...B¹

Corresponding author: Tel: 301-975-5865; Fax: 301-990-6891; E-mail: dale.bentz@nist.gov.

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... DT²

Certain commercial equipment is identified by name in this paper to adequately specify the experimental procedure. In no case does such identification imply endorsement by the National Institute of Standards and Technology, nor does it imply that the products are necessarily the best available for the purpose.

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