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Proton Transfer and Transport in Fuel Cells - 213th ECS Meeting

作者： Akhtar, Naveed Decent, Stephen P. Loghin, Daniel Kendall, Kevin School of Applied Mathematics University of Birmingham Edgbaston B15 2TT United Kingdom Department of Chemical Engineering University of Birmingham Edgbaston B15 2TT United Kingdom

ISBN: (纸本)9781615672875

A comparison of the gas flow distribution and reactant utilization in a single chamber solid oxide fuel cell (SC-SOFC) between the parallel and perpendicular cell configuration (with respect to the gas flow direction) has been discussed in detail. An electrochemical-fluid coupled numerical model in a five layer membrane electrode assembly (MEA) is developed. The model accounts for the major transports of convective and diffusive mass transfer, electrode kinetics, and potential fields. The results show gas flow and electrochemical effects inside the cell in each configuration and suggest that the parallel design provides better gas flow than perpendicular configuration. A uniform reactant utilization is observed in case of perpendicular design as compared to the parallel configuration. In order to take advantage of both the gas flow and electrochemical performance of the cell, use of a fully porous cell (including porosity of the electrolyte) is suggested in perpendicular configuration. The model can predict the effect of gas flow/ electrochemical performance, especially in situations where several cells are placed at different distances in the duct. The model is solved using COMSOL Multiphysics 3.3a, a commercial finite element analysis (FEM) software package. ©The Electrochemical Society.

关键词： Flow of gases

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On slip velocity boundary conditions for electroosmotic flow near sharp corners

On slip velocity boundary conditions for electroosmotic flow...

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Symposium of the International Union of Theoretical and applied Mechanics on Recent Advances in Multiphase Flows: Numerical and Experimental, IUTAM

作者： Craven, Thomas J. Rees, Julia M. Zimmerman, William B. Department of Chemical and Process Engineering University of Sheffield Newcastle Street Sheffield S1 3 DJ United Kingdom Department of Applied Mathematics University of Sheffield Hounsfield Road Sheffield S3 7 RH United Kingdom

The Helmholtz-Smoluchowski (HS) slip velocity boundary condition is often used in computational models of microchannel flows because it allows the motion of the electric double layer (EDL) to be approximated without resolving the charge density profiles close to the walls while dramatically reducing the computational effort required to solve the flow model. The approximation works well for straight channel flows but breaks down in areas of high wall curvature such as sharp corners, where large nonphysical velocities are generated. Many microfluidic applications such as the on-chip focusing and separation of biomolecules rely on the interaction of electroosmosis and electrophoresis in complex channel geometries. In order for these effects to be properly treated using the slip velocity boundary condition, the errors introduced into the solution at corners must be understood. In this article, a complete model for the ion concentrations, electric field, and fluid flow in complex microchannel geometries is presented and is used to compute a pure electroosmotic flow in a two-dimensional microchannel cross slot. The full model solution near the corner at the edge of the EDL is compared to the approximate solution computed by using the HS boundary condition, and it is shown that the accuracy of the approximate solution may be greatly increased by "patching" the full solution as a boundary condition for the approximate solution at the edge of the double layer region. Finally, an empirically derived modified slip velocity boundary condition for electroosmotic flow is proposed. It is shown to improve the accuracy of the flow solution at sharp corners by about 60% when compared to the original boundary condition while also delivering a modest improvement in computational performance because of the elimination of a singularity in the velocity field. © 2008 American Institute of Physics.

关键词： Boundary conditions

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Domain Formation in the Plasma Membrane: Roles of Nonequilibrium Lipid Transport and Membrane Proteins

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Physical Review Letters 2008年第17期100卷 178102-178102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 and lifetimes of these spatially extended domains are poorly understood at the moment. Here we show that the competition between phase separation in an immiscible lipid system and active cellular lipid transport processes naturally leads to the formation of such domains. Furthermore, we demonstrate that local interactions with immobile membrane proteins can spatially localize the rafts and lead to further clustering.

