We describe the results of a bilateral measurement comparison of optical fiber time delay between the National Institute of Standards and Technology (NIST, USA) and Laboratorio de Metrología, Instituto Costarricense de Electricidad (LAMETRO-ICE, Costa Rica), which was conducted on a single-mode optical fiber reference spool at wavelengths of 1310 nm and 1550 nm. The measurement results showed the largest difference to be less than 0.93 ns, which is within the combined standard uncertainty (coverage factor k = 1) for the measurement systems at the two laboratories.
Ultraviolet-C (UV-C) radiation, spanning wavelengths between 200 nm and 280 nm, has proven germicidal qualities and medical, industrial, and environmental applications. The need for new disinfection technologies and the prospect of eliminating mercury-based radiation sources compels research on ultraviolet (UV) light-emitting diodes (LEDs). UV-LED technology could be used for customized and point-of-use products for disinfection and sterilization. We focused on the design and development of a surface disinfection device using UV-C LEDs, including potential user targets, important design parameters, and final validation methods. Optical and thermal simulations were used to illustrate the design process and associated challenges. A sample device prototype was developed, and microbial validation results are presented.
The NIST Vacuum Double-Crystal Spectrometer (VDCS) has been modernized and is now capable of recording reference-free wavelength-dispersive spectra in the 2 keV to 12 keV x-ray energy range. The VDCS employs crystals in which the lattice spacings are traceable to the definition of the meter through x-ray optical interferometry with a relative uncertainty <10−8. VDCS wavelength determination relies upon precision angle difference measurements for which the encoders of the rotation stages have been calibrated using the circle closure method for accurate, absolute angle measurement. The new vacuum-compatible area detector allows quantification of the aberration functions contributing to the observed line shape and in situ alignment of the crystal optics. This latter procedure is augmented with the use of a thin lamella as the first crystal. With these new techniques, x-ray spectra are registered with the VDCS on an absolute energy scale with a relative uncertainty of 10−6.
High-quality recordings of radio frequency (RF) emissions from commercial communication hardware in realistic environments are often needed to develop and assess spectrum-sharing technologies and practices, e.g., for training and testing spectrum sensing algorithms and for interference testing. Unfortunately, the time-consuming, expensive nature of such data collections together with data-sharing restrictions pose significant challenges that limit data set availability. Furthermore, developing accurate models of real-world RF emissions from first principles is often very difficult because system parameters and implementation details are at best only partially known, and complex system dynamics are difficult to characterize. Hence, there is a need for flexible, data-driven methods that can leverage existing data sets to synthesize additional similar waveforms. One promising machine-learning approach is unsupervised deep generative modeling with generative adversarial networks (GANs). To date, GANs for RF communication signals have not been studied thoroughly. In this paper, we present the first in-depth investigation of generated signal fidelity for GANs trained with baseband orthogonal frequency-division multiplexing (OFDM) signals, where each subcarrier is digitally modulated with quadrature amplitude modulation (QAM). Building on prior GAN methods, we developed two novel GAN models and evaluated their performance using simulated data sets with known ground truth. Specifically, we investigated model performance with respect to increasing data set complexity over a range of OFDM parameters and conditions, including fading channels. The findings presented here inform the feasibility of use cases and provide a foundation for further investigations into deep generative models for RF communication signals.
