1. Department of Mathematics, ETH Zürich, Rämistrasse 101, CH-8092 Zürich, Switzerland. E-mail: habib.ammari@math.ethz.ch
2. Department of Mathematics, University of California at Irvine, 340 Rowland Hall, Irvine, California 92697-3875, USA. E-mail: lgiovang@uci.edu
3. Department of Computational Science and Engineering, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul 120-749, Korea. E-mails: 3c273-85@daum.net, seoj@yonsei.ac.kr
4. Department of Mathematics and Applications, Ecole Normale Supérieure, 45 Rue d’Ulm, 75005 Paris, France. E-mail: timothee.wintz@ens.fr