1. Department of Forest Products Technology, School of Science and Technology, Aalto University, P.O. Box 16300, 00076 Aalto, Finland
2. Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki University, Finland
3. Centre de Recherche sur les Macromolécules Végétales (CERMAV-CNRS), BP 53, 38041 Grenoble Cedex 9, France