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1.
Desimoni and Brunetti raise some questions about the use of Eurachem/CITAC guide, because the Eurachem/CITAC guide does not
discuss an ISO recommendation before performing a test, it should be decided whether it is to be a test for conformity or
a test for non-conformity. In response, it is pointed out that although this recommendation is not discussed explicitly, it
is of necessity covered by the decision rule that describes how the measurement uncertainty will be taken into consideration
with regard to accepting or rejecting a product according to its specification and the result of a measurement. In addition,
they propose the introduction of an ‘inconclusive’ zone. We do not think that this is necessary, since the Eurachem/CITAC
guide takes the view that action on rejection should be covered by the ‘decision rule’ and this can make equivalent provision
for confirmation or interpretation. 相似文献
2.
Robin Willink 《Accreditation and quality assurance》2009,14(7):353-358
This paper builds on recent letters to the editor to consider different ways in which the ‘sample standard deviation’ of a
set of repeated measurements might be used in the expression of accuracy or uncertainty. A distinction is made between using
the sample standard deviation, s, to calculate a figure of merit for the measurement procedure and using s to express uncertainty in the estimate of a measurand. In particular, we consider whether s should be adjusted for bias. It is shown that most procedures involving s are valid without the application of any such adjustment. The paper emphasizes the importance of clear definitions and an
unambiguous statement of purpose, and also emphasizes the need for a distinction in notation between a random variable and
its observed value. 相似文献
3.
R. Willink 《Accreditation and quality assurance》2010,15(9):521-527
This article discusses the measurement of the sum of small positive quantities each estimated in separate analyses. It extends
criticism recently given of ‘objective Bayesian’ methodology (Accred Qual Assur 15:181–188, 2010) and identifies two troublesome
effects: the inherent bias in an analysis for a single quantity is compounded when the measurand is the sum of such quantities,
and the precaution of overestimating measurement variability can actually make the resulting interval of measurement uncertainty
less reliable! Unacceptable results are obtained. A cause of this behavior is identified, and a distinction between ‘objective’
and ‘subjective’ Bayesian statistics is discussed. 相似文献
4.
S. Sterlinski 《Journal of Radioanalytical and Nuclear Chemistry》2009,280(3):539-540
A paper by R. Michel in this journal (J. Radioanal. Nucl. Chem., 245 (2000) 137) describes, among other things, a numerical example: the calculation
of characteristic limits in an analysis of 129I via radiochemical NAA. A key problem in Bayesian characteristic limits is a proper formulation of the expression for the
uncertainty associated with the measurand if its true value is equal to zero, ũ(0). We show that MICHEL’s expression for ũ
2(0) is not correct and propose a new one. Some numerical errors found in the paper are also indicated. 相似文献
5.
M. Sanopoulou P. P. Roussis J. H. Petropoulos 《Journal of Polymer Science.Polymer Physics》1995,33(7):993-1005
Various aspects of the kinetics of sorption of acetone vapor by cellulose acetate films at 30°C have been studied in detail, the principal aim being to understand more thoroughly the physical nature and causes of non-Fickian behavior in this and other similar polymer-micromolecular penetrant systems. Particular attention was given to the changes in sorption (including absorption, desorption, and resorption) kinetics caused by (a) systematic variation of the vapor pressure of acetone in different ways and (b) changes in membrane thickness. It has been shown that both viscous volume swelling relaxation and longitudinal differential swelling stress effects must be invoked, in order to explain fully the observed behavior. Detailed analysis of two-stage sorption kinetics indicated (1) reasonable agreement between estimates of the diffusion coefficient reported by different authors, as long as a consistent analysis of the first stage is used, although the significance of the values given is open to some doubt, because the said first stage is found not to be free of non-Fickian features; and (2) reasonable conformity of the second stage to a first-order volume relaxation process (except a long times), with a relaxation frequency strongly dependent on the width of the concentration interval covered by the sorption experiment (and hence on the applied “osmotic stress”). The close similarity of second-stage sorption to nonlinear viscoelastic creep behavior, previously found in the cellulose-water system was confirmed and is taken further here, by demonstrating semiquantitative agreement between the corresponding “elastic swelling” and mechanical bulk moduli. ©1995 John Wiley & Sons, Inc. 相似文献
6.
