1. Institute of Physical Chemistry, Attila Jözsef University, Szeged, Hungary; on leave from Faculty of Science, University of Kragujevac
2. Institute of Mathematics, Academia Sinica, Taipei, Taiwan, R.O.C.
3. Department of Chemistry, N ational Chung-Cheng University, Chia-Yi, Taiwan, R.O.C.
4. Department of Information Sciences, Ochanomizu University, Tokyo, Japan
5. Division of Physical Chemistry, University of Trondheim, Trondheim, Norway