Supported by grants of Natural Science Foundation of China(No.31070052);Ministry of Science and Technology of China(No.2005DFA30280;No.2007AA021506);a grant of Natural Science Foundations of Jiangsu Province,China(No.BK2009084;No.BK2010027)
Supported by a grant from Natural Science Foundation of Education Department of Jiangsu Province(No.05k36012);a grant of Natural Science Foundation of Jiangsu Province (No.BK2006.34);a grant of Natural Science Foundation of Xuzhou Normal University (No.08XLY14)
Supported by a grant from Natural Science Foundations of Education Department of Jiangsu Province (No. 05KJA36012);a grant of Natural Science Foundations from the Government of Jiangsu Province (No. BK2006034)