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Continuum Approach (continuum + approach)
Selected AbstractsINTERNATIONAL AND INTRA-NATIONAL TRADE: A CONTINUUM APPROACH,THE JAPANESE ECONOMIC REVIEW, Issue 3 2009SUGATA MARJIT We build up a Ricardian trade model with multiple regions within a nation and examine how international trade determines interregional patterns of production and specialization. We show that the degree of interregional concentration of economic activities moves in different directions in two trading nations. The role of "absolute advantage" becomes crucial in dictating the course of income disparity across regions. We discuss cases with varying degrees of labour mobility and reconfirm the result on post-trade interregional concentration and dispersion. Later we explore the impact of "scale factor" in this model and show how principle of comparative advantage and economies of scale interact to determine the pattern of specialization and volume of trade. [source] Dynamic response of intrinsic continua for use in biological and molecular modeling: Explicit finite element formulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2009Michael J. Leamy Abstract An intrinsic beam formulation has recently appeared (AIAA J. 2003; 41(6):1131,1137), which presents the three-dimensional equations of motion governing spatial and temporal changes in a one-dimensional continua's curvature, strain, rectilinear velocity, and angular velocity. The formulation would suggest several computational advantages over more-traditional displacement-based continua approaches: low-order interpolation functions can describe generally curved and twisted continua configurations; inter-element displacements, slopes, strains, and curvatures can be matched; and finite rotational variables and their complexities are absent. Here, we present a completed intrinsic continua finite element development and critical analysis, which follows from an earlier preliminary treatment as applied to carbon nanotubes (Int. J. Solids Struct. 2007; 44:874,894). Modeling of nodal displacements and rotations are included. Explicit time stepping, with desired high-frequency damping, is accomplished using an implementation of the generalized-, method. Zero-energy modes inherent in the formulation are also identified and rectified. Finally, we document very good agreement between results predicted with the intrinsic continua finite element simulator and results generated using more-traditional finite element simulations. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of microcracking on the micromechanics of fatigue crack growth in austempered ductile ironFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2001J. Ortiz The effect of microcracking on the mechanics of fatigue crack growth in austempered ductile iron is studied in this paper. The mechanism of fatigue crack growth is modelled using the boundary element method, customized for the accurate evaluation of the interaction effects between cracks and microcracks emanating from graphite nodules. The effects of nodule size and distribution and crack closure are considered, with deviation bounds of computed results estimated through weight-function analyses. A continuum approach is employed as a means of quantifying the shielding effect of microcracking on the dominant propagating crack, due to the reduction of stiffness of the material in the neighbourhood of the crack tip. Although the results obtained may not yield actual numbers for real cases, they are in accordance with experimental observations and demonstrate how the main factors affect the crack growth of the macrocrack. [source] Flow,stress coupled permeability tensor for fractured rock massesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2008Chuang B. Zhou Abstract In this paper a new analytical model is proposed to determine the permeability tensor for fractured rock masses based on the superposition principle of liquid dissipation energy. This model relies on the geometrical characteristics of rock fractures and the corresponding fracture network, and demonstrates the coupling effect between fluid flow and stress/deformation. This model empirically considers the effect of pre-peak shear dilation and shear contraction on the hydraulic behavior of rock fractures and can be used to determine the applicability of the continuum approach to hydro-mechanical coupling analysis. Results of numerical analysis presented in this paper show that the new model can effectively describe the permeability of fractured rock masses, and can be applied to the coupling analysis of seepage and stress fields. Copyright © 2008 John Wiley & Sons, Ltd. [source] Calculation of affinities of peptides for proteinsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2004Serena Donnini Abstract Several methodologies were employed to calculate the Gibbs standard free energy of binding for a collection of protein,ligand complexes, where the ligand is a peptide and the protein is representative for various protein families. Almost 40 protein,ligand complexes were employed for a continuum approach, which considers the protein and the peptide at the atomic level, but includes solvent as a polarizable continuum. Five protein,ligand complexes were employed for an all-atom approach that relies on a combination of the double decoupling method with thermodynamic integration and molecular dynamics. These affinities were also computed by means of the linear interaction energy method. Although it generally proved rather difficult to predict the absolute free energies correctly, for some protein families the experimental ranking order was correctly reproduced by the continuum and all-atom approach. Considerable attention has also been given to correctly analyze the affinities of charged peptides, where it is required to judge the effect of one or more ions that are being decoupled in an all-atom approach to preserve electroneutrality. The various methods are further judged upon their merits. