Nonlinear transport in β-Na 0.33V 2O 5 S. Sirbu, T. Yamauchi, Y. Ueda and P. H.M. van Loosdrecht Eur. Phys. J. B, 53 3 (2006) 289-296 Published online: 20 October 2006 DOI: 10.1140/epjb/e2006-00386-3