国家自然科学基金(30872367),安徽省教育厅自然科学研究项目(2006kj101A),安徽省自然科学基金(070413088).
Supported by National Natural Science Foundation of China(30872367), Natural Science Foundation of Education Department of Anhui Province (2006kj101A), and Natural Science Foundation of Anhui Province(070413088).