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Microstructures: Structure and Energetics of Dislocations at Micro‐Structured Complementary Interfaces Govern Adhesion (Adv. Funct. Mater. 27/2013)

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Advanced Functional Materials 2013年第27期23卷

作者： Congrui Jin Anand Jagota Chung‐Yuen Hui Field of Theoretical and Applied Mechanics Sibley School of Mechanical and Aerospace Engineering Cornell University Ithaca NY 14850 USA Department of Chemical Engineering and Bioengineering Program Lehigh University Bethlehem PA 18015 USA

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Minimum-Time Trajectory Planning for Helicopter UAVs using Computational Dynamic Optimization

Minimum-Time Trajectory Planning for Helicopter UAVs using C...

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IEEE International Conference on Systems, Man, and Cybernetics

作者： Nathan Xu Wei Kang Guowei Cai Ben M. Chen Summer Intern Program Department of Applied Mathematics Naval Postgraduate School Department of Applied Mathematics Naval Postgraduate School Department of Electrical and Computer Engineering National University of Singapore

ISBN: (纸本)9781467317139

In this paper, we apply pseudospectral optimal control, a computational algorithm of dynamic optimization, to the problem of helicopter UAV for minimum-time trajectory planning in the presence of obstacles. The problem is formulated as a nonlinear optimal control subject to the dynamics and limitations of helicopter UAVs, in which the obstacles are formulated as inequality constraints by using p-norms. The dynamical system is defined by a set of fifteen states nonlinear differential equations developed for HeLion, a helicopter UAV constructed in National University of Singapore (NUS). The problem does not have an analytic solution. We numerically solve the problem using a pseudospectral method. Various terrain scenarios were tested, from a single obstacle to multiple obstacles. We found bifurcation points of minimum-time trajectories near obstacles. The bifurcation points and their relationship with the distance to the obstacle are analyzed.

关键词： Minimum-time control Helicopter UAV Computational optimal control Obstacle avoidance Unmanned Aerial Vehicle Helicopters trajectory planning barriers BIFURCATION nonlinear differential equations inequality constraint drone honey bees

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Effect of Film Thickness Variation on (100)-Surface Texturing of MPS Processed Polycrystalline Si Films

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MRS Online Proceedings Library 2012年第1期1426卷 257-262页

作者： Monica Chahal P. C. van der Wilt D. Van Gestel A. B. Limanov A. M. Chitu James S. Im Program in Materials Science and Engineering Department of Applied Physics and Applied Mathematics Columbia University New York USA IMEC Solar Cell Tech. Group Leuven Belgium WCU Program Department of Materials Science and Engineering College of Engineering Korea Advanced Institute of Science and technology (KAIST) Korea

We have investigated the effect of varying the film thickness on the surface orientation texturing in polycrystalline Si films obtained via mixed-phase solidification (MPS) of initially a-Si precursor films on SiO2. It is found that, for a given number of MPS exposure cycles, the degree of (100)-surface texturing is reduced as the film thickness is increased. We discuss how this trend can be accounted for by the previously proposed thermodynamic model of MPS, wherein a decreasing local solid/liquid interface curvature with increasing film thickness is identified as the primary cause for decreasing the influence which anisotropic solid-Si/SiO2 interfacial energies have on the survivability of the grains. This, in turn, leads to other factors becoming more significant in determining the grains that survive the MPS cycle, thereby reducing the degree of (100)-surface texturing in the resulting films.

关键词： Si microstructure texture

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Computation of sparse low degree interpolating polynomials and their application to derivative-free optimization

Computation of sparse low degree interpolating polynomials a...

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作者： Bandeira, A.S. Scheinberg, K. Vicente, L.N. Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Department of Industrial and Systems Engineering Lehigh University Harold S. Mohler Laboratory 200 West Packer Avenue Bethlehem PA 18015-1582 United States CMUC Department of Mathematics University of Coimbra 3001-501 Coimbra Portugal

Interpolation-based trust-region methods are an important class of algorithms forDerivative-Free Optimizationwhich rely on locally approximating an objective function by quadratic polynomial interpolation models, frequently built from less points than there are basis components. Often, in practical applications, the contribution of the problem variables to the objective function is such that many pairwise correlations between variables are negligible, implying, in the smooth case, a sparse structure in the Hessian matrix. To be able to exploit Hessian sparsity, existing optimization approaches require the knowledge of the sparsity structure. The goal of this paper is to develop and analyze a method where the sparse models are constructed automatically. The sparse recovery theory developed recently in the field of compressed sensing characterizes conditions under which a sparse vector can be accurately recovered from few random measurements. Such a recovery is achieved by minimizing the l1-norm of a vector subject to the measurements constraints. We suggest an approach for building sparse quadratic polynomial interpolationmodels byminimizing the l1-norm of the entries of themodel Hessian subject to the interpolation conditions. We show that this procedure recovers accurate models when the function Hessian is sparse, using relatively few randomly selected sample points. Motivated by this result, we developed a practical interpolation-based trust-region method using deterministic sample sets and minimum l1-norm quadratic models. Our computational results show that the new approach exhibits a promising numerical performance both in the general case and in the sparse one. © Springer and Mathematical Optimization Society 2012.

