1. Department of Physical Chemistry, University of Debrecen, H-4010 Debrecen, P.O.Box 31, Hungary
2. Research Institute of Applied Earth Sciences, University of Miskolc, P.O.Box 2, H-3515 Miskolc-Egyetemváros, Hungary
3. Institute of Complex Systems 3, Jülich Research Center, D-52425 Jülich, Germany