1. School of Mechanical & Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078 USA.
2. Department of Engineering Cybernetics, Norwegian University of Science and Technology, N-7465, Trondheim, Norway.
3. Department of Mathematics, Virginia Tech, Blacksburg, VA 24061 USA.
4. Department of Mathematics, Department of Computer Science, Emory University, Atlanta, GA 30322 USA.