1. a Department of Mathematics and Computer Science , Odense University , 5230 , Odense , Denmark
2. b Chemical Physics Department , Institute of Isotope and Radiation Research , 0-7050 , Leipzig , Germany
3. c E. Hála Laboratory of Thermodynamics, Institute of Chemical Process Fundamentals, Czech Academy of Sciences , 165 02 Prague 6 – Suchdol, Czechoslovakia