An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 92 Search : equation
acoustic wave equation
  هموگش ِ موج ِ صدایی   
hamugeš-e mowj-e sedâyi

Fr.: équation de l'onde acoustique   

A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇2φ = (1/c2)∂2φ/∂t2, where c is → velocity of → longitudinal waves and ∇2 is the → Laplacian operator.

acoustic; → wave; → equation.

algebraic equation
  هموگش ِ جبری   
hamugeš-e jabri

Fr.: équation algébrique   

An equation in the form of P = 0, where P is a → polynomial having a finite number of terms.

algebra; → equation.

annual equation
  هموگش ِ سالانه   
hamugeš-e sâlâné

Fr.: équation annuelle   

An irregularity in the Moon's orbit, which can amount to 11 degrees in a period of one year. It results from the Sun's disturbing effect on the motion of the Moon due to varying distance between them.

annual; → equation.

Antoine equation
  هموگش ِ آنتوان   
hamugeš-e Antoine

Fr.: équation d'Antoine   

A mathematical expression, derived from the → Clausius-Clapeyron equation, of the relation between the vapor pressure and the temperature of pure substances. It shows that the logarithm of vapor pressure is linearly dependent on the reciprocal of → absolute temperature.

Named after Louis Charles Antoine (1825-?), a French marine engineer, who derived the equation; → equation.

Arrhenius equation
  هموگش ِ آرنیوس   
hamugeš-e Arrhenius

Fr.: équation d'Arrhenius   

An important relationship in physical chemistry that combines the concepts of → activation energy and the → Maxwell-Boltzmann distribution law. It is expressed by: k = Ae-Ea/(RT), where k is the chemical → reaction rate, Ea is the activation energy, R is the → gas constant, and T is → temperature.

Named for Svante Arrhenius (1859-1927), Swedish chemist and physicist who suggested the relationship in 1889.

Bernoulli equation
  هموگش ِ برنویی   
hamugeš-e Bernoulli

Fr.: équation de Bernoulli   

The equation expressing → Bernoulli's theorem: P + (1/2)ρV2 + ρgz = constant, where P is the fluid → pressure, V is → velocity, ρ is → density, g is the acceleration due to → gravity, and z is the vertical reference → level. The theree terms are called → static pressure, → dynamic pressure, and → hydrostatic pressure, respectively. The Bernoulli equation states that the total pressure along a → streamline is → constant.

Bernoulli's theorem; → equation.

Bessel equation
  هموگش ِ بسل   
hamugeš-e Besel

Fr.: équation de Bessel   

A linear second-order differential equation, the solutions to which are called Bessel functions.

From → Bessel; → equation

Hamugeš, → equation.

Boltzmann's equation
  هموگش ِ بولتسمن   
hamugeš-e Boltzmann

Fr.: équation de Boltzmann   

1) An equation that expresses the relative number (per unit volume) of → excited atoms in different states as a function of the temperature for a gas in → thermal equilibrium: Nu/Nl = (gu/gl) exp (-ΔE/kTex), where Nu and Nl are the upper level and lower level populations respectively, gu and gl the → statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h  → Planck's constant.

Boltzmann's constant; → equation.

canonical equation
  هموگشِ هنجاروار   
hamugeš-e hanjârvâr

Fr.: équation canonique   

The most general form of an equation.

canonical; → equation.

Cauchy's equation
  هموگش ِ کوشی   
hamugeš-e Cauchy

Fr.: équation de Cauchy   

A relationship between the → refractive index (n) and the wavelength of light (λ) passing through a medium. It is commonly stated in the following form: n = A + B2 + C4, where A, B, and C are constants characterizing the medium. The two-component Cauchy equation is n = A + B2, from which the dispersion becomes dn/dλ = -2B3 showing that dispersion varies approximately as the inverse cube of the wavelength. The dispersion at 4000 A will be about 8 times as large as at 8000 Å.

