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Multiscale Coherent Structures and Broadband Waves due to Parallel Inhomogeneous Flows

Physical Review Letters 2000年第20期85卷 4285-4285页

作者： Valeriy V. Gavrishchaka Gurudas I. Ganguli Wayne A. Scales Steven P. Slinker Christopher C. Chaston James P. McFadden Robert E. Ergun Charles W. Carlson Science Applications International Corporation McLean Virginia Plasma Physics Division Naval Research Laboratory Washington D.C. Bradley Department of Electrical and Computer Engineering Virginia Polytechnic Institute and State University Blacksburg Virginia Space Sciences Laboratory University of California Berkeley California Department of Astrophysical and Planetary Science Laboratory for Atmospheric and Space Physics Colorado University Boulder Colorado

Linear theory analysis and particle-in-cell simulations show that a spatial transverse gradient in the ion drift parallel to the magnetic field, dVdi/dx≤Ωi, where Ωi is the ion cyclotron frequency, can generate a broadband multimode spectrum extending from ω≪Ωi to ω≫Ωi. Nonlinearly, these waves lead to multiscale spatially coherent structures, substantial cross-field transport, ion energization, and phase-space diffusion. Large spikes are formed in the parallel electric field time series. These signatures are similar to the Fast Auroral Snapshot satellite observations in the upward current region.

关键词： .generate coherent structures drift Plasma Physics Inhomogeneous upward time series electric fields ion beams

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Higher-order dynamics in lattice-based models using the Chapman-Enskog method

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Physical Review E 2000年第2期61卷 2103-2103页

作者： Yue-Hong Qian Ye Zhou Department of Applied Physics and Applied Mathematics Columbia University New York New York 10027 IBM Research Division Thomas J. Watson Research Center P.O. Box 218 Yorktown Heights New York 10598 Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23681

In this paper, we investigate the existence of higher-order dynamics in lattice-based models. We have identified two conditions that determine whether a model would allow some Burnett-like equations when the Chapman-Enskog expansion is used. These two conditions are the number of the conserved quantity as well as the space and time discretization. We shall demonstrate these conditions by discussing (1) pure diffusion equation and (2) hydrodynamic equations. While the fact that diffusion equation allows the higher-order dynamics can be shown easily, we will illustrate that care must be taken when deriving Burnett-like equations for lattice-based hydrodynamics models using the Chapman-Enskog method.

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Higher-order dynamics in lattice-based models using the Chapman-Enskog method

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Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 2000年第2期61卷 2103-2106页

作者： Qian, Yue-Hong Zhou, Ye Department of Applied Physics and Applied Mathematics Columbia University New YorkNY10027 United States IBM Research Division Thomas J. Watson Research Center P.O. Box 218 Yorktown HeightsNY10598 United States Institute for Computer Applications in Science and Engineering NASA Langley Research Center HamptonVA23681 United States Exa Corp 450 Bedford Street LexingtonMA02420 United States

关键词： Hydrodynamics

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On the implementation of the Opus coordination language

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Concurrency and Computation: Practice and Experience 2000年第4期12卷

作者： Erwin Laure Matthew Haines Piyush Mehrotra Hans Zima Institute for Software Technology and Parallel Systems University of Vienna Liechtensteinstrasse 22 A-1090 Vienna Austria Department of Computer Science University of Wyoming Laramie WY 82071-3682 U.S.A. Institute for Computer Applications in Science and Engineering NASA Langley Research Center Mail Stop 132C Hampton VA 23681-0001 U.S.A.

Opus is a new programming language designed to assist in coordinating the execution of multiple, independent program modules. With the help of Opus, coarse grained task parallelism between data parallel modules can be expressed in a clean and structured way. In this paper we address the problems of how to build a compilation and runtime support system that can efficiently implement the Opus constructs. Our design considers the often-conflicting goals of efficiency and modular construction through software re-use. In particular, we present the system requirements for an efficient Opus implementation, the Opus runtime system, and describe how they work together to provide the underlying services that the Opus compiler needs for a broad class of machines. Copyright © 2000 John Wiley & Sons, Ltd.

