Journal of Research of the National Institute of Standards and Technology最新文献

Industrial wireless is a potential networking solution in many scenarios due to its flexibility and ease of communications in harsh environments. Industrial wireless in gas-sensing and air-quality monitoring applications is essential when wired communications cannot perform the task safely and effectively. A major example of such environments is confined spaces where attaching mobile gas sensors with wires is a major concern for safety and cannot be deployed in some cases. At the National Institute of Standards and Technology (NIST), we developed an end-to-end characterization method for industrial wireless networks. We employed this characterization method to study the end-to-end error and delay performance for a confined-space gas-sensing scenario. We have built the scenario using the NIST industrial wireless test bed, which includes ISA100.11a wireless devices, a channel emulator, and a high-performance programmable logic controller (PLC), where the physical process is simulated. In this work, we studied the effects of the size of the confined space, the relaying, input signal rate, and the impact of the existing workers in the confined space.

As part of a revision to the International System of Units (SI) approved in 2018 and to take effect in May 2019, the seven base units will be defined by giving fixed numerical values to seven defining constants. This article shows how the definitions of all seven base units can be derived efficiently from the defining constants, with the result appearing as a table. The table's form makes evident a number of connections between the defining constants and the base units. Appendices show how the same methodology could have been used to define the same base units in the present SI, as well as the mathematics that underpins the methodology. Since the base units are now defined in terms of constants, then all units in the SI are now defined in terms of those constants.

Most models currently used for complex phases in the calculation of phase diagrams (Calphad) method are based on the compound energy formalism. The way this formalism is presently used, however, is prone to poor extrapolation behavior in higher-order systems, especially when treating phases with complex crystal structures. In this paper, a partition of the Gibbs energy into effective bond energies, without changing its configurational entropy expression, is proposed, thereby remarkably improving the extrapolation behavior. The proposed model allows the use of as many sublattices as there are occupied Wyckoff sites and has great potential for reducing the number of necessary parameters, thus allowing shorter computational time. Examples for face centered cubic (fcc) ordering and the σ phase are given.

Current-to-voltage converters are used in many photometric and radiometric applications. The calibration of current-to-voltage converters at a few input currents is not always sufficient to understand the linearity and the bias of a device. Many devices have structure deviating from a linear response over the operating range of a gain setting. Measurement services that rely on these devices now have decreased uncertainties to a level that requires quantifying the uncertainties and understanding how they propagate. The National Institute of Standards and Technology has developed a system to calibrate the current-to-voltage conversion factor or "gain" and offset of these devices for direct current photocurrents. The equipment used for the calibration is described here, and the results and uncertainties are discussed.