1. Honorary Fellow, School of Mech. Engrg., Univ. of Edinburgh, King's Buildings, Edinburgh, EH9 3JL, U.K.
2. Reader, School of Mech. Engrg., Univ. of Edinburgh, King's Buildings, Edinburgh, EH9 3JL, U.K.
3. Lect., School of Mech. Engrg., Univ. of Edinburgh, King's Buildings, Edinburgh, EH9 3JL, U.K. E-mail: Tom.Bruce@ed.ac.uk