*E-mail: xia991002@163.com **E-mail: abiaoa@163.com ***E-mail: shp7971@163.com 1This project is supported by the Specialized Research Fund for the Doctoral Program of Higher Eduction of China (No. 20114410110002), National Natural Science Foundation of China (No. 11101098) and Natural Science Foundation of Guangdong Province (No. S2013010014460).