morphology-density relation bâzâneš-e rixt-cagâli Fr.: relation morphologie-densité An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation. → morphology; → density; → relation. |
neutral density filter pâlâye-ye cagâli-ye natâr Fr.: filtre neutre A filter having a flat response over the range of wavelengths of interest. Also called neutral filter or gray filter. |
nuclear density cagâli-ye haste-yi (#) Fr.: densité nucléaire The density of an atomic nucleus (about 10^{14} g/cm^{3}). |
number density cagâli-ye adadi Fr.: densité nmérique Number of a particular type of object found in each unit volume. |
optical density cagâli-ye nuri Fr.: densité optique The transmittance of a point on a photographic negative equal to the log to the base 10 of the reciprocal of the transmittance through the negative at that point. |
period-mean density relation bâzâneš-e dowré-cagâli-ye miyângin Fr.: relation période-densité moyenne A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)^{1/2}, where ρ is the mean density, γ the ratio of → specific heats (C_{p}/C_{v}), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs. |
Planck density cagâli-ye Planck Fr.: densité de Planck The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρ_{P} = c^{5}/(ħG^{2}) ≅ 5.16 x 10^{93} g cm^{-3}, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant. |
potential density cagâli-ye tavand Fr.: densité potentielle Of a fluid parcel at pressure P, the density that it would acquire if adiabatically brought to a reference pressure. |
power spectral density cagâli-ye binâbi-ye tavân Fr.: densité spectrale de puissance Same as → spectral density. |
probability density function karyâ-ye cagâli-ye šavânâyi Fr.: fonction de densité de probabilité A mathematical function whose integral over any interval gives the probability that a continuous → random variable has values in this interval. Also known as → density function, frequency function, → probability function. → probability; → density; → function. |
radiation density constant pâypa-ye cagâli-ye tâbeš Fr.: constante de rayonnement The constant related to the total energy radiated by a → blackbody and defined as: a = 4σ/c, where σ is the → Stefan-Boltzmann constant and c the → speed of light. Its value is a = 7.5657 x 10^{-15} erg cm^{-3} K^{-4}. Same as → radiation constant. |
radio flux density cagâli-ye šârr-e râdioyi Fr.: densité de flux radio The flux of → radio waves that falls on a → detector per → unit → surface area of the detector per unit → bandwidth of the radiation per unit → time. The unit is → jansky. |
relative density cagâli-ye bâzâni Fr.: densité relative The ratio of the density of a substance to the density of a given reference material. For a solid or liquid, it is the density (at 20°C) relative to the maximum density of water (at 4°C). For a gas is its density divided by the density of hydrogen (or sometimes dry air) at the same temperature and pressure. Also called → specific density. |
scalar density cagâli-ye marpeli Fr.: densité scalaire A → tensor density of → order 0. |
specific density cagâli-ye âbizé Fr.: densité spécifique Same as → relative density. |
spectral density cagâli-ye binâbi Fr.: densité spectrale For a specified → bandwidth of radiation consisting of a continuous → frequency spectrum, the total → power in the bandwidth divided by the bandwidth. Spectral density describes how the power (or variance) of a time series is distributed with frequency. Also called power spectral density. |
surface density cagâli-ye ruye-yi Fr.: densité de surface The amount of a quantity distributed over a surface area divided by the area, such as a surface-charge density. |
tensor density cagâli-ye tânsor Fr.: densité de tenseur A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor. |
vector density cagâli-ye bordâr Fr.: densité de vecteur A → tensor density of → order 1. |
weight of a tensor density vazn-e cagâli-ye tânsor Fr.: poids d'une densité de tenseur A constant the value of which is characteristic for any given → tensor density. |