An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 40 Search : density
morphology-density relation
  بازانش ِ ریخت-چگالی   
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
  پالایه‌ی ِ چگالی ِ نتار   
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.

neutral; → density; → filter.

nuclear density
  چگالی ِ هسته‌ای   
cagâli-ye haste-yi (#)

Fr.: densité nucléaire   

The density of an atomic nucleus (about 1014 g/cm3).

nuclear; → density.

number density
  چگالی ِ عددی   
cagâli-ye adadi

Fr.: densité nmérique   

Number of a particular type of object found in each unit volume.

number; → density.

optical density
  چگالیِ نوری   
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.

optical; → density.

period-mean density relation
  باز‌آنش ِ دوره-چگالی ِ میانگین   
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 (Cp/Cv), 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.

period; → mean; → density; → relation.

Planck density
  چگالی ِ پلانک   
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: ρP = c5/(ħG2) ≅ 5.16 x 1093 g cm-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.

Planck; → density.

potential density
  چگالی ِ توند   
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.

potential; → density.

power spectral density
  چگالی ِ بینابی ِ توان   
cagâli-ye binâbi-ye tavân

Fr.: densité spectrale de puissance   

Same as → spectral density.

power; → spectral; → density.

probability density function
  کریای ِ چگالی ِ شوانایی   
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
  پایای ِ چگالی ِ تابش   
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.

radiation; → density; → constant.

radio flux density
  چگالی ِ شار ِ رادیویی   
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.

radio; → flux; → density.

relative density
  چگالی ِ بازانی   
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.

relative; → density.

scalar density
  چگالی ِ مرپلی   
cagâli-ye marpeli

Fr.: densité scalaire   

A → tensor density of → order 0.

scalar; → density.

specific density
  چگالی ِ آبیزه   
cagâli-ye âbizé

Fr.: densité spécifique   

Same as → relative density.

specific; → density.

spectral density
  چگالی ِ بینابی   
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.

spectral; → density.

surface density
  چگالی ِ رویه‌ای   
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.

surface; → density.

tensor density
  چگالی ِ تانسور   
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.

tensor; → density.

vector density
  چگالی ِ بردار   
cagâli-ye bordâr

Fr.: densité de vecteur   

A → tensor density of → order 1.

vector; → density.

weight of a tensor density
  وزن ِ چگالی ِ تانسور   
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.

weight; → tensor; → density.

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