(01/18-Present) Department Chair, Department of Mathematics, George Washington University.
(11/12-01/13) Visiting Scholar, Center for Mathematics, Computing and Cognition, ABC Federal University, Brazil.
(09/12-10/12) Visiting Scholar, Institute of Computational Science, Universita della Svizzera Italiana, Lugano, Switzerland.
(06/11-08/11) Visiting Researcher, NASA Glenn Faculty Fellowship, Antenna and Optical System Branch, NASA Glenn Research Center, Cleveland OH.
(01/99)-(06/99) Visiting Scholar, Sonderforschungsbereich~256, Nichtlineare partielle Differentialgleichungen, Institut fur Angewandte Mathematik, Universitat Bonn.
(09/98-10/99) Visiting Scholar, Mathematics Department, Krieger School of Arts and Sciences, The Johns Hopkins University.
(06/92-08/92) Visiting Researcher, NASA Balloon Projects, Wallops Flight Facility, Wallops Island, VA.
(09/91-05/92) Visiting Researcher, Center for Geometry, Analysis, Numerics & Graphics, Department of Mathematics, University of Massachusetts at Amherst.