We simulated the effects of gimbal-alignment errors and rotational step-size errors on measurements of the sensitivity matrix and intrinsic properties of a triaxial accelerometer. We restricted the study to measurements carried out on a two-axis calibration system using a previously described measurement and analysis protocol. As well as imperfections in the calibration system, we simulated imperfect orthogonality of the accelerometer axes and non-identical sensitivity of the individual accelerometers in an otherwise perfect triaxial accelerometer, but we left characterization of other accelerometer imperfections such as non-linearity for future study. Within this framework, sensitivity-matrix errors are caused by imperfections in the construction and installation of the accelerometer calibration system, but not by the accelerometer imperfections included in the simulations. We use the results of this study to assign type B uncertainties to the components of the sensitivity matrix and related intrinsic properties due to imperfections in the measurement system. For calibrations using a reasonably well manufactured and installed multi-axis rotation stage such as that studied in this paper, we estimated upper bounds to the standard uncertainties of the order of 1 ×10−5 , 2 ×10−5 , 2 ×10−4 , and 5 ×10−5 for the intrinsic sensitivities, diagonal elements of the sensitivity matrix, off-diagonal elements of the sensitivity matrix, and zero-acceleration offsets, relative to a sensitivity-matrix element of 1, respectively, and 5 ×10−3 degrees for the intrinsic angles
Keyphrase extraction is an important facet of annotation tools that offer the provision of the metadata necessary for technical language processing (TLP). Because TLP imposes additional requirements on typical natural language processing (NLP) methods, we examined TLP keyphrase extraction through the lens of a hypothetical toolkit which consists of a combination of text features and classifiers suitable for use in low-resource TLP applications. We compared two approaches for keyphrase extraction: The first which applied our toolkit-based methods that used only distributional features of words and phrases, and the second was the Maui automatic topic indexer, a well-known academic method. Performance was measured against two collections of technical literature: 1153 articles from Journal of Chemical Thermodynamics (JCT) curated by the National Institute of Standards and Technology Thermodynamics Research Center (TRC) and 244 articles from Task 5 of the Workshop on Semantic Evaluation (SemEval). Both collections have author-provided keyphrases available; the SemEval articles also have reader-provided keyphrases. Our findings indicate that our toolkit approach was competitive with Maui when author-provided keyphrases were first removed from the text. For the TRC-JCT articles, the Maui automatic topic indexer reported an F -measure of 29.4 % while our toolkit approach obtained an F -measure of 28.2 %. For the SemEval articles, our toolkit approach using a Naïve Bayes classifier resulted in an F -measure of 20.8 %, which outperformed Maui’s F -measure of 18.8 %.
The coronavirus disease 2019 (COVID-19) pandemic led to the need for tracking of physical contacts and potential exposure to disease. Traditional contact tracing can be augmented by electronic tools called "electronic contact tracing" or "exposure notification.". Some methods were built to work with smartphones; however, smartphones are not prevalent in some high-contact areas (e.g., schools and nursing homes). We present the design and initial testing of low-cost, highly privacy preserving wearable exposure notification devices. Several devices were constructed based on existing hardware and operated independently of a smartphone. The method (devices and analyses) was not able to reliably use the received signal strength indicator (RSSI) as a proxy for distance between pairs of devices; the accuracy of RSSI as a proxy for distance decreased dramatically outside of the idealized conditions. However, even an imperfect device could be useful for research on how people use and move through spaces. With some improvement, these devices could be used to understand disease spread and human or animal interaction in indoor environments.
Uniaxial tensile tests are routinely conducted to obtain stress-strain data for forming applications. It is important to understand the deformation behavior of test specimens at plastic strains, temperatures, and strain rates typically encountered in metal forming processes. In this study, the Johnson-Cook (J-C) flow stress model was used to describe the constitutive behavior of ASTM International (ASTM) A 1008 steel specimens during uniaxial tensile tests at three different average strain rates (10-⁵ s-¹, 10-³ s-¹, and 10-¹ s-¹). The digital image correlation (DIC) technique was used for displacement and strain measurement, and two-dimensional (2D) infrared (IR) imaging was employed for temperature measurement. Separate optimization studies involving relevant finite element (FE) modeling with appropriate measured data yielded optimum values of convective heat transfer coefficients, J-C parameters, and inelastic heat fraction variables. FE modeling employing these optimum parameter values was then used to study the mechanical behavior. While FE predictions matched measured strain localization and thermal field very well in the intermediate- and low-rate experiments, the high-rate test showed narrower strain localization and a sharper temperature peak in the experiment. Possible use of a higher steel thermal conductivity value and/or exclusion of material inhomogeneities may have resulted in discrepancies between computed and measured temperature and strain fields. The study shows that an optimized set of parameters obtained with a controlled test could be reasonably applied for other tests conducted at very different strain rates.
