Acknowledgements

during the two years I spent in his research group. He was always willing to help all of his students and patient enough to explain his reasoning repeatedly. In addition, I want to express my sincere gratitude to him for helping me wrap up the life as a graduate student. I also thank Professor Jiali Gao for his kind help while I was in his research group and even after I left the group. Professor Yuichi Kubota was very helpful in solving many problems encountered as a graduate student. I am also very grateful to the other members of my final examination committee: Professor Charles Campbell, Professor Tim Lodge, and Professor Oriol Valls. Professor Marcus Müller at the University of Göttingen graciously helped me run his computer program to generate important data for this thesis. Over the last six years I spent at the University of Minnesota, I met so many wonderful friends. Jian was almost like a second academic adviser to me. Raghu and Andrew kept me from feeling isolated from the rest of the world. Jorge was alway