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Identification of the hydrogen-saturated self-interstitials in silicon and germanium

Physical Review B 1998年第8期57卷 4397-4397页

作者： M. Budde B. Bech Nielsen P. Leary J. Goss R. Jones P. R. Briddon S. Öberg S. J. Breuer Edinburgh Parallel Computing Centre University of Edinburgh Edinburgh EH9 3JZ United Kingdom

Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4cm−1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5cm−1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.

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Performance of hard real-time transaction scheduling policies in parallel database systems

Performance of hard real-time transaction scheduling policie...

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International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS)

作者： S. Takkar S.P. Dandamudi Centre for Parallel and Distributed Computing School of Computer Science Carleton University Ottawa ONT Canada

Real-time transactions, in addition to preserving consistency of the database as in traditional transactions, have to meet the deadlines. Scheduling real-time transactions in parallel database systems has not received much attention. This paper focuses on real-time transaction scheduling in shared-nothing parallel database systems. We evaluate the performance of a new priority-based scheduling policy, in which all scheduling decisions are made locally by each node. In contrast, several other algorithms, proposed for the distributed systems, require communication among the nodes to globally synchronize their local block and abort decisions. Such synchronization can deteriorate performance as real-time transactions will have to meet deadlines. We use miss ratio as the performance metric and show that, in general, the new policy provides a superior performance for the workload and system parameters considered in this study.

关键词： Real time systems Database systems Transaction databases Processor scheduling System recovery Timing Distributed computing Computer science Distributed databases Measurement

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Formal specification of evolving distributed software architectures

Formal specification of evolving distributed software archit...

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International Workshop on Database and Expert Systems Applications

作者： G.R. Ribeiro Justo V.C. de Pania P.R.F. Cunha Centre for Parallel Computing University of Westminster London UK University of Westminster London London GB Department of Informatics UFPE Recife Brazil

As the complexity of software increases, there is a need to describe and evaluate the system structure or software architecture. The software architecture of a distributed system is particularly important when a system is allowed to evolve or be reconfigured during its execution, without major interruption. In this paper, we study the formalisation of evolving distributed software architectures and present a formal framework, based on Z, for the development of this type of software architecture. The paper also includes an example which shows how our framework can be applied to specify properties of evolving distributed software architectures.

关键词： Formal specifications Computer architecture Software architecture Libraries Radio access networks parallel processing Informatics Software systems Data structures Software algorithms

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Hierarchical architecture for parallel query processing on networks of workstations

Hierarchical architecture for parallel query processing on n...

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International Conference on High Performance computing

作者： Boquan Xie S.P. Dandamudi Centre for Parallel and Distributed Computing School of Computer Science Carleton University Ottawa ONT Canada Nortel Technologies Inc. Ottawa Canada

Networks of workstations (NOWs) are cost-effective alternatives to multiprocessor systems. Recently, NOWs have been proposed for parallel query processing. Idle CPU cycles of workstations in a NOW-based system can be used to process database query operations. We report on the performance of the hierarchical architecture for parallel query processing on a NOW. We have implemented the hierarchical architecture using PVM on a Pentium-based NOW. The experimental results reported suggest that the hierarchical architecture is successful in achieving good scale-ups and speedups indicating that the idle processor cycles are effectively used for query processing. The hierarchical system can also handle both light and heavy workloads in a load sharing fashion. Our results also suggest that the performance is sensitive to the minimum fragmentation size (chunk size) for partial operations and the structure of queries.

关键词： Query processing Workstations Database systems Computer architecture Delay Performance gain Distributed computing Computer science Transaction databases Personal communication networks

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Algorithms for solving a spatial optimisation problem on a parallel computer

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Concurrency and Computation: Practice and Experience 1998年第8期9卷

作者： Felicity George Nicholas Radcliffe Mark Smith Mark Birkin Martin Clarke High Performance Research Centre Tandem Computers Wallace View Stirling FK9 5PY UK Edinburgh Parallel Computing Centre University of Edinburgh Kings Buildings Mayfield Road Edinburgh EH9 3JZ UK GMAP Ltd GMAP House Cromer Terrace Leeds LS2 9JU UK

In a collaborative project between GMAP Ltd and EPCC, an existing heuristic optimisation scheme for strategic resource planning was parallelised to run on the data parallel Connection Machine CM-200. The parallel software was found to run over 2700 times faster than the original workstation software. This has allowed the exploration of complex business planning strategies at a national, rather than regional, level for the first time. The availability of a very fast evaluation program for planning solutions also enabled an investigation of the use of genetic algorithms in place of GMAP's existing heuristic optimisation scheme. The results of this study show that genetic algorithms can provide better quality solutions in terms of both predicted profit from the solution and spatial diversity to provide a range of possible solutions. This paper discusses both the parallelisation of the original optimisation scheme and the use of genetic algorithms in place of this method. © 1997 John Wiley & Sons, Ltd.

