“dispersion”的概念、定义、翻译、参考文献-科学参考

dispersion

Physics

The splitting up of a ray of light of mixed wavelengths by refraction into its components. Dispersion occurs because the deviation for each wavelength is different on account of the different speeds at which waves of different wavelengths pass through the refracting medium. If a ray of white light strikes one face of a prism and passes out of another face, the white light will be split into its components and the full visible spectrum will be formed. The dispersive power of a prism (or other medium) for white light is defined by

$(n_{b} - n_{r}) / (n_{y} - 1),$

where n_b, n_r, and n_y are the refractive indices for blue, red, and yellow light respectively. The term is sometimes applied to the separation of wavelengths produced by a diffraction grating.

Mathematics

A measure of dispersion is a way of describing how scattered or spread out the observations in a sample are. The term is also applied similarly to a random variable. Common measures of dispersion are the range, interquartile range, mean absolute deviation, variance, and standard deviation. The range may be unduly affected by odd high and low values. The mean absolute deviation is difficult to work with algebraically. The standard deviation is in the same units as the data, and it is this that is most often used. The interquartile range may be appropriate when the median is used as the measure of location.

Astronomy

1. The splitting of light into its constituent colours by a prism or diffraction grating. High dispersion means that the spectrum of an object is spread out more than in low dispersion, and thus more details can be seen; the degree of dispersion thus governs spectral resolution. A high-resolution spectrograph will produce a typical dispersion of 1–2 nm/mm.

2. A phenomenon in which electromagnetic waves of different frequencies travel at different speeds in certain media, such as ionized gases (plasmas). Interstellar matter is largely ionized hydrogen and is therefore dispersive. The time delay of a wave introduced by dispersion depends on the electron density along the line of sight and is inversely proportional to the square of the observing frequency. Dispersion smears out rapid fluctuations in the source, a matter of great importance in the observation of pulsars. See also Dedispersion.

Statistics

See index of dispersion.

Chemical Engineering

The mixture of one substance dispersed within another as bubbles, drops, or particles. A dispersed phase is the dispersion of one phase within another such as suspended gas bubbles, droplets, or solid particles dispersed in a liquid. Fog is the dispersion of water droplets in air, a colloid is a dispersion of suspended particles, and margarine consists of water dispersed in a hydrogenated fat phase. Compare continuous phase. Dispersed flow is a two-phase flow of liquid in a vapour or gas in which the liquid is almost entirely entrained as fine droplets.

Computer

See measures of variation.

Electronics and Electrical Engineering

Any process that separates radiation into components with different frequencies, energies, velocities, or other characteristics. In a transmission system in which the wave velocity is not constant with frequency, the components of a multifrequency signal will travel different distances in a certain time, leading to dispersion of the signal.

Geology and Earth Sciences

1. The spreading of a body of water as it flows. Lateral dispersion is the widening of the path taken by groundwater as it flows from a known point of origin through a rock matrix, due to its movement around individual mineral grains within the main rock body. Unless it flows in well-defined fissures or fractures, water does not travel through a rock in a straight line but is forced to flow across a widening front because of the granular nature of the rock matrix. Longitudinal dispersion is the spreading out of a body of water along its own flow path, due to the differences in water velocities in larger and smaller pores of the rock. Both modes of dispersion are normally observed by means of tracers. Lateral and longitudinal dispersion also occur in river channels, where they are due to differences in flow velocity across the channel and between the water surface and the bed, and also to random fluctuations in velocity caused by turbulent eddies.
2. The process of separating soil particles (as in aggregates) from each other so that they may react as individual particles. Aggregates or peds of soil particles are destroyed by dispersion (and their formation is initiated by flocculation).
3. The distortion of a wave train that occurs when velocity varies with frequency and consequently the phase velocity is not the same as the group velocity. There is minimal dispersion for most body waves (although electromagnetic body waves are subject to considerable dispersion) but it is important for surface waves, especially Love waves, particularly in the presence of velocity-layering near the surface.
4. In mineral optics, a measure of the difference in refractive index, determined by direct observation of the biaxial interference figure using the two extreme wavelengths of the visible spectrum (red and violet). Both isogyres are observed for red and violet tints.
5. See also swell.

Economics

Scattering or spread of the data points around the sample mean. Commonly used measures of dispersion are the standard deviation and the sample coefficient of variation, defined as the ratio of the standard deviation to the sample mean; the advantage of the latter is that it does not depend on the units of measurement.

