Fr.: 1) faisceau, 2) lobe, 3) tache de diffraction
1) A collection of nearly parallel → light
→ rays or a concentrated stream of
→ particles. See also → beam of light.
M.E. beem, from O.E. beam "tree;" akin to O.H.G boum "tree," Ger. Baum.
Tâbé, from tâb; tâbidan "light; to shine" + -é noun suffix.
Fr.: efficacité de lobe
A parameter indicating the quality of an antenna as a direction measuring device. It is given by the ratio of the total received power contained in the main beam of an antenna to the total power (including the sidelobes); the same as main beam efficiency. See also → beamwidth.
beam of light
tâbe-ye nur (#)
Fr.: faisceau lumineux
beam of particles
Fr.: faisceau de particules
A narrow unidirectional flow of particles
Fr.: lame séparatrice
A partially reflecting mirror which permits a part of the light beam to pass through and reflects the rest.
→ beam; splitter, from to split, from M.Du. splitten, from P.Gmc. *spl(e)it-, PIE *(s)plei- "to split, splice."
Fâqgar, from fâq "split, breach, division" + tâbé→ beam.
Fr.: permutation de lobe
In single dish radio astronomy, any technique which forms the difference of signals received from two (or more) pointings on the sky without physically moving the main reflector of the antenna. By rapidly forming differences between sky positions that do and do not contain astronomical sources, beam switching can minimize the corruption of spectral baselines by non-idealities in the instrumental frequency response, or of continuum observations by atmospheric fluctuations.
Fr.: largeur de lobe
The angle between the two directions in the main beam at which the power response has fallen to half its maximum value. → beam efficiency.
The periodic and alternatively strengthening and weakening of two waves of similar frequencies when they interfere with one another. In particular, the soft and loud sounds created by the interference of two sound waves of similar frequencies.
M.E. beten, from O.E. beaten, from P.Gmc. *bautan; IER *bhau- "to strike."
Zaneš, noun from zan- present tense stem of zadan "to beat, strike" + -š verbal noun suffix. Zadan from Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *gwhen- "to strike, kill."
Fr.: céphéide à battement
A Cepheid variable in which two or more almost identical periods of variability pass into and out of phase with each other, producing periodic amplitude fluctuations in their light curves. Beat periods are typically about 2 hours.
Fr.: échelle de Beaufort
A system for estimating and reporting wind speeds which has 13 standardized categories and associated descriptions. The Beaufort scale ranges from 0 for complete calm to 12 for a cyclone. In this scale, the wind speed (in km/h) equals 3B1.5, where B is the Beaufort number of the wind. The scale was originally devised for use at sea but has subsequently been modified for use over land.
Named after Admiral Sir Francis Beaufort (1774-1857), who introduced the first version of the system in 1805; → scale.
A combination of qualities that pleases the mind.
M.E. be(a)ute, from O.Fr. beautez, beltet "beauty, seductiveness, beautiful person" from V.L. bellitatem (nominative bellitas) "state of being handsome," from L. bellus "pretty, charming."
Zibâyi, from zibâ "beautiful," related to zib "beauty, elegance, ornament," zibidan "to suit, to adorn."
Fr.: parce que
For the reason that; on account of.
M.E. bi cause "by cause," from O.E. bi "by" (akin to Du. bij, O.H.G. bi, Ger. bei, Goth. bi) + → cause.
Zirâ, variants azirâ, zirâk, azirâk, from Mid.Pers. êt rây cê or ê(t) râd cê "because," literally "this reason why;" from êd "this" (O.Pers. aita; Av. aēta "this;" cf. Skt. etá); rây, → reason; cê "what" (O.Pers/Av. ci- "what, any," collateral stem to ka- "who?, what?;" cf. Skt. ka-; Gk. po-; L. quo-; E. what, who; PIE *qwos/*qwes).
Fr.: objet de Becklin-Neugebauer
A compact infrared source in the Orion molecular cloud (OMC-1). It is thought to be a very dusty compact H II region surrounding a young B0 or B1 star.
After Eric Becklin (1940-), and Gerry Neugebauer (1932-) who discovered the object in 1967; → object.
To come, change, or grow to be.
M.E. becumen; O.E. becuman "happen, come about," also "meet with, arrive;" akin to Du. bekomen, O.H.G. biqueman "obtain," Ger. bekommen, Goth. biquiman; from be- a prefix denoting several meanings, and → come.
Šodan "to become, to go, to pass, to change," from Mid.Pers. šudan, šaw- "to go;" Av. š(ii)auu-, šiyav- "to move, go," šiyavati "goes," šyaoθna- "activity; action; doing, working;" O.Pers. šiyav- "to go forth, set," ašiyavam "I set forth;" cf. Skt. cyu- "to move to and fro, shake about; to stir," cyávate "stirs himself, goes;" Gk. kinein "to move;" Goth. haitan "call, be called;" O.E. hatan "command, call;" PIE base *kei- "to move to and fro."
Named for the French physicist Henri Becquerel (1852-1908), who discovered radioactivity in 1896.
Bedrock, from bed (O.E. bed, from P.Gmc. *badjam "sleeping place dug in the ground;" PIE *bhedh- "to dig, pierce") + → rock.
Sangbastar, from sang "stone, rock," → stone, + bastar "bed" (Mid.Pers. vistarak, cognate with Mod.Pers. gostar "a bed; spreading; scatterer," Av. star-, starəta- "spread," from star- "to spread," Skt. strnâti).
Any tree of the genus Fagus, especially Fagus sylvatica of Europe, having smooth grayish bark. In Iran Fagus orientalis populates Caspian highland forests from Âstârâ to Gorgân.
M.E. beche, from O.E. becew; cf. Dutch beuk, Ger. Buche, from PIE root *bhagos "beech tree;" also cf. Gk. phegos "oak," L. fagus "beech," Rus. buzina "elder."
Râš, as named in Gilân, Râmsar, Šahsavâr, Kalârdašt. Its other names: (Mâzandarân) mers, (Ammaârlu, Manjil) râj, (Tevâleš, Mt. Dorfak) aluš, alâš, âlâš, (Nur) celer, celar (Iranica).
Fr.: amas de la ruche
Manner of behaving or acting.
M.E. behavour, from behaven "to behave," altered by model havour, from O.Fr. avoir "to have."
Raftâr "behavior, walking, going," from raft past tense stem of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack") + -âr prefix forming action noun.
Fr.: formule de Bekenstein
The mathematical expression giving the → entropy, S, of a → black hole as a function of the area of its → event horizon, A: S = (kc3A)/(4Għ), where k is → Boltzmann's constant, ħ is the → reduced Planck's constant, and G the → gravitational constant. It can also be expressed by S = (kA)/(4lP2), where lP is the → Planck length. The existence of this entropy led to the prediction of the → Hawking radiation, because an entropy is associated with a temperature and a temperature to a → thermal radiation. The entropy of a black hole increases continuously because the fall of material into it increases its area.
For Jacob D. Bekenstein (1947-), an Israeli theoretical physicist, who contributed to the foundation of black hole thermodynamics; → formula.