1. Department of Physics; University of Helsinki; 00560 Helsinki Finland
2. Research Institute of Wood Industry; Chinese Academy of Forestry; 100091 Beijing China
3. Department of Forest Products Technology; Aalto University; School of Chemical Technology; 00076 Aalto Finland
4. VTT Technical Research Centre of Finland; 02044 Espoo Finland
5. Natural Resources Institute Finland; 01300 Vantaa Finland