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Fr.: proposition atomique
Fr.: transition atomique
1) The act or faculty of attending, especially by directing the mind to an object.
The falling off of the energy density of radiation with distance from the source, or with passage through an absorbing or scattering medium.
Verbal noun of → attenuate.
Fr.: coefficient d'bsorption
The fraction of a beam of → X-rays or → gamma rays that is absorbed or scattered per unit thickness of the → absorber. The linear attenuation coefficient, denoted by the symbol μ, appears in the equation I(x) = I0e-μx, where I(x) is the intensity at depth of x cm and I0 is the original intensity.
Fr.: facteur d'atténuation
The ratio of the radiation intensity after traversing a layer of matter to its intensity before.
The act or capability of attracting. A physical force (gravitational, electric, magnetic, etc.) exerted by material bodies.
Attraction, n. from → attract.
1) The act of attributing.
Verbal noun of → attribute.
Fr.: émission aurorale
Computers: The process by which a user's identity is checked within the network to ensure that the user has access to the requested resources.
Verbal noun of → authenticate.
1) In radio astronomy, a process performed by an → autocorrelator.
Autocorrelation, from → auto- "self" + → correlation.
Xod-hambâzâneš, from xod- "self" + hambâzâneš, → correlation.
Fr.: fonction d'autocorrélation
A mathematical function that describes the correlation between two values of the same variable at different points in time.
Fr.: fonction d'autocovariance
The autocovariance function (ACF) is defined as the sequence of
covariances of a stationary process.
Fr.: accélération moyenne
Of a body traveling from A to B, the change of → velocity divided by the time interval: ā = (v2 - v1) / (t2 - t1).
negâh-e kaž (#)
Fr.: regard oblique
The technique of looking slightly to the side of a faint object being studied while continuing to concentrate on the object. The technique helps bring out details which otherwise would be missed by looking directly at an object. The reason is that the portion of the eye's retina that best detects dim light (fovea) is located all around the edges rather than the center.
Negâh, → vision; kaž "averted."
Fr.: inclinaison de l'axe
The angle at which a planet's axis of rotation is tilted, with respect to that of the planet's orbit.
Fr.: précession axiale
1) A change in the orientation of the → rotation axis
of a non-spherical, spinning body caused by → gravity.
A rotating top will precess in a direction determined by the
→ torque exerted by its → weight.
→ angular velocity is
inversely proportional to the spin angular velocity, so that the
precession is faster and more pronounced as the top slows down.
A hypothetical weakly-interacting → boson of small mass required by models of → particle physics in order to solve the strong CP problem and explain a number of observed astrophysical/cosmological phenomena, including → dark matter, and the dimming of → type Ia → supernovae (→ accelerating Universe). Photons traveling in the → intergalactic medium would in part turn into axions in the presence of magnetic fields. The transformed photons are not detected on Earth and therefore supernovae would appear fainter even if the Universe is not accelerating.
Axion, first coined by Frank Wilczek (2004 Nobel Prize in Physics) apparently after a brand of washing detergent! The reason seems to be the idea that the particle will iron out a wrinkle in the → standard model of fundamental particles and forces while solving the problem of the Universe's → missing mass.
axis of rotation
Fr.: axe de rotation
Fr.: projection azimutale
A map projection on which the → azimuths of all points are shown correctly with respect to the center. A plane tangent to one of the Earth's poles is the basis for polar azimuthal projection.