Fr.: loi de Dulong et Petit
The product of the → specific heat and → atomic weight of most solid elements at room → temperature is nearly the same. In other words, specific heat is constant for a solid and independent of temperature. Experiment shows that at moderate temperatures this law is satisfied for → crystals with rather simple structure. However, the law fails for crystals with more complex structures. More specifically the law cannot explain the variation of specific heat with temperature. The specific heat drops to zero as the temperature approaches 0 K. This behavior is explained only with the quantum theory. → Debye model.
Named after Pierre L. Dulong (1785-1838) and Alexis T. Petit (1797-1820), French chemists, who proposed the law in 1819. They collaborated in several important investigations, including studies of thermal expansion of gases and of liquids and the specific heats of substances; → law.
Dumbbell Nebula (M27, NGC 6853)
Fr.: Nébuleuse de l'Haltère
One of the brightest planetary nebulae; it lies in the constellation → Vulpecula at a distance of about 1000 light-years. It was discovered by Charles Messier in 1764.
Dumbbell "a short bar with weights at each end that is used for exercise," from dumb + bell. When viewed in a small telescope, the brighter portion of the nebula shows like a bipolar geometry, hence the name; → nebula.
Dambel loanword from dumbbell, as above; → nebula.
Consisting of twelve → years.
duodecennial animal calendar
gâhšomâr-e davâzdahsâli-ye janevari (#)
Fr.: calendrier duodécennal
A → lunisolar calendar in which the years are named after each of the following twelve animals: rat, ox, tiger, hare, dragon, snake, horse, sheep, monkey, cock, dog, pig. An animal presides over one year in the twelve-year cycle, which is then repeated. The calendar was/is mainly used by central Asian cultures (Khotanese, Sogdians, Buddhists, Kucheans, Mongols, and Chinese). It was also used in Iran after the Mongol invasion in the thirteenth century.
1) dotâyidan, dotâ kardan; 2) dotâkard
Fr.: 1) faire un double de; 2) double, copie exacte
1) To make an exact copy of.
Dotâyidan, "to double," infinitive from dotâyi, → double.
An act or instance of duplicating; the state of being duplicated.
Verbal noun of → duplicate.
The ability to withstand damage or decay.
Capable of lasting, enduring; withstanding deterioration.
Continuance in time; a period of existence or persistence; length of time during which anything continues.
Noun of action from L. durare "to harden," → during.
Pâyeš, noun of action from pâyidan, → last (v.).
In the course of, in the time of, throughout the continuance of.
M.E. Duryng, durand, pr.p. of duren "to last, endure, continue, be or exist," from O.Fr. durer, from L. durare "to harden," from durus "hard;" PIE root *deru- "be firm, solid, steadfast."
qobâr(#), gard (#)
Tiny pieces of solid material, such as carbon and silicate grains, in the → interstellar medium that are about 0.1-1.0 micron in size. → Dust grains embedded in → molecular clouds may be significantly larger.
O.E. dust, akin to O.H.G. tunst "storm," from P.Gmc. *dunstaz, from PIE base dhem-/dhemə- "to smoke, to blow," cf. Skt. dhūmá "smoke," Mod.Pers. dam "smoke; to blow, breathe," Av. dāδmainya- "blowing up," Gk. thumiao "to fumigate, burn incense," thymos "spirit, mind, soul," L. fumus "smoke," Ossetic dymyn/dumun "to smoke, blow up," Lith. dumai "smoke."
Qobâr, from Ar.; gard "dust," Mid.Pers. gart, gard.
Fr.: analogue de poussière
A chemical compound produced in laboratory experiments to simulate real → interstellar dust grains and thus study them.
mâseš-e qobâr, roceš-e ~
Fr.: coagulation de la poussière
Fr.: tourbillon de poussière
A small but vigorous → whirlwind, usually of short duration, rendered visible by → dust, → sand, and → debris picked up from the ground (Meteorology Glossary, Amer. Meteo. Soc.). See also → dust storm, → dust whirl.
Fr.: émission des poussières
Thermal emission in infrared from interstellar → dust grains receiving photons. Dust grains absorb ultraviolet and visible light emitted by nearby stars and re-radiate in the infrared wavelengths. Since the infrared light is of lower energy than the ultraviolet/visible light, the difference goes into heating the dust grain. Typical temperatures for interstellar grains are tens of degrees Kelvin.
Fr.: marque de poussière, signature de ~, motif spectral de ~
An emission or absorption mark in the spectrum of an astronomical object, the origin of which is attributed to the presence of dust in the object or on the line of sight.
dâne-ye qobâr (#)
Fr.: grains de poussière
A small, solid flake of → graphite and/or → silicates coated with water ice, found in the → interstellar medium or the → interplanetary medium. Dust grains are irregularly shaped with sizes from microns to Angstroms (→ very small grain; → big grain; → PAH). It is believed that the dust is mainly formed in the cool outer layers of → red giants and dispersed in the interstellar medium. In dense environments, such as → molecular clouds and around → protostars, dust grains grow due to collisions (→ grain growth). Therefore, dust grains in → protostellar disks should be larger than interstellar grains. Dust grains absorb and scatter optical and ultraviolet light and re-radiate in infrared (→ dust emission). Dust acts as a catalyst in the interstellar medium, because molecules form via reactions on the surface of dust grains.
Fr.: bande de poussière
A narrow, elongated structure of absorbing matter seen running over extended emission objects such as nebulae and galaxies.
→ dust; lane, from O.E. lane, lanu "narrow hedged-in road," cf. Du. laan "lane," O.N. lön "row of houses," of unknown origin.
Bâriké "a narrow thing," from bârik "narrow," from Mid.Pers. bārīk "narrow," Av. bāra-, as in tiži.bāra- "sharp-edged," from brāy- "to cut," Mod.Pers. bor-, boridan "to cut;" qobâr→ dust.
Fr.: modèle de poussière
A model of → dust grains conceived to describe the observed → interstellar extinction properties. It is characterized by the abundance of the different → chemical elements locked up in the dust, and by the → composition, → morphology, and → size distribution of its individual grains. For example, → MRN dust model.