Various Sources Of Error Research Articles

Decomposition of sources of errors in seasonal streamflow forecasting over the U.S. Sunbelt

AbstractSeasonal streamflow forecasts, contingent on climate information, can be utilized to ensure water supply for multiple uses including municipal demands, hydroelectric power generation, and for planning agricultural operations. However, uncertainties in the streamflow forecasts pose significant challenges in their utilization in real‐time operations. In this study, we systematically decompose various sources of errors in developing seasonal streamflow forecasts from two Land Surface Models (LSMs) (Noah3.2 and CLM2), which are forced with downscaled and disaggregated climate forecasts. In particular, the study quantifies the relative contributions of the sources of errors from LSMs, climate forecasts, and downscaling/disaggregation techniques in developing seasonal streamflow forecast. For this purpose, three month ahead seasonal precipitation forecasts from the ECHAM4.5 general circulation model (GCM) were statistically downscaled from 2.8° to 1/8° spatial resolution using principal component regression (PCR) and then temporally disaggregated from monthly to daily time step using kernel‐nearest neighbor (K‐NN) approach. For other climatic forcings, excluding precipitation, we considered the North American Land Data Assimilation System version 2 (NLDAS‐2) hourly climatology over the years 1979 to 2010. Then the selected LSMs were forced with precipitation forecasts and NLDAS‐2 hourly climatology to develop retrospective seasonal streamflow forecasts over a period of 20 years (1991–2010). Finally, the performance of LSMs in forecasting streamflow under different schemes was analyzed to quantify the relative contribution of various sources of errors in developing seasonal streamflow forecast. Our results indicate that the most dominant source of errors during winter and fall seasons is the errors due to ECHAM4.5 precipitation forecasts, while temporal disaggregation scheme contributes to maximum errors during summer season.

Sea level budget over 2005–2013: missing contributions and data errors

Abstract. Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (depths not covered by observations). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed differences in trend of the residuals of the sea level budget equation can be as large as ~ 0.55 mm yr−1 (i.e., ~ 17 % of the observed GMSL rate of rise). These trend differences essentially result from differences in trends of the GMSL time series. Using the ORAS4 reanalysis (providing complete geographical coverage of the steric sea level component), we also show that lack of Argo data in the Indonesian region leads to an overestimate of the absolute value of the residual trend by about 0.25 mm yr−1. Accounting for this regional contribution leads to closure of the sea level budget, at least for some GMSL products. At short timescales (from sub-seasonal to interannual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), suggesting that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content.

Use of LUCAS LC Point Database for Validating Country-Scale Land Cover Maps

In this study, the Land Use/Cover Area frame statistical Survey (LUCAS) of 2009 was used as a reference dataset for validating a Land Cover Map of Greece for 2007, produced with remote sensing by the Greek Office of the World Wildlife Fund (WWF Hellas). First, all class definitions were decomposed in terms of four vegetation parameters (type, height, density, and composition), considered as critical in indicating unconformities between LUCAS and the WWF Hellas map; their inter-class relations were described in a table of correspondence. Then, a two-tier methodology was applied: an “automated” process, where thematic agreement was based exclusively on the main land cover attribute of LUCAS (LC1); and a “supervised” process, where thematic agreement was based on the reinterpretation of LUCAS ground photos and use of ancillary earth observation imagery; non-square error matrix was deployed in both processes. For the supervised process specifically, a decision-tree was designed, using the critical vegetation parameters (mentioned above) as quantified criteria, thus allowing objective labelling of testing points in both systems. The results show that only a small proportion of the reassessed points verified the WWF Hellas map predictions and that the overall accuracy of the supervised process was reduced compared to that of the automated process. In conclusion, the LUCAS point database was found to be supportive, but not fully efficient, for identifying the various sources of error in country-scale land cover maps derived with remote sensing. Synergy with very high resolution satellite images and air photos, or a dedicated ground truth campaign, seems to be inevitable in order to validate their thematic accuracy, especially in highly heterogeneous environments. In this direction, LUCAS could be used as a verification, rather than a validation, dataset.

