An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 21 Search : coefficient
absorption coefficient
  همگر ِ درشم   
hamgar-e daršam

Fr.: coefficient d'absorption   

The fraction of normally incident light that is absorbed per unit path length or by a unit mass of absorbing medium.

absorption; → coefficient.

attenuation coefficient
  همگر ِ تنکش   
hamgar-e tonokeš

Fr.: coefficient d'bsorption   

The fraction of a beam of → X-rays or → gamma rays that is absorbed or scattered per unit thickness of the → absorber. The linear attenuation coefficient, denoted by the symbol μ, appears in the equation I(x) = I0ex, where I(x) is the intensity at depth of x cm and I0 is the original intensity.

attenuation; → coefficient.

binomial coefficient
  همگر ِ دونامین   
hamgar-e donâmin

Fr.: coefficient binomial   

The factor multiplying the variable in a term of a → binomial expansion. For example, in (x + y)4 = x4 + 4x3y + 6x2y2 + 4xy3 + y4 the binomial coefficients are 1, 4, 6, 4, and 1. In general, the r-th binomial coefficient in the expression (x + y)n is: (n,r) = n!/[r!(n - r)!].

binomial; → coefficient.

hamgar (#)

Fr.: coefficient   

1) Math.: A number or letter placed before an algebraic expression to indicate that the expression is to be multiplied by that factor, e.g. in the expression 2 x3, 2 is the coefficient of x3. In general, any factor of a product is called the coefficient of the product of the remaining factors.
2) Physics: Factor which measures some specified property of a given substance, and is constant for that substance under given conditions, such as the coefficient of friction. → factor.

Hamgar, from ham- "together," → com- + -gar agent suffix, from kar-, kardan "to do, to make," Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base kwer- "to do, to make."

coefficient of viscosity
  همگر ِ وشکسانی   
hamgar-e vošksâni

Fr.: coefficient de viscosité   

A quantity that indicates a property of fluids and is defined by the ratio of shearing → stress to the rate of change of shearing → strain. It is also simply called viscosity. The coefficient of viscosity is expressed by: μ = (F/A) / (dv/dy), where F is the force required to maintain a steady velocity difference dv between any two parallel layers of the fluid, A is the area of the layers, and dv/dy is the → velocity gradient between two points separated by a small distance measured at right angles to the direction of flow. The unit of viscosity is that of force times distance divided by area times velocity. Thus, in the cgs system, the unit is 1, which reduces to 1 dyne.s/cm2. This unit is called 1 → poise.

viscosity; → coefficient.

correlation coefficient
  همگر ِ هم‌باز‌آنش   
hamgar-e hambâzâneš

Fr.: coefficient de corrélation   

A number between -1 and 1 which measures the degree to which two variables are linearly related.

correlation; → coefficient.

coupling coefficient
  همگر ِ جفسری   
hamgar-e jafsari

Fr.: coefficient de couplage   

A parameter that indicates the strength of the interaction between two systems.

coupling; → coefficient.

diffusion coefficient
  همگر ِ پخش   
hamgar-e paxš

Fr.: coefficient de diffusion   

A factor of proportionality involved in the → diffusion equation. It may be defined as the amount of the quantity diffusing across a unit area through a unit concentration gradient in unit time. → magnetic diffusivity.

diffusion; → coefficient.

dominant coefficient
  همگر ِ چیرنده   
hamgar-e cirandé

Fr.: coefficient dominant   

Of a → non-zero polynomial, the coefficient of the → monomial which has the highest → degree.

Dominant, adj. from → dominant; → coefficient.

Einstein coefficient
  همگر ِ اینشتین   
hamgar-e Einstein

Fr.: coefficient d'Einstein   

A measure of the probability that a particular atomic transition leading to the formation of an atomic spectral line occurs. The coefficient of spontaneous emission is denoted by Aij, and the coefficient of stimulated emission by Bij, i representing the lower level and j is the upper level.

Named after Albert Einstein (1879-1955) who introduced the coefficients in 1916; → coefficient.

emission coefficient
  همگر ِ گسیل   
hamgar-e gosil

Fr.: coefficient d'émission   

Electromagnetic flux emitted by a source per unit volume per unit time.

emission; → coefficient.

extinction coefficient
  همگر ِ خاموشی   
hamgar-e xâmuši

Fr.: coefficient d'extinction   

Gradient of apparent magnitude with air mass.

extinction; → coefficient.

Fourier coefficient
  همگر ِ فوریه   
hamgar-e Fourier

Fr.: coefficient de Fourier   

One of the coefficients an or bn of cos (nx) and sin (nx) respectively in the → Fourier series representation of a function. They are expressed by:
an = (1/π) ∫f(x) cos nx dx, for n≥ 0, summed over 0 to 2π
bn = (1/π) ∫f(x) sin nx dx, for n≥ 1, summed over 0 to 2π.

Fourier analysis; → series.

gravity darkening coefficient
  همگر ِ تاریکش ِ گرانشی   
hamgar-e târikeš-e gerâneši

Fr.: coefficient de l'assombrissement gravitationnel   

According to the → von Zeipel theorem, the emergent flux, F, of total radiation at any point over the surface of a rotationally or tidally distorted star in → hydrostatic equilibrium varies proportionally to the local gravity acceleration: F ∝ geffα, where geff is the → effective gravity and α is the gravity darkening coefficient. See also the → gravity darkening exponent.

gravity; → darkening; → coefficient.

mass absorption coefficient
  همگر ِ درشم ِ جرمی   
hamgar-e daršm-e jermi

Fr.: coefficient d'absorption de masse   

A measure of the rate of absorption of radiation, expressed as the linear absorption coefficient divided by the density of the medium through which radiation is passing.

mass; → absorption; → coefficient.

recombination coefficient
  همگر ِ بازمیازش   
hamgar-e bâzmiyâzeš

Fr.: coefficient de recombinaison   

A measure of the specific rate at which oppositely charged ions join to form neutral particles. It is given by the rate at which those ions recombine, divided by the product of the densities of the two species involved.

recombination; → coefficient.

reddening coefficient
  همگر ِ سرخش   
hamgar-e sorxeš

Fr.: coefficient de rougissement   

A dimensionless quantity determined from the comparison of the observed → Balmer decrements with respect to the theoretical values for given physical conditions of electron temperature and density. The reddening coefficient at Hβ is defined as c(Hβ) = log (I(Hβ)/F(Hβ)), where I(Hβ) and F(Hβ) are → de-reddened and reddened fluxes respectively. Also called logarithmic extinction.

reddening; → coefficient.

reflection coefficient
  همگر ِ بازتاب   
hamgar-e bâztâb (#)

Fr.: coefficient de réflexion   

The ratio given by the → amplitude (or energy) of a reflected wave divided by the amplitude (or energy) of the incident wave.

reflection; → coefficient.

regression coefficient
  همگر ِ وایازش   
hamgar-e vâyâzeš (#)

Fr.: coefficient de régression   

The slope of the straight line that most closely relates two correlated variables.

regression, → coefficient.

scattering coefficient
  همگر ِ پراکنش   
hamgar-e parâkaneš

Fr.: coefficient de diffusion   

The fraction of light scattered per unit distance in a medium.

scattering; → coefficient.

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