The AbsorbanceQ app converts brightfield microscope images into absorbance images that can be analyzed and compared across different operators, microscopes, and time. Because absorbance-based measurements are comparable across these parameters, they are useful when the aim is to manufacture biotherapeutics with consistent quality. AbsorbanceQ will be of value to those who want to capture quantitative absorbance images of cells. The AbsorbanceQ app has two modes - a single image processing mode and a batch processing mode for multiple images. Instructions for using the app are given on the ‘App Information’ tab when the app is opened. The input and output images for the app have been defined, and synthetic images were used to validate that the output images are correct. This article provides a description of how to use the app, software specifications, a description of how the app works, instructive advice on how to use the tools and a description of the methods used to generate the software. In addition, links are provided to a website where the app and test images are deployed.
Data for interpreting virus inactivation on N95 face filtering respirators (FFRs) by ultraviolet (UV) radiation are important in developing UV strategies for N95 FFR disinfection and reuse for any situation, whether it be everyday practices, contingency planning for expected shortages, or crisis planning for known shortages. Data regarding the integrity, form, fit, and function of N95 FFR materials following UV radiation exposure are equally important. This article provides these data for N95 FFRs following UV-C irradiation (200 nm to 280 nm) in a commercial UV-C enclosure. Viral inactivation was determined by examining the inactivation of OC43, a betacoronavirus, inoculated on N95 FFRs. Different metrological approaches were used to examine irradiated N95 FFRs to determine if there were any discernible physical differences between non-irradiated N95 FFRs and those irradiated using the UV-C enclosure. Material integrity was examined using high-resolution scanning electron microscopy. Form, fit, and function were examined using flow resistance, tensile strength, and particle filtration measurements. A separate examination of filter efficiency, fit, and strap tensile stress measurements was performed by the National Personal Protective Technology Laboratory. Data from these metrological examinations provide evidence that N95 FFR disinfection and reuse using the UV-C enclosure can be effective.
A portable calorimeter for direct realization of absorbed dose in medical computed tomography (CT) procedures was constructed and tested in a positron emission tomography (PET) CT scanner. The calorimeter consists of two small thermistors embedded in a polystyrene (PS) cylindrical "core" (1.5 cm diameter) that can be inserted into a cylindrical high-density polyethylene (HDPE) phantom (30 cm diameter). The cylindrical design of core and phantom allows coaxial alignment of the system with the scanner rotation axis, which is necessary to minimize variations in dose that would otherwise occur as the X-ray source is rotated during scanning operations. The core can be replaced by a cylindrical ionization chamber for comparing dose measurement results. Measurements using the core and a calibrated thimble ionization chamber were carried out in a beam of 6 MV X-rays from a clinical accelerator and in 120 kV X-rays from a CT scanner. Doses obtained from the calorimeter and chamber in the 6 MV beam exhibited good agreement over a range of dose rates from 0.8 Gy/min to 4 Gy/min, with negligible excess heat. For the CT beam, as anticipated for these X-ray energies, the calorimeter response was complicated by excess heat from device components. Analyses done in the frequency domain and time domain indicated that excess heat increased calorimetric temperature rise by a factor of about 15. The calorimeter's response was dominated by dose to the thermistor, which contains high-atomic-number elements. Therefore, for future construction of calorimeters for CT beams, lower-atomic-number temperature sensors will be needed. These results serve as a guide for future alternative design of calorimeters toward a calorimetry absorbed dose standard for diagnostic CT.
The development of an international, precompetitive, collaborative, ultraviolet (UV) research consortium is discussed as an opportunity to lay the groundwork for a new UV commercial industry and the supply chain to support this industry. History has demonstrated that consortia can offer promising approaches to solve many common, current industry challenges, such as the paucity of data regarding the doses of ultraviolet-C (UV-C, 200 nm to 280 nm) radiation necessary to achieve the desired reductions in healthcare pathogens and the ability of mobile disinfection devices to deliver adequate doses to the different types of surfaces in a whole-room environment. Standard methods for testing are only in the initial stages of development, making it difficult to choose a specific UV-C device for a healthcare application. Currently, the public interest in UV-C disinfection applications is elevated due to the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the respiratory coronavirus disease 19 (COVID-19). By channeling the expertise of different UV industry stakeholder sectors into a unified international consortium, innovation in UV measurements and data could be developed to support test methods and standards development for UV healthcare equipment. As discussed in this paper, several successful examples of consortia are applicable to the UV industry to help solve these types of common problems. It is anticipated that a consortium for the industry could lead to UV applications for disinfection becoming globally prolific and commonplace in residential, work, business, and school settings as well as in transportation (bus, rail, air, ship) environments. Aggressive elimination of infectious agents by UV-C technologies would also help to reduce the evolution of antibiotic-resistant bacteria.
