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differential equation hamugeš-e degarsâneyi Fr.: équation différentielle An equation expressing a relationship between an → independent variable, x, an unknown → function, y = f(x), and its → derivatives. The general form of a differential equation is: F(x, y, y', y'', ..., y^{(n)}) = 0, or F(x,y, dy/dx, d^{2}y/dx^{2}, ..., d^{n}y/dx^{n}) = 0. See also: → ordinary differential equation; → partial differential equation; → linear differential equation; → exact differential equation; → first-order differential equation; → homogeneous linear differential equation; → nonhomogeneous linear differential equation; → differential equation with separated variables; → differential equation with separable variables. → differential; → equation. |
differential equation with separable variables hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâyi-pazir Fr.: équation différentielle à variables séparables A → differential equation of the form: M_{1}(x) N_{1}(y) dx + M_{2}(x) N_{2}(y) dy = 0, which can be reduced to a → differential equation with separated variables. → differential; → equation; → separate; → variable. |
differential equation with separated variables hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâ Fr.: équation différentielle à variables séparées A → differentail equation that can be transformed into the form: M(x)dx + N(x)dy = 0. → differential; → equation; → separate; → variable. |
differential geometry hendese-ye degarsâneyi Fr.: géométrie différentielle The study of curved spaces using differential calculus. → differential; → geometry. |
differential image motion monitor (DIMM) pahregar-e jonbeš-e degarsâneyi-ye tasvir Fr.: moniteur de mouvements d'images différentiels,
moniteur seeing A device that is commonly used to measure the → seeing at optical astronomical sites. The DIMM delivers an estimate of the → Fried parameter based on measuring the variance of the differential image motion in two small apertures, usually cut out in a single larger telescope pupil by a mask. The DIMM concept was introduced by Stock & Keller (1960, in Stars and Stellar Systems, Vol. 1, ed. G. P. Kuiper & B. M. Middlehurst, p. 138), whereas its modern implementation was first described by Sarazin & Roddier (1990, A&A 227, 294). → differential; → image; → motion; → monitor. |
differential refraction šekast-e dagarsâneyi Fr.: refraction différentielle A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction. → differential; → refraction. |
differential rotation carxeš-e degarsâneyi Fr.: rotation différentielle 1) Of a single body (such as a star or a gaseous planet), the axial rotation of
equatorial latitudes faster than polar latitudes. → differential; → rotation. |
differentially rotating system râžmân-e degarsâné carxân Fr.: système en rotation différentielle A system characterized by → differential rotation. In such a system the → angular velocity decreases as the distance from the rotation center increases. → differential; → rotating; → system. |
differentiate degarsânidan Fr.: différencier General:
To perceive or show the difference in or between. M.L. differentiatus "distinguished," p.p. of differentiare. Degarsânidan, verbal form of → difference. |
differentiated interior darune-ye degarsânidé Fr.: intérieur différencié A description of a planet's interior which is composed of a rocky, dense inner core and a less dense outer crust. Differentiated, p.p. of → differentiate; → interior. |
differentiated meteorite 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. Differentiated, p.p. of → differentiate; → meteorite. |
differentiation degarsâneš Fr.: (Math.) dériver; (Astro.) différenciation 1) Math.: The operation of finding the → derivative
of a function. Verbal noun of → differentiate. |
diffract parâšidan (#) Fr.: diffracter Verbal form of → diffraction. → diffraction. |
diffraction parâš (#) Fr.: 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. |
diffraction grating 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. → diffraction; → grating. |
diffraction pattern 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; parâš→ diffraction. |
diffraction spike 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. |
diffraction-limited 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 karân→ boundary + -mand possession suffix; parâš→ diffraction. |
diffuse 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 *pek^{w}- "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, N_{H}, less than about 5 × 10^{20} 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). |
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