| negative base excess | A measure of metabolic acidosis, usually predicted from the Siggaard-Andersen nomogram; the amount of strong alkali that would have to be added per unit volume of whole blood to titrate it to pH 7.4 while at 37캜 and at a carbon dioxide pressure of 40 mm Hg. (05 Mar 2000) |
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| negative binomial distribution | <epidemiology> A distribution which is parameterised by a mean m and an aggregation parameter k which is large when aggregation is small; in fact as k becomes large, the negative binomial distribution approximates the Poisson distribution. (05 Dec 1998) |
| negative control | Regulation of an enzyme activity by an inhibitor of that enzyme or regulation of a protein by repression of transcription. (05 Mar 2000) |
| negative convergence | The slight divergence of the visual axes when convergence is at rest, as when observing the far point or during sleep. (05 Mar 2000) |
| negative cooperativity | Cooperativity in which successive ligand molecules appear to bind with decreasing affinity. (05 Mar 2000) |
| negative crystal | <microscopy> A uniaxial crystal is optically negative if epsilon is less than omega A biaxial crystal is said to be optically negative if gamma minus beta is less than beta is less than beta minus alpha. Otherwise the crystal is positive. (05 Aug 1998) |
| negative electrode | <chemistry, physics> The electrode in an electrochemical cell toward which cations are drawn and where reduction occurs. The negatively charged electrode in a vacuum tube. (16 Mar 1998) |
| negative electrotaxis | Electrotaxis by which an organism is attracted toward an anode or repelled from a cathode. (05 Mar 2000) |
| negative end-expiratory pressure | A subatmospheric pressure at the airway at the end of expiration. (05 Mar 2000) |
| negative eyepiece | <microscopy> An eyepiece in which the real image of the object is formed between the lens elements of the eyepiece. (05 Aug 1998) |
| negative, false | A result that appears negative but fails to reveal a situation. An example of a false negative: a particular test designed to detect cancer of the toenail is negative but the person has toenail cancer. (12 Dec 1998) |
| negative feedback | This occurs where the products of a process can act at an earlier stage in the process to inhibit their own formation. The term was first used widely in conjunction with electrical amplifiers where negative feedback was applied to limit distortion of the signal by the amplification mechanism. Tends to stabilise the process. In contrast to positive feedback. (18 Nov 1997) |
| negative focal length | <physics> The focal length of a negative lens. Parallel rays impinging on a negative lens can be traced to a virtual focus which exists on the same side of the lens as the impinging rays. The distance from the second principal point of the lens to this second focal point is measured on the same side of the lens as is the object. See: negative lens, focal length. (05 Aug 1998) |
| negative G | Gravity in a foot-to-head direction in flying, or in standing on one's head; opposite of positive G. (05 Mar 2000) |
| negative image | Continuation of visual impression after cessation of stimuli causing the original image. (12 Dec 1998) |