国家自然科学基金项目(81071196,81541126)%卫生公益性行业科研专项项目(201402019)%北京市卫生系统高层次卫生技术人才培养计划项目(编号:2013-2-005)ACKNOWLEDGMENTS This work was part of National Natural Science Foundation of China(81071196, 81541126)%Health Public Welfare Industry Special Scientific Research Projects(201402019)%Beijing Health System High Level Health Technical Personnel Training Plan(2013-2-005)