<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara Arc ari Arr ash ass ast ast asy atm ato att aut ave axi Bab bal Bal bar bar bea Bek Bes bia Big bin bin bip biv bla bli blu Boh Bol Bos bou bra bri bro buo cal cal can cap car Car cat cat CCD Cen cen CH cha cha che Che chr cir cir cit cla clo clo clu Coa coe coh col col col com com com com com com com com Com con con con con con con con con con con con con Cop Cor cor cor cos cos cou cou Cow cre cri cro cry cur cya Cyg dan dar dat de- deb dec dec ded def deg del dem den dep des det dev dia dif dif dih dio Dir dis dis dis dis dis dis DO don dou dow dro dur dwa dyn Dys ear ebb ecl edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ esc eth Eur Eve exa exc exe exi exp exp ext ext ext fac fal far fed Fer fer fie fin fir fis fla flo flu fol for for fou fra fre Fre fro fut G-t gal gal gam gas Gau Gem gen geo geo geo gia Gli Gol gra gra gra gra gre gri gui H I Hag hal har hat He- hea hel Hel her Hes hie hig his hom hor hot Hub Hug hur hyd hyd hyg hyp ice ide ima Ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv Io ion iro isl iso iso Jac jet jud jur Kel Kep kil Klo Kui Lag lam Lap Lar lat law lea len lep Lib lig lim lin lin Lio lit loc LOF lon Lor low lum lun Lup Lyo mac mag mag mag mag mag mai man Mar mas mas mat Max mea mec Meg Mer Mer met met Met mic Mid Mil min Mir mit mod mod mol mon Mor mou mul mul mys nan Nat nau nec neo neu nev New NGC no nom non non nor not nuc nuc num nut obj obs obs occ ocu oft ome Oor ope opp opt opt orb ord ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per per pha phi pho pho pho phy pio Pla pla pla pla Pla plu Poi pol pol pol poo pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro Pro pro pse pul pur qua qua qua qua que rac rad rad rad rad rad rad ran rar ray rea rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot Rus Sac sal sat sca sca Sch sci Scu sec sec Sed sel Sel sen ser Sex Sha she sho sid sig sil sim sin siz sla Sma sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi spr squ sta sta sta sta ste ste ste Sto Str str str sub sub suc sun sup sup sup sup sur swa syn syn tab tar tek tem ter tes the the the the Tho thr tid tim Tis Too Tor tra tra Tra tra tra tri tri tru Tul tur two Typ ult un- und uni uni unk upp Urc utt val var vec vel ver vib vio vir vis voi vor wan wat wav wax wea Wei whi Wil win WN9 wor X-r yel you zer zod > >>
Schottky barrier varqe-ye Schottky Fr.: barrière de Schottky A junction between a metal and a semiconductor, which exhibits rectifying characteristics. A Schottky barrier has a very fast switching action and low forward voltage drop of about 0.3 volts, compared with 0.6 volts in silicon diodes, which use adjacent p-type and n-type semiconductors. Named after Walter Hans Schottky (1886-1976), German physicist, who described the phenomenon; → barrier. |
Schottky defect âk-e Schottky Fr.: défaut de Schottky An unoccupied position in a crystal lattice which forms when oppositely charged ions leave their lattice sites, creating vacancies. Named after Walter Hans Schottky (1886-1976), German physicist; → defect. |
Schottky diode diod-e Schottky (#) Fr.: diode Schottky A → semiconductor diode containing a → Schottky barrier. Such a diode has a low forward voltage drop and very fast switching characteristics. Also called Schottky barrier diode and hot electron diode. → Schottky barrier; → diode. |
Schottky noise nufe-ye Schottky Fr.: bruit de Schottky Excess voltage generated by random fluctuations in the emission of electrons from a hot cathode, causing a hissing or sputtering sound (shot noise) in an audio amplifier and causing snow on a television screen. Same as → shot effect, → shot noise. Named after Walter Hans Schottky (1886-1976), German physicist; → noise. |
Schrödinger equation hamugeš-e Schrödinger Fr.: équation de Schrödinger A fundamental equation of physics in → quantum mechanics the solution of which gives the → wave function, that is a mathematical expression that contains all the information known about a particle. This → partial differential equation describes also how the wave function of a physical system evolves over time. Named after Erwin Schrödinger (1887-1961), the Austrian theoretical physicist, Nobel Prize 1933, who first developed the version of quantum mechanics known as → wave mechanics; → equation. |
Schrödinger's cat gorbe-ye Schrödinger (#) Fr.: chat de Schrödinger A → thought experiment intended to illustrate the → superposition principle in → quantum mechanics. A cat is put in a steel box which is separated from the outside world. The box also contains a vial of lethal acid, a tiny amount of a radioactive substance, a → Geiger counter, and a hammer. If an atom decays and the Geiger counter detects an → alpha particle, the hammer breaks the vial which kills the cat. According to Schrödinger, as long as the box stays closed the cat's fate is tied to the → wave function of the atom, which is itself in a superposition of decayed and un-decayed states. Thus the cat must itself be in a superposition of dead and alive states before the observer opens the box, "observes" the cat, and "collapses" its wave function. However, Schrödinger's argument fails because it rests on the assumption that macroscopic