1. VTT Building Technology, Wood Technology, P.O. Box 1806, FIN-02044 VTT, Finland
2. Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland
3. Engineering Research Center for Plasma-Aided Manufacturing, University of Wisconsin, Madison, Wisconsin 53706
4. Forest Products Laboratory, USDA Forest Service, One Gifford Pinchot Drive, Madison, Wisconsin 53705-2398