Visiting Appointments
- 1976, January-March, Applied Mathematics Dept., Liege University, Belgium, Visiting Assistant Professor
- Summer 1984-1991, Scuola Normale Superiore, Pisa, Italy, CNRS Fellow and Visiting Professor
- 1986, 1991 August, Int. Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria, Visiting Professor
- 1984, 1990, 1991, 1992 July, Department of Mathematics, University of Bologna, Bologna, Italy, Visiting Professor
- 1992 Oct.-Dec. (sabbatical leave), Department of Mathematics, University of Trento, Italy, Visiting Professor
- 1992, Nov. 1-30 (sabbatical leave), IMA Institute for Mathematics with Applications, University of Minnesota, Minneapolis, IMA Fellow
- 1993, University of Jyväskylä, Finland. Series of lectures, Visiting Professor.
- 1994, June-July, Instituto di Calcolo Scientifico (IAQ "Al Picone" Rome, Italy. CNRS Fellow.
- 1995, March, IMA Institute for Mathematics and Applications, University of Minnesota, Minneapolis, IMA Fellow
- Summer 1997, 1998, Scuola Normale Superiore, Pisa, Italy
- 2001, July. IMA Institute for Mathematics and Applications, University of Minnesota, Minneapolis. IMA Fellow.
- 2002, February-September. Scuola Normale Superiore, Pisa. Italy.
- 2003, January. Mittag Leffler Institute, Stokholm (Drujholm), Sweden.
- 2008, Fall, Scuola Normale Superiore, Pisa, Centro de Giorgi.