cold sard (#) Fr.: froid Having a relatively low temperature. M.E., from O.E. cald, ceald "cold, cool" (cf. O.Fr. and O.Sax. kald, O.H.G. and Ger. kalt, Goth. kalds "cold"), from PIE root *gel-/*gol- "cold;" cf. L. gelare "to freeze," gelu "frost," glacies "ice;" Kurd. girsân, girsiân "to coagulate" (Cheung 2007). Sard "cold, cool," afsordan, afsârdan "to congeal;" Mid.Pers. sard/sart "cold;" Av. sarəta- "cold;" cf. Skt. śiśira- "cold;" L. calidus "warm;" Lith. šaltas "cold;" Welsh clyd "warm;" PIE *keltos- "cool." |
cold absorber daršamgar-e sard Fr.: absorbeur froid A broad → absorption feature observed in → X-ray spectra of → active galactic nuclei (AGN). It is caused by material associated with the → interstellar medium in our → Galaxy and/or the host galaxy of the AGN or cold material near the AGN. → Quasars commonly have their X-ray spectrum absorbed by cold gas between us and the quasar X-ray source (along our → line of sight). This is particularly common in less luminous quasars. See also → warm absorber. |
cold accretion flow tacân-e farbâl-e sard Fr.: écoulement d'accrétion froid 1) A type of → accretion flow by a
→ compact object
such as a → black hole
that consists of cool → optically thick
gas and has a relatively high mass → accretion rate,
in contrast to → hot accretion flows. |
cold dark matter (CDM) mâdde-ye sard-e târik (#) Fr.: matière noire froide Any → hypothetical → non-baryonic → dark matter that is → non-relativistic at the point of → decoupling in the → early Universe. CDM plays a key role in → cosmic structure formation. See also → CDM model, → lambda cold dark matter, → Meszaros effect, → missing satellites problem. |
cold disk accretion gerde-ye farbâl-e sard Fr.: disque d'accrétion froid An accretion process whereby material coming from an → accretion disk settles onto the → protostellar surface through a geometrically thin layer or thin accretion columns. Heat brought into the protostar in the accretion flow radiates freely into space until the temperature attains the photospheric value. Most of the stellar surface is unaffected by the accretion flow (see, e.g., Hosokawa et al. 2010, ApJ 721, 478). |
e-folding time zamân-e e-tâyi Fr.: The time within which the amplitude of an oscillation increases or decreases by a factor e (= 2.71828...). From e the base of the natural, or Napierian, system of logarithms; folding, from -fold suffix meaning "of so many parts," or denoting multiplication by the number indicated by the stem or word to which the suffix is attached (as in twofold; manifold), from O.E. -feald, related to Ger. -falt; Gk. altos, -plos, -plus; → time. Zamân, → time; e, as above; tâyi noun of tâ multiplicative suffix, also "fold, plait, wrinkle; like, resembling." |
flat manifold baslâ-ye taxt Fr.: variété plate A manifold with a → Riemannian metric that has → zero → curvature. |
gold talâ (#), zarr (#) Fr.: or A yellow, → ductile → metal which occurs naturally in veins and alluvial deposits associated with → quartz or → pyrite; symbol Au (L. aurum "shining dawn"). → Atomic number 79; → atomic weight 196.9665; → melting point 1,064.43 °C; → boiling point 2,808 °C; → specific gravity 19.32 at 20 °C. Like other → chemical elements the gold found on Earth has an → interstellar origin. However, the new-born Earth was too hot and most of the molten gold, mixed with → iron, sank to its center to make the core during the first tens of millions of years. The removal of gold to the → Earth's core should have left the Earth's crust depleted of gold. Nevertheless, the precious metal is tens to thousands of times more abundant in the → Earth's mantle than predicted. One explanation for this over-abundance is the → Late Heavy Bombardment. Several hundred million years after the core formation a flux of → meteorites enriched the → Earth's crust with gold (Willbold et al., 2011, Nature 477, 195). M.E., from O.E. gold, from P.Gmc. *gulth- (cf. O.H.G. gold, Ger. Gold, Du. goud, Dan. guld, Goth. gulþ), from PIE base *ghel-/*ghol- "yellow, green;" cf. Mod.Pers. zarr "gold," see below. Talâ "gold," variants tala, tali. |
Goldbach's conjecture hâšan-e Goldbach Fr.: conjecture de Goldbach Every number greater than 2 is the sum of two → prime numbers. Goldbach's number remains one of the most famous unsolved mathematical problems of today. Named after the German mathematician Christian Goldbach (1690-1764); → conjecture. |
golden number adad-e zarrin (#) Fr.: nombre d'or 1) The number giving the position of any year in the lunar or
→ Metonic cycle of about 19 years.
