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Number of Results: 13 Search : critical

critical paržani Fr.: critique 1) Of or pertaining to → |

critical angle zâviyeh-ye paržani Fr.: angle critique Angle of incidence of light proceeding from a denser medium toward a thinner, at which grazing refraction occurs (angle of refraction 90°). |

critical Bonnor-Ebert mass jerm-e paržani-ye Bonnor-Ebert Fr.: masse critique de Bonnor-Ebert The upper value of mass that a → a = (kT/m) is the isothermal
→ ^{1/2}sound speed inside the sphere, G is the
→ gravitational constant, and P the pressure
of the external medium (see, e.g., F. H. Shu, 1977, ApJ 214, 488)._{ext}→ |

critical density cagâli-ye paržani Fr.: densité critique 1) c is the → speed of light,
G is the → gravitational constant, and
H the → _{t}Hubble parameter.
The critical density is currently 9.3 × 10^{-30}g cm^{-3},
about 6 hydrogen atoms per cubic meter
(for H = 70 km s_{0}^{-1} Mpc^{-1}). 2) In → gravitational lensing, the minimum density that
would be needed by an intervening object to bend light rays.
It is expressed by:
Σ = (c^{2}/4πG)(d),
where _{os}/d_{ol}d_{ls}c is the speed of light, G is
the gravitational constant,
d, _{os}d, and _{ol}d
represent angular diameter distances between the observer and the source,
the observer and the lens, and the lens and the source respectively.
It has units of mass per unit solid angle. _{ls}3) Radiative processes: The density at which the collisional
→ de-excitation rate
equals the → radiative transition rate.
The critical density for level j is given by:
n,
where _{c} = Σ_{i < j} A_{ji} = Σ_{i ≠ j} q_{ji}A is the → _{ji}Einstein coefficient of
→ spontaneous emission
and q is the rate for collisional de-excitation
of → _{ji}energy level j, summed over all possible processes.
This expression often simplifies to the ratio
of two numbers, since in many cases there is a single
important path for emission and a dominant collisional de-excitation process.
In the low density limit the → emissivity
is proportional to the product
N (electron density) x _{e}N (ion density),
whereas for densities exceeding the critical density, the emissivity is proportional to
_{i}N. Thus, line emission in a nebula occurs most efficiently near
the critical density._{i} |

critical mass jerm-e paržani Fr.: masse critique Of a fissile material ( |

critical metallicity felezigi-ye paržani Fr.: métallicité critique The → → |

critical opalescence opâlesti-ye paržani Fr.: opalescence critique The strong → → |

critical velocity tondâ-ye paržani Fr.: vitesse critique 1) Velocity of → |

subcritical zir-paržani Fr.: sous-critique Of or pertaining to a state, value, or quantity that is less than critical,
especially the condition of a → |

subcritical mass jerm-e zir-paržani Fr.: masse sous-critique An amount of → → |

subcritical reactor vâžirgar-e zir-paržani Fr.: réacteur sous-critique A → → |

supercritical abar-paržani Fr.: supercritique 1) |

supercritical fluid šârre-ye abar-paržani Fr.: fluide supercritique A fluid that is at a temperature and pressure above its thermodynamic critical point. In these conditions the substance acquires unique characteristics of density and mobility. Supercritical fluids exist deep inside some planets; for example, there is supercritical water deep inside the Earth. → |