sentences:  He then spent two years working as a post-doctorate at the Naval Ordnance Laboratory before transferring to the Institute for Computer Applications in Science and Engineering at NASA until 1976.He then became an associate professor and professor of mathematics at the University of Tennessee, a position he held from 1976 to 1982.Transferring again, he moved from Carnegie Mellon University in 1981 to 1989, to Virginia Polytechnic Institute and State University from 1987 to 1997.