Fr.: exact, précis
1) Conforming exactly to truth or to a standard; free from error.
Accurate, from L. accuratus, → accuracy.
accurate to n decimal places
rašmand bâ n raqam pas az jodâgar yâ momayez
Fr.: précis à n décimale, ~ avec n chiffres après la virgule, à n décimales près
An expression specifying the number of meaningful digits to the right of the → decimal point. For example, e = 2.71828 ... = 2.718 is said to be accurate to three decimal places and 2.72 to two decimal places.
accurate to n significant digits
rašmand bâ n raqam-e nešânâr
Fr.: écrit avec n chiffres significatifs
An expression specifying the number of meaningful digits used to express the value of a measured quantity. Same as accurate to n significant figures. For example, e = 2.71828 ... = 2.718 is rounded to four significant digits, and 2.72 to three significant digits. → accurate to n decimal places.
Achernar (Alpha Eridani)
Âxer-e nahr (#), Rudpâyân
The brightest star in the constellation → Eridanus. A → subgiant of → spectral type B5; apparent visual magnitude 0.5, about 140 → light-years distant (other names: HR 472, HD 10144). Recent interferometric observations show it to have a flattened shape imposed by fast rotation.
Achernar, from Ar. Axir an-Nahr "end of the river," from axir "end" + nahr "river".
Âxer-e nahr, from Axir an-Nahr.
Achondrite, from Gk. prefix a- (an- before stems beginning with a vowel or h) "not, without, lacking" + Gk. chondrite, from chondr-, from chondros "grain," + affix -ite.
afâm (#), bifâm (#)
Of or relating to an optical system which is capable of transmitting light without decomposing it into constituent colors.
adasi-ye afâm, ~ bifâm
Fr.: lentille achromatique
Lens (or combination of lenses) that brings different wavelengths within a ray of light to a single focus, thus overcoming chromatic aberration.
A substance that releases hydrogen ions to form a solution with a pH of less than 7, reacts with a base to form a salt, and turns blue litmus red.
From Fr. acide, from L. acidus "sour," adj. of state from acere "to be sour," acer "sharp, pungent, bitter;" from PIE base *ak- "sharp, pointed."
Being or containing an acid; of a solution having an excess of hydrogen atoms (having a → pH of less than 7).
Pertaining to the sense of hearing, or to → sound waves.
Fr.: pic acoustique
One of several peaks appearing in the → CMB angular power spectrum of the → cosmic microwave background radiation which are ripples left by acoustic oscillations of the plasma-radiation fluid in the early Universe (→ baryon acoustic oscillations). When the Universe was small and very hot, the free electron density was so high that photons could not propagate freely without being scattered by electrons. Ionized matter, electrons and radiation formed a single fluid, with the inertia provided by the baryons and the radiation pressure given by the photons.
Fr.: pression acoustique
Same as → sound pressure.
Fr.: onde acoustique, ~ sonore
A type of → longitudinal wave that consists of mechanical → vibrations of small → amplitude propagated in an → elastic medium. Acoustic waves exhibit phenomena like → diffraction, → reflection, and → interference, but not → polarization. Also called → sonic and → sound waves. See also → acoustic wave equation. The branch of physics concerned with the properties of sonic waves is called → acoustics.
acoustic wave equation
hamugeš-e mowj-e sedâyi
Fr.: équation de l'onde acoustique
A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇2φ = (1/c2)∂2φ/∂t2, where c is → velocity of → longitudinal waves and ∇2 is the → Laplacian operator.
1) The study of sound, especially of its generation, propagation,
From Fr. acoustique, from Gk. akoustikos "pertaining to hearing," from akoustos "heard, audible," from akouein "to hear," from copulative prefix a- + koein "to mark, perceive, hear," from PIE root *(s)keu- "to notice, observe."
