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22nd IEEE international parallel and distributed Processing symposium (IPDPS 2008)

作者： Majedi, M. Shaw, R. E. Garey, L. E. Univ New Brunswick Dept Comp Sci & Appl Stat St John NB E2L 4L5 Canada

ISBN: (纸本)9781424416936

The large scale of linear systems of equations results in costly solving time. These systems usually have specific properties that can be used for designing fost algorithms. In addition, using parallel programming on distributed memory clusters enables us to get the results even faster. This work introduces a new fast parallel algorithm for solving systems with a strictly diagonally dominant three-band Toeplitz coefficient matrix. We call this new method the sewing method because the boundaries sew the adjacent subsystems together.

关键词： the sewing method parallel algorithms tridiagonal Toeplitz systems tridiagonal strictly diagonally dominant

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Running OpenMP applications efficiently on an everything-shared SDSM

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JOURNAL OF parallel AND distributed COMPUTING 2006年第5期66卷 647-658页

作者： Costa, JJ Cortes, T Martorell, X Ayguade, E Labarta, J Univ Politecn Catalunya Dept Arquitectura Computadors Barcelona Spain

Traditional software distributed shared memory (SDSM) systems modify the semantics of a real hardware shared memory system by relaxing the coherence semantic and by limiting the memory regions that are actually shared. These semantic modifications are done to improve performance of the applications using it. In this paper. we will show that a SDSM system that behaves like a real shared memory system (without the afore-mentioned relaxations) can also be used to execute OpenMP applications and achieve similar speedups as the ones obtained by traditional SDSM systems. This performance can be achieved by encouraging the cooperation between the SDSM and the OpenMP runtime instead of relaxing the semantics of the shared memory. In addition, techniques like boundaries alignment and page presend are demonstrated as very useful to overcome the limitations of the current SDSM systems. (c) 2005 Elsevier Inc. All rights reserved.

关键词： OpenMP software distributed shared memory scalability adaptability cooperation

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Heuristic algorithms for distributed query processing

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Proceedings international symposium on databases in parallel and distributed systems

作者： Bodorik, P. Riordon, J.S. Tech Univ of Nova Scotia Sch of Comput Sci Halifax NS Can

ISBN: (纸本)0818608935

An examination is made of heuristic algorithms for processing distributed queries using generalized joins. As this optimization problem is NP-hard, a heuristic algorithm is used to form/formulate strategies to process queries. It has a special property in that its overhead can be controlled. The higher its overhead the better the strategies it produces. Modeling on a testbed of queries demonstrates that there is a tradeoff between the strategy's execution and formulation delays. The modeling results also support the notion that simple greedy heuristic algorithms are sufficient in that they are likely to lead to near-optimal strategies and that increasing the overhead in forming strategies is only marginally beneficial. Both the strategy formulation and execution delays are examined in relation to the number of operations specified by the strategy and the total size of partial results.

关键词： Database systems

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Byzantine Agreement with Unknown Participants and Failures 35

Byzantine Agreement with Unknown Participants and Failures

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35th IEEE international parallel and distributed Processing symposium (IPDPS)

作者： Khanchandani, Pankaj Wattenhofer, Roger Swiss Fed Inst Technol Zurich Switzerland

ISBN: (纸本)9781665440660

A set of mutually distrusting participants that want to agree on a common opinion must solve an instance of a Byzantine agreement problem. These problems have been extensively studied in the literature. However, most of the existing solutions assume that the participants are aware of n - the total number of participants in the system - and f - an upper bound on the number of Byzantine participants. In this paper, we show that most of the fundamental agreement problems can be solved without affecting resiliency even if the participants do not know the values of (possibly changing) n and f. Specifically, we consider a synchronous system where the participants have unique but not necessarily consecutive identifiers, and give Byzantine agreement algorithms for reliable broadcast, approximate agreement, rotor-coordinator, early terminating consensus and total ordering in static and dynamic systems, all with the optimal resiliency of n > 3f. Moreover, we show that some synchrony is necessary as an agreement with probabilistic termination is impossible in a semi-synchronous or asynchronous system if the participants are unaware of n and f.

