1. Grad. Student, Northwestern Univ., School of Engrg. and Appl. Sci., Evanston, IL 60208.
2. Walter P. Murphy Prof., Dir. of ACBM, Northwestern Univ., School of Engrg. and Appl. Sci., Evanston, IL 60208.
3. Asst. Prof., Northwestern Univ., School of Engrg. and Appl. Sci., Evanston, IL 60208.