A method is described for inactivation of pathogens, especially airborne pathogens, using ultraviolet (UV) radiation emitted directly into occupied spaces and exposing occupants to a dose below the accepted actinic exposure limit (EL). This method is referred to as direct irradiation below exposure limits, or DIBEL. It is demonstrated herein that low-intensity UV radiation below exposure limits can achieve high levels of equivalent air changes per hour (ACHeq) and can be an effective component of efforts to combat airborne pathogens such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19). An ACHeq of 4 h−1 is presently achievable over a continuous 8 h period for the SARS-CoV-2 virus with UV-C light-emitting diodes (LEDs) having peak wavelength at 275 nm, and future improvements in LED technology and optics are anticipated to enable improvements up to 150 h−1 in the coming decade. For example, the actinic EL is 60 J/m2 at 254 nm, and human coronaviruses, including SARS-CoV-2, have a UV dose required for 90 % inactivation of about 5 J/m2 at 254 nm. Irradiation by 254 nm UV-C at the EL is expected to provide 90 % inactivation of these organisms in air in about 40 min when the UV-C is delivered at a constant irradiance over 8 h, or in about 5 min if the UV-C is delivered at a constant irradiance over 1 h. Since the irradiation is continuous, the inactivation of initial contaminants accumulates to 99 % and then 99.9 %, and it also immediately begins inactivating any newly introduced (e.g., exhaled) pathogens at the same rate throughout the 8 h period. The efficacy for inactivating airborne pathogens with DIBEL may be expressed in terms of ACHeq, which may be compared with conventional ventilation-based methods for air disinfection. DIBEL may be applied in addition to other disinfection methods, such as upper room UV germicidal irradiation, and mechanical ventilation and filtration. The ACHeq of the separate methods is additive, providing enhanced cumulative disinfection rates. Conventional air disinfection technologies have typical ACHeq values of about 1 h−1 to 5 h−1 and maximum practical values of about 20 h−1. UV-C DIBEL currently provides ACHeq values that are typically about 1 h−1 to 10 h−1, thus either complementing, or potentially substituting for, conventional technologies. UV-C DIBEL protocols are forecast herein to evolve to >100 ACHeq in a few years, potentially surpassing conventional technologies. UV-A (315 nm to 400 nm) and/or UV-C (100 nm to 280 nm) DIBEL is also efficacious at inactivating pathogens on surfaces. The relatively simple installation, low acquisition and operating costs, and unobtrusive aesthetic of DIBEL using UV LEDs contribute value in a layered, multi-agent disinfection strategy.
The tragedy of the radium poisoning of young women dial painters in the 1920s has been the subject of best-selling books, plays, and motion pictures.With knowledge about radium and its accurate measurements in the hands of a very few scientists, what responsibilities did they have to sound the alarm and mitigate the hazards to workers and the general public?This two-part analysis looks at the role of the staff of the U.S. Bureau of Standards (the National Bureau of Standards [NBS] after 1934) in developing measurements and standards for accurate determinations of radium-226 and radon-222 that ultimately led to national standards for exposure to radioactive substances.Part I looks at the efforts of Elizabeth Hughes, with guidance from her senior colleague at the NBS, to assist dial painters with obtaining redress for their injuries.Part II examines the role of NBS in establishing the national radiation protection standards that were promulgated by the U.S. Department of Commerce (DOC) and the National Council on Radiation Protection and Measurements (NCRP).
