Equivalence Hypothesis Research Articles

Hypothesis testing methods for multi-reader multi-case studies

ABSTRACT Rationale and Objectives: Multi-reader multi-case (MRMC) studies are widely used to compare the diagnostic accuracies of different imaging modalities. Although Dorfman–Berbaum–Metz (DBM) method is the most popular one among the MRMC methods, the adaptions of ANOVA statistic for linear mixed model (LMM) are not based on solid theory and the assumption of ANOVA that all groups have the same number of samples might not be met in some situations. The purpose of the article is to investigate whether the statistics for testing fixed effect in linear mixed model can yield a closer type I error rate to nominal level. Materials and Methods: We proposed to use the statistics such as likelihood ratio test (LRT) and Wald statistic to test the hypothesis of equivalence in several imaging modalities. Extensive simulations were conducted and the application to a clinical example dataset was illustrated. Results: The simulation results showed the type I error rates of Wald statistic were closer to the nominal level under many simulated situations, especially when the simulated data was ordinal and the number of diseased and non-diseased were 100. Conclusion: The Wald statistic whose degrees of freedom ware approximated by Satterthwaite's method showed competitive performance, indicating the potential of the statistic applied in DBM model for MRMC analysis.

Does the emotional stance of human and virtual instructors in instructional videos affect learning processes and outcomes?

This study investigates the positivity principle – the idea that people respond more positively and learn better from an instructor who displays positive emotion than from an instructor who displays negative emotion – and the equivalence hypothesis – the idea that learners respond similarly to the emotional tone displayed by both human and virtual instructors. In this between-subjects design experiment, participants viewed one of eight instructional videos on binomial probability, varying in the emotion portrayed by the voice and gestures of an onscreen instructor and varying in whether the instructor was human or virtual. Participants either saw a positive instructor (happy or content) or a negative instructor (bored or frustrated) and that instructor was either human or virtual. In support of the positivity principle, participants recognized the positive or negative emotional tone of the instructor, felt a similar emotion to the instructor, and had more favorable social connection ratings for positive instructors. However, the positivity of the instructor did not impact how well participants performed on a delayed posttest. In support of the equivalence hypotheses, all of these effects were found for both human and virtual instructors. Overall, this study provided support for three of the four links in the positivity principle, and showed that the principle applied to both human and virtual instructors as per the equivalence hypothesis.

Impact of Budget Deficit Financing on Money Supply in Nigeria

This study empirically investigated the impact of budget deficit financing on money supply in Nigeria. The study is modeled using a framework of Keynesian theory of budget deficit financing and Richadian Equivalent hypothesis. Due to the homogeneity of macroeconomic variables, it adopted a vector error correction mechanism (VECM) which shows the existence of long run relationship between money supply and indicators of financing budget deficit. The general findings revealed that external source of financing budget deficit; internal source of financing budget deficit as well as debt servicing has a significant effect on money supply for the period under review in the Nigerian context. Base on these findings, the study recommended that external and internal source of financing budget deficit should be encouraged for effective and increased economic stability in Nigeria and not for political reasons. It should be properly channeled to productive sector of the economy that enhances economic stability.

The role of fiscal policies for external imbalances: Evidence from the European Union

We revisit the relation between budget deficits and current account deficits for 28 European Union countries from 1996 to 2019. We find that an increase in budget deficit of 1 pp of GDP results in a deterioration of the current account deficit of 0.318 pp of GDP, which supports the Twin Deficits Hypothesis. On the other hand, dynamic panel estimates partially corroborate the Ricardian Equivalence Hypothesis in the presence of a fiscal rules index. In addition: i) the relation between the two deficits is asymmetric and the negative impact of the recent Eurozone banking and sovereign debt crisis on the current account balance is observed; ii) with right-wing governments, the impact of the budget balance on the current account balance is mitigated; if the government is on the left, the impact of the budget balance on the current account balance is amplified; iii) after 2010, the budget balance positively affects the current account balance; and iv) the positive impact of the budget balance on the current account balance is higher in the cases of non-Eurozone countries, high budget deficit countries, and low exports countries, whereas it is lower in the cases of Eurozone countries, low budget deficit countries, and high exports countries.

