1. Max-Planck-Institut für Mathematik in den Naturwissenschaften Inselstr. 22-26, D-04103 Leipzig, Germany
2. Department of Geology and Physics, Georgia Southwestern State University, 800 Wheatly St., Americus, GA 31709, USA
3. Department of Physics and Astronomy, Indiana University South Bend, 1700 Mishawaka Av., South Bend, IN 46634, USA