Key Error Sources Research Articles

External calibration for laser altimetry mission in Chang’E-1

When calculating the lunar digital elevation model by using LAM data of ChangE-1 lunar orbiter, the radical error of measurement in lunar mass center fixed coordinate is one kind of the key error sources. For LAM, two stages of oscillators, with one from satellite bus system and one from LAM itself, supplied time synchronization, timing and frequency standard of lunar altimetry. The independent unstable oscillations of them created the relevant errors to LAM. We analyzed the time slips and drifts in data time tags, estimated the possible systematic bias of reference frequency of LAM oscillator. Then we calibrated the effects of them on LAM data. The budgets of these three kinds of error sources are 0.7-1.2 m, ~10 m and ~145 m, respectively. Using the calibrated LAM data, a new 360 orders and degrees lunar topography model, CLTM-s03, has been obtained. By combining the new DEM model of the moon with CEGM02 lunar gravity model, a couple of middle scale type II lunar mascon basins, Fitzgerald-Jackson and Amundsen-Ganswindt, have been newly identified.

Miss Distance Error Analysis of Strapdown Seeker Imaging System

Providing an exact miss distance is the goal of strapdown seeker imaging system. Real-time correction of target miss distance is always introduced. The values of miss distance are the key factor influencing exactness of LOS (line of sight) rates. Thus the miss distance needs to be stable. Three key measurement error sources of strapdown seeker imaging system are analyzed. There are imaging errors, tracking errors and time delay errors. The causes of different errors are discussed in this paper. The influence of the errors on outputting of miss distance is analyzed. The goal of image error analysis is to reduce the errors. Finally, some methods for reducing error are presented.

Measurement repeatability of tibial tuberosity-trochlear groove offset distance in red fox (Vulpes vulpes) cadavers

To describe CT image reconstruction criteria for measurement of the tibial tuberosity-trochlear groove (TT-TG) offset distance, evaluate intra- and inter-reconstruction repeatability, and identify key sources of error in the measurement technique, as determined in vulpine hind limbs. 12 red fox (Vulpes vulpes) cadavers. CT images of each hind limb in intact cadavers were obtained; at 1-week intervals, 3 reconstructions were performed that were based on 1 plane passing through the centers of the femoral head and medial condyle and parallel to the caudal femoral condyles, 1 plane aligned with the femoral trochlea, and a third orthogonal plane. Randomized and anonymized reconstructions were assessed for TT-TG offset distance with a single-image technique by 1 observer, and inter-reconstruction repeatability and intra- and inter-reconstruction measurement repeatability were assessed via the repeatability coefficient and intraclass correlation coefficient. Multiplanar reconstructions of hind limb images were repeatedly made to within a few degrees of each other. Intra- and inter-reconstruction repeatability for TT-TG offset distance measurement was good. Repeatability was most affected by accurate identification of the tibial tuberosity and femoral trochlea landmarks. Results obtained from vulpine hind limb CT images indicated that reconstructions can be made with a high degree of repeatability when based on strictly defined and applied criteria. The TT-TG offset distance has potential as an objective assessment of alignment of the distal portion of the quadriceps mechanism; its use as an aid in case selection for corrective femoral osteotomy among dogs with medial patellar luxation warrants investigation.

An Ultra-High-Speed Scheimpflug Camera for Evaluation of Corneal Deformation Response and Its Impact on IOP Measurement

To investigate the test-retest variability of and factors associated with the corneal deformation response, and evaluate its impact on IOP measurement. Forty normal and 140 glaucoma suspect/glaucomatous eyes of 104 individuals were prospectively included for repeated measurements of corneal deformation response by an ultra-high-speed Scheimpflug camera, followed by corneal hysteresis and corneal resistance factor measurements by the ocular response analyzer, and dynamic contour tonometry (DCT) (the reference standard) and Goldmann applanation tonometry (GAT) during the same visit. The test-retest variability of corneal deformation response was evaluated. Univariate and multivariate linear mixed models were used to identify factors (age, manifest spherical refractive error, axial length, IOP, central corneal thickness [CCT], corneal curvature, corneal hysteresis, and corneal resistance factor) associated with corneal deformation response and the difference between DCT and GAT measurements. Corneal deformation amplitude (CDA) had an intraclass correlation coefficient of 0.86. There was no difference in CDA between the glaucoma and nonglaucoma groups. A higher IOP, a younger age, and a greater CCT were associated with a smaller CDA (P ≤ 0.002) (n = 180). In the univariate analysis (n = 180), the difference between DCT and GAT measurements was associated with spherical refractive error (P = 0.037), CCT (P = 0.004), and CDA (P < 0.001) after adjusting the effect of IOP (DCT). In the multivariate analysis, the only factor associated with the IOP difference was CDA (P = 0.003). CDA was a reliable indicator to quantify corneal deformation response. CDA, rather than CCT, was the key source of measurement error of GAT.