Constitutive model for fibre reinforced composites with progressive damage based on the spectral decomposition of material stiffness tensor

Complex nature of the fibre reinforced composites, their non-homogeneity and anisotropy make their modelling a challenging task. Although the linear – elastic behaviour of the composites is well understood, there is still a significant uncertainty regarding prediction of damage initiation, damage evolution and material failure especially for a general loading case characterised with triaxial state of stress or strain. Consequently, simplifying assumptions are often unavoidable in development of constitutive models capable of accurately predicting damage. The approach used in this work uses decomposition of the strain energy based on spectral decomposition of the material stiffness tensor and an assumption that each strain energy component represent free energy for a characteristic deformation mode. The criteria for damage initiation are based on an assumption that the damage corresponding to a deformation mode is triggered when the strain energy for that mode exceeds a specified critical limit. In the proposed model the deformation modes are not interacting at continuum scale due to orthogonality of the eigenvectors, i.e. the stiffness tensor symmetry. Damage and its evolution are modelled by reduction of the principal material stiffness based on the effective stress concept and the hypothesis of strain energy equivalence. The constitutive model was implemented into Lawrence Livermore National Laboratory (LLNL) Dyna3d explicit hydrocode and coupled with a vector shock Equation of State. The modelling approach was verified and validated in a series of single element tests, plate impact test and high velocity impact of hard projectile impact on an aerospace grade carbon fibre reinforced plastic. The model accurately predicted material response to impact loading including the test cases characterised by presence of shock waves, e.g. the plate impact test. It was also demonstrated that the model was capable of predicting damage and delamination development in the simulation of the high velocity impact tests, where the numerical results were within 5% of the post impact experimental measurements.

Constitutive modelling of a self-healing composite matrix polymer material

In this work, a constitutive model of an intrinsically self-healing composite matrix material is presented. The developed model comprises a micro-damage initiation and evolution model, and a healing evolution model, which are combined with the von Mises linear isotropic hardening plasticity. It is implemented into the Abaqus/Standard user material subroutine UMAT and validated using experimental results of static tensile and two-cycle tensile tests performed on partially neutralised poly(ethylene-co-methacrylic acid) (EMAA) ionomer copolymer, Surlyn® 8940. In the development of the model, Continuum Damage Healing Mechanics (CDHM) concepts of nominal and healing configurations are used. In addition, these concepts are used along with the strain equivalence hypothesis to streamline the numerical implementation. The strain equivalence hypothesis relates strain and stress tensors in the nominal and the healing configuration. Finally, successful validation has shown that the developed model is able to accurately predict behaviour of Surlyn® 8940 coupons during tensile tests and it can precisely predict the accumulation of plastic strain.

Scalings of scale-by-scale turbulence energy in non-homogeneous turbulence

A theory of non-homogeneous turbulence is developed and applied to boundary-free shear flows. The theory introduces assumptions of inner and outer similarity for the non-homogeneity of two-point statistics, and predicts power-law scalings of second-order structure functions that have some similarities with but also some differences from Kolmogorov scalings. These scalings arise as a consequence of these assumptions, of the general interscale and interspace energy balance, and of an inner–outer equivalence hypothesis for turbulence dissipation. They reduce to the usual Kolmogorov scalings in stationary homogeneous turbulence. Comparisons with structure function data from three qualitatively different turbulent wakes provide support for the theory's predictions but also raise new questions for future research.

