Fr.: ampoule fluorescente
A compound (salt of hydrofluoric acid) containing → fluorine.
Gaseous chemical element; symbol F. It is the most reactive of all chemical elements. It is a yellowish, corrosive gas, which reacts with most organic and inorganic substances. → Atomic number 9; → atomic weight 18.9984; → melting point -219.62 °C; → boiling point -188.14 °C; → density 1.696 grams per liter at STP; → valence -1. Fluorine and its compounds are used in producing uranium (from the → hexafluoride) and more than 100 commercial fluorochemicals, including many high-temperature plastics.
From L. fluere "flow, → flux," since fluorspar (CaF2) was used as a flux in metallurgy because of its low melting point. It was discovered in hydrofluoric acid by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 but it was not isolated until 1886 by the French pharmacist and chemist Ferdinand Moisson.
Fr.: fluorite, fluorine
Same as → fluorite.
From fluor-, → fluorine, + spar "a crystalline mineral."
The amount of energy, fluid, or particles passing in a given direction in a unit of time.
O.Fr. flux, from L. fluxus, p.p. of fluere "to flow," PIE base *bhleug- (cf. L. flumen "river;" Gk. phluein "to boil over, bubble up," phlein "to abound").
Šâr "outpouring of water, wine, etc.," šâridan "to flow (as rivers), with a great noise; to pour," âbšâr "waterfall;" saršâr "overflowing; brim-full;" Ossetic ægzælyn "to pour down;" Pashto zγâstəl/zγâl- "to swim;" Av. γžār- "to flow;" cf. Skt. ksar- "to flow;" Gk. phtheirein "to destroy, perish."
Fr.: calibration de flux
The → calibration of the flux received by a detector in terms of absolute units.
Fr.: densité de flux
Flux of radiation that falls on a detector per unit surface area of the detector per unit bandwidth of the radiation per unit time.
Fr.: unité de flux
In radio astronomy, same as → jansky (symbol Jy), a unit of electromagnetic flux equivalent to 10-26 watts per square meter per Hertz.
parvâz kardan (#), parvâzidan (#)
To move through the air using wings. Travel through the air or outer space.
M.E. flien, O.E. fleogan; cognate with O.H.G. fliogan, Ger. fliegen, O.Norse fljuga.
Infinitive from parvâz, → flight.
A trajectory that takes a → space probe close to a Solar System body (planet, satellite, asteroid, comet) but does not permit it to enter an orbit about the body.
→ fly + by, from M.E., from O.E. be or bi, from P.Gmc. *bi "around, about" (cf. Du. bij, Ger. bei "by, at, near"), from *umbi, (cf. L. ambi "around, about," Gk. amphi "around, about," Skt. abhi "on both sides," Av. aibi, aiwi, O.Pers. aiby "to, against, in addition to," Mid.Pers. aw-, ab-, Mod.Pers. af- (as in afzudan "to increase, add," afruxtan "to inflame, kindle, blaze," afqân "lamentation, groaning, cires for help").
Of or relating to a focus; placed at or measured from a focus.
Fr.: distance focale
same as → focal length.
Fr.: longueur focale
The distance between the optical center of a lens, or the surface of a mirror, and its focus.
Fr.: plan focal
A plane at right angles to the principal axis of a lens or mirror on which the best image is formed.
Fr.: point focal
Same as → focus.
Fr.: rapport focal
The ratio of the → focal length of a reflecting surface or lens to its effective diameter, i.e. to its → aperture. The smaller the focal ratio, the smaller the image scale and the more luminous the image for a given aperture.
kâhande-ye kânuni, bâzhâzande-ye ~
Fr.: réducteur focal
1) kânun; 2) kânunidan
Fr.: 1) foyer; 2) focaliser
1) (n.) A point where parallel light rays from an object are gathered together by a
lens or a concave mirror. It is the place where the clearest image of a distant object
forms. Also called focal point. See also → focal distance.
From L. focus "hearth, fireplace," of unknown origin,
Kânun "hearth, fireplace."
Of an optical system, being in focus or brought into focus; adjusted to produce a clear image.
Past participle of → focus.