This work was supported by the NSFC (No.10661001);partially by the NSF of Guangxi (No.0832275,No.0897012);the Science Foundation of Guangxi Education Department (No.200807MS001);the Natural Science Foundation of Liuzhou Teachers College (LSZ2007A003);the Science Foundation of Guangxi University of Finance and Economics (2009B02)
Supported by the National Natural Science Foundation of China(10661001);partially by the Guangxi Natural Science Foundation(0832275);the Natural Science Foundation of Liuzhou Teacher's College(LSZ2007A003)
Project supported by the Natural Science Foundation of China(10661001),Guangxi Science Foundation(0249002,0007002)and Innovation Pro-ject of Guangxi Graduate Education(2006105930701 M14).
Supported by NSFC (10661001); Guangxi Science Foundation(0640002);the Innovation Project of Guangxi Graduate Education(2006105930701M14);Science Foundation of Guangxi University(X061022).