Back-calculation Models Research Articles

A new perspective of Mugil liza: The fast growth in an impacted subtropical bay

Mugil liza is one of the most important fishery resources in west margin of Southwestern Atlantic. Its northern population (northward of 23°40’S) is distributed along the Brazilian coast and, including the Guanabara Bay (GB, 22°50’S, 43°10’W). This study aimed to evaluate the ring formation in the sagitta to estimate the fish age and growth. Based on monthly samplings (2011–2013), 815 individuals were caught (285–815 mm TL), and a subsample of 299 otoliths were analyzed. The otoliths were embedded, cross-sectioned and read in terms of “annual” rings (macrostructural analysis). Then, they were analyzed in terms of daily rings (microstructural analysis) and the deposition of calcium carbonate (ultrastructural analysis). The comparison among the three methods revealed that five macro rings are formed in the first year. Ulterior to this diagnosis, back-calculation and growth models were simulated and tested to describe the growth in the first year and the general growth pattern. The ages varied from 0.63- up to 5 years-old, with a high variability of total lengths by ages. The von Bertalanffy growth model based on back-calculated lengths of Dahl-Lea best described the growth pattern. Mugil liza at GB presented sexual dimorphism in terms of growth, females being longer and older, and it was revealed a fast growth pattern. These findings reinforce the identity of a probable stock of M. liza at GB and change drastically the current knowledge their age and growth. The regulatory marks for the species must be reviewed, at least for GB. The current results evidence the need of current assessment and monitoring of fisheries resources, identifying the patterns of population groups.

Ontogenetic and interpopulation differences in otolith shape of the European perch (Perca fluviatilis)

Fish otoliths are conservative structures that are widely used on fishery science for multiple purposes. Despite its relevance in the research field, little is known about the ontogeny and inter-population effects on the otolith of freshwater fish. In this study we used otoliths from 1800 European perch (Perca fluviatilis) individuals from 9 different populations to analyze the ontogenetic and inter-population differences on the otolith shape using six morphometric indices. The relationship between fish and otolith length was fitted using three different regression models (linear, power and logistic) to identify the best allometric relationship. Our results show that there are strong ontogenetic and interpopulation differences in P. fluviatilis otolith shapes. We also show that the relationship between the fish and otolith length follows a logistic curve. The ontogenetic differences on otolith shape might be related to extrinsic factors (diet shift and intra and interspecific competition) in each ecosystem, given that the reservoirs are different and no clear pattern on the otolith shapes can be distinguished among populations. Our results imply that the available back-calculation models may not always provide accurate estimates of P. fluviatilis length and that a model that takes into account the real allometric relationship for the species can improve the fish length estimations of back-calculated fish lengths for the European perch.

Extended experimental inferential structure determination method in determining the structural ensembles of disordered protein states

Proteins with intrinsic or unfolded state disorder comprise a new frontier in structural biology, requiring the characterization of diverse and dynamic structural ensembles. Here we introduce a comprehensive Bayesian framework, the Extended Experimental Inferential Structure Determination (X-EISD) method, which calculates the maximum log-likelihood of a disordered protein ensemble. X-EISD accounts for the uncertainties of a range of experimental data and back-calculation models from structures, including NMR chemical shifts, J-couplings, Nuclear Overhauser Effects (NOEs), paramagnetic relaxation enhancements (PREs), residual dipolar couplings (RDCs), hydrodynamic radii (Rh), single molecule fluorescence Förster resonance energy transfer (smFRET) and small angle X-ray scattering (SAXS). We apply X-EISD to the joint optimization against experimental data for the unfolded drkN SH3 domain and find that combining a local data type, such as chemical shifts or J-couplings, paired with long-ranged restraints such as NOEs, PREs or smFRET, yields structural ensembles in good agreement with all other data types if combined with representative IDP conformers.

Assessing artificial neural network performance for predicting interlayer conditions and layer modulus of multi-layered flexible pavement

The objective of this study is to evaluate the performance of the artificial neural network (ANN) approach for predicting interlayer conditions and layer modulus of a multi-layered flexible pavement structure. To achieve this goal, two ANN based back-calculation models were proposed to predict the interlayer conditions and layer modulus of the pavement structure. The corresponding database built with ANSYS based finite element method computations for four types of a structure subjected to falling weight deflectometer load. In addition, two proposed ANN models were verified by comparing the results of ANN models with the results of PADAL and double multiple regression models. The measured pavement deflection basin data was used for the verifications. The comparing results concluded that there are no significant differences between the results estimated by ANN and double multiple regression models. PADAL modeling results were not accurate due to the inability to reflect the real pavement structure because pavement structure was not completely continuous. The prediction and verification results concluded that the proposed back-calculation model developed with ANN could be used to accurately predict layer modulus and interlayer conditions. In addition, the back-calculation model avoided the back-calculation errors by considering the interlayer condition, which was barely considered by former models reported in the published studies.

