Alfven Mach number
adad-e Mach-e Alfvéni
Fr.: nombre de Mach alfvénique
The ratio of the flow velocity to the → Alfvén speed in a medium.
Fr.: point d'Alfvén
In magnetized disk models, the point where the → poloidal velocity equals the → Alfven speed. Within this point, the magnetic energy density dominates, and the gas is forced to flow along the field lines. Well beyond this point, the kinetic energy acquired by the flowing gas prevails and the field is forced to follow the flow.
Fr.: rayon d'Alfvén
1) In theories of magnetized → accretion disks,
the distance from a non-rotating star where the → free fall
of a spherical accretion flow is stopped, which occurs where the
→ ram pressure of the infalling matter equals the
→ magnetic pressure of the star.
Fr.: vitesse d'Alfvén
The speed at which → Alfven waves are propagated along the magnetic field. It is a characteristic velocity at which perturbations of the lines of force travel. Alfvén speed is given by: vA = B/(μ0.ρ)1/2, where B is the → magnetic field strength, μ0 is the → magnetic permeability, and ρ is the density of the plasma. Alfvén speed plays a role analogous to the sound speed in non-magnetized fluid dynamics. Same as Alfvén velocity.
Fr.: surface d'Alfvén
In a magnetized wind, the geometric loci of the points where the magnetic pressure equals the flow pressure. See also → Alfven point.
Fr.: vitesse d'Alfvén
same as → Alfven speed.
Fr.: onde d'Alfvén
A → magnetohydrodynamic wave in a → magnetized plasma, arising as a result of restoring forces associated with the magnetic field. It is a → transverse wave which propagates in the direction of the magnetic field. Also called magnetohydrodynamic wave.
Involving → Alfvén waves.
Fr.: fluctuation alfvénique
Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ0ρ)1/2. Also called Alfvénicity.
A single-celled or multicellular plant living in water or moist conditions, which contain chlorophyll and other pigments but has no true root, stem, or leaf. Algae include seaweeds and pond scum.
From alga (singular), from L. alga "seaweed," of uncertain origin.
The branch of mathematics which deals with the properties and relations of numbers using symbols (usually letters of the alphabet) to represent numbers or members of a specified set; the generalization and extension of arithmetic.
Algebra, from M.L., from Ar. al jabr "reunion of broken bones," the first known use in the title of a book by the Persian mathematician and astronomer Abu Ja'far Mohammad ibn Musa al-Khwarizmi (c780-c850), who worked in Baghdad under the patronage of Caliph Al-Mamun. The full title of the tratise was Hisab al-Jabr w'al-Muqabala "Arithmetic of Completion and Balancing." → algorithm.
Jabr, from Ar. al jabr, as above.
Relating to, involving, or according to the laws of algebra.
Fr.: équation algébrique
An equation in the form of P = 0, where P is a → polynomial having a finite number of terms.
Fr.: fonction algébrique
A function expressed in terms of → polynomials and/or roots of polynomials. In other words, any function y = f(x) which satisfies an equation of the form P0(x)yn + P1(x)yn - 1 + ... + Pn(x) = 0, where P0(x), P1(x), ..., Pn(x) are polynomials in x.
adad-e jabri (#)
Fr.: nombre algébrique
A number, → real or → complex, that is a → root of a → non-zero polynomial equation whose → coefficients are all → rational. For example, the root x of the polynomial x2 - 2x + 1 = 0 is an algebraic number, because the polynomial is non-zero and the coefficients are rational numbers. The imaginary number i is algebraic, because it is the solution to x2 + 1 = 0.
Algenib (γ Pegasi)
Algenib, from Ar. Aljanb al-Faras "the horse's flank," from al "the" + janb "flank" + faras "horse".
Algieba (γ Leo)
A binary system in Leo the brighter component of which (magnitude 2.6) is a giant K star and the partner a giant G (magnitude 3.8). The angular separation of just over 4'' means that the two stars are at least 170 AU apart, for a distance of 126 → light-years, and have an orbital period of over 500 years.
Algieba, from Ar. Al-Jabhah "the forehead" (of the Lion).
Algol (β Persei)
Alqul, Ra's-ol-Qul (#)
A variable star in the constellation → Perseus, which was the first eclipsing binary discovered. Its brightness varies between 2.2 and 3.5 magnitudes. Lying at a distance of about 82 → light-years, it consists of at least three components. The brightest component (A) is of spectral type B8 V, and the second one (B) a K type giant. The components A and B turn around each other with a period of about 68.8 hours.
Algol, from Ar. Ra's al-ghul "the ghoul's head".
Fr.: variables de type Algol
The same as eclipsing binary stars, the prototype of which is Algol.