Constitutive modelling of plastically deformable self-healing materials

A novel elasto-plastic constitutive model of self-healing materials is proposed coupling continuum damage–healing mechanics (CDHM) framework with kinematic and isotropic hardening cases. A novel secondary damage internal variable is presented, eliminating an assumption in the existing literature that the healed area does not undergo damage again, thus improving the existing CDHM framework. The necessity of the proposed secondary damage variable is successfully demonstrated by a four spring material model. The improved CDHM framework is coupled with the three-dimensional elasto-plastic formulation containing nonlinear kinematic hardening and isotropic strain hardening effects. The proposed formulation is finally numerically implemented by return mapping approach employing the strain energy equivalence hypothesis from CDHM, and the macro-scale stress update is performed applying several different strain histories. A continuum tangent modulus expression is also derived, and a boundary value problem is successfully solved employing an in-house developed plane strain nonlinear finite element code. It is finally demonstrated, by the numerical results, that the secondary damage variable is crucial while obtaining the physically realistic stress–strain response of self-healing materials leading to the complete failure upon exhaustion of the healing capabilities.

Planar‐biaxial low‐cycle fatigue behavior of the nickel‐base alloy Inconel 718 at elevated temperatures under selected loading conditions

AbstractThe isothermal planar‐biaxial fatigue behavior was studied for two different disk batches of nickel‐base superalloy Inconel 718 using cruciform specimens at 400°C and 630°C under equi‐biaxial and shear loading. Additionally, non‐proportional tests were performed. The planar‐biaxial test results were compared with uniaxial reference tests using the von Mises equivalent strain hypothesis, a shear strain parameter of the critical plane, and a modified crack‐opening‐displacement strain range approach. Additionally, the crack initiation mechanism was analyzed. Using a modified crack‐opening‐displacement strain range approach, the low‐cycle fatigue lifetimes of the proportional planar‐biaxial tests (i.e., lifetimes up to 40,000 cycles) were described within a scatter band of two. Thus, it was better than using the equivalent strain of von Mises or a shear strain parameter. The fatigue crack initiation took place at oxidized primary carbides at the surface. The crack paths were presented.

Thermal Damage Constitutive Model and Brittleness Index Based on Energy Dissipation for Deep Rock

In deep underground engineering, rock usually encounters a high temperature problem. The stress–strain relationship of rock under high temperatures is the basis of engineering excavation. Based on the Lemaitre’s equivalent strain hypothesis and energy dissipation theory, the thermal damage constitutive model of rock is established. The results show that the peak stress, ultimate elastic energy and dissipated energy at the peak all decrease with the increase of temperature in a logistic function, which indicates that the increase of temperature aggravates the deterioration of rock’s mechanical properties. Compared with rock’s constitutive model that is established on strength criterion, the thermal damage constitutive model based on energy dissipation better reflects the phenomenon of stress drop after the peak and well describes the whole stress-strain curve of rock failure, which verifies the rationality of the model. The damage model further improves the theoretical system of the rock damage constitutive model and makes up for the defect in that the traditional damage model cannot reasonably explain the nature of rock failure. The brittleness index, defined based on the energy drop coefficient, shows a logistic function with the increase of temperature, which has good physical meaning. Analyzing the phenomenon of the rock stress drop from the perspective of energy is of great significance for deeply understanding the brittle fracture mechanism of rock.

The macroeconomic impacts of government debt in Pakistan

This paper examines the Ricardian equivalence hypothesis for Pakistan using a vector error-correction model. The sample period extends from June 2002 to January 2020. The results are reported using variance decompositions and impulse response functions. The base model contains six variables and is estimated with 4 lags. We find support for the idea that wealth does not increase as government debt increases; Hence, it proves the fact that economic agents are rational actors and foresee current expansionary actions of the government that result in accumulation of debt as the present value of future taxation that they have to pay and not an increase in wealth. The results remain robust to a change in sample, in Choleski ordering of the variables and in the lag length of the estimated models.

