National Institute Of Standards And Technology Values Research Articles

The Problem With National Institute of Standards and Technology Thermodynamics Tables in Continuum Mechanics.

Thermodynamics is a fundamental topic of continuum mechanics and biomechanics, with a wide range of applications to physiological and biological processes. This study addresses two fundamental limitations of current thermodynamic treatments. First, thermodynamics tables distributed online by the U.S. National Institute of Standards and Technology (NIST) report properties of fluids as a function of absolute temperature T and absolute pressure P. These properties include mass density ρ, specific internal energy u, enthalpy h=u+P/ρ, and entropy s. However, formulations of jump conditions across phase boundaries derived from Newton's second law of motion and the first law of thermodynamics employ the gauge pressure p=P-Pr, where Pr is an arbitrarily selected referential absolute pressure. Interchanging p with P is not innocuous as it alters tabulated NIST values for u while keeping h and s unchanged. Using p for functions of state and governing equations solves the problem with using NIST entries for the specific internal energy u in standard thermodynamics tables and analyses of phase transformation in continuum mechanics. Second, constitutive models for the free energy of fluids, such as water and air, are not typically provided in standard thermodynamics treatments. This study proposes a set of constitutive models and validates them against suitably modified NIST data.

Multiconfiguration Dirac-Hartree-Fock calculations of Landég-factors for ions of astrophysical interest: B II, C I−IV, Al I−II, Si I−IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II

Aims.The Landég-factor is an important parameter in astrophysical spectropolarimetry, used to characterize the response of a line to a given value of the magnetic field. The purpose of this paper is to present accurate Landég-factors for states in B II, C I−IV, Al I−II, Si I−IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II.Methods.The multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, are employed in the present work to compute the Landég-factors for states in B II, C I−IV, Al I−II, Si I−IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II. The accuracy of the wave functions for the states, and thus the accuracy of the resulting Landég-factors, is evaluated by comparing the computed excitation energies and energy separations with the National Institute of Standards and Technology (NIST) recommended data.Results.All excitation energies are in very good agreement with the NIST values except for Ti II, which has an average difference of 1.06%. The average uncertainty of the energy separations is well below 1% except for the even states of Al I; odd states of Si I, Ca I, Ti II, Zr III; and even states of Sn II for which the relative differences range between 1% and 2%. Comparisons of the computed Landég-factors are made with available NIST data and experimental values. Analysing theLS-composition of the wave functions, we quantify the departures fromLS-coupling and summarize the states for which there is a difference of more than 10% between the computed Landég-factor and the Landég-factor in pureLS-coupling. Finally, we compare the computed Landég-factors with values from the Kurucz database.

Methods for quantitative infrared directional-hemispherical and diffuse reflectance measurements using an FTIR and a commercial integrating sphere.

We have developed methods to measure the directional-hemispherical (ρ) and diffuse (ρd) reflectances of powders, liquids, and disks of powders and solid materials using a commercially available, matte gold-coated integrating sphere and Fourier transform infrared spectrometer. To determine how well the sphere and protocols produce quantitative reflectance data, measurements were made of three diffuse and two specular standards prepared by the National Institute of Standards and Technology (NIST), LabSphere Infragold and Spectralon standards, hand-loaded sulfur and talc powder samples, and water. Relative to the NIST measurements of the NIST standards, our directional hemispherical reflectance values are within ±4% for four of the standards and within ±7% for a low reflectance diffuse standard. For the three diffuse reflectance NIST standards, our diffuse reflectance values are within ±5% of the NIST values. For the two specular NIST standards, our diffuse reflectance values are an order of magnitude larger than those of NIST, pointing to a systematic error in the manner in which diffuse reflectance measurements are made for specular samples using our methods and sphere. Sources of uncertainty are discussed in the paper.

A comprehensive study for mass attenuation coefficients of different parts of the human body through Monte Carlo methods

The gamma-ray mass attenuation coefficients of blood, bone, lung, eye lens, adipose, tissue, muscle, brain and skin were calculated at different energies (60, 80, 150, 400, 500, 600, 1000, 1250, 1500, and 2000 keV) by various theoretical methods such as FLUKA, GEANT4 Monte Carlo (MC) methods and XCOM program in this work. Calculated coefficients were also compared with the National Institute of Standards and Technology (NIST) values. Obtained results were highly in accordance with each other and NIST values. Our results showed that FLUKA was quite convenient in comparison to GEANT4 in the calculation of the mass attenuation coefficients of the used human body samples for low-energy photons (60, 80, and 150 keV) when compared with the NIST values.

