• since 10/07 W3-Professor  of Mathematics and its Education, University of Cologne
• 9/06 – 9/07 Head of Teacher Education, University of Nijmegen, NL
• 8/05 – 9/06 Assistant Professor, Technical University Delft, NL
• 8/01 – 9/07 Assistant Professor, Graduate School of Teacher Education, University of Nijmegen, NL
• 8/00 – 8/05 Mathematics Teacher, Canisius College Nijmegen, NL
• 9/00 – 9/01 Teacher Education, University of Nijmegen, NL (after a first phase in 96)
• 1/99 – 8/00 Assistant Professor (C1), Heinrich-Heine-University Düsseldorf with Prof. Dr. G. Fischer
• 6/98 – 1/99 Postdoc, Heinrich-Heine-University Düsseldorf with Prof. Dr. G. Fischer
• 10/97–5/98 Postdoc, University of Utrecht, NL, NWO-Project with Prof. Dr. E. Looijenga
• 6/93 – 5/97 PhD, University of Nijmegen, NL, with Prof. Dr. J.H.M. Steenbrink
• 10/92–3/93 Research Assistant, University of Bonn, with Prof. Dr. E. Brieskorn

Awards:

• 1996 NWO-Grant, Duke University, NC, USA, 1/96-4/96 with Prof. Dr. R. Hain
• 1995 Maître des Conférences invité, Université d’Angers, France
• 1993 Marie Curie Research fellow (5/93-4/95), University Nijmegen, NL
• 1993 Felix-Hausdorff-Gedächtnispreis, University of Bonn

Funded by:

• Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), NL
• European Community (Human Capital and Mobility)
• Geometry and Quantum Theory (GQT) cluster, NL

Committees:

• 3/03–11/07 Editor Nieuw Archief voor Wiskunde, NL
• 2/05–10/07 Dutch Committee for Teaching of Mathematics, NOCW, NL
• 2/05–10/07 Curriculum Committee, cTWO, Ministery OCW, NL

Research:
My current research focuses on teacher research for the design and implementation of mathematics teaching for active and autonomous learning of mathematics. These teaching activities concern in particular the transfer of aspects of mathematical culture and contents in research mathematics, science and engineering to school mathematics. Moreover, I am interested in didactical phenomenology of mathematical structures and elementary mathematics from a higher pint of view.

Dissertations:

• At present, 1 graduate student is working under my supervision at his dissertation.
• Several master theses (Examensarbeiten) are presently completed under my supervision

Teaching activities:

• Regular lectures in various areas of mathematics and in mathematics education
• Seminars on special topics mathematics and in mathematics education

10 important publications:

• (with Ludwig Balke) On a certain type of Coxeter-Dynkin diagrams of plane curve singularities, Topology, 35, No.1 (1996), 39-54.
• The Seifert form of a plane curve singularity determines its intersection multiplicities, Indagationes Mathematicae, N.S., 7(2) (1996), 185-197.
• Die Diagonalfläche aus Keramik , Mitteilungen der DMV 4-99.
• The Mixed Hodge Structure on the Fundamental Group of a Punctured Riemann Surface, Proc. of the AMS, 129(5), 1271-1281, 2000.
• (with M. van den Aarssen, H. Alink, A. van den Hombergh, B. Jordens, R. Klein Breteler, C. Tacken) Spelen op een slimme manier, Nieuwe Wiskrant 23(4), 10-16, 2004.
• Kranen en Lemniscaten, in De schijf van vijf (Meetkunde – Algebra – Analyse – Discrete wiskunde –  Stochastiek, Syllabus CWI vakantiecursus, 136 pages, 2005.
• Hij gooide boeken uit de trein, Freudenthal 100, Nieuwe Wiskrant, 24-4, september 2005
• (with Gerard Alberts) Ik liet de kinderen wél iets leren, Interview met P.M. van Hiele, Nieuw Archief voor Wiskunde, vijfde serie, deel 6, nr. 3, 2005.
• Zahlbegriff zwischen dem Teufel und der tiefen See, Der Mathematikunterricht,  52 (5), 2006.
• Dubbelplaneten, Nieuw Archief voor Wiskunde, 5de serie, deel 8, nr.4. (287-298), 2007.