Of a circle, any straight line segment extending from the center to a point on the
From L. radius "staff, spoke of a wheel, beam of light," of unknown origin.
Šo'â', loan from Ar.
radius of gyration
Same as → Larmor radius.
bordâr-e šo'â'i (#)
Fr.: rayon vecteur
Math.: In a system of polar or spherical coordinates, a line joining a point
to the origin.
The base of a number system; thus 2 is the radix of the binary system, 10 the radix of the decimal system, 12 the radix of the duodecimal system.
From L. radix "root;" akin to Gk. rhiza "root;" cf. O.N. rot "root," O.E. wyrt "plant, herb;" E. radish.
Pâyé "basis, foundation; step," from pâ "foot, step" (from Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-).
A gaseous radioactive chemical element; symbol Rn. Atomic number 86; mass number of most stable isotope 222; melting point about -71°C; boiling point -61.8°C. Radon was discovered in 1900 by the German chemist Friedrich Ernst Dorn and it was first isolated in 1910 by the Scottish chemist William Ramsay and the English chemist Robert Whytlaw-Gray. The longest half-life associated with this unstable element is 3.8 day.
The name indicates its origin from → radium. It had first been called radium emanation or just emanation (with chemical symbol Em) because it was a decay product of radium. Ramsay subsequently suggested the name "niton" (with chemical symbol Nt), which means "shining" in Latin. It was finally changed to radon in 1923.
A flat structure made up of a collection of logs or planks fastened together for floating or transportation on water.
M.E. rafte, rafter, from O.N. raptr "log."
Sal "raft," probably related to PIE base *sel-, *swel- "beam, board," cf. Gk. selma "beam;" O.E. syll "beam, large timber," O.N. svill "framework of a building," M.L.G. sull, O.H.G. swelli, Ger. Schwelle "sill," and also akin to Mid.Pers. sard "ladder," Pers. dialectal variants (Lârestâni) se, si "ladder," (Gilaki, Tâleqâni) sardi, (Qazvini) sorda, (Hamedâni) serda, (Kâšâni) sart, sârda, serde, and others all meaning "ladder."
Water that is condensed from the aqueous vapor in the atmosphere and falls to earth in drops greater than 0.5 mm in diameter.
M.E. rein; O.E. regn; cf. O.S. regan; O.N. regn; M.Du. reghen; Ger. Regen; maybe cognate with Pers. (Tabari) rag "thunder;" (Šahmirzâdi, Semnâni, Sorxe-yi) rak "thunder;" (Gilaki) râk "cloudburst;" L. rigare "to wet, moist;" PIE *reg- "rain, damp."
Bârân, from bâridan "to rain;" Mid.Pers. vârân "rain," vâritan "to rain;" Av. vār- "rain; to rain;" cf. Skt. vār- "rain, water; to rain;" L. urinari "to plunge under water, to dive;" Gk. ourein "to urinate;" PIE base *uer- "water, rain, river."
rain and snow mixed
Fr.: mélange de pluie et de neige
A precipitation consisting of rain and partially melted snow. It usually occurs when the temperature of the air layer near the ground is slightly above freezing. Called sleet in British English speaking countries, but not in the United States where the term has a different meaning in meteorology.
Šaliv, of dialectal origin, Kurd. šalêwa "rain and snow mixed," Aftari šelâp, Qasrâni šelâb with the same meaning, Tabari šalâb "strong cloudburst." The first element šal, šel, šor, šâr, âbšâr, šâridan "to flow." The second element iv, êw, âp, âb, → water.
Fr.: nuage de pluie
Any cloud from which rain falls.
Zafâk "rain cloud" (Dehxodâ); Mid.Pers. zafâ.
rangin kamân (#)
A color effect produced by the → refraction and → internal reflection of sunlight passing through a mist of tiny spherical water → droplets in the air. The effect is visible only when the observer has his back to the Sun. It appears as a colored band at about 138° from the Sun, hence 42° from the → antisolar pint. In other words, 42° is the angle between the direction of the → incident sunlight and the → line of sight. The → primary rainbow is caused from one reflection inside water droplets; the red color appears on the top and violet on the bottom. At solar elevations higher than 42° the bow is entirely below the → horizon and therefore invisible in the sky. A full rainbow is actually a complete circle, but from the ground we see only part of it. From an airplane, in the right conditions, one can see an entire circular rainbow. A → secondary rainbow appears if the sunlight is reflected twice inside the water droplets. Secondary rainbows are fainter, and the order of the color is reversed, with red on the bottom and violet on the top. See also: → Alexander's dark band, → supernumerary rainbow.
Fr.: angle d'arc-en-ciel
Fr.: rayon d'arc-en-ciel
The sunlight incident on a tiny spherical droplet of water.
The total liquid product of precipitation or condensation from the atmosphere, as received and measured in a rain gauge.
Bâreš verbal noun of bâridan "to rain," bâridan "to rain;" Mid.Pers. vârân "rain," vâritan "to rain;" Av. vār- "rain; to rain;" cf. Skt. vār- "rain, water; to rain;" L. urinari "to plunge under water, to dive;" Gk. ourein "to urinate;" PIE base *uer- "water, rain, river."
General: Slope or inclination away from the perpendicular or the
horizontal; departure from a reference base.
Rake, etymology unknown.
Varkeš "slope" in Gilaki dialect. It can also be literally interpreted as "departure from a surface, a side, depart away" from var, variant bar, "side, surface" + keš present stem of kešidan "to pull, drag."
1) quc, garând; 2) qucvâr
M.E. ram, from O.E. ramm "male sheep," also "battering ram," earlier rom "male sheep," a W.Gmc. word of unknown origin (cf. M.L.G., M.Du., Du., O.H.G. ram). The verb meaning "to beat with a heavy implement" is first recorded c.1330.
Quc "ram, horned male sheep," loan from Turkish.
Fr.: pression dynamique
The pressure exerted on a body moving through a → fluid medium. For example, a → meteor traveling through the Earth's atmosphere produces a → shock wave generated by the extremely rapid → compression of air in front of the → meteoroid. It is primarily this ram pressure (rather than → friction) that heats the air which in turn heats the meteoroid as it flows around the meteoroid. The ram pressure increases with → velocity according to the relation P = (1/2)ρv2, where ρ is the density of the medium and v the relative velocity between the body and the medium. Similarly, → ram pressure stripping produces → jellyfish galaxies. Same as → dynamic pressure.
ram pressure stripping
loxtkard bâ fešâr-e qucvâr
Fr.: balayage par la pression dynamique
A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 107 K) and tenuous (~ 10-4 cm-3) gas (several 1013 → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).
Fr.: effet Raman
Same as → Raman scattering.
Named after the Indian physicist Sir Chandrasekhara Venkata Raman (1888-1970), who discovered the effect; recipient of the 1930 Nobel Prize in Physics; → effect.
parâkaneš-e Raman (#)
Fr.: diffusion Raman
The scattering of monochromatic light (visible or ultraviolet) by molecules in which the scattered light differs in wavelength from the incident light. It is caused by the light's interaction with the vibrational or rotational energy of the medium's scattering molecules.
gerde-ye Ramsden, disk-e ~ (#)
Fr.: disque de Ramsden
The small circular patch of light visible in the back focal plane of an eyepiece.
Named after Jesse Ramsden (1735-1800), English maker of astronomical instruments; → disk.