Bayesian interpretation of immunotherapy trials with dynamic treatment effects

IntroductionThe mechanism of action of immune checkpoints inhibitors hinders the writing of rational statistical analysis plans for phase III randomised clinical trials (RCTs) because of their unpredictable dynamic effects. The purpose is to illustrate the advantages of Bayesian reporting of treatment efficacy analysis in immunotherapy RCTs, in contrast to frequentist reporting. MethodFourteen RCTs (one with two pairwise comparisons) that failed to achieve their primary objective (overall survival, OS) were selected. These RCTs were reanalysed using Bayesian Cox models with dynamic covariate coefficients and time-invariant models. ResultsThe RCTs that met inclusion criteria were 7 lung cancer trials, various other tumours, with antiPD1, antiPDL1 or antiCTLA4 therapies. The minimum detectable effect (δS) was superior to the true benefit observed in all cases, in conditions of non-proportional hazards. Schoenfeld tests indicated the existence of PH assumption violations (p<0.05) in 6/15 cases.The Bayesian Cox models revealed a probability of benefit >79% in all the RCTs, with the therapeutic equivalence hypothesis unlikely. The OS curves diverged after a median of 9.1 months. Since the divergency, no non-proportionality was evinced in 13/15, while the Wald tests achieved p<0.05 in 12/15 datasets. In all cases, the Bayesian Cox models with dynamic coefficients detected fluctuations of the hazard ratio, and increased 2-year OS was the most likely hypothesis. ConclusionWe recommend progressively implementing Bayesian and dynamic analyses in all RCTs of immunotherapy to interpret and assess the credibility of frequentist results.

Impact of Budget Deficit Financing on Money Demand in Nigeria

The study empirically investigates the impact of budget deficit financing on money demand in Nigeria with an objective of finding the effect of budget deficit financing indicators such as external debt financing, domestic debt as well as debt servicing on money demand. The study is modeled using a framework of Keynesian theory of budget deficit financing and Richadian Equivalent hypothesis. The study adopted an auto redistributive lag model (ARDL) which shows the existence of long run relationship between money demand and indicators of financing budget deficit and ordinary Least Square. The general findings revealed that external source of financing budget deficit, internal source of financing budget deficit as well as debt servicing has a significant effect on money demand in the Nigerian context. Base on this findings, the study recommend that external and internal source of financing deficit should be encouraged for effective demand leading to economic stability reasons and not for political reasons and it should be properly channeled to productive sector of the economy that will enhance economic stability.

Mechanical properties of ultra-high strength cement-based materials (UHSC) incorporating metal powders and steel fibers

In this work, the mechanical properties of ultra-high strength cement-based materials (UHSC) incorporating metal powders and steel fibers under steam curing and autoclave curing were studied, with the special attention devoted to the flexural load-deflection response and compressive stress-strain behavior. Additionally, the hydration degree, pore structure characteristics and micro interface morphology were investigated to provide a thorough insight into the enhancement mechanism of metal powders and steel fibers on UHSC. The results show that the incorporation of Fe and Cu powders could enhance the flexural performance of UHSC, including the increased flexural strength and energy absorption capacity. Under uniaxial compression, improved peak stress, secant modulus, and energy absorption capacity of UHSC could be observed after the addition of Fe powders, but this improvement was negligible after the addition of Cu powders. Moreover, the statistical damage constitutive model based on strain equivalence hypothesis and improved statistical damage theory could reasonably describe the stress-strain behavior of UHSC under uniaxial compression. Furthermore, incorporating Fe and Cu powders could ameliorate the pore structure of UHSC, in which the harmful pores was converted into less harmful pores. Micro-interface morphology demonstrated that metal powders were closely bonded with cement paste, and no cracks or micro pores could be detected around the interface.

Study on Damage Statistical Constitutive Model of Triaxial Compression of Acid-Etched Rock under Coupling Effect of Temperature and Confining Pressure.

