1. Statistical Physics Group, P2M Dpt, Institut Jean Lamour, Nancy Université, BP 70239, F-54506 Vandoeuvre les Nancy, France
2. Applied Mathematics Research Centre, Coventry University, Coventry CV1 5FB, UK
3. Institut für Theoretische Physik II, Heintich-Heine Universität Düsseldorf, D-40225 Düsseldorf, Germany
4. Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine