国家自然科学基金青年科学基金21203098,2013g130;南京信息工程大学校科研启动基金批准号:2013x023资助的课题.* Project supported by the Young Scientists Fund of the National Natural Science Foundation of ChinaGrant .21203098,2013g130;the Scientific Research Staring Foundation of Nanjing University of Information Science and Technology, ChinaGrant 2013x023