1. Ph.D. Student, Dept. of Mechanical Engineering, Johns Hopkins Univ., 230 Latrobe Hall, 3400 N. Charles St., Baltimore, MD 21218.
2. Dept. of Mechanical Engineering, Johns Hopkins Univ., 230 Latrobe Hall, 3400 N. Charles St., Baltimore, MD 21218; Dept. of Science and Technology, Univ. of Twente, Postbus 217, AE 7500, Enschede, Netherlands; presently, Professor, Dept. of Mechanical Engineering, Univ. of Houston, Houston, TX 772014 (corresponding author).