šaxâne-ye degarsânidé, šahâbsang-e ~
Fr.: météorite différenciée
A meteorite that has distinctly separated stone, metal, and glass. It is derived from a differentiated parent body and hence not primitive. The parent body accreted surrounding material until it was large enough to start melting in the middle. The denser metals sank to the center and the stones and glasses floated to the top. A differentiated meteorite made completely of metal comes from the center of a parent meteoroid which was broken apart. → undifferenciated meteorite.
Fr.: (Math.) dériver; (Astro.) différenciation
1) Math.: The operation of finding the → derivative
of a function.
Verbal noun of → differentiate.
Verbal form of → diffraction.
A wave property of light which allows it to curl around obstacles whose size is
about that of the wavelength of the light. As a → wavefront
of light passes by an opaque edge or through an opening, secondary weaker wavefronts
are generated, apparently originating at that edge. These secondary wavefronts will interfere
with the primary wavefront as well as with each other to form a
→ diffraction pattern.
From Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from → dis- "apart" + frangere "to break."
Parâš "dispersion, scattering," variant of pâš, pâšidan, → dispersion.
turi-ye parâš (#)
Fr.: réseau de diffraction
An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.
olgu-ye parâš (#)
Fr.: tache de diffraction
A series of concentric rings of dark and light color produced by interference.
Olgu, loanword from Turkish; parâš→ diffraction.
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.
karânmand bé parâš
Fr.: limité par la diffraction
1) paxšidan (#); 2) paxšidé (#)
Fr.: 1) diffuser; 2) diffus
1a) To pour out, to spread in all directions.
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
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 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.