Work as Guest Scientist for a period of more than 2 months.

• Bielefeld University, FRG, groups of Profs.
  H.O. Lutz and U. Heinzmann, February-April 1990, 3 months;
  July - December 1992, 6 month; July 1996 - November 1997, 17 months;
  February 1999 - present.
• Fritz-Haber-Institut der MPG, Berlin, FRG,
  group of Prof. U. Becker, February - July andOctober 1993, 7 months;
  January - September 2003, 9 months.
• Freiburg University, FRG, group of Prof. W. Mehlhorn,
  November 1993 - April 1994, 6 months.
• Groningen University, The Netherlands, group of Prof. D.O. Boerma,
  August-October 1994, 3 months; April - July 1996, 3 months.
• Tohoku University, Sendai, Japan, group of Prof. K. Ueda,
  January - July 1998, 6 months.
• Max-Planck-Institut für Mikrostrukturphysik, Halle,
  Theory dept., group of Dr. J. Berakdar October - December 2003, 3 months.

Besides there were several shorter visits for a period of 1-2 months to: