I would like to thank Prof. Yan Zhenzhen, one of my co-authors, for her invaluable assistance and insights leading to my research. I also want to thank my thesis committee member, Prof. Li Yi and Prof. Cong Gao, their feedback and comments are truly helpful in my research.Many thanks to my parents, Wang Liping and Wang Ruizhan, without their encouragement and support, I cannot finish my Ph.D. study. When I am upset and want to give up, they are always there for me and telling me that I am awesome.Thanks to my labmates Lu Xinhang, Yang Chunxue, Li Zihao, Wang Hongao, and Liu Shengxin. I enjoy the time working with them and the time we go hiking, play card games together.