I would also like to thank all of you who have contributed so much to the completion of this thesis. In particular, I would like to express my gratitude to Sabrina Bowen, who has greatly helped me with her English revisions during the process of writing high quality articles.Half of all the successes I have achieved in my life is due to the love and dedication of my beloved parents. My father, who died seven years ago, will surely smile when he sees me receive my PhD. I am dedicated, without giving up under any circumstances and I believe this is the valuable heritage that my father taught me through his example. Without my mother, who has always loved me and prayed for me, I would not have obtained any of my achievements. I would like to say that I love and appreciate my mother. In addition, I want to express my gratitude to my younger sister, Hyunjung, who has always been encouraging to me. I would not have attained this achievement without her help in Korea.The other half of the successes that I have achieved in my life are due to my beloved wife Ji Yeon. I met her for the first time in the winter of 2005, and until now, she has stayed silently by my side, praying and cheering for me so that I do not lose my self-esteem. I will love her and devote myself to her all my life. I would also like to share this honor with my beloved daughter Seungju, who is always proud of her dad and celebrates her dad's achievements more than her own. I really want to tell my daughter that her dad loves her so much. I will never forget the gratitude I feel now and with a feeling of repayment, I will do my best to change this world into a more livable place with the little power I have. Thank you.