Substituting Eq. 4.15.68 and Eq. 4.15.70 into Eq. 4.15.64 and applying aila = H2IHi and aDj/a - 1 we reduce the Eq. 4.15.64 to the form
3 of dz
In a similar way we shall obtain from the Eq. 4.15.65 the following relation:
- 2 at (1 - D-1 )A1// ^NL -ZE|2L N++ 2a a 2, N .(4.15.73)
The left hand parts of the latter equations are equal. Therefore it is convenient to pass to the other two equations, which are obtained by subtracting corresponding term and summing of Eq. 4.15.72 and Eq. 4.15.73. The summing results in a relation in the right hand part of which the summands have the order of (AEk/Ek )N << N and cA" (dN/dz) << N . This means that the difference N1 - N2
is small compared to N1, N2 and it can be equated to zero: N1 ~ N2 at z = 0. As the result of subtraction, we have:
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