Each year has a golden number between 1 and 19. It is found by adding
1 to the given year and dividing by 19; the remainder in the division
is the golden number. If there is no remainder the golden number
is 19 (e.g., the golden number of 2007 is 13). |
golden ratio vâbar-e zarrin Fr.: nombre d'or If a line segment is divided into a larger subsegment (a) and a smaller subsegment (b), when the larger subsegment is related to the smaller exactly as the whole segment is related to the larger segment, i.e. a/b = (a + b)/a. The golden ratio, a/b is usually represented by the Greek letter φ. It is also known as the divine ratio, the golden mean, the → golden number, and the golden section. It was believed by Greek mathematicians that a rectangle whose sides were in this proportion was the most pleasing to the eye. Similarly, the ratio of the radius to the side of a regular → decagon has this proportion. The numerical value of the golden ratio, given by the positive solution of the equation φ^{2} - φ - 1 = 0, is φ = (1/2)(1 + √5), approximately 1.618033989. The golden ratio is an → irrational number. It is closely related to the → Fibonacci sequence. |
Goldschmidt classification radebandi-ye Goldschmidt Fr.: classification de Goldschmidt A → geochemical classification scheme in which → chemical elements on the → periodic table are divided into groups based on their → affinity to form various types of compounds: → lithophile, → chalcophile, → siderophile, and → atmophile. The classification takes into account the positions of the elements in the periodic table, the types of electronic structures of atoms and ions, the specifics of the appearance of an affinity for a particular → anion, and the position of a particular element on the → atomic volume curve. Developed by Victor Goldschmidt (1888-1947); → classification. |
Humboldt current jarayân-e Humboldt (#) Fr.: courant de Humboldt A cold ocean current that flows northward along the western side of South America, offshore Chile and Peru. Dominate weather in this area includes coastal fog and low clouds. The presence or lack of this current is a vital part of the weather pattern known as El Niño. Named after the German naturalist and explorer Alexander von Humboldt (1769-1859). → current. |
lambda cold dark matter model model-e lâmbdâ-mâde-ye-sard-e-târik Fr.: modèle ΛCDM The → standard model of → Big Bang that incorporates both → dark matter and → dark energy. See also → cold dark matter (CDM). → lambda, → cosmological constant; → cold; → dark; → matter; → model. |
large Reynolds number flow tacân bâ adad-e bozorg-e Reynolds Fr.: écoulement à grand nombre de Reynolds A turbulent flow in which viscous forces are negligible compared to nonlinear advection terms, which characterize the variation of fluid quantities. The dynamics becomes generally turbulent when the Reynolds number is high enough. However, the critical Reynolds number for that is not universal, and depends in particular on boundary conditions. → large; → Reynolds number; → flow. |
magnetic Reynolds number adad-e Reynolds-e meqnâtisi Fr.: nombre de Reynolds magnétique A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → magnetic advection to → magnetic diffusion. It is given by: R_{m} = σμ_{0}νLU_{0}, where σ is the → conductivity of the fluid, μ_{0} is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and U_{0} the characteristic velocity of the flow. A typical value for the Earth is R_{m} ~ 200. → magnetic; → Reynolds number. |
manifold baslâ (#) Fr.: variété A → topological space in which every point has a → neighborhood which resembles → Euclidean space (R^{n}), but in which the global structure may be different. An example of a one-dimensional manifold would be a circle; if you zoom around a point the circle looks locally like a line (R^{1}). An example of a two-dimensional manifold would be a sphere; a small portion looks locally like a plane (R^{2}). See also → flat manifold. O.E. monigfald (Anglian), manigfeald (W.Saxon) "varied in appearance," from manig "many" + -feald "fold." Baslâ, from bas "many, much" (Mid.Pers. vas "many, much;" O.Pers. vasiy "at will, greatly, utterly;" Av. varəmi "I wish," vasô, vasə "at one's pleasure or will," from vas- "to will, desire, wish") + lâ "fold." |
old kohan (#), pir (#) Fr.: vieux Of an astronomical object, having existed as specified with relation to younger or newer objects of the same category; e.g. → old star. From M.E., from O.E. eald, ald; cf. Du. old, Ger. alt, Goth. altheis; akin to O.N. ala "to nourish." Kohan "old, ancient," kohné "worn;" Mid.Pers. kahwan "old, aged,
worn." |
old star setâre-ye kohan (#), kohan-setâré (#), setâre-ye pir (#) Fr.: vielle étoile A member of a population of stars that, according to stellar evolution theories, are almost as aged as the galaxy in which it resides. |
old stellar population porineš-e setâre-yi-ye kohan Fr.: population stellaire vielle A population of stars in a stellar system that have definitely left the → main sequence. → old; → stellar; → population. |