A~~~~~~--E x p e r i m e n t and analysis have been done tocMrrent-~i~ed Nb-(constrictions)-NbN (S-c-S') conkacts is well described by existing theories of a mesoscopic two~r~i n~1 conductor. The quasiparticle characteristics of the Se-S' which has a~j M s~~~~e current-voltage curve Is also welt ~~~~y~ using the theory based on the single Andreev reflection mode1 without heating. In the clean S-e-S' cantxwts, there is no ~e~M r a~I e ewess noise CQnt~ibut~on associated with the Andreev reflection itself. w that the low frequency vottage noise

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