Fr.: enrichissement chimique
The → process by which the relative → abundance of a given → chemical element or → species in an → astrophysical object is increased. For example the the → increase of the → heavy element content of the → interstellar medium due to → stellar evolution.
Fr.: enrichissement de deutérium
The → enrichment of deuterium (D) with respect to
→ hydrogen (H) in
→ Solar System molecules
when compared with the D/H ratio in the
→ interstellar → solar nebula.
H-bearing molecules in → comets,
→ planets, and → chondrite
→ meteorites show a systematic D enrichment
relative to the → molecular hydrogen of the solar
nebula. Because there is no nuclear source for D in the Universe,
the observed → isotopic enrichment must have its
origin in chemical reactions having faster reaction rates for D than for H.
In the Solar nebula the → isotopic fractionation
of D between → water and H followed the reversible reaction:
deuterium enrichment factor
karvand-e pordâri-ye doteriom
Fr.: facteur d'enrichissement en deutérium
Fr.: condition de Dirichlet
One of the following conditions for a → Fourier series
pordâridan, pordâr kardan
From en- a prefix forming verbs with a particular sense + → rich.
Pordâridan, pordâr kardan, infinitives from pordâr, → rich.
Past participle of → enrich.
Fr.: gaz enrichi
Fr.: uranium enrichi
1) A process that changes the → isotopic ratio
in a material. For example, for uranium
the ratio of U-235 to U-238 may be increased by gaseous
diffusion of uranium hexafluoride.
Verbal noun of → enrich.
Fr.: galaxie riche en gaz
A galaxy, usually young, which has a relatively important gas content.
Fr.: environnement riche en métaux
M.E., from O.E. rice "wealthy, powerful" (cf. Du. rijk, Ger. reich "rich"), from PIE base *reg- "move in a straight line," hence, "to direct, rule" (cf. Mod.Pers./Mid.Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).
Por "full, much, very, too much" (Mid.Pers. purr "full;" O.Pers. paru- "much, many;" Av. parav-, pauru-, pouru-, from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full); pordâr, literally "having much possession," from por + dâr "having, possessor," from dâštan "to have, to possess," → property.
Fr.: amas riche
A → galaxy cluster with a particularly large number of galaxies.
Fr.: cascade de Richarson
Same as → energy cascade
Named after L. F. Richardson (1922), Weather Prediction by Numerical Process (Cambridge Univ. Press); → cascade.
Fr.: critère de Richardson
Named after the British meteorologist Lewis Fry Richardson (1881-1953), who first arrived in 1920 to the dimensionless ratio now called → Richardson number. The first formal proof of the criterion, however, came four decades later for → incompressible flows (Miles, J. W. 1961, J. Fluid Mech., 10, 496; Howard, L. N., 1961, J. Fluid Mech., 10, 509). Its extension to → compressible flows was demonstrated subsequently (Chimonas 1970, J. Fluid Mech., 43, 833); → criterion.
Fr.: nombre de Richardson
A dimensionless number which is used according to the → Richardson criterion to describe the condition for the → stability of a flow in the presence of vertical density stratification. If the → shear flow is characterized by linear variation of velocity and density, with velocities and densities ranging from U1 to U2 and ρ1 to ρ2 (ρ2>ρ1), respectively, over a depth H, then the Richardson number is expressed as: Ri = (ρ2 - ρ1) gH / ρ0 (U1 - U2)2. If Ri < 0.25, somewhere in the flow turbulence is likely to occur. For Ri > 0.25 the flow is stable.
The property of being very abundant.
Fr.: classe de richesse
A classification of → galaxy clusters into six groups (0 to 5), as in the → Abell catalog. It depends on the number of galaxies in a given cluster that lie within a → magnitude range m3 to m3+2, where m3 is the magnitude of the 3rd brightest member of the cluster. The first group contains 30-49 galaxies and the last group more than 299 galaxies.
The property of some crystals of exhibiting three different colors when viewed from three different directions under white lights. → dichroism.
From Gk. tri- "three" + chroic, from chroma "color" + -ism.
Sefâmi, from se, → three, + fâm "color," + -i noun suffix.
Fr.: enrichissement de l'uranium
The process by which the percentage of → fissile uranium in a sample is increased. Uranium obtained from mining contains several → isotopes of uranium in different compositions, such as U-238 (~99%), U-235 (~0.7%), and U-234 (~0.02%). Among them, U-235 is the only one that is fissile, i.e. can be used in a → nuclear reactor to produce heat (and consequently electricity) in a controlled manner. As such, the concentration of U-235 as a fuel used in a reactor needs to be increased, which is done using several techniques, such as → gaseous diffusion.