“…Taking these forces into account, a factor is introduced, called the orthokinetic collision e ciency, , which shows the relation between the number of particle collisions that actually lead to aggregation and the total number of particle collisions. It is also known as the inverse of the stability ratio, W (i.e., = 1=W ) (Fuchs, 1934;van de Ven and Mason, 1977;Mishra et al, 1998).…”