A comparative study of fiber-matrix interactions by using micromechanical models

The purpose of this study is to describe the interfacial interactions in terms of stress distributions on short fibers in fiber-matrix unit-cell models. The fiber and matrix are subjected to tensile loading. The study consists of three main parts. First, fiber-matrix cell segments are modeled using a 3D finite-element analysis (FEA) with ANSYS. Three different finite-element geometrical unit-cell models are generated in order to simulate the Cox analytical model: a fiber-matrix combination, a single fiber, and a single matrix element. The second part contains the results of 3D FE analyses, which are applied to the Cox formulations by using a computer program developed. In the last part, the analytical solutions for distributions of normal and shear stresses are investigated. Cox 2D linear elasticity solutions, together with finite-element ones, are presented in detail in graphs. The interfacial interactions between the fibers and matrix are also discussed considering the relative changes in the distributions of normal and shear stresses. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 505–520, July–August, 2008.     

A comparative study of parametric mortality projection models

The relative merits of different parametric models for making life expectancy and annuity value predictions at both pensioner and adult ages are investigated. This study builds on current published research and considers recent model enhancements and the extent to which these enhancements address the deficiencies that have been identified of some of the models. The England & Wales male mortality experience is used to conduct detailed comparisons at pensioner ages, having first established a common basis for comparison across all models. The model comparison is then extended to include the England & Wales female experience and both the male and female USA mortality experiences over a wider age range, encompassing also the working ages.     

A comparative study of Gaussian geostatistical models and Gaussian Markov random field models

Gaussian geostatistical models (GGMs) and Gaussian Markov random fields (GMRFs) are two distinct approaches commonly used in spatial models for modeling point-referenced and areal data, respectively. In this paper, the relations between GGMs and GMRFs are explored based on approximations of GMRFs by GGMs, and approximations of GGMs by GMRFs. Two new metrics of approximation are proposed : (i) the Kullback-Leibler discrepancy of spectral densities and (ii) the chi-squared distance between spectral densities. The distances between the spectral density functions of GGMs and GMRFs measured by these metrics are minimized to obtain the approximations of GGMs and GMRFs. The proposed methodologies are validated through several empirical studies. We compare the performance of our approach to other methods based on covariance functions, in terms of the average mean squared prediction error and also the computational time. A spatial analysis of a dataset on PM_2.5 collected in California is presented to illustrate the proposed method.     

A graphics processor for comparative studies using microscopic traffic simulation models

Computer traffic simulation models are valuable tools for the design and deployment of Intelligent Transportation Systems (ITS). Simulations of traffic flow can be used for the analysis and assessment of potential ITS technologies. Using simulations, alternative systems can be tested under identical conditions so the effects of oversaturated conditions, spillback, queuing, and overlapping bottlenecks can be measured. The Federal Highway Administration (FHWA) microscopic traffic simulation models, NETSIM, FRESIM, and CORSIM, are regarded as highly comprehensive but somewhat difficult to use. A graphics processor, TRAFVU, has recently been developed for analyzing the output of these microscopic models. TRAFVU was designed to support direct comparison of alternatives to facilitate design and evaluation. Applications of the CORSIM traffic simulation model and the TRAFVU graphics processor to interchange design and developing incident management strategies are presented.     

A comparative study of a heat and fluid flow problem using three models of different levels of sophistication

Three mathematical models of different levels of sophistication have been used to study a practical problem on underground heat and fluid flow, associated with the seasonal storage of hot water in an aquifer. A number of scenarios have been examined using the three models. For the basic problem the three models yield similar results, so use of the simplest is preferred. For several variations on the problem, only the more complicated models are adequate to properly address the problem. In general, the choice of an appropriate model is very problem-specific and requires not only experience with modelling methods, but also an understanding of the physics of the problem.     

Estimating criterion weights using eigenvectors: A comparative study

In addition to Saaty's eigenvector, there are infinitely many eigen weight vectors which can be constructed for any given data of estimated weight ratios. As the judgment of the ratios are dependent on personal experience, learning, situations and state of mind, inconsistencies and degree of easiness or judgment on these individual ratios can be different, we study the properties of the different eigen weight vectors, including that of Saaty and that recently proposed by Cogger and Yu. A general framework for the construction of eigen weight vectors incorporating that confidence in obtaining the individual ratios can be different will be proposed and discussed.     

