| artefact | Something artificial, a distortion that does not reflect normal anatomy or pathology, not usually found in the body. For example: in radiology, the appearance on an X-ray of a surgical metal clip that obscures the clear view of an anatomical structure. (16 Dec 1997) |
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| Gibbs | J. Willard, U.S. Mathematician and physicist, 1839-1903. See: Gibbs-Donnan equilibrium, Gibbs-Helmholtz equation, Helmholtz-Gibbs theory, Gibbs' theorem, Gibbs free energy, Gibbs energy of activation. (05 Mar 2000) |
| gibbs-donnan effect | The observation that charged molecules starting on one side of a semipermeable membrane sometimes will not evenly distribute themselves by diffusion on both sides of the membrane. This effect is probably because there are other charged substances already present which cannot move through the membrane themselves and which are creating an electric field that influences the movement of the incoming charged molecules. (09 Oct 1997) |
| Gibbs-Donnan equilibrium | An equilibrium established between a charged, immobile colloid (such as clay, ion exchange resin or cytoplasm) and a solution of electrolyte. Characteristics: ions of like charge to the colloid tend to be excluded, ions of opposite charge tend to be attracted, the colloid compartment is electrically polarized relative to the solution in the same direction as the colloid charges (a Donnan potential) and the osmotic pressure is higher in the colloid compartment. (18 Nov 1997) |
| Gibbs energy of activation | The Gibbs energy that must be added to that already possessed by a molecule or molecules in order to initiate a reaction. (05 Mar 2000) |
| gibbs free energy | The total amount of energy which is either used up or released during a chemical reaction. Gibbs free energy (delta G) = (delta H) - t (delta s): where (delta H) is the change in enthalpy, calculated by adding up the amount of energy released or used up to break or form chemical bonds during the reaction, t is the temperature at which the reaction took place, and (delta S) is the change in entropy, or amount of disorder, that occurs in the molecules involved during the reaction. (09 Oct 1997) |
| Gibbs-Helmholtz equation | An equation expressing the relationship in a galvanic cell between the chemical energy transformed and the maximal electromotive force obtainable. (05 Mar 2000) |
| Gibbs' theorem | Substances that lower the surface tension of the pure dispersion medium tend to collect in its surface, whereas substances that raise the surface tension tend to remain out of the surface film. (05 Mar 2000) |
| Helmholtz-Gibbs theory | An equation expressing the relationship in a galvanic cell between the chemical energy transformed and the maximal electromotive force obtainable. (05 Mar 2000) |
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