supported by the National Natural Science Foundation of China(Nos.51007031,51277194 and 61273154);the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20123227110012);the Natural Science Foundation of Jiangsu Province(No.BK2012711);the Priority Academic Program Development of Jiangsu Higher Education Institutions;the Fund Program of Jiangsu University for Excellent Youth Teachers