单词	dispersion
释义	dispersion Physics The splitting up of a ray of light of mixed wavelengths by refraction into its components. Dispersion occurs because the deviation for each wavelength is different on account of the different speeds at which waves of different wavelengths pass through the refracting medium. If a ray of white light strikes one face of a prism and passes out of another face, the white light will be split into its components and the full visible spectrum will be formed. The dispersive power of a prism (or other medium) for white light is defined by $(n_{b} - n_{r}) / (n_{y} - 1),$ where n_b, n_r, and n_y are the refractive indices for blue, red, and yellow light respectively. The term is sometimes applied to the separation of wavelengths produced by a diffraction grating. Mathematics A measure of dispersion is a way of describing how scattered or spread out the observations in a sample are. The term is also applied similarly to a random variable. Common measures of dispersion are the range, interquartile range, mean absolute deviation, variance, and standard deviation. The range may be unduly affected by odd high and low values. The mean absolute deviation is difficult to work with algebraically. The standard deviation is in the same units as the data, and it is this that is most often used. The interquartile range may be appropriate when the median is used as the measure of location. Astronomy 1. The splitting of light into its constituent colours by a prism or diffraction grating. High dispersion means that the spectrum of an object is spread out more than in low dispersion, and thus more details can be seen; the degree of dispersion thus governs spectral resolution. A high-resolution spectrograph will produce a typical dispersion of 1–2 nm/mm. 2. A phenomenon in which electromagnetic waves of different frequencies travel at different speeds in certain media, such as ionized gases (plasmas). Interstellar matter is largely ionized hydrogen and is therefore dispersive. The time delay of a wave introduced by dispersion depends on the electron density along the line of sight and is inversely proportional to the square of the observing frequency. Dispersion smears out rapid fluctuations in the source, a matter of great importance in the observation of pulsars. See also Dedispersion. Statistics See index of dispersion. Chemical Engineering The mixture of one substance dispersed within another as bubbles, drops, or particles. A dispersed phase is the dispersion of one phase within another such as suspended gas bubbles, droplets, or solid particles dispersed in a liquid. Fog is the dispersion of water droplets in air, a colloid is a dispersion of suspended particles, and margarine consists of water dispersed in a hydrogenated fat phase. Compare continuous phase. Dispersed flow is a two-phase flow of liquid in a vapour or gas in which the liquid is almost entirely entrained as fine droplets. Computer See measures of variation. Electronics and Electrical Engineering Any process that separates radiation into components with different frequencies, energies, velocities, or other characteristics. In a transmission system in which the wave velocity is not constant with frequency, the components of a multifrequency signal will travel different distances in a certain time, leading to dispersion of the signal. Geology and Earth Sciences 1. The spreading of a body of water as it flows. Lateral dispersion is the widening of the path taken by groundwater as it flows from a known point of origin through a rock matrix, due to its movement around individual mineral grains within the main rock body. Unless it flows in well-defined fissures or fractures, water does not travel through a rock in a straight line but is forced to flow across a widening front because of the granular nature of the rock matrix. Longitudinal dispersion is the spreading out of a body of water along its own flow path, due to the differences in water velocities in larger and smaller pores of the rock. Both modes of dispersion are normally observed by means of tracers. Lateral and longitudinal dispersion also occur in river channels, where they are due to differences in flow velocity across the channel and between the water surface and the bed, and also to random fluctuations in velocity caused by turbulent eddies. 2. The process of separating soil particles (as in aggregates) from each other so that they may react as individual particles. Aggregates or peds of soil particles are destroyed by dispersion (and their formation is initiated by flocculation). 3. The distortion of a wave train that occurs when velocity varies with frequency and consequently the phase velocity is not the same as the group velocity. There is minimal dispersion for most body waves (although electromagnetic body waves are subject to considerable dispersion) but it is important for surface waves, especially Love waves, particularly in the presence of velocity-layering near the surface. 4. In mineral optics, a measure of the difference in refractive index, determined by direct observation of the biaxial interference figure using the two extreme wavelengths of the visible spectrum (red and violet). Both isogyres are observed for red and violet tints. 5. See also swell. Economics Scattering or spread of the data points around the sample mean. Commonly used measures of dispersion are the standard deviation and the sample coefficient of variation, defined as the ratio of the standard deviation to the sample mean; the advantage of the latter is that it does not depend on the units of measurement.
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