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作者： Chini, Gregory P. Dianati, Navid Zhang, Zhexuan Doering, Charles R. Department of Mechanical Engineering University of New Hampshire Durham NH 03824 United States Center for Fluid Physics University of New Hampshire Durham NH 03824 United States Program in Integrated Applied Mathematics University of New Hampshire Durham NH 03824 United States Department of Physics University of Michigan Ann Arbor MI 48109-1040 United States Department of Mathematics University of Michigan Ann Arbor MI 48109-1043 United States Center for the Study of Complex Systems University of Michigan Ann Arbor MI 48109-1107 United States

A novel model reduction strategy for forced dissipative infinite-dimensional nonlinear dynamical systems is described. Unlike popular but empirical methods, this new approach does not require extensive data sets from experiments or direct numerical simulations of the governing field equations. Instead, truly predictive reduced dynamical models are constructed using Galerkin projection onto a priori eigenfunctions drawn from energy stability and upper bound theory. Within the context of porous medium convection, we show that these eigenfunctions contain information about boundary layers and other complex dynamic features and, thus, are well suited for the low-order description of highly nonlinear phenomena. Crucially, our analysis reveals the existence of a gap in the eigenvalue spectrumeven for strongly supercritical forcing conditionsenabling the identification of a rational truncation scheme. We demonstrate the efficacy of our approach via comparison with FourierGalerkin approximations of various orders. © 2010 Elsevier B.V. All rights reserved.

关键词： Chaos theory

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Competitive outcomes changed by evolution

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Journal of Biological Dynamics 2011年第3期5卷 227-252页

作者： Rael, R.C. Vincent, T.L. Cushing, J.M. Interdisciplinary Program in Applied Mathematics University of Arizona Tucson AZ United States Aerospace and Mechanical Engineering University of Arizona Tucson AZ United States Department of Mathematics and Interdisciplinary Program in Applied Mathematics University of Arizona Tucson AZ United States

When evolution plays a role, population dynamic models alone are not sufficient for determining the outcome of multi-species *** an expansion of Maynard Smith's concept of an evolutionarily stable strategy, evolutionary game theory (EGT) combines population and evolutionary dynamics so that natural selection becomes a dynamic game with phenotypic traits as strategies. Using EGT,we showhowevolution can change the outcome of the interaction between two competing *** are particularly interested in situations where the interaction changes from one of competitive exclusion to one of coexistence and where the interaction changes from the exclusion of one species to the exclusion of the other. There are two crucial factors that determine whether or not such events can occur: the rate of evolution (which is proportional to the amount of variability in phenotypic traits within a species) and what we term the boxer effect, a phenomenon that concerns how the intensity of interspecies competition relates to species' trait differences. We apply the theory to data from two historical competition experiments involving species of flour beetle from the genus Tribolium. In both applications, we show how EGT can explain certain seemingly 'anomalous' experimental results. © 2011 Taylor & Francis.

关键词： Competition Competitive coexistence Competitive exclusion Evolutionarily stable strategy Evolutionary game theory

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Continuum model of irradiation-induced spinodal decomposition in the presence of dislocations

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Physical Review B 2011年第17期83卷 174106-174106页

作者： J. J. Hoyt M. Haataja Department of Materials Science and Engineering McMaster University Hamilton Ontario Canada L8S4L7 Department of Mechanical and Aerospace Engineering Princeton Institute for the Science and Technology of Materials (PRISM) Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08544

A model of phase-separation kinetics in systems exposed to energetic particle irradiation has been extended to include the effects of mobile dislocations. It is shown that when dislocations are allowed to participate in the decomposition reaction, phase separation can occur at temperatures above the coherent spinodal, which is in agreement with several experiments on irradiated alloys. A linear stability analysis of the governing kinetic equations is performed and three regimes of microstructural evolution are identified within the parameter space of damage cascade size vs incident flux: complete phase separation, solid-solution behavior, and compositional patterning. In addition, numerical simulations of the evolving dislocation density and composition fields are performed. The numerical results provide the amplitude and wavelength of the stable patterns that can form under irradiation and elucidate the role of misfit dislocations in reducing the coherency strain due to atomic size mismatch.

关键词： PHASE transformations (Physics) THERMODYNAMICS PARTICLES (Nuclear physics) ALLOYS IRRADIATION STRAINS & stresses (Mechanics)

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Goldshirt transitional program: Creating engineering capacity and expanding diversity through a performance-enhancing year

Goldshirt transitional program: Creating engineering capacit...

