active galactic nucleus (AGN)
haste-ye kahkašân-e žirâ
Fr.: noyau actif de galaxie
A central region of an → active galaxy, which is a → light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (→ gamma rays, → X-rays, → ultraviolet) and shows → variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 104 km s-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. See also → broad-line region, → narrow-line region, → quasar.
Fr.: galaxie active
A galaxy that produces huge amounts of energy at its center, which cannot be attributed to normal processes from stars, interstellar medium, and their interactions. There are several types of active galaxies: → Seyfert galaxies, → quasars, and → blazars. All of these objects show brightness variations, some as short as 3 hours. These fluctuations indicate a relatively very small size for the central object, because an object cannot vary in brightness faster than light can travel across it. For example, an object that is one → light-year in diameter cannot vary significantly in brightness over a period of less than one year.
Fr.: optique active
A technique for improving the → resolving power of a telescope by controlling the shape of the main mirror at a relatively slow rate. The → image quality is optimized automatically through constant adjustments by in-built corrective → actuators operating at fairly low temporal frequency ~0.05 Hz or less. → adaptive optics.
Fr.: protubérance active
Fr.: région active
Fr.: soleil actif
The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radiofrequency radiation are at a maximum.
1) The doctrine or practice of vigorous action or involvement as a
means of achieving political or other goals, sometimes by
demonstrations, protests, etc. (Dictionary.com). See also
An especially active, vigorous advocate of a cause, especially a political cause (Dictionary.com).
Agent noun from → activism.
For a radioactive substance, the average number of atoms disintegrating per unit time.
Activity, from → active + -ity.
Žirandegi, noun from žirandé, → active.
1) One who takes part; a participant.
Žirandé adj./noun from žir, → act + suffix -andé. Žirmand, from žir + mand.
1) Existing in act or fact; real.
M.E. actuel, from O.Fr. actuel "now existing, up to date," from L. actualis "active, pertaining to action," adj. form of actus, → act.
Žirvand, from žir, → act, + -vand a suffix forming adjectives denoting "possessed of, similarity, relation," variants -âvand, -van (e.g. xodâvand "possessor, master," pulâdvand "hard as steel, name of a hero," dowlatvand "rich," setarvan "mule-like, barren," polvan "bridge-like, a raised path"), from Mid.Pers. -âwand (hunarâwand "skilled," warzâwand "powerful"); Av. -vant (aurvant- "swift," surunvant- "audible"); cf. Skt. -vant (amavant- "having attacking power").
1) The quality or state of being actual or something that is actual; reality.
The act or process of actualizing.
živandidan, živand kardan
To make actual or real; turn into action or fact.
Fr.: actionner, déclencher
1) To put into mechanical action or motion.
From L. actuatus, p.p. of actuare, from actus, → act.
Fr.: actionnement, déclenchement
The act or process of putting into action; activation.
Verbal noun of → actuate.
A mechanism to activate process control equipment by use of pneumatic, hydraulic, or electronic signals.
Sharpness; acuteness; keenness of perception.
M.E., from M.Fr. acuité, from M.L. acuitatem (nom. acuitas) "sharpness," from L. acus "needle," acuere "to sharpen," from PIE root *ak- "be sharp."
Tiznâ "sharpness," from tiz, "→ sharp," + -nâ, a suffix that transforms adjective into noun (compare with tangnâ, derâznâ, farâxnâ, etc.).
acuity of vision
Fr.: acuité visuelle
The ability of the → eye to see separately two points close to each other. It is a measure of the → resolving power of the eye's → optical system and depends on the density of cells in the → retina. The maximum acuity of the normal human eye is around 0.5 minutes of arc.
Fr.: ad hoc
For the specific purpose at hand, as opposed to a general solution; also, by extension, improvised or impromptu.
From L. ad "to, with, in," cf. Skt. adhi "near," PIE *ad- "to, near, at."
Pad im, from Mid.Pers. pad "to, at, for, in" (Mod.Pers. bé "to, for, in, on, with, by"); O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti "to, toward, in, at;" cf. Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti) + Mid.Pers. im "this;" from Old.Pers./Av. ima "this;" Skt. imá; cf. Lori (Laki) im "this side." The Mid.Pers. im occurs in Mod.Pers. as em- in emruz "today," emšab "tonight," and emsâl "this year."