P. Wodniecki, A. Kulińska, B. Wodniecka, S. Cottenier, H.M. Petrilli, M. Uhrmacher, K.P. Lieb EPL (Europhysics letters) 77 (4), 430012007A1Published while none of the authors were employed at the CMMDOI http://dx.doi.org/10.1209/0295-5075/77/43001