Based on Lemaitre’s strain equivalence hypothesis theory, it is assumed that the strength of acid-etching rock microelements under the coupling effect of temperature and confining pressure follows the Weibull distribution. Under the hypothesis that micro-element damage meets the D-P criterion and based on continuum damage mechanics and statistical theory, chemical damage variables, thermal damage variables and mechanical damage variables were introduced in the construction of damage evolution equations and constitutive models for acid-etching rocks considering the coupled effects of temperature and confining pressure. The required model parameters were obtained by theoretical derivation, and the model was verified based on the triaxial compression test data of granite. Comparing the experimental stress-strain curve with the theoretical stress-strain curve, the results show that they were in good agreement. By selecting reasonable model parameters, the damage statistical constitutive model can accurately reflect the stress-strain curve characteristics of rock in the process of triaxial compression. The comparison between the experimental and theoretical results also verifies the reasonableness and reliability of the model. This model provides a new rock damage statistical constitutive equation for the study of rock mechanics and its application in engineering, and has certain reference significance for rock underground engineering.

A new anisotropic elasto-plastic-damage model for quasi-brittle materials using strain energy equivalence

An anisotropic elasto-plastic-damage model is developed for quasi-brittle materials within the thermodynamics framework. The anisotropic damage is characterized by second-order damage tensors that are different under tensile and compressive loadings. The hypothesis of strain energy equivalence is adopted with two components, including the hypothesis of elastic strain energy equivalence and the hypothesis of plastic strain energy equivalence. The hypothesis of plastic strain energy equivalence is extended from metals to quasi-brittle materials so as to derive the relations of hardening stresses, which are previously assumed between the undamaged and damaged configurations for quasi-brittle materials. A plastic yield criterion is adopted simultaneously with a damage criterion to account for the coupled elasto-plastic-damage behavior under different loadings. The damage criterion can capture larger axial damage in uniaxial tension and smaller axial damage in uniaxial compression as compared with the lateral damage. The Helmholtz free energy functions are derived for three components: elastic, plastic, and damage. The constitutive laws are derived for three scenarios: the elastoplastic behavior without further damage evolution, the damage behavior without further plasticity evolution, and the coupled elasto-plastic-damage behavior. The anisotropic elasto-plastic-damage model is implemented in ABAQUS as a user material (UMAT) subroutine. The coupled constitutive laws in the continuum domain are implemented in an uncoupled way in the discrete domain with three steps, elastic predictor, plastic corrector, and damage corrector. The UMAT is validated in different conditions, including uniaxial, biaxial, and three-point bending tests. The advantage of considering the plastic free energy in anisotropic damage is illustrated through the strength envelope in biaxial loadings. The numerical results generally agree with experimental results, including the stress-strain curves in uniaxial tests, strength envelope in biaxial tests, and load-deflection curves in three-point bending tests.

Functional equivalence revisited: Costs and benefits of priming action with motor imagery and motor preparation.

The functional equivalence (FE) hypothesis suggests motor imagery (MI) is comparable with the planning stages of action. A strong interpretation of this hypothesis suggests MI can prime subsequent actions in a way that should be indistinguishable from motor preparation (MP). Alternatively, MI could involve more richly informative motor plans than MP, producing different effects on the performance of subsequent actions. Although past research has demonstrated MI can prime action, little research has directly compared it with MP, and so the value of a strong FE interpretation for understanding MI remains unclear. In the present study, a precueing paradigm was used in 4 experiments, and congruency effects of MI and MP on subsequent action were compared. Precues instructed participants to prepare for (MP condition) or imagine (MI condition) a corresponding response prior to making a real response to the imperative stimulus, which was either congruent or incongruent with the precue information. Experiment 1 provided first evidence favoring our alternative hypothesis that imagery-primed responses should result in larger response priming effects than prepared-responses, suggesting that MI might involve more richly informative motor plans than preparation for action alone. In experiment 2, we manipulated interstimulus foreperiods and replicated the MI-priming effect, showing it to be independent of differences in temporal uncertainty between MI and MP. Experiment 3 showed the MI-priming effect is present in both foot and finger responses, and Experiment 4 suggested the larger congruency effects in the MI condition could not be explained by differences in cognitive load between MI and MP. These results suggest that a strong FE hypothesis does not hold. Findings are discussed in line with the predictive processing models of action and MI. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A NEW ANISOTROPIC PLASTIC-DAMAGE MODEL AND ITS NUMERICAL IMPLEMENTATION FOR PLAIN CONCRETE