关键词： Opus task parallelism data parallelism coordination

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Parallel compact multi-dimensional numerical algorithm with application to aeroacoustics 14th

Parallel compact multi-dimensional numerical algorithm with ...

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14th Computational Fluid Dynamics Conference, 1999

作者： Povitsky, Alex Morris, Philip J. Institute for Computer Applications in Science and Engineering NASA Langley Research Center MS 132C HamptonVA23681 United States Department of Aerospace Engineering The Pennsylvania State University University ParkPA16802 United States

In this study we propose an efficient method to parallelize high-order compact numerical algorithms for the solution of three-dimensional PDEs in a spacetime domain. The proposed parallelization method includes 3-D partitioning and the solution of sets of linear banded systems that split onto processors. Efficient. parallelization of the Thomas algorithm is difficult due to its pipelined nature. We use processors for either non-local data independent computations, solving lines in the next spatial direction, or local datadependent computations by the Runge-Kutta method while processors are idle due to the forward and backward recurrences of the Thomas algorithm. Control of processor communication and computations by a static schedule is adopted in this study. The obtained parallelization speed-up of the novel algorithm is about twice as much as that for the standard pipelined algorithm and close to that for the explicit algorithm. © 1999 by Alex Povitsky & Philip J. Morris. Published by the American Institute of Aeronautics and Astronautics, Inc.

关键词： Runge Kutta methods

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Automatic image orientation detection

Automatic image orientation detection

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IEEE International Conference on Image Processing

作者： A. Vailaya Hong Jiang Zhang A. Jain Department of Computer Science and Engineering Michigan State University East Lansing MI USA Internet Systems & Applications Lab Hewlett Packard Laboratories Palo Alto CA USA Microsoft Research China Beijing China

We present an algorithm for automatic image orientation estimation using a Bayesian learning framework. We demonstrate that a small codebook (the optimal size of codebook is selected using a modified MDL criterion) extracted from a vector quantizer can be used to estimate the class-conditional densities of the observed features needed for the Bayesian methodology. We further show how feature clustering can be used as a feature selection mechanism to remove redundancies in the high-dimensional feature vectors used for classification. Experiments on a database of 17,901 images have shown that our proposed algorithm achieves an accuracy of approximately 97% on the training set and over 89% on an independent test set.

关键词： Bayesian methods Image databases Object recognition Object detection Image retrieval Image storage State estimation Redundancy Object oriented databases Spatial databases

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X-band photoinjector for a chirped-pulse FEL

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AIP Conference Proceedings 1999年第1期474卷 433-451页

作者： E. C. Landahl R. M. Alvis A. L. Troha F. V. Hartemann G. P. Le Sage W. E. White H. A. Baldis C. V. Bennett K. Li J. P. Heritage C. H. Ho N. C. Luhmann, Jr. 1Applied Science Department University of California Davis California 95616 2Institute for Laser Science and Applications LLNL Livermore California 94550 3Lawrence Livermore National Laboratory Livermore California 94550 4Electrical Engineering Department University of California Los Angeles California 90024 5Electrical and Computer Engineering Department University of California Davis California 6Synchrotron Radiation Research Center Taiwan

The phase noise and jitter characteristics of the laser and rf systems of a high gradient X-band photoinjector have been measured experimentally. The laser oscillator is a self-modelocked Titanium:Sapphire system operating at the 108th subharmonic of the rf gun. The X-band signal is produced from the laser by a phase-locked dielectric resonance oscillator, and amplified by a pulsed TWT and klystron. A comparison between the klystron and TWT amplifier phase noise and the fields excited in the rf gun demonstrates the filtering effect of the high Q structure, thus indicating that the rf gun can be used as a master oscillator, and could be energized by either a rf oscillator such as a magnetron or a compact source such as a cross-field amplifier. In particular, the rf gun can play the role of a pulsed rf clock to synchronize the photocathode laser system: direct drive of a synchronously modelocked AlGaAs quantum well laser has been achieved using the X-band gun rf fields. This novel, GHz repetition rate, laser system is being developed to replace the more conventional femtosecond Ti:Al2O3 system. Some advantages include pumping this laser with a stabilized current source instead of a costly, low efficiency pump laser. Finally, dark current measurements and initial photoelectron measurements are reported.

