The author thanks A. Badertscher, M. Daum, P. Froelich, P.F.A. Goudsmit, F. Kottmann, B. Lauss, H.J. Leisi, L.I. Ponomarev, V.P. Popov, J. Schottmüller, L.M. Simons, E.A. Solov'ev, D. Taqqu, and J. Wallenius for fruitful discussions.
