Quantification Of Measurement Uncertainty Research Articles

Single-Molecule Motility: Statistical Analysis and the Effects of Track Length on Quantification of Processive Motion

In vitro, single-molecule motility assays allow for the direct characterization of molecular motor properties including stepping velocity and characteristic run length. Although application of these techniques in vivo is feasible, the challenges involved in sample preparation, as well as the added complexity of the cell and its systems, result in a reduced ability to collect large datasets, as well as difficulty in simultaneous observation of the components of the motility system, namely motor and track. To address these challenges, we have developed simulations to characterize motility datasets as a function of sample size, processive run length of the motor, and distribution of track lengths. We introduce the use of a simple bootstrapping technique that allows for the quantification of measurement uncertainty and a Monte Carlo permutation resampling scheme for the measurement of statistical significance and the estimation of required sample size. In addition, we have found that, despite conventional wisdom, the measured characteristic run length is directly coupled to the characteristic track length that describes the microtubule length distribution. To be able to make comparisons between motility experiments performed on different track populations as well as make measurements of motility when motors and tracks cannot be simultaneously resolved, we have developed a theoretical framework for the determination of the effect that track length has on observed characteristic run lengths. This shows good agreement with in vitro motility experiments on two kinesin constructs walking on microtubule populations of different characteristic track lengths.

Quantitative Assessment of Single Molecule Motility In Vivo

In vitro single molecule motility assays allow for the direct characterization of molecular motor properties including stepping velocity and characteristic run length. While application of these techniques in vivo is feasible, the challenges involved in sample preparation as well as the added complexity of the cell and its systems result in reduced ability to collect large datasets, as well as difficulty in simultaneous observation of the components of the motility system, namely motor and track. To address these challenges, we have developed simulations to characterize motility datasets in order to understand data behavior and the effects of undersampling. We introduce the use of a simple bootstrapping technique that allows for the quantification of measurement uncertainty and a Monte Carlo permutation resampling scheme for the measurement of statistical significance and the estimation of required sample size. In addition, we have modeled motility collected in the absence of simultaneous track observation and developed a theoretical framework for the determination of characteristic run length in systems where motility and track length must be characterized sequentially, which shows good agreement with in vitro motility experiments on two kinesin constructs walking on microtubules stabilized by either paclitaxel or the GTP analog GMPCPP.

Vertical structure of Jupiter’s Oval BA before and after it reddened: What changed?

To constrain the properties of Oval BA before and after it reddened, we use Hubble methane band images from 1994 to 2009 to find that the distribution of upper tropospheric haze atop the oval and its progenitors remained unchanged, with reflectivity variations of less than 10% over this time span. We quantify measurement uncertainties and short-term fluctuations in velocity fields extracted from Cassini and Hubble data, and show that there were no significant changes in the horizontal velocity field of Oval BA in 2000, 2006, and 2009. Based on models of the oval’s dynamics, the static stability of the oval’s surroundings was also unchanged. The vertical extent of the oval did not change, based on the unchanged haze reflectivity and unchanged stratification. Published vortex models require Brunt–Väisälä frequencies of about 0.08 s −1 at the base of the vortex, and we combine this value with a review of prior constraints on the vertically variable static stability in Jupiter’s troposphere to show that the vortex must extend down to the condensation level of water in supersolar abundance. The only observable change was an increase in short-wavelength optical absorption that appeared not at the core of the oval, but in a red annulus. The secondary circulation in the vortex keeps this red annulus warmer than the vortex core. Although the underlying cause of the color change cannot be proven, we explore the idea that the new chromophores in the red annulus may be related to a global or hemispheric temperature change.

Sensitivity of multi-angle photo-polarimetry to vertical layering and mixing of absorbing aerosols: Quantifying measurement uncertainties

