| gel diffusion precipitin tests | Precipitin test's in which the immune precipitate forms in a gel medium (usually agar) into which one or both reactants have diffused; generally classified in two types, in one dimension, and in two dimensions. Synonym: gel diffusion reactions. (05 Mar 2000) |
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| gel diffusion precipitin tests in one dimension | Precipitin test's in which antigen solution and antibody incorporated in agar are layered in tubes, permitting effective diffusion in the vertical dimension; the antibody-containing agar may be overlaid directly with antigen solution (single (gel) diffusion in one dimension). (05 Mar 2000) |
| gel diffusion precipitin tests in two dimensions | Precipitin test's made in a layer of agar that permits radial diffusion, in both of the horizontal dimensions, of one or both reactants. Double (gel) diffusion in two dimensions (Ouchterlony test, technique, or method) incorporates antigen and antibody solutions placed in separate wells in a sheet of plain agar, permitting radial diffusion of both reactants; this method is widely used to determine antigenic relationships; the bands of precipitate that form where the reactants meet in optimal concentration are of three patterns, referred to as reaction of identity, reaction of partial identity (cross-reaction), and reaction of nonidentity. (05 Mar 2000) |
| precipitin tests | Serologic tests in which a positive reaction manifested by visible precipitation occurs when a soluble antigen reacts with its antibody. (12 Dec 1998) |
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| 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) |
| gel diffusion reactions | Precipitin test's in which the immune precipitate forms in a gel medium (usually agar) into which one or both reactants have diffused; generally classified in two types, in one dimension, and in two dimensions. Synonym: gel diffusion reactions. (05 Mar 2000) |
| aspergillosis precipitin | <investigation> A test which is used to detect the presence of aspergillus antibodies in the blood. The normal result is read as negative or no antibodies. A strong reaction can indicate pulmonary aspergillosis. Some forms of hypersensitivity pneumonia may also yield a weakly positive test result. (27 Sep 1997) |
| ring precipitin test | A precipitin test in which antigen solution is carefully layered over antibody solution in a tube; as diffusion proceeds, a disk of precipitate forms where the antibody ratio is optimal. Synonym: ring test. (05 Mar 2000) |
| precipitin | <protein> Any antibody that forms a precipitating complex (a precipitin line) with an appropriate multivalent antigen. The term is now outmoded. (18 Nov 1997) |
| precipitin reaction | See: precipitin, precipitin test. (05 Mar 2000) |
| precipitin test | An in vitro test in which antigen is in soluble form and precipitates when it combines with added specific antibody in the presence of an electrolyte. See: gel diffusion precipitin tests, ring precipitin test. Synonym: precipitation test. (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) |
| passive diffusion | See: facilitated transport. (05 Mar 2000) |
| classical diffusion | <radiobiology> In plasma physics, diffusion due solely to scattering (collisions) of charged particles (with unlike charges) via electrical (Coulomb) interactions. (See also diffusion.) (09 Oct 1997) |
| 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) |
| neoclassical diffusion | <radiobiology> In a magnetised plasma, _classical_ diffusion refers to transport of particles due to Coulomb collisions, taking the spiral orbits in the magnetic field into account. In a toroidal magnetic field, the actual rate of diffusive transport is much higher due to slow changes in the positions of the centres of the spirals, known as banana orbits. This faster transport is called _neo-classical_. With very few exceptions the transport in toroidal devices is observed to be 10-100 times larger still, presumably due to small-scale turbulence. The observed transport is called _anomalous_ (although it actually is the normal state). (09 Oct 1997) |