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Rydberg correction aršâyeš-e Rydberg Fr.: correction de Rydberg A term inserted into a formula for the energy of a single electron in the outermost shell of an atom to take into account the failure of the inner electron shells to screen the nuclear charge completely. → rydberg; → correction. |
Saha equation hamugeš-e Saha Fr.: équation de Saha An equation that gives the number of atoms of a given species in various stages of → ionization that exist in a gas in → thermal equilibrium as a function of the temperature, density, and ionization energies of the atoms. Named after the Indian astrophysicist Megh Nad Saha (1894-1956), who first derived the equation in 1920; → equation. |
Saiph (κ Orionis) Seyf (#) Fr.: Saiph A → supergiant star of visual magnitude 2.06 and → spectral type B0.5 Ia marking the right knee of Orion. It is about 700 light-years away. Saiph "sword," from Ar. as-saiph al-jabbâr
( |
Sakharov conditions butârhâ-ye Sakharov Fr.: conditions de Sakharov The three conditions that are necessary for the generation of a
→ baryon asymmetry in the
→ early Universe. These conditions are: Named after Andrei Sakharov (1921-1989), who in 1967 described these three minimum conditions (A. D. Sakharov, 1967, Zh. Eksp. Teor. Fiz. Pis'ma 5, 32; 1967, JETP Lett. 91B, 24); → condition. |
Salpeter function karyâ-ye Salpeter Fr.: équation de Salpeter The first mathematical description of the → initial mass function (IMF) of newly formed stars of solar to → intermediate-masses. It is proportional to M^{ -2.35}, where M is the stellar mass. → Salpeter slope. Named after the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter (1924-2008); → function. |
sandstone mâse-sang (#) Fr.: grès Variously colored → sedimentary rock composed mainly of sand-like quartz grains cemented by calcite, clay, or iron oxide. The sand accumulated originally underwater in shallow seas or lakes, or on the ground along shorelines or in desert regions. |
saturated solution luyeš-e anjâlidé Fr.: solution saturée A solution which can exist in equilibrium with excess of solute. The saturation concentration is a function of the temperature. |
saturation anjâl, anjâleš Fr.: saturation Physics: Degree of magnetization of a substance which cannot be exceeded
however strong the applied magnetizing field. Verbal noun of → saturate. |
saturation current jarayân-e anjâl, ~ anjâleš Fr.: courant de saturation The maximum current that can be obtained in a specific circuit under specified conditions. → saturation; → current. |
saturation induction darhâzeš-e anjâl, ~ anjâleš Fr.: induction à saturation The maximum intrinsic magnetic induction possible in a material. → saturation; → induction. |
saturation signal nešâl-e anjâl, ~ anjaalesh Fr.: signal de saturation, ~ saturé In radar, a signal whose amplitude is greater than the dynamic range of the receiving system. → saturation; → signal. |
scalar perturbation partureš-e marpeli Fr.: perturbation scalaire The energy density fluctuations in the → photon-baryon plasma that bring about hotter and colder regions. This perturbation creates velocity distributions that are out of phase with the acoustic density mode. The fluid velocity from hot to cold regions causes blueshift of the photons, resulting in → quadrupole anisotropy. → scalar; → perturbation. |
Schechter function karyâ-ye Schechter Fr.: fonction de Schechter A mathematical expression that describes the → luminosity function of galaxies. The function correctly reflects the facts that the luminosity function decreases with increasing luminosity and that the decrease is particularly marked at high luminosities. It is expressed as: φ(L) = φ^{*}(L/L^{*})^{α} exp (-L/L^{*}), which has two parts and three parameters: φ^{*} is an empirically determined amplitude, α is an empirically derived exponent, and L^{*} is a characteristic luminosity which separates the low and high luminosity parts. For small luminosities (L much smaller than L^{*}) the Schechter function approaches a power law, while at high luminosities (L much larger than L^{*}) the frequency of galaxies drops exponentially. φ^{*}, L^{*}, and the faint-end slope α depend on the observed wavelength range, on the → redshift, and on the environment where the galaxies are observed. Named after the American astronomer Paul Schechter (1948-), who proposed the function in 1976 (ApJ 203, 297); → function. |
Schmidt-Kennicutt relation bâzâneš-e Schmidt-Kennicutt Fr.: relation Schmidt-Kennicutt Same as the → Schmidt law. Named after the American astrophysicists Maarten Schmidt (1929-), the pioneer of research in this field, and Robert C. Kennicutt, Jr. (1951-), who developed the study; → relation. |
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. |
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. |
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 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 notation namâdgân-e dâneši, ~ dânešik Fr.: notation scientifique A compact format for writing very large or very small numbers. Numbers are made up of three parts: the coefficient, the base and the exponent. For example 3.58 x 10^{4} is the scientific notation for 35,800. → scientific; → notation. |
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