Fr.: espèce deutérée
Verbal noun of → deuterate.
The first heavy → isotope of
→ hydrogen (2H), the
→ nucleus of which consists of one
→ proton and one → neutron.
Like hydrogen, the deuterium atom has one
electron, and therefore has similar chemical properties to hydrogen, forming, e.g.,
→ heavy water (HDO). Deuterium is generated only during
→ Big Bang nucleosynthesis. It is destroyed in stars through the
reaction D + p → 3He + γ (→ deuterium burning).
As there is no net source of deuterium in stars, its abundance has decreased steadily since the
→ Big Bang, and any value measured today must be a lower limit
on the primordial value. However, → fractionation
processes lead to local → deuterium enhancements; see
→ deuterium abundance for more details. Theoretical models
of Big Bang nucleosynthesis predict D/H to be (2.61 ± 0.15) x 10-5
(Steigman et al. 2007, MNRAS 378, 576) and this is closely matched by measurements from
intergalactic Dα line absorption observations toward high-redshift quasars
that give 2.53±0.04 x 10-5 (Cooke et al. 2014, ApJ 781, 31).
From Gk. deutero-, combining form of deuterios "second" + -ium suffix occurring in scientific coinages on a Latin model. Coined in 1933 by U.S. chemist Harold C. Urey (1893-1981).
Fr.: abondance de deutérium
The number of → deuterium (D) atoms with respect to
→ hydrogen (H) in an astrophysical object.
Deuterium is a primordial product of → Big Bang nucleosynthesis.
According to theoretical models, the primordial D/H ratio is estimated to be
(2.61 ± 0.15) x 10-5 (Steigman et al. 2007, MNRAS 378, 576).
Nuclear reactions in stars convert D into
He tending to a lower D/H ratio in the → interstellar medium
over time (→ deuterium burning).
However, chemical and physical → fractionation
processes can produce local → enhancements in the D/H ratio.
For example, low-temperature ion-molecule reactions in
→ molecular cloud cores can enhance
the D/H ratio in icy grains by as much as two orders of magnitude
above that observed in the interstellar medium.
Fr.: combustion du deutérium
The fusion of a deuterium nucleus with a proton which produces the lightest isotope of helium: D + H → 3He + γ. Deuterium burning occurs in stellar cores at a temperature exceeding 106 K. The onset of deuterium burning marks the end of the → protostellar collapse. It is the only → nuclear reaction that occurs in → brown dwarfs. In normal stars, it is the second step in the → proton-proton chain which leads to the formation of 4He, allowing stars to arrive on the → main sequence.
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.: fractionnement de deutérium
The difference between the deuterium (D)/hydrogen (H) → abundance → ratio in an object with respect to that representing a standard or mean value for that type of objects. Same as → isotope fractionation of deuterium. In the gas phase chemistry many of the D fractionation reactions produce an excess of D atoms relative to → hydrogen atoms. Deuterium fractionation in → interstellar cloud cores, → protostars, and → Solar System bodies is frequently used to infer important aspects of their physical and chemical histories. For example, the → deuterium enhancement in the Earth's sea water, with respect to the cosmic abundance, has been interpreted as being due to → enrichment by → comet-like → planetesimals colliding with the young Earth.
A nucleus of a deuterium atom (a combination of a proton and a neutron).
From Gk. deutero-, combining form of deuterios "second" + -ion a suffix used in the names of subatomic particles.
1) To elaborate or expand in detail, for example a theory.
From M.Fr. développer, O.Fr. desveloper, from des- "undo" prefix + veloper "wrap up," of unknown origin.
Govâlidan, from Proto-Iranian *vi-uar, cf. Skt. vi-vardh- "to grow up; to blossom," Av. *vi-varəd-, from Skt./Av. prefix vi- "out, apart" + varəd- "to increase, augment, strengthen, cause to prosper," Mid.Pers. vâlitan, Mod.Pers. bâlidan "to grow, to wax great."
