| visual extinction | A condition in which individual stimuli are seen correctly, but when the nasal visual field of one eye and the temporal visual field of the fellow eye are stimulated simultaneously, one field is blind. Synonym: visual extinction. (05 Mar 2000) |
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| molar extinction coefficient | Absorbance (of light) per unit path length (usually the centimeter) and per unit of concentration (moles per liter); a fundamental unit in spectrophotometry. Synonym: absorbancy index, absorptivity, molar absorbancy index, molar absorptivity, molar extinction coefficient. (05 Mar 2000) |
| high extinction microscopy | <technique> Polarized-light, interference, fluorescence, and other modes of microscopy using polarization rectifiers and other devices to achieve a high degree of back- ground extinction in order to bring out the signal originating from a very small degree of birefringence, optical path difference, fluorescence etc. (05 Aug 1998) |
| specific extinction | Absorbance (of light) per unit path length (usually the centimeter) and per unit of mass concentration. Compare: molar absorption coefficient. Synonym: absorbancy index, absorptivity, extinction coefficient, specific extinction. (05 Mar 2000) |
| extinction | 1. <ecology> The death of an entire species. 2. <psychology> The procedure of presenting the conditioned stimulus without reinforcement to an organism previously conditioned. It refers also to the diminution of a conditioned response resulting from this procedure. (27 Jun 1999) |
| extinction angle | <microscopy> The angle between the nearer vibration direction and a prominent direction of the crystal. It never exceeds 45 degrees (05 Aug 1998) |
| extinction coefficient | <chemistry> A constant used in the Beer-Lambert Law which relates the concentration of the substance being measured (in moles) to the absorbance of the substance in solution (how well the substance in solution blocks light beamed through it from getting out on the other side). (09 Oct 1997) |
| extinction factor | <microscopy> In a polarizing or Differential Interference Contrast microscope, the ratio of the amount of light that is transmitted with the axes of the polars parallel over the amount transmitted with their axes crossed. Unless the lenses are rectified, the extinction factor drops exponentially as the numerical aperture is increased. Acronym: EF (26 Mar 1998) |
| extinction oblique | <microscopy> Vibration directions oblique to the long direction of the crystal or fibre. (05 Aug 1998) |
| extinction parallel | <microscopy> Vibration directions parallel and perpendicular to the long direction of the crystal or fibre. (05 Aug 1998) |
| extinction symmetrical | <microscopy> Vibration directions bisecting a prominent crystal profile angle. (05 Aug 1998) |
| undulose extinction | <microscopy> Nonuniform extinction of a substance between crossed polars. The areas of complete extinction move progressively with a fanlike motion across the surface of the substance as the stage is rotated. (05 Aug 1998) |
| adhesion phenomenon | A phenomenon manifested by the adherence of antigen-antibody-complement complex to "indicator cells" (microorganisms, platelets, leukocytes, or erythrocytes), the reaction being sensitive and specific for the antigen and antibody in the complex. Synonym: erythrocyte adherence phenomenon, immune adherence phenomenon, red cell adherence phenomenon. (05 Mar 2000) |
| AFORMED phenomenon | As induced pulsus alternans progresses, a state in which alternating heart depolarisations fail to eject any blood, thus allowing longer diastolic filling; the subsequent beat is then able to produce a significant ejection; at high rates the cardiac minute volume and blood pressure may appear normal. Origin: Alternating, failure of response, mechanical, to electrical depolarisation (05 Mar 2000) |
| all-or-nothing phenomenon | <physiology> Refers to the phenomenon where the strength of a nerve impulse is not dependent on the strength of the stimulus. Instead, there is a threshold level of stimulus strength that must be reached before the nerve will fire an impulse (at full capacity). Below the threshold, the nerve will not fire at all. <cardiology> It also refers to the same phenomenon observed in the heart muscle, which will either contract fully or not at all. <psychology> In studies of behaviour, it refers to the same phenomenon where a behavioural stimulus will either produce a complete response or no response at all. Also called all-or-nothing principle, all-or-none law, all-or-none responsiveness, etc. (15 Nov 1997) |