Historical, hydraulic, hydrological and meteorological reconstruction of 1874 Santa Tecla flash floods in Catalonia (NE Iberian Peninsula)

Summary A multidisciplinary methodology for historical floods reconstruction was applied to 1874 Santa Tecla floods occurred in Catalonia (NE Iberian Peninsula), using both historical information and meteorological data from 20th Century Reanalysis. The results confirmed the exceptionality of the event: the highest modeled specific peak flow was around 14.6 m3 s−1 km−2 in a 100 km2 catchment and all the modeled total rainfall values were above 110 mm in about six hours, with maximum intensities around 60 mm min−1. The peak-flows peak flows' return periods were about 260 years and the rainfalls periods were between 250 and 500 years. The meteorological cause of the rainstorms was the flash triggering effect, initiated by the withdrawal of a mass of hot air at mid-levels. A sensitivity analysis on the various sources of error shows that peak flow errors from hydraulic modeling ranged from 5% to 44%, and rainfall errors from hydrological modeling were about 36%.

Analysis of Flanged Rectangular Waveguide Probe for Nondestructive Absorbing Materials Characterization Using FDTD Simulation

In this paper, the flanged open-ended rectangular waveguide probe technique is studied using Finite Difference Time-Domain simulation (FDTD). Both generally lossy and high loss electromagnetic materials are considered to investigate the influence of probe flange size, operating frequency and sample thickness on complex permittivity (er) and permeability (μr) and thickness measurement. Variations in the probe flange size for different frequencies, material under test type and thickness are simulated. It is found that using of waveguide probe with finite flange affects probe input reflection coefficient substantially in some cases. To verify the obtained simulations results, a series of experiments are conducted for this purpose. Both er and μr of material under test under different measurement conditions are extracted using FDTD modeling and compared with reference data. In order to evaluate the degree of accuracy of this technique, error analysis to various sources of errors and most importantly the effect of finite flange size are also demonstrated by using the measured data compared with the analytical model results. Simulations and measurements results have shown that the consideration of probe flange large enough for the practical purpose to be infinite is restricted by the constitutive parameters (er and μr) and operating frequency as well as the thickness of the material under test. The FDTD simulations and experiments results are presented.

High precision Os isotopic measurement using N-TIMS: Quantification of various sources of error in 186Os/188Os measurements

The 190Pt–186Os system could be useful to study a number of different geologic processes. Over the last decade, this system has received considerable attention owing to its potential to detect core–mantle signatures in plume-derived lavas. Additionally, this system may also be useful as a proxy for melt depletion, examining the role of pyroxenites/sulfides in mantle melting and for dating of Platinum Group Element (PGE) based ores. The total natural variation of 186Os/188Os is limited (~150ppm in the mantle), which thus requires extremely high levels of accuracy and precision to discern natural variations. 186Os/188Os ratios were measured in laboratory standards and natural samples to examine and quantify the sources of error affecting high precision 186Os/188Os measurements and a set of refined analytical procedures to minimize and reduce these various sources of error were recommended.Inter and intra-run variations in oxygen isotopic composition used in oxide correction of OsO3− peaks can produce systematic shifts in 186Os/188Os. Useful analysis time is wasted in measuring O isotopic composition line-by-line and it is sufficient to utilize pre- and post-run determination of O isotopic composition for performing oxide correction. Although the use of 189Os/188Os as a normalizing ratio for mass fractionation results in lower uncertainty in Os isotopes from oxide correction, this benefit is overwhelmed by the increased error propagation from mass fractionation. Instead, usage of the 192Os/188Os normalization generates the least propagated error due to mass fractionation and is recommended. Earlier studies have variably used different O isotopic compositions for oxide correction and different normalizations for mass fractionation correction, which can generate systematic shifts in the reduced data. Use of mutually consistent normalizing values for mass fractionation largely reduces the offsets between reduced data using different normalizing schemes, thus improving data comparison across laboratories.For the quantities of Os and beam intensities of 186Os utilized in previous 186Os/188Os studies (several 10's of ng Os, 80–250mV of 186Os with a 1011 Ω resistor), the largest source of analytical error is derived from Johnson noise on baseline integrations. Increasing the duration of baseline measurement significantly reduces the Johnson noise error, allowing to achieve maximum external precision for a given sample size. Several 186Os/188Os analyses reported in the literature seem to have been compromised by an interference, which may be WO3−, organics or some other unidentified species that affects both the 186Os/188Os and the 184Os/188Os ratios. This makes it extremely critical to monitor and correct PtO2− interferences, which could mask other potential interferences that directly affect 186Os/188Os measurements.