A study of solute-solvent interactions by conductance measurements

Proceedings - Mathematical Sciences - The interaction of a number of alkali, alkaline earth and transition element cations with solvents like triethyl phosphate, dimethyl sulphoxide and dimethyl...     

A comparative study of transient capillary rise using direct numerical simulations

The rise of liquid in capillaries, or between two parallel plates as the 2D variant thereof, represents a challenging test case for two-phase flow solvers without a full analytic solution. Four different numerical approaches are compared for the rise of liquid, also providing reference data being of high relevance for capillarity-dominated wetting processes. The used methods are an Arbitrary Lagrangian–Eulerian method (OpenFOAM solver interTrackFoam), a geometric Volume of Fluid code (FS3D), an algebraic Volume of Fluid method (OpenFOAM solver interFoam), and a level-set based extended discontinuous Galerkin discretization (BoSSS).While the transient rise height shows excellent agreement between the different implementations, the velocity fields at the interface demonstrate a different level of local accuracy of the available approaches. Reducing the slip length reduces the overall dynamics of the system, thus yielding a qualitative change in the rise behavior – a behavior that is not covered by simplified ODE models. The obtained rise height results are vailable online: http://dx.doi.org/10.25534/tudatalib-173     

A comparative study of deformations of elastic-viscoplastic plates using different structural hypotheses

In the present study, circular metal plates are subjected to impulsive loadings leading to geometrically and physically non-linear deformations. In the theoretical model, different structural hypotheses are implemented into a finite element code and the hypotheses leading to the most precise numerical predictions are studied. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Discrete kernels,loss functions and parametric models in discrete discrimination: A comparative study

Two kernel-based approaches to discriminant analysis are considered: the traditional one where kernels are used to estimate the distribution of the predictor variables given the group and a direct kernel method where kernels are used to estimate the a posteriori probabilities directly. For both approaches cross-validatory choice of smoothing parameters is based on various loss functions which are directly connected to the separation of groups. Comparison with parametric models shows the improvement gained by the more flexible kernel approaches.     

A collective risk comparative study

Infinite time ruin probabilities are computed by the convolution method, the incomplete gamma function method, and an inverse Gaussian method for a real-life example involving data from 24,000 life insurance policies. Some analysis of the methods, and computational suggestions are included.     

Soliton interactions of integrable models

The solution of integrable (n+1)-dimensional KdV system in bilinear form yields a dromion solution that is localized in all directions. The interactions between two dromions are studied both in analytical and in numerical for three (n+1)-dimensional KdV-type equations (n=1, 2, 3). The same interactive properties between two dromions (solitons) are revealed for these models. The interactions between two dromions (solitons) may be elastic or inelastic for different form of solutions.     

Thermoelastic homogenization of periodic composites using an eigenstrain-based micromechanical model

This paper presents a study on effective thermoelastic properties of composite materials with periodic microstructures. The overall elastic moduli and coefficients of thermal expansion of such materials are evaluated by a micromechanical model based on the Eshelby equivalent inclusion approach. The model employs Fourier series in the representation of the periodic strain and displacement fields involved in the homogenization procedures and uses the Levin's formula for determining the effective coefficients of thermal expansion. Two main objectives can be highlighted in the work. The first of them is the implementation and application of an efficient strategy for computation of the average eigenstrain vector which represents a crucial task required by the thermoelastic homogenization model. The second objective consists in a detailed investigation on the behavior of the model, considering the convergence of results and efficiency of the strategy used to obtain the approximate solution of the elastic homogenization problem. Analyses on the complexity of the eigenstrain fields in function of the inclusion volume fractions and contrasts between the elastic moduli of the constituent phases are also included in the investigation. Comparisons with results provided by other micromechanical methods and experimental data demonstrate the very good performance of the presented model.     

Some selection criteria for nested binary choice models: a comparative study

This paper deals with the problem of choosing the optimum criterion to select the best of a set of nested binary choice models. Special attention is given to the procedures which are derived in a decision-theoretic framework, called model selection criteria (MSC). We propose a new criterion, which we call C ₂, whose theoretical behaviour is compared with that of the AIC and SBIC criteria. The result of the theoretical study shows that the SBIC is the best criterion whatever the situation we consider, while the AIC and C ₂ are only adequate in some cases. The Monte Carlo experiment that is carried out corroborates the theoretical results and adds others: finite sample behaviour and robustness to changes in some aspects of the data generating process. The classical hypothesis testing procedures LR and LM are included and compared with the three criteria of the MSC category. The authors wish to thank the financial support provided by the Spanish Department of Education under project BEC 2003-01757.     

