Torsional stiffness of viscoelastic spheres in contact E. Dintwa, M. van Zeebroeck, E. Tijskens and H. Ramon Eur. Phys. J. B, 39 1 (2004) 77-85 Published online: 18 June 2004 DOI: 10.1140/epjb/e2004-00173-2