1. Structure and Motion Laboratory, Royal Veterinary College, Hatfield AL9 7TA, UK.
2. Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan.
3. Pharmacy and Biomolecular Sciences, University of Brighton, Moulsecoomb, Brighton BN2 4GJ, UK.
4. Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.