supported by the National Natural Science Foundation (Nos 30672523, 90713037 and 21002125);Specialized Research Fund for the Doctoral Program of Higher Education of China (No 2009121114452820);the program for New Century Excellent Talents in University (NCET-05-0495)~~
supported by National Natural Science Foundation of China (Nos. 30672523 and 90713037);research grants from Chinese Ministry of Education (Nos. 706030 and 20050316008)~~