上海大学学报(自然科学版) ›› 2007, Vol. 13 ›› Issue (6): 732-735 .
任九生1,2,程昌钧1,2
REN Jiu-sheng1,2,CHENG Chang-jun1,2
1. School of Sciences, Shanghai University, Shanghai 200444, China;
2. Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University,Shanghai 200072, China