ACKNOWLEDGMENTS

I would like to express my deep appreciation to my supervising professor Dr. D.L. Hawkins for his constant patience, motivation, and encouragement with me. His knowledge, insight, and invaluable advice have guided me through the course of my doctoral studies. He is always devoted to his students, even during the hardest times of his life. I am so lucky to be one of his students. I also would like to thank Dr. Chien-Pai Han, Dr. Danny Dyer, Dr. Shan Sun-Mitchell, and Dr. Andrzej Korzeniowski for taking time from their busy schedules to be on my committee. I am especially grateful to Dr. Korzeniowski for his help and invaluable advice with my paper. Of course, the financial support from Department of Mathematics provides me a peaceful mind t