[1] Univ Freiburg, Inst Phys, D-79104 Freiburg, Germany
[2] Vienna Univ Technol, Inst Theoret Phys, A-1040 Vienna, Austria
[3] Ben Gurion Univ Negev, Dept Phys, IL-84105 Beer Sheva, Israel
[4] Wesleyan Univ, Dept Phys, Middletown, CT 06459 USA
[5] MPI Dynam & Self Org, D-37077 Gottingen, Germany