Validation of a paediatric thyroid phantom using different multidetector computed tomography models

The aim of this study was to compare the attenuation values of a fabricated paediatric thyroid phantom material using different MDCT models. A paediatric thyroid phantom was designed to mimic the shape and size of a paediatric patient with an age of 9 years using high- density Polyethylene as the phantom material. The fabricated phantom was scanned using two different multidetector CT scanners (16- and 128-row detectors). The CT numbers were evaluated and the mass attenuation coefficients (μ/ρ) of the phantom material were obtained at each applied energy from each scanner. The results were compared with the tables of the National Institute of Standards and Technology (NIST). The CTs of 16- and 128-row detectors showed that the obtained attenuation values are very similar to the NIST's values. However, the CT of the 128-row detectors showed a slightly much closer match to the NIST's values. This refers to the type and quality of the electronic connections between the detectors. Furthermore, the type and number of detectors (16- and 128-detectors) could affect the details and quality of the output images. The results show that different multidetector CTs can be used to validate the phantom and determine the mass attenuation coefficients of its material.

Development of a Northern Continental Air Standard Reference Material.

The National Institute of Standards and Technology (NIST) recently began to develop standard mixtures of greenhouse gases as part of a broad program mandated by the 2009 United States Congress to support research in climate change. To this end, NIST developed suites of gravimetrically assigned primary standard mixtures (PSMs) comprising carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-natural air balance at ambient mole fraction levels. In parallel, the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, charged 30 aluminum gas cylinders with northern hemisphere air at Niwot Ridge, Colorado. These mixtures, which constitute NIST Standard Reference Material (SRM) 1720 Northern Continental Air, were certified by NIST for ambient mole fractions of CO2, CH4, and N2O relative to NIST PSMs. NOAA-assigned values are also provided as information in support of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) Program for CO2, CH4, and N2O, since NOAA serves as the WMO Central Calibration Laboratory (CCL) for CO2, CH4, and N2O. Relative expanded uncertainties at the 95% confidence interval are <±0.06% of the certified values for CO2 and N2O and <0.2% for CH4, which represents the smallest relative uncertainties specified to date for a gaseous SRM produced by NIST. Agreement between the NOAA (WMO/GAW) and NIST values based on their respective calibration standards suites is within 0.05%, 0.13%, and 0.06% for CO2, CH4, and N2O, respectively. This collaborative development effort also represents the first of its kind for a gaseous SRM developed by NIST.

Mass attenuation coefficient calculations of different detector crystals by means of FLUKA Monte Carlo method

Calculations of gamma-ray mass attenuation coefficients of various detector materials (crystals) were carried out by means of FLUKA Monte Carlo (MC) method at different gamma-ray energies. NaI, PVT, GSO, GaAs and CdWO4 detector materials were chosen in the calculations. Calculated coefficients were also compared with the National Institute of Standards and Technology (NIST) values. Obtained results through this method were highly in accordance with those of the NIST values. It was concluded from the study that FLUKA MC method can be an alternative way to calculate the gamma-ray mass attenuation coefficients of the detector materials.

An assessment of 25-hydroxyvitamin D measurements in comparability studies conducted by the Vitamin D Metabolites Quality Assurance Program

BackgroundThe National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health Office of Dietary Supplements, established the first accuracy-based program for improving the comparability of vitamin D metabolite measurements, the Vitamin D Metabolites Quality Assurance Program. MethodsThe study samples were human serum or plasma Standard Reference Materials (SRMs) with 25-hydroxyvitamin D values that were determined at NIST. Participants evaluated the materials using immunoassay (IA), liquid chromatography (LC) with mass spectrometric detection, and LC with ultraviolet absorbance detection. NIST evaluated the results for concordance within the participant community as well as trueness relative to the NIST value. ResultsFor the study materials that contain mostly 25-hydroxyvitamin D3 (25(OH)D3),the coefficient of variation (CV) for the participant results was consistently in the range from 7% to 19%, and the median values were biased high relative to the NIST values. However, for materials that contain significant concentrations of both 25-hydroxyvitamin D2 (25(OH)D2) and 25(OH)D3, the median IA results were biased lower than both the LC and the NIST values, and the CV was as high as 28%. The first interlaboratory comparison results for SRM 972a Vitamin D Metabolites in Human Serum are also reported. ConclusionsRelatively large within-lab and between-lab variability hinders conclusive assessments of bias and accuracy.