关键词： distributed processing Upper bound Heuristic algorithms Probabilistic logic Approximation algorithms Reliability Dynamical systems

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Modeling parallel and distributed computing resources using structured metadata 12

Modeling parallel and distributed computing resources using ...

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12th international Conference on Database and Expert systems Applications (DEXA)

作者： Tomsich, P Vienna Tech Univ Inst Software Technol A-1040 Vienna Austria

ISBN: (纸本)0769512305

Modern database systems-and in particular multidatabase systems, federated database systems and OLAP-oriented data-warehouses-factor the stored data into actual content and meta-data, which structures the available information. This separation is particularly popular in the data-warehousing community, where large amounts of data are structured by and accessible through far smaller amounts of meta-data. Given a parallel or distributed database system, a sophisticated query optimizer requires information on the specific structure of the computing resource, the data distribution, data replication and interconnection bandwidths in order to optimally schedule computational subtasks. Such optimizations are of an even greater importance for next-generation OLAP engines, which attempt to substitute on-demand aggregation into virtual data-cubes and caching for eager preaggregation. Given the demand for ever faster response times and exponentially growing data sets, the parallelization of analytical database systems continuously gains in importance. As a result a portable and comprehensive framework for the representation of optimization-related information becomes necessary. This presentation discusses the possibilities for query optimization in parallel and distributed OLAP systems, given a detailed description of the underlying computing and storage infrastructure. A modeling framework for the description of the computing resource is introduced, which may be applied to a wide array of database systems. A discussion of using profiling information gathered during the execution of queries to dynamically refine the cost estimates given in the meta-data is also provided.

关键词： Concurrent computing Data analysis Data warehouses Database systems Delay distributed computing distributed databases Frequency Relational databases Transaction databases

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An Improved parallel Strategy for Auxiliary Inverter without Control Interconnection in Metro Applications 10

An Improved Parallel Strategy for Auxiliary Inverter without...

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IEEE 10th international symposium on Power Electronics for distributed Generation systems (PEDG)

作者： Xu, Mingxia Wang, Zhiqiang Che, Xiangzhong Wang, Ninghui Dalian Univ Technol Sch Elect Engn Dalian Peoples R China CRRC Dalian R&D CO LTD Technol Ctr Dalian Peoples R China

ISBN: (纸本)9781728124551

This paper proposes an improved parallel control strategy which suits for the auxiliary inverter under different working conditions in metro. Firstly, differential droop coefficient and virtual impedance are introduced to improve the stability and dynamic response of the system. Meanwhile, the proportional-resonant control is introduced to enhance the ability of the auxiliary inverter under the sudden load change condition or with the non-linear load. Furthermore, mathematical modeling of the auxiliary inverters is carried out in the system. Finally, the improved droop control, virtual impedance and current resonant control strategies are applied to two paralleled inverters test platform of 120kVA. The experimental results show that the proposed control algorithm can greatly improve the voltage waveform and dynamic response of the parallel inverters, and improve the ability of the system under non-linear loads.

关键词： parallel control virtual impedance auxiliar inverters differential droop coefficient resonant control

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A Status Monitoring Method for Multi-parallel Choppers in Wind Turbine Converters 11

A Status Monitoring Method for Multi-parallel Choppers in Wi...

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IEEE 11th international symposium on Power Electronics for distributed Generation systems (PEDG)

作者： Wu, Rui Parkhou, Masoud Vestas Wind Syst AS Aarhus Denmark

ISBN: (纸本)9781728169903

The multi-parallel chopper system is commonly used in modern MW-level wind turbine converters. Even though the chopper is usually considered as robust and reliable, the semiconductor module can suffer critical junction temperature in extreme fault ride through (FRT) events. This paper proposes a method to monitor and identify if the individual chopper is functioning, degraded, or failed by means of collecting and comparing the parallel semiconductors' temperatures during FRT events. A simulation model is created in PLCES, the accuracy of which is further validated by a dedicated experimental setup including an infrared camera. The proposed method is verified by PLECS simulations.

关键词： DC chopper Insulated Gate Bipolar Transistor (IGBT) fault ride through status monitoring temperature infrared measurement

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Analysis of Negative Influence of Harmonic Circulation between parallel STATCOMs and Suppression Method 10

Analysis of Negative Influence of Harmonic Circulation betwe...

