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stereoscope estereyo-namâ, barjaste-namâ Fr.: stéréoscope An optical instrument for viewing an overlapping pair of photographs (or perspective drawings) in order to see a three-dimensional image. |
sterile setarvan (#) Fr.: stérile Incapable of producing offspring; not producing offspring (Dictionary.com). M.Fr. stérile "not producing fruit," from L. sterilis "barren, unproductive, unfruitful," from PIE *ster- "stiff, rigid, firm, strong." Satarvan, literally "mule-like, resembling a mule," from setar, variant of astar, → mule, + -van similarity and attribution suffix. |
sterile neutrino notrino-ye setarvan Fr.: neutron stérile A hypothetical type of → neutrino which does not participate in the → weak interaction. It would arise only from ordinary neutrinos oscillating into a sterile form (singlet, right handed → helicity). The sterile neutrino is a candidate for the → dark matter. Sterile neutrinos might have been produced in primordial plasma in the → early Universe. The idea of sterile neutrino was first proposed by Bruno Pontecorvo (1967) in a paper which also discussed neutrino oscillations. |
Stern-Gerlach experiment âzmâyeš-e Stern-Gerlach (#) Fr.: expérience de Stern et Gerlach An experiment devised for measuring the → magnetic moment of → silver atoms. A → beam of silver atoms is directed between the → poles of a non-homogeneous → magnetic field. Contrarily to the prediction of the classical theory, the atoms divide into two distinct parts. One half of atoms are deflected up, the other half deflected down. The amount of deflection up or down is exactly of the same magnitude. Whether an individual atom is deflected up or down appears to be random. From a measurement of the → deflection, one can find the strength of the magnetic moment. This experience provides proof that there exist only two permitted orientations, called the → quantization of → spin. In honor of Otto Stern (1888-1969), German physicist, Nobel laureate in Physics 1943, and Walter Gerlach (1889-1979), German physicist, who carried out the experiment in 1922. They used a beam of silver atoms from a hot oven because they could be readily detected on a photograph emulsion. Moreover, the silver atoms allowed studying the magnetic properties of a single electron because the atoms have a single outer electron; → experiment. |
stilb (sb) estilb Fr.: stilb Optics: A unit of luminance equal to one candle per square cm. From Gk. stilbe "lamp." |
stimulate gavâzidan Fr.: stimuler To cause physical activity in something; e.g. → stimulated emission. Verb from → stimulus. |
stimulated emission gosil-e gavâzidé Fr.: émission stimulée The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or "ground state"), can "stimulate" a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission. |
stimulated star formation diseš-e gavâlide-ye setâré Fr.: formation stimulée d'étoiles A process in which a star is not formed spontaneously but is provoked by the action of external forces, such as pressure and shock on a molecular cloud by close-by → massive stars, → supernova explosions, etc. See also → sequential star formation. Stimulated, p.p. of → stimulate; → star formation. |
stimulus gavâz Fr.: stimulus Something that incites or rouses to action; an incentive. From L. stimulus "goad, spur;" cognate with Pers. tiz→ sharp. Gavâz "goad, a stick with a pointed end, for driving cattle," Mid.Pers. *gawâz, lowned in Arm. gawazan "goad;" Av. gauuāza- "whip, stick for driving cattle," from gao- "cattle, cow" (→ Bootes) + āza-, from az- "to drive," azaiti "drives;" cf. Skt. aj- "to drive," ájati "drives;" Gk. agein "to lead, guide, drive;" L. agere "to do, set in motion," → act. |
Stirling's approximation nazdineš-e Stirling Fr.: approximation de Stirling A mathematical formula yielding an approximate value for → factorial n, when n is large: n! ≅ (2πn)^{1/2}n^{n}e^{-n}, where e is the base of → natural logarithm. Named after James Stirling (1692-1770), a Scottish mathematician; → approximation. |
stochastic kâturgin Fr.: stochastique Involving or containing a random variable or variables. A stochastic variable is neither completely determined nor completely random. A system containing one or more stochastic variables is probabilistically determined. From Gk. stokhastikos "able to guess, conjecturing," from stokhazesthai "to aim at, guess," from stokhos "a guess, target," literally "pointed stake." Kâturgin, from kâtur, kâturé, → random + -gin, adj. suffix, contraction of âgin "filled." |
