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作者： Hoang, Roger V. Sgambati, Matthew R. Brown, Timothy J. Coming, Daniel S. Harris Jr., Frederick C. Department of Computer Science and Engineering University of Nevada Reno Reno NV 89557 United States Center for Advanced Visualization Computation and Modeling Desert Research Institute 2215 Raggio Parkway Reno NV 89512 United States

The destruction caused by wildfires has led to the development of various models that try to predict the effects of this phenomenon. However, as the computational complexity of these models increases, their utility for real-time applications diminishes. Fortunately, the burgeoning processing power of the graphics processing unit can not only mitigate these concerns but also allow for high-fidelity visualization. We present VFire, an immersive wildfire simulation and visualization system. Users are placed in a virtual environment generated from real-world data regarding topology and vegetation. There they can simulate wildfires in real-time under various conditions. They can then experiment with various suppression techniques, such as fire breaks and water drops. The simulation is performed on the graphics card, which then provides visualization of the results. The system is intended to train fire chiefs in planning containment efforts and to educate firefighters, policymakers, and the general public about wildfire behavior and the effects of preventative measures. © 2010 Elsevier Ltd. All rights reserved.

关键词： Virtual reality

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Suppression of blow-up in Parabolic-Parabolic Patlak-Keller-Segel via strictly monotone shear flows

arXiv

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arXiv 2017年

作者： Siming, He Department of Mathematics and Center for Scientific Computation and Mathematical Modeling University of Maryland College Park United States

In this paper we consider the parabolic-parabolic Patlak-Keller-Segel models in T × R with advection by a large strictly monotone shear flow. Without the shear flow, the model is L1 critical in two dimensions with critical mass 8π: solutions with mass less than 8π are global in time and there exist solutions with mass larger than 8π which blow up in finite time [41]. We show that the additional shear flow, if it is chosen sufficiently large, suppresses one dimension of the dynamics and hence can suppress blow-up. In contrast with the parabolic-elliptic case [8], the strong shear flow has destabilizing effect in addition to the enhanced dissipation effect, which make the problem more difficult. Copyright © 2017, The Authors. All rights reserved.

关键词： Shear flow

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ON BILINEAR HILBERT TRANSFORM ALONG TWO POLYNOMIALS

arXiv

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arXiv 2017年

作者： Dong, Dong Center for Scientific Computation and Mathematical Modeling University of Maryland College ParkMD20742 United States

We prove that the bilinear Hilbert transform along two polynomials BP,Q(f, g)(x) = RR f(x−P (t))g(x−Q(t)) dtt is bounded from Lp ×Lq to Lr for a large range of (p, q, r), as long as the polynomials P and Q have distinct leading and trailing degrees. The same boundedness property holds for the corresponding bilinear maximal function MP,Q(f, g)(x) = supǫ>0 21ǫR−ǫǫ |f(x − P (t))g(x − Q(t))|dt.42B20, 47B38 Copyright © 2017, The Authors. All rights reserved.

关键词： Polynomials

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Information theory based estimator of the number of sources in a sparse linear mixing model

Information theory based estimator of the number of sources ...

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Annual Conference on Information Sciences and Systems (CISS)

作者： Radu Balan Department of Mathematics Center for Scientific Computation and Mathematical Modeling and Norbert Wiener Center University of Maryland College Park MD USA

In this paper we present an Information theoretic estimator for the number of sources mutually disjoint in a linear mixing model. The approach follows the Minimum Description Length prescription and is roughly equal to the sum of negative normalized maximum log-likelihood and the logarithm of number of sources. Preliminary numerical evidence supports this approach and compares favorably to both the Akaike (AIC) and Bayesian (BIC) Information Criteria.

