1. Department of Mechanical Engineering, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, British Columbia V6T 1Z4, Canada
2. Department of Engineering Technology, University of Houston, 4730 Calhoun Road 304, Houston, Texas 77204-4020, USA
3. Department of Mathematics, University of British Columbia, 1984 Mathematics Road, Vancouver, British Columbia V6T 1Z2, Canada