Modeling the Microstructure Curvature of Boron-Doped Silicon in Bulk Micromachined Accelerometer.

Microstructure curvature, or buckling, is observed in the micromachining of silicon sensors because of the doping of impurities for realizing certain electrical and mechanical processes. This behavior can be a key source of error in inertial sensors. Therefore, identifying the factors that influence the buckling value is important in designing MEMS devices. In this study, the curvature in the proof mass of an accelerometer is modeled as a multilayered solid model. Modeling is performed according to the characteristics of the solid diffusion mechanism in the bulk-dissolved wafer process (BDWP) based on the self-stopped etch technique. Moreover, the proposed multilayered solid model is established as an equivalent composite structure formed by a group of thin layers that are glued together. Each layer has a different Young’s modulus value and each undergoes different volume shrinkage strain owing to boron doping in silicon. Observations of five groups of proof mass blocks of accelerometers suggest that the theoretical model is effective in determining the buckling value of a fabricated structure.

Sensitivity Analysis of Geometric Errors for Five-Axis CNC Machine Tool Based on Multi-Body System Theory

Abstract: In order to determine that the effect of geometric error to the machining accuracy is an important premise for the error compensation, a sensitivity analysis method of geometric error is presented based on multi-body system theory in this paper. An accuracy model of five-axis machine tool is established based on multi-body system theory, and with 37 geometric errors obtained through experimental verification, key error sources affecting the machining accuracy are finally identified by sensitivity analysis. The analysis result shows that the presented method can identify the important geometric errors having large influence on volumetric error of machine tool and is of help to improve the accuracy of machine tool economically.

Improving sub‐daily strain estimates using GPS measurements

We present an improved GPS analysis strategy that reduces the noise level of GPS‐based sub‐daily strain measurements by a factor of ~5 or more and improves sub‐daily resolution of positions and baseline estimates by a factor of ~2–5. These improvements are accomplished by reducing the key sources of error due to diurnal effects from path delays caused by reflections and refractions of the GPS signal near the receiver (multipath), and from tropospheric delays. Errors due to poorly determined tropospheric path delays are mitigated by using the tropospheric parameters estimated in static positioning runs as fixed values. The multipath effects are treated as periodic errors and are mitigated by a modified sidereal filter applied to the phase prior to processing. This combination of path error modeling results in sub‐daily strain resolution on the order of ~0.1μstrain for a ~100 km baseline.

Towards improved damage location using acoustic emission

The acoustic emission technique is a passive non-destructive testing technique that has significant potential for use as a structural health monitoring technique for many large-scale structures, allowing continuous global monitoring. The location capability of the acoustic emission technique is its most beneficial attribute; however, the location accuracy can often be limited in complex materials and structures. This article discusses recent advances in the location of acoustic emission signals. The key sources of errors are identified as signal arrival time measurement and processing algorithm limitations. A series of strategies for reducing the effects of both causes of error are presented. Additionally, the results of a case study are used to demonstrate a novel mapping technique for acoustic emission source location of fatigue crack signals in an aircraft landing gear component. Improvements in location accuracy of up to 87.5% were observed when compared with standard location calculation algorithms.

Calculation of Host-Guest Binding Affinities Using a Quantum-Mechanical Energy Model.

The prediction of protein-ligand binding affinities is of central interest in computer-aided drug discovery, but it is still difficult to achieve a high degree of accuracy. Recent studies suggesting that available force fields may be a key source of error motivate the present study, which reports the first mining minima (M2) binding affinity calculations based on a quantum mechanical energy model, rather than an empirical force field. We apply a semi-empirical quantum-mechanical energy function, PM6-DH+, coupled with the COSMO solvation model, to 29 host-guest systems with a wide range of measured binding affinities. After correction for a systematic error, which appears to derive from the treatment of polar solvation, the computed absolute binding affinities agree well with experimental measurements, with a mean error 1.6 kcal/mol and a correlation coefficient of 0.91. These calculations also delineate the contributions of various energy components, including solute energy, configurational entropy, and solvation free energy, to the binding free energies of these host-guest complexes. Comparison with our previous calculations, which used empirical force fields, point to significant differences in both the energetic and entropic components of the binding free energy. The present study demonstrates successful combination of a quantum mechanical Hamiltonian with the M2 affinity method.

