Ni : Average population density in area i. To simplify the analysis, Earth’s surface is divided into a grid of squares i, and the distribution is assumed to be uniform in each.
It is generally assumed the solution of galactic shock wave is local one and takes no account of gaseous self-gravitation in the theory of density wave.
密度波理论中星系激波的解大都假设为局部的,并且往往不考虑星际气体自引力的影响。
3
It was assumed that the recombination rate is proportional to the density of injected carriers.