An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 11 Search : virial
 virial   ویریال   viriyâlFr.: viriel   Of or pertaining to the interactive forces between components of a system, such as particles or molecules in a gas or stars in a cluster. → virial equation of state, → virial equilibrium, → virial mass, → virial parameter, → virial radius, → virial temperature, → virial theorem, → virialization.From L. vires, plural of vis "strength," and by extension "force" or "energy," first used by Rudolf Clausius in the investigation of problems in molecular physics.Viriyâl, loan from E., as above. virial equation of state   هموگش ِ حالت ِ ویریال   hamugeš-e hâlat-e viriyalFr.: équation d'état du viriel   In thermodynamics, a generalized → equation of state obtained when the → compression factor Z is expanded in terms of a power series, e.g.: Z = 1 + B(T) / Vm + C(T) / Vm2 + ... virial equilibrium   ترازمندی ِ ویریال   tarâzmandi-ye viriyâlFr.: équilibre du viriel   The condition of a physical system which obeys the → virial theorem.→ virial; → equilibrium. virial mass   جرم ِ ویریال   jerm-e viriyâlFr.: masse du viriel   The mass of a cluster of stars or galaxies in statistical equilibrium derived by using the → virial theorem.→ virial; → mass. virial parameter   پارامون ِ ویریال   pârâmun-e viriyâlFr.: paramètre du viriel   A dimensionless parameter that measures the ratio of thermal plus kinetic energies to gravitational energy of a physical system, such as a molecular cloud. The virial parameter is expressed as: αvir = 5σ2R / GM, where R and M are the radius and mass of the cloud respectively, σ is the one-dimensional → velocity dispersion inside the cloud, and G the → gravitational constant. It indicates whether a cloud could be bound or not. For molecular clouds that are confined by their surface pressure and for which self-gravity is unimportant, αvir is much larger than unity, whereas αvir is ~ 1 when the gravitational energy of a clump becomes comparable to its kinetic energy. See, e.g., Bertoldi & McKee, 1992 (ApJ 395, 140). See also → virial theorem.→ virial; → parameter. virial radius   شعاع ویریال   šo'â'-e viriyâlFr.: rayon du viriel   The radius centered on a galaxy containing matter at 200 times the → critical density of the Universe.→ virial; → radius. virial temperature   دمای ِ ویریال   damâ-ye viriyâlFr.: température du viriel   The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kTvir/μ, where k is → Boltzmann's constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature Tvir = (1/3)(GM/kR).→ virial; → temperature. virial theorem   فربین ِ ویریال   farbin-e viriyâlFr.: théorème du viriel   A general equation applicable to a gravitationally → bound system of equal mass objects (stars, galaxies, etc.), which is stable against → dynamical disruption. It states that in such a system the average → gravitational potential energy (Wvir) is twice the average → kinetic energy (Kvir) of the system: Wvir = -2Kvir. This general proposition, first derived by Rudolf Clausius (1822-1888), has important applications in a variety of fields ranging from statistical mechanics to astrophysics. See also → virialization, → virial equilibrium, → virialized.→ virial; → theorem. virialization   ویریالش   viriaylešFr.: virialisation   The process whereby a system of gravitationally interacting particles attains stability. The comparable mass components interact with each other, but the whole system does not expand or collapse. Virialization occurs when the → potential energy is twice the negative → kinetic energy: - Wvir = 2 Kvir (→ virial theorem). In the case of a → galaxy cluster, when the cluster is virialized the merging process and the collapse of matter have finished and the formation process of the galaxy cluster is considered to be done. A cluster has formed by → hierarchical clustering. Virialized clusters, in other words finished clusters, can be found by looking at their radius and density. A cluster is virialized when it satisfies the condition: Rvir ~ Rmax/2, where Rvir is the radius when the cluster is virialized and Rmax is the radius when the collapse starts. From this condition it follows that the object is 8 times denser at virialization than when the collapse started.Verbal noun of → virialize. virialize   ویریالیدن   viriyâlidanFr.: virialiser   To undergo → virialization.→ virial; → -ize. virialized   ویریالیده   viriyâlidéFr.: virialisé   That has undergone → virialization.Past participle of → virialize.