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central limit theorem
farbin-e hadd-e markazi
Fr.: théorème central limite
A statement about the characteristics of the sampling distribution of means of → random samples from a given → statistical population. For any set of independent, identically distributed random variables, X1, X2,..., Xn, with a → mean μ and → variance σ2, the distribution of the means is equal to the mean of the population from which the samples were drawn. Moreover, if the original population has a → normal distribution, the sampling distribution of means will also be normal. If the original population is not normally distributed, the sampling distribution of means will increasingly approximate a normal distribution as sample size increases.
Central Molecular Zone (CMZ)
zonâr-e molekuli-ye markazi
Fr.: zone moléculaire centrale
A vast, turbulent region encircling the → Milky Way's nucleus that contains a large fraction of the → Galaxy's dense → molecular clouds and → star formation regions. Spanning -1 to +1.5 degrees of → Sgr A*, the CMZ is about 400 pc × 100 pc in size and contains at least 107→ solar masses of → giant molecular clouds, approximately 10% of the Galaxy's molecular gas. The gas in the CMZ is at higher temperature than typical giant molecular clouds and has high velocity dispersion reflecting the → turbulent nature of the gas in the area. Despite these extensive molecular reserves, the → star formation rate within the CMZ is actually lower than expected based on the analysis of nearby → star-forming regions in the quiescent → Galactic disk. A common assumption is that this is a result of the extreme conditions within the CMZ, where the density, pressure, temperature, → velocity dispersion and → radiation field are all significantly greater than elsewhere in the Milky Way (Clark et al. 2018, The Messenger 173, 22 and references therein).
Fr.: pic central
The uplift of the central parts of the → crater floor due to the impacting force of a large → meteorite. The shock wave entering the Earth will first move in as a compressional wave (P-wave), but after passage of the compressional wave an expansion wave (rarefaction wave) will move back toward the surface. This will cause the floor of the crater to be uplifted and may also cause the rock around the rim of the crater to bent upward.
central processing unit (CPU)
yekâ-ye âmâyeš-e markazi
Fr.: unité centrale de traitement
The primary component of a → computer that processes instructions. It runs the → operating system and → applications, constantly receiving input from the user or active → software programs. The CPU has two typical components: 1) Control Unit, which extracts instructions from memory and decodes and executes them. 2) Arithmetic Logic Unit (ALU), which handles arithmetic and logical operations.
Fr.: pic central
Same as → central peak.
Fr.: longueur d'onde centrale
1) In an interference filter, the wavelength of peak
Acting or moving in a direction away from the axis of rotation or the center of a circle along which a body is moving.
From Mod.L., coined 1687 by Sir Isaac Newton from L. centri-, combining form of centrum, → center, + fugere "to run away, flee."
Markaz-goriz, from markaz, → center, + goriz "running away," from gorixtan, gorizidan "to run away," Mid.Pers. virextan, proto-Iranian *vi-raik, from vi- "apart, asunder" + *raik, Av. raek- "to leave, set free, let off," Mid./Mod.Pers. reg/rig (in mordé-rig "inheritance," Skt. ric- "to leave," rinakti "gives up, evacuates," Gk. leipein "to leave," L. linquere "to leave," from PIE *linkw-, from *leikw- "to leave behind" (cf. Goth. leihvan, O.E. lænan "to lend;" O.H.G. lihan "to borrow;" O.N. lan "loan").
šetâb-e markaz-goriz (#)
Fr.: accélération centrifuge
Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v2/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.
niru-ye markaz-goriz (#)
Fr.: force centrifuge
A force in a rotating reference frame directed outward from the axis of rotation.
From Mod.L., coined 1687 by Sir Isaac Newton from L. centri- combining form of centrum "center" + petere "to fall, rush out;" cf. Av. pat- " to fly, fall, rush," Skt. patati "he flies, falls," Mid.Pers. patet "falls," opastan "to fall," Mod.Pers. oftâdan "to fall;" Gk. piptein "to fall," petomai "I fly;" PIE base *pet- "to fly, to rush."
šetâb-e markaz-gerâ (#)
Fr.: accélération centripète
The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: ac = v2/r = rω2. According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.
niru-ye markaz-gerâ (#)
Fr.: force centripète
The force exerted on an object in → circular motion which is directed toward the center and keeps the body in motion. Centripetal force produces → centripetal acceleration, according to → Newton's second law: Fc = mac. Its direction is always inward along the → radius vector, and its magnitude is given by: Fc= mac = mvt2/r = mω2r.
