Fr.: activité solaire
solar activity cycle
carxe-ye žirandegi-ye xoršid
Fr.: cycle d'activité solaire
Same as the → solar cycle.
Stokes friction factor
karvand-e mâleš-e Stokes
Fr.: facteur de friction de Stokes
For the translational motion of a spherical body moving in a → viscous fluid, the proportionality factor between the uniform flow velocity far from the sphere and the drag force, provided no-slip boundary condition and small → Reynolds numbers: f = 6πηR, where η is the Reynolds number and R radius of the sphere.
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.