stochastic excitation barangizeš-e kâturgin Fr.: excitation stochastique The mechanism arising from turbulent convection in the → convective zone of stars, which is responsible for the driving of stellar → pulsation modes. In stars cooler than typically ~ 7 500 K (→ F-type stars and cooler), the stochastic excitation occurs in the convection envelope. In massive stars, it may develop either in the → convective core or in the convective layer beneath the → photosphere. Recent studies suggest that in → Be stars stochastic excitation takes place in the convective core. The stochastic waves can transport → angular momentum from the core to the surface. Fast rotation, as in Be stars, amplifies the stochastic excitation. → stochastic; → mode. |
stochastic process farâravand-e kâturgin Fr.: processus stochastique Any process involving a sequence of random variables. The future evolution of a stochastic process is therefore described by probability distributions. → stochastic; → process. |
stochastic self-propagating star formation diseš-e setâregân bâ xod-tuceš-e kâturgin Fr.: formation d'étoiles par auto-propagation stochastique A mechanism that could be responsible for global → spiral structure in galaxies either by itself or in conjunction with spiral → density waves. In this mechanism, star formation is caused by → supernova-induced → shocks which compress the → interstellar medium. The → massive stars thus formed may, when they explode, induce further → star formation. If conditions are right, the process becomes self-propagating, resulting in agglomerations of young stars and hot gas which are stretched into spiral shaped features by → differential rotation. Merging of small agglomerations into larger ones may then produce large-scale spiral structure over the entire galaxy. The SSPSF model, first suggested by Mueller & Arnett (1976) was developed by Gerola & Seiden (1978). While the → density wave theory postulates that spiral structure is due to a global property of the galaxy, the SSPSF model examines the alternative viewpoint, namely that spiral structure may be induced by more local processes. The two mechanisms are not necessarily mutually exclusive, but they involve very different approaches to the modeling of galaxy evolution. The SSPSF gives a better fit than the density wave theory to the patchy spiral arms found in many spiral galaxies. However, it cannot explain → galactic bars. → stochastic; → self; → propagate; → star; → formation. |
stoicheiology stoyxiyošenâsi Fr.: stoicheiologie 1) The statement or discussion of the first principles of any science or art (1913 Webster). → stoichiometry, → -logy. |
stoichiometric stoyxiyosanjik Fr.: stoechiométrique 1) Of or pertaining to → stoichiometry. → stoichiometry; → -ic. |
stoichiometry stoyxiyosanji Fr.: stoechiométrie 1) The branch of chemistry that studies chemical processes within the context of the laws of
definite proportions
and conservation of matter and energy. From Gk. stoikheion "element, component, principle," Stoikheia
"elements" (the title of Euclid's great collection of Gk. mathematics);
loaned in Ar. and Pers. (9-th century A.D.) as ustuqus ( Stoyxiyosanji, from stoyxiyo loan from Gk., as above, + -sanji, → -metry. |
stokes (st) stokes (#) Fr.: stokes The unit of → viscosity in the → cgs system, cm^{2} s^{-1}, equal to 10^{-4} m^{2} s^{-1}. After Sir George Gabriel Stokes (1819-1903), a British mathematician and physicist, who made important contributions to fluid dynamics, optics, and mathematical physics; → Stokes law; → Stokes parameter. |
Stokes friction factor karvand-e mâleš-e Stokes Fr.: facteur de friction de Stokes For the translational motion of a spherical body moving in a → viscous fluid, the proportionality factor between the uniform flow velocity far from the sphere and the drag force, provided no-slip boundary condition and small → Reynolds numbers: f = 6πηR, where η is the Reynolds number and R radius of the sphere. |
Stokes law qânun-e Stokes (#) Fr.: loi de Stokes 1) Fluid mechanics: At low velocities, the frictional force on a
spherical body moving through a fluid at constant velocity is equal to
6πRηv, where R is the radius of the sphere,
η the fluid → viscosity, and v the velocity. |
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