1. Research Unit of Financial and Actuarial Mathematics, Vienna University of Technology, Wiedner Hauptstr. 8/105-1, A-1040Vienna, Austria
2. Research Unit of Financial and Actuarial Mathematics, Vienna University of Technology and Arithmetica Versicherungs- und Finanzmathematische Beratungs-GmbH, A-1040Vienna, Austria
3. Christian Doppler Laboratory for Portfolio Risk Management, Vienna University of Technology, Wiedner Hauptstr. 8/105-1, A-1040Vienna, Austria
4. Department of Statistics, University of California, Berkeley, CA94720-3860, USA