| two-stream instability | <radiobiology> Instability which can develop when a stream of particles of one type has a velocity distribution with its peak well separated from that of another type of particle through which it is flowing. A stream of energetic electrons passing through a cold plasma can, for example: excite ion waves which will grow rapidly in magnitude at the expense of the kinetic energy of the electrons. (09 Oct 1997) |
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| two-sympathin theory | A theory, now obsolete, advanced by Cannon and Rosenblueth that two different types of substances (sympathin E and I) diffuse into circulation when adrenergic nerves are stimulated, although the mediator itself is the same. (05 Mar 2000) |
| two-tail test | A statistical test based on the assumption that the data are distributed in both directions from some central value. (05 Mar 2000) |
| two-way catheter | A catheter with two lumens, allowing irrigation and aspiration. Synonym: two-way catheter. (05 Mar 2000) |
| uniform rate hypothesis | <biology> This states that any two evolving organismal lineages diverge from a common ancestor at a constant rate with respect to each other. (09 Oct 1997) |
| unineme hypothesis | <cell biology, molecular biology> This states that that a chromatid has only one DNA duplex, which goes from one end of the chromatid to the other. (09 Oct 1997) |
| zwitter hypothesis | That an amphoteric molecule (e.g., an amino acid) has, at its isoelectric point, equal numbers of positive and negative charges, thus becoming a zwitterion. (05 Mar 2000) |
| frustration-aggression hypothesis | The theory that frustration may lead to aggression, but that aggression is always the result of some form of frustration. (05 Mar 2000) |
| Lyon hypothesis | <genetics> Hypothesis, first advanced by Lyon, concerning the random inactivation of one of the two X chromosomes of the cells of female mammals. In consequence females are chimaeric for the products of the X chromosomes, a situation that has been exploited in female Negroes (who are heterotypic for isozymes of glucose 6 phosphate dehydrogenase) as a means to confirm the monoclonal origin of papillomas and of atherosclerotic plaques. (20 Mar 1998) |