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IEEE International Symposium on Network Computing and applications

作者： L. Lipsky M. Jobmann M. Greiner H.-P. Schwefel Department of Computer Science and Engineering Taylor L.Booth Center for Computer Applications and Research University of Connecticut Storrs CT USA Institut für Informatik Technische Universität Munchen Germany Institut für Informatik Technische Universität München Munchen Germany Siemens AG Munchen Germany

A wide variety of traffic models are presently used to study the performance of telecommunications networks. These are shown to be limiting cases of N-burst/G/1 queues. The analytic N-burst model describes traffic as superposition of N packet streams of ON/OFF type. When using power-tail distributions for the duration of the ON periods, self-similar properties, which are critical for understanding tele-traffic, are observed. For very low intraburst packet rates, the N-burst/G/1 model reduces to an M/G/1 queue. For /spl lambda//sub p/ /spl rarr/ /spl infin/ all packets in a burst arrive simultaneously and the model becomes a bulk arrival, or M/sup (X)//G/1, queue. In the same limit, the packet-based model can be compared to a model of the burst level, an M/G/1 queue where the individual customers represent complete bursts rather than individual packets. Thus the mean system time describes the mean delay for the last packet in a burst rather than the average over all packets. The continuous flow model is also shown to be a limiting case of the N-burst model by letting the number of packets in a burst, n/sub p/, and the router's packet service rate, /spl nu/, go to infinity while holding their ratio constant. Numerical results are presented comparing the steady-state results for mean packet delay and for buffer overflow probabilities of the different analytic models. They collectively show the critical importance of the burstiness parameter. The N-burst/M/1 model with self-similar properties shows drastically changing steady-state performance for specific values of the burstiness parameter. The limiting models are incapable of describing the detailed structure of the performance in this transition region.

关键词： Telecommunication traffic Traffic control Steady-state Switches Delay effects H infinity control computer science computer applications Tail Telecommunication standards

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Breakup of dipolar rings under a perpendicular magnetic field

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Physical Review E 2001年第6期64卷 061503-061503页

作者： F. Kun Weijia Wen K. F. Pál K. N. Tu Department of Theoretical Physics University of Debrecen P. O. Box 5 H-4010 Debrecen Hungary Institute for Computer Applications (ICA1) University of Stuttgart D-70569 Stuttgart Germany Department of Physics The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong Institute of Nuclear Research (ATOMKI) P. O. Box 51 H-4001 Debrecen Hungary Department of Materials Sciences and Engineering University of California at Los Angeles Los Angeles California 90095-1595

An experimental and theoretical study of the breakup process of rings, formed by magnetic microspheres, under the application of an external magnetic field perpendicular to the plane of the ring is presented. We found experimentally that when the value of the external magnetic field falls below a lower critical field the dipoles rotate in the ring without any distortion of the ring structure. However, exceeding the upper critical field causes sudden breakup of the ring into short chains aligned with the field. Between the lower and upper critical fields the system is in a metastable state, and hence, it is very sensitive to external perturbations. The spiral opening was found experimentally to be the lowest energy transition from the ring to the chain conformation. We worked out an analytic approach and we performed computer simulations, the results of which are in good agreement with experiments.

关键词： Magnetic materials

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Four horizons for enhancing the performance of parallel simulations based on partial differential equations 6

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6th International European Conference on Parallel Computing, Euro-Par 2000

作者： Keyes, David E. Department of Mathematics and Statistics Old Dominion University NorfolkVA23529-0077 United States Institute for Scientific Computing Research Lawrence Livermore National Laboratory LivermoreCA94551-9989 United States Institute for Computer Applications in Science and Engineering NASA Langley Research Center HamptonVA23681-2199 United States

ISBN: (纸本)9783540679561

Simulations of PDE-based systems, such as flight vehicles, the global climate, petroleum reservoirs, semiconductor devices, and nuclear weapons, typically perform an order of magnitude or more below other scientific simulations (e.g., from chemistry and physics) with dense linear algebra or N-body kernels at their core. In this presentation, we briefly review the algorithmic structure of typical PDE solvers that is responsible for this situation and consider possible architectural and algorithmic sources for performance improvement. Some of these improvements are also applicable to other types of simulations, but we examine their consequences for PDEs: potential to exploit orders of magnitude more processor-memory units, better organization of the simulation for today’s and likely near-future hierarchical memories, alternative formulations of the discrete systems to be solved, and new horizons in adaptivity. Each category is motivated by recent experiences in computational aerodynamics at the 1 Teraflop/s scale. © Springer-Verlag Berlin Heidelberg 2000.

关键词： Semiconductor devices

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On AUV control architecture

On AUV control architecture

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IEEE International Workshop on Intelligent Robots and Systems (IROS)

作者： P. Ridao J. Yuh J. Batlle K. Sugihara Informatics and Applications Institute University of Girona Spain Mechanical Engineering Department University of Girona Honolulu HI USA University of Girona Spain Information and Computer Science Department University of Hawaii Manoa Honolulu HI USA

This paper surveys control architectures proposed in the literature and describes a control architecture that is being developed for a semi-autonomous underwater vehicle for intervention missions (SAUVIM) at the University of Hawaii. Conceived as hybrid, this architecture has been organized in three layers: planning, control and execution. The mission is planned with a sequence of subgoals. Each subgoal has a related task supervisor responsible for arranging a set of pre-programmed task modules in order to achieve the subgoal. Task modules are the key concept of the architecture. They are the main building blocks and can be dynamically re-arranged by the task supervisor. In our architecture, deliberation takes place at the planning layer while reaction is dealt through the parallel execution of the task modules. Hence, the system presents both a hierarchical and an heterarchical decomposition, being able to show a predictable response while keeping rapid reactivity to the dynamic environment.

关键词： Robot sensing systems Mobile robots computer architecture Control systems Actuators Underwater vehicles Vehicle dynamics Communication system control Delay Fault tolerance

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Multiscale Coherent Structures and Broadband Waves due to Parallel Inhomogeneous Flows

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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： Plasma flow

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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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