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Density-decomposed orbital-free density functional theory for covalently bonded molecules and materials

Physical Review B 2012年第23期86卷 235109-235109页

作者： Junchao Xia Emily A. Carter Department of Mechanical and Aerospace Engineering Princeton University Princeton New Jersey 08544-5263 USA Program in Applied and Computational Mathematics and Andlinger Center for Energy and the Environment Princeton University Princeton New Jersey 08544-5263 USA

We propose a density decomposition scheme using a Wang-Govind-Carter- (WGC-) based kinetic energy density functional (KEDF) to accurately and efficiently simulate various covalently bonded molecules and materials within orbital-free (OF) density functional theory (DFT). By using a local, density-dependent scale function, the total density is decomposed into a highly localized density within covalent bond regions and a flattened delocalized density, with the former described by semilocal KEDFs and the latter treated by the WGC KEDF. The new model predicts reasonable equilibrium volumes, bulk moduli, and phase-ordering energies for various semiconductors compared to Kohn-Sham (KS) DFT benchmarks. The decomposition formalism greatly improves numerical stability and accuracy, while retaining computational speed compared to simply applying the original WGC KEDF to covalent materials. The surface energy of Si(100) and various diatomic molecule properties can be stably calculated and also agree well with KSDFT benchmarks. This linear-scaled, computationally efficient, density-partitioned, multi-KEDF scheme opens the door to large-scale simulations of molecules, semiconductors, and insulators with OFDFT.

关键词： PHYSICAL sciences research MOLECULES SEMICONDUCTORS BENCHMARKING (Management) CRYSTALS SURFACE energy COVALENT bonds (Chemistry)

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Model reduction for agent-based social simulation: Coarse-graining a civil violence model

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Physical Review E 2012年第6期85卷 066106-066106页

作者： Yu Zou Vladimir A. Fonoberov Maria Fonoberova Igor Mezic Ioannis G. Kevrekidis Department of Chemical and Biological Engineering and Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Aimdyn Inc. 1919 State Street Suite 207 Santa Barbara California 93101 USA Department of Mechanical Engineering University of California Santa Barbara Santa Barbara California 93106 USA

Agent-based modeling (ABM) constitutes a powerful computational tool for the exploration of phenomena involving emergent dynamic behavior in the social sciences. This paper demonstrates a computer-assisted approach that bridges the significant gap between the single-agent microscopic level and the macroscopic (coarse-grained population) level, where fundamental questions must be rationally answered and policies guiding the emergent dynamics devised. Our approach will be illustrated through an agent-based model of civil violence. This spatiotemporally varying ABM incorporates interactions between a heterogeneous population of citizens [active (insurgent), inactive, or jailed] and a population of police officers. Detailed simulations exhibit an equilibrium punctuated by periods of social upheavals. We show how to effectively reduce the agent-based dynamics to a stochastic model with only two coarse-grained degrees of freedom: the number of jailed citizens and the number of active ones. The coarse-grained model captures the ABM dynamics while drastically reducing the computation time (by a factor of approximately 20).

关键词： VIOLENCE SOCIAL dynamics STOCHASTIC models CITIZENS SOCIAL interaction DEGREES of freedom

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Nonlinear Geometric Effects in mechanical Bistable Morphing Structures

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Physical Review Letters 2012年第11期109卷 114302-114302页

作者： Zi Chen Qiaohang Guo Carmel Majidi Wenzhe Chen David J. Srolovitz Mikko P. Haataja Department of Mechanical and Aerospace Engineering Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials (PRISM) Princeton University Princeton New Jersey 08544 USA Department of Biomedical Engineering Washington University St. Louis Missouri 63130 USA College of Materials Science and Engineering Fuzhou University Fuzhou Fujian 350108 China Department of Mathematics and Physics Fujian University of Technology Fuzhou Fujian 350108 China Department of Mechanical Engineering Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA Department of Materials Science and Engineering Fujian University of Technology Fuzhou Fujian 350108 China Institute for High Performance Computing 1 Fusionopolis Way Singapore 138632 Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA School of Mathematics Institute for Advanced Study Princeton New Jersey 08540 USA

Bistable structures associated with nonlinear deformation behavior, exemplified by the Venus flytrap and slap bracelet, can switch between different functional shapes upon actuation. Despite numerous efforts in modeling such large deformation behavior of shells, the roles of mechanical and nonlinear geometric effects on bistability remain elusive. We demonstrate, through both theoretical analysis and tabletop experiments, that two dimensionless parameters control bistability. Our work classifies the conditions for bistability, and extends the large deformation theory of plates and shells.