A documentary standard produced by the American Society of Mechanical Engineers (ASME) for performance evaluation of industrial X-ray computed tomography (XCT) systems for dimensional measurements was released in early 2021. This standard, ASME B89.4.23-2020, specifies test procedures that may be performed to determine whether a system meets the manufacturer’s accuracy specifications for acceptance before or after purchase, or for periodic reverification. While there are some core testing requirements in the standard, there is also some flexibility, allowing for a variety of testing configurations that meet the requirements of the standard. It is important that the chosen testing configuration be sensitive to the different systematic sources of error in XCT systems to provide confidence that the system will meet the manufacturer’s accuracy specifications for measurements performed by the user subsequent to testing. In this paper, we provide guidance on how to optimally apply the ASME 89.4.23 standard in industry to achieve high sensitivity to geometry errors in cone-beam XCT systems. Through simulation studies, we present some examples of testing configurations that meet the requirements of the ASME B89.4.23 standard and discuss their sensitivity to geometry errors of the detector and the rotation stage. We show that there are some testing configurations that achieve maximal sensitivity to these errors, while other configurations do not capture these error sources with adequate sensitivity.
The multi-source common-view disciplined clock (MSCVDC) is a recent NIST invention designed to support critical infrastructure timing systems that require a verifiably accurate and fail-safe clock. This paper introduces the MSCVDC, provides a technical description of how it works, and discusses its reliability, redundancy, security, and performance. It also discusses the possibility of a commercially available MSCVDC product.
We present a new paradigm for the primary standardization of radionuclide activity per mass of solution (Bq/g). Two key enabling capabilities are 4π decay-energy spectrometry using chip-scale sub-Kelvin microcalorimeters and direct realization of mass by gravimetric inkjet dispensing using an electrostatic force balance. In contrast to traditional traceability, which typically relies on chemical separation of single-radionuclide samples, 4π integral counting, and additional spectrometry methods to verify purity, the system described here has both 4π counting efficiency and spectroscopic resolution sufficient to identify multiple radionuclides in the same sample at once. This enables primary standardization of activity concentrations of mixed-radionuclide samples. A major benefit of this capability, beyond metrology, is in assay of environmental and forensics samples, for which the quantification of multiplenuclide samples can be achieved where presently inhibited by interferences. This can be achieved without the need for chemical separations or efficiency tracers, thereby vastly reducing time, radioactive waste, and resulting measurement uncertainty.
The goal of this project was to create and optimize the performance of portable chambers for reliable ultraviolet (UV) disinfection of personal protective equipment (PPE) and enable its safe reuse. During unforeseen times of high demand for PPE, such as during the coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), single-use PPE supply can be quickly depleted. UV radiation has been shown to disinfect materials with high efficacy. This paper reports the design and construction of two 280 nm ultraviolet-C (UV-C) disinfection chambers in the form of portable chambers with 46 cm × 46 cm × 46 cm interior dimensions, one using light-emitting diodes and the other using mercury vapor lamps. This paper summarizes and presents a review of SARS-CoV-2 UV deactivation research during 2020 to 2021. Additionally, this paper discusses efforts to increase the uniformity and overall intensity of the UV-C radiation within the chambers through the installation of a UV-reflective, porous polytetrafluoroethylene (PTFE) material. A calculator prototype was additionally designed to calculate the reduction of SARS-CoV-2 as a result of UV-C disinfection, and the prototype code is presented. The paper describes the selection of UV-C radiation sources for the chambers and the chambers’ mechanical and electrical design, PTFE installation, testing, and safety considerations.
This paper reports the powder X-ray diffraction patterns, argon isotherms at 87 K, Brunauer-Emmett-Teller surface areas, pore size distributions, pore volumes, skeletal densities, and thermal gravimetric analyses for three National Institute of Standards and Technology zeolitic reference materials, RM 8850 (zeolite Y), RM 8851 (zeolite A), and RM 8852 (ZSM-5).
A first-principles-based model for predicting the effect of germicidal radiation interventions for air disinfection is presented. Calculation of the "capacity" of an intervention expressed in volumetric flow rate allows for a direct comparison against fresh-air dilution ventilation and filtration systems, which are quantified in terms of the clean air provided. A closed-form expression to predict the combined quantitative impact of spatial gradients and mixing currents on the efficiency with which an intervention is applied is introduced. If validated, this would allow for systems to be selected and sized based on simple metrics across a broad range of settings and applications. The expressions developed are compared against available experimental data sets, and future validation efforts are proposed. Additionally, a method to identify an optimal operating capacity for a given setting by comparing costs associated with disease transmission against the cost of capacity is derived using the Wells-Riley equation and presented as an appendix.
