George Stephanopoulos, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 66-440, Cambridge, MA 02139, Eric W. Kaler, Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, 102 P.S. DuPont Hall, Newark, DE 19716, and L. Louis Hegedus, 900 First Avenue, King of Prussia, PA 19406.