Spatial normalization of reverse phase protein array data.

Reverse phase protein arrays (RPPA) are an efficient, high-throughput, cost-effective method for the quantification of specific proteins in complex biological samples. The quality of RPPA data may be affected by various sources of error. One of these, spatial variation, is caused by uneven exposure of different parts of an RPPA slide to the reagents used in protein detection. We present a method for the determination and correction of systematic spatial variation in RPPA slides using positive control spots printed on each slide. The method uses a simple bi-linear interpolation technique to obtain a surface representing the spatial variation occurring across the dimensions of a slide. This surface is used to calculate correction factors that can normalize the relative protein concentrations of the samples on each slide. The adoption of the method results in increased agreement between technical and biological replicates of various tumor and cell-line derived samples. Further, in data from a study of the melanoma cell-line SKMEL-133, several slides that had previously been rejected because they had a coefficient of variation (CV) greater than 15%, are rescued by reduction of CV below this threshold in each case. The method is implemented in the R statistical programing language. It is compatible with MicroVigene and SuperCurve, packages commonly used in RPPA data analysis. The method is made available, along with suggestions for implementation, at http://bitbucket.org/rppa_preprocess/rppa_preprocess/src.

The Superconvergence Phenomenon and Proof of the MAC Scheme for the Stokes Equations on Non-uniform Rectangular Meshes

For decades, the widely used finite difference method on staggered grids, also known as the marker and cell (MAC) method, has been one of the simplest and most effective numerical schemes for solving the Stokes equations and Navier---Stokes equations. Its superconvergence on uniform meshes has been observed by Nicolaides (SIAM J Numer Anal 29(6):1579---1591, 1992), but the rigorous proof is never given. Its behavior on non-uniform grids is not well studied, since most publications only consider uniform grids. In this work, we develop the MAC scheme on non-uniform rectangular meshes, and for the first time we theoretically prove that the superconvergence phenomenon (i.e., second order convergence in the $$L^2$$L2 norm for both velocity and pressure) holds true for the MAC method on non-uniform rectangular meshes. With a careful and accurate analysis of various sources of errors, we observe that even though the local truncation errors are only first order in terms of mesh size, the global errors after summation are second order due to the amazing cancellation of local errors. This observation leads to the elegant superconvergence analysis even with non-uniform meshes. Numerical results are given to verify our theoretical analysis.

Abstract C11: Impact of pathologic specimen quality on classifying molecular subtypes of breast cancer: A pilot study from three hospitals in Ghana, Africa

