国家自然科学基金31070087,30570046;湖北省自然科学基金重点项目2011CDA079,2008CDB076;中央科研基本业务费CZW16005,YCZW15104Supported by the National Natural Science Foundation of China31070087,30570046;by the Natural Science Foundation of Hubei Province2011CDA079,2008CDB076;by the Central Science Research Study Basic ExpensesCZW16005,YCZW15104