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operational calculus afmârik-e âpâreši Fr.: calcul opérationnel A method of mathematical analysis which in many cases makes it possible to reduce the study of differential operators, pseudo-differential operators and certain types of integral operators, and the solution of equations containing them, to an examination of simpler algebraic problems. It is also known as operational analysis. → operational; → calculus. |
operationalism âpârešbâvari Fr.: opérationalisme In the philosophy of science, the view that → concepts are defined in terms of measuring operations which determine their applicability. Same as operationism. |
optical aberration birâheš-e nuri Fr.: aberration optique An imperfection in the imaging properties of a lens or mirror. The main aberrations are → chromatic aberration, → spherical aberration, → coma, → astigmatism, → field curvature, → distortion. → optical; → aberration. |
orbital migration kuc-e madâri Fr.: migration orbitale Theoretical prediction according to which a → giant planet, formed in the outer regions of a → protoplanetary disk, could migrate inward by losing → energy and → angular momentum as the result of → gravitational interactions with the remnants of the disk. This orbital migration could explain the presence of giant gaseous Jupiter-like planets (→ hot Jupiters) very close to their host stars. |
partition ratio vÃ¢bar-e parkeš Fr.: rapport de partition The ratio of the → concentration of a → solute in a single definite form in the stationary phase to its concentration in the same form in the other phase at equilibrium. |
pejoration pastÃ¢eš Fr.: pÃ©joration 1) Depreciation; a lessening in worth, quality, etc. Verbal noun of → pejorate. |
photodisintegration šidvâpâši, nurvâpâši Fr.: photodésintégration The process by which atomic nuclei are broken apart into their constituent protons and neutrons by the impact of high energy gamma photons. Photodisintegration takes place during the core collapse phase of a → Type II supernova explosion. → photo- + → disintegration. |
photoevaporation šidboxâreš, nurboxâreš Fr.: photoévaporation A process going on in a molecular cloud surface whereby the surface material ionized by ultraviolet photons of neighboring stars is dissipated. → photo- + → evaporation. |
photometric calibration kabizeš-e šidsanjik, ~ nursanjik Fr.: calibration photométrique A calibration which converts the measured relative magnitudes into an absolute photometry. → photometric + → calibration. |
physical libration halÃ¢zÃ¢n-e fiziki, roxgard-e ~ Fr.: libration physique A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon's rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon's near side. The Moon's physical libration is about 0.03Â° in longitude and about 0.04Â° in latitude. |
plane of vibration hâmon-e šiveš Fr.: plan de vibration In a → linearly polarized light, a plane perpendicular to the → plane of polarization and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the electric vector (E) of the electromagnetic light wave. → plane; → polarization. |
planetary aberration birâheš-e sayyâreyi Fr.: aberration planétaire The difference between the true position of a planet and its apparent position, due to the time required for light to travel the distance from the planet to Earth. Correction for planetary aberration is necessary in determining orbits. → planetary; → aberration. |
Pogson's ratio vâbar-e Pogson Fr.: rapport de Pogson The constant 2.512, which is the 5th → root of 100 (2.512^{5} = 100); the ratio between two successive stellar → magnitudes. → Pogson's relation; → ratio. |
radial migration kuc-e šo'â'i Fr.: migration radiale The process whereby a → disk star changes its → galactocentric distance. Radial migration involves → angular momentum transfer, resulting from → resonances created by transient → density waves such as → bars or → spiral arms in → galactic disks. According to → galactic dynamics models, → churning is the main cause of radial migration. Radial migration of stars plays an important role in shaping the properties of galactic disks. |
radiative acceleration šetâb-e tâbeši Fr.: accélération radiative The acceleration imparted to matter by → radiation pressure. → radiative; → acceleration. |
radius of gyration šo'â'-e lereš Fr.: gyrorayon Same as → Larmor radius. |
ratio vâbar Fr.: rapport Math.: The quotient of two quantities arrived at by dividing one by the other. From L. ratio "reckoning, calculation," also "reason," from rat-,
p.p. stem of reri "to reckon, calculate," also "think," → reason. Vâbar, on the model of Fr. rapport "bringing back," as above, from vâ- prefix meaning "back to the original place, again," → re-, + bar present stem of bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry"). |
rational 1) râyani, râyanvâr; 2) xeradâné, xeradmandâné; 3) vâbari Fr.: rationnel 1) Having or exercising the ability to → reason. M.E. racional, from O.Fr. racionel, from L. rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason," from rat-, pp. stem of reri "to reckon, calculate; consider, think." 1) Râyani, of or pertaining to râyan, → reason. |
rational number 'adad-e vâbari Fr.: nombre rationnel Any number that can be expressed as a ratio of two integers, providing the second number is not zero. |
rationale râyanal Fr.: raisonnement, exposé raisonné 1) The fundamental reason or reasons serving to account for something. L. neuter of rationalis. |
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