Abstract Background: Breast cancer is a heterogeneous disease with clinically, molecularly and pathologically defined subtypes that have different etiologies, clinical presentations and outcomes. African women reportedly have especially high rates of breast cancers that are estrogen receptor (ER) or progesterone receptor (PR) negative, or triple negative [ER, PR and human epidermal growth factor receptor-2 (HER-2) negative], with the proportion reported for triple negative breast cancers ranging from 28-82%, compared to 11-20% among Caucasian populations. However, it is unclear to what extent pathology and specimen handling affect receptor measurements in Africa. Here we sought to determine pathology specimen quality of breast tumor tissues from three hospitals in Ghana where we are conducting a molecular epidemiologic study of breast cancer. Methods: We acquired 15 formalin-fixed paraffin-embedded (FFPE) archived breast cancer tissue blocks with specimens obtained at biopsy (N=5) or surgery (N=10) from three hospitals in Ghana. Blocks were re-embedded and four 0.5um whole sections were cut for hematoxylin and eosin stains, and immunohistochemistry (IHC) using previously validated protocols for ER (clone 1D5), PR (clone PgR1294) and HER2 (polyclonal), all obtained from Dako (Carpinteria CA). Specimens were considered ER or PR positive if 10% or more cells stained positive, while HER2 was considered positive if intensity of staining was 3+. Results: Specimens were noted to be embedded in high-melting temperature paraffin. To perform ER, PR, and HER2 IHC staining, deparaffinization procedures were optimized for hard paraffin. Zonal and gradient staining patterns were noted in surgical specimens, features that are likely due to delayed/prolonged fixation. Zonal/gradient staining issues were not identified in the needle biopsies, which were smaller compared to specimens collected at surgery and generally placed in buffered formalin immediately after collection. IHC assays of the tumor specimens revealed that 67% were ER-positive, 20% PR-positive, and 66% HER2 positive. The proportion negative for all three markers was 13%. Conclusion: In contrast to previous reports for African breast cancer patients, within our sample of FFPE breast cancers from Ghana we found a higher prevalence of ER positive tumors and a lower prevalence of tumors negative for all three markers. These results suggest that the high rates of hormone receptor negativity previously reported in African populations may be inaccurate due to various sources of error, particularly fixation time and IHC staining protocols. Future studies focusing on proper documentation of sample collection procedures and optimization of IHC methods are required to determine the true prevalence of molecular subtypes of breast cancer among African women. Such efforts are essential for breast cancer surveillance, identifying etiologic factors for prevention efforts and developing more effective treatment programs. Citation Format: Jonine D. Figueroa, Lawrence Edusei, Ernest Adjei, Nicholas Titiloye, Kris Ylaya, Beatrice Addai, Joe Nat Clegg-Lamptey, Baffour Awuah, Kofi Nyarko, Daniel Ansong, Seth Wiafe, Louise A. Brinton, Stephen Hewitt. Impact of pathologic specimen quality on classifying molecular subtypes of breast cancer: A pilot study from three hospitals in Ghana, Africa. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C11. doi:10.1158/1538-7755.DISP13-C11

Measurements of the Thermal Conductivity of Propane in the Supercritical Region

Measurements of the thermal conductivity of propane performed in a coaxial cylinder cell operating in steady state conditions are reported. The measurements of the thermal conductivity of propane were carried out along eight quasi-isotherms above the critical temperature. The present data cover the temperature range from (370.83 to 381.00) K, and the pressure range (0.1 to 15) MPa. An analysis of the various sources of error leads to an estimated uncertainty of approximately 3 %. The parameters of a background equation were determined from experimental data in order to analyze the critical enhancement of the thermal conductivity as a function of temperature and density. On the basis of the measurement of more than 500 experimental points, a phenomenological equation is provided to describe the thermal conductivity of propane, from the critical temperature 369.825 K to 600 K and densities up to 550 kg·m–3. This equation can be generalized to calculate the supercritical behavior of the thermal conductivity for any fluid.

Body Mass Index: Accounting for Full Time Sedentary Occupation and 24-Hr Self-Reported Time Use

ObjectivesWe used linked existing data from the 2006–2008 American Time Use Survey (ATUS), the Current Population Survey (CPS, a federal survey that provides on-going U.S. vital statistics, including employment rates) and self-reported body mass index (BMI) to answer: How does BMI vary across full time occupations dichotomized as sedentary/non-sedentary, accounting for time spent in sleep, other sedentary behaviors, and light, moderate, and vigorous intensity activities?MethodsWe classified time spent engaged at a primary job (sedentary or non-sedentary), sleep, and other non-work, non-sleep intensity-defined behaviors, specifically, sedentary behavior, light, moderate, and vigorous intensity activities. Age groups were defined by 20–29, 30–39, 40–49, and 50–64 years. BMI groups were defined by 18.5–24.9, 25.0–27.4, 27.5–29.9, 30.0–34.9, and ≥35.0 kg/m2. Logistic and linear regression were used to examine the association between BMI and employment in a sedentary occupation, considering time spent in sleep, other non-work time spent in sedentary behaviors, and light, moderate, and vigorous intensity activities, sex, age race/ethnicity, and household income.ResultsThe analysis data set comprised 4,092 non-pregnant, non-underweight individuals 20–64 years of age who also reported working more than 7 hours at their primary jobs on their designated time use reporting day. Logistic and linear regression analyses failed to reveal any associations between BMI and the sedentary/non-sedentary occupation dichotomy considering time spent in sleep, other non-work time spent in sedentary behaviors, and light, moderate, and vigorous intensity activities, sex, age, race/ethnicity, and household income.ConclusionsWe found no evidence of a relationship between self-reported full time sedentary occupation classification and BMI after accounting for sex, age, race/ethnicity, and household income and 24-hours of time use including non-work related physical activity and sedentary behaviors. The various sources of error associated with self-report methods and assignment of generalized activity and occupational intensity categories could compound to obscure any real relationships.

