This research effort is dedicated to my family, in particular to my mother, LI Yun who has always stood by my side, encouraging and supporting me through the entire process. She talked to me when I faced some difficulties and almost gave up. She taught me hard work disciplines and made me continue my research and this also served me well in all aspect in my life. Additionally, I would like to dedicate this to my best friends, Ziming Zhao, Marianela Rivera, Yuan Cai. Thanks for being there whenever I need you. You are more than friends. You are my.
