| population diffusion coefficient | <cell biology> Coefficient that describes the tendency of a population of motile cells to diffuse through the environment. Its use presupposes that the cells move in a random walk. (18 Nov 1997) |
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| diffusion coefficient | For the translational diffusion of solutes, diffusion is described by Fick's First Law, that states that the amount of a substance crossing a given area is proportional to the spatial gradient of concentration and the diffusion constant (D), that is related to molecular size and shape. A useful derived relationship is that the mean square distance moved by molecules in time t is 6Dt. (18 Nov 1997) |
| main | 1. Very or extremely strong. "That current with main fury ran." (Daniel) 2. Vast; huge. "The main abyss." 3. Unqualified; absolute; entire; sheer. "It's a man untruth." . 4. Principal; chief; first in size, rank, importance, etc. "Our main interest is to be happy as we can." (Tillotson) 5. Important; necessary. "That which thou aright Believest so main to our success, I bring." (Milton) By main force, by mere force or sheer force; by violent effort; as, to subdue insurrection by main force. "That Maine which by main force Warwick did win." (Shak) By main strength, by sheer strength; as, to lift a heavy weight by main strength. Main beam, the principal or true keel of a vessel, as distinguished from the false keel. Synonym: Principal, chief, leading, cardinal, capital. Origin: From Main strength, possibly influenced by OF. Maine, magne, great, L. Magnus. Cf. Magnate. Source: Websters Dictionary (01 Mar 1998) |
| main d'accoucheur | Position of the hand in tetany or in muscular dystrophy; the fingers are flexed at the metacarpophalangeal joints and extended at the phalangeal joints, with the thumb flexed and adducted into the palm; in resemblance to the position of the physician's hand in making a vaginal examination. Synonym: main d'accoucheur, obstetrical hand. (05 Mar 2000) |
| main en crochet | A permanent flexure of the fourth and fifth fingers, resembling the hand of a woman crocheting with three fingers bent to guide the thread. (05 Mar 2000) |
| main en griffe | Atrophy of the interosseous muscles of the hand with hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints. Synonym: main en griffe. (05 Mar 2000) |
| main en lorgnette | A deformity of the hand seen in chronic absorptive arthritis, the fingers and wrists being shortened and the covering skin wrinkled into transverse folds; the phalanges appear to be retracted into one another like an opera glass or miniature telescope. Synonym: main en lorgnette. (05 Mar 2000) |
| main fourchee | A congenital deformity in which the division between the fingers, especially between the third and fourth, extends into the metacarpal region. See: lobster-claw deformity. Synonym: main fourchee, split hand. (05 Mar 2000) |
| main succulente | Oedema of the hand with coldness and lividity of the skin, observed in syringomyelia. Synonym: main succulente. (05 Mar 2000) |
| right main bronchus | It arises at the bifurcation of the trachea and enters the hilum of the right lung, giving off the superior lobe bronchus and continuing downward to give off the middle and inferior lobe bronchi. It is shorter, of greater caliber, and more nearly-vertical than the left main bronchus, thus, aspirated objects more frequently lodge on the right side. Synonym: bronchus principalis dexter. (05 Mar 2000) |
| left main bronchus | It arises at the bifurcation of the trachea, passes in front of the oesophagus and enters the hilum of the left lung where it divides into a superior lobe bronchus and an inferior lobe bronchus. It is longer, of narrower caliber, and more nearly-horizontal than the right main bronchus, hence, aspirated objects enter it less frequently. Synonym: bronchus principalis sinister. (05 Mar 2000) |
| ambipolar diffusion | <radiobiology> Diffusion process in which buildup of spatial charge creates electric fields which cause electrons and ions to leave the plasma at the same rate. (Such electric fields are self-generated by the plasma and act to preserve charge neutrality.) (09 Oct 1997) |
| anomalous diffusion | <radiobiology> Diffusion in most plasma devices, particularly tokamaks, is higher than what one would predict from understood causes. The observed, typical diffusion is referred to as anomalous because it has not yet been explained. Anomalous diffusion includes all diffusion which is not due to collisions and geometric effects. While such effects were not understood when the term was coined, and most still are not, diffusion due to well-understood wave phenomena is still 'anomalous'. Classical diffusion and Neo-classical diffusion are the two well-understood diffusion theories, although neither is adequate to fully explain the observed anomalous diffusion. See: entries for classical diffusion and neoclassical diffusion. Anomalous resistivity (09 Oct 1997) |
| bohm diffusion | <radiobiology> A rapid loss of plasma across magnetic field lines caused by microinstabilities. Theory formulated by the physicist David Bohm. Semiempirical formula for the diffusion coefficient given by Bohm in 1946 (noted by Bohm, Burhop, and Massey, who were developing a magnetic arc for use in uranium isotope separation). Bohm diffusion was proposed (not derived from first principles) to scale as 1/B rather than the 1/B^2 scaling predicted by classical diffusion. A 1/B scaling results from assuming that particles diffuse across field lines at an optimum rate (effective collision frequency=cyclotron frequency). The 1/B scaling is observed (approximately) in most reactors. See: diffusion, microinstabilities, field lines. (09 Oct 1997) |
| gel diffusion | Diffusion in a gel, as in the case of gel diffusion precipitin tests in which the immune reactants diffuse in agar. See: immunodiffusion. (05 Mar 2000) |