Determination of 252–302 Da and tentative identification of 316–376 Da polycyclic aromatic hydrocarbons in Standard Reference Materials 1649a Urban Dust and 1650b and 2975 Diesel Particulate Matter by accelerated solvent extraction–HPLC-GC-MS

We have assessed and compared the extraction recoveries of polycyclic aromatic hydrocarbons (PAHs) with molecular weights of 252, 276, 278, 300 and 302 from diesel particulate matter (PM) and urban air particles using ultrasonically assisted extraction and accelerated solvent extraction methods, and evaluated the effects of sample and treatment parameters. The results show that accelerated solvent extraction can extract PAHs more efficiently from diesel PM than ultrasonically assisted extraction. They also show that PAHs are more difficult to extract from diesel PM than from urban air particles. Using toluene and maximum instrumental settings (200 degrees C, 3,000 psi and five extraction cycles) with 30-min static extraction times > 85% of the analytes were estimated to be extracted from the diesel particles, but four extraction cycles with just 5-min static extraction times under these conditions seem to be sufficient to extract > 95% of the analytes from the urban air particles. The accelerated solvent extraction method was validated using the Standard Reference Materials (SRM) 1649a, Urban Dust, and SRM 2975 and SRM 1650a, Diesel Particulate Matter, from the US National Institute of Standards and Technology (NIST). PAH concentrations determined by on-line high-performance liquid chromatography-gas chromatography-mass spectrometry (HPLC-GC-MS) following the developed accelerated solvent extraction method were generally higher than the certified and reference NIST values and concentrations reported in the literature (e.g. the estimated concentration of benzo[a]pyrene in SRM 2975 was 15-fold higher than the NIST-certified value), probably because the extraction recoveries were higher than in previous studies. The developed accelerated solvent extraction method was used to analyse high molecular (HMW) weight PAHs (MW > 302) in the investigated SRMs, and more than 170 (SRM 1649a), 80 (SRM 1650b) and 60 (SRM 2975) potential high molecular weight PAHs were tentatively identified in them, with molecular weights (depending on the SRM sample analysed) of 316, 326, 328, 340, 342, 350, 352, 366, 374 and 376. This is, to our knowledge, the first study to tentatively report PAHs with molecular weights of 316, 326, 328, 342, 350, 352, 366 and 376 in diesel particulate matter. GC-MS chromatograms obtained in selected ion monitoring mode (extracted ions for the abovementioned m/z) and full-scan mass spectra of tentatively identified high molecular weight PAHs are shown in the Electronic supplementary material.

Measurements of the Singly Ionized Oxygen Auroral Doublet Lines λλ7320, 7330 Using High‐Resolution Sky Spectra

The wavelengths of the individual [O II] 2s22p3 2D-2s22p3 2P λ7320 and [O II] 2s22p3 2D-2s22p3 2P λ7330 auroral doublet component lines have been measured directly in the nightglow for the first time, from high-resolution spectra obtained with the High Resolution Echelle Spectrophotometer (HIRES) spectrograph on the Keck I telescope at the W. M. Keck Observatory. Specifically, we find doublet splittings of 1.077±0.003 A and 1.080±0.003 A at λ7320 and λ7330, respectively, with the former significantly larger than the often quoted and utilized value of 0.8 A from Moore and in line with the National Institute of Standards and Technology (NIST) (1.07 A) as well as more recent astrophysical observations of the lines in planetary nebulae, including 1.07 A from De Robertis, Osterbrock, & McKee and 1.09 A from Barnett & McKeith. Our results suggest, however, that adjustments of +0.124 A and +0.131 A should be made to current NIST wavelengths for the blue and red components of the λ7320 doublet respectively, while our wavelengths of the λ7330 doublet components are little changed from current NIST values. The observed intensity ratio of λ7320/λ7330 from these measurements agrees with the theoretical value calculated under conditions of thermally populated 2Po levels.

