An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 285 Search : if
diffuse interstellar medium
  مدیم ِ اندر‌اختری ِ پخشیده   
madim-e andaraxtari-ye paxšidé

Fr.: milieu interstellaire diffus   

The interstellar matter outside condensed molecular clouds. Diffuse interstellar medium consists of a hot intercloud medium, a warm intercloud medium, and a cold neutral medium with hydrogen atom densities nH ~ 0.003, ~ 0.25, and ~ 40 cm-3, and mean gas → kinetic temperatures Tk ~ 5 x 105, ~ 104, and 80 K, respectively.

diffuse; → interstellar; → medium.

diffuse molecular cloud
  ابر ِ مولکولی ِ پخشیده   
abr-e molekuli-ye paxšidé

Fr.: nuage moléculaire diffus   

A type of → molecular cloud in which the → interstellar radiation field is sufficiently attenuated, so that the local fraction of → molecular hydrogen (H2) becomes substantial (> 0.1). However, enough interstellar radiation is still present to → photoionize any atomic carbon, or to → photodissociate → carbon monoxide (CO) such that carbon is predominantly still in the form of C+ (> 0.5). In steady state, diffuse molecular clouds must necessarily be surrounded by diffuse atomic gas, in order to provide the → shielding of radiation. This means that most sightlines that cross a diffuse molecular cloud will also cross → diffuse atomic gas (Snow & McCall, 2006, ARA&A 44, 367).

diffuse; → molecular; → cloud.

diffuse nebula
  میغ ِ پخشیده   
miq-e paxšidé

Fr.: nébuleuse diffuse   

An irregularly shaped and low density interstellar cloud visible in the optical wavelengths.

diffuse; → nebula.

diffuse reflection
  بازتاب ِ پخشیده   
bâztâb-e paxšidé

Fr.: réflexion diffuse   

Reflection of light from a rough or granular surface, which takes place in all directions due to the microscopic irregularities of the interface; opposed to → specular reflection.

diffuse; → reflection.

diffuse transmission
  تراگسیل ِ پخشیده   
tarâgosil-e paxšidé

Fr.: transmission diffuse   

Transmission accompanied by diffusion or scatter to the extent that there is no regular or direct transmission.

diffuse; → transmission.

diffuser
  پخشنده، پخشگر   
paxšandé, paxšgar

Fr.: diffuseur   

A device used to scatter or disperse light emitted from a source.

From → diffuse + -er.

From paxš, present stem of paxšidan, → diffuse, + -andé or -gar (→ detector).

diffusion
  پخش   
paxš (#)

Fr.: diffusion   

1) Movement of a gas or liquid as a result of the random thermal motion of its atoms or molecules.
2) The random spreading out of a beam of radiation on reflection (→ diffuse reflection) or transmission through a translucent medium (such as amber, milk, or frosted glass).
3) In chemical thermodynamics, the process of attaining an equilibrium distribution of the → concentration within the phases. A result of diffusion at constant equilibrium is the equalization of the → chemical potentials.
Related terms: → diffraction; → dispersion; → distribution; → scatter; → scattering.

L. diffusionem, from stem of diffundere "scatter, pour out," from dif- "apart, in every direction," → dis-, + fundere "to melt, cast, pour out," from PIE *gheud-, from root *gheu- "to pour."

Paxš, verbal noun and stem of paxšidandiffuse.

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.

diffusion equation
  هموگش ِ پخش   
hamugeš-e paxš

Fr.: équation de diffusion   

An equation that expresses the time rate of change of a quantity in terms of the product of the diffusion coefficient and the → Laplacian operating on the quantity. For example the diffusion equation for temperature is: ∂T/∂t = D2T.

diffusion; → equation.

diffusion region
  ناحیه‌ی ِ پخش   
nâhiye-ye paxš

Fr.: région de diffusion   

A narrow boundary layer above the solar → photosphere, between two magnetic field lines, where the plasma becomes demagnetized or unfrozen. The presence of a localized magnetic region is necessary for → magnetic reconnection.

local; → -ize; → diffusion; → region.

diffusive
  پخشنده، پخشی   
paxšandé, paxši

Fr.: diffusif, de diffusion   

Tending to diffuse; characterized by → diffusion.

diffuse + → -ive.

diffusivity
  پخشندگی، همگر ِ پخش   
paxšandegi, hamgar-e paxš

Fr.: coefficient de diffusion   

1) The ability to permit or undergo diffusion.
2) → magnetic diffusivity.

diffusive; → -ity.

disqualification
  واچونایش   
vâcunâyeš

Fr.: disqualification   

An act or instance of disqualifying; the state of being disqualified.

disqualify; → -tion.

disqualified
  واچوناییده، واچونامند   
vâcunâyide, vâcunâmand

Fr.: non qualifié   

(of a person) declared ineligible for an office, activity, or competition because of an offence or infringement (OxfordDictionaries.com).

dis-; → qualified.

disqualify
  واچوناییدن، واچونامند کردن   
vâcunâyidan, vâcunâmand kardan,

Fr.: disqualifier   

To deprive of qualification or fitness; render unfit; incapacitate (Dictionary.com).

dis-; → qualify.

Doppler shift
  کیب ِ دوپلر   
kib-e Doppler

Fr.: décalage Doppler   

Effect of the relative motion of a wave source (light, sound) and the observer. If the source is moving away, the wavelength is stretched (shifted toward lower frequencies). If the source is approaching, the wavelength is compressed (shifted toward higher frequencies). These effects, known as Doppler shifts, are in the case of light waves called redshift and blueshift, respectively.

Doppler effect; → shift.

double-diffusive convection
  همبز ِ دوپخشی   
hambaz-e do paxši

Fr.:   

An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).

double;→ diffusive; → system.

drift
  ۱) دلک؛ ۲) دلکیدن   
1) delek; 2) delekidan

Fr.: 1) dérive; 2) dériver   

1a) General: A driving movement or force; impulse; impetus; pressure.
1b) Physics: A slight change of a quantity with time, for example the sensitivity of an electronic detector continuously operated during a long period as an effect of continued use.
1c) A slow change in frequency of a radio transmitter.
1d) Aerospace: The gradual deviation of a rocket or guided missile from its intended trajectory.
2) (v.intr.) To be carried along by currents of water or air, or by the force of circumstances.

From M.E. drift, from O.E. drifan "to drive," or from O.N. or M.Du. drift, from P.Gmc. *driftiz, related to *dribanan "to drive."

Delek from Lori, Laki, Hamadâni, Malâyeri "push, shove, drive;" variants Gilaki duko, Tâleši dako, Baluchi dhakkk(a) "push, shove, blow," Choresmian dh- "to hit," Kurd. dân/di- "to beat, hit," Proto-Iranian *daH- "to beat, hit, strike" (Cheung 2007); PIE base *dhen- "to hit, push;" delekidan, verb from delek.

drift curve
  خم ِ دلک   
xam-e delek

Fr.: courbe de passage   

In radio astronomy, the output response as a function of position for a given filter as the source passes through the beam.

drift; → curve.

drift rate
  نرخ ِ دلک   
nerx-e delek

Fr.: taux de dérive   

The amount of drift, in any of its several senses, per unit time.

drift; → rate.

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