Affiliation: | 1. Department of Mathematics, University of Houston, 651 PGH, Houston, TX 77204-3008, USA;2. Institute of Applied Mathematics (LS III), Dortmund University of Technology, Vogelpothsweg 87, D-44227 Dortmund, Germany;3. Department of Mathematics, University of Pittsburgh, 301 Thackeray Hall, Pittsburgh, PA 15260, USA |