国家自然科学基金资助项目81373130,81001308;江苏省自然科学基金资助项目BK2010315;扬州大学大学生创新创业训练计划项目.Project supported by the National Natural Science Foundation of China81373130,81001308;the Natural Science Foundation of Jiangsu ProvinceBK2010315;the Science and Technology Innovation Foundation for Undergraduates of Yangzhou University