国家自然科学基金项目41361019;国家社会科学基金项目08BMZ041;教育部“新世纪优秀人才支持计划”NCET-12-0652;广西自然科学基金项目2011GXNSFA018004 Project supported by the National Natural Science Foundation of China,No.41361019;Project supported by the National Social Science Foundation of China,No.08BMZ041;Project supported by Program for New Century Excellent Talents in University,No.NCET-12-0652;Project supported by Guangxi Natural Science Foundation,No.2011GXNSFA018004