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A Historical Review of U.S. Contributions to the Atomic Redefinition of the SI Second in 1967
No full textThis paper was written to commemorate the 50th anniversary of the atomic redefinition of the second in the International System (SI) in 1967. It focuses on the work of individuals and organizations in the United States who made significant contributions to the redefinition of the SI second and helped to establish the era of atomic timekeeping
Development of NIST Standard Reference Material 2082, a Pathlength Standard for Measurements in the Ultraviolet Spectrum
No full textNew spectrophotometers and cuvettes have been designed to allow the measurement of absorbance values from samples using microliter volume sizes. These measurements are done using short pathlengths to decrease the sample volumes required. The major applications for these spectrophotometers and cuvettes are samples that are difficult to obtain in large amounts, such as proteins and nucleic acids that absorb light in the ultraviolet range. Existing ultraviolet absorbance standards have been designed for longer pathlength measurements. Standard Reference Material (SRM) 2082 was developed to validate the pathlengths of short-pathlength cuvettes and instruments using materials with absorbance spectra that are similar to the most commonly used samples. SRM 2082 consists of three individual components: a blank buffer solution, a solution of the amino acid tryptophan in the buffer, and a solution of the nucleobase uracil in the buffer. The tryptophan solution has an absorbance spectrum (peak at 280 nm) similar to proteins, and the uracil has an absorbance spectrum (peak at 260 nm) similar to nucleic acids. The absorbance values of these solutions were determined using a series of cuvettes with pathlengths from 0.1 mm to 2 mm. The pathlengths of the cuvettes used for the absorbance measurements were determined at the National Institute of Standards and Technology by physical and optical measurements. The effects of temperature and spectral bandwidth variations on the absorbance values of SRM 2082 were also investigated
A loose nugget sits in the weathered pocket of this sample of sandstone from Cumberland, Ohio
No full textThe NIST stone wall was built using 2,352 stones from 47 US states and 320 from 16 foreign countries. The wall is approximately 12 m long, 4 m high, 0.6 m thick at the bottom, and 0.3 m at the top. The aim of the wall construction was to study the aging process of stones used in construction under outside weathering conditions
A view of the NIST stone wall
No full textA view of the NIST stone wall was built using 2,352 stones from 47 US states and 320 from 16 foreign countries. The wall is approximately 12 m long, 4 m high, 0.6 m thick at the bottom, and 0.3 m at the top. The aim of the wall construction was to study the aging process of stones used in construction under outside weathering conditions
A close-up view of coarse limestone from New Bern, North Carolina, set in the NIST stone wall
No full textThe NIST stone wall was built using 2,352 stones from 47 US states and 320 from 16 foreign countries. The wall is approximately 12 m long, 4 m high, 0.6 m thick at the bottom, and 0.3 m at the top. The aim of the wall construction was to study the aging process of stones used in construction under outside weathering conditions
Portrait of Francis Sullivan
No full textOff-site Collaborator, Applied and Computational Mathematics Division, Information Technology Laborator
A close-up view of black basalt from the state of Puebla in Mexico, set in the NIST stone wall
No full textThe center of thise image is Black basalt from the state of Puebla in Mexico. It is part of the NIST stone wall, which was built using 2,352 stones from 47 US states and 320 from 16 foreign countries. The wall is approximately 12 m long, 4 m high, 0.6 m thick at the bottom, and 0.3 m at the top. The aim of the wall construction was to study the aging process of stones used in construction under outside weathering conditions
A view of the NIST stone wall
No full textA view of the NIST stone wall was built using 2,352 stones from 47 US states and 320 from 16 foreign countries. The wall is approximately 12 m long, 4 m high, 0.6 m thick at the bottom, and 0.3 m at the top. The aim of the wall construction was to study the aging process of stones used in construction under outside weathering conditions