| 1. |
- Warnecke, H., et al.
(författare)
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New metrological capabilities for measurements of dynamic liquid flows
- 2022
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Ingår i: Metrologia. - : IOP Publishing Ltd. - 0026-1394 .- 1681-7575. ; 59:2
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Tidskriftsartikel (refereegranskat)abstract
- The capability to calibrate flow and volume devices dynamically has gained increasing interest over the years. Within the scope of the EMPIR project 17IND13 'Metrology for real-world domestic water metering', several test rigs were developed with which dynamic flow profiles can be generated and measured that reflect characteristics of real-world drinking water consumption. The dynamic component of the test rigs is realized based on different technologies such as valves, cavitation nozzles or piston provers. For validation purposes, an intercomparison of the test rigs was carried out in the scope of an EURAMET pilot study no. 1506. Between September 2020 and February 2021, a transfer standard specially developed for the intercomparison was calibrated at eight laboratories. The measurement error was determined for three dynamic flow profiles representative of drinking water consumption in Europe. In addition to determining the measurement errors and the degree of equivalence, five additional key parameters were derived to characterize the test rig properties: (1) repeatability of the profile measurements, (2) mean value of the residuals, (3) deviation between measured total mass and total mass resulting from the given profile and (4) duration of the flow change for an increasing change (5) and duration of the flow change for a decreasing change. These key parameters comprehensively describe the quality with which the dynamic flow profiles were generated and measured on the test rigs and can be used for evaluations in future intercomparisons of this kind. A main outcome of the intercomparison is that there is no technology to be preferred in terms of technical implementation. All test rigs agree well with each other, taking into account their expanded measurement uncertainties.
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| 2. |
- Janssen, T J B M, et al.
(författare)
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Precision comparison of the quantum Hall effect in graphene and gallium arsenide
- 2012
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Ingår i: Metrologia. - : Institute of Physics. - 0026-1394 .- 1681-7575. ; 49:3, s. 294-306
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Tidskriftsartikel (refereegranskat)abstract
- The half-integer quantum Hall effect in epitaxial graphene is compared with high precision to the well-known integer effect in a GaAs/AlGaAs heterostructure. We find no difference between the quantized resistance values within the relative standard uncertainty of our measurement of 8.7 x 10(-11). The result places new tighter limits on any possible correction terms to the simple relation R-K = h/e(2), and also demonstrates that epitaxial graphene samples are suitable for application as electrical resistance standards of the highest metrological quality. We discuss the characterization of the graphene sample used in this experiment and present the details of the cryogenic current comparator bridge and associated uncertainty budget.
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| 3. |
- Amer, Eynas, et al.
(författare)
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Towards traceable dynamic pressure calibration using a shock tube with an optical probe for accurate phase determination
- 2022
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Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 59:3
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduce a robust method for dynamic characterization of pressure measuring systems used in time-varying pressure applications. The dynamic response of the pressure measuring systems in terms of sensitivity and phase as a function of frequency at various amplitudes of the measurand can be provided. The shock tube which is the candidate primary standard for dynamic pressure calibration at the National Laboratory for pressure, Sweden, was used to realize the dynamic pressure. The shock tube setup used in this study can realize reference pressure with amplitudes up to 1.7 MPa in the frequency range from below a kilohertz up to a megahertz. The amplitude of the realized step pressure was calculated using the Rankine–Hugoniot step relations. In addition, the accurate time of arrival of the generated shock at the device under test (DUT) was measured using an optical probe based on shadowgraphy. The optical detector has a response time in nanosecond time scale which is several orders of magnitude faster than the response time of any pressure measuring system. Hereby, the latency between physical stimuli and response of the DUT can be measured. By the knowledge of the amplitude and the accurate time of arrival of the reference step pressure, the transfer function of the DUT can be calculated and presented in Bode diagrams of sensitivity and phase response versus frequency. The uncertainty in sensitivity and phase measurements was estimated. The information provided by this work is useful for developing reliable models of dynamic pressure measuring system and provide accurate information about their dynamic response. That in turn will contribute to establish a traceability chain for dynamic pressure calibration.
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| 4. |
- Bodnar, Olha, senior lecturer, 1979-, et al.
