First of all, I would like to express my deep appreciation to my supervisor, Associate Professor Chang Chip Hong. Without his intellectual guidance, encouragement and support, I could never finish this thesis in four years of my PhD pursuit. His research attitude of striving for the best and being precise, enthusiasm for work and responsible and kind personality have not only shown me how to be a good researcher, but also been an excellent model for me to follow in my future career and life. I am also very grateful to my parents, my younger brother and my girlfriend. Their love, consideration and company were and will continue to be what drives me to move forward and become my better self. My gratitude also goes to my friends in Singapore,