| ADT | Accepted Dental Therapeutics; adenosine triphosphate; admission, discharge, transfer; agar-gel diffu... |
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| AGDD | agar gel double diffusion |
| CDC | calculated date of confinement; cancer diagnosis center; capillary diffusion capacity; cell division... |
| DC | daily census; data communication; data conversion; decrease; deep compartment; Dental Corps; deoxych... |
| DD | dangerous drug; data definition; day of delivery; degenerated disc; degenerative disease; delusional... |
| Hufner's equation | <physiology> An equation expressing the relationship between myoglobin dissociation and oxygen partial pressure: ([MBO2]/[Mb]) = (K x pO2). (05 Mar 2000) |
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| 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) |
| Nernst equation | <physics> A basic equation of biophysics that describes the relationship between the equilibrium potential difference across a semipermeable membrane and the equilibrium distribution of the ionic permeant species. It is described by: E = (RT/zF).ln[C1/C2 Where E is the potential on side 2 relative to side 1 in volts), R is the gas constant (8.314 J Kexp 1 molexp 1), T is the absolute temperature, z is the charge on the permeant ion, f is the Faraday constant (96500 C molexp 1) and C1 and C2 are the concentrations (more correctly activities) of the ions on sides 1 and 2 of the membrane. It can be seen that this equation is a solution of the more general equation of electrochemical potential, for the special case of equilibrium. The equation described the voltage generated by ion selective electrodes, like the laboratory pH electrode and approximates the behaviour of the resting plasma membrane (see resting potential). (13 Nov 1997) |
| Nernst's equation | The equation relating the equilibrium potential of electrodes to ion concentrations; the equation relating the electrical potential and concentration gradient of an ion across a permeable membrane at equilibrium: E = [RT / nF Origin: Ln (C1/C 2)], where E = potential, R = absolute gas constant, T = absolute temperature, n = valence, F = the Faraday, ln = the natural logarithm, and C1 and C2 are the ion concentrations on the two sides; in nonideal solutions, concentration should be replaced by activity. See: Nernst's theory, activity. (05 Mar 2000) |
| Svedberg equation | See: sedimentation constant. (05 Mar 2000) |
| difference equation | <epidemiology> The mathematical formulation corresponding to a discrete time model. (05 Dec 1998) |
| differential equation | <epidemiology> The mathematical formulation corresponding to a continuous model; an equation involving derivatives. (05 Dec 1998) |
| diffusion | The process of becoming diffused or widely spread, the spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to the system. (18 Nov 1997) |
| diffusion anoxia | Diffusion hypoxia severe enough to result in the absence of oxygen in alveolar gas. (05 Mar 2000) |
| diffusion chambers, culture | Devices used in a technique by which cells or tissues are grown in vitro or, by implantation, in vivo within chambers permeable to diffusion of solutes across the chamber walls. The chambers are used for studies of drug effects, osmotic responses, cytogenic and immunologic phenomena, metabolism, etc., and include tissue cages. (12 Dec 1998) |
| 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) |
| diffusion constant | 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) |
| diffusion hypoxia | Abrupt transient decrease in alveolar oxygen tension when room air is inhaled at the conclusion of a nitrous oxide anaesthesia, because nitrous oxide diffusing out of the blood dilutes the alveolar oxygen. (05 Mar 2000) |
| diffusion limitation | The boundary layer hypothesis, that the proliferation of cells in culture is limited by the rate at which some essential component (almost certainly a growth factor) diffuses from the bulk medium into the layer immediately adjacent to the plasma membrane. By spreading out, a cell obtains a supra threshold level of the factor and can divide, if unable to spread (because of crowding or poor adhesion) then the cell will remain in the G0 stage of the cell cycle. (18 Nov 1997) |
| diffusion method | A method for the study of bacterial enzymes in which agar is mixed with the material (e.g., starch or milk) which is to serve as an indicator of the enzyme action and is inoculated and plated; if the bacteria produce enzymes digesting the admixed material, there will be a zone of clearing in the medium about each colony. Synonym: diffusion method. (05 Mar 2000) |