In 2008, with the dream of improving the research skills, I went to Nanyang Technological University to pursue my Ph.D. degree. I have been very lucky to get the guidance, help and support from a lot of people. Herein, I would like to express my deep and sincere thanks to them. Assoc. Prof. Zhang Hua, my supervisor, who gave me the opportunity to join this warm group, leads me to the interesting research fields, always supports and encourages me to pursuit exciting research results, and provides all his experience, knowledge and resource of science, and life experiences to us. Dear Assoc. Prof. Zhang, please accept I my sincere gratitude. I thank Asst. Prof. Xue Can, Asst. Prof. Huang Yizhong, Ms. Guo Jun for their patience and helpful discussions about my work enriching my knowledge and expanding my research range.