| bond dissociation energy | This is the energy needed to break the bonds between two linked atoms. (09 Oct 1997) |
|---|---|
| molecular dissociation theory | A theory, pertaining to colour vision, that gray is the earliest of colour sensations, from which are derived, by molecular change, two paired substances that, respectively, detect yellow and blue, and that the yellow gives rise to paired substances for detection of red and green. Synonym: Ladd-Franklin theory. (05 Mar 2000) |
| complete atrioventricular dissociation | A-V dissociation not interrupted by ventricular captures. Synonym: complete A-V block. (05 Mar 2000) |
| heat of dissociation | The heat (expressed in calories or joules) expended in the dissociation of 1 mol of a substance into specified products. (05 Mar 2000) |
| pupillary light-near dissociation | A stronger near pupil response than light response; due to weak pupillomotor input, Argyll Robertson pupil, dorsal midbrain syndrome, or to misdirection of ciliary muscle fibres into the iris sphincter. Synonym: light-near dissociation. (05 Mar 2000) |
| sleep dissociation | <neurology, physiology> A condition that occurs in REM stage sleep. There is no movement of the skeletal muscles in this stage of sleep. See: REM stage sleep. (27 Sep 1997) |
| syringomyelic dissociation | Loss of pain and temperature sensation with relative retention of tactile sensation, related to a cavity in the central portion of the cord interrupting the decussation of nerve fibres. (05 Mar 2000) |
| dissociation | 1. The act of separating or state of being separated. 2. <chemistry> The separation of a molecule into two or more fragments (atoms, molecules, ions or free radicals) produced by the absorption of light or thermal energy or by solvation. 3. <psychology> A defense mechanism in which a group of mental processes are segregated from the rest of a person's mental activity in order to avoid emotional distress, as in the dissociative disorders or in which an idea or object is segregated from its emotional significance, in the first sense it is roughly equivalent to splitting, in the second, to isolation. 4. A defect of mental integration in which one or more groups of mental processes become separated off from normal consciousness and, thus separated, function as a unitary whole. Origin: L. Sociatio = union (18 Nov 1997) |
| dissociation by interference | The simultaneous operation of two separate cardiac pacemaking foci that are unassociated because of interference (a normal physiologic phenomenon) due to rendering their respective territories refractory to each other. Usually atrioventricular dissociation is indicated, the rates being quite close to each other with the atrial rate slightly faster than that of the pacemaker in control of the ventricles. Capture is in either direction, usually the ventricle by the atrium, in incomplete dissociation. H Synonym: dissociation by interference. (05 Mar 2000) |
| dissociation constant | <chemistry> In a chemical equilibrium of form A + B = AB, the equilibrium concentrations (strictly, activities) of the reactants are related such that A x B/AB = a constant, Kd, the dissociation constant, that in this simplest case has the dimensions of concentration. When A is H, this is the acid dissociation constant often designated Ka and expressed as pKa (log10Ka). (18 Nov 1997) |
| dissociation constant of a base | Expressed by the general equation [B+][OH-]/[BOH] = Kb, where BOH is the undissociated base. (05 Mar 2000) |
| dissociation constant of an acid | Expressed by general equation [H+][A-]/[HA] = Ka, where HA is the undissociated acid. (05 Mar 2000) |
| dissociation constant of water | Expressed by the equation [H+][OH-] = Kw = 10-14 at 25캜. (05 Mar 2000) |
| dissociation sensibility | The loss of the pain and the thermal senses with preservation of tactile sensibility or vice versa. (05 Mar 2000) |
| incomplete atrioventricular dissociation | A-V dissociation interrupted by ventricular captures. (05 Mar 2000) |