Fr.: interaction forte
The interaction between quarks that is transmitted by gluons. The characteristic range of the strong interaction is 10-13 cm, and the time scale over which it operates is on the order of 10-23 second. Also called → strong force.
Fr.: réacteur sous-critique
To take one number away from another; deduct. To perform the arithmetic operation of → subtraction.
From L. subtractus, p.p. of subtrahere "to draw from beneath, take away, draw off," from → sub- "from under" + trahere "to pull, draw."
Zirkaršidan, literally "to draw beneath," from zir-,
→ sub-, + karšidan "to draw, pul, drag," variant of
kašidan "to draw, protract, trail, drag, carry;"
Av. karš- "to draw; to plow," karša-
"furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;"
cf. Skt. kars-, kársati "to pull, drag, plow;"
Gk. pelo, pelomai "to move, to bustle;" PIE base kwels-
The operation of finding the difference between two numbers or quantities.
Verbal noun of → subtract.
Fr.: synthèse soustractive
Color produced by mixing pigments rather than light. Mixing all of the subtractive colors together results in the color black. See also → additive color.
supergalactic coordinate system
râžmân-e hamârâhâ-ye abarkahkašâni
Fr.: système des coordonnées supergalactiques
A spherical → coordinate system in which the → equator is the → supergalactic plane. Supergalactic longitude, SGL, is measured → counterclockwise from direction l = 137.37 deg, b = 0 deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined by the intersection of this plane with the → Galactic plane. In the → equatorial coordinate system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB, is measured from the supergalactic plane, positive northward and negative southward. The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9 h, +15.7 deg.
Fr.: latitude supergalactique
Fr.: longitude supergalactique
Fr.: plan supergalactique
The symmetry plane of the → Local Supercluster, where density of galaxies in our environment is the largest. The plane passes through the → Virgo cluster of galaxies, about which many of the brightest galaxies in the sky are concentrated. The supergalactic plane was recognized by Gérard de Vaucouleurs (1918-1995) in 1953 from the → Shapley-Ames catalogue.
Fr.: contraction de tenseur
An operation of tensor algebra that is obtained by setting unlike indices equal and summing according to a summation convention.
vâžireš-e garmâhaste-yi (#)
Fr.: réaction thermonucléaire
A nuclear reaction in which two or more atomic nuclei fuse into a single heavier nucleus by a collision of the interacting particles at extremely high temperatures. Chains of thermonuclear reactions, such as the → proton-proton chain and the → CNO cycle, account for the energy radiated from the Sun and more massive stars.
Fr.: troisième contact
The end of the total phase of a solar eclipse marked by the trailing edge of the Moon first revealing the Sun.
threshold of reaction
Fr.: seuil de réaction
The minimum energy, for an incident particle or photon, below which a particular reaction does not occur.
ultracompact dwarf galaxy (UCD)
kahkešân-e kutule-ye ultar-hampak
Fr.: galaxie naine ultracompacte
A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).
ultracompact H II region
nâhiye-ye H II-ye ultar hampak
Fr.: région H II ultracompacte
A very young → H II region fully embedded in its natal molecular cloud. Ultracompact H II regions are distinguished from classical H II regions by their small sizes (diameter ≥ 0.1 pc), high densities (Ne ≥ 105 cm-3), and high emission measures (EM ≥ 107 pc cm-6). Their typical ionized gas content is about 10-2 → solar masses, in contrast to classical H II regions with a mass of about 105 solar masses. Due to very important extinction, ultracompact H II regions are not accessible to visible wavelengths.
Fr.: veine contractée
L. vena "channel;" contracta, "contracted," → contract.