1. Research and Technology, AlliedSignal, 101 Columbia Road, Morristown, NJ 07962–1021, USA.
2. Intelligent Polymer Research Institute, University of Wollongong, New South Wales 2522, Australia.
3. School of Engineering, University of Pisa, Centro E. Piaggio, Via Diotisalvi, 2–56100 Pisa, Italy.
4. Department of Physics, University of Florida, Gainesville FL 32611–8440, USA.
5. Max Planck Institut für Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
6. Department of Chemistry, Georgetown University, Washington, DC 20057–1227, USA.