This project was financially supported by the National Basic Research Program of China (No. 2010CB732403), NSFC (21222506 and 21175024, 21001033), Program for New Century Excellent Talents in University (NCET-12-0619) and the Program for Chang- jiang Scholars and Innovative Research Team in University (No. IRT1116). This work was also supported by Natural Science Foundation of Fujian Province of China (2012J06005).