The impact of tropospheric aerosols on climate can vary greatly based upon relatively small variations in aerosol properties, such as composition, shape and size distributions, as well as vertical layering. Polarimetric measurements have been advocated in recent years as an additional tool to better understand and retrieve the aerosol properties needed for improved predictions of aerosol radiative forcing on climate. The goal of this study is to introduce a formal approach to assessing the sensitivity of both intensity and polarization signals to absorbing aerosol layering, explicitly accounting for instrument measurement uncertainties. If ignored, sensitivity to aerosol height can introduce biases in aerosol property retrievals at short (ultraviolet or blue) wavelengths; if properly exploited, it may enable the extraction of some basic information on aerosol profiles. Employing a vector successive-orders-of-scattering (SOS) radiative transfer code, we conducted modeling experiments to determine how the measured Stokes vector elements are affected at 446 nm (blue band) by the vertical distribution, mixing and layering of smoke and dust aerosols under the assumption of a simple Lambertian surface and predefined aerosol microphysical properties. We find that smoke and dust vertical layering, if ignored, can introduce biases in radiometric and polarimetric aerosol property retrievals for aerosol optical depth ( AOD) above 0.3 (polarimetric) and AOD above 0.5 (radiometric), and should, therefore, be accounted for in retrievals at high aerosol loadings.

Application of ANN and SVM for Uncertainty Quantification and Propagation

All measurements have error that obscures the true value. The error creates uncertainty about the quality of the measured value, which is requiring testing and calibration laboratories to provide estimates of uncertainty with their measurements. Measurement uncertainties include input uncertainty, the propagation of input uncertainty, the output uncertainty and the systematic error uncertainty. Several methods for estimating the uncertainty of measurements have been introduced for different kinds of uncertainty quantification, and two data mining methodologies-Artificial Neural Network (ANN) and Support Vector Machine (SVM) are used to build the unknown propagation model. This paper will discuss the quantification of measurement uncertainty (MU) and the separation of various uncertainty sources to MU and will discuss the advantages and limitations of SVM and ANN for building the propagation model of MU.

Development of UV/VIS spectrometric methodology for corrosion inhibitor residuals monitoring in oilfield brine

AbstractThis work focuses on the development of UV/VIS spectrometric methodology for corrosion inhibitor residuals monitoring in oilfield brine. There is no standard method for the determination of corrosion inhibitor concentration in oilfield brine. Developed methodology can be described as a rugged and simple alternative to the sophisticate separation techniques and can be easily applied in the field. The applicability of the method is demonstrated by the analyses of three commercial products. The extensive performance characteristics test, in combination with study and quantification of measurement uncertainty, shows that developed method meets all required criteria and can be directly applied for routine monitoring purposes within quality management system conditions. Therefore, this new method was accredited by the respectable accreditation agency. Valid and reliable determination of corrosion inhibitor residuals in oilfield brine is important in order to ensure effective corrosion protection of metal construction.

Comparação entre os métodos linear e não linear para a avaliação da incerteza de medição

O principal método reconhecido pelos metrologistas para a avaliação da incerteza de medição é de facto o Guia para a Expressão da Incerteza de Medição (Guia ISO). Entretanto, devido a algumas limitações do método proposto pelo Guia ISO, a ISO desenvolveu um método suplementar para a avaliação da incerteza de medição baseado na propagação de funções de densidade de probabilidade através do método de Monte Carlo (ISO-S1). O presente artigo visa discutir esses métodos de quantificação da incerteza de medição. Os autores realizam uma revisão da literatura focando nos principais artigos que apresentam essas abordagens modernas, bem como discutem os méritos e as limitações de ambos os métodos. Além disso, um estudo comparativo entre os métodos foi realizado através de dois estudos de caso. Os resultados obtidos mostraram que é necessário avaliar a influência do grau de não linearidade na estimativa da incerteza antes de optar por quaisquer um dos métodos

Uncertainty in field and laboratory acoustical testing: A challenge for the acoustical industry.

The statistical uncertainty in acoustical testing has been insufficiently studied in the acoustical community. There are a limited number of studies quantifying measurement uncertainties, especially in the field, but even where uncertainties have been documented, they are largely ignored in practice. As was documented in a previous case [LoVerde and Dong, J. Acoust. Soc. Am. 124, 2441 (2008)], it is common practice to assume that the test results have low uncertainties (even if published uncertainties are large) and that variations in the results are due to variations in materials, errors in construction, etc. This can be particularly important in noise litigation, where acoustical ratings that are lower than expected are often automatically assumed to be due to construction defect, even though they may be within the expected range. Even without errors in construction, the uncertainties in the acoustical test procedure may be such that some assemblies will meet the relevant statutory requirements and othe...

