Upon finishing this thesis, I would like to express my great gratitude towards allthose who have offered me sincere assistance in the three years.
First and foremost, my hearty thanks go to my supervisor, Professor ZhangRuwen, who has given me insightful suggestions and constant encouragement both inmy study and in my life. Furthermore, Professor Zhang's painstaking teaching andvaluable advice have profoundly contributed to the completion of the present thesis.
Also, I own my thanks to all the professors who have taught and enlightening meduring my studies in the campus, for guiding me in the field of research work, whichis both challenging and fantastic. The experience and profit I obtained will be ofgrand importance to my further studies.
Finally, I am also grateful to my family and friends, who encourage and supportme and share with me my worries, frustrations, and happiness.
Time is a bird forever on the wing. For the past two years' post-graduate study, Ireally had a fulfilling life here. Not only have I met many knowledgeable teachers, butalso truthful friends. I would like to give my deep gratitude to many of them. First of all, Iam most grateful to Professor Zhang Ruwen, my supervisor, who offers me invaluableguidance and help both in my study and my life. Without her enlightening suggestions andinstructions, it would be a tough task for me to finish my thesis. Besides, I also appreciatemany other teachers who have offered their useful suggestions and inspire me a lot. Mythanks also go to my parents, grandparents, my classmates and my loving friends. Theircompany is a great consolation to me. I wish everyone could live in peace and happiness.
I would like to express my gratitude to all those who helped me during the processof writing of this thesis and during my study years at this school.
My deepest gratitude goes first and foremost to Professor Xu, my supervisor, forhis constant encouragement and guidance. He has offered me valuable suggestions inthe academic studies. In the preparation of this thesis, he has spent much time readingthrough each draft and provided me with inspiring advice. Without his consistent andilluminating instruction, this thesis could not have reached its present form.
Special thanks should go to express my heartfelt gratitude to the professors andteachers at our school as well, who have instructed and helped me a lot during the pastthree years.
At last, my thanks would go to my beloved family for their loving considerationsand great confidence in me all through these years and their supporting without a wordof complaint. I also owe my sincere gratitude to my friends and my fellow classmateswho have given me their help and their time in listening to me and helping me work outmy problems during the difficult course of the thesis.
The completion of the thesis is attributed to many people's support andencouragement.
First and foremost, I want to extend my heartfelt gratitude to my supervisor,Professor Cao Daogen, whose patient guidance, valuable suggestions and constantencouragement make me successfully complete this thesis. His conscientious academicspirit and modest, open-minded personality inspire me both in academic study and dailylife. He gives me much help and advice during the whole process of my writing, whichhas made my accomplishments possible.
Also, I would like to express my sincere gratitude to all the professors who havetaught me in this university. Their instructions have helped broaden my horizon andtheir enlightening teaching has provided me with a solid foundation to accomplish thispaper and will always be of great value for my future career and academic research.
My thanks also go to the authors whose books and articles have given meinspiration in the writing of this paper.
Last but not least, I would like to express my special thanks to my parents, whosecare and support motivate me to move on and make me want to be a better person.