国家自然科学基金资助项目81370952;陕西省科技计划项目2013K21-22-03;2015年西安交通大学省级大学生创新训练项目No.89Supported by the National Natural Science Foundation of China No.81370952 ,the Natural Science Basic Research Program of Shaanxi Province2013K21-22-03;the Provincial Innovative Training Program for College Students in Xi'an Jiaotong University89