Fr.: intégrales de Fresnel
Two integrals that involve quadratic equations in the sine and cosine functions and are defined as: C(x) = ∫ cos (πt2/2) dt and C(y) = ∫ sin (πt2/2) dt, integrated from 0 to x. They are quite frequently used in optics studying → Fresnel diffraction and similar topics. The Fresnel integrals are also used in railway and freeway constructions. These integrals may be evaluated to arbitrary precision using → power series. Alternatively the amplitudes may be found graphically by use of → Cornu's spiral.
adasi-ye ferenel (#)
Fr.: lentille de Fresnel
An optical lens composed of a series of rings of glass so curved that they all have the same focus. It is flat on one side and ridged on the other making it possible that nearly every ray of light from the source be re-directed out on a horizontal path. This design enables the construction of lenses of large aperture and short focal length avoiding thus the large weights and volumes of material which would be required in conventional lenses. The first Fresnel lens, designed for use in a lighthouse on the river Gironde, was installed in France in 1823, and by the 1850s many examples were in use everywhere. Fresnel lenses are most often used in light gathering applications, such as condenser systems or emitter/detector setups. They can also be used as magnifiers and projection lenses. Nowadays, Fresnel lenses made of optical plastics are widely used for various applications.
âyene-ye Fresnel (#)
Fr.: miroir de Fresnel
A pair of plane mirrors which are slightly inclined to one another. It is used for producing two coherent images in interference experiments.
Fr.: parallélépipède de Fresnel
A piece of special glass in the form of an oblique → parallelepiped so cut that a ray of light entering one of its faces at right angles shall emerge at right angles at the opposite face, after undergoing two internal reflections. It is a type of → quarter-wave retarder used to produce a → circularly polarized light from a → plane polarized light, or the reverse.
domanšur-e Fresnel (#)
Fr.: biprisme de Fresnel
An optical element consisting of two small angle → prisms, joined together at their bases, used to produce two → coherent sources. The thin double prism refracts the light from a source into two overlapping beams, which produce → interference fringes. With this experiment Fresnel was able to produce interference without relying upon → diffraction to bring the interfering beams together.
âyenehâ-ye Fresnel (#)
Fr.: miroirs de Fresnel
Two plane mirrors, fitted side by side at a small angle, used to create two mutually → coherent sources in a famous → interference experiment first suggested by A. Fresnel. A point source reflected at the mirrors appears as a pair of → virtual light sources, positioned close together, which interfere with each other due to their → coherence. This arrangement removes the problem that two separate light sources do not produce observable interference on account of their incoherence. Same as Fresnel's double mirror. See also → Fresnel's biprism, → Lloyd's mirror.
The resisting force offered by one body to the relative motion of another body in contact with the first.
From L. frictionem "a rubbing, rubbing down," from fricare "to rub."
Mâleš, verbal noun of mâlidan "to rub," from, variants parmâs "contact, touching," marz "frontier, border, boundary," Mid.Pers. mâlitan, muštan "to rub, sweep;" Av. marəz- "to rub, wipe," marəza- "border, district;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin.
Fr.: paramètre de Fried
One of the parameters that characterize atmospheric → seeing. It is the diameter of the largest aperture that can be used before → turbulence starts to degrade the image quality. As the turbulence gets stronger, the Fried parameter, denoted r0, becomes smaller. The Fried parameter is wavelength dependent: r0 ∝ λ6/5. On best astronomical mountain tops it ranges between 20 and 30 cm for λ = 5000 A.
Named after David L. Fried, who defined the parameter 10 1966; → parameter.
Fr.: équation de Friedmann
An equation that expresses energy conservation in an → expanding Universe. It is formally derived from → Einstein's field equations of → general relativity by requiring the Universe to be everywhere → homogeneous and → isotropic. It is expressed by H2(t) = (8πG)/(3c2)ε(t) - (kc2)/R2(t), where H(t) is the → Hubble parameter, G is the → gravitational constant, c is the → speed of light, ε(t) is the → energy density, k is the → curvature of space-time, and R(t) is the → cosmic scale factor. See also → Big Bang, → accelerating Universe. See also → Friedmann-Lemaitre Universe.
Named after the Russian mathematician and physical scientist Aleksandr Aleksandrovich Friedmann (1888-1925), who was the first to formulate an → expanding Universe based on Einstein's theory of → general relativity ; → equation.