关键词： Interpolation

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Efficient coarse simulation of a growing avascular tumor

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Physical Review E 2012年第3期85卷 031912-031912页

作者： Michail E. Kavousanakis Ping Liu Andreas G. Boudouvis John Lowengrub Ioannis G. Kevrekidis School of Chemical Engineering National Technical University of Athens 9 Heroon Polytechniou St. Zographos Athens GR-15780 Greece Department of Chemical and Biological Engineering Princeton University Princeton New Jersey 08544 USA Department of Mathematics University of California 103 MSTB Irvine California 92697 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

The subject of this work is the development and implementation of algorithms which accelerate the simulation of early stage tumor growth models. Among the different computational approaches used for the simulation of tumor progression, discrete stochastic models (e.g., cellular automata) have been widely used to describe processes occurring at the cell and subcell scales (e.g., cell-cell interactions and signaling processes). To describe macroscopic characteristics (e.g., morphology) of growing tumors, large numbers of interacting cells must be simulated. However, the high computational demands of stochastic models make the simulation of large-scale systems impractical. Alternatively, continuum models, which can describe behavior at the tumor scale, often rely on phenomenological assumptions in place of rigorous upscaling of microscopic models. This limits their predictive power. In this work, we circumvent the derivation of closed macroscopic equations for the growing cancer cell populations; instead, we construct, based on the so-called “equation-free” framework, a computational superstructure, which wraps around the individual-based cell-level simulator and accelerates the computations required for the study of the long-time behavior of systems involving many interacting cells. The microscopic model, e.g., a cellular automaton, which simulates the evolution of cancer cell populations, is executed for relatively short time intervals, at the end of which coarse-scale information is obtained. These coarse variables evolve on slower time scales than each individual cell in the population, enabling the application of forward projection schemes, which extrapolate their values at later times. This technique is referred to as coarse projective integration. Increasing the ratio of projection times to microscopic simulator execution times enhances the computational savings. Crucial accuracy issues arising for growing tumors with radial symmetry are addressed by applying th

关键词： SIMULATION methods & models TUMORS -- Growth MATHEMATICAL models CANCER invasiveness STOCHASTIC models COMPUTATIONAL biology BIONICS PHENOMENOLOGY

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Corrigendum to “On the correlation between single-frequency impedance measurements and human skin permeability to water” [Toxicology in Vitro 25 (2011) 2095–2104]

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Toxicology in Vitro 2013年第2期27卷 993-993页

作者： Erick A. White Alan Horne Jill Runciman Mark E. Orazem William C. Navidi Clive S. Roper Annette L. Bunge Chemical and Biological Engineering Department Colorado School of Mines Golden CO 80401 USA In Vitro Sciences Charles River Tranent Edinburgh EH33 2NE UK Department of Chemical Engineering University of Florida Gainesville FL 32611 USA Department of Applied Mathematics and Statistics Colorado School of Mines Golden CO 80401 USA

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Heart wall myofibers are arranged in minimal surfaces to optimize organ function (vol 109, pg 9253, 2012)

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2012年第49期109卷 20166-20166页

作者： Savadjiev, Peter Strijkers, Gustav J. Bakermans, Adrianus J. Piuze, Emmanuel Zucker, Steven W. Siddiqi, Kaleem [a]Psychiatry Neuroimaging Laboratory and Laboratory for Mathematics in Imaging Brigham and Women’s Hospital Harvard Medical School Boston MA 02215 [b]Department of Biomedical Engineering Eindhoven University of Technology 5600 MB Eindhoven The Netherlands [c]School of Computer Science and Centre for Intelligent Machines McGill University Montréal Canada H3A 2A7 and [d]Departments of Computer Science and Biomedical Engineering and Program in Applied Mathematics Yale University New Haven CT 06520-8285

Heart wall myofibers wind as helices around the ventricles, strengthening them in a manner analogous to the reinforcement of concrete cylindrical columns by spiral steel cables [Richart FE, et al. (1929) Univ of Illinois, Eng Exp Stn Bull 190]. A multitude of such fibers, arranged smoothly and regularly, contract and relax as an integrated functional unit as the heart beats. To orchestrate this motion, fiber tangling must be avoided and pumping should be efficient. Current models of myofiber orientation across the heart wall suggest groupings into sheets or bands, but the precise geometry of bundles of myofibers is unknown. Here we show that this arrangement takes the form of a special minimal surface, the generalized helicoid [Blair DE, Vanstone JR (1978) Minimal Submanifolds and Geodesics 13-16], closing the gap between individual myofibers and their collective wall structure. The model holds across species, with a smooth variation in its three curvature parameters within the myocardial wall providing tight fits to diffusion magnetic resonance images from the rat, the dog, and the human. Mathematically it explains how myofibers are bundled in the heart wall while economizing fiber length and optimizing ventricular ejection volume as they contract. The generalized helicoid provides a unique foundation for analyzing the fibrous composite of the heart wall and should therefore find applications in heart tissue engineering and in the study of heart muscle diseases. [PUBLICATION ABSTRACT]