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 393,411, 2004 [source] Beyond Stages of Change: Multi-Determinant Continuum Models of Action Readiness and Menu-Based InterventionsAPPLIED PSYCHOLOGY, Issue 1 2008Charles Abraham The merits of modelling action readiness as a series of stages is discussed, focusing on the Health Action Process Approach (HAPA) which postulates a motivational stage (for non-intenders) and a volitional stage (for intenders). The HAPA helpfully clarifies that the relationship between self-efficacy and action may be different for inexperienced intenders and experienced actors. This model also usefully distinguishes between different types of planning undertaken by intenders and it is suggested that further specification of planning tasks could explain why some intenders act while others do not. Despite the advantages of the HAPA, it is argued that the distinction between intenders and non-intenders is fuzzy and unstable and that demarcation of the stage boundary is arbitrary. A multi-determinant, multi-goal continuum approach is recommended. Such modelling recognises graded discontinuities throughout the development of action readiness from attitude formation to behaviour change maintenance. It is argued that menu-based interventions designed to deliver different messages and materials to people with different action-readiness deficits may be more cost effective than stage-tailored interventions. On discute de l'intérêt qu'il y a de modéliser la préparation à l'action en une série de stades à partir de l'Approche des Processus d'Action en faveur de la Santé (HAPA) qui pose l'existence d'une phase motivationnelle (pour ceux qui n'ont pas l'intention d'agir) et d'une phase volitionnelle (pour ceux qui l'ont). L'HAPA met utilement en évidence que la relation entre l'auto-efficience et l'action peut différer selon que l'on a affaire à un acteur expérimenté ou à une personne sans expérience qui pense agir. Ce modèle fait aussi une distinction utile entre les différentes sortes de planification qui s'offrent à ceux qui ont l'intention d'agir et laisse entendre qu'un approfondissement de la planification des tâches pourrait expliquer pourquoi certains passent à l'action et d'autres pas. En dépit de l'intérêt de l'HAPA, on peut penser que la distinction entre l'intention et l'absence d'intention est floue et instable et que le découpage en stades est arbitraire. On recommande une approche retenant un continuum à déterminants et à buts multiples. Cette modélisation reconnaît l'existence de discontinuités échelonnées tout au long du développement de la préparation à l'action depuis la formation de l'attitude jusqu'au changement effectif du comportement. On défend l'idée que les interventions à la carte conçues pour procurer différents messages et fournitures aux gens qui présentent différentes carences de préparation à l'action peuvent être plus rentables que les interventions basées sur les stades. [source] Predicting the tautomeric equilibrium of acetylacetone in solution.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2010Abstract This study investigates how the various components (method, basis set, and treatment of solvent effects) of a theoretical approach influence the relative energies between keto and enol forms of acetylacetone, which is an important model system to study the solvent effects on chemical equilibria from experiment and theory. The computations show that the most popular density functional theory (DFT) approaches, such as B3LYP overestimate the stability of the enol form with respect to the keto form by ,10 kJ mol,1, whereas the very promising SCS-MP2 approach is underestimating it. MP2 calculations indicate that in particular the basis set size is crucial. The Dunning Huzinaga double , basis (D95z(d,p)) used in previous studies overestimates the stability of the keto form considerably as does the popular split-valence plus polarization (SVP) basis. Bulk properties of the solvent included by continuum approaches strongly stabilize the keto form, but they are not sufficient to reproduce the reversal in stabilities measured by low-temperature nuclear magnetic resonance experiments in freonic solvents. Enthalpic and entropic effects further stabilize the keto form, however, the reversal is only obtained if also molecular effects are taken into account. Such molecular effects seem to influence only the energy difference between the keto and the enol forms. Trends arising due to variation in the dielectric constant of the solvent result from bulk properties of the solvent, i.e., are already nicely described by continuum approaches. As such this study delivers a deep insight into the abilities of various approaches to describe solvent effects on chemical equilibria. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Multiscale simulation of polycrystal mechanics of textured ,-Ti alloys using ab initio and crystal-based finite element methodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008D. Ma Abstract Crystal-based finite element methods (FEM) are versatile continuum approaches for predicting mechanical properties and deformation-induced crystallographic textures. They can be applied to both, elastic,plastic and elastic problems. The methodology is based on (i) a detailed understanding of the underlying crystal deformation mechanisms and (ii) a number of constitutive material parameters that are often difficult to measure. First principle calculations, that take into account the discrete nature of matter at the atomic scale, are an alternative way to study mechanical properties of single crystals without using empirical parameters. In this study we demonstrate how to combine these two well-established modeling tools, viz., ab initio modeling and crystal mechanical FEM, for an improved approach to design of polycrystalline materials. The combination is based on (i) the determination of basic thermodynamic and elastic parameter trends in metallurgical alloy design using density-functional (DFT) calculations (P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964), W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965) [1, 2], respectively) and (ii) the up-scale transfer of these results into crystal-based finite element simulations which take into account the anisotropic nature of the elastic,plastic deformation of metals. The method is applied to three body-centered cubic (bcc, ,) Ti,Nb alloys for bio-medical applications. The study addresses two technological processes, namely, the prediction of texture evolution during cold rolling (elastic-plastic problem) and elastic bending of textured polycrystals (elastic problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||