D is the hydrodynamical dispersion factor, and it can be repre sented by two items. (2) The al is called dynamical dispersion factor, and D'is molecule dis persion factor. Since the D"is very small, we can neglect it For convenience, we consider the density of the pollutants source is o before the new pollution occurring, and become Co just after that time timc e Figure 1 step-change source This model of pollution source has pracical value because the pollution that lasts for a long time does more harm to people than that lasts for a short period, and we must locate it and manage to eliminate it. So in this model, we put the emphasis on the step change source and try to locate it Use the step-change source to represent the boundary cond tions C(l,0)=0 >=0 (3) C(0,l)=C (4) (+∞,t)=0 >=0 (5) Then use these boundary conditions, we can get the analytic solution of the equation (1) C_1 Croc( tl 0 2√D)(6) 234 PDF文件使用" pdffactory"试用版本创建w, fineprint,com,cnPDF 文件使用 "pdfFactory" 试用版本创建 www.fineprint.com.cn