free expansion phase
fâz-e gostareš-e âzâd
Fr.: phase d'expansion libre
The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy ESN is transformed into → kinetic energy of the ejected gas, the ejection velocity ve can be estimated from ESN by using ESN = (1/2) Meve2, which leads to ve = (2ESN / Me)(1/2), where Me is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, RSW, is defined by Me = (4π/3) RSW3ρ0, that is RSW = (3Me / 4πρ0)(1/3), where ρ0 is the initial density of the ISM. This radius is reached at the sweep-up time tSW = RSW/ve. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.
oft-e âzâd (#)
Fr.: chute libre
Fr.: écoulement libre
A fluid flow which develops when density differences within the fluid are the only driving forces. See also → forced flow.
Fr.: occurrence libre
Fr.: oscillation libre
Oscillation of any system in stable equilibrium under the influence of internal forces only, or of a constant force originating outside the system, or of both.
Fr.: radical libre
A chemical radical that can exist independently from atoms or group of atoms.
Fr.: système libre
Fr.: émission libre-liée
zamân-e oft-e âzâd
Fr.: temps de chute libre
The characteristic time it would take a body to collapse under its own → gravitational attraction, if no other forces existed to oppose the collapse. It is given by: tff = (3π/32 ρ0 G)1/2, where ρ0 denotes the initial density and G the → gravitational constant. Free-fall time is independent of the starting radius. Also known as → dynamical time scale.
Fr.: objets flottants
A population of → substellar objects which are not bound to stars; they are detected in young star clusters. Their masses, estimated from their fluxes, is several Jupiter masses, lower than those of → brown dwarfs. Their formation is not yet explained. Among the envisaged possibilities: 1) These objects form like stars, from protostellar core collapse and subsequent accretion; 2) they form as low-mass members of small groups, and are ejected from the group; 3) they form like planets within circumstellar disks of higher-mass objects, but are ejected either due to internal dynamics or external interactions.
Barâxt, → object; šenâvar "that swims, floats," from šenâ "swimming;" Mid.Pers. šnâz "swim," šnâzidan "to swim;" Av. snā- "to wash, swim;" cf. Skt. snā- "to bathe, to wash;" L. nare, natare "to swim" (Fr. nage, nager, natation; Sp.nadar, natacion).
gosil-e âzâd-âzâd (#)
Fr.: emission libre-libre
The state of being free or at liberty.
From M.E. fredom, from O.E. freodom, from freo "free; noble, joyful," → free.
Âzâdi "freedom," noun from âzâd, → free.
Fr.: loi de Freeman
A statistical finding about "normal" → spiral galaxies, whereby there is an upper limit on the mean central → surface brightness of disks. This value is constant for different spiral types, amounting to 21.65 ± 0.30 mag arcsec2 in the B band.
Named after K. C. Freeman (1970, Ap.J. 160, 811); → law.
1) yax bastan; 2) rocidan
1) To change from the liquid to the solid state by loss of heat; become hardened into ice.
Freeze, from O.E. freosan "turn to ice," from P.Gmc. *freusanan (cf. O.H.G. friosan, Ger. frieren "to freeze"), from *freus-, from PIE base *preus- "to freeze" also "to burn" (cf. Skt. pruśva- "hoar-frost, ice;" L. pruina "hoar-frost," Skt. pruśta- "burnt;" Albanian prus "burning coals;" L. pruna "a live coal").
1) Yax bastan, from yax "ice" + bastan "to bind, shut; to congeal, coagulate." The first component yax, from Av. aexa- "ice, frost," isav-, isu- "icy, chilly," cf. Sarikoli (Pamir dialect) īš "cold," P.Gmc. *isa- (O.N. iss, O.Fris. is, Du. ijs, Ger. Eis). The second component bastan, from Mid.Pers. bastan/vastan "to bind, shut;" Av./O.Pers. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind). 2) Rocidan, → coagulate.
1) yaxbast; 2) roceš
Fr.: gel, congélation
1) The phase transition of a substance passing from the liquid to the solid state;
the opposite of → fusion. In meteorology, the freezing of water.
Verbal noun from → freeze.
Fr.: point de congélation
1) The temperature at which a liquid of specified composition changes into a solid under
a specified pressure.
French Republican Calendar
gâhšomâr-e jomhuri-ye Farâncé
Fr.: Calendrier républicain, Calendrier révolutionnaire français
A calendar composed by Fabre d'Eglantine and others during the French Revolution which divided the year into 12 months of 30 days each, with five odd days called → Sansculottides. The year started at → autumnal equinox and the months were: Vendémiaire (Vintage), Brumaire (Fog), Frimaire (Frost), Nivôse (Snow), Pluviôse (Rain), Ventôse (Wind), Germinal (Buds), Floréal (Flowers), Prairial (Meadows), Messidor (Harvest), Termidor (Heat), Fructidor (Fruits). The week consisted of 10 days, and was called a Décade; each 10th day of Décade (called Décadi) was a day of rest. The calendar was used by the French government for about 12 years, from late 1793 to 1805, when it was suppressed by Napoleon.
M.E. Frensh, French, O.E. Frencisc "of the Franks," from Frank; republican, from republic, from Fr. république, from L. respublica, from res publica "public interest, the state," from res "affair, matter, thing" + publica, feminine of publicus "public;" → calendar.
basâmad (#), feregi (#)
The number of complete oscillations per unit time of a vibrating system. The reciprocal of the → period, T.
From L. frequentia "assembly, multitude, crowd."
Basâmad, 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")
+ âmad past stem of âmadan "to occur, to come, to become"
O.Pers. gam- "to come; to go,"
Av. gam- "to come; to go," jamaiti "goes;"
Proto-Iranian *āgmatani; Skt. gamati "goes;"
Gk. bainein "to go, walk, step;" L. venire "to come;"
Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come;
PIE root *gwem- "to go, come").
Fr.: bande de fréquence
A range of frequencies that is continuous between two specified limits, selected from a more extended range of frequencies.
Fr.: dérive de fréquence
An undesired progressive change in an oscillator's frequency with time.