Fr.: univers Friedmann-Lemaître
Fr.: glacial, froid, glacé, frigide
Very cold in temperature.
From Latin frigidus "cold, chill, cool," from stem of frigere "be cold;" related to noun frigus "cold, coldness, frost," from PIE root *srig- "cold;" cf. Gk. rhigos "cold, frost."
Sajan "very cold," variants šaja,, sajâm, šajad, Oss. I. syjyn/syd, D. sujun/sud "to freeze," Yaghnobi ši-, Yazghulami šed/šiy- "to freeze," Shughni šitô , Sariqoli š(i)tu "cold, ice." Proto-Ir. *saiH-/siH- "to freeze." Skt. syā- "to freeze, coagulate, become rigid."
1) One of the alternating bright or dark bands produced by
→ interference or → diffraction.
From M.E. frenge, from O.Fr. frange, from V.L. *frimbia, metathesis of L. fimbriæ "fibers, threads, fringe," of uncertain origin.
Fariz, contraction of farâviz "fringe, lace, edging," from far-, par-, variant pirâ- "around, about" (Mid.Pers. pêrâ; O.Pers. pariy "around, about," Av. pairi "around, over;" Skt. pari; Indo-Iranian *pari- "around;" PIE base *per- "through, across, beyond;" cf. Gk. peri "around, about, beyond;" L. per "through") + âviz "anything suspended; a place where things are hung up; a border, margin," from âvixtan, âvizidan "to hang, suspend;" Mid.Pers. âwextan "to hang;" Av. vij- "to shake, swing," frauuaēγa- "swinging forward;" cf. Skt. vej- "to dart up or back, move up;" Proto-Iranian *uij- "to shake, swing."
Fr.: face, front
1) The part or side of anything that faces forward.
→ ionization front.
From O.Fr. front "forehead, brow," from L. frontem "forehead," perhaps lit. "that which projects," from PIE *bhront-, from base *bhren- "to project, stand out."
Pišân, from pišâni "front, forehead," from piš
"before; in front," from Mid.Pers. pêš "before, earlier;"
O.Pers. paišiya "before; in the presence of" + -ân suffix
of place and time.
A device containing a radio-frequency amplifier and associated cryogenic systems, routers, and converters (mixers), whose input is the voltage from a receptor and whose output is an intermediate-frequency signal. → back-end.
→ front + end, from O.E. ende, from P.Gmc. *andja, originally "the opposite side," from PIE *antjo "end, boundary," from base *anta-/*anti- "opposite, in front of, before."
Piš-tah, from piš, → front, + tah "end;" Mid.Pers. tah "bottom." The origin of this term is not clear. It may be related to Gk. tenagos "bottom, swamp," Latvian tigas "depth;" PIE *tenegos "water bottom."
A border between two countries.
From O.Fr. fronter, from front "forehead, brow," → front.
Marz, from Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin.
Fr.: givre, gelée
Ice crystals that are formed by deposition of water vapor on a relatively cold surface.
O.E. forst, frost "a freezing, becoming frozen, extreme cold," from P.Gmc. *frusta- (cf. O.H.G. frost, Du. vorst), related to freosan "to freeze."
Bašmé, from bašm "hoar-frost; dew," variants bažm, bašk, pašak "frost; dew," may be related to (Âštiyâni, Qomi dialects) bašand, vašand, vašan "rain" (vašan-sâl "rainy year"), (Lori, Laki) vašt "rain shower," (Gurâni) wašt, wišani "rain" (Tâti Karingâni) vurasten "to rain;" Av. -varšta- "rain," aiwi-varšta- "rained upon;" Skt. vars- "to rain," varsá- "rain;" M.Irish frass "rain shower, torrent;" Gk. eérse "dew," oureo "to urinate."
Fr.: nombre de Froude
A → dimensionless number that gives the ratio of local acceleration to gravitational acceleration in the vertical.
Named after William Froude (1810-1879), English engineer.
yax basté, rocidé
Past participle of → freeze.
frozen magnetic field line
xatt-e meydân-e meqnâtisi-ye yax basté, ~ ~ ~ rocidé
Fr.: ligne de champ magnétique gelée
âb-e yax basté, âb-e rocidé
Fr.: eau gelée
Past participle of → freeze.