Selection of parameter values in environmental models using sparse data: A case study

Models of environmental processes must often be constructed without the use of extensive data sets. This can occur because the exercise is preliminary (aimed at guiding future data collection) or because requisite data are extremely difficult, expensive, or even impossible to obtain. In such cases traditional, statistically based methods for estimating parameters in the model cannot be applied; in fact, parameter estimation cannot be accomplished in a rigorous way at all. We examine the use of a regionalized sensitivity analysis procedure to select appropriate values for parameters in cases where only sparse, imprecise data are available. The utility of the method is examined in the context of equilibrium and dynamic models for describing water quality and hydrological data in a small catchment in Shehandoah National Park, Virginia. Results demonstrate that (1) models can be “tentatively calibrated” using this procedure; (2) the data most likely to provide a stringent test of the model can be identified; and (3) potential problems with model identifiability can be exposed in a preliminary analysis.     

Throughput optimization in robotic cells with input and output machine buffers: A comparative study of two key models

We consider the problem of scheduling operations in a robotic cell processing a single part type. Each machine in the cell has a one-unit input buffer and a one-unit output buffer. The machines and buffers are served by one single gripper robot. The domain considered is free-pickup cells with additive inter-machine travel time. The processing constraints specify the cell to be a flow shop. The objective is to find a cyclic sequence of robot moves that minimizes the long-run average time to produce a part or, equivalently, maximizes throughput. Bufferless robotic cells have been studied extensively in the literature. However, the few studies of robotic cells with output buffers at each machine have shown that the throughput can be improved by such a configuration. We show that there is no throughput advantage in providing machine input buffers in addition to output buffers. The equivalence in throughput between the two models has significant practical implications, since the cost of providing additional buffers at each machine is substantial.     

Robust canonical correlations: A comparative study

Summary  Several approaches for robust canonical correlation analysis will be presented and discussed. A first method is based on the definition of canonical correlation analysis as looking for linear combinations of two sets of variables having maximal (robust) correlation. A second method is based on alternating robust regressions. These methods are discussed in detail and compared with the more traditional approach to robust canonical correlation via covariance matrix estimates. A simulation study compares the performance of the different estimators under several kinds of sampling schemes. Robustness is studied as well by breakdown plots.     

A comparative evaluation of interactive solution methods for multiple objective decision models

This paper describes a laboratory experiment which compares the performance from the user's point of view of four different solution methods for multiple objective decision models with continuous variables. These are the method of Zionts and Wallenius, the surrogate worth tradeoff method, the method of Steuer and Choo and a simplistic ‘naive’ solution method. The users exhibited different preferences among the different solution methods with the method of Steuer and Choo favoured overall. The results highlight a need for solution methods to accommodate the decision making characteristics of the user.     

A comparative study of crossover in differential evolution

In order to understand the role of crossover in differential evolution, theoretical analysis and comparative study of crossover in differential evolution are presented in this paper. Two new crossover methods, namely consecutive binomial crossover and non-consecutive exponential crossover, are designed. The probability distribution and expectation of crossover length for binomial and exponential crossover used in this paper are derived. Various differential evolution algorithms with different crossover methods including mutation-only differential evolution are comprehensively compared at system level instead of parameter level. Based on the theoretical analysis and simulation results, the effect of crossover on the reliability and efficiency of differential evolution algorithms is discussed. Some insights are revealed.     

A comparative study of methodologies for designing IDSSs

In this paper, we describe a comprehensive study conducted to understand the methodologies which are being used to design Intelligent Decision Support Systems (IDSSs) and to identify the key methodological problems and benefits with using these methodologies. This comprehensive study consists of two parts. The first part is two surveys which together identify the design methodologies being used by a group of IDSS developers and how acceptable they believe their methodologies were for designing their IDSSs. The second part is a comparison of six major formal IDSS design methodologies recently published in the literature and which are not yet known to many developers. This paper is presented to assist IDSS developers in understanding what support can be gained from using existing design methodologies and hence choose the correct one for their project. Furthermore, the paper may be used by IDSS developers to compare the way that they work with the approach proposed by other developers.