1. VTT Technical Research Centre of Finland Ltd., Tietotie 2, P.O. Box 1000, FI-02044 VTT, Espoo, Finland
2. Department of Bioproducts and Biosystems, Aalto University, Vuorimiehentie 1, P.O. Box 16300, FI-00076 Aalto, Espoo, Finland
3. Depa rtment of Physics, University of Helsinki, Gustaf Hällströmin katu 2, P.O. Box 64, 00014 Helsinki, Finland