Decoupling of otolith and somatic growth during anadromous migration in a northern salmonid

We assessed the fish length – otolith length relationship (FL–OL) in Dolly Varden (Salvelinus malma malma) to verify proportional growth. A decoupling was detected during first ocean migration where fish growth was occurring at a greater rate than otolith growth. Because of this decoupling, the application of traditional back-calculation models overestimated the size-at-age in premigratory char. We developed modified back-calculation equations from existing traditional models to account for this decoupling based on discontinuous piecewise regressions. The new biological intercept breakpoint method (BI–BP) provided the most accurate representation of fish size-at-age throughout all life history stages when compared with known size-at-capture values in fish. The decoupling indicates that factors other than somatic growth are important for otolith accretion. Physiological changes during smoltification likely alter calcium uptake and thereby affect calcium deposition rates on otoliths during this short but biologically critical time period of life history. It is probable that species exhibiting similar complex ontogenetic shifts in life history will likely exhibit decoupling to some extent in the FL–OL relationship.

Models for length back-calculation in Caspian kutum, Rutilus kutum (Pisces: Cyprinidae) from the Caspian Sea

The Caspian Kutum, Rutilus Kutum (Kamensky 1901) specimens were sampled by purse seine in the northern Iranian coast of the Caspian Sea at four locations: Feridoonkenar Shahed, Mahmoudabad Khoram, Lariim Azadi fishing coop, and the Shiroud River in Ramsar city. “Back-calculation” is a retrospective method of estimating the characteristics of growth of fish in terms of length and rate of growth in the years preceding capture. Back-calculation of fish lengths at previous ages from scales or otoliths is a widely used approach to estimate both individual and population growth history. The back-calculated lengths of the Caspian kutum,Rutilus kutum (Kamensky 1901) were obtained using six different models, namely scale proportional hypothesis, body proportional hypothesis, Fraser Lee, nonlinear scale proportional hypothesis, nonlinear body proportional hypothesis, and the newest method, Morita Matsuishi model. The results showed that the preferred back-calculation models is Fraser Lee model for both males and females, while the nonlinear body proportional hypothesis is only for the females.

A Comparison of Dynamic Soil Models for Backcalculation of Engineering Soil Properties from Falling Weight Deflectometer Data

The falling weight deflectometer (FWD) test is one of the most widely used nondestructive tests for backcalculation evaluation of pavement and soil properties. Despite the advantages in accounting for the time-dependent load and responses, the accuracy of evaluating elastic moduli based on dynamic backcalculation analyses is, however, significantly depended on the forward dynamic soil models employed in the backcalculation process. To serve this challenge, a comparison for advantages, limitations and the reliability of different dynamic soil models employed in the backcalculation of engineering soil properties is presented in this paper. Two types of dynamic soil forward models in the FWD backcalculation, namely, dynamic single-degree-offreedom (SDOF) and dynamic half-space models are considered. The study in this paper provides a better understanding of dynamic backcalculation processes which is essential for the development of dynamic backcalculation program and its applications.

The Human Immunodeficiency Virus Continuum of Care in European Union Countries in 2013: Data and Challenges.

The Joint United Nations Programme on HIV/AIDS (UNAIDS) has set a "90-90-90" target to curb the human immunodeficiency virus (HIV) epidemic by 2020, but methods used to assess whether countries have reached this target are not standardized, hindering comparisons. Through a collaboration formed by the European Centre for Disease Prevention and Control (ECDC) with European HIV cohorts and surveillance agencies, we constructed a standardized, 4-stage continuum of HIV care for 11 European Union countries for 2013. Stages were defined as (1) number of people living with HIV in the country by end of 2013; (2) proportion of stage 1 ever diagnosed; (3) proportion of stage 2 that ever initiated ART; and (4) proportion of stage 3 who became virally suppressed (≤200 copies/mL). Case surveillance data were used primarily to derive stages 1 (using back-calculation models) and 2, and cohort data for stages 3 and 4. In 2013, 674500 people in the 11 countries were estimated to be living with HIV, ranging from 5500 to 153400 in each country. Overall HIV prevalence was 0.22% (range, 0.09%-0.36%). Overall proportions of each previous stage were 84% diagnosed, 84% on ART, and 85% virally suppressed (60% of people living with HIV). Two countries achieved ≥90% for all stages, and more than half had reached ≥90% for at least 1 stage. European Union countries are nearing the 90-90-90 target. Reducing the proportion undiagnosed remains the greatest barrier to achieving this target, suggesting that further efforts are needed to improve HIV testing rates. Standardizing methods to derive comparable continuums of care remains a challenge.

