| dipole theory | A theory in which the activation current of the heart is conceived as a single net moving dipole, the positive pole leading. (05 Mar 2000) |
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| DLVO theory | <cell biology> Theory of colloid flocculation advanced independently by Derjaguin & Landau and by Vervey & Overbeek and subsequently applied to cell adhesion. There exist distances (primary and secondary minima) at which the forces of attraction exceed those of electrostatic repulsion, an adhesion will thus be formed. For cells there is quite good correlation between the calculated separations of primary and secondary minima and the cell separations in tight junctions (1-2nm) and more general cell cell appositions (12-20nm) respectively, although it is clear that other factors (particularly cell adhesion molecules) also play an important part. (18 Nov 1997) |
| double bind theory | Contradictions in verbal and behavioural communication between parent and child (patient) which entrap the child because he is unable to comment on the incongruity or to escape from the situation. (12 Dec 1998) |
| duplicity theory of vision | That the cones of the retina function in bright light and the rods function in dim light. (05 Mar 2000) |
| implantation theory of the production of endometriosis | That, at the time of menstruation, cells of the uterine mucosa pass through the fallopian tubes and escape into the pelvic cavity where they implant themselves on the peritoneum. (05 Mar 2000) |
| incasement theory | Archaic theory that the embryo was fully formed in miniature within a gamete at the time of conception. See: homunculus. Synonym: emboitement, incasement theory. (05 Mar 2000) |
| quantum theory | The theory that the radiation and absorption of energy take place in definite quantities called quanta (e) which vary in size and are defined by the equation e=hv in which h is planck's constant and v is the frequency of the radiation. (12 Dec 1998) |
| quasilinear theory | <physics> A weakly nonlinear theory of plasma oscillations which uses perturbation theory and the random phase approximation to find the time-evolution of the plasma state. (09 Oct 1997) |
| information theory | An interdisciplinary study dealing with the transmission of messages or signals, or the communication of information. Information theory does not directly deal with meaning or content, but with physical representations that have meaning or content. It overlaps considerably with communication theory and cybernetics. (12 Dec 1998) |
| instructive theory | Theory of antibody production, now considered untenable, in which antigen acted as template for the production of specific antibody as opposed to the clonal selection theory in which pre existing variation occurs and appropriate clones are selectively expanded. (18 Nov 1997) |
| Ollier's theory | A theory of compensatory growth; after resection of the articular extremity of a bone, the articular cartilage of the other bone entering into the structure of the joint takes on an increased growth. (05 Mar 2000) |
| omega-oxidation theory | That the oxidation of fatty acids commences at the CH3 group, i.e., the terminal or omega-group; beta-oxidation then proceeds at both ends of the fatty acid chain. (05 Mar 2000) |
| overproduction theory | The loss or destruction of a part or element in the organic world is likely to result in compensatory replacement and overproduction of tissue during the process of regeneration or repair (or both), as in the formation of callus when a fractured bone heals. Synonym: overproduction theory. (05 Mar 2000) |
| oxygen deprivation theory of narcosis | That narcotics inhibit oxidation, which causes the cell to be narcotised. (05 Mar 2000) |
| telephone theory | A theory of pitch perception which states that the cochlea possesses no faculty of sound analysis, but that the frequency of the impulses transmitted over the auditory nerve fibres corresponds to the frequency of the sound vibrations, and is the sole basis for pitch discrimination; a theory no longer tenable. (05 Mar 2000) |