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activate žirândan Fr.: activer 1) To induce activity in a system that is static, as in neutron activation
of radioactivity. Activate, verb from → active. Žirândan, transitive verb from žir, → act. |
activation žirâneš Fr.: activation 1) The process of inducing or creating a state of → activity. |
activation energy kâruž-e žirâneš Fr.: énergie d'activation Chemistry: The minimum amount of energy that is required to activate → atoms or → molecules to a condition in which they can undergo a → chemical reaction. Most reactions involving neutral molecules cannot take place at all until they have acquired the energy needed to stretch, bend, or otherwise distort one or more → bonds. In most cases, the activation energy is supplied by → thermal energy. → activation; → energy. |
active žirâ, žirande Fr.: actif 1) Being in a state of action; not quiescent. M.Fr. actif, from L. activus, from actus, p.p. of agere, → act. Žirâ, adj. from stem žir, → act + suffix -â. |
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. |
active galaxy kahkašân-e žirâ 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. |
active optics nurik-e žirâ 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. |
active prominence zabâne-ye žirâ Fr.: protubérance active A solar → prominence with very rapid motion (up to 2,000 km s-1), moving and changing in appearance over a few minutes of time, in contrast to a → quiescent prominence. → active; → prominence. |
active region nâhiye-ye žirâ Fr.: région active An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields. |
active sun xoršid-e žirâ 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. |
activity žirâyi, žirandegi Fr.: activité For a radioactive substance, the average number of atoms disintegrating per unit time. Activity, from → active + -ity. Žirandegi, noun from žirandé, → active. |
deactivate foružirândan Fr.: désactiver To cause to be → inactive; remove the → effectiveness of (Dictionary.com). |
inactive nâžirâ Fr.: inactif |
optically active nurâné žirâ Fr.: optiquement actif Relating to → optical activity. |
radioactive partow-žirâ Fr.: radioactive Possessing, or pertaining to, → radioactivity. |
radioactive dating sen yâbi-ye partow-žirâ Fr.: datation radioactive Determining the age of an object from the → radioactive decay of its constituting material. The technique consists of comparing the → abundance ratio of a → radioactive isotope to its → decay product. This will yield the number of half-lives that have occurred since the sample was formed. More specifically, if an object is made up of 50 % decay product then it has gone through 1 → half-life. 75% decay product equals 2 half-lives, 87.5% decay product equals 3 half-lives, 93.76% decay product equals 4 half-lives, and so on. For example, the decay product of → uranium-238 (238U) is → lead-206 (206Pb). The half-life of 238U is 4.5 billion years. Hence, if the sample has gone through two half-lives, it is 9 billion years old. See also: → radiocarbon dating. → radioactive; → dating. |
radioactive decay tabâhi-ye partow-žirâ Fr.: désintégration radioactive Spontaneous emission by a nucleus of photons or particles. → radioactive; → decay. |
radioactive isotope izotop-e partow-žirâ Fr.: isotope radioactif A → nuclide that is radioactive. → radioactive; → isotope. |
radioactive nuclide hastevâr-e partowžirâ Fr.: nucléide radioactif A → nuclide that disintegrates by emitting radiation and transforms into another nuclide. Same as → radionuclide. → radioactive; → nuclide. |
radioactive waste âxâl-e partow-žirâ Fr.: déchets radioactifs The radioactive by-products from the operation of a nuclear reactor or from the reprocessing of depleted nuclear fuel. Also known as nuclear waste. → radioactive; → waste. |
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