous calculation; left to chance; haphazard; as, a random guess. "Some random truths he can impart." (Wordsworth) "So sharp a spur to the lazy, and so strong a bridle to the random." (H. <medicine> Spencer) Random courses, stonework consisting of stones of unequal sizes fitted together, but not in courses nor always with flat beds. Source: Websters Dictionary (01 Mar 1998) |
| random allocation | A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects. (12 Dec 1998) |