An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

   Homepage   
   


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

<< < D l dar dat de deb dec dec dec def deg del Den dep des det dev dia dif dif dil dip Dir dis dis dis dis div dom dou dow dri dus dwa dyn > >>

Number of Results: 678
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.

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.

digit
  رقم   
raqam (#)

Fr.: chiffre   

A symbol, numeral, or graphic character that represents an integer.

From L. digitus "finger, toe."

Raqam, from Ar.

digital
  رقمی   
raqami (#)

Fr.: numérique   

1) Of or pertaining to a digit.
2) Representing data as a series of numerical values. Often opposed to → analogue.

digit + → -al.

digital computer
  رایانگر ِ رقمی   
râyângar-e raqami (#)

Fr.: ordinateur numérique   

A computer that accepts and operates with → discrete data in the form of combinations of digits, letters, or other characters. In modern terminology, generally called computer.

digital + → computer.

digitize
  رقمیدن   
raqamidan (#)

Fr.: numériser   

To convert an → analogue signal to a → digital signal that represents the same information as the analogue signal.

digit + → -ize.

dihedral
  دودیمه‌ای   
dodime-yi

Fr.: dihédral   

1) Having formed by two half-planes which intersect.
2) Of or relating to a → dihedron.

dihedron; → -al.

dihedral angle
  زاویه‌ی ِ دودیمی   
zâviye-ye dodimi

Fr.: angle dièdre   

An angle formed by two planes meeting along a common line. Compare with → face angle.

angle; → dihedral.

dihedron
  دودیمه   
dodimé

Fr.: dièdre   

A figure formed by two intersecting planes.

di-; → -hedron.

<< < D l dar dat de deb dec dec dec def deg del Den dep des det dev dia dif dif dil dip Dir dis dis dis dis div dom dou dow dri dus dwa dyn > >>