1. Department of Mathematics and Statistics, San Diego State University, San Diego, California 92182, USA
2. Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, USA
3. Mathematics and Computer Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont Illinois 60439, USA
4. Department of Mathematics, Statistics, and Computer Science, University of Illinois at Chicago, 851 South Morgan Street, Chicago, Illinois 60607, USA