关键词： NONLINEAR theories DEFORMATIONS (Mechanics) PARAMETER estimation OPTICAL bistability STRUCTURAL shells PLATES (engineering) CRYSTAL structure

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The Transmission Line Matrix method applied to the sound propagation through a 3D reconstructed vocal tract using Magnetic Resonance images

The Transmission Line Matrix method applied to the sound pro...

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18th International Congress on Sound and Vibration 2011, ICSV 2011

作者： Brandão, Alexandre S. Cataldo, Edson Leta, Fabiana R. Mechanical Engineering Department Mechanical Engineering Post-Graduation Program Universidade Federal Fluminense 24210-240 São Domingos Niterói RJ Brazil Applied Mathematics Department Universidade Federal Fluminense 24020-140 Valonguinho Niterói RJ Brazil

ISBN: (纸本)9781618392596

In this paper, the Transmission Line Method (TLM) is applied to generate a voice signal by simulating the acoustic propagation of a glottal signal, obtained by inverse filtering of the voice signal, through an /a/ vowel shaped vocal tract uniform TLM mesh. The vocal tract TLM mesh is constructed over a segmented Magnetic Resonance(MR) volume image. The tools for segmentation, mesh extraction and the TLM itself were implemented as part of the ModaVox program, which is an open source application constructed during the research presented here. The methodology was validated, firstly, simulating the acoustic propagation of a probe signal through tube model meshes. Then, the same probe signal was used as the input for the vocal tract TLM mesh and the resonant frequencies obtained by simulation were compared with those of the real vocal tract. Finally, the glottal signal is used as input for the vocal tract mesh and the reflective boundary conditions of the vocal tract walls were designed to reproduce the consistency of the soft tissues. The voice signal simulated was then compared with the original voice signal generated by the subject when his vocal tract was imaged.

关键词： Magnetic resonance

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GoldShirt transitional program: First-year results and lessons learned on creating engineering capacity and expanding diversity

GoldShirt transitional program: First-year results and lesso...

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作者： Ennis, Tanya D. Milford, Jana B. Sullivan, Jacquelyn F. Myers, Beth A. Knight, Daniel Engineering GoldShirt Program College of Engineering and Applied Science University of Colorado Boulder United States Department of Mechanical Engineering Engineering GoldShirt Program University of Colorado Boulder United States Integrated Teaching and Learning Program University of Colorado Boulder's College of Engineering and Applied Science United States Center CU's College of Engineering and Applied Science United States

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Characterization of heterogeneous response of Al bicrystal subject to micro scale laser shock peening

Characterization of heterogeneous response of Al bicrystal s...

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作者： Vukelic, S. Noyan, I.C. Kysar, J.W. Yao, Y.L. Mechanical Engineering Department Bucknell University Pennsylvania PA 17837 United States Program in Materials Science Department of Applied Physics and Applied Mathematics Columbia University New York NY 10027 United States Mechanical Engineering Department Columbia University New York NY 10027 United States

This letter shows the ability to perform character-ization of the strain field in an aluminium bicrystal subject to plane strain condition induced by micro scale laser shock peening. Intensity contrast method, previously used in topographic measurements of strain fields in thin films is employed here. Our results show that this method is applicable for measurements of the plastically deformed bulk materials. Moreover, heterogeneous response of the grain boundary is observed as periodic nature of deformation. © Society for Experimental Mechanics 2010.

关键词： X ray diffraction

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Characterization of heterogeneous response of Al bicrystal subject to micro scale laser shock peening

Characterization of heterogeneous response of Al bicrystal s...

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作者： Vukelic, S. Noyan, I.C. Kysar, J.W. Yao, Y.L. Mechanical Engineering Department Bucknell University Pennsylvania. PA 17837 United States Program in Materials Science Department of Applied Physics and Applied Mathematics Columbia University New York NY 10027 United States Mechanical Engineering Department Columbia University New York NY 10027 United States

This letter shows the ability to perform characterization of the strain field in an aluminium bicrystal subject to plane strain condition induced by micro scale laser shock peening. Intensity contrast method, previously used in topographic measurements of strain fields in thin films is employed here. Our results show that this method is applicable for measurements of the plastically deformed bulk materials. Moreover, heterogeneous response of the grain boundary is observed as periodic nature of deformation. © Society for Experimental Mechanics 2010.

