“…where: (x, y) is the event location coordinates, k, is the frequency of diffusion in direction q, starting from the location (x,y): kd -k qxyi(x,y),u(x',y'),r(x',y),s(x,y) (6) where the 1/4 factor follows from the number of permissible surface diffusion directions (4), (xc y) is the diffusion target location coordinates.…”