Evaluation of measurement uncertainties in human diffusion tensor imaging (DTI)‐derived parameters and optimization of clinical DTI protocols with a wild bootstrap analysis

To quantify measurement uncertainties of fractional anisotropy, mean diffusivity, and principal eigenvector orientations in human diffusion tensor imaging (DTI) data acquired with common clinical protocols using a wild bootstrap analysis, and to establish optimal scan protocols for clinical DTI acquisitions. A group of 13 healthy volunteers were scanned using three commonly used DTI protocols with similar total scan times. Two important parameters-the number of unique diffusion gradient directions (NUDG) and the ratio of the total number of diffusion-weighted (DW) images to the total number of non-DW images (DTIR)-were analyzed in order to investigate their combined effects on uncertainties of DTI-derived parameters, using results from both the Monte Carlo simulation and the wild bootstrap analysis of uncertainties in human DTI data. The wild bootstrap analysis showed that uncertainties in human DTI data are significantly affected by both NUDG and DTIR in many brain regions. These results agree with previous predictions based on error-propagations as well as results from simulations. Our results demonstrate that within a clinically feasible DTI scan time of about 10 minutes, a protocol with number of diffusion gradient directions close to 30 provides nearly optimal measurement results when combined with a ratio of the total number of DW images over non-DW images equal to six. Wild bootstrap can serve as a useful tool to quantify the measurement uncertainty from human DTI data.

The Multiple-Incremental Hole Drilling Method

Abstract Up to now the measurement uncertainties of residual stress determinations using the incremental hole-drilling-method had to be assessed by repeating the measurement at equivalent measurement spots or specimens. Often, the requirements for those repetitions are not given or the effort is spared. The determination of the stress state plus the related measurement uncertainty by only one course of measurement is the main feature of the Multiple-Incremental Hole Drilling Method developed by the Fraunhofer Institute for Mechanics of Materials IWM. The method is based on the generation and processing of multiple strain recordings for each depth increment through a stepwise enlargement of the hole in lateral direction. The results show that the new method allows revealing and quantifying measurement uncertainties of the determined stress-depth profile.

Quantification of measurement uncertainty in the sequential determination of 210Pb and 210Po by liquid scintillation counting and alpha-particle spectrometry

Methodologies for the quantification of measurement uncertainties associated with the determination of 210Pb- and 210Po-specific activities by liquid scintillation counting (LSC) and alpha-particle spectrometry are presented, and are demonstrated using the soil reference material IAEA-326. Major contributors to the combined uncertainty associated with the measurement result of 210Pb were the uncertainties of net count rates in the 210Pb energy region of the sample spectrum and in the 210Bi energy region of the blank spectrum. The predominant sources of uncertainty in the measurement of 210Po were the uncertainties of net count rates in the regions of interest of 209Po and 210Po. The relative standard uncertainty of 210Po exponentially increases with the time interval between the sampling date and the separation date of Po, and this effect is strongly dependent on the 210Po/210Pb activity ratio. When the specific activity of 210Pb is much higher than that of 210Po in the sample, the relative standard uncertainty of the 210Po determination increases significantly within a short time interval between the sampling date (or reference date) and the separation date of Po in samples.

Computer-assisted uncertainty assessment of k0-NAA measurement results

In quantifying measurement uncertainty of measurement results obtained by the k 0-based neutron activation analysis ( k 0-NAA), a number of parameters should be considered and appropriately combined in deriving the final budget. To facilitate this process, a program ERON (ERror propagatiON) was developed, which computes uncertainty propagation factors from the relevant formulae and calculates the combined uncertainty. The program calculates uncertainty of the final result—mass fraction of an element in the measured sample—taking into account the relevant neutron flux parameters such as α and f, including their uncertainties. Nuclear parameters and their uncertainties are taken from the IUPAC database (V.P. Kolotov and F. De Corte, Compilation of k 0 and related data for NAA). Furthermore, the program allows for uncertainty calculations of the measured parameters needed in k 0-NAA: α (determined with either the Cd-ratio or the Cd-covered multi-monitor method), f (using the Cd-ratio or the bare method), Q 0 (using the Cd-ratio or internal comparator method) and k 0 (using the Cd-ratio, internal comparator or the Cd subtraction method). The results of calculations can be printed or exported to text or MS Excel format for further analysis. Special care was taken to make the calculation engine portable by having possibility of its incorporation into other applications (e.g., DLL and WWW server). Theoretical basis and the program are described in detail, and typical results obtained under real measurement conditions are presented.

