An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 706
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.

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.


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-, + barqelectricity.

Diesel engine
  موتور ِ دیزل   
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
  هموگش ِ دیتریسی   
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.

  دگرسان بودن   
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").

degarsâni (#)

Fr.: différence   

The quality or condition of being different.
Math.: the amount by which one quantity is greater or less than another.
Of two sets A and B, the set consisting of all elements of A which do not belong to B.

Noun form of → differ.

degarsân (#)

Fr.: différent   

Not alike in character or quality; differing; dissimilar.

Adj. of → difference.


Fr.: différentiabilité   

Of a mathematical function, the quality of being → differentiable.

Noun from → differentiable.

  دگرسانی‌پذیر، دگرسانیدنی   
degarsânipazir, degarsânidani

Fr.: différentiable   

Capable of being → differentiated. → differentiable function.

From → differentiate + → -able.

differentiable function
  کریای ِ دگرسانی‌پذیر، ~ دگرسانیدنی   
karyâ-ye degarsânipazir, ~ degarsânidani

Fr.: différentiable   

Property of a mathematical function if it has a → derivative at a given point.

From → differentiable; → function.

  ۱) دگرسانه؛ ۲) دگرسانه‌ای   
1) degarsâné; 2) degarsâneyi

Fr.: différentiel   

1) Noun.
1a) General: A difference or the amount of difference, as in rate, cost, quantity, degree, or quality, between things that are comparable.
1b) Math.: An infinitesimally small change in a variable; a function of two variables that is obtained from a given function, y = f(x), and that expresses the increment in the given function as the derivative of the function, f'(x), times the increment in the independent variable, written as dy = f'(x) dx.
1c) Electronics: Referring to a circuit, device, or machine whose principle of operation depends on the difference between two opposing effects.
2) Adjective.
2a) General: Of, relating to, or constituting a difference.
2b) Physics: Pertaining to or involving the difference of two or more motions, forces, etc.
2c) Math.: Pertaining to or involving a → derivative or derivatives.

From M.L. differentialis, from differenti(a), → difference, + → -al.

Degarsâné, from degarsân, → different + noun suffix .

differential and integral calculus
  افماریک ِ دگرسانه‌ای و درستالی   
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
  افماریک ِ دگرسانه‌ای، ~ دگرسانه‌ها   
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
  هموگش ِ دگرسانه‌ای   
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, 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.

differential equation with separable variables
  هموگش ِ دگرسانه‌ای با ورتنده‌های ِ جدایی-پذیر   
hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâyi-pazir

Fr.: équation différentielle à variables séparables   

A → differential equation of the form: M1(x) N1(y) dx + M2(x) N2(y) dy = 0, which can be reduced to a → differential equation with separated variables.

differential; → equation; → separate; → variable.

differential equation with separated variables
  هموگش ِ دگرسانه‌ای با ورتنده‌های ِ جدا   
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
  هندسه‌ی ِ دگرسانه‌ای   
hendese-ye degarsâneyi

Fr.: géométrie différentielle   

The study of curved spaces using differential calculus.

differential; → geometry.

differential image motion monitor (DIMM)
  پهره‌گر ِ جنبش ِ دگرسانه‌ای ِ تصویر   
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
  شکست ِ دگرسانه‌ای   
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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