Over the past five years I have received support and encouragement from a great number of individuals. First, I owe my deepest gratitude to Dr. William O'Grady, my advisor, who found me in Jeju. Ever since the first day of my Ph.D. program, he has shown patience, great support, wonderful mentorship, and most of all incredible enthusiasm for the research. One evening, after a long day, I told him "It is still very difficult to keep up with you." he said "Don't worry, one day, you will." Without his inspiring and invaluable guidance and encouragement, this study would not have been completed.