Sedâyik from sedâ "sound" + Pers. suffix -ik, → -ics. Sedâ is most probably Persian, since it exists also in Indo-Aryan languages: Skt. (late Vedic): sabda "articulate sound, noise," Pali and Prakriti: sadda "sound, noise," Sindhi: sadu, sado "shout, call," Gujrâti sad "call, voice, echo," Marathi: sad "shouting to," Konkani sad "sound," Sinhali: sada "sound." Therefore, sadâ in Arabic "reverbrating noise, echo" may be borrowed from Persian, or a coincidence. Note that for the author of the classical Persian dictionary Borhân-e Qâte' (India, 1652 A.D.), the Arabic term is a loanword from Persian.
→ phone; →phonetics.
Relating to or occurring at sunset. → heliacal
Acronical, from Gk. akronukos, from akros "tip, end," cf. Av. aγra- "top, first," Skt. agra- "first, foremost, climax" + nuks, nuktos "night," → night.
Šâmgâhi, adj. of šâmgâh "evening," from šâm "evening, evening meal" + gâh "time." The first component, šâm, from Mid.Pers. šâm "evening meal, supper," from Av. xšāfnya- "evening meal," from Av. xšap-, xšapā-, xšapan-, xšafn- "night" (O.Pers. xšap- "night," Mid.Pers. šap, Mod.Pers. šab "night"); cf. Skt. ksap- "nigh, darkness;" Hittite ispant- "night." The second component gâh "time," Mid.Pers. gâh, gâs "time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."
Fr.: lever acronyque
The rising of a star in the sky at or just after sunset. → heliacal rising.
Fr.: coucher acronyque
The setting of a star at nightfall. → heliacal setting.
A southern hemisphere bright star (α Crucis) of magnitude 0.77 lying at a distance of 321 → light-years. It is apparently made up of three components. The primary component, Acrux A, is a blue subgiant of apparent magnitude 1.34 and spectral type B0.5 IV. The B component lies at about 4.1 arcsec away from the A component, which represents a distance of at least 400 AU, that is, more than 10 times the distance between the sun and planet Pluto. The C component lies about 90 arcsec away from A.
Acrux, from A, from Alpha, designating the brightest star of the constellation + crux, the constellation name. The name Acrux is probably a coinage of the American astronomer, Elijah H. Burritt, who published several editions of an astronomical atlas between 1833 and 1856.
žir (n.); žiridan (v.)
Fr.: acte, action; agir
1) The process of doing or performing something;
something done or performed.
Act, from O.Fr. acte, from L. actus "a doing" and actum "a thing done," both from agere "to do, set in motion, drive, urge, chase, stir up," from PIE root *ag- "to drive, draw out or forth, move" (cf. Gk. agein "to lead, guide, drive, carry off," agon "assembly, contest in the games," agogos "leader;" Av. az- "to drive (away)," azaiti "drives," Mod.Pers. govâz "stick for driving cattle," from Av. gauuāza-, from gao- "cow, ox, cattle" (→ Bootes) + āza-, from az-, as above; Skt. aj- "to drive, sling," ájati "drives," ajirá- "agile, quick." The E. agile "characterized by quickness, lightness, and ease of movement; mentally quick or alert" is from this root.
In major European languages there are two fundamental and very close verbs which convey "work, action, activity". These are: 1) to do (in French faire, Spanish hacer, German machen) and 2) to act (French agir, Spanish actuar, German handeln). In Persian there is only one word for these two concepts: kardan; and this is obviously a big handicap. An ad hoc equivalent for action has therefore been koneš, from kardan "to do." The problem is that this solution, despite being widely used, confounds "to do" with "to act," and is incapable of forming all the related derivatives. Therefore, we propose žir, which derives from Av. žirā- "active, agile, clever;" Mid.Pers. žir, zir "active, busy" (loaned in Arm. žir "active, busy, clear"), Mod.Pers. zirak "clever, alert, intelligent;" Kurd. žir "agile," žiri "agility."