关键词： Lipids

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Cellular automata simulation of topological effects on the dynamics of feed-forward motifs

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Journal of Biological engineering 2008年第1期2卷 1-12页

作者： Apte, Advait A. Cain, John W. Bonchev, Danail G. Fong, Stephen S. Department of Chemical and Life Science Engineering Virginia Commonwealth University Richmond VA 23284 P.O. Box 843028 United States Department of Mathematics and Applied Mathematics Virginia Commonwealth University Richmond VA 23284 P.O. Box 842014 United States Center for the Study of Biological Complexity Virginia Commonwealth University Richmond VA 23284 P.O. Box 842030 United States

Background: Feed-forward motifs are important functional modules in biological and other complex networks. The functionality of feed-forward motifs and other network motifs is largely dictated by the connectivity of the individual network components. While studies on the dynamics of motifs and networks are usually devoted to the temporal or spatial description of processes, this study focuses on the relationship between the specific architecture and the overall rate of the processes of the feed-forward family of motifs, including double and triple feed-forward loops. The search for the most efficient network architecture could be of particular interest for regulatory or signaling pathways in biology, as well as in computational and communication systems. Results: Feed-forward motif dynamics were studied using cellular automata and compared with differential equation modeling. The number of cellular automata iterations needed for a 100% conversion of a substrate into a target product was used as an inverse measure of the transformation rate. Several basic topological patterns were identified that order the specific feed-forward constructions according to the rate of dynamics they enable. At the same number of network nodes and constant other parameters, the bi-parallel and tri-parallel motifs provide higher network efficacy than single feed-forward motifs. Additionally, a topological property of isodynamicity was identified for feed-forward motifs where different network architectures resulted in the same overall rate of the target production. Conclusion: It was shown for classes of structural motifs with feed-forward architecture that network topology affects the overall rate of a process in a quantitatively predictable manner. These fundamental results can be used as a basis for simulating larger networks as combinations of smaller network modules with implications on studying synthetic gene circuits, small regulatory systems, and eventually dynamic whole-cell mode

关键词： Cellular Automaton Cellular Automaton Lattice Density Cellular Automaton Model Topological Effect

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How to match theoretical and experimental boundary conditions of a cantilever beam 7

How to match theoretical and experimental boundary condition...

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7th European Conference on Structural Dynamics, EURODYN 2008

作者： Ritto, Thiago Aguiar, Romulo Sampaio, Rubens Cataldo, Edson Mechanical Engineering Department PUC-Rio Rua Marquês de São Vicente Rua Marque͉ de São Vicente 225 Gávea22453-900 Brazil Graduate Program in Telecommunications Engineering Applied Mathematics Department Rua Mário Santos Braga S/N Centro Niterói24020-140 Brazil

ISBN: (纸本)9780854328826

The purpose of this paper is to describe how to match experimental and theoretical frequencies of a cantilever beam through a prescribed error tolerance. In some cases there is a clear difference between a clamped boundary condition in a real system or in an experiment (called in this article as e-clamped condition) and the clamped condition as regularly modeled in theory (the t-clamped condition). In such occasions the e-clamped (experimental) might not follow the t-clamped (theoretical) condition. Actually, it hardly will. Depending on the e-clamped boundary condition the error between the natural frequencies of t-clamped and e-clamped might be greater than 10%. This work presents a theoretical model that relaxes the boundary condition of zero rotation. One parameter, a torsional stiffness at the fixed end of the beam, is used in order to fit the natural frequencies of the numerical simulations with the experimental data. The idea is to identify the torsional stiffness that minimizes the error between the numerical and experimental frequencies. For the numerical simulations, the Finite Element Method (with Timoshenko beam element) is used, and for the experiments, multiple rubber layers are mounted to the clamped side of the beam so that different e-clamped conditions can be analyzed and reproduced if necessary. The numerical and the experimental results show excellent agreement.

关键词： Boundary conditions

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Ehrenfest model for condensation and evaporation processes in degrading aggregates with multiple bonds

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Physical Review E 2008年第3期78卷 031117-031117页

作者： M. B. Flegg P. K. Pollett D. K. Gramotnev Applied Optics and Nanotechnology Program School of Physical and Chemical Sciences Queensland University of Technology GPO Box 2434 Brisbane QLD 4001 Australia Department of Mathematics The University of Queensland St. Lucia QLD 4072 Australia

We present an explicit theory of the degradation and thermal fragmentation kinetics of polymerlike systems and aggregates with multiple bonds in the presence of stochastic evaporation and condensation (restoration) of bonds. The analysis is conducted on the basis of the determination of the first passage time to state zero (fragmented state) in the Ehrenfest diffusion model in continuous time. The main approximations of the developed theory include the assumption that multiple bonds in any link between the primary elements in the aggregate do not interact with each other and that the coagulation rate after thermal fragmentation of the aggregates is negligible (which gives the absorbing zero state in the Ehrenfest model). In particular, it is demonstrated that even small condensation rates (of ∼10 times smaller than the rates of bond evaporation) may have a significant effect on typical evolution times for the degrading aggregates and can result in a strong accumulation of nanoaggregates in the intermediate fragmentation modes. The simple asymptotic (predominantly exponential) behavior of the obtained solution at large evolution times is analyzed and discussed. The results will be important for the investigation of the degradation kinetics of a variety of polymerlike systems with multiple bonds, including self-arranged structures, polymer networks, different types of nanoclusters and their thermal fragmentation, etc.

