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dip angle zâviye-ye našib Fr.: angle d'inclinaison The angular difference between the → visible horizon and the → true horizon. Same as → dip of the horizon. |
dip of the horizon našib-e ofoq Fr.: inclinaison de l'horizon The angle created by the observer's line of sight to the → apparent horizon and the → true horizon. Neglecting the → atmospheric refraction, dip of the horizon can be expressed by θ (radians) = (2h/R)^{1/2}, where h is the observer's height and R the Earth's radius. An an example, for a height of 1.5m above the sea, and R = 6.4 x 10^{6} m, the dip angle is about 0.00068 radians, or 0.039 degrees, about 2.3 minutes of arc, quite appreciable by the eye. See also → distance to the horizon. Same as → dip angle. |
Diphda (β Ceti) Vazaq Fr.: Diphda The brightest star in the constellation → Cetus; a → red supergiant (K0 III) of visual magnitude 2.04. Diphda, from Ar. zafda' ( Mid.Pers. wazaγ, vak; Av. vazaγa- "frog," → tadpole orbit. |
diphthong dovâké Fr.: diphthongue Phonetics: A → vowel sound produced by a blended sequence of two separate vowels in a single syllable, where the sound begins as one vowel and moves toward another (as in loud, light, and lair). From M.Fr. diphthongue, from L.L. diphthongus, from Gk. diphthongos "having two sounds," from → di- "double" + phthongos "sound, voice." |
diplopia dobini (#) Fr.: diplopie A pathological condition of vision in which a single object appears double because the eyes are not focusing properly. Same as → double vision. From L. diplo- "double, in pairs," from Gk., combining form of diplos "twofold" + -opia, from Gk. -opia, from ops "eye." Dobini, from do→ two + bini "vision, seeing," from bin "to see; seer" (present stem of didan; Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know;" Gk. oida "I know," idein "to see;" L. videre "to see;" PIE base *weid- "to know, to see"). |
dipole doqotbé (#) Fr.: dipole 1) A combination of two electrically or magnetically charged particles
of opposite signs, which are separated by a very small distance. |
dipole anisotropy nâhamsângardi-ye doqotbé Fr.: anisotropie dipolaire A form of anistropy in the temperature of the → cosmic microwave background radiation, appearing as one hot pole and one cold pole, caused by our motion with respect to the cosmic background radiation. The temperature variations, amounting to 1 part in 1000, yield a velocity of about 600 km/sec for our Galaxy with respect to the background. → cosmic microwave background anisotropy. → dipole; → anisotropy. |
dipole antenna ânten-e doqotbé (#) Fr.: antenne dipôle One of the simplest kinds of antenna which is connected at the center to a radio-frequency feed line for transmitting or receiving radio frequency energy. It differs from the dish antenna in that it consists of many separate antennas that collect energy by feeding all their weak individual signals into one common receiving set. |
dipole moment gaštâvar-e doqotbé (#) Fr.: moment dipolaire 1) The product of the strength of either of the charges in an
→ electric dipole and the distance separating the two charges.
It is expressed in → coulomb meters. Dipole moment is a
→ vector quantity.
Its direction is defined as toward the positive charge. In chemistry dipole moment is
a quantitative measure of polarity in a molecule;
the unit is the → debye. |
dipole radiation tâbeš-e doqotbé Fr.: rayonnement dipolaire The electromagnetic radiation produced by an oscillating → electric dipole or → magnetic dipole. |
diproton diproton Fr.: diproton An → isotope of → helium that consists of two → protons, without any → neutrons. It is extremely → unstable. |
Dirac Dirac Fr.: Dirac Paul A. M. Dirac (1902-1984), English theoretical → physicist, one of the founders of → quantum mechanics and → quantum electrodynamics, Nobel Prize for Physics in 1933. → Dirac annihilation, → Dirac equation, → Dirac function, → Dirac's constant, → Fermi-Dirac statistics . |
Dirac annihilation nâbudi-ye Dirac Fr.: annihilation de Dirac Same as → pair annihilation. → Dirac; → annihilation. |
Dirac equation hamugeš-e Dirâk Fr.: équation de Dirac The equation that describes the behavior of an electron in a way that combines the requirements of quantum mechanics with the requirements of relativity. |
Dirac function karyâ-ye Dirâk Fr.: fonction de Dirac A function of x defined as being zero for all values of x other than x = x_{0} and having the definite integral from x = -∞ to x = +∞ equal to unity. |
Dirac's constant pâyâ-ye Dirac Fr.: constante de Dirac The → Planck's constant divided by 2π and denoted ħ, pronounced h-bar. Also called → reduced Planck's constant. |
direct 1) râst (#), sarrâst (#); 2) râštidan Fr.: 1) direct; 2) diriger 1a) Proceeding in a straight course or line without deviation or interruption. From L. directus "straight," p.p. of dirigere "set straight," from → dis- "apart" + regere "to guide;" cognate with Pers. râst, as explained below. Râst "right, straight" (râšt in afrâštan); Mid.Pers.
râst; O.Pers. rāsta- "straight, true," rās-
"to be right, straight, true," rād- "to prepare;" Av. rāz-
"to direct, put in line, set," razišta- "straightest, most correct,"
erezu- "correct, straight," rāzayeiti "directs," razan- "order;"
Skt. raj- "to direct, stretch," rjuyant- "walking straight;"
Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule,"
p.p. rectus "right, straight;" Ger. recht; E. right;
PIE base *reg- "right, just; to move in a straight line." |
direct correlation hambâzâneš-e sarrâst Fr.: corrélation directe A correlation between two variables such that as one variable becomes large, the other also becomes large, and vice versa. The correlation coefficient is between 0 and +1. Also called positive correlation. → direct; → correlation. |
direct current (DC) jarayân-e sarrâst Fr.: courant continu An → electric current which flows in one direction only and which is substantially constant in magnitude. Virtually all electronic and computer hardware needs direct current to function. → Alternating current can be converted to direct current by means of a power supply consisting of a → transformer. |
direct motion jonb eš-e farârow, ~ sarrâst Fr.: mouvement direct The motion of a solar system body from West to East across the sky against the background stars. It is the "normal" direction of motion within the solar system. For rotating or orbiting solar system objects it is anti-clockwise as seen from above the solar system in the direction of the North Pole. The same as → prograde motion. See also → retrograde motion. |
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