1. Res. Fellow, Dept. of Computing and Electr. Engrg., Heriot-Watt Univ., Edinburgh, EH14 4AS, Scotland, U.K. E-mail: ywang@cee. hw.ac.uk
2. Prof., Dept. of Mech. Engrg., James Watt Build., Univ. of Glasgow, Glasgow, G12 8QQ, Scotland, U.K. E-mail: matthewc@mech.gla.ac.uk