attenuation


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attenuation

 [ah-ten″u-a´shun]
1. the act of thinning or weakening.
2. the change in the virulence of a pathogenic microorganism induced by passage through another host species, decreasing its virulence for the native host and increasing it for the new host. This is the basis for the development of live vaccines.
3. the change in a beam of radiation as it passes through matter. The intensity of the electromagnetic radiation decreases as its depth of penetration increases.

at·ten·u·a·tion

(ă-ten'yū-ā'shŭn),
1. The act of attenuating.
2. Diminution of virulence in a strain of an organism, obtained through selection of variants that occur naturally or through experimental means.
3. Loss of energy of a beam of radiant, ultrasound, or other energy because of absorption, scattering, beam divergence, and other causes as the beam propagates through a medium.
4. Regulation of termination of transcription; involved in control of gene expression in specific tissues.

attenuation

A generic term for a reduction or diminution of activity, intensity, power or virulence of a reaction or effect, or an organism’s ability to grow and/or multiply.
 
Homeopathy
A decrease of an absolute concentration of a homeopathic remedy by serial dilution; according to the law of the infinitesimal dose, the more the substance is attenuated (diluted), the greater its effect.

Imaging
The decrease in intensity of a beam by either absorption or scattering attenuation.
 
Molecular biology
The regulation of transcription termination by interfering with mRNA elongation, a process restricted to prokaryotes. Slowed translation through a regulatory region allows formation of an RNA 2º structure that promotes termination; attenuation requires coupled transcription and translation.
 
Microbiology
A decrease in virulence of a microorganism (e.g., that of bacille Calmette-Guerin (BCG), a strain of Mycobacterium bovis that has been weakened by multiple (238) subcultures on a bile-glycerine medium). The resulting bacterium is immunogenic—i.e., capable of eliciting antibody formation—but non-virulent; live attenuated organisms are used to produce the poliomyelitis vaccine, but these may revert to a wild type.
 
Radiation biology
A process by which a beam of radiation decreases in intensity when passing through material due to absorption and scattering processes, leading to a decrease in flux density of the beam when projected through matter.

attenuation

A generic term for a reduction or diminution of activity, intensity, power, or virulence of a reaction, effect, or organisms ability to grow and/or multiply Microbiology ↓ virulence of a microorganism–eg, that of bacillus Calmette-Guerin–BCG, a strain of Mycobacterium bovis that has been weakened by multiple–238–subcultures on a bile-glycerine medium; the resulting bacterium is immunogenic, ie capable of eliciting antibody formation, but non-virulent; live attenuated organisms are used to produce the poliomyelitis vaccine but these may revert to a wild type Radiation biology A process by which a beam of radiation is ↓ in intensity when passing through material, due to absorption and scattering processes, leading to a ↓ in flux density of the beam when projected through matter

at·ten·u·a·tion

(ă-ten'yū-ā'shŭn)
1. The act of attenuating.
2. Diminution of virulence in a strain of an organism, obtained through selection of variants that occur naturally or through experimental means.
3. Loss of energy of a beam of radiant energy due to absorption, scattering, beam divergence, and other causes as the beam propagates through a medium.
4. Regulation of termination of transcription; involved in the control of gene expression in specific tissues.

attenuation

  1. the loss of virulence of a microbial pathogen so that although still alive, it is no longer pathogenic. In this state it is able to stimulate beneficial ANTIBODY production when used as a VACCINE. Various procedures are used to attenuate the virulence of a pathogen, e.g. the ageing of cultures, or the passing of the pathogen through an unnatural host. Examples of vaccines using attenuated viruses are the Sabin polio vaccine, RUBELLA vaccine, MEASLES vaccine and MUMPS vaccine.
  2. a regulatory process in some prokaryotic biosynthetic operons in which mRNA synthesis terminates at an ATTENUATOR.

attenuation 

1. A reduction of intensity of a radiation as it passes through an absorbing or scattering medium.
2. Narrowing of a blood vessel.
3. See penalization.
References in periodicals archive ?
A list of 30 attenuation relations was selected (after Bommer et al., 2010).
One can observe the usual [[omega].sup.2] dependence of the attenuation in the low-frequency region, where [omega][tau] [much less than] 1.
So, a fixed value of a may introduce nonignorable errors in the retrieval of [A.sub.H], which in turn affects the attenuation correction of radar reflectivity.
The attenuation function [W.sub.[sigma]] just describes the propagation effect of planar earth with finite conductivity, without considering the curvature of the earth, and it can be expressed as below (e.g., Wait [19], Cooray [20], Zhang et al.
2 testing point = straight pipeline shock wave overpressure attenuation coefficient [K.sub.1]
The absorption index k, in terms of attenuation factor and phase factor is given as under [1]:
Consequently, it must be approximated to calculate the attenuation rate along the considered wave paths.
However, in the case of the present study the instrumental configuration is slightly different to that of [17]: as the radiation diagrams of the two low-cost antennas are slightly different, the attenuation cannot be analyzed using the signals recorded by the mast antenna.
Firstly, the parameter y in attenuation coefficient has a large value from its expression.
The linear attenuation coefficient ([mu]) is affected strongly by the energy of photons, which change along their paths inside the matter.
The designs utilize PIN diode semiconductor technology that generates extremely fast switching performance between attenuation states over wide frequency bands.