This thesis is an account of
work carried out between October 1997 and December 2000 at the University of
Bristol under the supervision of Dr D. J. Riley.
I declare that the work in
this dissertation was carried out in accordance with the Regulations of the
University of Bristol. The work is original except where indicated by special
reference in the text and no part of the dissertation has been submitted for
any other degree.
Any views expressed in the
dissertation are those of the author and in no way represent those of the
University of Bristol.
The dissertation has not
been presented to any other University for examination either in the United
Kingdom or overseas.