An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < D l dar dat de deb dec dec dec def deg del dem dep der det deu di- dif dif dif dio Dir dis dis dis dis dis div doo dou dra dua dus dyn dyn > >>

Number of Results: 692
diffraction pattern
  الگوی ِ پراش   
olgu-ye parâš (#)

Fr.: tache de diffraction   

A series of concentric rings of dark and light color produced by interference.

diffraction; → pattern.

Olgu, loanword from Turkish; parâšdiffraction.

diffraction spike
  سیخک ِ پراش   
sixak-e parâš

Fr.: aigrette de diffraction   

One of several light rays emanating from a bright light source in images taken with → reflecting telescopes. They are artifacts caused by light diffracting around the support or → spider vanes of the → secondary mirror.

diffraction; → spike.

  کران‌مند به پراش   
karânmand bé parâš

Fr.: limité par la diffraction   

The quality of an → optical system that is capable of producing images with angular resolution as small as the theoretical limit of the → Airy disk.

diffraction; limited, adj. of → limit.

Karânmand "bounded, limited," from karânboundary + -mand possession suffix; parâš diffraction.

  ۱) پخشیدن؛ ۲) پخشیده   
1) paxšidan (#); 2) paxšidé (#)

Fr.: 1) diffuser; 2) diffus   

1a) To pour out, to spread in all directions.
1b) To spread by → diffusion.
2) Spread out, diffused, scattered, as → diffuse reflection.
See also: → diffuse atomic cloud, → diffuse galactic light, → diffuse interstellar band, → diffuse interstellar band carrier, → diffuse interstellar cloud, → diffuse interstellar medium, → diffuse molecular cloud, → diffuse nebula, → diffuse reflection, → diffuse transmission, → diffusion.

L. diffusus "spread, poured forth," from dif- "apart, in every direction," variant of → dis- + fuse, from fusus "melted, poured, cast," p.p. of fundere "to melt, cast, pour out," from PIE *gheud-, from root *gheu- "to pour."

Paxšidan "to diffuse, scatter, disperse," infinitive of paxš "scattered, dispersed; withered, trodden," (Manichean) Mid.Pers. pxš "to wither, fade; to grow ripe," Proto-Iranian *paxš- "to cook," cf. Av. pac- "to cook," pacika- "cooked," Mod.Pers. paz-, poxtan "to cook, bake," Skt. pac- "to cook," pakva- "ripe," Gk. peptein "to cook, ripen," L. coquere "to cook," from which V.L. cocus "cook," from which O.E. coc "cook;" PIE *pekw- "to cook, ripen;" paxšidé, p.p. of paxšidan.

diffuse atomic cloud
  ابر ِ اتمی ِ پخشیده   
abr-e atomi-ye paxšidé

Fr.: nuage atomique diffus   

A type of cloud in the → interstellar medium with low molecular content that is fully exposed to the → interstellar radiation field, and therefore nearly all its → molecules are quickly destroyed by → photodissociation. Hydrogen is mainly in → neutral atomic form (→ neutral hydrogen), and atoms with → ionization potentials less than that of hydrogen (most notably → carbon) are almost fully → ionized, providing abundant electrons. The paucity of molecules implies that very little chemistry occurs in such clouds. Many → sightlines with low → extinction seem to pass exclusively through → diffuse atomic gas. Such sightlines typically have a → column density, NH, less than about 5 × 1020 cm-2, and are sufficiently → optically thin to be observable by means of → visible and → ultraviolet → absorption line measurements. Diffuse atomic clouds typically have a fairly low → density (~ 10-100 cm-3), and → temperatures of 30-100 K (Snow & McCall, 2006, ARA&A 44, 367).

diffuse; → atomic; → gas.

diffuse galactic light
  نور ِ کهکشانی ِ پخشیده   
nur-e kahkašâni-ye paxšidé

Fr.: lumière galactique diffuse   

A minor component of galactic light resulting from the diffusion of starlight by → interstellar dust near the → galactic plane.

diffuse; → galactic; → light.

diffuse interstellar band (DIB)
  باند ِ پخشیده‌ی ِ اندر‌اختری   
bând-e paxšide-ye andaraxtari

Fr.: bande diffuse interstellaire   

Absorption features in the spectrum of stars identified in the ultraviolet, visible, and infrared regions. They have an interstellar origin, but despite extensive efforts, their carrier(s) have not yet been clearly identified. See also → Aromatic Infrared Bands; → polycyclic aromatic hydrocarbons.

diffuse; → interstellar; → band.

diffuse interstellar band carrier
  برنده‌ی ِ باند ِ پخشیده‌ی ِ اندر‌اختری   
barande-ye bând-e paxšide-ye andaraxtari

Fr.: porteur des bandes diffuses interstellaires   

The chemical element or composition that is supposedly at the origin of a → diffuse interstellar band (DIB).

diffuse; → interstellar; → band; → carrier.

diffuse interstellar cloud
  ابر ِ اندر‌اختری ِ پخشیده   
abr-e andaraxtari-ye paxšidé

Fr.: nuage interstellaire diffus   

An → interstellar cloud in which hydrogen is completely dissociated and which is less dense and dusty than → molecular clouds. In diffuse interstellar clouds photoabsorption of the background → ultraviolet (UV) radiation field is an important dissociating and ionizing process. Typical densities and temperatures of diffuse clouds are 102 to 103 cm-3 and 20 to 100 K respectively. Because of modest extinctions (≤ 1 mag), → photodissociation processes are important in diffuse clouds preventing the formation of larger molecules.

diffuse; → interstellar; → cloud.

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.

  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).

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.

  پخشنده، پخشی   
paxšandé, paxši

Fr.: diffusif, de diffusion   

Tending to diffuse; characterized by → diffusion.

diffuse + → -ive.

<< < D l dar dat de deb dec dec dec def deg del dem dep der det deu di- dif dif dif dio Dir dis dis dis dis dis div doo dou dra dua dus dyn dyn > >>