1. Department of Solid Mechanics, School of Engineering Sciences, Royal Institute of Technology (KTH), Osquars Backe 1, SE-100 44 Stockholm, Sweden, Institute for Biomechanics, Center for Biomedical Engineering, Graz University of Technology, Kronesgasse 5-I, A-8010 Graz, Austria
2. Department of Mathematics, University of Glasgow, University Gardens, Glasgow G12 8QW, UK