| Copyright © 2011, R. Hilfer, Stuttgart | Content is made available under Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) License; additional terms may apply. |  |
The author gratefully acknowledges finacial support from the German-Norwegian research cooperation (Project B-2). He thanks Dr. B. Nøst for discussions and encouragement.
| Copyright © 2011, R. Hilfer, Stuttgart | Content is made available under Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) License; additional terms may apply. | |