| 释义 |
attenuation
at·ten·u·ate A0509700 (ə-tĕn′yo͞o-āt′)v. at·ten·u·at·ed, at·ten·u·at·ing, at·ten·u·ates v.tr.1. To make slender, fine, or small: The drought attenuated the river to a narrow channel.2. To reduce in force, value, amount, or degree; weaken: Medicine attenuated the fever's effect.3. To lessen the density of; rarefy.4. Biology To make (bacteria or viruses) less virulent.5. Electronics To reduce (the amplitude of an electrical signal) with little or no distortion.v.intr. To become thin, weak, or fine.adj. (-yo͞o-ĭt)1. Reduced or weakened, as in strength, value, or virulence.2. Botany Gradually tapering to a slender point.
[Latin attenuāre, attenuāt- : ad-, ad- + tenuāre, to make thin (from tenuis, thin; see ten- in Indo-European roots).]
at·ten′u·a′tion n.attenuation (əˌtɛnjʊˈeɪʃən) n1. the act of attenuating or the state of being attenuated2. (General Physics) the loss of energy suffered by radiation as it passes through matter, esp as a result of absorption or scatteringat•ten•u•a•tion (əˌtɛn yuˈeɪ ʃən)
n. 1. the act of attenuating or the state of being attenuated. 2. the process by which a virus, bacterium, etc., changes under laboratory conditions to become harmless or less virulent. [1585–95; (< Middle French) < Latin] attenuation1. Decrease in intensity of a signal, beam, or wave as a result of absorption of energy and of scattering out of the path of a detector, but not including the reduction due to geometric spreading, i.e., the inverse square of distance effect.
2. In mine warfare, the reduction in intensity of an influence as distance from the source increases.
3. In camouflage and concealment, the process of making an object or surface less conspicuous by reducing its contrast to the surroundings and/or background. Also called tone down.Thesaurus| Noun | 1. | attenuation - weakening in force or intensity; "attenuation in the volume of the sound"fadingweakening - becoming weaker | | 2. | attenuation - the property of something that has been weakened or reduced in thickness or densityweakness - the property of lacking physical or mental strength; liability to failure under pressure or stress or strain; "his weakness increased as he became older"; "the weakness of the span was overlooked until it collapsed" |
attenuationnounThe depletion or sapping of strength or energy:debilitation, depletion, devitalization, enervation, enfeeblement, impoverishment.Translationsaffaiblissementatténuationattenuazioneattenuation
Attenuation The reduction in level of a transmitted quantity as a function of a parameter, usually distance. It is applied mainly to acoustic or electromagnetic waves and is expressed as the ratio of power densities. Various mechanisms can give rise to attenuation. Among the most important are geometrical attenuation, absorption, and scattering. For unconfined radiation from a point source in free space, the power density (watts per square meter) decreases in proportion to the square of the distance. The power densities, I1 and I2, at distances r1 and r2 from the source, are related by Eq. (1). (1)  If the signal, in a parallel beam so that there is no geometrical attenuation, passes through a lossy medium, absorption reduces the power level, I, exponentially with distance, x, according to Eq. (2), where a (2)  is the attenuation coefficient. See Absorption of electromagnetic radiation, Sound absorption Scattering is said to occur if the power is not absorbed in the medium but scattered from inhomogeneities. See Scattering of electromagnetic radiation More complicated situations occur with guided waves, such as acoustic waves in pipes or electromagnetic waves in transmission lines or waveguides, where absorption may take place and irregularities may cause reflection of some power. In electric circuits, constituent elements are often described as attenuators when they reduce the level of signals passing through them. Attenuation is usually measured in terms of the logarithm of the power ratio, the units being the neper or the decibel. See Decibel attenuation (ă-ten-yoo-ay -shŏn) The reduction in magnitude of a quantity as a function of distance from source or of some other parameter. The attenuation of a beam of radiation, i.e. the reduction in intensity or flux density, results from absorption and/or scattering of the waves or particles as they pass through matter.attenuation[ə‚ten·yə′wā·shən] (botany) Tapering, sometimes to a long point. (electricity) The exponential decrease with distance in the amplitude of an electrical signal traveling along a very long uniform transmission line, due to conductor and dielectric losses. (engineering) A process by which a material is fabricated into a thin, slender configuration, such as forming a fiber from molten glass. (microbiology) Weakening or reduction of the virulence of a microorganism. (physics) The reduction in level of a quantity, such as the intensity of a wave, over an interval of a variable, such as the distance from a source. sound attenuationThe reduction in the intensity or in the sound pressure level of sound which is transmitted from one point to another. Also see sound insulation.attenuationThe decrease in the intensity of a signal, beam, or wave as a result of the absorption of energy (by the terrain or medium over which, or through which, the energy travels) and of scattering out of the path to the detector but not including the reduction as a result of geometric spreading. Attenuation is usually expressed in dB (decibles). The term is often used as a misnomer for attenuation coefficient, which is expressed in dB per kilometer.attenuation (communications)The progressive reduction in amplitude of asignal as it travels farther from the point of origin.
For example, an electric signal's amplitude reduces withdistance due to electrical impedance. Attenuation isusually measured in decibels Attenuation does not imply appreciable modification of theshape of the waveform (distortion), though as the signalamplitude falls the signal-to-noise ratio will also fallunless the channel itself is noise free or the signal isamplified at some intermediate point(s) along the channel.
["Networking Essentials, second edition",Microsoft Corporation, pub. Microsoft Press 1997].attenuationLoss of signal power in a transmission. Often abbreviated "ATTN."attenuation
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 matterat·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 - 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.
- 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.LegalSeeAttenuateAcronymsSeeATTENattenuation
Synonyms for attenuationnoun the depletion or sapping of strength or energySynonyms- debilitation
- depletion
- devitalization
- enervation
- enfeeblement
- impoverishment
Synonyms for attenuationnoun weakening in force or intensitySynonymsRelated Wordsnoun the property of something that has been weakened or reduced in thickness or densityRelated Words |