Of, pertaining to, or constituting a cycle or cycles.
hamârâ-ye nâdidé engâshté
Fr.: coordonnée ignorée
Same as → ignorable coordinate.
Fr.: groupe cyclic
A group in which each element can be expressed as a power of any other element.
Fr.: processus cyclique
Fr.: quadrilatère cyclique
A quadrilateral in which all four vertices lie on the circumference of a circle.
Of or pertaining to an → epicycle.
Fr.: fréquence épicyclique
In the → epicyclic theory of Galactic rotation, the frequency at which a star in the → Galactic disk describes an ellipse around its mean circular orbit. The epicyclic frequency relates to the → Oort's constants. In the solar neighborhood the epicyclic frequency is about 32 km s-1 kpc-1.
Fr.: oscillation épicyclique
Fr.: théorie épicyclique
The theory that describes the Galactic dynamics, that is the orbits of stars and gas clouds in the → Galactic disk, as well as the spiral → density wave. Formulated by Bertil Lindblad (1895-1965), the epicyclic theory assumes that orbits are circular with small deviations. Star orbits are described by the superposition of two motions: i) a rotation of the star (epicenter) around the Galactic center at the circular angular velocity, Ω, and ii) a retrograde elliptical motion at → epicyclic frequency, κ. The epicyclic motion in the Galactic plane occurs in a retrograde sense to conserve → angular momentum. In general Ω and κ are different and, therefore, orbits do not close. However, seen by an observer who rotates with the epicenter, orbits are closed ellipses.
polycyclic aromatic hydrocarbons (PAHs)
hidrocarburhâ-ye aromâtik-e polisiklik, ~ ~ bol-carxe-yi
Fr.: hydrocarbures aromatiques polycycliques
1) Chemistry: A family of → organic molecules composed
of carbon and hydrogen atoms (→ hydrocarbons) in which
→ carbon atoms appear in multiple loops (polycyclic)
with strong chemical → bonds that exist between them (aromatic).
PAHs are formed during the incomplete burning of coal, oil and gas, garbage, or other
organic substances like tobacco or charbroiled meat. As a pollutant, they are of
concern because some compounds (benzo(a)pyrene) have been identified as tending to