1. College of Automation , Harbin Engineering University , 150001 Harbin , P. R. China
2. Faculty of Applied Mathematics , AGH University of Science and Technology , 30-059 Kraków , Poland ; and Institute of Mathematics, Physics and Mechanics, 1000 Ljubljana, Slovenia; and Department of Mathematics, University of Craiova, Street A.I. Cuza No. 13, 200585 Craiova, Romania
3. College of Automation; and College of Mathematical Sciences , Harbin Engineering University , 150001 Harbin , P. R. China
4. College of Mathematical Sciences , Harbin Engineering University , 150001 Harbin , P. R. China ; and Department of Mathematics, University of Texas, Arlington, TX 76019, USA
5. College of Mathematical Sciences , Harbin Engineering University , 150001 Harbin , P. R. China