1. Schmid College of Science and Technology, Chapman University 1 , One University Drive, Orange, California 92866, USA
2. Department of Mathematics, CIDMA - Center for Research and Development in Mathematics and Applications, University of Aveiro 2 , Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
3. Department of Physics and Astronomy, Purdue University 3 , West Lafayette, Indiana 47907, USA