1. Dept. of Mechanical Engineering, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, Scotland, UK
2. Dept. of Mechanical Engineering, University of Minnesota, 111 Church Street S.E., Minneapolis, MN 55455, USA
3. Mechanical Engineering, University of California, A317 Bourns Hall, Riverside, CA 92521, USA
4. Mechanical Engineering, University of California, 5133 Etcheverry Hall, Berkeley, CA 94720-1740, USA