NSFC(10671183);NSFHN(082300410190);NSF of the Education Department of Henan Province (2008A110004);the Science Foundation (07XJC002);Doctor Science Foundation of Henan University of Technology
Acknowledgements: The authors are grateful for professors LIN Yi-xun and YUAN Jin-jiang for the helpful suggestions. The research in part was supported by NSFC (10671183), NSFHN(082300410190), The Nature Science Foundation of the Education Department of Henan (2008AI10004), Science Foundation (07XJCO02) and Doctor Science Foundation of Henan University of Technology.