1. INRA – Bordeaux, EPHYSE – 69, route d’Arcachon, F–33612 Gazinet Cedex, France;
2. CIRAD Departement AMIS – Laboratoire de Rhéologie du Bois de Bordeaux (UMR CNRS, INRA, Université Bordeaux I, 69 route d’Arcachon, F−33612 Gazinet Cedex, France;
3. Present address: LIAMA – Institute of Automation, Chinese Academy of Sciences, PB 2728, Beijing 100080, China