# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 75 Search : iff
 homogeneous linear differential equation   هموگش ِ دگرسانه‌ای ِ خطی همگن   hamugeš-e degarsâne-yi-ye xatti hamgenFr.: équation différentielle linéaire homogène   A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.→ homogeneous; → linear; → differential; → equation. if and only if (iff)   اگر و ایواز اگر، ~ ~ تنها ~   agar va ivâz agar, ~ ~ tanhâ ~Fr.: si et seulement si   Logic, Math.: An → expression indicating that two → statements so connected are → necessary and sufficient conditions for one another. The corresponding logical symbols usually used are: ↔, ⇔, ≡, and iff.→ if; → and; → only. linear differential equation   هموگش ِ دگرسانه‌ای ِ خطی   hamugeš-e degarsâne-yi-ye xattiFr.: équation différentielle linéaire   An equation in which the → dependent variable y and all its differential coefficients occur only in the first degree. A linear differential equation of → order  order n has the form: fn(x)y(n) + fn-1(x)y(n-1) + ... + f1(x)y' + f0(x)y = Q(x), where f0(x), f1(x), ..., fn(x) and Q(x) are each continuous functions of x defined on a common interval I and fn(x)≠ 0 in I. A linear differential equation cannot have, for example, terms such as y2 or (y')1/2. See also: → homogeneous linear differential equation; → nonhomogeneous linear differential equation.→ linear; → differential; → equation. linearized differential equation   هموگش ِ دگرسانه‌ای ِ خطی   hamugeš-e degarsâneyi-ye xattiFr.: équation différentielle linéarisée   A differential equation that has been derived from an original nonlinear equation.Linearized, p.p. of → linearize; → differential; → equation. magnetic diffusion   پخش ِ مغناتیسی   paxš-e meqnâtisiFr.: diffusion magnétique   The process whereby the magnetic field tends to diffuse across the plasma and to smooth out any local inhomogeneities under the influence of a finite resistance in the plasma. For a stationary plasma the → induction equation becomes a pure → diffusion equation: ∂B/∂t = Dm∇2B, where Dm = (μ0σ0)-1 is the → magnetic diffusivity.→ magnetic; → diffusion. magnetic diffusivity   پخشندگی ِ مغناتیسی   paxšandegi-ye meqnâtisiFr.: diffusivité magnétique   The → diffusion coefficient for a magnetic field. It is expressed as: η = 1/(μ0σ), where μ0 is the → magnetic permeability and σ the → conductivity.→ magnetic; → diffusivity. nonhomogeneous linear differential equation   هموگش ِ دگرسانه‌ای ِ خطی ناهمگن   hamugeš-e degarsâne-yi-ye xatti nâhamgenFr.: équation différentielle linéaire non homogène   A → linear differential equation if Q(x)≠ 0 on interval I.→ nonhomogeneous; → linear; → differential; → equation. ordinary differential equation   هموگش ِ دگرسانه‌ای شونیک   hamugeš-e degarsâneyi-ye šunikFr.: équation différentielle ordinaire   A → differential equation in which the unknown function depends on only one → independent variable, as contrasted with a → partial differential equation.→ ordinary; → differential; → equation. partial differential equation   هموگش ِ دگرسانه‌ای با واخنه‌ی ِ پاری   hamugeš-e degarsâne-yi bâ vâxane-ye pâriFr.: équation différentielle aux dérivées partielles   A type of differential equation involving an unknown function (or functions) of several independent variables and its (or their) partial derivatives with respect to those variables.→ partial; → differential; → equation. phase difference   دگرسانی ِ فاز   degarsâni-ye fâzFr.: différence de phase   The difference of phase (usually expressed as a time or an angle) between two periodic quantities which vary sinusoidally and have the same frequency.→ phase; → difference. potential difference   دگرسانی ِ توند   degarsâni-ye tavandFr.: différence de potentiel   Between two points, the work done in taking the unit test object from one point to the other. Potential is a scalar quantity.→ potential; → difference. radiative diffusion   پخش ِ تابشی   paxš-e tâbešiFr.: diffusion radiative   A process of → radiative transfer in which photons are repeatedly absorbed and re-emitted by matter particles.→ radiative; → diffusion. thermal diffusion   پخش ِ گرمایی   paxš-e garmâyiFr.: diffusion thermique   A physical process resulting from → temperature gradients in stellar interiors, whereby more highly charged and more massive chemical species are concentrated toward the hottest region of the star, its center. Therefore, thermal diffusion and → gravitational settling tend to make heavier species sink relative to the light ones.→ thermal; → diffusion. undifferentiated meteorite   شهاب‌سنگ ِ نا-دگرسانیده   šahâbsang-e nâdegarsânidéFr.: météorite indifférenciée   A type of meteorite in which the constituting materials (stone, glass, metal) are mixed together in a disorderly mass, in contrast to → differentiated meteorites.→ un-; → differentiated meteorite. X-ray diffraction   پراش ِ پرتو ِ ایکس   parâš-e partow-e iksFr.: diffraction de rayons X   The diffraction of X-rays by the atoms or ions of a crystal. The wavelength of X-rays are comparable to the size of interatomic spacings in solids. Since the atoms in a crystal are arranged in a set of regular planes, crystals serve as three-dimensional diffraction gratings for X-rays. Planes of repetition within the atomic structure of the mineral diffract the X-rays. The pattern of diffraction thus obtained is therefore used to identify minerals by bombarding them with X-rays.→ X-ray; → diffraction.

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