1. Tribology Group, Department of Mechanical Engineering, Imperial College London, South Kensington, Exhibition Road, London SW7 2AZ, U.K.
2. Faculty of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan
3. Department of Mechanical Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
4. Department of Mechanical Engineering, Tokyo University of Science, Tokyo 125-8585, Japan
5. Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan