Institution: | (1) Nonlinear Systems Laboratory, Mathematics Institute, University of Warwick, Coventry, CV4 7AL, United Kingdom;(2) Condensed Matter Theory Group, The Blackett Laboratory, Imperial College, London, SW7 2BZ, United Kingdom;(3) Present address: R & D devices, Hewlett-Packard Ipswich Components Operation, Ipswich, Suffolk, IP1 5PB, United Kingdom |