Age and growth of the smooth hammerhead, Sphyrna zygaena, in the Atlantic Ocean: comparison with other hammerhead species

ABSTRACTThe smooth hammerhead Sphyrna zygaena (Sphyrnidae) is a pelagic shark occasionally caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Age and growth of S. zygaena was studied along a wide Atlantic region covering both the northern and southern hemispheres. Data from 304 specimens, caught between October 2009 and September 2014, ranging in size from 126 to 253 cm fork length (FL), were analysed. Growth models were fitted using the three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L0 (size at birth). Growth models were fitted to the sample data and data from several back-calculation models. The model fit to the quadratic modified Dahl-Lea back-calculated data seems to be the most appropriate to describe growth in this species, with resulting growth parameters of Linf = 285 cm FL, k = 0.09 year−1 for males and Linf = 293 cm FL, k = 0.09 year−1 for females. Compared with other species of the same genus, estimated growth coefficients for S. zygaena seem to fall in the low to middle range. Although further work is still needed, this study adds to knowledge of the vital life-history parameters of smooth hammerheads in the Atlantic Ocean, which can be used in the management and conservation of this species.

HIV Trends in the United States: Diagnoses and Estimated Incidence.

BackgroundThe best indicator of the impact of human immunodeficiency virus (HIV) prevention programs is the incidence of infection; however, HIV is a chronic infection and HIV diagnoses may include infections that occurred years before diagnosis. Alternative methods to estimate incidence use diagnoses, stage of disease, and laboratory assays of infection recency. Using a consistent, accurate method would allow for timely interpretation of HIV trends.ObjectiveThe objective of our study was to assess the recent progress toward reducing HIV infections in the United States overall and among selected population segments with available incidence estimation methods.MethodsData on cases of HIV infection reported to national surveillance for 2008-2013 were used to compare trends in HIV diagnoses, unadjusted and adjusted for reporting delay, and model-based incidence for the US population aged ≥13 years. Incidence was estimated using a biomarker for recency of infection (stratified extrapolation approach) and 2 back-calculation models (CD4 and Bayesian hierarchical models). HIV testing trends were determined from behavioral surveys for persons aged ≥18 years. Analyses were stratified by sex, race or ethnicity (black, Hispanic or Latino, and white), and transmission category (men who have sex with men, MSM).ResultsOn average, HIV diagnoses decreased 4.0% per year from 48,309 in 2008 to 39,270 in 2013 (P<.001). Adjusting for reporting delays, diagnoses decreased 3.1% per year (P<.001). The CD4 model estimated an annual decrease in incidence of 4.6% (P<.001) and the Bayesian hierarchical model 2.6% (P<.001); the stratified extrapolation approach estimated a stable incidence. During these years, overall, the percentage of persons who ever had received an HIV test or had had a test within the past year remained stable; among MSM testing increased. For women, all 3 incidence models corroborated the decreasing trend in HIV diagnoses, and HIV diagnoses and 2 incidence models indicated decreases among blacks and whites. The CD4 and Bayesian hierarchical models, but not the stratified extrapolation approach, indicated decreases in incidence among MSM.ConclusionsHIV diagnoses and CD4 and Bayesian hierarchical model estimates indicated decreases in HIV incidence overall, among both sexes and all race or ethnicity groups. Further progress depends on effectively reducing HIV incidence among MSM, among whom the majority of new infections occur.

Monitoring of the HIV Epidemic Using Routinely Collected Data: The Case of the United Kingdom.

We report on measures used to monitor the response to the UK HIV epidemic. We present analyses of routine data on HIV testing, diagnosis and care, and of CD4 back-calculation models to estimate country of HIV acquisition and incidence. Over the past decade, HIV and AIDS diagnoses and deaths declined while HIV testing coverage increased. Linkage into care, retention in care, and viral suppression was high with few socio-demographic differences. However, in 2013, incidence among MSM, and undiagnosed infection, also remained high, and more than half of heterosexuals newly diagnosed with HIV (the majority of whom were born-abroad) probably acquired HIV in the UK and were diagnosed late. HIV care following diagnosis is excellent in the UK. Improvements in testing and prevention are required to reduce undiagnosed infection, incidence and late diagnoses. Routinely collected laboratory and clinic data is a low cost, robust and timely mechanism to monitor the public health response to national HIV epidemics.

