Address for correspondence:
Dr. T. Farid
Scientific Secretary, ITCPP--2001
Theoretische Physik IV,
Ruhr-Universitaet Bochum,
D-44780 Bochum, Germany
Fax: 49 234 32 14177
Tel: 49 234 32 23729
E-mail: tf@tp4.ruhr-uni-bochum.de
E-Mail: itcpp@tp4.ruhr-uni-bochum.de