qânun-e Titius-Bode (#)
Fr.: loi de Titius-Bode
The empirical rule relating the approximate distances of the → solar system → planets from the → Sun. The original formulation was: a = (n + 4) / 10, where a is the mean distance of a planet from the Sun in → astronomical units and n = 0, 3, 6, 12, 24, 48, 96, 192 (doubling for each successive planet). The planets were seen to fit this sequence quite well, provided the → asteroids between → Mars and → Jupiter are counted as one planet, as did → Uranus discovered in 1781. However, → Neptune and the ex-planet → Pluto do not conform to the rule. The question of whether there is any physical significance to the "law," i.e. some dynamical reason that will explain planetary orbit spacing has led to much discussion during the past two centuries. Today, many astronomers are very skeptical and consider this "laws" to be numerical coincidence.
Named after the German mathematician Johann Titius (1729-1796), who first found the law in 1766, and the German astronomer Johann Elert Bode (1747-1826), who published it in 1772; → law.
Fr.: équivalent TNT
A measure of the explosive strength of a nuclear bomb, expressed in terms of the weight of → trinitrotoluene which could release the same amount of energy when exploded. The Hiroshima atomic (fission) bomb created a blast equivalent to 16 kilotons of TNT. The first hydrogen (thermonuclear) bomb test released an energy of about 10 megatons of TNT. See also → megaton of TNT.
From Rus. Tokamak, acronym from toroidal'naya kamera s magnitnymi katushkami "toroidal chamber with magnetic coils." It was invented in the 1950s by Soviet physicists Igor Yevgenyevich Tamm and Andrei Sakharov (who had been inspired by an original idea of Oleg Lavrentyev).
Fr.: Tables de Tolède
A set of astronomical tables drawn up by a group of astronomers in Toledo, Spain, mainly Zarqâli, and compiled after 1068. This work, which represents the first original development of Andalusian astronomy, was extremely influential in Europe for three centuries until the advent of the → Alfonsine Tables. The main sources for the bulk of the table collections were those of the Persian astronomer Khwârizmi (mainly planetary latitudes), Battâni (planetary equations), and Ptolemy. In fact the oldest version of the Toledan Tables was mainly modeled on Khwârizmi's Sindhind, but had admixture from Battâni. In addition, the oldest versions of the Toledan Tables preserve some tables of Khwârizmi that are rare or absent elsewhere. The Toledan Tables also incorporated the theory of → trepidation. The original Arabic version of the Toledan Tables has been lost, but two Latin versions have survived, one by Gerard of Cremona (12th century) and one by an unknown author.
Toledo, a city in central Spain, 70 km south of Madrid; → table.
The maximum permissible error or variation in a dimension of an object.
M.E., from O.Fr. tolerance, from L. tolerantia "endurance," from tolerans, pr.p. of tolerare "to bear, endure, tolerate."
Ravâdâri, noun from ravâdâr "consenter; judging right; lawful," from ravâ "admissible; allowable; tolerated" (from raftan "to go, walk; to flow;" Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack" + -dâr "having, possessor" (from dâštan "to have, to possess," Mid.Pers. dâštan, O.Pers./Av. root dar- "to hold, keep back, maitain, keep in mind," Skt. dhr-, dharma- "law," Gk. thronos "elevated seat, throne," L. firmus "firm, stable," Lith. daryti "to make," PIE *dher- "to hold, support").
A colorless, flammable liquid, insoluble in water and soluble in alcohol and ether, used as a solvent and in the manufacture of other organic chemicals and explosives. Chemical formula C6H5CH3. Same as methylbenzene and phenylmethane. See also → trinitrotoluene.
From tolu, from the older name toluol, which refers to tolu balsam, an aromatic extract from the tropical Colombian tree Myroxylon balsamum, from which it was first isolated, + -ene suffix used to form names of unsaturated hydrocarbons, from Gk. -ene denoting origin or source.
Any of several techniques, such as → Doppler tomography, for constructing a spatial distribution of physical quantity given measurements that are essentially line-integrals ("projections") through the distribution. Most famously, in medical tomography, the absorption of X-rays by a specimen is directly related to the line integral to make detailed images of a predetermined plane section of a solid object while blurring out the images of other planes.
From Gk. tomo- combining form of tomos "a cut, section, slice" tome "cutting" + → -graphy.
Borešnegâri, from boreš "section, slice, cutting," from boridan "to cut" (Mid.Pers. britan, brinitan "to cut off;" Av. brī- "to shave, shear," brin-; cf. Skt. bhrī- "to hurt, injure," bhrinanti "they hurt") + -negâri, → -graphy.
