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First publ. in: Journal of Low Temperature Physics 150 (2008), 3/4, pp. 247-251
Konstanzer Online-Publikations-System (KOPS) URN: http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-88411
URL: http://kops.ub.uni-konstanz.de/volltexte/2009/8841/
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