Hopping on a zig-zag course L. Haeggqwist, L. Schimansky-Geier, I. M. Sokolov and F. Moss Eur. Phys. J. Special Topics, 157 (2008) 33-42 Published online: 23 April 2008 DOI: 10.1140/epjst/e2008-00628-8