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dichroism dofâmi (#) Fr.: dichroïsme Property of some crystals in which radiation polarized in one plane relative to the crystalline axes is freely transmitted, but radiation polarized perpendicular to this is absorbed. Tourmaline is a natural mineral with this property; Polaroid is a synthetic dichroic substance. From Gk. dichro(os), from di- "two," → di-, + chroma "color" + -ism. Dofâmi, from do "two," → bi- + fâm "color," + -i noun suffix. |
dictionary farhang (#) Fr.: dictionnaire A reference source in print or electronic form containing words alphabetically arranged along with information about their forms, meanings, pronunciations, etymologies, etc. M.L. dictionarium "collection of words and phrases," from L. dictionarius "of words," from dictio "word" from dic-, p.p. stem of L. dicere "speak, tell, say," from PIE root *deik- "to point out;" cf. Av. daēs- "to show," daēsa- "sign, omen;" cf. Skt. deś- "to show, point out;" → form. Farhang, → culture. |
dielectric nâbarq Fr.: diélectrique A substance in which an electric field gives rise to no net flow of electric charge but to a displacement of charge in opposite directions. The displacement is usually small compared to atomic dimensions. Dielectrics differ from conductors in that they have no free electrons to move through the material under the influence of an electric field. Most insulating materials, e.g. air, porcelain, mica, glass, are dielectrics. A perfect vacuum would constitute a perfect dielectric. → diamagnetic. Dielectric, from Gk. dia- a prefix used with several meanings "passing through; thoroughly; completely; going apart," and in the present case "not, opposed;" → electric. Nâbarg, from nâ- "not," → un-, + barq→ electricity. |
Diesel engine motor-e Diesel (#) Fr.: moteur Diesel Any internal combustion → engine in which → adiabatic compression raises the temperature of air high enough so that fuel ignites spontaneously when injected. After Rudolf Diesel (1858-1913), German engineer; → engine. |
Dieterici equation hamugeš-e Dieterici Fr.: équation de Dieterici An → equation of state for → real gases which leads to the → van der Waals equation as a → first approximation. It is of the form P(V - b) [exp (a/VRT)] = RT, where P is the pressure, V is the volume, T is the thermodynamic temperature, R is the → gas constant, and a and b are the constants characteristic of the gas. Named after Conrad Dieterici (1858-1929), a German physicist; → equation. |
differ 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"). |
difference degarsâni (#) Fr.: différence The quality or condition of being different. Noun form of → differ. |
different degarsân (#) Fr.: différent Not alike in character or quality; differing; dissimilar. Adj. of → difference. |
differentiability degarsânipaziri Fr.: différentiabilité Of a mathematical function, the quality of being → differentiable. Noun from → differentiable. |
differentiable degarsânipazir, degarsânidani Fr.: différentiable Capable of being → differentiated. → differentiable function. From → differentiate + → -able. |
differentiable function karyâ-ye degarsânipazir, ~ degarsânidani Fr.: différentiable Property of a mathematical function if it has a → derivative at a given point. From → differentiable; → function. |
differential 1) degarsâné; 2) degarsâneyi Fr.: différentiel 1) Noun. From M.L. differentialis, from differenti(a), → difference, + → -al. Degarsâné, from degarsân, → different + noun suffix -é. |
differential and integral calculus afmârik-e degarsâne-yi va dorostâli Fr.: calcul différentiel et intégral The two branches of mathematics that make up the → calculus. → differential calculus; → integral calculus. → differential; → integral; → calculus. |
differential calculus 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. → differential; → calculus. |
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. |
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