Polymer and surface roughness effects on the drag crisis for falling spheres N. Lyotard, W. L. Shew, L. Bocquet and J.-F. Pinton Eur. Phys. J. B, 60 4 (2007) 469-476 Published online: 16 January 2008 DOI: 10.1140/epjb/e2008-00018-0