Bayesian hierarchical model used to analyze regression between fish body size and scale size: application to rare fish speciesZingel asper

Key-words: hierarchical Bayes model, backcalculation, fish, scales, Zingel asper Back-calculation allows to increase available data on fish growth. The accuracy of back-calculation models is of paramount importance for growth analysis. Frequentist and Bayesian hierarchical approaches were used for regression between fish body size and scale size for the rare fish species Zingel asper. The Bayesian approach permits more reliable estimation of back-calculated size, taking into account biological information and cohort variability. This method greatly improves estimation of backcalculated length when sampling is uneven and/or small.

Differences in Human Immunodeficiency Virus Care and Treatment Among Subpopulations in the United States

Early diagnosis of human immunodeficiency virus (HIV) infection, prompt linkage to and sustained care, and antiretroviral therapy are associated with reduced individual morbidity, mortality, and transmission of the virus. However, levels of these indicators may differ among population groups with HIV. Disparities in care and treatment may contribute to the higher incidence rates among groups with higher prevalence of HIV. To examine differences between groups of persons living with HIV by sex, age, race/ethnicity, and transmission category at essential steps in the continuum of care. We obtained data from the National HIV Surveillance System of the Centers for Disease Control and Prevention to determine the number of persons living with HIV who are aware and unaware of their infection using back-calculation models. We calculated the percentage of persons linked to care within 3 months of diagnosis on the basis of CD4 level and viral load test results. We estimated the percentages of persons retained in care, prescribed antiretroviral therapy, and with viral suppression using data from the Medical Monitoring Project, a surveillance system of persons receiving HIV care in select areas representative of all such persons in the United States. All HIV-infected persons in the United States. Percentage of persons living with HIV who are aware of their infection, linked to care, retained in care, receiving antiretroviral therapy, and achieving viral suppression. Of the estimated 1,148,200 persons living with HIV in 2009 in the United States, 81.9% had been diagnosed, 65.8% were linked to care, 36.7% were retained in care, 32.7% were prescribed antiretroviral therapy, and 25.3% had a suppressed viral load (≤200 copies/mL). Overall, 857 276 persons with HIV had not achieved viral suppression, including 74.8% of male, 79.0% of black, 73.9% of Hispanic/Latino, and 70.3% of white persons. The percentage of blacks in each step of the continuum was lower than that for whites, but these differences were not statistically significant. Among persons with HIV who were 13 to 24 years of age, only 40.5% had received a diagnosis and 30.6% were linked to care. Persons aged 25 to 34, 35 to 44, and 45 to 54 years were all significantly less likely to achieve viral suppression than were persons aged 55 to 64 years. Significant age disparities exist at each step of the continuum of care. Additional efforts are needed to ensure that all persons with HIV receive a diagnosis and optimal care to reduce morbidity, mortality, disparities in care and treatment, and ultimately HIV transmission. Ensuring that people stay in care and receive treatment will increase the proportion of HIV-infected individuals who achieve and maintain a suppressed viral load.

Can backcalculation models unravel complex larval growth histories in a tropical freshwater fish?

This experimental study compared the precision and accuracy of the biological intercept (BI), modified fry (MF) and time-varying growth (TVG) backcalculation models in estimating the early growth of the tropical freshwater purple-spotted gudgeon Mogurnda adspersa. Larvae were reared up to 41 days post hatching under two temperatures and four different feeding regimes. Food and temperature treatments induced complex growth profiles among fish, and although total length (LT ) and otolith radius were related under all conditions, some uncoupling was evident in the otolith-somatic-growth (OSG) relationship of fish subjected to periods of changing food availability. Furthermore, otolith growth was found to be significantly influenced by temperature, but not by food availability. Analysis of backcalculation residuals by linear mixed effects modelling revealed that BI and TVG were equally precise in predicting somatic growth, with the highest accuracy provided by TVG. The performance of all the three models declined as the OSG relationship weakened under low-food conditions, with maximum errors estimated to be 39, 60 and 36% of observed LT for the BI, MF and TVG models, respectively. The need for careful validation of backcalculation models is emphasized when examining fishes subjected to variable environmental conditions, and when exploring the differential influence of temperature and food on fish LT and otolith growth.

Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010

Non-fatal health outcomes from diseases and injuries are a crucial consideration in the promotion and monitoring of individual and population health. The Global Burden of Disease (GBD) studies done in 1990 and 2000 have been the only studies to quantify non-fatal health outcomes across an exhaustive set of disorders at the global and regional level. Neither effort quantified uncertainty in prevalence or years lived with disability (YLDs).Of the 291 diseases and injuries in the GBD cause list, 289 cause disability. For 1160 sequelae of the 289 diseases and injuries, we undertook a systematic analysis of prevalence, incidence, remission, duration, and excess mortality. Sources included published studies, case notification, population-based cancer registries, other disease registries, antenatal clinic serosurveillance, hospital discharge data, ambulatory care data, household surveys, other surveys, and cohort studies. For most sequelae, we used a Bayesian meta-regression method, DisMod-MR, designed to address key limitations in descriptive epidemiological data, including missing data, inconsistency, and large methodological variation between data sources. For some disorders, we used natural history models, geospatial models, back-calculation models (models calculating incidence from population mortality rates and case fatality), or registration completeness models (models adjusting for incomplete registration with health-system access and other covariates). Disability weights for 220 unique health states were used to capture the severity of health loss. YLDs by cause at age, sex, country, and year levels were adjusted for comorbidity with simulation methods. We included uncertainty estimates at all stages of the analysis.Global prevalence for all ages combined in 2010 across the 1160 sequelae ranged from fewer than one case per 1 million people to 350,000 cases per 1 million people. Prevalence and severity of health loss were weakly correlated (correlation coefficient -0·37). In 2010, there were 777 million YLDs from all causes, up from 583 million in 1990. The main contributors to global YLDs were mental and behavioural disorders, musculoskeletal disorders, and diabetes or endocrine diseases. The leading specific causes of YLDs were much the same in 2010 as they were in 1990: low back pain, major depressive disorder, iron-deficiency anaemia, neck pain, chronic obstructive pulmonary disease, anxiety disorders, migraine, diabetes, and falls. Age-specific prevalence of YLDs increased with age in all regions and has decreased slightly from 1990 to 2010. Regional patterns of the leading causes of YLDs were more similar compared with years of life lost due to premature mortality. Neglected tropical diseases, HIV/AIDS, tuberculosis, malaria, and anaemia were important causes of YLDs in sub-Saharan Africa.Rates of YLDs per 100,000 people have remained largely constant over time but rise steadily with age. Population growth and ageing have increased YLD numbers and crude rates over the past two decades. Prevalences of the most common causes of YLDs, such as mental and behavioural disorders and musculoskeletal disorders, have not decreased. Health systems will need to address the needs of the rising numbers of individuals with a range of disorders that largely cause disability but not mortality. Quantification of the burden of non-fatal health outcomes will be crucial to understand how well health systems are responding to these challenges. Effective and affordable strategies to deal with this rising burden are an urgent priority for health systems in most parts of the world.Bill & Melinda Gates Foundation.

Back-calculation of previous fish size using individually tagged and marked Atlantic cod (Gadus morhua)

The performance of five back-calculation (B-C) models was tested with individually tagged and multiple alizarin-marked Atlantic cod ( Gadus morhua ) reared at seasonally varying water temperature and food regimes over a 10-month period. The otoliths were transversely sectioned and the otolith growth between marks was measured along the dorsal, distal, and ventral radii and across the otolith width. Observed fish lengths at each marking time were compared with back-calculated lengths using linear and nonlinear scale and body proportional hypotheses (SPH and BPH) and biological intercept (BI) models. Measurements along the dorsal and distal radius with SPH and BI provided more accurate fish length estimates but with lower precision, whereas measurements of the ventral radius consistently produced greater overestimations by any model. Otolith width measurements produced moderately overestimated fish length estimates but with the highest precision and were significantly affected by temperature in all models. Certain combinations of model and otolith dimension were more sensitive to the length of the back-calculation time interval, whereas varying feeding regime induced temporary biases only. The selection of B-C model and otolith dimension thus depends not only on the environmental conditions that the fish experience, but also on the requirements of the application for which the B-C is used.