(författare)
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Bayesian estimation in multivariate inter-laboratory studies with unknown covariance matrices
- 2023
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Ingår i: Metrologia. - : IOP Publishing Ltd. - 0026-1394 .- 1681-7575. ; 60:5
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Tidskriftsartikel (refereegranskat)abstract
- In the paper we present Bayesian inference procedures for the parameters of multivariate random effects model, which is used as a quantitative tool for performing multivariate key comparisons and multivariate inter-laboratory studies. The developed new approach does not require that the reported covariance matrices of participating laboratories are known and, as such, it can be used when they are estimated from the measurement results. The Bayesian inference procedures are based on samples generated from the derived posterior distribution when the Berger and Bernardo reference prior and the Jeffreys prior are assigned to the model parameter. Three numerical algorithms for the construction of Markov chains are provided and implemented in the CCAUV.V-K1 key comparisons. All three approaches yield similar Bayesian estimators with wider credible intervals when the Berger and Bernardo reference prior is used. Also, the Bayesian estimators for the elements of the inter-laboratory covariance matrix are larger under this prior than for the Jeffreys prior. Finally, the constructed joint credible sets for the components of the overall mean vector indicate the presence of linear dependence between them which cannot be captured when only univariate key comparisons are performed.
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| 5. |
- Bodnar, Olha, senior lecturer, 1979-, et al.
(författare)
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Bayesian estimation in multivariate inter-laboratory studies with unknown covariance matrices
- 2023
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Ingår i: Metrologia. - : IOP Publishing Ltd. - 0026-1394 .- 1681-7575. ; 60:5
-
Tidskriftsartikel (refereegranskat)abstract
- In the paper we present Bayesian inference procedures for the parameters of multivariate random effects model, which is used as a quantitative tool for performing multivariate key comparisons and multivariate inter-laboratory studies. The developed new approach does not require that the reported covariance matrices of participating laboratories are known and, as such, it can be used when they are estimated from the measurement results. The Bayesian inference procedures are based on samples generated from the derived posterior distribution when the Berger and Bernardo reference prior and the Jeffreys prior are assigned to the model parameter. Three numerical algorithms for the construction of Markov chains are provided and implemented in the CCAUV.V-K1 key comparisons. All three approaches yield similar Bayesian estimators with wider credible intervals when the Berger and Bernardo reference prior is used. Also, the Bayesian estimators for the elements of the inter-laboratory covariance matrix are larger under this prior than for the Jeffreys prior. Finally, the constructed joint credible sets for the components of the overall mean vector indicate the presence of linear dependence between them which cannot be captured when only univariate key comparisons are performed.
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| 6. |
- Bodnar, Olha, senior lecturer, 1979-, et al.
(författare)
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Bayesian inference for heterogeneity in meta-analysis
- 2020
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Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 57:6
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Tidskriftsartikel (refereegranskat)abstract
- A generalized marginal random effects model is described that enables exact Bayesian inference using either the Jeffreys or Berger-Bernardo non-informative prior distributions without the need for Markov Chain Monte Carlo sampling, requiring only numerical integrations. This contribution focuses on inference for the heterogeneity parameter, often called "dark uncertainty" and denoted tau in this contribution. The proposed models are used for consensus building in meta-analyses of measurement results for the Newtonian constant of gravitation, G, and for the effectiveness of anti-retroviral pre-exposure prophylaxis in preventing HIV infection.The estimates of tau that seventeen alternative different methods produce, including those that we propose, were also compared. The relative impact (gauged in terms of the ratio of the range of estimates to their median) that model choice had on the estimate of tau was very substantial: 79 % for G and 87 % for HIV prophylaxis. For G, the estimates of tau ranged from 0.0009x10(-10)m(3)kg(-1)s(-2) to 0.0013x10(-10) m(3) kg(-1) s(-2). For Truvada they ranged from 0.49 to 0.92.Since the estimate of tau impacts the quality of the estimate of the measurand substantially, we recommend the Bayesian approaches to estimate tau because they take the whole posterior distribution of tau into account, hence the corresponding uncertainty, rather than using a single value and pretending that it is known with certainty.In the case of the measurement results for G, we found that the model with Student's t random effects and the Jeffreys prior provides the best fit, while for the Truvada data the normal marginal random effects model, also with Jeffreys prior, produces an estimate of tau closest to classical estimators like DerSimonian-Laird, but offers the advantage of recognizing and propagating the uncertainty associated with tau, which the classical procedures ignore.
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| 7. |
- Bodnar, Olha, senior lecturer, 1979-, et al.
