angular differential imaging (ADI)
tasvigari-ye degarsâne-yi-ye zâviye-yi
Fr.: imagerie différentielle angulaire
A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556).
Fr.: binôme différentiel
An expression of the form xm(a + bxn)pdx, where m, n, p, a, and b are constants.
calculus of finite differences
afmârik-e degarsânihâ-ye karânmand
Fr.: calcul des différences finies
degarsân budan (#)
Fr.: différer, être différent
To be unlike, dissimilar, or distinct in nature or qualities.
From O.Fr. différer, from L. differre "to set apart, differ," from → dis- "away from" + ferre "to carry, bear" (cf. Av. baraiti "carries," O.Pers. barantiy "they carry," Mod.Pers. barad "carries," Skt. bharati "carries," Arm. berem "I carry," Gk. pherein "to carry," O.E., O.H.G. beran, Rus. brat' "to take," bremya "a burden").
Degarsân "different," from degar "another, other" (Mid.Pers. dit, ditikar "the other, the second," O.Pers. duvitiya- "second," Av. daibitya-, bitya- "second," Skt. dvitiya- "second," PIE *duitiio- "second") + sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career") + budan "to be" (Mid.Pers. budan, from O.Pers./Av. bav- "to be; become, take place," Av. buta- perf. ptcpl. pass., bavaiti "becomes," Skt. bhavati "becomes, happens," bhavah "becoming; condition, state," PIE *bheu- "to be, come into being, become;" cf. Gk. phu- "become," phuein "to bring forth, make grow," L. fui "I was" (perf. tense of esse), futurus "that is to be, future," Ger. present first and second person sing. bin, bist, E. to be, O.Ir. bi'u "I am," Lith. bu'ti "to be," Rus. byt' "to be").
The quality or condition of being different.
Noun form of → differ.
Not alike in character or quality; differing; dissimilar.
Adj. of → difference.
Of a mathematical function, the quality of being → differentiable.
Noun from → differentiable.
karyâ-ye degarsânipazir, ~ degarsânidani
Property of a mathematical function if it has a → derivative at a given point.
1) degarsâné; 2) degarsâneyi
Degarsâné, from degarsân, → different + noun suffix -é.
differential and integral calculus
afmârik-e degarsâne-yi va dorostâli
Fr.: calcul différentiel et intégral
afmârik-e degarsâneyi, ~ degarsânehâ
Fr.: calcul différentiel
A branch of calculus which is concerned with the instantaneous rate of change of quantities with respect to other quantities, or more precisely, the local behavior of functions. → integral calculus.
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, d2y/dx2, ..., dny/dxn) = 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 with separable variables
hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâyi-pazir
Fr.: équation différentielle à variables séparables
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.
Fr.: géométrie différentielle
The study of curved spaces using differential calculus.
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).
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.
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.
differentially rotating system
râžmân-e degarsâné carxân
Fr.: système en rotation différentielle