Potential for timing high-energy marine inundation events in the recent geological past through age-dating of reef boulders in Fiji

Transported coastal boulders have increasingly come to represent a valuable element of investigations within the broader framework of multi-proxy approaches applied to coastal hazard studies. Through a case study on Taveuni Island in Fiji, this paper outlines some approaches and hindrances to effective timing of prehistorical high-energy marine inundation events (storms and tsunamis) on tropical coastlines from the evidence of reef-platform carbonate boulders. Various sources of errors are outlined that investigators must consider when attempting to use carbonate boulder ages as a surrogate for timing past events. On Taveuni, uranium : thorium dates with a high level of precision (1–7 years) suggest that major inundation events have a return period of approximately 40–45 years since 1650 AD. Of particular importance, considerably different age dates are provided by coral samples sourced from the top and bottom (i.e. opposite faces) of individual boulders, so highlighting interpretation biases that must be avoided.

Protocol for machine tool volumetric verification using commercial laser tracker

This paper presents a protocol as the preliminary phase of the volumetric verification of geometric errors in a real machine tool using a commercial laser tracker as the measurement system. The final error admissible in machine tool verification is defined as a range by the verification protocol presented in this paper. To obtain it, an independent study of the various sources of error that affect the machine tool’s accuracy was conducted. These errors are the tracking error, the repeatability error, the backlash of each axe, the heating time and the non-geometric errors of the machine. Furthermore, the thermal influence and errors from the measuring system are studied. For all of these errors, different calculation and measurement methods are used by performing a series of real tests on a three lineal-axis milling machine. In this paper, the different techniques that determine the errors of any machine tool are presented in a verification protocol. Depending on the influence of these sources of error obtained by applying the verification protocol to the volumetric error, the protocol determines the adequacy and scope of the volumetric verification process performed.

A comparison of remotely sensed and pollen‐based approaches to mapping Europe's land cover

AbstractAimRemote sensing coupled with direct observation allows recent changes in vegetation to be investigated but, in order to extend our understanding of land‐cover change further back in time, different proxies for vegetation are required. The pseudobiomization (PBM) approach has been developed to transform fossil pollen data into land‐cover classes (LCCs) in order to reconstruct broad‐scale anthropogenic land‐use change through time. The aim of this study was to test and refine the PBM approach through application to an extensive modern pollen dataset and comparison with remotely sensed CORINE land‐cover maps for Europe.LocationThe study area comprised 2471 modern pollen sites from across Europe.MethodsPollen sites were assigned to one of eight LCCs using the pollen‐based PBM method, which draws upon biomization techniques to transform pollen data into records of land‐cover change. Five of the LCCs were ‘pure’ classes (e.g. broad‐leaf forest) and three of them were mixed vegetation. Remotely sensed CORINE land‐cover maps were used to assign LCCs to sites, and the results were compared with pollen‐assigned LCCs.ResultsThe results revealed a good correspondence between the proportions of different LCCs that were registered using CORINE and pollen‐based PBM, when data were aggregated at a pan‐European scale. However, the match between the two datasets was much less close at a site‐specific level. The overall results were improved to c. 60% when the target was broadened to include similar as well as identical LCCs. The spatial correspondence was best across north‐central Europe and least good in south‐west Europe, the Mediterranean and northern Scandinavia.Main conclusionsThe ability of distinct data types to sense actual vegetation is limited by various sources of error; for example, both pollen and remote sensing vary in terms of spatial and temporal heterogeneity and taxonomic resolution. It is likely that many of the main sources of error are common to both methods, rather than being approach‐specific. We conclude that pollen‐based methods of intermediate complexity can be used as a proxy for broad‐scale land‐cover change across most of temperate Europe, but may be less reliable at a site‐specific scale.

