Fr.: densité spectrale
For a specified → bandwidth of radiation consisting of a continuous → frequency spectrum, the total → power in the bandwidth divided by the bandwidth. Spectral density describes how the power (or variance) of a time series is distributed with frequency. Also called power spectral density.
Fr.: variabilité spectrale
The state of a spectrum from an astronomical object in which the lines change with time as far as their intensity, profile, and wavelength are concerned.
The quality or fact of being → spiritual.
Noun from adj. → stable.
Fr.: luminosité stellaire
The total amount of energy emitted by a star per unit time. According to the → Stefan-Boltzmann law, the stellar luminosity is given by: L* = 4πR*2σTeff4, where R* is radius, σ is the → Stefan-Boltzmann constant, and Teff is → effective temperature. A star's luminosity depends, therefore, on two factors, its size and its surface temperature. Stellar luminosity is measured either in ergs per second or in units of → solar luminosity or in → absolute magnitude. See also → luminosity class.
Fr.: métallicité stellaire
The metallicity derived from observations of stars in galaxies. It is mainly based on spectral → absorption lines in → ultraviolet (UV) and optical ranges. Stellar metallicity is a direct measure of the amount of metals in a galaxy, since large part of heavy elements lies in its stars.
Fr.: nature sous-stellaire
The phenomenon in which certain materials, when cooled to a sufficiently low temperature, lose all resistance to the flow of electricity.
Fr.: densité de surface
The amount of a quantity distributed over a surface area divided by the area, such as a surface-charge density.
gerâni-ye ruyé, ~ ruye-yi
Fr.: gravité de surface
1) The rate at which a small object in free fall near the surface of a body is
accelerated by the gravitational force of the body: g = GM / R2,
where G is the gravitational constant, and M and R
are the mass and radius of the object. The
surface gravity of Earth is equal to 980 cm s-2.
State or character of being susceptible. → magnetic susceptibility
M.L. susceptibilitas, from susceptibilis "capable, sustainable, susceptible," from susceptus, p.p. of suscipere "sustain, support, acknowledge," from sub "up from under" + capere "to take" ......
Barxodgiri, from bar- "up; upon; on; in; into; at; forth; with; near; before; according to" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + xod "self, own" (Mid.Pers. xwad "self; indeed;" Av. hva- "self, own") + giri vebal noun of gereftan "to take, seize, hold" (Mid.Pers. griftan, gir- "to take, hold, restrain;" O.Pers./Av. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha- "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE *ghrebh- "to seize").
An ecological concept, the property or condition of being → sustainable.
Quality, state noun from → sustainable.
Fr.: vitesse tangentielle
1) The instantaneous linear velocity of a body moving in a circular path.
It is equal to the → angular velocity multiplied
by the radius: vt = ωr.
Fr.: instabilité de Taylor-Couette
A hydrodynamic instability in the → Taylor-Couette flow that arises when the rotation velocity of the fluid exceeds a critical value. The instability arises for → Taylor numbers larger than about 1700. At the beginning the fluid elements will move in simple rolls, but turbulence in the form of complex spirals will appear with increasing rotation velocity.
Temporal character or nature.
Fr.: densité de tenseur
A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor.
Fr.: vitesse terminale
1) The constant maximum velocity reached by a body falling under gravity through a
liquid or gas, especially the atmosphere. The body ceases
to accelerate downward because the force of gravity is equal
to the opposing force of resistance by the medium.