Maurice Cox - Academia.edu (original) (raw)

Papers by Maurice Cox

Accreditation and Quality Assurance, 2022

The Guide to the expression of uncertainty in measurement (GUM) has been the enduring guide on me... more The Guide to the expression of uncertainty in measurement (GUM) has been the enduring guide on measurement uncertainty for metrologists since its first publication in 1993. According to the GUM, a measurement should always be accompanied by a reasoned and defensible expression of uncertainty, and the primary such expression is the standard uncertainty. In this article, we distinguish between the use of an expression of uncertainty as information for the recipient of a measurement result and its use when propagating uncertainty about inputs to a measurement model in order to derive the uncertainty in a measurand. We propose a new measure of uncertainty, the characteristic uncertainty, and argue that it is more fit for these purposes than standard uncertainty. For the purpose of reporting a measurement result, we demonstrate that standard uncertainty does not have a meaningful interpretation for the recipient of a measurement result and can be infinite. These deficiencies are resolved...

Vector-based instrumentation for the determination of Specific Absorption Rate (SAR) uses measure... more Vector-based instrumentation for the determination of Specific Absorption Rate (SAR) uses measurements of the complex E-field inside a phantom at multiple locations. Re-construction algorithms are used to calculate the SAR and its peak spatial value. The required measurements can be made by using an E-field vector probe that is controlled by a robot, or by using a static array of vector probes (for example, dipole antennas and receivers). The latter approach potentially offers much reduced measurement times, which is particularly advantageous for type-approval tests on smart phones as these can have 30 or more transmitting modes. To enable traceable measurement of SAR, an array-based system requires calibration data for its individual antennas, which can be obtained by exposing the individual antennas to a characterised complex E-field from a stable antenna (which will be referred to as a reference antenna). This report describes the process for characterising a reference antenna: t...

This report describes a methodology for the measurement of large or complex artefacts by co-ordin... more This report describes a methodology for the measurement of large or complex artefacts by co-ordinate measuring machines (CMMs) using repositioning. The approach is applicable to measurement tasks where it is not possible or practical to measure all relevant parts of the workpiece surfaces without repositioning the artefact. By tracking the position of three or more registration points defmed by reference features (sphere centres, for example) that move rigidly with the workpiece it is possible to relate measurements taken in different positions to one frame of reference. Practical aspects of implementing the methodology are discussed and the results of measurement experiments presented. The method provides an effective way of extending significantly the measuring capability of a CMM.

WIT transactions on engineering sciences, 1970

While the verification of the performance of coordinate measuring machines (CMMs) is self-evident... more While the verification of the performance of coordinate measuring machines (CMMs) is self-evidently important, the point coordinates they provide are usually the input to form and tolerance assessment software that calculate associated geometric features, such as a best fit cylinder to the data. For the measurement result to be reliable, it is also necessary to ensure that the calculations performed by this software are fit for purpose. The forthcoming standard ISO 10360-6:2001 [1] specifies the procedure by which Gaussian (least-squares) form assessment software should be tested. Many tolerance assessment problems relate to Chebyshev (minimumzone) fitting criteria in which the maximum error is minimized. These criteria lead to nonlinearly constrained optimization problems that are difficult to solve reliably if appropriate algorithms are not employed. Many existing and proposed algorithms fail on seemingly simple data sets. In this paper we examine the problem of how to generate re...

International Journal of Environmental Research and Public Health, 2020

The authors of this reply published an article in International Journal of Environmental Research... more The authors of this reply published an article in International Journal of Environmental Research and Public Health and received comments from Douglas and Kuster. Responses are made to these comments with complementary explanations and numerical results.

Metrologia, 2019

According to the CIPM Mutual Recognition Arrangement, a calibration and measurement capability (C... more According to the CIPM Mutual Recognition Arrangement, a calibration and measurement capability (CMC) uncertainty for a laboratory offering a particular calibration or measurement service is normally expressed at a \SI{95}{\percent} level of confidence. When laboratories' CMC claims are unsupported by the relevant key comparison (KC), one option is for modified values to be assigned to their CMC uncertainties. In many cases when CMCs apply to a continuous interval of values such as mass concentration or wavelength, there is no directly relevant KC that can be used in support since KCs are carried out only for selected discrete values of the quantity concerned. Under realistic assumption, we developed a method that is applicable in such an instance and for which the reported CMC uncertainties are amplified so that they are underpinned by the results of the KC. The amplification factors depend on the laboratories' degrees of equivalence (DoEs) for these discrete values, and judiciously adjusted to achieve consistency with the key comparison reference values. The method is based on the patterns in the individual behaviour of the DoEs of the participating laboratories for the discrete values, implying the presence of correlation associated with the DoE values. It applies when the weighted mean of some or all of the measured values reported by the participating laboratories in the KC is used to obtain the KC reference value.

Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine, Jun 16, 2016

Over the last years (177)Lu has received considerable attention from the clinical nuclear medicin... more Over the last years (177)Lu has received considerable attention from the clinical nuclear medicine community thanks to its wide range of applications in molecular radiotherapy, especially in peptide-receptor radionuclide therapy (PRRT). In addition to short-range beta particles, (177)Lu emits low energy gamma radiation of 113keV and 208keV that allows gamma camera quantitative imaging. Despite quantitative cancer imaging in molecular radiotherapy having been proven to be a key instrument for the assessment of therapeutic response, at present no general clinically accepted quantitative imaging protocol exists and absolute quantification studies are usually based on individual initiatives. The aim of this work was to develop and evaluate an approach to gamma camera calibration for absolute quantification in tomographic imaging with (177)Lu. We assessed the gamma camera calibration factors for a Philips IRIX and Philips AXIS gamma camera system using various reference geometries, both ...

Physics in Medicine and Biology, 2015

International Progress in Precision Engineering, 1993

Coordinate metrology plays a key role in computer-aided inspection in modern manufacturing. A maj... more Coordinate metrology plays a key role in computer-aided inspection in modern manufacturing. A major component of this activity is the assessment software which analyses the data gathered by a coordinate measuring machine from the surface of a manufactured workpiece. How can we be sure that this software is giving correct results? If this type of measurement activity is to be traceable to national standards for length then it is important to have a satisfactory answer to this question. In this paper, we argue for the creation of a standards infrastructure for coordinate metrology software and discuss current activity in this field.

Series on Advances in Mathematics for Applied Sciences, 2000

ABSTRACT

Measurement Science and Technology, 2007

The performance of underwater electroacoustic transducers often depends on water temperature and,... more The performance of underwater electroacoustic transducers often depends on water temperature and, for accurate calibrations, it is necessary to take account of this influence on measurement data. Doing so is particularly important for open-water calibration facilities where the environmental conditions cannot be controlled and seasonal variations in temperature can contribute significant measurement uncertainty. This paper describes the characterization of the sensitivity of underwater electroacoustic transducers in terms of their variation with water temperature. A model containing adjustable parameters is developed for providing frequency-dependent temperature coefficients whose use enables measurement data to be corrected for temperature. Estimates of these coefficients are determined by applying the model to the time history of measurement data obtained over a period of several years. The influence of seasonal temperature variation can then be separated from the slow temporal drift in the transducer sensitivity. The uncertainties associated with the corrected sensitivity values are evaluated.

International Journal of Thermophysics, 2008

: The least-squares analysts of Two-Way Satellite Time and Frequency (TWSTFT) data, with the aim ... more : The least-squares analysts of Two-Way Satellite Time and Frequency (TWSTFT) data, with the aim of determining optimal estimates of phase and frequency offsets, is considered. An overview of the application of Gauss-Markov estimation to the analysts of a uniformly spaced time series is presented. Two aspects of TWSTFT data analysis are examined in depth. Firstly, measures based on second difference statistics for characterizing the consistently but unevenly spaced TWSTFT measurements are introduced. Secondly, an approach to the estimation of the occasional and unknown delay steps in TWSTFT data, for example due to hardware replacement, is presented.

Metrologia

The medical use of radionuclides depends on the accurate measurement of activity (Bq) for regulat... more The medical use of radionuclides depends on the accurate measurement of activity (Bq) for regulatory compliance, patient safety, and effective treatment or image quality. In turn, these measurements rely on the realization of primary standards of activity by national metrology institutes, with uncertainties that are fit for purpose. This article reviews the current status of primary standards of activity for radionuclides used in medical imaging and therapy applications. Results from international key comparisons carried out through the International Bureau of Weights and Measures transfer instruments (SIR and SIRTI) are used to verify that standards for a variety of radionuclides are consistent and conform with practitioners’ expectations.

Metrologia, 2017

The eutectic alloys rhenium–carbon, platinum–carbon and cobalt–carbon have been proposed as refer... more The eutectic alloys rhenium–carbon, platinum–carbon and cobalt–carbon have been proposed as reference standards for thermometry, with temperature and uncertainty values specified within the mise en pratique of the definition of the kelvin. These alloys have been investigated in a collaboration of eleven national measurement institutes and laboratories. Published results reported the point-of-inflection in the melting curve with extremely low uncertainties. However, to be considered as standards it is necessary to stipulate what phenomenon a temperature value has been ascribed to; specifically, this should be a thermodynamic state. Therefore, the data have been further evaluated and the equilibrium liquidus temperatures determined based on a consideration of limits and assuming a rectangular probability distribution. The values are: for rhenium–carbon 2747.91 ± 0.44 K, for platinum–carbon 2011.50 ± 0.22 K and for cobalt–carbon 1597.48 ± 0.14 K, with uncertainties at approximately a 95% coverage probability. It is proposed that these values could be used as the basis of thermodynamic temperature measurement at high temperatures (above 1300 K).

Accreditation and Quality Assurance