1. Maurice Morton Institute and Department of Polymer Science, The University of Akron, Akron, Ohio 44328-3909; Institut of Charles Sadron, 6 Rue Boussingault, Strasbourg 67083, France; Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada