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. → linear; → perturbation; → theory. |
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. → method; → small; → perturbation. |
perturb parturidan Fr.: perturber To cause a small → deviation in the → behavior of a → physical system, e.g. in the → orbit of a planet. O.Fr. perturber, from L. perturbare "to confuse, disorder, disturb," from per- "through" + turbare "disturb, confuse," from turba "turmoil, crowd," turbidus "muddy, full of confusion." Parturidan, from par-, related to pirâ- (cf. Av. per- "to pass across, through") + turidan "to run away, be very much ashamed," tur "withdrawal, flight;" Lori, Laki tur "restive, disobedient," Laki turyâyen "to get angry, lose one's temper," probably cognate with L. turba, as above. |
perturbation partureš Fr.: perturbation 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. |
perturbation equation hamugeš-e partureš Fr.: équation de perturbation Any equation governing the behavior of a → perturbation. → perturbation; → equation. |
perturbation method raveš-e partureš 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. → perturbation; → method. |
perturber body jesm-e parturandé Fr.: corps perturbateur A celestial body that causes a perturbation in the orbit of another body. |
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. → primordial; → curvature; → perturbation. |
scalar perturbation partureš-e marpeli 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. → scalar; → perturbation. |
secular perturbation partureš-e diryâz Fr.: perturbation séculaire A variation of planetary orbital elements which is always in the same direction as time increases. → secular; → perturbation. |
tensor perturbation partureš-e tânsori 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. → tensor; → perturbation. |
vector perturbation partureš-e bordâri Fr.: perturbation vectorielle The perturbation in the → primordial Universe plasma caused by → vorticity. These perturbations cause → Doppler shifts that result in → quadrupole anisotropy. → vector; → perturbation. |