关键词： Information theory Estimation theory Signal analysis Mathematical model Hydrogen Vectors Statistics Time frequency analysis Maximum likelihood estimation Mathematics

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On signal reconstruction from its spectrogram

On signal reconstruction from its spectrogram

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Annual Conference on Information Sciences and Systems (CISS)

作者： Radu Balan Department of Mathematics Center for Scientific Computation and Mathematical Modeling and Norbert Wiener Center University of Maryland College Park MD USA

This paper presents a framework for discrete-time signal reconstruction from absolute values of its short-time Fourier coefficients. Our approach has two steps. In step one we reconstruct a band-diagonal matrix associated to the rank-one operator K x = xx*. In step two we recover the signal x by solving an optimization problem. The two steps are somewhat independent, and one purpose of this paper is to present a framework that decouples the two problems. The solution to the first step is connected to the problem of constructing frames for spaces of Hilbert-Schmidt operators. The second step is somewhat more elusive. Due to inherent redundancy in recovering x from its associated rank-one operator K x , the reconstruction problem allows for imposing supplemental conditions. In this paper we make one such choice that yields a fast and robust reconstruction. However this choice may not necessarily be optimal in other situations. It is worth mentioning that this second step is related to the problem of finding a rank-one approximation to a matrix with missing data.

关键词： Signal reconstruction Spectrogram Hilbert space Fourier transforms Algorithm design and analysis Robustness Reconstruction algorithms Mathematics Mathematical model Educational institutions

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A molecular dynamics study of polymer/graphene nanocomposites 16

A molecular dynamics study of polymer/graphene nanocomposite...

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16th European Conference on Composite Materials, ECCM 2014

作者： Rissanou, Anastassia N. Harmandaris, Vagelis Department of Applied Mathematics University of Crete Heraklion CreteGR-71409 Greece Archimedes Center for Analysis Modeling and Computation University of Crete P.O. Box 2208 HeraklionGR-71003 Greece Heraklion CreteGR-71110 Greece

In this work, we study three hybrid polymer/graphene interfacial systems (polystyrene/graphene, poly(methyl-methacrylate)/graphene and polyethylene/graphene) through detailed atomistic molecular dynamics (MD) simulations. Density profiles, structural characteristics and mobility aspects are being examined at the molecular level for all model systems. In addition, we compare the properties of the hybrid systems to the properties of the corresponding bulk ones, as well as to theoretical predictions. Qualitative and quantitative differences in density profiles, in structure and dynamic properties of the polymer chains in particular at the polymer/graphene interface are establised.

关键词： Molecular dynamics

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Numerical Simulation of Compositional Flow in Porous Media under Gravity

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Communications in computational Physics 2006年第5期1卷 827-846页

作者： Zhangxin Chen Guoqiang(Joe)Zhou Dan Carruthers Center for Scientific Computation Southern Methodist UniversityDallasTX 75275-0156USA Research Center for Science Xi’an Jiaotong UniversityXi’an 710049P.R.China Center for Advanced Reservoir Modeling and Simulation College of EngineeringPeking UniversityP.R.China The Permedia Research Group 577 Somerset St.W.OttawaOntario K1R 5K1Canada

This paper is concerned with the numerical simulation of multiphase,multi-component flow in porous *** model equations are based on compositional flow with mass interchange between *** compositional model consists of Darcy’s law for volumetric flow velocities,mass conservation for hydrocarbon components,ther-modynamic equilibrium for mass interchange between phases,and an equation of state for ***-accurate finite volume methods on unstructured grids are used to discretize the model governing *** emphasis is placed on studying the influence of gravitational effects on the overall displacement *** particular,free and forced convections,diffusions,and dispersions are studied in separate and com-bined cases,and their interplays are intensively analyzed for gravitational *** numerical experiments are presented to validate the numerical study under consideration.

关键词： Compositional model reservoir simulation finite volume method unstructured grids gravitational effect free and forced convections diffusions dispersions numerical experiments

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Non-Oscillatory Hierarchical Reconstruction for Central and Finite Volume Schemes

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Communications in computational Physics 2007年第5期2卷 933-963页

作者： Yingjie Liu Chi-Wang Shu Eitan Tadmor Mengping Zhang School of Mathematics Georgia Institute of TechnologyAtlantaGA 30332-0160USA. Division of Applied Mathematics Brown UniversityProvidenceRI 02912USA Department of Mathematics Institute for Physical Science and Technologyand Center of Scientific Computation and Mathematical Modeling(CSCAMM)University of MarylandCollege ParkMD 20742USA Department of Mathematics University of Science and Technology of ChinaHefeiAnhui 230026China