(författare)
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Bayesian inference for measurements of ionizing radiation under partial information
- 2017
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Ingår i: Metrologia. - : BIPM & IOP Publishing Ltd. - 0026-1394 .- 1681-7575. ; 54:3, s. 29-33
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Tidskriftsartikel (refereegranskat)abstract
- We derive a new Bayesian approach for estimating activity when partial information about the detection efficiency and the background activity is available. Explicit formulas based on the hypergeometric function are given for the mean and the variance of the obtained posterior distribution. A Monte Carlo method is developed that allows the results of the Bayesian procedure to be determined in a simple way. The proposed inference is illustrated by analyzing measurements of activity, and the results are compared with those obtained by applying a current ISO standard.
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| 8. |
- Dimarcq, N., et al.
(författare)
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Roadmap towards the redefinition of the second
- 2024
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Ingår i: Metrologia. - : Institute of Physics. - 0026-1394 .- 1681-7575. ; 61:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper outlines the roadmap towards the redefinition of the second, which was recently updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of optical frequency standards (OFS) call for reflection on the redefinition of the second, but open new challenges related to the performance of the OFS, their contribution to time scales and UTC, the possibility of their comparison, and the knowledge of the Earth’s gravitational potential to ensure a robust and accurate capacity to realize a new definition at the level of 10−18 uncertainty. The mandatory criteria to be achieved before redefinition have been defined and their current fulfilment level is estimated showing the fields that still needed improvement. The possibility to base the redefinition on a single or on a set of transitions has also been evaluated. The roadmap indicates the steps to be followed in the next years to be ready for a sound and successful redefinition.
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| 9. |
- Fu, Jinglin, et al.
(författare)
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Survey of bidirectional transmittance distribution function measurement facilities by multilateral scale comparisons
- 2024
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Ingår i: Metrologia. - : Institute of Physics. - 0026-1394 .- 1681-7575. ; 61:3
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, a growing demand for the capability of performing accurate measurements of the bidirectional transmittance distribution function (BTDF) has been observed in industry, research and development, and aerospace applications. However, there exists no calibration and measurement capabilities-entry for BTDF in the database of the Bureau International des Poids et Mesures and to date no BTDF comparison has been conducted between different national metrology institutes (NMIs) or designated institutes (DIs). As a first step to a possible future key comparison and to test the existing capabilities of determining this measurand, two interlaboratory comparisons were performed. In comparison one, five samples of three different types of optical transmissive diffusers were measured by five NMIs and one DI. By specific sample choice, the focus for this study lay more on orientation-dependent scatter properties. In comparison two, where one NMI, one DI, one university, and three industrial partners investigated their measurement capabilities, the dependence on the orientation was not assessed, but two additional samples of the same material and different thickness were measured. Results of the two comparisons are presented, giving a good overview of existing experimental solutions, and showing specific sample-related problems to be solved for improved future BTDF measurements.
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| 10. |
- He, Hans, et al.
(författare)
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Polymer-encapsulated molecular doped epigraphene for quantum resistance metrology
- 2019
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Ingår i: Metrologia. - : Institute of Physics Publishing. - 0026-1394 .- 1681-7575. ; 56:4
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Tidskriftsartikel (refereegranskat)abstract
- One of the aspirations of quantum metrology is to deliver primary standards directly to end-users thereby significantly shortening the traceability chains and enabling more accurate products. Epitaxial graphene grown on silicon carbide (epigraphene) is known to be a viable candidate for a primary realisation of a quantum Hall resistance standard, surpassing conventional semiconductor two-dimensional electron gases, such as those based on GaAs, in terms of performance at higher temperatures and lower magnetic fields. The bottleneck in the realisation of a turn-key quantum resistance standard requiring minimum user intervention has so far been the need to fine-tune the carrier density in this material to fit the constraints imposed by a simple cryo-magnetic system. Previously demonstrated methods, such as via photo-chemistry or corona discharge, require application prior to every cool-down as well as specialist knowledge and equipment. To this end we perform metrological evaluation of epigraphene with carrier density tuned by a recently reported permanent molecular doping technique. Measurements at two National Metrology Institutes confirm accurate resistance quantisation below 5n-1. Furthermore, samples show no significant drift in carrier concentration and performance on multiple thermal cycles over three years. This development paves the way for dissemination of primary resistance standards based on epigraphene
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