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Peter T. Gallagher,               |           Tel: +44 1232 273708
Dept. of Pure and App. Physics,   |           Fax: +44 1232 438918
The Queen's University of Belfast,|  E-mail: P.Gallagher@qub.ac.uk
Belfast, BT7 1NN,                 | http://star.pst.qub.ac.uk/~ptg
N. Ireland.                       |
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