A technique in which the thickness, density, or quantity of a material is determined by the amount of radiation it absorbs.
Fr.: facteur de Gaunt
In the atomic theory of spectral line formation, a quantum mechanical correction factor applied to the absorption coefficient in the transition of an electron from a bound or free state to a free state.
Gaunt, after John Arthur Gaunt (1904-1944), English physicist born in China, who significantly contributed to the calculation of continuous absorption using quantum mechanics; → factor
The c.s.g. unit of magnetic flux density (or magnetic induction), equal to 1 maxwell per square centimeter, or 10-4 tesla.
Named after the German mathematician and physicist Carl Friedrich Gauss (1777-1855).
Gauss's law for electricity
qânun-e Gauss dar barq
Fr.: loi de Gauss en électricité
The total electric flux ψ out of an arbitrary closed surface in free space is equal to the net charge within the surface divided by the → permittivity. In differential form: ∇ . E = ρ/ε0, where ρ is the → charge density and ε0 the permittivity. The integral form of the law: ∫E . dS = Q/ε0 (closed surface integral). This is one of the four → Maxwell's equations.
Gauss's law for magnetism
qânun-e Gauss dar meqnâtmandi
Fr.: loi de Gauss en magnétisme
The → magnetic flux through an arbitrary closed surface equals zero. Mathematically, in differential form: ∇ . B = 0 and in integral form: ΦB = ∫B.dS = 0 (closed surface integral). This is one of the four → Maxwell's equations. This law expresses the fact that there are no free magnetic poles (→ monopoles) in nature and that all the lines of force of a magnetic field are closed curves.
Fr.: lemme de Gauss
Fr.: théorème de Gauss
The total normal induction over any closed surface drawn in an electric field is equal to 4π times the total charge of electricity inside the closed surface. Gauss's theorem applies also to other vector fields such as magnetic, gravitational, and fluid velocity fields. The theorem can more generally be stated as: the total flux of a vector field through a closed surface is equal to the volume → integral of the vector taken over the enclosed volume. Also known as → divergence theorem, Ostrogradsky's theorem, and Gauss-Ostrogradsky theorem.
vâbâžeš-e Gaussi (#)
Fr.: distribution gaussienne
A theoretical frequency distribution for a set of variable data, usually represented by a bell-shaped curve with a mean at the center of the curve and tail widths proportional to the standard deviation of the data about the mean.
Fr.: élimination de Gauss
A method of solving a matrix equation of the form A x = b, where A is a matrix and x and b are vectors. The process consists of two steps, first reducing the elements below the diagonal to 0 and second, back substituting to find the solutions.
Fr.: fonction de Gauss
Gaussian gravitational constant
pâyâ-ye gerâneši-ye Gauss
Fr.: constante gravitationnelle de Gauss
The constant, denoted k, defining the astronomical system of units of length (→ astronomical unit), mass (→ solar mass), and time (→ day), by means of → Kepler's third law. The dimensions of k2 are those of Newton's constant of gravitation: L 3M -1T -2. Its value is: k = 0.01720209895.
Fr.: entier de Gauss
Fr.: profile gaussien
The shape of a curve representing a normal distribution.
Math.: The condition of having → Gaussian distribution. The extent to which something is Gaussian.
qânun-e Gay-Lussac (#)
Fr.: loi de Gay-Lussac
1) Law of combining volumes. The volumes of gases used and produced in a
chemical reaction, are in the ratio of small whole numbers when measured
at constant temperature and pressure.
Named after Joseph Louis Gay-Lussac (1778-1850), a French chemist and physicist; → law.
Fr.: GD 165B
The prototype of the → L dwarf class. It has a spectral type of L4 V. This object was discovered by Becklin & Zuckerman (1988, Nature 336, 656) as the red companion to a → white dwarf (DA4) lying 104 → light-years away. Its true nature was however recognized several years later (Kirkpatrick et al. 1993, ApJ 406, 701). It has an → effective temperature of 1900 K and a luminosity about 10-4 times that of the Sun (→ solar luminosity).
GD, referring to Giclas Dwarf, a catalog of white dwarf stars compiled at the Lowell Observatory (Giclas et al. 1980, LowOB 8, 157).
Fr.: gegenschein, lueur anti-solaire
A faint glow of light in the night sky seen exactly opposite the Sun. The gegenschein is sunlight back-scattered off millimeter-sized dust particles along the ecliptic. In comparison with zodiacal light (forward-scattered sunlight), which is triangular in shape and found near the horizon, the gegenschein is roughly circular. Same as counterglow.
Gegenschein, from Ger. gegen "counter, opposed to" (O.H.G. gegin, gagan, M.Du. jeghen, E. against, again) + Schein "glow, shine" (M.H.G. schinen, O.H.G. skinan, P.Gmc. *skinanan; E. shine; cf. Mod.Pers. sâyé "shadow;" Mid.Pers. sâyak "shadow;" Av. a-saya- "throwing no shadow;" Skt. chāya- "shadow;" Gk. skia "shade;" Rus. sijat' "to shine;" PIE base *skai- "bright").
Pâdfrouq "counterglow," from pâd- "agaist, contrary to" (from Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; 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) + foruq "light, brightness" (related to rôšan "light; bright, luminous;" ruz "day," afruxtan "to light, kindle;" Mid.Pers. payrog "light, brightness," rošn light; bright," rôc "day;" O.Pers. raucah-; Av. raocana- "bright, shining, radiant," raocah- "light, luminous; daylight;" cf. Skt. rocaná- "bright, shining, roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna; E. light, Ger. Licht, and Fr. lumière; PIE base *leuk- "light, brightness").
šomârgar-e Geiger (#)
Fr.: compteur Geiger
A device for detecting ionizing radiations, whether corpuscular (α-, β-particles), or electromagnetic (X- and gamma-rays). It consists essentially of a fine wire anode (e.g., tungsten) surrounded by a coaxial cylindrical metal cathode, mounted in a glass envelope containing gas at low pressure. A large potential difference (800 to 2000 volts) is maintained between the anode and the cathode. The ionizing particle can enter through a thin glass or mica window. The particle produces ionization of gas molecules. The ions are accelerated by the electric field and produce more ions by collisions, causing the ionization current to build up rapidly. The current, however, decays quickly since the circuit has a small time constant. There is therefore a momentary potential surge which may be amplified and made to actuate a relay to advance a mechanical counter, or to produce a click in a loudspeaker. Same as Geiger-Mulle counter.
Named after Hans Geiger (1882-1945), the German physicist, who invented the instrument. He is also known for his work on atomic theory and cosmic rays; → counter.
Fr.: hongrer, castrer, châtrer
To castrate (an animal, especially a horse).
M.E. gelden, from O.Norse gelda, ultimately from PIE *ghel- "to cut."
Axtan, variant of âxtan, âhixtan, âhiz- "to draw out; castrate, geld," → object.