1) Math.: Independent extension in a given direction; a property of space.
From L. dimensionem (nom. dimensio), from stem of dimetri "to measure out," from → dis- + metri "to measure."
Vâmun, from vâ-, → dis-, + mun, variant mân "measure" (as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl"), from O.Pers./Av. mā(y)- "to measure;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum.
Of or pertaining to → dimension.
ânâlas-e vâmuni, ânâkâvi-ye ~
Fr.: analyse dimensionnelle
A technique used in physics based on the fact that the various terms in a
physical equation must have identical → dimensional formulae
if the equation is to be true for all consistent systems of unit. Its main uses are:
Fr.: formule dimensionnelle
Symbolic representation of the definition of a physical quantity obtained from its units of measurement. For example, with M = mass, L = length, T = time, area = L2, velocity = LT-1, energy = ML2T-2. → dimensional analysis.
Fr.: sans dimension
A physical quantity or number lacking units.
Fr.: quantité sans dimension
A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number.
A molecule resulting from combination of two identical molecules.
An electronic component with two active terminals, an → anode and a → cathode, through which current passes in one direction (from anode to cathode) and is blocked in the opposite direction. Diodes have many uses, including conversion of → alternating current to → direct current, regulation of votage, and the decoding of audio-frequency signals from radio signals.
→ di- "two, twice, double," + hodos "way."
Dione (Saturn IV)
The fourth largest moon of Saturn and the second densest after Titan. Its diameter is 1,120 km and its orbit 377,400 km from Saturn. It is composed primarily of water ice but must have a considerable fraction of denser material like silicate rock.
Discovered in 1684 by Jean-Dominique Cassini, Italian born French astronomer (1625-1712). In Gk. mythology Dione was the mother of Aphrodite (Venus) by Zeus (Jupiter).
A unit of optical measurement that expresses the refractive power of a lens or prism. In a lens or lens system, it is the reciprocal of the focal length in meters.
L. dioptra, from Gk. di-, variant of dia- "passing through, thoroughly, completely" + op- (for opsesthai "to see") + -tra noun suffix of means.
Dioptr loanword from Fr.
An instrument used in antiquity to measure the apparent diameter of the Sun and the Moon. It was a rod with a scale, a sighting hole at one end, and a disk that could be moved along the rod to exactly obscure the Sun or Moon. The Sun was observed directly with the naked eye at sunrise or sunset in order to prevent eye damage. Aristarchus (c.310-230 B.C.), Archimedes (c. 290-212 B.C.), Hipparchus (died after 127 B.C.), and Ptolemy (c.100-170 A.D.) used the dioptra. The instrument could also serve for measurement of angles, land levelling, surveying, and construction of aqueducts and tunnels.
1) Navigation: The angular difference between the visible horizon and
the true horizon. Same as → dip of the horizon.
O.E. dyppan "to immerse," cognate with Ger. taufen "to baptize," and with → deep.
Našib, → depression.
Fr.: angle d'inclinaison
dip of the horizon
Fr.: inclinaison de l'horizon
The angle created by the observer's line of sight to the → apparent horizon and t he → 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 106 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)
Diphda, from Ar. zafda' (
Mid.Pers. wazaγ, vak; Av. vazaγa- "frog," → tadpole orbit.
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."
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").
Of or relating to a → dipole.
dipolar magnetic field
meydân-e meqnâtisi-ye dipoli, ~ ~ diqotbi
Fr.: champ magnétique dipolaire