Stiffness characterisation of full-scale airfield test pavements using computational intelligence techniques

The falling weight deflectometer (FWD) is a non-destructive test equipment used to assess the structural condition of highway and airfield pavement systems and to determine the moduli of pavement layers. The backcalculated moduli are not only good pavement layer condition indicators but are also necessary inputs for conducting mechanistic based pavement structural analysis. In this study, artificial neural networks (ANNs)-based backcalculation models were employed to rapidly and accurately predict flexible airport pavement layer moduli from realistic FWD deflection basins acquired at the U.S. Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF). The uniformity characteristics of NAPTF flexible pavements were successfully mapped using the ANN predictions.

The back-calculation of size and growth from otoliths: Validation and comparison of models at an individual level

Multiple internal and external tagging experiments tested the applicability of five back-calculation models (Biological Intercept, Modified-Fry, Body Proportional Hypothesis, Time-Varying Growth, and an Age-Effects model) as predictors of individual growth trajectories of two marine cleaning gobies, Elacatinus evelynae and E. prochilos, that were raised in aquaria under conditions that resulted in variable growth. Mixed-effect model analyses of longitudinal records of otoliths and somatic growth collected at the individual level revealed that E. evelynae and E. prochilos produced daily increments on their otoliths for up to two months post-settlement and that the Modified-Fry model provided the most accurate size-at-age estimates despite the presence of age, growth and time-varying growth effects in the dataset. Very large errors in predicted size were produced by the Age-Effects model. The four other back-calculation models all provided slightly biased estimates of back-calculated size-at-age, with the Modified-Fry model providing the least biased estimates. Regardless of bias, both experimental and theoretical evidence indicated that back-calculated size was a better proxy of fish length than otoliths radius. Relationships between fish length and otoliths radius were allometric at the level of individuals, which explained why the Modified-Fry model performed better. However, this allometry was undetectable at the population level. This study represents the first attempt to validate modern back-calculation models using longitudinal data collected and analysed at the individual level. Our results suggest the use of the Modified-Fry model as a conservative approach in routine back-calculations of fish size at age from otoliths.

Neural Network-Based Approach for Analysis of Rigid Pavement Systems Using Deflection Data

This paper focuses on the development of backcalculation models based on artificial neural networks (ANNs) for predicting the layer moduli of the jointed plain concrete pavements, that is, the elastic modulus of the portland cement concrete (PCC) layer and the coefficient of subgrade reaction for the pavement foundation. The ANN-based models were trained to predict the layer moduli by using the falling-weight deflectometer (FWD) deflection basin data and the thickness of the concrete pavement structure. The ISLAB2000 finite element program, extensively tested and validated for more than 20 years, has been employed as an advanced structural model for solving the responses of the rigid pavement systems and generating a knowledge database. ANN-based backcalculation models trained with the results from the ISLAB2000 solutions have been found to be viable alternatives for rapid assessment (capable of analyzing 100,000 FWD deflection profiles in a single second) of the rigid pavement systems. The trained ANN-based models are capable of predicting the concrete pavement parameters with very low (&lt;0.4%) average absolute error values. The ANN model predictions and closed-form solutions were compared through the use of the FWD deflection data, and the results are summarized in the paper. In addition, a sensitivity study was conducted to verify the significance of the layer thicknesses and the effect of bonding between the PCC and the base layer in the backcalculation procedure. The results of this study demonstrated that the ANN-based models are capable of successfully predicting the rigid pavement layer moduli with high accuracy.

Consideration of Finite Slab Size in Backcalculation Analysis of Jointed Concrete Pavements

The effects of finite slab size and load transfer across joints usually are ignored in the backcalculation analysis of jointed concrete pavements when the test load is applied on an interior point of the slab concerned. Although correction factors have been proposed to take these effects into consideration, the benefits of doing so have yet to be established, and their use has not been accepted in routine backcalculation tests. A study was conducted to assess whether significant improvements in the accuracy of backcalculation analysis could be achieved by considering finite slab size and load transfer at joints in the backcalculation analysis of jointed concrete pavement systems. Five backcalculation methods were evaluated with measured deflection data extracted from the Long-Term Pavement Performance database, and comparisons were made with the measured pavement properties. The analysis based on the measured field data offered affirmative evidence of the theoretical lower- and upper-bound estimates provided by backcalculation solutions based on the infinite slab model and one-slab model, respectively. An error analysis was presented to show that the infinite slab model gave superior solutions as compared with the one-slab model. A nine-slab model that considered finite slab size and joint load transfer effects resulted in only marginal improvements in the backcalculation results. Two finite slab size models that applied correction factors to infinite-slab solutions were found to produce the largest errors among the five backcalculation models studied.