objects can remain unobserved in a superposition state. When an atom decays, its wave function becomes entangled with the enormously complex wave function of the macroscopic Geiger counter. The atom is therefore "observed" by the Geiger counter. Since a Geiger counter cannot, for all practical purposes, be isolated from the rest of the world, the rest of the world observes the atom, and the cat is either dead or alive. → collapse of the wave function. Named after Erwin Schrödinger (1887-1961), → Schrödinger equation, who proposed the thought experiment in 1935 in order to illustrate the inconsistency of the Copenhagen interpretation of quantum mechanics; cat, from M.E. cat, catte; O.E. catt, catte (cf. O.Fris, M.D. katte, O.H.G. kazza, Ir. cat, Welsh cath), probably from L.L. cattus, catta "cat." Gorbé, from Mid.Pers. gurbag "cat;" → Schrodinger equation, |
Schröter's effect oskar-e Schröter Fr.: effet de Schröter A phenomenon in which the observed and predicted phases of Venus do not coincide. At eastern elongation, when the planet is visible in the evening sky, dichotomy (half-phase) usually comes a day or two earlier than predicted, while at western elongation dichotomy occurs a day or two later. Named after Johan Schröter (1745-1816), German astronomer, who first described the effect in 1793; → effect. |
Schrodinger equation hamugeš-e Schrödinger Fr.: équation de Schrödinger A fundamental equation of physics in → quantum mechanics the solution of which gives the → wave function, that is a mathematical expression that contains all the information known about a particle. This → partial differential equation describes also how the wave function of a physical system evolves over time. Named after Erwin Schrödinger (1887-1961), the Austrian theoretical physicist, Nobel Prize 1933, who first developed the version of quantum mechanics known as → wave mechanics; → equation. |
Schrodinger's cat gorbe-ye Schrödinger (#) Fr.: chat de Schrödinger A → thought experiment intended to illustrate the → superposition principle in → quantum mechanics. A cat is put in a steel box which is separated from the outside world. The box also contains a vial of lethal acid, a tiny amount of a radioactive substance, a → Geiger counter, and a hammer. If an atom decays and the Geiger counter detects an → alpha particle, the hammer breaks the vial which kills the cat. According to Schrödinger, as long as the box stays closed the cat's fate is tied to the → wave function of the atom, which is itself in a superposition of decayed and un-decayed states. Thus the cat must itself be in a superposition of dead and alive states before the observer opens the box, "observes" the cat, and "collapses" its wave function. However, Schrödinger's argument fails because it rests on the assumption that macroscopic objects can remain unobserved in a superposition state. When an atom decays, its wave function becomes entangled with the enormously complex wave function of the macroscopic Geiger counter. The atom is therefore "observed" by the Geiger counter. Since a Geiger counter cannot, for all practical purposes, be isolated from the rest of the world, the rest of the world observes the atom, and the cat is either dead or alive. → collapse of the wave function. Named after Erwin Schrödinger (1887-1961), → Schrodinger equation, who proposed the thought experiment in 1935 in order to illustrate the inconsistency of the Copenhagen interpretation of quantum mechanics; cat, from M.E. cat, catte; O.E. catt, catte (cf. O.Fris, M.D. katte, O.H.G. kazza, Ir. cat, Welsh cath), probably from L.L. cattus, catta "cat." Gorbé, from Mid.Pers. gurbag "cat;" → Schrodinger equation, |
Schroter's effect oskar-e Schröter Fr.: effet de Schröter A phenomenon in which the observed and predicted phases of Venus do not coincide. At eastern elongation, when the planet is visible in the evening sky, dichotomy (half-phase) usually comes a day or two earlier than predicted, while at western elongation dichotomy occurs a day or two later. Named after Johan Schröter (1745-1816), German astronomer, who first described the effect in 1793; → effect. |
Schwarzschild barrier varqe-ye Schwarzschild Fr.: barrière de Schwarzschild An upper theoretical limit to the → eccentricity of orbits near a → supermassive black hole (SBH). It results from the impact of → relativistic precession on the stellar orbits. This phenomenon acts in such a way as to "repel" inspiralling bodies from the eccentric orbits that would otherwise lead to capture as → extreme mass ratio inspiral (EMRI)s. In other words, the presence of the Schwarzschild barrier reduces the frequency of EMRI events, in contrast to that predicted from → resonant relaxation. Resonant relaxation relies on the orbits having commensurate radial and azimuthal frequencies, so they remain in fixed planes over multiple orbits. In the strong-field potential of a massive object, orbits are no longer Keplerian but undergo significant perihelion precession. Resonant relaxation is only efficient in the regime where precession is negligible. The Schwarzschild barrier refers to the boundary between orbits with and without significant precession. Inside this point resonant relaxation is strongly quenched, potentially reducing inspiral rates. |
