(1) Fakultät für Physik, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany; (2) MPI für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden, Germany; pleutin(at)physik.uni-freiburg.de
Received 11 January 2002, accepted 21 February 2002 by U. Eckern
Physics Department, Faculty of Science, Al-Azhar University, PO Box 1277, Gaza, Palestine; talaath55(at)yahoo.com
Received 20 August 2001, revised 4 December 2001, accepted 30 January 2002 by U. Eckern
Institute of Physics, Szczecin University, 70-453 Szczecin, Poland; garecki(at)wmf.univ.szczecin.pl
Received 16 October 2001, revised 11 April 2002, accepted 27 April 2002 by F. W. Hehl
h.ortmanns(at)iu-bremen.de / H.Meyer-Ortmanns(at)ThPhys.Uni-Heidelberg.DE
Received 16 April 2002, accepted 23 April 2002 by F. W. Hehl
Institute of Physics, Mainz University, Staudingerweg 7, 55099 Mainz, Germany (etc.); nepijko(at)mail.uni-mainz.de
Received 16 January 2002, accepted 25 April 2002 by U. Eckern