A class of luminous, → yellow supergiants that are pulsating variables and whose period of variation is a function of their → luminosity. These stars expand and contract at extremely regular periods, in the range 1-50 days. Their highest brightness and surface temperature occur when their expansion velocity is greatest. Similarly, their minima in brightness and temperature occur when they are in the contraction phase. The longer the period, the more luminous the star. The process that drives the pulsation of → Cepheid variables is the → kappa mechanism. In fact, Cepheids provide one of the most powerful tools for measuring distances to other galaxies (→ period-luminosity relation). However, this method is limited to the distance of the → Virgo cluster of galaxies (15-20 → Mpc) even with the → HST or the largest ground-based telescopes. One particularly special Cepheid is the North Star, → Polaris. See also → RR Lyrae star.
Fr.: variable Céphée
A → constellation in the Northern Hemisphere lying next to → Cassiopeia. It contains several pulsating variable stars, including the prototype → Cepheid variable Delta Cephei. Abbreviation: Cep, genitive: Cephei.
Kefeus, from Gk. Cepheus. Arabicizd form qifâvus (
Once qualified as the largest known → asteroid, Ceres is now classified as a → dwarf planet (2006 IAU General Assembly). It is approximately 950 km across, and resides with tens of thousands of asteroids in the main → asteroid belt; it is the largest body of the belt. Its mass is 9.4 × 1020 kg, its → rotation period 9.074 hours, its → orbital period 4.60 years, and its → semi-major axis 2.767 AU. NASA's → Dawn spacecraft, which was placed in orbit around Ceres in 2015, has mapped its surface in great detail from a distance. Dawn caught sight of bright spots that soon resolved into more than 130 bright patches, most of them tied to craters. The most prominent of these spots lie inside the crater → Occator. The patches turned out to be carbonate salts, which only form in the presence of water. Since water skips to gas almost immediately on the dwarf planet's surface, the discovery of carbonates suggested that there was liquid beneath the dwarf planet's crust. Aside from craters, the only outstanding feature On Ceres is a single mountain, Ahuna Mons. It formed about 250 million years ago when plumes of saltwater and mud rose and erupted from within Ceres.
Ceres in Roman mythology was the goddess of growing plants and of motherly love. She was equivalent to Demeter in Gk. mythology.
Fr.: Centre Européen pour la Recherche Nucléaire (CERN)
European Organization for Nuclear Research, founded in 1954, and located on the Franco-Swiss border near Geneva, Switzerland. CERN is one of the world's largest centres for scientific research. At CERN, the world's largest and most complex scientific instruments are used to study the basic constituents of matter, i.e. the → elementary particles. The instruments used at CERN are particle → accelerators and → detectors. Currently it has 20 Member States.
CERN, acronym of the organization's original name Centre Européen pour la Recherche Nucléaire.
Cerro Tololo Inter-American Observatory (CTIO)
Nepâhešgâh-e andar-Âmrikâyi-ye Kuh-e Tololo
Fr.: Observatoire inter-américain du Cerro Tololo
A complex of astronomical telescopes and instruments located approximately 80 km to the East of La Serena, Chile, at an altitude of 2,200 m. CTIO headquarters are located in La Serena, Chile, about 480 km north of Santiago. The principal telescopes on site are the 4-m Victor M. Blanco Telescope and the 4.1-m Southern Astrophysical Research (SOAR) telescope. One of the two 8-m telescopes comprising the Gemini Observatory is co-located with CTIO on the Association of Universities for Research in Astronomy (AURA) property in Chile, together with more than 10 other telescopes and astronomical projects.
Determined, fixed; established beyond doubt or question; indisputable. → determinism.
From O.Fr. certain, from V.L. *certanus, from L. certus "sure, fixed," originally a variant p.p. of cernere "to distinguish, decide."
Tâštig, from Mid.Pers. tâštig "certain," tâšitan "to cut, cleave, create," Mod.Pers. tarâšidan, Gilaki tâštan "to shave, scrape, cut," Av. taš- "to cut, fashion, shape, form," taša- "ax, hatchet," tašan- "creator, maker," cf. Skt. taks- "to cut, chop, form by cutting, make, create," taksan "carpenter," Gk. tekhne "art, skill, craft, method," L. textere "to weave;" PIE base *tek- "to shape, make."