Named after Augustin Louis Cauchy (1789-1857), French mathematician and physicist who found the first equation of dispersion in 1836; → equation.

characteristic equation
  هموگش ِ سرشتاری   
hamugeš-e sereštâri

Fr.: équation caractéristique   

Physics: An analytical relationship between a set of physical variables that determines the state of a physical system.
Math.: The equation which is solved to find a matrix's eigenvalues, also called the characteristic polynomial.

characteristic; → equation.

chemical equation
  هموگش ِ شیمیایی   
hamugeš-e šimiyâyi

Fr.: équation chimique   

The symbolic representation of a chemical reaction where the formulae of the → reactants are placed on the left and the formulae of → products on the right of an arrow.

chemical; → equation.

Clapeyron equation
  هموگش ِ کلاپرون   
hamugeš-e Clapeyron

Fr.: équation de Clapeyron   

An equation that relates the temperature and pressure dependence of phases in equilibrium with the heat interaction and volume change associated with a phase change: dP/dT = L/T ΔV, where dP/dT is the slope of the coexistence curve, L is the → latent heat, T is the temperature, and ΔV is the volume change of the phase transition.

Named after Émile Clapeyron (1799-1864), a French engineer and physicist, one of the founders of → thermodynamics; → equation.

Clausius equation
  هموگش ِ کلاؤزیوس   
hamugeš-e Clausius

Fr.: équation de Clausius   

A first-order improvement on the → ideal gas law that corrects for the finite volume of molecules.

After Rudolf Clausius (1822-1888), a German physicist and mathematician, → equation.

Clausius-Clapeyron equation
  هموگش ِ کلاؤزیوس-کلاپرون   
hamugeš-e Clausius-Clapeyron

Fr.: équation de Clausius-Clapeyron   

An approximation of the → Clapeyron equation for liquid-vapor equilibrium that incorporates the → ideal gas law and states that the logarithm of vapor pressure is inversely proportional to temperature.

Clausius equation; → Clapeyron equation.

Compton equation
  هموگشِ کامپتون   
hamugeš-e Compton

Fr.: équation de Compton   

Theoretical equation which gives the change in the photon wavelength due to the → Compton effect.

Compton; → equation.

cosmic energy equation
  هموگش ِ کاروژ ِ کیهانی   
hamugeš-e kâruž-e keyhâni

Fr.: équation de l'énergie cosmique   

Same as the → Layzer-Irvine equation.

cosmic; → energy; → equation.

cubic equation
  هموگش ِ کابی   
hamugeš-e kâbi

Fr.: équation cubique   

An equation containing unknowns of the third power; the general form: ax3 + bx2 + cx + d = 0.

Cubic, of or pertaining to → cube; → equation.

de Broglie equation
  هموگش ِ دوبروی   
hamugeš-e de Broglie

Fr.: équation de de Broglie   

According to the → de Broglie hypothesis, which has been verified by experiments, every → particle of matter, whatever its nature, has a characteristic → wavelength associated with its wavelike quantum aspect. The de Broglie equation gives the equivalent wavelength of a moving particle: λ = h/mv, where h is → Planck's constant, m the mass of the particle, and v its velocity.
See also: → de Broglie wavelength, → Davisson-Germer experiment.

Named after Louis Victor de Broglie (1892-1987), French physicist, creator of a new field in physics, wave mechanics, who won the Nobel prize in physics in 1929. → equation

Dieterici equation
  هموگش ِ دیتریسی   
hamugeš-e Dieterici

Fr.: équation de Dieterici   

An → equation of state for → real gases which leads to the → van der Waals equation as a → first approximation. It is of the form P(V - b) [exp (a/VRT)] = RT, where P is the pressure, V is the volume, T is the thermodynamic temperature, R is the → gas constant, and a and b are the constants characteristic of the gas.

Named after Conrad Dieterici (1858-1929), a German physicist; → equation.

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