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2010 ASEE Annual Conference and Exposition

作者： Ennis, Tanya Milford, Jana Myer, Beth Sullivan, Jacquelyn Knight, Daniel Sieber, Diane Scarritt, Ann Boulder's College of Engineering and Applied Science Engineering GoldShirt Program University of Colorado Boulder United States Department of Mechanical Engineering Engineering GoldShirt Program University of Colorado Boulder United States Integrated Teaching and Learning Program Boulder's College of Engineering and Applied Science University of Colorado Boulder United States University of Colorado Boulder United States

At our nation's universities, too few rural, low-income, underrepresented minority and firstgeneration students pursue engineering degrees, and most well-prepared women show little interest. Because inadequate pre-college academic preparation is a known critical barrier to university-level engineering admission, one pathway for engineering colleges to increase their undergraduate student population diversity is to commit to boosting the performance of under-prepared high school graduates admitted under transitional status. The engineering GoldShirt program at the University of Colorado at Boulder, supported by National Science Foundation funding, provides a performance-enhancing year for under-prepared students directly admitted to the engineering college. The highly-structured approach closely monitors student performance against seven goals. One goal is to increase student interest in, and knowledge of, an engineering career - supported by creating a strong community among GoldShirt students and the larger college population. Another goal is to ensure that students are prepared to academically perform in a traditional engineering program after their transitional GoldShirt year. By achieving all program goals, we seek to create a national model for significantly boosting recruitment, retention and graduation of under-prepared students in engineering. The engineering GoldShirt program enrolled its first cohort of 16 highly-motivated yet under-prepared students in fall 2009. In the pilot group, 11 represent the first-generation in their families to attend college, 13 are underrepresented minority students, and seven are female. This paper describes the College of engineering and applied Science's unique approach to expanding opportunity for students from historically underrepresented groups to succeed in engineering, and shares the lessons learned thus far about recruitment, admissions, curriculum development, course placement, and student support services - all stra

关键词： Students

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Hydrogen in tungsten: Absorption, diffusion, vacancy trapping, and decohesion

Hydrogen in tungsten: Absorption, diffusion, vacancy trappin...

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作者： Johnson, Donald F. Carter, Emily A. Department of Chemistry Princeton University Princeton NJ 08544 United States Department of Mechanical and Aerospace Engineering Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States

Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations. © 2010 Materials Research Society.

关键词： Tungsten

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Nonlocal orbital-free kinetic energy density functional for semiconductors

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Physical Review B 2010年第4期81卷 045206-045206页

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

We propose a nonlocal kinetic energy density functional (KEDF) for semiconductors based on the expected asymptotic behavior of its susceptibility function. The KEDF’s kernel depends on both the electron density and the reduced density gradient, with an internal parameter formally related to the material’s static dielectric constant. We determine the accuracy of the KEDF within orbital-free density functional theory (DFT) by applying it to a variety of common semiconductors. With only two adjustable parameters, the KEDF reproduces quite well the exact noninteracting KEDF (i.e., Kohn-Sham DFT) predictions of bulk moduli, equilibrium volumes, and equilibrium energies. The two parameters in our KEDF are sensitive primarily to changes in the local crystal structure (such as atomic coordination number) and exhibit good transferability between different tetrahedrally-bonded phases. This local crystal structure dependence is rationalized by considering Thomas-Fermi dielectric screening theory.

关键词： .Phases orbital-free KEDF bulk moduli

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Influence of nonequilibrium lipid transport, membrane compartmentalization, and membrane proteins on the lateral organization of the plasma membrane

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Physical Review E 2010年第1期81卷 011908-011908页

作者： Jun Fan Maria Sammalkorpi 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

Compositional lipid domains (lipid rafts) in plasma membranes are believed to be important components of many cellular processes. The mechanisms by which cells regulate the sizes, lifetimes, and spatial localization of these domains are rather poorly understood at the moment. We propose a robust mechanism for the formation of finite-sized lipid raft domains in plasma membranes, the competition between phase separation in an immiscible lipid system and active cellular lipid transport processes naturally leads to the formation of such domains. Simulations of a continuum model reveal that the raft size distribution is broad and the average raft size is strongly dependent on the rates of cellular and interlayer lipid transport processes. We demonstrate that spatiotemporal variations in the recycling may enable the cell to localize larger raft aggregates at specific parts along the membrane. Moreover, we show that membrane compartmentalization may further facilitate spatial localization of the raft domains. Finally, we demonstrate that local interactions with immobile membrane proteins can spatially localize the rafts and lead to further clustering.