People, Communities, and Education at the Coast

This special issue titled “People,Communities, and Education at the Coast” of the Journal of Coastal Conservation, Planning and Management (JCCPM) gathers 8 of the submitted contributions to the 3rd International Conference on Coastal Conservation and Management in the Atlantic and Mediterranean (ICCCM10), held at Estoril, Portugal, in April 2010. The conference was attended by 800 participants from twenty-one countries, providing an expanded forum for scientists, engineers, planners and managers to discuss recent and new advances in scientific, technical, and socio-economic understanding of environmental issues related to coastal processes. The eight papers in this issue cover several aspects from governance, social sustainability, public perception to environmental education. The paper by Vasconcelos et al. presents the MARGov project, using as a case study the Marine Park Professor Luiz Saldanha (Portugal) to build a Model of Collaborative Governance for Marine Protected Areas, to empower local communities enabling them to be agents for change for the sustainable governance of the Ocean, through an eco-social dialogue supported by active participation. Kalisch examines the crowding effects in a coastal National Park in Germany, using the social carrying capacity concept as a tool to coastal recreation management. Concerning coastal protection of sand dune systems in Portugal, Mendonca et al. describes an application of the Boussinesq-type COULWAVE model to study the wave hydrodynamics in the vicinity of a multi-functional artificial reef. From the public perception perspective, Baumann et al. examine the impact of the occurrence of jellyfish along the German Baltic coastline, show different methods to learn more about jellyfish accumulations and discuss information strategies in terms of improved beach management. Ferreira et al. present a beach profiling method to improve understanding of coastal processes by providing quantitative information on the spatial/ temporal evolution of beaches, which is crucial for coastal management and useful for environmental education. Quintela et al. focus on public perception of bathing users regarding Bathing Area quality in Sao Miguel (Portugal), namely litter, one of the top concerns of the users. Root-Bernstein et al. discuss and propose innovative and effective design solutions of multiple product proposals that would support a range of human-sea lion interactions in public parks and the fish market in Valdivia, Chile. Using local tidal records to identify relative sea level change, Powell et al. examine some of the key sources of error when working with historical tidal datasets in local geographic areas. They also identify the limitations of locally derived data thereby assisting in the determination of relative sea level trends that are of widespread value to infrastructure and policy makers. We wish to thank the authors and the reviewers for their valuable efforts, and the Editor for his support in producing this special issue Paula Sobral, Jose Carlos Ferreira and Francisco Taveira Pinto P. Sobral (*) IMAR – Institute for Marine Research, Faculty of Sciences & Technology, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal e-mail: psobral@fct.unl.pt

Measuring Classroom Assessment Practice Using Instructional Artifacts: A Validation Study of the QAS Notebook

We report the results of a pilot validation study of the Quality Assessment in Science Notebook, a portfolio-like instrument for measuring teacher assessment practices in middle school science classrooms. A statewide sample of 42 teachers collected 2 notebooks during the school year, corresponding to science topics taught in the fall and spring. Each notebook was scored on 9 dimensions of assessment practice by 3 trained raters. Our analysis investigated the reliability and validity of notebook ratings, with particular emphasis on identifying key sources of error in the ratings. The results suggest that variation in teacher practice across notebooks (i.e., over time) was more important than idiosyncratic rater inconsistencies as a source of error in the scores. The validity results point to a dominant factor underlying the ratings and some predictive power of notebook ratings on student achievement. We discuss implications of the results for measuring assessment practice through artifacts, drawing conceptual and methodological lessons about our model of assessment practice, the consistency of raters, and the estimation of variance over time with classroom-based measures of instruction.

Use of local tidal records to identify relative sea level change: accuracy and error for decision makers

The Intergovernmental Panel on Climate Change (IPCC) considers eustatic sea level rise to be a major impact driven by climate change. Relative sea level change, whether positive or negative, will affect industries, communities and ecology along the world’s coastlines and estuaries. Estimates of global eustatic sea level rise between 1961 and 2003 are 1.8 ± 0.5 mm a−1, reflecting results from validated global tide gauge records. Over the last two decades, several studies have used automatic tide gauge records with at least 80 years of data to generate global prediction models. The IPCC recognises that global change is not uniform, therefore local policy for flood management and coastal protection should rely on local change models that incorporate glacio-isostatic adjustment (GIA) and apply accurate data correction techniques. Some of the longest tidal records are held within the Northern Hemisphere, e.g. Cascais, Amsterdam, Aberdeen, Sheerness and Newlyn. The UK provides several important case studies highlighting changes in relative sea level between the north and the south, primarily due to variations in GIA rates of land uplift and subsidence. Tide gauge records are held by a variety of governmental, non-governmental and private organisations. However, each source may typically compile data in different ways, relying on diverse equipment and recording techniques, often with variations in frequency, length, quality and corrections applied. Even within a single organisation there may be differences in dataset quality. This paper examines some of the key sources of error when working with historical tidal datasets in local geographic areas and aims to identify the limitations of locally derived data thereby assisting in the determination of relative sea level trends that are of widespread value to infrastructure and policy makers.

