An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1965 Search : ion
 dilution factor   کروند ِ اوتالش   karvand-e owtâlešFr.: facteur de dilution   The energy density of a radiation field divided by the equilibrium value for the same color temperature.→ dilution; → factor. dimension   وامون   vâmunFr.: dimension   1) Math.: Independent extension in a given direction; a property of space. 2) Physics: → physical dimension.From L. dimensionem (nom. dimensio), from stem of dimetri "to measure out," from → dis- + metri "to measure."Vâmun, from vâ-, → dis-, + mun, variant mân "measure" (as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl"), from O.Pers./Av. mā(y)- "to measure;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum. dimensional   وامونی   vâmuniFr.: dimensionnel   Of or pertaining to → dimension.→ dimension; → -al. dimensional analysis   آنالس ِ وامونی، آناکاوی ِ ~   ânâlas-e vâmuni, ânâkâvi-ye ~Fr.: analyse dimensionnelle   A technique used in physics based on the fact that the various terms in a physical equation must have identical → dimensional formulae if the equation is to be true for all consistent systems of unit. Its main uses are: a) To test the probable correctness of an equation between physical quantities. b) To provide a safe method of changing the units in a physical quantity. c) To solve partially a physical probable whose direct solution cannot be achieved by normal methods.→ dimensional; → analysis. dimensional formula   دیسول ِ وامونی   disul-e vâmuniFr.: formule dimensionnelle   Symbolic representation of the definition of a physical quantity obtained from its units of measurement. For example, with M = mass, L = length, T = time, area = L2, velocity = LT-1, energy = ML2T-2. → dimensional analysis.→ dimensional; → formula. dimensionless   بی‌وامون   bivâmunFr.: sans dimension   A physical quantity or number lacking units.→ dimension; → -less. dimensionless quantity   چندای ِ بی‌وامون   candâ-ye bivâmunFr.: quantité sans dimension   A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number.→ dimension; → quantity. Dione (Saturn IV)   دیونه   DionéFr.: Dioné   The fourth largest moon of Saturn and the second densest after Titan. Its diameter is 1,120 km and its orbit 377,400 km from Saturn. It is composed primarily of water ice but must have a considerable fraction of denser material like silicate rock.Discovered in 1684 by Jean-Dominique Cassini, Italian born French astronomer (1625-1712). In Gk. mythology Dione was the mother of Aphrodite (Venus) by Zeus (Jupiter). dipole radiation   تابش ِ دوقطبه   tâbeš-e doqotbéFr.: rayonnement dipolaire   The electromagnetic radiation produced by an oscillating → electric dipole or → magnetic dipole.→ dipole; → radiation. Dirac annihilation   نابودی ِ دیراک   nâbudi-ye DiracFr.: annihilation de Dirac   Same as → pair annihilation.→ Dirac; → annihilation. Dirac equation   هموگش ِ دیراک   hamugeš-e DirâkFr.: équation de Dirac   The equation that describes the behavior of an → electron in a way that combines the requirements of → quantum mechanics with the requirements of → special relativity. The Dirac equation predicted the existence of antimatter→ Dirac; → equation. Dirac function   کریای ِ دیراک   karyâ-ye DirâkFr.: fonction de Dirac   A function of x defined as being zero for all values of x other than x = x0 and having the definite integral from x = -∞ to x = +∞ equal to unity.→ Dirac; → function direct correlation   هم‌باز‌آنش ِ سرراست   hambâzâneš-e sarrâstFr.: corrélation directe   A correlation between two variables such that as one variable becomes large, the other also becomes large, and vice versa. The correlation coefficient is between 0 and +1. Also called positive correlation.→ direct; → correlation. direct motion   جنبش ِ فرارو، ~ سرراست   jonb eš-e farârow, ~ sarrâstFr.: mouvement direct   The motion of a solar system body from West to East across the sky against the background stars. It is the "normal" direction of motion within the solar system. For rotating or orbiting solar system objects it is anti-clockwise as seen from above the solar system in the direction of the North Pole. The same as → prograde motion. See also → retrograde motion.→ direct; → motion. direction   راستا، سو؛ ۲) راشتاری   1) râstâ, su (#); 2) râštâriFr.: direction   1) A position to which motion or another position is referred. 2) The act or an instance of directing.M.E. direccioun, from M.Fr., from L. direction-, stem of directio "arranging in line, straightening," → direct.1) Râstâ, from direct→ direct + -â dimension suffix; su, from Mid.Pers. sôk "side." 2) Râštâri, noun from râštâr→ director + suffix -i. direction angle   زاویه‌ی ِ راستا   zâviye-ye râstâFr.: angle de direction   An angle made by a given vector and a coordinate axis. The angle between the North and a chosen direction.→ direct; → angle. Dirichlet condition   بوتار ِ دیریکله   butâr-e DirichletFr.: condition de Dirichlet   One of the following conditions for a → Fourier series to converge: 1) The function f(x) is defined and single valued, except possibly at a finite number of points in the interval -π, +π. 2) f(x) has a period of 2π. 3) f(x) and f'(x) are → piecewise continuous functions on -π, +π. Then, the Fourier series converges to: (a) f(x) if x is a point of continuity. (b) (f(x + 0) + f(x - 0))/2, if x is a point of discontinuity.Named after Peter Gustav Lejeune Dirichlet (1805-1859), German mathematician who made valuable contributions to → number theory, → analysis, and → mechanics; → condition. disallocation   واتسک   vâteskFr.: desallouation   The act of disallocating or the state of being disallocated.→ dis- + → allocate. discrete absorption component (DAC)   همنه‌ی ِ درشمی ِ گسسته   hamne-ye daršami-ye gosastéFr.: composante d'absorption discrète   The rapid, systematic changes in the absorption parts of the → P Cygni profiles of the ultraviolet → resonance lines (Si IV, C IV, and N V) observed in a majority of massive → hot stars. DACs are typically seen to accelerate to the → blue wing of the profile over a few days, becoming narrower as they approach the → terminal velocity.→ discrete; → absorption; → component. discrete transition   گذرش ِ گسسته   gozareš-e gosastéFr.: transition discrète   A transition between two quantum-mechanical energy levels. See also → discrete spectrum.→ discrete; → transition.