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The integral
can be further modified, knowing, that
dV
da )y,x(h
= ⋅
4
( )
( , )
dL
d da h x y d
Ω
π
= Φ Ω Ω ⋅
Ω
∫
ur
d
( )
dL
d V d
Ω
= Φ Ω Ω ⋅
Ω
∫
ur
5.2
Since
we obtain
dL
dV
Φ =
or
dL
dV
= Φ ⋅
4
π
4
( )
d d
Ω
π
Φ Ω Ω Ω = Φ
∫
ur
58