| antigenic modulation | Loss of detectable antigen from the surface of a cell after incubation with antibodies. This is one method in which some tumours escape detection by the immune system. Antigenic modulation of target antigens also reduces the therapeutic effectiveness of treatment by monoclonal antibodies. (12 Dec 1998) |
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| modulation | Alteration in the effectiveness of voltage gated or ligand gated ion channels by changing the characteristics of current flow through the channels. The mechanism is thought to involve second messenger systems. (18 Nov 1997) |
| modulation transfer function | <microscopy> A mathematical function that expresses the ability of an optical or electronic device to transfer signals faithfully as a function of the spatial or temporal frequency of the signal. The modulation transfer function is the ratio of percentage modulation of a sinusoidal signal leaving to that entering the device over the range of frequencies of interest. The modulation transfer function is usually presented as a graph of modulation transfer function versus log (frequency). For a square wave signal, the function is known as the CTF. Acronym: MTF (26 Mar 1998) |
| amplitude | 1. State of being ample; extent of surface or space; largeness of dimensions; size. "The cathedral of Lincoln . . . Is a magnificent structure, proportionable to the amplitude of the diocese." (Fuller) 2. Largeness, in a figurative sense; breadth; abundance; fullness. Of extent of capacity or intellectual powers. "Amplitude of mind." . "Amplitude of comprehension." . Of extent of means or resources. "Amplitude of reward." . 3. <astronomy> The arc of the horizon between the true east or west point and the center of the sun, or a star, at its rising or setting. At the rising, the amplitude is eastern or ortive: at the setting, it is western, occiduous, or occasive. It is also northern or southern, when north or south of the equator. The arc of the horizon between the true east or west point and the foot of the vertical circle passing through any star or object. 4. The horizontal line which measures the distance to which a projectile is thrown; the range. 5. <physics> The extent of a movement measured from the starting point or position of equilibrium; applied especially to vibratory movements. 6. <mathematics> An angle upon which the value of some function depends; a term used more especially in connection with elliptic functions. Magnetic amplitude, the angular distance of a heavenly body, when on the horizon, from the magnetic east or west point as indicated by the compass. The difference between the magnetic and the true or astronomical amplitude (see 3 above) is the "variation of the compass." Origin: L. Amplitudo, fr. Amplus: cf. F. Amplitude. See Ample. Source: Websters Dictionary (01 Mar 1998) |
| amplitude of accommodation | The difference in refractivity of the eye at rest and when fully accommodated. (05 Mar 2000) |
| amplitude of convergence | The distance between the near point and far point of convergence. Synonym: range of convergence. (05 Mar 2000) |
| amplitude of pulse | See: average pulse magnitude, peak magnitude. (05 Mar 2000) |
| phase-amplitude contrast | <microscopy> The separation and recombination of direct vs. Diffracted rays in a light microscope adjusted to Kohler illumination. at the lower focal plane of the condenser there is an annular diaphragm with an opaque central stop. Through this diaphragm rays are focused as a hollow cone onto the specimen. In the back focal plane of the objective there is a conjugate annular diaphragm (phase plate). If here the undiffracted rays are retarded (by a transparent film of proper thickness on the annulus of the phase plate), bright contrast results. If, instead, the phase-delay film is on the central spot, dark contrast results. With either a bright or a dark-contrast phase plate, the annulus is usually coated with a partially absorbing (very thin) film of silver (Zernike method) or carbon soot (Wilska method) to reduce the higher amplitude (intensity) of the undiffracted rays. (05 Aug 1998) |
| minimal amplitude nystagmus | Nystagmus of so small an amplitude that it is not detected by the usual clinical tests. Synonym: minimal amplitude nystagmus. Origin: micro-+ G. Nystagmos, a nodding (05 Mar 2000) |
| half amplitude pulse duration | The time, in milliseconds, required for a wave form to reach half of its full magnitude. (05 Mar 2000) |
| tidal amplitude | The magnitude of the difference in elevation between low and high tides at a particular point in a body of water. (09 Oct 1997) |