Bem Haja

My sincere thanks go to Professor Keikichi Hirose and Dr. Md. Khademul Islam Molla for their generosity in providing me with ideas, comments, suggestions, constant support and materials.

I acknowledge the University of Tokyo and the Japanese Ministry of Education for their precious support and, last but not least, I want to express my deepest gratitude to my family and friends because life without them would be meaningless.