homogeneous linear differential equation
hamugeš-e degarsâne-yi-ye xatti hamgen
Fr.: équation différentielle linéaire homogène
A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.
if and only if (iff)
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.
linear differential equation
hamugeš-e degarsâne-yi-ye xatti
Fr.: 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:
linearized differential equation
hamugeš-e degarsâneyi-ye xatti
Fr.: équation différentielle linéarisée
A differential equation that has been derived from an original nonlinear equation.
Fr.: 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.
Fr.: diffusivité magnétique
nonhomogeneous linear differential equation
hamugeš-e degarsâne-yi-ye xatti nâhamgen
Fr.: équation différentielle linéaire non homogène
A → linear differential equation if Q(x)≠ 0 on interval I.
ordinary differential equation
hamugeš-e degarsâneyi-ye šunik
Fr.: équation différentielle ordinaire
partial differential equation
hamugeš-e degarsâne-yi bâ vâxane-ye pâri
Fr.: 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.
Fr.: 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.
Fr.: 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.
Fr.: diffusion radiative
A process of → radiative transfer in which photons are repeatedly absorbed and re-emitted by matter particles.
Fr.: 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.
ultra-diffuse galaxy (UDG)
Fr.: 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).
Fr.: 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.
parâš-e partow-e iks
Fr.: 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.