A new and relatively simple anisotropic plastic-damage constitutive model is developed to facilitate the numerical simulation of the failure of concrete structures. For better describe the different damage mechanisms of concrete under tensile and compressive loadings, two different damage evolution equations, being suitable for determining the anisotropic tensile and compressive damage variables, are established. Moreover, the strain equivalence hypothesis is used to assume that the strains in both the effective and nominal configurations are equal. Through this method, the deducing process of the model can be simplified, and the effective stress calculation and the damage evolution are able to be implemented by a decoupled algorithm. Thusly, the plastic part of the model can be implemented implicitly, and the damage part and nominal stress calculation can be implemented explicitly, which is convenient for numerical implementation. Finally, the model response is compared to a wide range of test results. The results show that the model is able to describe the nonlinear behavior of concrete in three-dimensional stress state well. The simulation of double-edge-notched (DEN) specimen shows that: the model can reflect the characteristics of concrete damage anisotropy. The results are more consistent with the actual situation, and the computational efficiency is also higher than that of the concrete damage plasticity (CDP) model provided by ABAQUS software.

On the constitutive modelling of elasto-plastic self-healing materials

A novel three-dimensional elasto-plastic damage-healing (EPDH) model, based on continuum damage mechanics, is proposed capturing the self-healing phenomenon occurring in plastically deforming materials. A novel secondary damage variable, with separate evolution law, is introduced removing an assumption in the existing literature that the healed area cannot undergo damage again or healed area undergoes damage only once. The implicit damage-healing formulation, based on the irreversible thermodynamics, is developed detailing evolution equations of all internal variables. A novel pressure-dependent yield surface (qualitatively behaving like Gurson model) is developed by damage-healing equivalent stress modifying von Mises yield surface. The physical interpretation of damage and healing energy release rates are presented to elucidate their impact on the energy dissipation within the system. The proposed formulation is numerically implemented by return mapping approach employing elastic strain equivalence hypothesis. The applicability of newly proposed EPDH + secondary damage framework is successfully demonstrated considering different strain histories. The secondary damage variable is finally found crucial while obtaining the physically realistic stress–strain response of self-healing materials leading to complete failure upon exhaustion of healing capabilities.

Study on implicit finite-element method for steel-arch support

The steel-arch structure in soft-rock tunnels is very small and densely arranged. Too many elements would exist if the solid element is adopted for its simulation, and applying these elements in actual engineering practice is difficult. Therefore, an implicit finite-element method (FEM) to simulate the support effect of steel arches was proposed based on the principle of stiffness superposition. First, an equivalent mechanical model of a steel arch was established based on the principle of stiffness equivalence and deformation-coordination hypothesis. Then, a new concept called auxiliary element was presented. According to this concept, an implicit finite-element model of the equivalent element of the steel arch was developed using the reconstruction technology of elements. The equivalent-stiffness equation of the implicit equivalent element was derived based on the interpolation theory and element-equilibrium equation of FEM, and the equivalent stiffness of the implicit equivalent element was superposed on the stiffness matrix of the auxiliary element to simulate the support effect of the steel arch. Finally, a numerical case was presented to verify the rationality of this method and correctness of the programming. Establishing a solid model of the steel arch using this method was not necessary. Thus, the modeling work was greatly simplified, and adjusting the support scheme was convenient, which provided a new numerical simulation method for the support design of steel arch in soft-rock tunnels.