M.E. tunne unit of weight or capacity (cf. O.Fris. tunne, M.Du. tonne, O.H.G. tunna, Ger. tonne), also found in M.L. tunna and O.Fr. tonne, perhaps from a Celtic source.
A musical sound of definite pitch, consisting of several relatively simple constituents called partial tones, the lowest of which is called the fundamental tone and the others harmonics or overtones.
M.E., from O.Fr. ton, from L. tonus "a sound, tone, accent," literally "stretching," from Gk. tonos "vocal pitch, raising of voice," related to teinein "to stretch," cognate with Pers. tanidan "to spin, weave," → tension.
Ton, loan from Fr., as above.
Fr.: critère d'Ostriker-Peebles
Fr.: longueur de Toomre
The scale beyond which for a thin, rotating disk, rotation stabilizes self-gravitational contraction. The Toomre length is given by: λT = 4π2GΣ / κ2, where G is the → gravitational constant, Σ is the mass → surface density, and κ is the → epicyclic frequency (Toomre 1964, ApJ 139, 1217).
Fr.: paramètre de Toomre
A quantity that measures the stability of a differentially rotating disk of matter against → gravitational collapse. It is expressed by the relation: Q = csκ / πGΣ, where cs is the → sound speed, κ the → epicyclic frequency, G the → gravitational constant, and Σ the → surface density. The disk is linearly stable for Q > 1 and linearly unstable for Q < 1.
After Alar Toomre (1936-), an American astrophysicist of Estonian origin, professor of mathematics at the Massachusetts Institute of Technology; → parameter.
âzmâyeš-e carx-e dandâne-dâr
Fr.: expérience de la roue dentée
The experiment which provided the first accurate measurement of the speed of light. The experiment, conducted by the French physicist Armand H. L. Fizeau (1819-1896) in 1849, used a rotating wheel containing 720 teeth. The function of the wheel was to cut a light beam into short pulses and to measure the time required for these pulses to travel to a distant mirror and back (17.34 km). The round-trip time for each pulse could be calculated to be about 1/18,000 sec, which yielded the value of 315,300 km/sec for the speed of light. Leon Foucault (1819-1868) improved on Fizeau's method by replacing the cogwheel with a rotating mirror. Foucault's estimate, published in 1862, was 298,000 km/s.
Âzmâyeš, → experiment; carx→ wheel; dandâne-dâr "toothed," from dandân "tooth," Mid.Pers. dandân; Av. dantan-; cf. Skt. dánta-; Gk. odontos; L. dens (Fr. dent); Lith. dantis, O.Ir. det, Welsh dent; PIE base *dont-/*dent- "tooth."
Fr.: sommet, du haut, haut
The highest point or part. The higher end of anything on a slope.
M.E., O.E. top "summit, crest, tuft;" cf. O.N. toppr "tuft of hair," O.Fris. top "tuft," O.Du. topp, Du. top, O.H.G. zopf "end, tip, tuft of hair," Ger. Zopf "tuft of hair."
Bâlâ "up, above, high, elevated, height" (variants boland "high, tall, elevated, sublime," borz "height, magnitude" (it occurs also in the name of the mountain chain Alborz), Laki dialect berg "hill, mountain;" Mid.Pers. buland "high;" O.Pers. baršan- "height;" Av. barəz- "high, mount," barezan- "height;" cf. Skt. bhrant- "high;" L. fortis "strong" (Fr. and E. force); O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- "high."
top-down structure formation
diseš-e sâxtâr az bâlâ bé pâyin
Fr.: formation des structures du haut vers le bas
A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.
A star formation process in which → massive stars form more abundantly than that predicted by standard models, whereby the top end of the → initial mass function is significantly flatter than the canonical → Salpeter slope.
Fr.: coordonées topocentriques
A coordinate system that uses the observer's location as its central reference point. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric coordinates is very small because most celestial objects are so far away. However, for nearby objects this is not true. The Sun, for example, may appear displaced as much as eight arcseconds from its geocentric position, and the Moon by as much as one degree.
Hamârâhâ, → coordinate; jâ-markazi "topocentric," from jâ "place" (from Mid.Pers. giyâg "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night") + markazi, of, pertaining to markaz, → center.
Of or relating to → topology.
âk-e topošenâxti, ~ topošenâsik
Fr.: défaut topologique
In → cosmological models, a stable configuration of → matter formed when the → early Universe underwent → phase transitions during which fundamental symmetries were broken. There are a number of possible types of defects, such as domain walls, → cosmic strings, → magnetic monopoles, and → texture s. Same as → cosmic defect.
Fr.: espace topologique
A set X together with a collection of open subsets T that satisfies the three following conditions: 1) The empty set Ø and X are in T. 2) The intersection of a finite number of sets in T is also in T. 3) The union of an arbitrary number of sets in T is also in T.