Department of Mathematical Sciences, Indiana University, 402 N. Blackford Street, Indianapolis, IN 46202, United States
Department of Geomorphology, Institute of Geography and Regional Development, University of Wroclaw, pl. Uniwersytecki 1, Wroclaw, 50-137, Poland ; Space Research Centre, Polish Academy of Sciences, Bartycka 18a, Warsaw, 00-716, Poland
Space Research Centre, Polish Academy of Sciences, Bartycka 18a, Warsaw, 00-716, Poland