1. Department of Physics, University of the Free State, Bloemfontein, ZA9300, South Africa
2. Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544, USA
3. Department of Aeronautics, ONERA the French Aerospace Lab, 92190 Meudon, France
4. Lehrstuhl für Technische Thermodynamik, Otto-von-Guericke-Universität Magdeburg, 39106 Magdeburg, Germany