Grad's assumption allows to split the collision operator in a gain and a loss part, Q( f, g) = Q + ( f, g) − Q − ( f, g) = Gain - Loss But not pointwise bounds are assumed on b(û · σ) The loss operator has the following structure Q − ( f, g) = f R(g), with R(g), called the collision frequency, given by The loss bilinear form is a convolution.
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