line profile variability (LPV)
vartandegi-ye farâpâl-e xatt
Fr.: variabilité du profil de raie
binâb-e xatti (#)
Fr.: spectre de raies
Spectrum consisting of discrete lines (emission or absorption), each corresponding to a particular wavelength, as opposed to a continuous spectrum.
Fr.: intensité de raie
Same as → line intensity.
xatbâl, bâl-e xatt
Fr.: aile de raie
Part of the line profile between the continuum level and the half value of the emission or absorption peak. The wings are due to matter traveling at much greater speeds than that providing the main peak. → red wing; → blue wing.
A stellar atmosphere model which includes metals or uses methods to reproduce their effects, → line blanketing.
Fr.: vent induit par raie
Same as → radiation-driven wind.
Any of a countless number of dark streaks visible on → Europa's surface that crisscross the whole → Galilean satellite. They are up to 1,000 km long, 20 km wide, and 1 km deep, but only hundred of meters high. In many cases, the ridges are double, often with dark outer edges and a central band. Images show that on each side of the lines, the edges have moved relative to each other. According to the most likely hypothesis, lineae result from eruptions of warm water, in a scenario similar to the present day mid- oceanic ridges on Earth.
From L. linea, → line.
Xaš, → streak.
Confined to first-degree algebraic terms in the relevant variables.
Adj. of → line.
Fr.: approximation linéaire
Taking the first term in the Taylor series as an approximation to a mathematical function at a given point. → first approximation.
Fr.: astrolabe linéaire
A version of → planispheric astrolabe in which the → celestial sphere and the various circles of altitude and declination are projected on to a line represented by a staff. The staff is equivalent to the meridian line and contains markings to indicate the centers of these circles and their intersections with the meridian. By attaching three ropes to the appropriate points on the staff to act as radii, the circles and their intersections can be reconstructed. One of the ropes was attached to a plumb line. A scale giving chord lengths in the meridian circle extended the linear astrolabe's range of applications. It was invented by the Iranian mathematician and astronomer Sharafeddin Tusi (c1135-1213), but no early example has survived. Same as → Sharafeddin's staff and Tusi's staff.
Fr.: corrélation linéaire
A measure of how well data points fit a straight line. When all the points fall on the line it is called a perfect correlation. When the points are scattered all over the graph there is no correlation.
Fr.: diamètre linéaire
The real physical diameter, as opposed to angular diameter.
linear differential equation
hamugeš-e degarsâne-yi-ye xatti
Fr.: équation différentielle linéaire
An equation in which the → dependent variable y
and all its differential coefficients occur only
in the first degree. A linear differential equation of → order
order n has the form:
Fr.: équation linéaire
An equation composed of first degree variables and representing a straight line.
Fr.: fonction linéaire
nâpâydâri-ye xatti (#)
Fr.: instabilité linéaire
An instability that can be described (to first-order accuracy) by linear (or tangent linear) equations.
Fr.: quantité de mouvement linéaire
The product of an object's → mass and → velocity. It is a → vector and points in the same direction as the velocity vector. Linear momentum is distinguished from → angular momentum. When there is no opportunity for confusion, usually the term momentum is used instead of linear momentum.
linear perturbation theory
negare-ye partureš-e xatti
Fr.: théorie de perturbation linéaire
Assumption that the variations in the plasma parameters, due to the presence of waves, are small (to the first order) as compared to the undisturbed parameters. This makes it possible to linearize equations by dropping out second order (and higher) nonlinear terms.
qotbeš-e xatti (#)
Fr.: polarisation linéaire
Of an electromagnetic radiation, a → polarization in which the electric vibrations are confined to one plane along the direction of propagation. Also called → plane polarization. See also → circular polarization.
barnâme-sâzi-ye xatti (#)
Fr.: programmation linéaire
A procedure for finding the maximum or minimum of a → linear function where the → arguments are subject to linear → constraints. For problems involving more than two variables or problems involving a large number of constraints, solution methods used are those that are adaptable to computers. A well-known such → algorithm is the → simplex method.