关键词： myocardium myofiber geometry diffusion tensor MRI

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Characteristics of Leachate at Sukawinatan Landfill, Palembang, Indonesia

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Journal of Physics: Conference Series 2013年第1期423卷

作者： Eka Sri Yusmartini Dedi Setiabudidaya Ridwan Marsi Faizal PhD Candidate Postgraduate Program Sriwijaya University Indonesia Department of Physics Faculty of Mathematics and Science Sriwijaya University Indonesia Nuclear Industrial Materials Technology Centre Serpong Indonesia Faculty of Agriculture Sriwijaya University Indonesia Department of Chemical Engineering Faculty of Engineering Sriwijaya University Indonesia

Landfill (TPA) Sukawinatan Palembang is an open dumping system which covers an area of 25 hectares. This system may bring an environmental damage to the surrounding area because it does not provide leachate treatment. Leachate is the landfill waste that dissolves many compounds that contain pollutants from both organic substances and heavy metal origin. This paper presents the results of laboratory analysis on samples of leachate as well as shallow groundwater from the surrounding area. The results were compared to established quality standards to evaluate whether the leachate has influenced the quality of the shallow groundwater in the surrounding area. The results show that there are some indications that the quality of groundwater has been polluted by the leachate of both organic substances and heavy metals produced by the Sukawinatan landfill.

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Importance of reference Hamiltonians containing exact exchange for accurate one-shot GW calculations of Cu2O

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Physical Review B 2012年第23期85卷 235142-235142页

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

We show that a “one-shot” GW approach (denoted G0W0) can accurately calculate the photoemission/inverse-photoemission properties of Cu2O. As the results of any perturbative method are heavily dependent on the reference state, the appropriate reference Hamiltonian for G0W0 is identified by evaluating the performance of density-functional-theory-based input wave functions and eigenvalues generated with selected exchange-correlation functionals. It is shown that a reference Hamiltonian employing the hybrid Heyd-Scuseria-Ernzerhof functional used in conjunction with G0W0 produces an accurate photoemission/inverse-photoemission band gap and photoemission spectrum whose character is then further analyzed. The physical origin of why a hybrid functional is required for the zeroth-order wave function is discussed, giving insight into the unique electronic structure of Cu2O in comparison to other transition-metal oxides.

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Kinetic hydrate inhibition of poly(N -isopropylmethacrylamide)s with different tacticities

Kinetic hydrate inhibition of poly(N -isopropylmethacrylamid...

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作者： Chua, Pei Cheng Kelland, Malcolm A. Ishitake, Kenji Satoh, Kotaro Kamigaito, Masami Okamoto, Yoshio Department of Mathematics and Natural Sciences Faculty of Science and Technology University of Stavanger N-4036 Stavanger Norway Department of Applied Chemistry Graduate School of Engineering Nagoya University Nagoya 464-8603 Japan Nagoya University Nagoya 464-8603 Japan College of Material Science and Chemical Engineering Harbin Engineering University Nantong St. Harbin China

Poly(N-isopropylmethacrylamide)s (PNIPMAMs) have become commercially available as kinetic hydrate inhibitors (KHIs). PNIPMAMs are usually made by standard radical polymerization, which does not allow control over the polymer tacticity. We have now synthesized PNIPMAMs using stereospecific radical polymerization giving a fairly high degree of tacticity control. In this paper we present results on the performance of different tacticities in KHI tests with synthetic natural gas in stirred autoclaves and on tetrahydrofuran (THF) structure II hydrate crystal growth. The molecular weights of these polymers are almost the same. From the results, we can conclude the effect of polymer tacticity on the KHI performance of PNIPMAMs is noticeable but not very significant. PNIPMAMs with a higher syndiotactic percentage performed slightly better than PNIPMAMs with a lower syndiotactic percentage. Both polymers also gave a similar effect on the morphology of the THF hydrate crystals, indicating some kind of crystal surface adsorption. The PNIPMAMs investigated have a fairly high syndiotactic percentage. In fact, we found that it was difficult to make PNIPMAMs with less than 45% syndiotactic percentage, even using standard radical polymerization methods. This suggests that any method to make commercial NIPMAM-based polymer KHIs via radical polymerization will necessarily give polymers with a fairly high percentage of syndiotacticity. © 2012 American chemical Society.

关键词： Hydration

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