SU-E-T-159: Evaluation of a Patient Specific QA Tool Based On TG119

Purpose: To evaluate the accuracy of a 3D patient specific QA tool by analysis of the results produced from associated software in homogenous phantom and heterogonous patient CT. Methods: IMRT and VMAT plans of five test suites introduced by TG119 were created in ECLIPSE on a solid water phantom. The ten plans -of increasing complexity- were delivered to Delta4 to give a 3D measurement. The Delta4's “Anatomy” software uses the measured dose to back-calculate the energy fluence of the delivered beams, which is used for dose calculation in a patient CT using a pencilbeam algorithm. The effect of the modulated beams' complexity on the accuracy of the “Anatomy” calculation was evaluated. Both measured and Anatomy doses were compared to ECLIPSE calculation using 3% - 3mm gamma criteria.We also tested the effect of heterogeneity by analyzing the results of “Anatomy” calculation on a Brain VMAT and a 3D conformal lung cases. Results: In homogenous phantom, the gamma passing rates were found to be as low as 74.75% for a complex plan with high modulation. The mean passing rates were 91.47% ± 6.35% for “Anatomy” calculation and 99.46% ± 0.62% for Delta4 measurements.As for the heterogeneous cases, the rates were 96.54%±3.67% and 83.87%±9.42% for Brain VMAT and 3D lung respectively. This increased error in the lung case could be due to the use of the pencil beam algorithm as opposed to the AAA used by ECLIPSE.Also, gamma analysis showed high discrepancy along the beam edge in the “Anatomy” calculated results. This suggests a poor beam modeling in the penumbra region. Conclusion: The results show various sources of errors in “Anatomy” calculations. These include beam modeling in the penumbra region, complexity of a modulated beam (shown in homogenous phantom and brain cases) and dose calculation algorithms (3D conformal lung case).

Understanding validity issues in international large scale assessments

Purpose – This policy brief, the third in the AERI-NEPC eBrief series “Understanding validity issues around the world”, discusses validity issues surrounding International Large Scale Assessment (ILSA) programs. ILSA programs, such as the well-known Programme of International Student Assessment (PISA) and the Trends in International Mathematics and Science Study (TIMSS), are rapidly expanding around the world today. In this eBrief, the authors examine what “validity” means when applied to published results and reports of programs like the PISA. Design/methodology/approach – This policy brief is based on a synthesis of conference proceedings and review of selected pieces of extant literature. It begins by summarizing perspectives of an invited expert panel on the topic. To that synthesis, the authors add their own analysis of key issues. They conclude by offering recommendations for test developers and test users. Findings – ILSA programs and tests, while offering valuable information, should be read and used cautiously and in context. All parties need to be on the same page to maximize valid use of ILSA results, to obtain the greatest educational and social benefits, and to minimize negative consequences. The authors propose several recommendations for test makers and ILSA program leaders, and ILSA users. To ILSA leaders and researchers: provide more cautionary information about how to correctly interpret the ILSA results, particularly country rankings, given contextual differences among nations. Provide continuing psychometric or research resources so as to address or reduce various sources of error in reports. Encourage policy makers in different nations to share the responsibility for ensuring more contextualized (and valid) interpretations of ILSA reports and subsequent policy development. Raise awareness among policy makers to look beyond simple rankings and pay more attention to inter-country differences. For consumers of ILSA results and reports: read the fine print, not just the country rankings, to interpret ILSA results correctly in particular regions/nations. When looking to high-ranking countries as role models, be sure to consider the “whole picture”. Use ILSA data as complements to other national- and state-level educational assessments to better gauge the status of the country's education system and subsequent policy directions. Originality/value – By translating complex information on validity issues with all concerned ILSA stakeholders in mind, this policy brief will improve uses and applications of ILSA information in national and regional policy contexts.

