B. J. Coomer* and R. Jones
Department of Physics, The University of Exeter,
Exeter, EX4 4QL, United Kingdom
S. Öberg**
Department of Mathematics, University of Luleå,
Luleå, S95 187, Sweden
P. R. Briddon
Department of Physics, The University of Newcastle
upon Tyne,
Newcastle upon Tyne, NE1 7RU, United Kingdom
*
EPSRC and the ENDEASD network are thanked for computer
time and financial support respectively.
** Financially support by NFR and TFR, and
computer support by PDC at KTH in Sweden are gratefully
acknowledged.