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Global Positioning System (GPS) râžmân-e nehešdâd-e jahâni Fr.: système de positionnement par satellites A coordinate positioning tool, using a combination of satellites that can rapidly and accurately determine the → latitude, → longitude, and the → altitude of a point on or above the Earth's surface. The GPS is based on a constellation of 24 Earth-orbiting satellites at an altitude of about 26,000 km. The system is a direct application of the thories of → special relativity and → general relativity. → global; → positioning; → system. |
gluon gluon (#) Fr.: gluon The hypothetical particle, in the → quantum chromodynamics theory, that carries the force between → quarks. There are eight independent types of gluon. From glue (O.Fr. glu, from L.L. glus "glue," from L. gluten "glue") + → -on. |
gnomon bâhu Fr.: gnomon 1) A rod oriented in such a way that its shadow, cast by the Sun's
rays, shows the hours on a → sundial; a style. From L. gnomon, from Gk. gnomon "carpenter's square, rule; indicator," literally "one who discerns," from gignoskein "to know, think, judge," cognate with L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" Mid.Pers. šnâxtan, šnâs- "to know, recognize," dânistan "to know;" Mod.Pers. šenâxtan, šenâs- "to recognize, to know," dânestan "to know;" Skt. jñā- "to recognize, know," jānāti "he knows;" P.Gmc. *knoeanan; O.E. cnawan, E. know; Rus. znat "to know;" PIE base *gno- "to know." Bâhu "stick, staff; arm (from the elbow to the shoulder)," related to bâzu "arm," Mid.Pers. bâzûk "arm;" Av. bāzu- "arm;" cf. Skt. bāhu- "arm, forearm," also "the shadow of the gnomon on a sundial; the bar of a chariot pole;" Gk. pechys "forearm, arm, ell;" O.H.G. buog "shoulder;" Ger. Bug "shoulder;" Du. boeg; O.E. bôg, bôh "shoulder, bough;" E. bough " a branch of a tree;" PIE *bhaghu- "arm." |
gnomonic projection farâšâneš-e bâhu-yi Fr.: projection gnomonique The projection of a spherical surface onto a plane through a point. A gnomonic → map projection displays all great circles as straight lines, and therefore indicates the shortest path between two points. Small circles are projected as conic sections. → gnomon; → -ic; → projection. |
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. |
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. |
graduation padâkeš, padâk dehi, padâk giri Fr.: graduation 1) Marking the scale of an instrument, e.g. the stem of a thermometer is graduated in
degrees. Verbal noun of → graduate. |
grain coagulation mâseš-e dâné Fr.: coagulation des grains Sticking together of micron- to centimetre-sized grains occurring in the interstellar and protoplanetary environments to form larger grain agglomerates. → grain; → coagulation. |
grain evaporation boxâreš-e dâné Fr.: évaporation des grains Conversion of dust grains into smaller grains due to high environmental temperatures. → grain; → evaporation. |
grain formation diseš-e dâné Fr.: formation des grains The process by which dust grains are assembled or produced. |
granulation dâne-bandi Fr.: granulation The mottled appearance of the solar → photosphere, caused by → convective cells, resembling → granules, which rises from the interior of the Sun. Each granule has a mean size of about 1,000 km and an upward velocity of about 0.5 km/sec. Granules are separated by intergranular walls about 400 K colder. They emerge from the fragments of the preceding granules and their lifetimes are about 20 minutes. From → granule + -ation a combination of -ate and -ion, used to form nouns from stems in -ate. Dâne-bandi, from dâné, → grain, + bandi verbal noun of bastan, vastan "to bind, shut;" O.Pers./Av. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind). |
gravitation gerâneš (#) Fr.: gravitation 1) The universal phenomenon of attraction between material bodies.
→ Newton's law of gravitation. Verbal noun of → gravitate. |
gravitational gerâneši (#) Fr.: gravitationnel Of or relating to or caused by → gravitation. Adj. of → gravitation. |
gravitational acceleration šetâb-e gerâneši (#) Fr.: accélération gravitationnelle The acceleration caused by the force of gravity. At the Earth's surface it is determined by the distance of the object form the center of the Earth: g = GM/R^{2}, where G is the → gravitational constant, and M and R are the Earth's mass and radius respectively. It is approximately equal to 9.8 m s^{-2}. The value varies slightly with latitude and elevation. Also known as the → acceleration of gravity. → gravitational; → acceleration. |
gravitational attraction darkešeš-e gerâneši Fr.: attraction gravitationnelle The force that pulls material bodies toward one another because of → gravitation. → gravitational; → attraction. |
gravitational collapse rombeš-e gerâneši (#) Fr.: effondrement gravitationnel Collapse of a mass of material as a result of the mutual → gravitational attraction of all its constituents. → gravitational; → collapse. |
gravitational constant pâyâ-ye gerâneši (#) Fr.: constante gravitationnelle A fundamental constant that appears in → Newton's law of gravitation. It is the force of attraction between two bodies of unit mass separated by unit distance: G = 6.673 x 10^{-8} dyn cm^{2} g^{-2} or 6.673 x 10^{-8} cm^{3}s^{-2}g^{-1}, or 6.673 x 10^{-11} N m^{2} kg^{-2} or 6.673 x 10^{-11} m^{3}s^{-2}kg^{-1}. It was first measured in 1798 by Henry Cavendish (1731-1810), 71 years after Newton's death. Same as the → Newtonian constant of gravitation. → gravitational; → constant. |
gravitational contraction terengeš-e gerâneši Fr.: contraction gravitationnelle Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force. → gravitational; → contraction. |
gravitational coupling constant pâyâ-ye jafsari-ye gerâneši Fr.: constante de couplage gravitationnel The dimensionless gravitational constant defined as the gravitational attraction between pair of electrons and normally given by: α_{G} = (Gm_{e}^{2}) / (ħc) = (m_{e} / m_{P})^{2} ~ 1.7518 × 10^{-45}, where ħ is → Planck's reduced constant, c the → speed of light, m_{e} is the → electron mass, and m_{P} is the → Planck mass. → gravitational; → coupling; → constant. |
gravitational encounter ruyâruyi-ye gerâneši Fr.: rencontre gravitationnelle An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction. → gravitational; → encounter. |
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