I sincerely express my greatest gratitude to my supervisor Prof. Zhiping Lin, for being the most crucial guide academically and mentally throughout my Ph.D. career. He is kind, wise, and hard-working, providing me with numerous resources, patience and attention for my research. He immediately advises me when I have doubts about research and daily-life trifles. Also, his highest moral and academic standards influence me well. He undeniably sets an excellent example for my later career and life. I feel very fortunate to be his student. I thank Prof. Guang-Bin Huang for his supervision in the first two years. I would thank Dr. Hanhui Li, Prof. Huiping Zhuang, Prof. Qi Cao,Mr. Rongzihan Song and Ms. Yuxuan Lin for their valuable advice and discussions with me. I also like to thank my old friends in China and other colleagues in NTU.I would express my greatest gratefulness to my parents. They have spent as much as they can to support my education since my kindergarten. They always try their best to provide me with the best, even beyond their capability. They choose to accept all my negative feelings and make me believe families always stand behind me. The love they give me can not be expressed in words. I express my deep thanks to my parents-in-law, too. They treat me as their son and give me great patience and support in my life in Singapore. I would also like to thank my other family members, especially my cousin and brother-in-law, who frequently share academic advice and life tips.Finally, but most importantly, I would like to express my greatest thanks to my wife, Yi Luo, who left her job in China and started the journey with me without hesitation. This journey started right away after our marriage, and we started v vi our new married life in Singapore from nothing. My Ph.D. career is more than an academic pursuit but is more like an adventure. With the accompany by her, it will become one of the most valuable memories in my life. I overcame obstacles with her accompany, encouragement, support and love. More importantly, we share laughs and tears all the time. No matter good or bad, we are always together. She trusts me and makes me responsible and reliable. Words cannot express my gratitude and love. Being with her makes me the luckiest man in the world. Ever thine, ever mine, ever ours.