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detonation tarâk (#) Fr.: détonation Instantaneous combustion or conversion of a solid, liquid, or gas into larger quantities of expanding gases accompanied by heat, shock, and a noise. → deflagration; → explosion. Verbal noun of → detonate. |
deuteration dotereš Fr.: deutération The process of introducing → deuterium into a → chemical compound. Verbal noun of → deuterate. |
deuterium fractionation barxâneš-e doteriom 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. → deuterium; → fractionation. |
deuteron doteron (#) Fr.:deutéron 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. |
deviation kažraft Fr.: déviation The act of deviating; departure from a standard or norm. Verbal noun form of → deviate. |
devotion âdâxt, âdâzeš Fr.: dévouement, attachement 1) Profound dedication; consecration. Verbal noun of → devote. |
dextrorotation râstcarxeš Fr.: dextrorotation The clockwise rotation of the → plane of polarization of light (as viewed by an observer looking straight in the incoming light) by certain substances. See also → levorotation. |
diagonal tarâkonj Fr.: diagonale In a → polygon, a line segment joining any two non-adjacent vertices (→ vertex). From M.Fr. diagonal, from L. diagonalis, from diagonus "slanting line," from Gk. diagonios "from angle to angle," from dia- "across, dividing two parts" + gonia "angle," related to gony "knee," L. genu "knee," Mod.Pers. zânu "knee," Av. žnav-, žnu- "knee," Skt. janu-; PIE base *g(e)neu-, see below. Tarâkonj, from tarâ- "across, through," → trans-, + konj "angle, corner, confined place" (variants xong "corner, angle," Tabari kânj, Kurd. kunj, Hamadâni kom), maybe from the PIE base *g(e)neu-, as above, and related to Mod.Pers. zânu "knee" (Av. žnu-), Skt. kona- "angle, corner," Gk. gony, gonia, L. cuneus "a wedge," Albanian (Gheg dialect) kân "angle, corner," Albanian (Toks) kënd "angle, corner." |
diamond almâs (#) Fr.: diamant A crystalline form of → carbon, which is the hardest substance known. Each carbon in a diamond crystal is bonded to four other carbon atoms forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Diamond has a very high → refractive index and → dispersive power. It is colorless when pure, and sometimes colored by traces of impurities. Natural diamond was formed billions of years ago within the Earth → mantle at depths greater than 150 km, where pressure is roughly 5 giga→ pascals and the temperature is around 1200 °C. Diamonds reach the surface of the Earth via volcanic eruptions. Similarly very small diamonds (micrometer and nanometer sizes) are usually found in impact sites of → meteorites. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. When diamond is exposed to high temperatures or ion bombardment, it will be transformed into → graphite. Diamond, from O.Fr. diamant, from M.L. diamant-, diamas-, from L. adamant-, adamas "hardest metal," from Gk. adamas "unbreakable," from → a- "not" + daman "to subdue, to tame;" cognate with Pers. dâm "a tame animal." Almâs, loanword from Gk., as above. |
diamond ring effect oskar-e angoštar-e almâs Fr.: effet anneau de diamant An intense flash of light that happens a few seconds before and after totality during a solar eclipse. The effect is caused by the last rays of sunlight before totality (or the first rays of sunlight after totality) shining through valleys on the edge of the Moon. Oskar, → effect; angoštar "a ring worn on the finger," from angošt "finger," Mid.Pers. angušt "finger, toe," Av. angušta- "toe," from ank- "curved, crooked," cf. Skt. angustha- "thumb," ankah "hook, bent," Gk. angkon "elbow," angkura "anchor," L. angulum "corner" (E. angle), Lith. anka "loop," O.E. ancleo "ankle," O.H.G. ango "hook," PIE base *ang-/*ank- "to bend"; → diamond. |
dictionary farhang (#) Fr.: dictionnaire A reference source in print or electronic form containing words alphabetically arranged along with information about their forms, meanings, pronunciations, etymologies, etc. M.L. dictionarium "collection of words and phrases," from L. dictionarius "of words," from dictio "word" from dic-, p.p. stem of L. dicere "speak, tell, say," from PIE root *deik- "to point out;" cf. Av. daēs- "to show," daēsa- "sign, omen;" cf. Skt. deś- "to show, point out;" → form. Farhang, → culture. |
Dieterici equation hamugeš-e Dieterici Fr.: équation de Dieterici An → equation of state for → real gases which leads to the → van der Waals equation as a → first approximation. It is of the form P(V - b) [exp (a/VRT)] = RT, where P is the pressure, V is the volume, T is the thermodynamic temperature, R is the → gas constant, and a and b are the constants characteristic of the gas. Named after Conrad Dieterici (1858-1929), a German physicist; → equation. |
differentiable function karyâ-ye degarsânipazir, ~ degarsânidani Fr.: différentiable Property of a mathematical function if it has a → derivative at a given point. From → differentiable; → function. |
differential equation hamugeš-e degarsâneyi Fr.: équation différentielle An equation expressing a relationship between an → independent variable, x, an unknown → function, y = f(x), and its → derivatives. The general form of a differential equation is: F(x, y, y', y'', ..., y^{(n)}) = 0, or F(x,y, dy/dx, d^{2}y/dx^{2}, ..., d^{n}y/dx^{n}) = 0. See also: → ordinary differential equation; → partial differential equation; → linear differential equation; → exact differential equation; → first-order differential equation; → homogeneous linear differential equation; → nonhomogeneous linear differential equation; → differential equation with separated variables; → differential equation with separable variables. → differential; → equation. |
differential equation with separable variables hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâyi-pazir Fr.: équation différentielle à variables séparables A → differential equation of the form: M_{1}(x) N_{1}(y) dx + M_{2}(x) N_{2}(y) dy = 0, which can be reduced to a → differential equation with separated variables. → differential; → equation; → separate; → variable. |
differential equation with separated variables hamugeš-e degarsâne-yi bâ vartandehhâ-ye jodâ Fr.: équation différentielle à variables séparées A → differentail equation that can be transformed into the form: M(x)dx + N(x)dy = 0. → differential; → equation; → separate; → variable. |
differential image motion monitor (DIMM) pahregar-e jonbeš-e degarsâneyi-ye vine, ~ ~ ~ tasvir Fr.: moniteur de mouvements d'images différentiels,
moniteur seeing A device that is commonly used to measure the → seeing at optical astronomical sites. The DIMM delivers an estimate of the → Fried parameter based on measuring the variance of the differential image motion in two small apertures, usually cut out in a single larger telescope pupil by a mask. The DIMM concept was introduced by Stock & Keller (1960, in Stars and Stellar Systems, Vol. 1, ed. G. P. Kuiper & B. M. Middlehurst, p. 138), whereas its modern implementation was first described by Sarazin & Roddier (1990, A&A 227, 294). → differential; → image; → motion; → monitor. |
differential refraction šekast-e dagarsâneyi Fr.: refraction différentielle A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction. → differential; → refraction. |
differential rotation carxeš-e degarsâneyi Fr.: rotation différentielle 1) Of a single body (such as a star or a gaseous planet), the axial rotation of
equatorial latitudes faster than polar latitudes. → differential; → rotation. |
differentiation degarsâneš Fr.: (Math.) dériver; (Astro.) différenciation 1) Math.: The operation of finding the → derivative
of a function. Verbal noun of → differentiate. |
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