This work was done as a visiting researcher of Sharp Corporation at UMIST. I wish to thank Mr Mikio Ohsaki and Mr Shigeki Kuga of Sharp Corporation, and Prof Juan Sager and Prof Jun-ichi Tsujii of UMIST, for giving me this opportunity.
Many thanks to my supervisor, Bill Black, and to John Bateman, Brian Chandler, Robin Fawcett, Kristiina Jokinen, Takashi Kamiko, Osamu Nishida, John Phillips, Erich Steiner, Pete Whitelock, Kenji Yoshimura and others for their help and valuable discussions. To Pat Olver, and to Jiri and Susan Jelinek, I owe more than thanks.