• Bernd Billhardt, University of Kassel, Alemanha, from March 16 until April 3, and from September 17 until October 7, 2007.
• Ralph Matthes, CNRS and Université de Toulouse III, Franca, from May 27 until June 3, 2007.
• Robert P. Sullivan, University of Western Australia, from February 10 until March 10, and from June 17 until July 14, 2007.
• Robert E. Hartwig, North Carolina State University, from September 4 until October 2, 2007.