Pertains to a @F02370@ of a @S05723@ changing in area at constant mass and is the differential change of its @S06192@ with relative change in area \(A\), \[E=A\ (\frac{\partial \sigma }{\partial A})_{T,p,n_{i}}\] where \(T\) is the @T06321@, \(p\) is the pressure, and \(n_{i}\) is the @A00297@ of the species \(i\).