first-order partial derivative واخنهی ِ پاری ِ رایهی ِ نخست vâxane-ye pâri-ye râye-ye naxost
*Fr.: dérivée partielle du premier degré*
For a → *function* with several → *variable*s,
the derivative, done only once, with respect to one of the
variables. For example ∂*u*/∂*x* for *u = u(x,y)*. → *first*; → *order*;
→ *partial*; → *derivative*. |

partial پاری، پارال pâri (#), pârâl
*Fr.: partiel*
Being such in part only; not total or general; incomplete.
See also:
→ *partial derivative*,
→ *partial differential equation*,
→ *partial eclipse*,
→ *partial ionization zone*,
→ *partial lunar eclipse*,
→ *partial solar eclipse*,
→ *partial truth*. M.E. *parcial*, from O.Fr. *parcial*, from M.L. *partialis*
"pertaining to a part," from L. *pars*, → *part*;
→ *-al*. → *part*; → *-al*. |

partial derivative واخنهی ِ پاری vâxane-ye pâri
*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*; → *derivative*. |

partial differential equation هموگش ِ دگرسانهای با واخنهی ِ پاری 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. → *partial*; → *differential*;
→ *equation*. |

partial eclipse گرفت ِ پاری gereft-e pâri
*Fr.: éclipse partielle*
An eclipse that is not total. → * partial lunar eclipse*,
→ * partial solar eclipse*. → *partial*; → *eclipse*. |

partial ionization zone زنار ِ یونش ِ پاری 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 → *pulsation*s.
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 10^{4} 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 10^{4} 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 → *Cepheid*s.
See also → *gamma mechanism*. → *partial*; → *ionization*;
→ *zone*. |

partial lunar eclipse مانگگرفت ِ پاری mânggereft-e pâri
*Fr.: éclipse partielle de lune*
A → *lunar eclipse* when the Earth's → *umbra*
passes over only part of the Moon, causing
only moderate darkening of the full Moon. See also
→ *penumbral lunar eclipse*. → *partial*; → *lunar*;
→ *eclipse*. |

partial solar eclipse خورگرفت ِ پاری xorgereft-e pâri
*Fr.: éclipse partielle de soleil*
A → *solar eclipse* when only the
→ *penumbra* of the Moon touches the Earth.
The → *umbra* passes either just above the North Pole or
just below the South Pole, missing the Earth. → *partial*; → *solar*;
→ *eclipse*. |

partial truth راستینی ِ پاری، ~ پارال râstini-ye pâri, ~ pârâl
*Fr.: vérité partielle*
A → *truth value*
in → *fuzzy logic* where it can
range between "completely true" and "completely false." → *partial*; → *truth*. |