Field Monitoring of Rebar Debonding in Concrete Bridge Decks under Traffic-Induced Vibrations

Concrete deck resurfacing is conducted through staged construction under active traffic conditions in lanes adjacent to the newly poured concrete. Many engineers are concerned about the potential of cracking and rebar debonding and other factors, such as shrinkage, thermal expansion and contraction, and live loads. There is a need to evaluate these detrimental effects with techniques that are reliable under field conditions. In this paper, results are presented from a field study that measured peak rebar velocities during concrete pours. The peak velocities were then compared with experimentally established limits for the cracking potential of the concrete surrounding the rebar. However, it is often more feasible to process accelerometer measurements to obtain velocity indirectly from common processing techniques, such as direct integration. A numerical approach was developed to mitigate the various sources of error in the integration and produce accurate estimates of velocities and displacements from raw accelerometer data. The comprehensive field testing of a rehabilitated bridge span was conducted to capture the dynamic response of the bridge girders, stringers, and deck reinforcement. The bridge was monitored during the pour of a simple span and for several hours after the initial concrete placement. The response predicted by the numerical analysis compared well with the field results: the time histories of velocity and displacement were accurately reconstructed. A comparison with the established limits of peak particle velocity suggested that vibrations induced by typical truck traffic during the initial concrete setting period should not pose any significant risk of debonding.

Damage Detection of Bridges Using Vibration Data by Adjoint Variable Method

This research entails a theoretical and numerical study on a new damage detection method for bridges, using response sensitivity in time domain. This method, referred to as “adjoint variable method,” is a finite element model updating sensitivity based method. Governing equation of the bridge-vehicle system is established based on finite element formulation. In the inverse analysis, the new approach is presented to identify elemental flexural rigidity of the structure from acceleration responses of several measurement points. The computational cost of sensitivity matrix is the main concern associated with damage detection by these methods. The main advantage of the proposed method is the inclusion of an analytical method to augment the accuracy and speed of the solution. The reliable performance of the method to precisely identify the location and intensity of all types of predetermined single, multiple, and random damages over the whole domain of moving vehicle speed is shown. A comparison study is also carried out to demonstrate the relative effectiveness and upgraded performance of the proposed method in comparison to the similar ordinary sensitivity analysis methods. Moreover, various sources of errors including the effects of noise and primary errors on the numerical stability of the proposed method are discussed.

Measurement error in air pollution epidemiology: Guidance for uncertain times.

EnvironmetricsVolume 24, Issue 8 p. 529-530 Discussion Paper Measurement error in air pollution epidemiology: guidance for uncertain times Roger D. Peng, Corresponding Author Roger D. Peng Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, U.S.A.Correspondence to: Roger D. Peng, Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, U.S.A. [email protected]Search for more papers by this author Roger D. Peng, Corresponding Author Roger D. Peng Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, U.S.A.Correspondence to: Roger D. Peng, Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, U.S.A. [email protected]Search for more papers by this author First published: 21 January 2014 https://doi.org/10.1002/env.2242Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume24, Issue8December 2013Pages 529-530 RelatedInformation

Evaluating the reliability and sensitivity of the Kerr electro-optic field mapping measurements with high-voltage pulsed transformer oil

Transformer oil is the most widely used dielectric liquid for high voltage insulation. Measurements of the electric field distribution in high voltage pulsed transformer oil are of both practical and theoretical interests. Due to its low Kerr constant, previous electro-optic measurements with transformer oil rely on a technique called ac modulation, which works only for dc steady-state electric field mapping. With the help of a high-sensitivity charge-coupled device, we directly measure the Kerr electro-optic effect between parallel electrodes in transformer oil stressed by high voltage pulses. This work aims at demonstrating the reliability and evaluating the sensitivity of the measurements for three cases with identical electrodes: space-charge free, uniform electric field in the mid-region of the gap; space-charge free, non-uniform fringing electric field; and space charge distorted electric field in the mid-region of the gap. Future directions to improve accuracy by identifying and handling various sources of error and noise are suggested.