Fr.: transition discrète
A transition between two quantum-mechanical energy levels. See also → discrete spectrum.
Fr.: valeur discrète
A quantity that has certain magnitudes and does not represent a → continuous variable.
Fr.: variable discret
A variable which has only → discrete values and has no in-between values.
discrete-time quantum walk
puyeš-e kuântomi bâ zamân-e gosasté
Fr.: marche quantique à temps discret
A → quantum walk involving a probabilistic → operator that changes the direction while leaving the position fixed, and a shift operator that changes the position. Discrete-time quantum walk was introduced by J. Watrous (2001, Journal of Computer and System Sciences 62, 376)
bahsidan, bahs kardan
M.E., from Anglo-Fr. discusser, from L. discussus "struck asunder, shaken, scattered," p.p. of discutere to break up, "strike asunder," from → dis- "apart," + quatere "to shake, strike."
Bahsidan, infinitive from bahs, from Ar. baHS (
Verbal noun from → discuss.
Fr.: antenne parabolique
A large parabolic structure that collects radio waves and focuses them on a detector by means of a secondary reflector. A similar device used as antenna for radar transmitting.
O.E. disc "plate, bowl, platter," from L. discus "dish, platter, quoit," from Gk. diskos "disk, platter."
Jâm "cup, chalice, goblet, bowl," Mid.Pers. jâm "vessel, goblet; glass," Av. yama- "glass, glass vessel," yāmô.pacika- "baked glass;" related to Skt. camasa- "a vessel used at sacrifices for drinking Soma, kind of flat dish or cup?"
vâpâši, forupâši (#)
The breaking up of a body into fragments. For example, that of an unstable nuclei either spontaneously or as a result of bombardment by fast-moving particles, or the breaking up of a comet.
Any of the components in a logical → disjunction.
A → proposition of the form "A or B" (A ∨ B), where A and B are themselves propositions. A disjunction is → true when one or the other of its components (called → disjuncts) is true, and false otherwise.
gerdé (#), disk
1) General: Any thin, flat, circular plate or object.
From L. discus "quoit, discus, disk," from Gk. diskos, from dikein "to throw." → dish.
Gerdé, from Mid.Pers. girdag "disk, round," from gird/girt "round, all around," Proto-Iranian *gart- "to twist, to wreathe," cf. Skt krt "to twist threads, spin; to wind; to surround;" kata- "a twist of straw," Pali kata- "ring, bracelet," Gk. kartalos "a kind of basket," kyrtos "curved;" disk loanword from Fr.
farbâl-e gerde-yi, ~ pat geredé, ~ ~ disk
Fr.: accrétion par disque
An accretion process involving an → accretion disk.
Fr.: galaxie à disque
nâpâydâri-ye gerdé, ~ disk
Fr.: instabilité de disque
The process by which an → accretion disk
cools, causing it to fragment into self-gravitating → clumps.
disk instability model (DIM)
model-e nâpâydâri-ye gerdé, ~ ~ disk
Fr.: modèle d'instabilité de disque
A model describing → dwarf novae and → Soft X-ray Transient (SXT)s. Accordingly, these objects are triggered by an → accretion disk instability due to an abrupt change in opacities (→ opacity) at → temperatures at which hydrogen is partially ionized. All versions of the DIM have this ingredient. They differ in assumptions about → viscosity, and about what happens at the inner and outer disk radii. Basically, during → quiescence, material accumulates in the accretion disk until a critical point is reached. The disk then becomes unstable and is dumped onto the → compact object, releasing a burst of → X-rays. However, the greater duration of SXT bursts (months) and the time interval between bursts (decades) cannot be accounted for by the standard disk instability model used for dwarf novae, and additional factors such as X-ray illumination and irradiation of the accretion disk are required for the model to match the observed properties of SXTs (J-P Lasota and J-M Hameury, 1995).
girkard-e disk, ~ gerdé
Fr.: blocage de disque
In star formation models involving magnetized accretion, a process whereby the stellar rotational → angular velocity becomes equal to the → Keplerian angular velocity of the → accretion disk. This happens at the → corotation radius. Disk locking is believed to be responsible for efficient loss of stellar → angular momentum during the → pre-main sequence contraction of → T Tauri stars. These stars are expected to spin up by a factor of about 3 due to contraction after being magnetically disconnected from the → circumstellar disk. However, observations show that a large fraction of pre-main sequence stars evolve at nearly constant angular velocity through the first 4 Myr. This process results from → magnetic braking. The idea of magnetic disk locking originated with the theory developed by Ghosh & Lamb (1979, ApJ 232, 259) for → neutron stars.
M.E., from O.E. lucan "to lock, to close," from loc "bolt, fastening, enclosure;" cf. M.L.G. lok, O.H.G. loh, O.N. lok "a cover, lid," Goth. -luk in usluk "opening," Ger. Loch "opening, hole," Du. luck "shutter."
porineš-e gerdé, ~ disk
Fr.: population disque
Of a spiral galaxy, those stars that lie in a flattened disk and move in nearly circular orbits around its centre. They are Population I stars of all ages up to the age of the disk, but in general are younger than stars in → halo population.
→ disk; population, from L.L. populationem "a people, multitude," from populatio, from populare "to inhabit," from populus "people," related to plebes "the common people," cf. Gk. plethos "people, multitude, great number," from PIE base *pel- "to be full;" Mod.Pers. por "full," O.Pers. paru- "much, many," Av. pouru- "much, many," pərəna- "full," par- "to fill," Skt. puru-, Gk. polus, O.E. full "completely, full," from P.Gmc. *fullaz, O.H.G. fol, Ger. voll, Goth. full.
Like Gk., Pers. uses the concepts of "multitude, many, full" to denote "people, group, herd, flock". The following examples are all terms derived from O.Pers. paru- "much, many," Av. par- "to fill," pouru- "much, many," pərəna- "full" (Mod.Pers. por "full"): literary Pers. bâré "herd, flock," parré "a rank or file of soldiers, a circular disposition of troops," Lori, Qâyeni bor "group, tribe, herd," Torbat-Heydariyeyi, Qomi borr "heap, bundle, group," Qomi borreh "group, assemblage of people," Pashtu parrak "flock, herd," Urdu para "flock, herd," Lârestâni baila "group, tribe," Tabari balik "herd, flock." With this introduction, porineš "population," verbal noun of porinidan "to populate," infinitive of porin "populous," from por "mutitude, many, full" + -in attribution suffix.
Fr.: quota de disque
Computers: The specific amount of disk space that a user or service is allowed to use.
niyâšeš-e gerdé, ~ disk
Fr.: stabilisation de disque
setâre-ye gerdé, ~ disk
Fr.: étoile de disque
A star that lies within the → galactic disk of a → spiral galaxy. Stars belonging to the → thin disk, such as the Sun or Alpha Centauri, lie at a typical distance of about 1,000 → light-years from the galactic midplane. There are also → thick disk stars, such as Lalande 21185, that lie at an average distance of about 3,500 light-years from the midplane.