国家自然科学基金11374002;湖南省高校科技创新团队支持计划和湖南省重点学科建设项目资助的课题.* Project supported by the National Natural Science Foundation of ChinaGrant 11374002;the Aid Program for the Science and Technology Innovation Team in Colleges and Universities of Hunan Province, China, and the Construct Program of the Key Discipline in Hunan Province, China