**5. Acknowledgements**

The workings carried out for this contribution where funded by the German Research Foundation under the reference numbers BA 851/93-1 and SPP 1299 BA 851/94-1) and the AiF Arbeitsgemeinschaft industrieller Forschungsvereinigungen "Otto von Guericke" e.V (IGF Nos. 14.509 N and 16.411 N). This support is gratefully acknowledged by the authors.
