[1] Lab Interdisciplinaire Phys CNRS UGA, F-38402 St Martin Dheres, France
[2] Saarland Univ, Dept Expt Phys, D-66041 Saarbrucken, Germany
[3] Saarland Univ, Theoret Med & Biosci, D-66424 Homburg, Germany
[4] Univ Luxembourg, Phys & Mat Sci Res Unit, L-1511 Luxembourg, Luxembourg