Toman B Duewer DL Aragon HG Guenther FR Rhoderick GC 《Analytical and bioanalytical chemistry》2012,403(2):537-548
Several recent international comparison studies used a relatively novel experimental design to evaluate the measurement capabilities
of participating organizations. These studies compared the values assigned by each participant to one or more qualitatively
similar materials with measurements made on all of the materials by one laboratory under repeatability conditions. A statistical
model was then established relating the values to the repeatability measurements; the extent of agreement between the assigned
value(s) and the consensus model reflected the participants’ measurement capabilities. Since each participant used their own
supplies, equipment, and methods to produce and value-assign their material(s), the agreement between the assigned value(s)
and the model was a fairer reflection of their intrinsic capabilities than provided by studies that directly compared time-
and material-constrained measurements on unknown samples prepared elsewhere. A new statistical procedure is presented for
the analysis of such data. The procedure incorporates several novel concepts, most importantly a leave-one-out strategy for
the estimation of the consensus value of the measurand, model fitting via Bayesian posterior probabilities, and posterior
coverage probability calculation for the assigned 95% uncertainty intervals. The benefits of the new procedure are illustrated
using data from the CCQM-K54 comparison of eight cylinders of n-hexane in methane. 相似文献
7.
In this work a novel graphical method is applied to the presentation of intercomparison results. This is demonstrated with
the results of a recent intercomparison in measuring the 137Cs, 40K, and 90Sr activity concentration in milk powder. The “PomPlot”, an intuitive graphical method, is used for producing a summary overview
of the participants’ results of a common measurand. The “PomPlot” displays (relative) deviations of individual results from
the reference value on the horizontal axis and (relative) uncertainties on the vertical axis. 相似文献
8.
In the evaluation of measurement uncertainty, the uncertainty budget is usually used to identify dominant terms that contribute
to the uncertainty of the output estimate. Although a feature of the GUF method, it is also recommended as a qualitative tool
in MCM by using ‘nonlinear’ equivalents of uncertainty contributions and sensitivity coefficients. In this paper, the use
of ‘linear’ and ‘nonlinear’ parameters is discussed. It is shown that when and only when the standard uncertainty of the output
estimate is nearly equal to the square root of the sum of the squares of the individual uncertainty contributions, will the
latter be a reliable tool to detect the degree of contribution of each input quantity to the measurand uncertainty. 相似文献
9.
Michael Thompson 《Accreditation and quality assurance》2012,17(1):93-94
Uncertainty is defined in VIM3 as a ‘parameter’ but that, in my view, is a mistake that detracts from the clarity of the concept.
Trying to overcome the resulting difficulties while retaining ‘parameter’ has brought about progressive amendments to the
definition, and an increasing list of footnotes that have failed to resolve the issue. Surely the uncertainty of a result
is the density function (or mass function) that best describes the probability of possible values of the measurand. 相似文献
10.
I. Kuselman Ioannis Papadakis Wolfhard Wegscheider 《Accreditation and quality assurance》2001,6(2):78-79
A new composite score for the evaluation of performance of proficiency testing participants is proposed. The score is based
on a combination of the z-score, uncertainty of a participant’s measurement result and uncertainty of the proficiency testing
scheme’s assigned value. The use of such a composite score will allow evaluation not only of the participant’s ability to
determine an analyte in corresponding matrix, but also their understanding of the uncertainty in the obtained analytical result.
The score may be helpful for the laboratory’s quality system and for laboratory accreditation according to ISO 17025. 相似文献
11.
Alex Lepek 《Accreditation and quality assurance》1999,4(6):256-258
Type A statistical uncertainty in measurements is usually derived from the standard deviation of the measured data. This
is correct as long as the measurand is stable over time and has a meaningful constant value. In such a case the average measurement
and the standard deviations are meaningful. However, as measurement methods are refined and become more precise, we can observe
that a given measurand may be unstable and change with time and the uncertainty in measurement must be redefined. This is
specifically true in the metrology of time which can be measured today more precisly than any other measurand. We argue that
in such a case the uncertainty in the prediction of the next measurement should be used instead of the uncertainty in measurement.
