2012-Present - Professor, Biological Systems Engineering, Virginia Tech 2005-2012 - Associate Professor, Biological Systems Engineering, Virginia Tech 1999-2005 - Assistant and Associate Professor, Civil and Environmental Engineering, University of Vermont 1995-1999 - Assistant Curator and Biosystems Engineering Section Leader, Patrick Center for Environmental Research, Academy of Natural Sciences of Philadelphia 1992-1995 - Doctoral Candidate and Research Engineer, Biosystems Engineering, Oklahoma State University 1989-1992 - Senior Environmental Engineer and NPS Modeling Coordinator, Virginia Department of Conservation and Recreation 1986-1989 - Assistant Scientist, USDA-Agricultural Research Service (Morris, MN)