1) The outermost portion of the Earth's → atmosphere.
Extremely tenuous, it lies above the → ionosphere
from a height of about 500 km, to the edge of
→ interplanetary space.
external photoelectric effect
oskar-e šid-barqi-ye boruni
Fr.: effet photoélectrique externe
The → photoelectric effect in solids where free electrons are emitted from the surface of a substance (e.g., → semiconductor) when radiation of appropriate frequency falls on it. Also called → photoemissive effect.
A → microorganism with the ability to thrive in extreme environmental conditions that would kill other species. These conditions include high temperatures, very low temperatures, high pressures, high levels of radiation, and high concentrations of salt in water.
Fr.: photoconductivité extrinsèque
Photoconductivity due to the addition of impurities or external causes.
Five-hundred-meter Aperture Spherical radio Telescope (FAST)
The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.
javv-e âzâd, havâsepehr-e ~
Fr.: atmosphère libre
That part of the atmosphere where the effects of the ground on the → turbulence conditions are negligible.
free expansion phase
fâz-e sopâneš-e âzâd
Fr.: phase d'expansion libre
The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy ESN is transformed into → kinetic energy of the ejected gas, the ejection velocity ve can be estimated from ESN by using ESN = (1/2) Meve2, which leads to ve = (2ESN / Me)(1/2), where Me is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, RSW, is defined by Me = (4π/3) RSW3ρ0, that is RSW = (3Me / 4πρ0)(1/3), where ρ0 is the initial density of the ISM. This radius is reached at the sweep-up time tSW = RSW/ve. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.
Fr.: γ Cephei
A bright, third → magnitude (3.22) → giant star of → spectral type K1, also called → Errai, HR 8974, HIP 116727, and HD 222404. γCephei has a → surface temperature of 4920 K a mass of 1.40 Msun, a → luminosity 10.6 solar, and a radius 4.8 solar. Its distance is estimated to be 45 → light-years. γ Cephei will become the → Pole Star in about 2,000 years. γ Cephei has a low mass → companion (B), a main → main sequence star of spectral type M4 V with a mass of 0.4 Msun. It orbits the → primary star every 67.5 years. An → extrasolar planet. (γ Cephe b) has been discovered orbiting the main star.
Of or pertaining to → geography.
geographic coordinate system
râžmân-e hamârâhâ-ye zaminnegârik
Fr.: système de coordonnées géographiques
Fr.: latitude géographique
geographic north pole
qotb-e hudar-e zaminnegârik
Fr.: pôle nord géographique
→ north pole.
geographic south pole
qotb-e daštar-e zaminnegârik
Fr.: pôle sud géographique
→ south pole.
The science dealing with the areal differentiation of the Earth's surface, as shown in the character, arrangement, and interrelations over the world of such elements as climate, elevation, soil, vegetation, population, land use, industries, or states, and of the unit areas formed by the complex of these individual elements (Dictionary.com).
The branch of physics that deals with the Earth and its environment, including meteorology, oceanography, seismology, and geomagnetism.
Of or pertaining to the force produced by the rotation of the Earth.
Fr.: équilibre géostrophique
Fr.: écoulement géostrophique
Oceanography: A flow resulting from → geostrophic balance. In geostrophic flow water moves along the lines of constant pressure or → isobars. Geostrophic flow is characterized by small → Rossby and → Ekman numbers.
Fr.: vent géostrophique
Meteo.: A wind which is balanced by the → Coriolis effect and → pressure gradient force. An air parcel initially at rest will move from high pressure to low pressure because of the pressure gradient force. However, the air parcel in its movement is deflected by the Coriolis force, to the right in the northern hemisphere and to the left on the southern hemisphere. As the wind gains speed, the deflection increases until the Coriolis force equals the pressure gradient force. At this point, the wind will be blowing parallel to the → isobars.
Fr.: diagramme, graphique, graphe
1) A visual representation of data that displays the relationship among variables,
usually cast along X and Y axes.
Short for graphic (formula), from L. graphicus "of painting or drawing," from Gk. graphikos "able to draw or paint," from graph(ein) "to draw, write" + -ikos, → ic.
Negâré, from negâr "picture, figure" (verb negârdan, negâštan "to paint"), from prefix ne-, O.Pers./Av. ni- "down; into," → ni-, + gâr, from kar-, kardan "to do, to make" (Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build;" Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base *kwer- "to do, to make").