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Everything you ever wanted to know about software engineering education, but were afraid to ask 98

Everything you ever wanted to know about software engineerin...

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3rd Annual Conference on Integrating Technology into computer science Education, ITiCSE 1998

作者： Mead, Nancy R. Hilburn, Thomas B. Bagert, Donald J. Ryan, Michael Benediktsson, Oddur Van Scoy, Frances Software Engineering Institute Carnegie Mellon University 5000 Forbes Ave. PittsburghPA15213 United States Department of Computer Science Embry-Riddle Aeronautical University United States Department of Computer Science Texas Tech University LubbockTX79409-3104 United States School of Computer Applications Dublin City University Glasnevin Dublin 9 Ireland University of Iceland Dunhaga 5 Reykjavik Iceland Computer Science West Virginia University MorgantownWV26506-0209 United States

ISBN: (纸本)1581130007

In this panel, we will address questions on software engineering education that are voted on by the conference attendees in advance of the session. A sample set of questions will be posted. Conference attendees who will then vote on the questions to be addressed by the panel will augment these. After the panellists provide answers to a given question, the discussion will be opened up for follow-up questions or comments by the conference attendees. © 1998 ACM.

关键词： Software engineering

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A hybrid structure for adaptive fixed weight recurrent networks

A hybrid structure for adaptive fixed weight recurrent netwo...

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International Joint Conference on Neural Networks (IJCNN)

作者： K. Meert M. Rijckaert J. Ludik Expert Systems Applications Development Grou Department of Chemical Engineering Katholieke Universiteit Leuven Heverlee Belgium Department of Computer Science University of Stellenbosch Stellenbosch South Africa

Due to the evolution of the underlying physical process, a correct model can transform into an erroneous one. We therefore propose a method which overcomes this problem by adapting the network along the way. Our method (clustered error injection) is based (a) on the ability of real-time recurrent learning networks to form clustered network structures and (b) on the error injection principle. The actual model error is fed back into the network as an input. This improves the model performance by adapting it to a changing environment. This technique is tested on two examples, a mathematical modelling problem and a real-life problem from the chemical process industry.

关键词： Adaptive systems Neural networks Chemical processes Expert systems Application software Chemical engineering computer science Africa computer errors Testing

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Training environment for inferior vena caval filter placement

Training environment for inferior vena caval filter placemen...

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6th Conferenc on Medicine Meets Virtual Reality, MMVR 1998

作者： Hahn, James K. Kaufman, Roger Winick, Adam B. Carleton, Thurston Park, Youngser Lindeman, Rob Oh, Kwang-Man Ai-Ghreimil, Nadia Walsh, Raymond J. Loew, Murray Gerber, Joanne Sankar, Siddarth Laboratory for Advanced Computer Applications in Medicine Institute for Computer Graphics George Washington University Washington DC 20052 United States Department of Electrical Engineering and Computer Science George Washington University Washington DC 20052 United States Department of Radiology George Washington University Washington DC 20052 United States Department of Civil and Mechanical Engineering George Washington University Washington DC 20052 United States Department of Anatomy and Cell Biology George Washington University Washington DC 20052 United States Institute for Medical Imaging and Image Analysis George Washington University Washington DC 20052 United States

ISBN: (纸本)9051993862

This paper describes a Virtual Environment system designed to aid in training interventional radiologists in inferior vena cava filter placement. It is being developed as part of a VE simulator for a number of surgical and interventional radiology procedures at the Laboratory for Advanced computer applications in Medicine at the George Washington University. In this procedure a filter is placed in the inferior vena cava to prevent blood clots from the lower portion of the body from reaching the lungs and causing a pulmonary embolus. The simulation is designed to provide both tutorial and testing modes for the filter placement procedure.

关键词： Virtual reality

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