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: 76 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. ultra-diffuse galaxy (UDG)   کهکشان ِ اولتر-پخشیده   kahkešân-e ultar-paxšideFr.: galaxie ultra-diffuse   A galaxy of low stellar density, defined to have low central → surface brightness (> 24 mag arcsec-2) and an → effective radius (Re) of over 1.5 kpc. The question of whether UDGs represent a separate class of galaxies is still under debate. Currently, known UDGs that have been discovered in clusters, in groups, and in the field can have Re as large as 5 kpc which is comparable to that of giant Milky Way like galaxies. This fact has been used to suggest that UDGs are "failed" giants. As Re captures (at most) the central parts of giant galaxies, whether this radius can be used to fairly compare the sizes of UDGs to the more massive galaxies is questionable (see, e.g., Chamba et al., 2020, A&A 633, L3).Term proposed by van Dokkum et al. (2015), arXiv: 1410.8141v2; → ultra-; → diffuse; → galaxy. 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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