linear perturbation theory
negare-ye partureš-e xatti
Fr.: théorie de perturbation linéaire
Assumption that the variations in the plasma parameters, due to the presence of waves, are small (to the first order) as compared to the undisturbed parameters. This makes it possible to linearize equations by dropping out second order (and higher) nonlinear terms.
method of small perturbations
raveš-e parturešhâ-ye kucak
Fr.: méthode des petites perturbations
The linearization of the appropriate equations governing a system by the assumption of a steady state, with departures from that steady state limited to small perturbations. Also called perturbation method.
1) Any departure introduced into a steady state of a system.
The magnitude is often assumed to be small so
that the resulting terms in the dependent variables may be neglected.
The term "perturbation" is therefore sometimes used as synonymous with "small perturbation."
Verbal noun of → perturb.
Fr.: équation de perturbation
Any equation governing the behavior of a → perturbation.
Fr.: méthode de perturbation
Approximate method of solving a difficult problem if the equations to be solved depart only slightly from those of a problem already solved.
primordial curvature perturbation
partureš-e xamidegi-ye bonâqâzin
Fr.: perturbation de courbure primordiale
In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.
Fr.: perturbation scalaire
The energy density fluctuations in the → photon-baryon plasma that bring about hotter and colder regions. This perturbation creates velocity distributions that are out of phase with the acoustic density mode. The fluid velocity from hot to cold regions causes blueshift of the photons, resulting in → quadrupole anisotropy.
Fr.: perturbation séculaire
A variation of planetary orbital elements which is always in the same direction as time increases.
Fr.: perturbation tensorielle
The perturbation in the → primordial Universe plasma caused by → gravitational waves. These waves stretch and squeeze space in orthogonal directions and bring about → quadrupole anisotropy in incoming radiation temperature.
Fr.: perturbation vectorielle