An Identification Approach for Key Geometric Error Sources of Machine Tool Based on Sensitivity Analysis

The volumetric error coupled by geometric errors of parts is the main reason affecting the machining accuracy.How to determine the influence degree on the processing precision generated by the geometric errors of parts,thus distribute the geometric errors of parts economically and reasonably,is currently a difficult problem of machine tool design.Based on the theory of multi-body system and sensitivity analysis,a new method of identifying the key geometric error sources parameters is proposed.Taking a four-axis precision horizontal machining center as example,the precision model of the machine center is built up with the theory of multi-body system,thus a mathematical model for error sensitivity analysis of four-axis computer numerical control machine tools is established with matrix differential method,finally the key geometric error sources which affect the machining precision are identified after sensitivity coefficient of error are calculated and analyzed.Calculation and example show that geometric error factors of major parts that have relatively significant influence on comprehensive spatial error of the machine tools can be identified effectively,thus important theoretical basis is provided for improving precision of machine tools reasonably and economically.

The Adaptive Compensation Method and Modeling of Gear Hobbing Machine Based on Numerical Control System

Thermal error is the main factor which affects the precision of gear hobbing. The paper discusses the individual feature of gear hobbing machine of thermal error, and uses the weighted grey correlativity to determine the key thermal error source of gear hobbing machine. Based on Least-square method, a fundamental model of thermal error compensation was constructed. An adaptive correction algorithm of thermal error compensation model on gear hobbing machine was proposed. An adaptive compensation method of thermal error on gear hobbing machine was given based on open numerical control system.

Geometric Errors Sensitivity Analysis of Precision Vertical Machining Center Based on Multi-Body System Theory

Parts of geometric error coupled into space error is the main reason that affects machining accuracy of machine tools; therefore, how to determine the effect of geometric error to the machining accuracy and then assigning geometry precision of parts economically is a difficult problem in machine tool designing process. Therefore, based on multi-body system theory, a sensitivity analysis method of geometric error is put forward in this paper. Let’s take precision vertical machining center for an example. Firstly, an accuracy model of machining center is established based on multi-body system theory, and with 21 geometric errors obtained through experimental verification, key error sources affecting the machining accuracy are finally identified by sensitivity analysis. The example analysis shows that the proposed method can effectively identify the main geometric errors of parts that have great influence on volumetric error of machine tool, and thus provides important theoretical basis to improve the accuracy of machine tool economically.

Analysis and correction of background velocity offsets in phase‐contrast flow measurements using magnetic field monitoring

The value of phase-contrast magnetic resonance imaging for quantifying tissue motion and blood flow has been long recognized. However, the sensitivity of the method to system imperfections can lead to inaccuracies limiting its clinical acceptance. A key source of error relates to eddy current-induced phase fluctuations, which can offset the measured object velocity significantly. A higher-order dynamic field camera was used to study the spatiotemporal evolution of background phases in cine phase-contrast measurements. It is demonstrated that eddy current-induced offsets in phase-difference data are present up to the second spatial order. Oscillatory temporal behaviors of offsets in the kHz range suggest mechanical resonances of the MR system to be non-negligible in phase-contrast imaging. By careful selection of the echo time, their impact can be significantly reduced. When applying field monitoring data for correcting eddy current and mechanically induced velocity offsets, errors decrease to less than 0.5% of the maximum velocity for various sequence settings proving the robustness of the correction approach. In vivo feasibility is demonstrated for aortic and pulmonary flow measurements in five healthy subjects. Using field monitoring data, mean error in stroke volume was reduced from 10% to below 3%.

