diffuse galactic light
nur-e kahkašâni-ye paxšidé
Fr.: lumière galactique diffuse
diffuse interstellar band (DIB)
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 carrier
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 cloud
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 medium
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 molecular cloud
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).
Fr.: nébuleuse diffuse
An irregularly shaped and low density interstellar cloud visible in the optical wavelengths.
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.
Fr.: transmission diffuse
Transmission accompanied by diffusion or scatter to the extent that there is no regular or direct transmission.
A device used to scatter or disperse light emitted from a source.
From → diffuse + -er.
1) Movement of a gas or liquid as a result of the random thermal motion of its atoms or
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 paxšidan→ diffuse.
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.
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 = D∇2T.
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.
Fr.: diffusif, de diffusion
Tending to diffuse; characterized by → diffusion.
paxšandegi, hamgar-e paxš
Fr.: coefficient de diffusion
1) The ability to permit or undergo diffusion.
A symbol, numeral, or graphic character that represents an integer.
From L. digitus "finger, toe."
Raqam, from Ar.
1) Of or pertaining to a digit.
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.