关键词： Aggregates

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Pore characterization through propagator-resolved transverse relaxation exchange

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Physical Review E 2008年第5期77卷 051203-051203页

作者： K. E. Washburn C. H. Arns P. T. Callaghan School of Chemical and Physical Sciences Victoria University of Wellington Wellington New Zealand Department of Applied Mathematics Research School of Physical Sciences and Engineering Australian National University Canberra ACT 0200 Australia

We use the propagator-resolved transverse relaxation exchange experiment to characterize the pore space and fluid behavior of water saturated, tight-packed quartz sand. The experiment uses T2 exchange plots to observe the number of molecules that shift their environment for a range of mixing times. The propagator dimension allows us to determine how far the molecules have moved. The peak intensities are integrated and then plotted as a function of displacement and mixing time. We also model our system using both a probabilistic pore-hopping simulation and a spreading Gaussian model. We use the results of these simulations to interpret the peak intensity plots. From this, we can estimate pore features such as characteristic time, pore radii, and interpore spacing. The tortuosity of the different pore sizes can then be calculated from these values.

关键词： POROUS-MEDIA DIFFUSION MEASUREMENTS FIELD GRADIENT SPIN ECHOES

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Analytic form for a nonlocal kinetic energy functional with a density-dependent kernel for orbital-free density functional theory under periodic and Dirichlet boundary conditions

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Physical Review B 2008年第4期78卷 045105-045105页

作者： Gregory S. Ho Vincent L. Lignères Emily A. Carter Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Mechanical and Aerospace Engineering and Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544-5263 USA

We derive an analytic form of the Wang-Govind-Carter (WGC) [Wang et al., Phys. Rev. B 60, 16350 (1999)] kinetic energy density functional (KEDF) with the density-dependent response kernel. A real-space aperiodic implementation of the WGC KEDF is then described and used in linear scaling orbital-free density functional theory (OF-DFT) calculations.

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A comparison of fuzzy methods for modeling

A comparison of fuzzy methods for modeling

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Annual Conference of Industrial Electronics Society

作者： Ayse Cisel Aras Okyay Kaynak Ildar Batyrshin Mechatronics Laboratory Department of Electrical and Electronics Engineering Bogazici University Istanbul Turkey Research Program of Applied Mathematics and Computations Mexican Petroleum Institute USA

The paper has the goal of comparing the performance of four different approaches to fuzzy modeling, using parameterized conjunctions, a novel concept named constrained fuzzy sets (CFSs), CFSs with parameterized conjunctions, and unnormalized interval type-2 Takagi Sugeno Kang (IT2 TSK). The theoretical and mathematical backgrounds of the four approaches are briefly described and their performances are compared in approximating a nonlinear function.

关键词： Fuzzy logic Fuzzy sets Mathematical model Mechatronics Laboratories Uncertainty Humans mathematics Petroleum Working environment noise

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The effect of hydroxyapatite/gemosil nanocomposites on extracellular matrix patterning through the promotion of osteoblast self-organization

The effect of hydroxyapatite/gemosil nanocomposites on extra...

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8th World Biomaterials Congress 2008, WBC 2008

作者： Ko, Ching-Chang Ma, Alice Kaku, Masaru Liu, Kai-Li Luo, T.-J.M. Tulloch, J.F.C. Hu, W.-S. Department of Orthodontics University of North Carolina Chapel Hill NC 27599-7450 United States Applied Materials Science Program University of North Carolina Chapel Hill NC 27599-7450 United States Department of Material Science Engineering North Carolina State University Raleigh NC 27695-7907 United States Department of Chemical Engineering and Material Sciences University of Minnesota Minneapolis MN 55455 United States

ISBN: (纸本)9781615670802

It was hypothesized that the hydroxyapatite(HAP)/GEMOSIL biomaterial could promote osteoblast (MC3T3) self-organization. This study using MC3T3 cell line demonstrated formation of trabecular bone-like extracellular matrix (ECM) on the material compared to unorganized ECM on the control (no-material). The study also initiated exploratory tests for the underlying mechanisms via gene analysis and proliferation assay.

关键词： Hydroxyapatite

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