1. HAS Centre for Energy Research, H-1525 POB 49, Budapest, Hungary
2. Departamento de
Reologı́a,
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, 04510, México
D.F., México
3. Institute of Physical Chemistry, University of Cologne, Luxemburger Str. 116, D-50939 Köln, Germany