Spin Brazil-nut effect and its reverse in a rotating double-walled drum Decai Huang, Ming Lu, Surajit Sen, Min Sun, Yaodong Feng and Anna Yang Eur. Phys. J. E, 36 4 (2013) 41 Published online: 23 April 2013 DOI: 10.1140/epje/i2013-13041-0