University of Augsburg, Institute of Physics, Electronic Correlations and Magnetism, Experimentalphysik VI, 86135 Augsburg, Germany; franz.giessibl(at)physik.uni-augsburg.de
Received 27 June 2001, accepted 2 July 2001 by U. Eckern
Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland; garecki(at)wmf.univ.szcsecin.pl
Received 14 March 2000, revised 13 January 2001, accepted 5 March 2001
by F. W. Hehl
Faculty of Physics and Center for Theoretical Physics, University of Craiova, 13 A. I. Cuza Str., Craiova RO-1100, Romania; bizdadea(at)central.ucv.ro
Received 13 March 2001, accepted 23 May 2001 by K. Fredenhagen
Universite Libre, Bruxelles; nboulang(at)ulb.ac.be
Received 6 June 2001, accepted 7 June 2001 by F. W. Hehl
Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, 634021 Tomsk, Russia; levzuev(at)mail.tomsknet.ru
Received 29 December 2000, revised 30 May 2001, accepted 22 June 2001
by U. Eckern