基金项目: | Supported by the National Natural Science Foundation of China under Grant Nos 10775061, 10505016 and 10575119, the Fundamental Research Fund for Physics and Mathematics of Lanzhou University (LZULL200805), the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCX-SYW-N02, the National Basic Research Program of China under Grant No 2007CB815004. |