During my seven years of study at Iowa State University, I met, worked, and interacted with many people. They helped me with my research, provided support, guidance, friendship, and inspiration when things got tough. I would like to express my sincere thanks and appreciation to all those people.First, I would like to express my sincere gratitude to my advisor and mentor, Dr. Zhiyou Wen, for offering me an opportunity to pursue the Ph.D. degree and for continuous supports of my research in the past four years. I am grateful for his patience, wisdom, enthusiasm, suggestions, and for motivating me farther than I thought I could go.Then, I would like to thank my committee members, Dr.