Both uncertainties coincide for a stable measurand. The prediction of the next measurement is achieved by means of predictors.
In this paper we describe the application of linear predictors and especially optimum linear predictors to predict in the
presence of various types of instability. To illustrate the issues we use clock instabilities and clock metrology as this
field is most developed. A measurand can be unstable but still predictable and thus useful. This is well known in the case
of white noise about a linear drift for which the optimum predictor is a linear regression. Since the deviations from prediction
of optimum prediction are of white noise, we can now use simple statistics to estimate the uncertainty of the optimum or close
to optimum prediction. In this paper we present the various optimum or close to optimum linear predictors optimized for different
types of instability and estimate the associated prediction uncertainties. 相似文献
12.
A method is suggested for the calculation of a reference value and its uncertainty to be used in the frame of an interlaboratory
comparison (ILC). It is assumed that the reference value of the measurand is determined independently from the ILC round.
It is derived from a limited set of measurement results obtained from one or several expert laboratories. The procedure involves
three stages: (1) check of the experimental data and possible corrections; (2) check of the consistency of data, and possibly
increase of the uncertainties in order to attain internal consistency; (3) choice between fully, partially or un-weighted
mean. 相似文献
13.
V. Elia L. Elia N. Marchettini E. Napoli M. Niccoli E. Tiezzi 《Journal of Thermal Analysis and Calorimetry》2008,93(3):1003-1011
An extensive study has been carried out on aqueous ‘extremely diluted solutions’ (EDS). The employed experimental methodologies
were well established physico-chemical techniques: flux calorimetry, conductometry, pH-metry, e.m.f. of suitable galvanic
cell. The obtained results show that the preparation procedure significantly alters the physico-chemical behaviour of such
solutions. Moreover, the analysis of the experimental data vs. the ‘arrow of time’ turned out to be astonishingly important.
In fact some measured physico-chemical parameters evolve with time. Some experimentally measurable physico-chemical properties
of the solvent water were largely affected by both time and the ‘life path’ of the samples. In particular, we evidenced two
new experimental phenomena characterizing the EDS: the presence of a series of maximums in the measured electrical conductivity
vs. the sample age; the dependence of said maximums on the volume of the EDS during its ageing.
All of these new experimental results clearly suggest the presence of an extended and ‘ordered’ dynamics involving the whole
of the water molecules in the liquid. A temporal evolution, featuring three maximums in the course of four years of ageing
and the dependence on the ageing volumes do not fit the framework of classical thermodynamics. It therefore seems appropriate
to interpret these phenomena on the basis of the thermodynamics of dissipative structures, which are far from equilibrium
systems. 相似文献
14.
Determination of parathion in biological fluids by means of direct solid-phase microextraction 总被引:1,自引:0,他引:1
Gallardo E Barroso M Margalho C Cruz A Vieira DN López-Rivadulla M 《Analytical and bioanalytical chemistry》2006,386(6):1717-1726
A new and simple procedure for the determination of parathion in human whole blood and urine using direct immersion (DI) solid-phase
microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) is presented. This technique was developed using only
100 μL of sample, and ethion was used as internal standard (IS). A 65-μm Carbowax/divinylbenzene (CW/DVB) SPME fibre was selected
for sampling, and the main parameters affecting the SPME process such as extraction temperature, adsorption and desorption
time, salt addition, agitation and pH effect were optimized to enhance the sensitivity of the method. This optimization was
also performed to allow the qualitative determination of parathion’s main metabolite, paraoxon, in blood. The limits of detection
and quantitation for parathion were 3 and 10 ng/mL for urine and 25 and 50 ng/mL for blood, respectively. For paraoxon, the
limit of detection was 50 ng/mL in blood. The method showed linearity between the LOQ and 50 μg/mL for both matrices, with
correlation coefficients ranging from 0.9954 to 0.9999. Precision and accuracy were in conformity with the criteria normally
accepted in bioanalytical method validation. The mean absolute recoveries were 35.1% for urine and 6.7% for blood. Other parameters
such as dilution of sample and stability were also validated. Its simplicity and the fact that only 100 μL of sample is required
to accomplish the analysis make this method useful in forensic toxicology laboratories to determine this compound in intoxications,
and it can be considered an alternative to other methods normally used for the determination of this compound in biological
media. 相似文献
15.
