Dept. of Appl. Math.;
Zhejiang Univ. of Technology;
Zhejiang 310032;
China;
Dept. of Math.;
Shanghai Univ.;
Shanghai 200444;
China;
College of Seience;
Hangzhou Dianzi Univ.;
Zhejiang 310018;
China;
College of Business Administration;
Zhejiang Univ. of Technology;
Zhejiang 310032;
China;