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IEEE 10th international symposium on Power Electronics for distributed Generation systems (PEDG)

作者： Chen, Jikai Wang, Peng Hu, Yang Shao, Hui Li, Guoqing Wang, Xiaozhe Qin, Jiangchao Northeast Elect Power Univ Sch Elect Engn Jilin Jilin Peoples R China McGill Univ Sch Elect Engn Montreal PQ Canada Arizona State Univ Sch Elect Comp & Energy Engn Tempe AZ USA

ISBN: (纸本)9781728124551

In this paper, the cascaded H-bridge STATCOM parallel system is taken as the research object to analyze the instability of STATCOM system caused by the interaction between parallel STATCOMs in wind farm afflux station. Firstly, the inherent relation of harmonic circulation and low-frequency disturbance will be revealed by CPS-PWM theory. Then, the output impedance and transfer function of STATCOM give an insight into the interaction between STATCOMs and low-frequency resonance, and the virtual impedance method is proposed to shape the resonant peak. Finally, the correctness of theoretical analysis is verified by real-time simulation.

关键词： cascaded H-bridge STATCOM harmonic current low-frequency disturbance virtual impedance

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Evaluating Asynchronous parallel I/O on HPC systems 37

Evaluating Asynchronous Parallel I/O on HPC Systems

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37th IEEE international parallel and distributed Processing symposium (IPDPS)

作者： Ravi, John Byna, Suren Koziol, Quincey Tang, Houjun Becchi, Michela N Carolina State Univ Raleigh NC 27695 USA Lawrence Berkeley Natl Lab Berkeley CA 94720 USA

ISBN: (纸本)9798350337662

parallel I/O is an effective method to optimize data movement between memory and storage for many scientific applications. Poor performance of traditional disk-based file systems has led to the design of I/O libraries which take advantage of faster memory layers, such as on-node memory, present in high-performance computing (HPC) systems. By allowing caching and prefetching of data for applications alternating computation and I/O phases, a faster memory layer also provides opportunities for hiding the latency of I/O phases by overlapping them with computation phases, a technique called asynchronous I/O. Since asynchronous parallel I/O in HPC systems is still in the initial stages of development, there hasn't been a systematic study of the factors affecting its performance. In this paper, we perform a systematic study of various factors affecting the performance and efficacy of asynchronous I/O, we develop a performance model to estimate the aggregate I/O bandwidth achievable by iterative applications using synchronous and asynchronous I/O based on past observations, and we evaluate the performance of the recently developed asynchronous I/O feature of a parallel I/O library (HDF5) using benchmarks and real-world science applications. Our study covers parallel file systems on two large-scale HPC systems: Summit and Cori, the former with a GPFS storage and the latter with a Lustre parallel file system.

关键词： Performance Evaluation Modeling Asynchronous I/O parallel I/O

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distributed Ranking in Networks with Limited Memory and Communication

Distributed Ranking in Networks with Limited Memory and Comm...

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IEEE international symposium on Information Theory

作者： Jung, Kyomin Kim, Bo Young Vojnovic, Milan Korea Adv Inst Sci & Technol Taejon 305701 South Korea Microsoft Res Cambridge England

ISBN: (纸本)9781467325790

We study a basic information ranking problem in networks where each node holds an individual preference over a set of items and the goal for each node is to identify a sorted list of items with the largest aggregate preference. We would like to achieve this with a fully decentralized algorithm that uses a limited per-node memory and limited pair-wise communications. We show how this problem can be reduced to a plurality selection problem where the goal for each node is to identify an item with the largest aggregate ranking score, and show that solving the reduced problem solves the original ranking problem with high probability. Then we introduce a simple and natural plurality selection algorithm for the selection over m > 1 items that uses only log(2) (m) + 1 bits of per-node memory and per pair-wise communication. We prove correctness of the algorithm with high probability as the number of nodes grows large for the case when each node communicates with any other node, and establish tight convergence time bounds. The information ranking problem studied in this paper is a basic ranking problem that arises in various applications such as sorting elements in distributed computing systems, parallel databases, and may as well serve as a model of decentralized inference and opinion formation in distributed environments.

关键词： distributed computer systems

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