first-order partial derivative
vâxane-ye pâri-ye râye-ye naxost
Fr.: dérivée partielle du premier degré
pâri (#), pârâl
Being such in part only; not total or general; incomplete.
Fr.: dérivée partielle
The derivative of a function of two or more variables, e.g., z = f(x,y), with respect to one of the variables, the others being considered constants (denoted ∂z / ∂x).
partial differential equation
hamugeš-e degarsâne-yi bâ vâxane-ye pâri
Fr.: équation différentielle aux dérivées partielles
A type of differential equation involving an unknown function (or functions) of several independent variables and its (or their) partial derivatives with respect to those variables.
Fr.: éclipse partielle
partial ionization zone
zonâr-e yoneš-e pâri
Fr.: zone d'ionisation partielle
One of several zones of the stellar interior where increased → opacity can provide the → kappa mechanism to drive → pulsations. See also → Kramers' law. In these zones where the gases are partially ionized, part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. Partial ionization zones modulate the flow of energy through the layers of the star and are the direct cause of → stellar pulsation. The partial ionization zones were first identified by the Russian astronomer Sergei A. Zhevakin (1916-2001) in the 1950s. In most stars there are two main ionization zones. The hydrogen partial ionization zone where both the ionization of neutral hydrogen (H ↔ H+ + e-) and the first ionization of helium (He ↔ He+ + e-) occurs in layers with a characteristic temperature of 1.5 x 104 K. The second, deeper zone is called the He+ partial ionization zone, and involves the second ionization of helium (He+↔ He++ + e-), which occurs deeper at a characteristic temperature of 4 x 104 K. The location of these ionization zones within the star determines its pulsational properties. In fact if the → effective temperature of the star is ≥ 7500 K, the pulsation is not active, because the ionization zones will be located very near to the surface. In this region the density is quite low and there is not enough mass available to drive the oscillations. This explains the blue (hot) edge of the instability strip on the → H-R diagram. Otherwise if a star's surface temperature is too low, ≤ 5500 K, the onset of efficient convection in its outer layers may dampen the oscillations. The red (cool) edge of the instability strip is believed to be the result of the damping effect of convection. He+ ionization is the driving agent in → Cepheids. See also → gamma mechanism.
partial lunar eclipse
Fr.: éclipse partielle de lune
partial solar eclipse
Fr.: éclipse partielle de soleil
râstini-ye pâri, ~ pârâl
Fr.: vérité partielle