Quantifying Measurement Uncertainty of Thirty-Meter Shear-Wave Velocity

Thirty-meter shear-wave velocity ( V S 30) is commonly used to estimate near-surface conditions for site classification, seismic site response, liquefaction analysis, and other geotechnical earthquake engineering application. Quantifying the uncertainty in V S 30 measurements is important for determining the accuracy and precision of this geophysical test. This study gathers existing available comparative and blind shear-wave velocity tests to evaluate the apparent or observable intra- and intermethod variability. Presented in this article are estimates of V S 30 uncertainty for the invasive methods of downhole, suspension logging, and seismic cone penetration testing, the noninvasive method of spectral analysis of surface waves, and the method of shear-wave velocity correlated geologic units. Discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias. Results of this study indicate that uncertainty of shear-wave velocity measurements are on the order of 1%–3% coefficient of variation (standard deviation/mean) for downhole, suspension logging, and seismic cone penetration testing, 5%–6% coefficient of variation for spectral analysis of surface waves, and 20%–35% coefficient of variation for shear-wave velocity correlated geologic units. Presented here are procedures for propagating the uncertainty and/or bias in forward analyses.

Error analysis at the NSF-Arizona AMS facility

This article presents a detailed explanation of the analytical method used to monitor and quantify measurement uncertainties at the NSF-Arizona Accelerator Mass Spectrometry (AMS) Laboratory. The method is applicable to all of the isotopes measured at the facility, including 14C, 10Be, 129I and 26Al. It is used for a variety of analytical purposes, including: calculation of random machine error (rme), calculation of radiocarbon dates, and as an indicator of daily and long-term machine performance. An algorithm for a diagnostic program used to monitor rme is described in detail. The performance of the AMS machine as measured by rme calculations is given for the most recent six month period. The long-term accuracy of the machine is discussed in terms of blind sample analyses made under the Third (TIRI), Fourth (FIRI) and Fifth (VIRI) International Radiocarbon Intercomparisons.

Uncertainty and traceable calibration – how modern measurement concepts improve product quality in process industry

Research and advanced manufacturing demand high-quality measurement. This requires the statement of measurement uncertainty and the access to traceably calibrated instruments (with traceability to an international reference). Traceability is not obvious, however, for all kinds of industry measurements. Certain industries produce products whose quality control is based on the measurement of fuzzy, complex parameters, “attributes”. Many of these parameters are nowadays measured by sophisticated instruments. They are often automated and can perform an increased number of measurements during the day. Traceability is often a problem for this type of instruments. There are solutions to solve their lack of traceability, for example round-robin rings, but they must be handled with care. Quantifying measurement uncertainty may also become problematic, since the establishment of an uncertainty budget is difficult for automated or semi-automated instruments. If traceability is lacking, an important task will be to evaluate the uncertainty of the repeatability of the instrument since this will be an important part of the uncertainty budget. This article discusses problems and solutions, using the attributes paper pulp quality and smell as illustrations.

Characterization of Spectral Analysis of Surface Waves Shear Wave Velocity Measurement Uncertainty

The spectral analysis of surface waves (SASW) method is a nondestructive test for characterization of the variation with depth of the shear modulus of soils. While the testing procedure is well developed, only one preliminary study has investigated measurement uncertainty associated with SASW, and the methods utilized to quantify measurement uncertainty were prohibitive to routine assessment. Knowledge of this uncertainty, and ability to include its assessment in routine testing, would allow for inclusion of SASW results in reliability-based design and in assessment of the spatial variability of shear modulus. In this study, a large sample of test data was collected from two test sites. Characteristic statistics, statistical distribution, and measurement uncertainty were determined for each phase of SASW. Using the empirical statistical properties and measurement uncertainty results as validation criteria, an analytically based uncertainty assessment system was developed. Phase angle, inverse phase angle, and phase velocity data typically display a coefficient of variation (COV) of 2%, and the COV for combined phase velocity data is typically 1.5%. The COV for shear wave velocity is typically between 5 and 10%, and thus the inversion appears to magnify measurement uncertainty. Phase angle, inverse phase angle, phase velocity, and combined phase velocity data are normally distributed. Shear wave velocity samples at a given depth are generally normally distributed. Using a small sample of experimental data and the analytically based process developed in this study, the measurement uncertainty of SASW test results can be assessed as part of routine testing.

