1. Honorary Professor, School of Engineering, Cardiff Univ., Cardiff CF24 3AA, Wales, U.K.
2. Professor, School of Engineering, Cardiff Univ., Cardiff CF24 3AA, Wales, U.K. E-mail: RobertsTM@cf.ac.uk
3. Postgraduate Student, School of Engineering, Cardiff Univ., Cardiff CF24 3AA, Wales, U.K.
4. Lecturer, Faculty of Engineering, Univ. of Malaysia Sarawak (UNIMAS), 94300 Kota Samaraham, Sarawak, Malaysia.