关键词： X ray diffraction

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Comprehensive analysis of compositional interface fluctuations in planar lipid bilayer membranes

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Physical Review E 2011年第5期84卷 051903-051903页

作者： Tao Han Mikko Haataja Department of Mechanical and Aerospace Engineering Princeton Institute for the Science and Technology of Materials (PRISM) and Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08544 USA

In this paper we present a comprehensive analysis of line tension-driven compositional interface fluctuations in planar lipid bilayer membranes. Our starting point is the advective Cahn-Hilliard equation for the local lipid composition in symmetric membranes, which explicitly incorporates both advective and diffusive lipid transport processes, and which is coupled to the continuum hydrodynamic equations governing the flow behavior of the membrane and surrounding solvent with finite subphase thickness. In order to extract the interface dynamics from the continuum phase-field formalism, we first derive the appropriate sharp-interface limit equations. We then carry out a linear perturbation analysis for the relaxational dynamics of small-amplitude sinusoidal interface fluctuations to yield the general dispersion relation ωk as a function of perturbation wave number k. The resulting expression incorporates the effects of diffusive and advective lipid transport processes within the membrane, viscous or viscoelastic membrane properties, coupling between membrane and solvent, and inertial effects within the membrane and solvent. It is shown that previously considered scenarios naturally emerge as limiting cases of the general result. Furthermore, we discuss two additional scenarios amenable to analysis, one in which the inertia of the solvent is relevant, and another one in which the membrane displays significant viscoelastic properties. Finally, we numerically evaluate the general dispersion relation for three representative model membrane systems.

关键词： BILAYER lipid membranes FLUCTUATIONS (Physics) PERTURBATION (mathematics) VISCOELASTICITY HYDRODYNAMICS

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Direct minimization of the optimized effective problem based on efficient finite differences

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Physical Review B 2011年第16期84卷 165122-165122页

作者： Chen Huang Emily A. Carter Department of Mechanical and Aerospace Engineering Program in Applied and Computational Mathematics and the Andlinger Center for Energy and the Environment Princeton University Princeton New Jersey 08544-5263 USA

To avoid the difficult-to-solve optimized effective potential (OEP) integral equation, we introduce an efficient direct minimization scheme for performing OEP calculations within Kohn–Sham density functional theory (KS-DFT). We reformulated the functional derivative of the total energy with respect to the KS effective potential in terms of efficient finite differences. Our method only uses the orbitals involved in the construction of the KS exchange-correlation functionals. We demonstrate our scheme by performing exact-exchange OEP for sodium clusters, in which only occupied KS orbitals are needed to obtain the OEP. Our efficient direct minimization scheme should aid future development of orbital-dependent density functionals and render OEP to be a practical choice for various applications.

关键词： INTEGRAL equations DENSITY functionals TOTAL energy systems (On-site electric power production) FINITE differences PHYSICS

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Artificial neural networks applied to the estimation of random variables associated to a two-mass model for the vocal folds

Artificial neural networks applied to the estimation of rand...

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18th International Congress on Sound and Vibration 2011, ICSV 2011

作者： Mauprivez, Julien Sampaio, Rubens Cataldo, Edson Mechanical Engineering Department-PUC-Rio Rua Marquěs de São Vicente 225 Gávea RJ CEP: 22453-900 Brazil Applied Mathematics Department Universidade Federal Fluminense Graduate Program in Telecommunications Engineering Rua M'ario Santos Braga S/N Centro Niteroi CEP: 24020-140 RJ Brazil

ISBN: (纸本)9781618392596

Low order non-linear mechanical models for vocal folds, in the phonation process, have been showed to be useful in the case of normal and disordered voice studies. Despite their relative simplicity, they are able to simulate the main features of the vocal fold dynamics. Good examples are the two-mass models (presented by Ishizaka and Flanagan or by Lous et al), which use few input parameters and have shown excellent results to understand phonation phenomena. However, to model a real voice, it is required to approach a set of parameters of the model, to fit the desired output radiated pressure. In general, these parameters are set by using an iterative process involving a large number of simulations and, consequently, much computational time. Recently, some authors pointed out the advantage of using probabilistic approaches to characterize vocal fold dynamics. In this case, the computational time of simulation is much larger due to the thousands of realizations necessary for each set of parameters. The aim of this work is then to propose a strategy to diminish the computational time by using artificial neural networks to solve an inverse stochastic problem related to the two-mass models used to produce voice. In general, the design of experiments (DOE) is a well developed methodology in Statistics and, here, it will be applied to the phonation process modeling. The results, involving the precision of the parameters found and also including the time to get them will be compared with those ones achieved in other works. Copyright © (2011) by the International Institute of Acoustics & Vibration.

关键词： Speech

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