Sources of judgment error in environmental sensemaking

PurposeThis paper forwards a conceptual model identifying some of the key sources of judgment error in individual environmental sensemaking. Recommendations are offered to mitigate some of these biasing dysfunctions and thereby improve the effectiveness of environmentally related business policy.Design/methodology/approachTheories of cognitive and behavioral sciences are reviewed and applied to create a conceptual model describing some of the key influences on individual sensemaking in regard to environmental risk and opportunity.FindingsIt is found that the model presented in this paper contributes to the literature of corporate social responsibility in explaining some of the heuristic phenomena that can lead to denial of a firm's negative environmental impact, or conversely, recognition of emerging opportunities arising from increasing societal concern for environmental integrity. Many environmental scientists believe denial is omnipresent in modern business and governmental organizations. In addition, because the model is grounded in well‐established theories of problematic heuristic bias, it helps identify “leverage points” where well‐designed interventions can be deployed to promote learning and improved decision making. The model helps the decision maker better understand and potentially influence ethical judgment because ethical decision making is conceived within the frame of bounded ethicality versus a less potent theory of intervention based upon espoused moral prescriptions.Research limitations/implicationsSome important influences on environmental sensemaking are not emphasized in the model to include dimensions of individual personality, early childhood experiences, gender, religious background, etc. Rather, the emphasis here is placed upon relatively ubiquitous cognitive heuristics and other cognitive phenomena likely to influence many organizational decision makers.Originality/valueThis analysis and resulting conceptual model should help change agents, students, policy makers and business practitioners avoid predictable biases and sensemaking distortions and, in so doing, improve the firm's social responsibility profile and recognition of emerging business opportunities growing out of sustainability imperatives.

Unscented Kalman Filter for DR/GPS Integrated Navigation System

In this paper, unscented Kalman filter (UKF) is studied to estimate the state of Dead reckoning (DR) and GPS integrated navigation system. The positioning error of DR system mainly comes from two factors, the azimuth error and odometer scale factor error. Conventional model of DR/GPS integrated navigation chooses acceleration, position and velocity as observation states, and azimuth error is not estimated, which is one of the key error sources. A new error model of DR/GPS system is adopted that includes azimuth error as a state, which makes it possible to estimate both of the two major error sources. UKF directly approximates the probability density distribution of random variable and avoids the linearization of nonlinear function, which improves the filtering precision. UKF is used to implement an improved DR/GPS system. Road test has been conducted to prove the effectiveness of the scheme.

Intra- and inter-annual variability of VOC emissions from natural and semi-natural vegetation in Europe and neighbouring countries

Biogenic VOC emission estimates from the earth's surface are crucial input parameters in air quality models. Knowledge accumulated in the last years about BVOC source distributions and chemical compound species emission profiles in Europe as well as the demand of air quality modellers for a finer resolution in space and time of BVOC estimates have led to the set-up of new emission modelling systems. An updated fast BVOC emission modelling platform explicitly considering the seasonality of emission potentials and leaf temperature gradients in forest canopies by the semi-empirical emission module (seBVOC) will be proposed and used for estimating hourly values of chemical compound-specific emissions in Europe (33–68° north; 10° west to 40° east) in the years 1997, 2000, 2001, and 2003. Spatial resolution will be 10 km by 10 km. The database used contains latest land and forest distributions, updated foliar biomass densities, leaf area indices (LAI), and plant as well as chemical compound-specific emission potentials, if available. Meteorological input parameters for the respective years will be generated using the non-hydrostatic meteorological model MM5. Highest BVOC emissions occur in daytime hours around noon from the end of May to mid-August in the Mediterranean area and from the mid of June to the end of July in the boreal forests. Comparison of 3 BVOC model approaches will reveal that for July 2003, the European isoprene and monoterpene totals range from 1124 Gg to 1446 Gg and from 338 Gg to 1112 Gg, respectively. Small-scale deviations may be as high as ±0.6 Mg km −2 for July 2003, reflecting the current uncertainty range for BVOC estimates. Key sources of errors in inventories are still insufficiently detailed land use data for some areas and lacking chemically speciated plant-specific emission potentials in particular in boreal, south-eastern, and northern African landscapes. The hourly emissions of isoprene, speciated terpenes, and oxyVOC have been made available by the NatAir database.

Capture and analysis of quantitative proteomic data.

Whilst the array of techniques available for quantitative proteomics continues to grow, the attendant bioinformatic software tools are similarly expanding in number. The data capture and analysis of such quantitative data is obviously crucial to the experiment and the methods used to process it will critically affect the quality of the data obtained. These tools must deal with a variety of issues, including identification of labelled and unlabelled peptide species, location of the corresponding MS scans in the experiment, construction of representative ion chromatograms, location of the true peptide ion chromatogram start and end, elimination of background signal in the mass spectrum and chromatogram and calculation of both peptide and protein ratios/abundances. A variety of tools and approaches are available, in part restricted by the nature of the experiment to be performed and available instrumentation. Currently, although there is no single consensus on precisely how to calculate protein and peptide abundances, many common themes have emerged which identify and reduce many of the key sources of error. These issues will be discussed, along with those relating to deposition of quantitative data. At present, mature data standards for quantitative proteomics are not yet available, although formats are beginning to emerge.