Characterization of SASW Phase Angle and Phase Velocity Measurement Uncertainty

Abstract The spectra-analysis-of-surface-waves (SASW) method is a nondestructive test for characterization of the variation with depth of the shear wave velocity of soils. While the testing procedure is well developed, only one preliminary study has investigated measurement uncertainty associated with SASW, and the methods utilized to quantify measurement uncertainty were prohibitive to routine assessment. Knowledge of this uncertainty, and ability to include its assessment in routine testing, would allow for inclusion of SASW results in reliability based design and in assessment of the spatial variability of shear modulus. In this study, a large sample of test data was collected from two test sites. Characteristic statistics, statistical distribution, and measurement uncertainty were determined for each phase of SASW. Using the empirical statistical properties and measurement uncertainty results as validation criteria, an analytically based uncertainty assessment system was developed. Specifically, it was shown that SASW phase angle and inverse phase angle typically display a coefficient of variation (COV) of 2 %, and samples appear normally distributed. Further, SASW phase velocity data typically display a coefficient of variation (COV) of 2 %, and the COV for combined phase velocity data is typically 1.5 %. Both phase velocity and combined phase velocity samples appear normally distributed. In addition, it was found that by using a small sample of experimental data and the analytically based process developed in this study, measurement uncertainty of SASW phase angle and phase velocity could be assessed as part of routine testing.

Evaluation of the analytical method performance for incurred samples

A methodology for the evaluation of the performance of an analytical method for incurred samples is presented. Since this methodology is based on intra-laboratory information, it is suitable for analytical fields that lack reference materials with incurred analytes and it can be used to evaluate the analytical steps prior to the analytical portion, which are usually excluded in proficiency tests or at the certification of reference materials. This methodology can be based on tests performed on routine samples allowing the collection of information on the more relevant combinations analyte/matrix; therefore, this approach is particularly useful for analytical fields that involve a high number of analyte/matrix combinations, which are difficult to cover even considering the frequent participation in expensive proficiency tests. This approach is based on the development of a model of the performance of the analytical method based on the differential approach for the quantification of measurement uncertainty and on the comparison of recovery associated with each one of the analytical steps whose performance can vary with the analyte origin, for spiked and incurred samples. This approach was applied to the determination of pesticide residues in apples. For the analytes covered, no evidence was found that the studied sample processing and extraction steps performance for this matrix varies with the analyte origins.

In situ measurement of the aerosol extinction‐to‐backscatter ratio at a polluted continental site

The extinction‐to‐backscatter ratio S is a crucial parameter for quantitative interpretation of lidar data, yet empirical knowledge of S for tropospheric aerosols is extremely limited. Here we review that knowledge and extend it using a recently developed in situ technique that employs a 180° backscatter nephelometer. This technique allows robust quantification of measurement uncertainties and permits correlations with other aerosol and meteorological properties to be explored. During 4 weeks of nearly continuous measurements in central Illinois, S was found to vary over a wide range, confirming previous indications that geographical location by itself is not necessarily a good predictor. The data suggest a modest dependence of S on relative humidity, but this explains only a small portion of the variation. Most variation was associated with changes between two dominant air mass types: rapid transport from the northwest and regional stagnation. The latter category displayed much higher aerosol concentrations and a systematically higher and more tightly constrained range of S. Averages and standard deviations were 64±4 sr for the stagnant category and 40±9 sr for the rapid transport category. Considering the 95% confidence precision uncertainty of the measurements, the difference between these averages is at least 13 sr and could be as large as 35 sr. The wavelength dependence of light scattering, as measured by a conventional nephelometer, is shown to have some discriminatory power with respect to S.

Hot-dome anemometry

Hot-dome anemometry obtains three components of flow velocity using an array of sensors, specifically five hot films in the present contribution, which are mounted around the hemispherical tip of a cylindrical support. Calibration for speed and angle resembles that of hot wires and split films except that the procedures accommodate heat transfer dominated by forced convection from the surface of a sphere rather than single or multiple cylinders. Measurements are obtained with hot domes, conventional hot wires, and impact probes in the wake of a wing to quantify measurement uncertainties.