NIST radiochemistry intercomparison program: a summary of four-year performance evaluation study

This paper summarizes the methods currently applied by the National Institute of Standards and Technology (NIST) for the preparation and verification of environmental and radiobioaasay performance evaluation materials for the traceability testing of low-level radioactivity measurements. The evaluation of measurement quality of the all participants indicated that over 90% of the intercomparison results complied with ANSI N42.22 and/or HPS N13.30 standards. Overall, the differences from the NIST values observed for all test nuclides and matrices are less than –7%, with a typical measurement precision better than 10% (1 s). The dependency of measurement quality on the test radionuclides, sample matrices, and radiochemical methods is identified by statistical analyses.

Critical Examination of the Quantification of Aromatic Compounds in Three Standard Reference Materials

Three standard reference materials from the National Institute of Standards and Technology (NIST), namely, SRM 1597 coal tar, 1582 crude oil, and 1580 shale oil, were investigated in detail to determine the concentration of polycyclic aromatic sulfur heterocycles using gas chromatography with the atomic emission detector in the carbon- and sulfur-selective modes. Coelution problems were found to be common, and the use of two capillary gas chromatographic columns with stationary phases of widely differing polarity was necessary for the separation of the important analytes phenanthrene, anthracene, dibenzothiophene, and the naphthothiophenes. On the commonly used nonpolar stationary phases, phenanthrene and dibenzothiophene coelute with the isomeric naphthothiophenes and this leads to too high concentrations being measured for the two major analytes and must be corrected for. For (sulfur and oxygen) heterocycles, individual response factors must be used if the flame ionization detector is employed. The NIST values were obtained without regard to those factors. This is done here for the three SRMs, and it is shown that the adjusted NIST values agree very well with the GC/AED values. It is suggested that the (noncertified) NIST values for several polycyclic aromatic compounds (PACs) should be reexamined. Very probably many other determinations of PACs might suffer from the same shortcomings.

Results of a NIST/VNIIOFI comparison of spectral-radiance measurements

A comparison of the spectral-radiance scales of the National Institute of Standards and Technology (NIST) and the All-Russian Research Institute for Optophysical Measurements (VNIIOFI) was carried out in 1989 and 1990. The spectral range of the comparison was between 240 nm and 2400 nm. The transfer standards were argon-filled tungsten ribbon filament lamps. The NIST/VNIIOFI agreement was 0,5 % to 1 % in the 240 nm to 800 nm range, and better than 0,5% between 900 nm and 2400 nm. On average, the spectral radiances measured at the VNIIOFI were slightly higher than the NIST values.

PS-39-3 A study of central and peripheral nerve conduction in primary hypothyroidism: the effect of treatment

This paper summarizes the methods currently applied by the National Institute of Standards and Technology (NIST) for the preparation and verification of environmental and radiobioaasay performance evaluation materials for the traceability testing of low-level radioactivity measurements. The evaluation of measurement quality of the all participants indicated that over 90% of the intercomparison results complied with ANSI N42.22 and/or HPS N13.30 standards. Overall, the differences from the NIST values observed for all test nuclides and matrices are less than –7%, with a typical measurement precision better than 10% (1 s). The dependency of measurement quality on the test radionuclides, sample matrices, and radiochemical methods is identified by statistical analyses.

FDA Quality assurance for radioactivity in foods and radiopharmaceuticals

The Food and Drug Administration (FDA) has regulatory responsibility for radionuclides in foods and radiopharmaceuticals and must maintain an ongoing Quality Assurance Program. These Quality Control Programs involve the U.S. Environmental Protection Agency (EPA) [1, 2] and the National Institute of Standards and Technology (NIST) [3], who supply the necessary reference materials and standards to ensure that the measurements are accurate and reproduceable. Data from EPA (1987 to 1991) and from a NIST “Blind” Source study (1985 to 1991) show the results are accurate with an average variation from NIST values of 1.8% [4–10]. The use of standard materials with the same matrices as the samples being analyzed provides credibility to the measurements.

Results of a CIE Detector Response Intercomparison.

A total of fifteen laboratories participated in the CIE detector response intercomparison which was designed to assess the level of agreement among participating laboratories in the absolute measurement (with respect to SI) of photodetector response in the visible spectral region. Most participants were either commercial laboratories or university laboratories with the National Institute of Standards and Technology (NIST) serving as the host laboratory. Each laboratory determined the absolute response of each of two silicon photodiode radiometers which were designed for the intercomparison by NIST. Approximately two-thirds of the laboratories reported response values which agreed with the NIST values to within ±1.0% at the two wavelengths of 488 and 633 nm.3