This is the continuation of the paper”Central discontinuous Galerkin methods on overlapping cells with a non-oscillatory hierarchical reconstruction”by the same *** hierarchical reconstruction introduced therein is applied to central schemes on overlapping cells and to finite volume schemes on non-staggered *** takes a new finite volume approach for approximating non-smooth solutions.A critical step for high-order finite volume schemes is to reconstruct a non-oscillatory high degree polynomial approximation in each cell out of nearby cell *** the paper this procedure is accomplished in two steps:first to reconstruct a high degree polynomial in each cell by using e.g.,a central reconstruction,which is easy to do despite the fact that the reconstructed polynomial could be oscillatory;then to apply the hierarchical reconstruction to remove the spurious oscillations while maintaining the high *** numerical computations for systems of conservation laws are performed without characteristic *** particular,we demonstrate that this new approach can generate essentially non-oscillatory solutions even for 5th-order schemes without characteristic decomposition.

关键词： Central scheme discontinuous Galerkin method ENO scheme finite volume scheme MUSCL scheme TVD scheme.

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Phase-field model for reconstructed stepped surface

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Physical Review E 2013年第1期88卷 014401-014401页

作者： Kanna Nakamura Dionisios Margetis Department of Mathematics University of Maryland College Park Maryland 20742 USA Institute for Physical Science and Technology and Center for Scientific Computation and Mathematical Modeling University of Maryland College Park Maryland 20742 USA

We formulate a phase-field, or diffuse-interface, model for the evolution of stepped surfaces under surface diffusion in the presence of distinct material parameters across nanoscale terraces. In the sharp-interface limit, our model reduces to a Burton-Cabrera-Frank (BCF)-type theory for the motion of noninteracting steps separating inhomogeneous terraces. This setting aims to capture features of reconstructed semiconductor, e.g., Si surfaces below the roughening transition. Our work forms an extension of the phase-field construction by Hu et al. [Physica D 241, 77 (2012)].

关键词： Phase-field reconstructed surface material parameter DIFFUSE INTERFACE phase-field model field simulation terraces phase field Hu-Yang terraces surface diffusion

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Synchronous collaborative tunnel design based on consistency-preserving multi-scale models

Synchronous collaborative tunnel design based on consistency...

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作者： Borrmann, André Flurl, Matthias Jubierre, Javier Ramos Mundani, Ralf-Peter Rank, Ernst Department of Computational Modeling and Simulation Leonhard Obermeyer Center of Digital Methods for the Built Environment Technische Universität München Arcisstraße 21 Munich80290 Germany Department of Computation in Engineering Leonhard Obermeyer Center of Digital Methods for the Built Environment Technische Universität München Arcisstraße 21 Munich80290 Germany

The planning of large infrastructure projects such as inner-city subway tracks is a highly collaborative process in which numerous experts from different domains are involved. While performing the planning task, widely differing scales have to be taken into consideration, ranging from the kilometer scale for the general routing of the track down to the centimeter scale for the detailed design of connection points. Currently there is no technology available which supports both the collaborative as well as the multi-scale aspect in an adequate manner. To fill this technological gap and better support the collaborative design and engineering activities involved with infrastructure planning, this paper introduces a new methodology which allows engineers to simultaneously manipulate a shared multi-scale tunnel model. This methodology comprises two main aspects. The first aspect is a multi-scale model for shield tunnels, which provides five different levels of detail (LoD) representing the different levels of abstraction required throughout the planning progress. The second aspect is a conceived collaboration platform, which enables simultaneous modifications of the multi-scale model by multiple users. In existing multi-scale approaches, where the individual representations are stored independently from each other, there is a high risk of creating inconsistencies, in particular in the highly dynamic collaborative planning context. To overcome this issue, the concept presented in this paper makes use of procedural modeling techniques for creating explicit dependencies between the geometric entities on the different LoDs. This results in a highly flexible, yet inherently consistent multi-scale model where the manipulation of elements on coarser LoDs results in an automated update of all dependent elements on finer LoDs. The proposed multi-scale model forms a well-suited basis for realizing the collaboration concept, which allows several experts to simultaneously manipulate

关键词： Product design

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