Schwarzschild black hole siyahcâl-e Schwarzschild Fr.: trou noir de Schwarzschild A → black hole with zero → angular momentum (non-rotating) and zero electric charge derived from Karl Schwarzschild 1916 exact solution to Einstein's vacuum → field equations. Karl Schwarzschild (1873-1916), German mathematical physicist, who carried out the first relativistic study of black holes. → black hole. |
Schwarzschild metric metrik-e Schwarzschild Fr.: métrique de Schwarzschild In → general relativity, the → metric that describes the → space-time outside a static mass with spherically symmetric distribution. |
Schwarzschild radius šo'â'-e Schwarzschild Fr.: rayon de Schwarzschild The critical radius at which a massive body becomes a → black hole, i.e., at which light is unable to escape to infinity: R_{s} = 2GM / c^{2}, where G is the → gravitational constant, M is the mass, and c the → speed of light. The fomula can be approximated to R_{s}≅ 3 x (M/Msun), in km. Therefore, the Schwarzschild radius for Sun is about 3 km and for Earth about 1 cm. |
Schwarzschild singularity takini-ye Schwarzschild Fr.: singularité de Schwarzschild A region of infinite → space-time curvature postulated to lie within a → black hole. |
Schwarzschild solution luyeš-e Schwarzschild Fr.: solution de Schwarzschild The first exact solution of → Einstein's field equations that describes the → space-time geometry outside a spherical distribution of mass. Briefly following Einstein's publication of → General Relativity, Karl Schwarzschild discovered this solution in 1916 (Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin, Phys.-Math. Klasse, 189); → Schwarzschild black hole. |
Schwarzschild's criterion sanjdiâr-e Schwarzschild Fr.: critère de Schwarzschild The condition in stellar interior under which → convection occurs. It is expressed as: |dT/dr|_{ad} < |dT/dr|_{}rad, where the indices ad and rad stand for adiabatic and radiative respectively. This condition can also be expressed as: ∇_{ad}<∇_{rad}, where ∇ = d lnT / d lnP = P dT / T dP with T and P denoting temperature and pressure respectively. More explicitly, in order for convection to occur the adiabatic temperature gradient should be smaller than the actual temperature gradient of the surrounding gas, which is given by the radiative temperature gradient if convection does not occur. Suppose a hotter → convective cell or gas bubble rises accidentally by a small distance in height. It gets into a layer with a lower gas pressure and therefore expands. Without any heat exchange with the surrounding medium it expands and cools adiabatically. If during this rise and → adiabatic expansion the change in temperature is smaller than in the medium the gas bubble remains hotter than the medium. The expansion of the gas bubble, adjusting to the pressure of the medium, happens very fast, with the speed of sound. It is therefore assumed that the pressure in the gas bubble and in the surroundings is the same and therefore the higher temperature gas bubble will have a lower density than the surrounding gas. The → buoyancy force will therefore accelerate it upward. This always occurs if the adiabatic change of temperature during expansion is smaller than the change of temperature with gas pressure in the surroundings. It is assumed that the mean molecular weight is the same in the rising bubble and the medium. See also → Ledoux's criterion; → mixing length. Named after Karl Schwarzschild (1873-1916), German mathematical physicist (1906 Göttinger Nachrichten No 1, 41); → criterion. |
science dâneš (#) Fr.: science 1) The study of the physical and natural phenomena, especially
by using systematic observation and experiment. M.E., from O.Fr. science, from L. scientia "knowledge," from sciens (genitive scientis), pr.p. of scire "to know," probably originally "to separate one thing from another, to distinguish," related to scindere "to cut, divide;" PIE base *skei- "to cut, split;" cf. Pers. gosastan "to tear, cut, break," from Mid.Pers. wisistan "to break, split," Av. saed-, sid- "to split, break," asista- "unsplit, unharmed;" Skt. chid- "to split, break, cut off;" Gk. skhizein "to split;" Goth. skaidan; O.E. sceadan "to divide, separate." Dâneš, verbal noun of dân-, dânestan "to know" (Mid.Pers. dânistan "to know"), variant šenâxtan, šenâs- "to recognize, to know" (Mid.Pers. šnâxtan, šnâs- "to know, recognize"); O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" cf. Skt. jñā- "to recognize, know," jānāti "he knows;" Gk. gignoskein "to know, think, judge," cognate with L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); P.Gmc. *knoeanan; O.E. cnawan, E. know; Rus. znat "to know;" PIE base *gno- "to know." |
science fiction dâneš-dizan Fr.: science fiction A form of fiction that draws imaginatively on scientific knowledge and speculation in its plot, setting, theme, etc. (Dictionary.com). |
scientific dâneši, dânešik Fr.: scientifique Of or pertaining to science or the sciences. From M.Fr. scientifique, from M.L. scientificus "pertaining to science," from L. scientia "knowledge," → science, + -ficus "making," from facere "to make." → -ic |
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