Wilfried Hinrichs 《Accreditation and quality assurance》2010,15(5):289-296
The reliability of test results and subsequent classification statements or product certification depend on the variability
of the product’s properties and on the validity of the test procedures used. With an emphasis on measurement uncertainty,
producer’s and user’s risks as well as probabilities of conformance, conformity and classification are calculated exemplarily
for two requirements for mineral aggregates used in construction. An important methodological basis is an international draft
document on measurement uncertainty in conformity assessment. The mathematical instruments given are applied and further developed
to a risk scenario for product classification. The results from a classification point of view show that the reliability of
test results for acid-soluble sulphates is mostly acceptable and both the producer’s and user’s risks are quite small. In
contrast, the magnesium sulphate index test produces results which are hardly usable for classification and certification
purposes or for risk management in production. Product certification bodies should generally have an appropriate approach
when dealing with results where precision data are poor. 相似文献
16.
Keith S. Taber 《Foundations of Chemistry》2006,8(2):189-219
Constructivism has been a key referent for research into the learning of science for several decades. There is little doubt that the research into learners’ ideas in science stimulated by the constructivist movement has been voluminous, and a great deal is now known about the way various science topics may commonly be understood by learners of various ages. Despite this significant research effort, there have been serious criticisms of this area of work: in terms of its philosophical underpinning, the validity of its most popular constructs, the limited scope of its focus, and its practical value to science teaching. This paper frames this area of work as a Lakatosian Research Programme (RP), and explores the major criticisms of constructivism from that perspective. It is argued that much of the criticism may be considered as part of the legitimate academic debate expected within any active RP, i.e. arguments about the auxiliary theory making up the ‘protective belt’ of the programme. It is suggested that a shifting focus from constructivism to ‘contingency in learning’ will allow the RP to draw upon a more diverse range of perspectives, each consistent with the existing hard core of the programme, which will provide potentially fruitful directions for future work and ensure the continuity of a progressive RP into learning science. 相似文献
17.
Considering measurement uncertainty is mandatory in assessing conformance to legal or compositional limits, and specific guidelines
are available issued by ASME, ISO and Eurachem/CITAC. However, differences between ISO and EURACHEM/CITAC wordings could induce
some perplexities in the most careful readers. Possible problems arise from considering that, before performing a test, it
should be decided whether it is to be a test for conformity or a test for non-conformity. This choice could perhaps require
some renaming of acceptance/rejection zones as defined in the EURACHEM/CITAC Guide. A tentative solution is discussed in this
contribution. 相似文献
18.
Proficiency testing as a means of external quality assessment plays the role of independent evidence of laboratories’ performance.
To enable laboratories to fulfil the requirements stated in legislation, methodology for evaluation of laboratories’ performance
in proficiency testing schemes should incorporate principles of measurement results which are fit for intended use and incorporate
evaluation of laboratories’ performances based on independent reference value. A proficiency testing scheme was designed to
support Drinking Water Directive (98/83/EC) specifically. The methodology for performance evaluation, which takes into account
a “fitness for purpose”-based standard deviation for proficiency assessment, is proposed and discussed in terms of requirements
of the Drinking Water Directive. A ζ′-score, modified by application of target uncertainty was developed in a way that fulfils requirements defined in the legislation.
As an illustration, results are reported for nitrate concentration in water. The approach presented can also be applied to
other fields of measurements. 相似文献
19.
Sarela García-Santamarina Mariona García-Panyella Xavier Fuentes-Arderiu 《Accreditation and quality assurance》2006,10(12):686-689
According to ISO/CD 18113-1:2005, the conventional true value of a control material can be an assigned value (obtained with a primary or reference measurement procedure), a consensus value or a procedure-defined value. The present study demonstrates that, for some biological quantities, the overall consensus value (“trimmed” mean value”) obtained in a proficiency testing program, which includes all results independently of the method of measurement, is not acceptable as a surrogate for a primary or reference method value. Therefore, for the biological quantities taken into account in this study, overall consensus value is not as good as primary or reference method value to estimate systematic error.
Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. Apart from exceptional circumstances, they are not submitted to the usual referee procedure and go essentially unaltered. 相似文献