1. Department of Mathematical Sciences , Ball State University , Muncie , IN 47306 , USA
2. Institute of Mathematics, Physics and Mechanics , 1000 Ljubljana , Slovenia ; and Faculty of Applied Mathematics, AGH University of Science and Technology, 30-059 Kraków, Poland; and Institute of Mathematics “Simion Stoilow” of the Romanian Academy, P.O. Box 1-764, 014700 Bucharest, Romania
3. Department of Civil Engineering , Universitá di Salerno , 84084 Fisciano (Salerno) , Italy