关键词： Cell membranes

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Lipid Microdomains: Structural Correlations, Fluctuations, and Formation Mechanisms

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Physical Review Letters 2010年第11期104卷 118101-118101页

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

Compositional lipid microdomains (“lipid rafts”) in mammalian plasma membranes are believed to facilitate many important cellular processes. While several physically distinct scenarios predicting the presence of finite-sized microdomains in vivo have been proposed in the past, direct experimental verification or falsification of model predictions has remained elusive. Herein, we demonstrate that the combination of the spatial correlation and temporal fluctuation spectra of the lipid domains can be employed to unambiguously differentiate between the existing theoretical scenarios. Furthermore, the differentiation of the raft formation mechanisms using this methodology can be achieved by collecting data at physiologically relevant conditions without the need to tune control parameters.

关键词： Cell membranes

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An end-to-end simulator for the all-electric ship MVDC integrated power system

An end-to-end simulator for the all-electric ship MVDC integ...

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Grand Challenges in Modeling and Simulation Symposium, GCMS 2010, Part of the 2010 Summer Simulation Multiconference, SummerSim 2010

作者： Milošević Marden, M. Prempraneerach, P. Kirtley, J.L. Karniadakis, G. Chryssostomidis, C. Design Laboratory MIT Sea Grant College Program United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA United States Department of Mechanical Engineering Rajamangala University of Technology Thunyaburi Pathumthani Thailand Division of Applied Mathematics Brown University Providence RI United States

ISBN: (纸本)9781617387043

In this paper, a large scale Medium Voltage DC all-electric ship integrated power system is modeled from the prime mover (gas turbine) to the propulsion load. This system has a three-phase 21MW synchronous machine as a main generator and a three-phase 19MW induction motor as a main propulsion drive. The influence of propeller emergence on both electrical and mechanical components of the system is investigated.

关键词： Ship propulsion

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Robust algorithm to generate a diverse class of dense disordered and ordered sphere packings via linear programming

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Physical Review E 2010年第6期82卷 061302-061302页

作者： S. Torquato Y. Jiao Department of Chemistry Department of Physics Princeton Center for Theoretical Science Princeton Institute for the Science and Technology of Materials Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Department of Mechanical and Aerospace Engineering Princeton University Princeton New Jersey 08544 USA

We have formulated the problem of generating dense packings of nonoverlapping, nontiling nonspherical particles within an adaptive fundamental cell subject to periodic boundary conditions as an optimization problem called the adaptive-shrinking cell (ASC) formulation [S. Torquato and Y. Jiao, Phys. Rev. E 80, 041104 (2009)]. Because the objective function and impenetrability constraints can be exactly linearized for sphere packings with a size distribution in d-dimensional Euclidean space Rd, it is most suitable and natural to solve the corresponding ASC optimization problem using sequential-linear-programming (SLP) techniques. We implement an SLP solution to produce robustly a wide spectrum of jammed sphere packings in Rd for d=2, 3, 4, 5, and 6 with a diversity of disorder and densities up to the respective maximal densities. A novel feature of this deterministic algorithm is that it can produce a broad range of inherent structures (locally maximally dense and mechanically stable packings), besides the usual disordered ones (such as the maximally random jammed state), with very small computational cost compared to that of the best known packing algorithms by tuning the radius of the influence sphere. For example, in three dimensions, we show that it can produce with high probability a variety of strictly jammed packings with a packing density anywhere in the wide range [0.6, 0.7408…], where π/18=0.7408… corresponds to the density of the densest packing. We also apply the algorithm to generate various disordered packings as well as the maximally dense packings for d=2, 4, 5, and 6. Our jammed sphere packings are characterized and compared to the corresponding packings generated by the well-known Lubachevsky-Stillinger (LS) molecular-dynamics packing algorithm. Compared to the LS procedure, our SLP protocol is able to ensure that the final packings are truly jammed, produces disordered jammed packings with anomalously low densities, and is appreciably more robust an

关键词： Packing

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