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A graphical toolset for simulation modelling of parallel systems

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parallel computing 1997年第13期22卷 1823-1836页

作者： Delaitre, T RibeiroJusto, GR Spies, F Winter, SC University of Westminster Centre for Parallel Computing 115 New Cavendish Street London WIM 8JS United Kingdom Now working for the Laboratoire d'Informatique de Besançon Université de Franche-Comté France

In this paper, a simulation model for incorporation within a performance-oriented parallel software development environment is presented. This development environment is composed of a graphical design tool, a simulation facility, and a visualisation tool. Simulation allows parallel program performance to be predicted and design alternatives to be compared. The target parallel system models a virtual machine composed of a cluster of workstations interconnected by a local area network. The simulation model architecture is modular and extensible which allows re-configuration of the platform, The model description and the validation experiments which have been conducted to assess the correctness and the accuracy of the model are also presented.

关键词： tools and environments parallel software engineering visual parallel programming, parallel program modelling and simulation

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EDPEPPS: An integrated graphical toolset for the design and performance evaluation of portable parallel software

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3rd International Conference on parallel Processing, Euro-Par 1997

作者： Delaitre, T. Vekariya, P. Bigeard, R. Justo, G.R. Winter, S.C. Zemerly, M.J. Centre for Parallel Computing University of Westminster 115 New Cavendish Street London WIM 8JS United Kingdom

ISBN: (纸本)9783540634409

This paper describes an integrated graphical toolset for performance-oriented design of portable parallel software. The toolset consists of a graphical design tool based on the PVM communications library for building parallel algorithms, a simulation engine and a visualisation tool for animation of program execution and visualisation of platform and network performance measures and statistics. The toolset is used to model a virtual machine composed of a cluster of workstations interconnected by a local area network. The simulation model used is modular and its components are interchangeable which allows easy reconfiguration of the platform. The model is validated using experiments on the COMMS1 Benchmark from the Parkbench suite, and a standard image processing algorithm with accuracy to within 10%.

关键词： Visualization

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Tentative time warp

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3rd International Conference on parallel Processing, Euro-Par 1997

作者： Kalantery, Nasser Centre for Parallel Computing University of Westminster 115 New Cavendish St London W1M 8JS United Kingdom

ISBN: (纸本)9783540634409

The Time-Warp machine, has emerged as the most effective parallel execution environment for discrete event simulation applications where parallelism or sequentiality of programmed interactions cannot be determined at program design stage. In this paper a new and more efficient implementation of the machine, the Tentative Time Warp algorithm, is introduced. In this implementation the number of cancellation messages are reduced;the need for searching the event list prior to propagation of rollbacks is eliminated (in primary rollbacks) or minimised(in secondary rollbacks);a more balanced and efficient event ordering structure, with O(1) event cancellation characteristic, is introduced and tentative cancellation, as opposed to eager or lazy cancellation, is supported. Detailed design of the data structures and empirical measurement of event ordering and cancellation costs, compared to the classic Time-Warp implementation, are presented.

关键词： Discrete event simulation

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Prototype-oriented development of high-performance systems

Prototype-oriented development of high-performance systems

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IEEE International Workshop on Software Engineering for parallel and Distributed Systems

作者： G.R.R. Justo P. Vekariya T. Delaitre J. Zemerly S. Winter Centre for Parallel Computing University of Westminster London UK

We discuss the problem of developing performance-oriented software and the need for methodologies. We then present the EDPEPPS (Environment for Design and Performance Evaluation of Portable parallel Software) approach to the problem of designing and evaluating high-performance (parallel) applications. The EDPEPPS toolset is based on a rapid prototyping philosophy, where the designer synthesises a model of the intended software which may be simulated, and the performance is subsequently analysed using visualisation. The toolset combines a graphical design tool, a simulation facility, and a visualisation tool. The same design is used to produce a code suitable for simulation and real execution.

关键词： Prototypes Software prototyping Application software Software performance Analytical models Skeleton parallel processing Virtual prototyping Visualization Software engineering

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A hierarchical processor scheduling policy for distributed-memory multicomputer systems

A hierarchical processor scheduling policy for distributed-m...

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International Conference on High Performance computing

作者： S.P. Dandamudi T.K. Thyagaraj Centre for Parallel and Distributed Computing School of Computer Science Carleton University Ottawa ONT Canada

Processor scheduling policies for distributed memory systems can be divided into space sharing or time sharing policies. In space sharing, the set of processors in the system is partitioned and each partition is assigned for the exclusive use of a job. In time sharing policies, on the other hand, none of the processors is given exclusively to jobs; instead, several jobs share the processors (for example, in a round robin fashion). There are advantages and disadvantages associated with each type of policy. Typically, space sharing policies are good at low to moderate system loads and when job parallelism does not vary much. However, at high system loads and widely varying job parallelism, time sharing policies provide a better performance. We propose a new policy that is based on a hierarchical organization that incorporates the merits of these two types of policies. The new policy is a hybrid policy that uses both space sharing as well as time sharing to achieve better performance. We demonstrate that, at most system loads of interest, the proposed policy outperforms both space sharing and time sharing policies by a wide margin.

关键词： Processor scheduling Time sharing computer systems Round robin parallel processing Distributed computing Computer science Large-scale systems Concurrent computing Message passing Delay

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