dy dx

+ v cos0f — imQfm = — fm foS° — (o Fo ">Sm dz

where m = 0, ±1, ±2, ..., and 8j is the Kronecker delta symbol. In particular, for m

= 0, Eq. 2.27.4 multiplied by 2np2 sin#, and integrated over d from d = 0 to d = n, yields the number density conservation equation:

where N = p2 j /dQ and S = p2 j v/dQ are the particle number density and current, and the integrations over dQ are over solid angle in momentum space. In the diffusion approximation one uses the approximate moment balance equations for m = 0 and 1:

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