Fr.: turbulence développée
A regime of → turbulence characterized by a high → Reynolds number, showing many general aspects that are common to different flows (statistical symmetries, persistent dissipation, energy cascade, → intermittency). Despite those universal features, the understanding of developed turbulence remains as one of the greatest unsolved conceptual problems, on the borderline between mathematics and physics, with numerous ramifications from astrophysics through meteorology to engineering.
1) The act, process, or result of developing. The state of being developed.
From → develop + -ment suffix forming nouns from verbs.
1) kažraftan; 2) kažrâh kardan
From L.L. deviatus "turned from the straight road," p.p. of deviare, from → de- + via "road," + -ate.
1) Kažraftan, from kaž "crooked, bent, being aside"
(cf. Skt. kubja- "hump-backed, crooked," Pali kujja- "bent,"
L. gibbus "hump, hunch," Lith. kupra "hump") +
raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers.
raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").
The act of deviating; departure from a standard or norm.
Verbal noun form of → deviate.
Fr.: appareil, dispositif
Something, thought out, invented, or adapted, for a special purpose.
From O.Fr. devis "division, separation, disposition, wish," from L. divisus, p.p. of dividere "to divide," → divide.
Dastgâh "means, implement, apparatus," originally "wealth, splendour," from dast "strength, superiority," originally "hand" (Mid.Pers. dast, O.Pers. dasta-, Av. zasta-, cf. Skt. hásta-, Gk. kheir, L. praesto "at hand," Arm. jern "hand," Lith. pa-žastis "arm-pit;" PIE *ghes-to-) + gâh "place, time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot" (Skt. gâtu- "going, motion; free space for moving; place of abode," PIE *gwem- "to go, come").
An evil spirit; demon. → dust devil.
M.E. devel, from O.E. deofol, from L.L. diabolus, from Gk. diabolos, literally, "slanderer," from diaballein "to throw across, slander," from dia- "across, through" + ballein to "throw."
Div "devil, demon" (Mid.Pers. dêw; O.Pers. daiva- "evil god, demon;" Av. daēva- "evil spirit, false god;" Skt. deva-; Gk. Zeus "supreme god;" L. deus "god;" PIE base *deiwos "god," from *dei- "to gleam, to shine").
1) Water condensed onto grass and other objects near the ground, the
temperatures of which have fallen below the dewpoint of the surface
air due to radiational cooling during the night, but are still above
O.E. deaw, from P.Gmc. *dawwaz, O.H.G. tow, Gk. thein, "to run," thoos "quick," PIE base *dheu- "to run, flow" (cf. Pers. dav-, davidan "to run," Skt. dhav- "to run, flow," dhavati "flows, runs").
Šabnam, from šab→ night + nam "moisture; dew; wet," Mid.Pers. namb, nam, Av. napta- "moist," nabas-câ "cloud," nabah- "sky," Skt. nábhas- "moisture, cloud, mist, sky," Gk. nephos "cloud," L. nebula "mist," PIE base *nebhos- "moisture, cloud, mist."
A hollow tube that extends out in front of the objective lens (refractors) or corrector lens (Schmidt-Cassegrains). It shields the exposed optics from wide exposure to the cool ambient air, slowing heat loss and preventing dew formation. Reflector telescopes do not need dew caps because the main mirror rests at the bottom of the tube, which acts as a dew shield.
→ dew + cap, from O.E. cæppe "hood, head-covering," from L.L. cappa "a cape, hooded cloak."
Kolâhak, from kolâh "cap," see below, + similarity suffix -ak. Kolâh "cap," cf. L. celare "to hide, conceal," occulere "to dissimulate," Gk. kalyptein "to cover," kalia "hut, nest," Skt. cala "hut, house," Goth. hilms "helmet," huljan "cover over," hulistr "covering," E. hull "seed covering," from O.E. hulu, from O.H.G. hulla, hulsa, O.E. hol "cave;" PIE base *kel- "conceal." Šabnam→ dew.
noqte-ye šabnam (#)
Fr.: point de rosée
The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.
Fr.: dewar, vase dewar
Insulated bottle containing a cryogenic fluid. The electronic detectors operated at very low temperature are mounted inside a dewar.
Named after its inventor Sir James Dewar (1842-1923), Scottish chemist and physicist.