Substrate effect on mechanical relaxation of polystyrene in ultrathin films K.-I. Akabori, K. Tanaka, A. Takahara, T. Kajiyama and T. Nagamura Eur. Phys. J. Special Topics, 141 (2007) 173-180 Published online: 29 March 2007 DOI: 10.1140/epjst/e2007-00036-8