1,514 research outputs found

    Synchronization in a ring of pulsating oscillators with bidirectional couplings

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    We study the dynamical behavior of an ensemble of oscillators interacting through short range bidirectional pulses. The geometry is 1D with periodic boundary conditions. Our interest is twofold. To explore the conditions required to reach fully synchronization and to invewstigate the time needed to get such state. We present both theoretical and numerical results.Comment: Revtex, 4 pages, 2 figures. To appear in Int. J. Bifurc. and Chao

    Shared versus distributed memory multiprocessors

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    The question of whether multiprocessors should have shared or distributed memory has attracted a great deal of attention. Some researchers argue strongly for building distributed memory machines, while others argue just as strongly for programming shared memory multiprocessors. A great deal of research is underway on both types of parallel systems. Special emphasis is placed on systems with a very large number of processors for computation intensive tasks and considers research and implementation trends. It appears that the two types of systems will likely converge to a common form for large scale multiprocessors

    GAME THEORETIC FLOW AND ROUTING CONTROL FOR COMMUNICATION NETWORKS

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    As the need to support high speed data exchange in modern communication networks grows rapidly, effective and fair sharing of the network resources becomes very important. Today's communication networks typically involve a large number of users that share the same network resources but may have different, and often competing, objectives. Advanced network protocols that are implemented to optimize the performance of such networks typically assume that the users are passive and are willing to accept compromising their own performance for the sake of optimizing the performance of the overall network. However, considering the trend towards more decentralization in the future, it is natural to assume that the users in a large network may take a more active approach and become more interested in optimizing their own individual performances without giving much consideration to the overall performance of the network. A similar situation occurs when the users are members of teams that are sharing the network resources. A user may find itself cooperating with other members of its team which itself is competing with the other teams in the network. Game theory appears to provide the necessary framework and mathematical tools for formulating and analyzing the strategic interactions among users, or teams of users, of such networks. In this thesis, we investigate networks in which users, or teams of users, either compete or cooperate for the same network resources. We considered two important network topologies and used many examples to illustrate the various solution concepts that we have investigated.. First we consider two-nodeiiiparallel link networks with non-cooperative users trying to optimally distribute their flows among the links. For these networks, we established a condition which guarantees the existence and uniqueness of a Nash equilibrium for the link flows. We derived an analytical expression for the Nash equilibrium and investigated its properties in terms of the network parameters and the users preferences. We showed that in a competitive environment users can achieve larger flow rates by properly emphasizing the corresponding term in their utility functions, but that this can only be done at the expense of an increase in the expected delay. Next, we considered a general network structure with multiple links, multiple nodes, and multiple competing users. We proved the existence of a unique Nash equilibrium. We also investigated many of its intuitive properties. We also extended the model to a network where multiple teams of users compete with each other while cooperating within the teams to optimize a team level performance. For this model, we studied the Noninferior Nash solution and compared its results with the standard Nash equilibrium solution

    Fast Optimization with Zeroth-Order Feedback in Distributed, Multi-User MIMO Systems

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    In this paper, we develop a gradient-free optimization methodology for efficient resource allocation in Gaussian MIMO multiple access channels. Our approach combines two main ingredients: (i) an entropic semidefinite optimization based on matrix exponential learning (MXL); and (ii) a one-shot gradient estimator which achieves low variance through the reuse of past information. This novel algorithm, which we call gradient-free MXL algorithm with callbacks (MXL0+^{+}), retains the convergence speed of gradient-based methods while requiring minimal feedback per iteration-a single scalar. In more detail, in a MIMO multiple access channel with KK users and MM transmit antennas per user, the MXL0+^{+} algorithm achieves ϵ\epsilon-optimality within poly(K,M)/ϵ2\text{poly}(K,M)/\epsilon^2 iterations (on average and with high probability), even when implemented in a fully distributed, asynchronous manner. For cross-validation, we also perform a series of numerical experiments in medium- to large-scale MIMO networks under realistic channel conditions. Throughout our experiments, the performance of MXL0+^{+} matches-and sometimes exceeds-that of gradient-based MXL methods, all the while operating with a vastly reduced communication overhead. In view of these findings, the MXL0+^{+} algorithm appears to be uniquely suited for distributed massive MIMO systems where gradient calculations can become prohibitively expensive.Comment: Final version; to appear in IEEE Transactions on Signal Processing; 16 pages, 4 figure

    C-MOS array design techniques: SUMC multiprocessor system study

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    The current capabilities of LSI techniques for speed and reliability, plus the possibilities of assembling large configurations of LSI logic and storage elements, have demanded the study of multiprocessors and multiprocessing techniques, problems, and potentialities. Evaluated are three previous systems studies for a space ultrareliable modular computer multiprocessing system, and a new multiprocessing system is proposed that is flexibly configured with up to four central processors, four 1/0 processors, and 16 main memory units, plus auxiliary memory and peripheral devices. This multiprocessor system features a multilevel interrupt, qualified S/360 compatibility for ground-based generation of programs, virtual memory management of a storage hierarchy through 1/0 processors, and multiport access to multiple and shared memory units

    A basic web-based distance education model

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    Thesis (Master)--Izmir Institute of Technology, Computer Engineering, Izmir, 2005Includes bibliographical references (leaves: 147)Text in English; Abstract: Turkish and Englishxv, 201 leavesDuring the recent years, the rapid growth of the Web and multimedia technologies urged a shift of Computer-Based Educational Technology towards the Web. In the leading universities of the developed countries, studies on Web-Based Education have started and in an increasing manner are going strong. In the last few years, the leading universities of Turkey are also greatly interested in Web-Based Education and have started their re-structuring accordingly.The goal of this study is to design a basic model to be utilized by a university aiming to offer web-based distance education. In achieving this; by the use of system approach, a model comprising of three subsystems, namely system analysis, system design and evaluation&control, working in coordination with each other, has been tried to be proposed. There may be only one missing point of this study, that is; since preparing a lesson or program according to this model was not foreseen in this thesis, the effectiveness evaluations suggested in the evaluation&control subsystem could not be realized. It is recommended to realize such an evaluation in a further study to make it possible to reveal the effectiveness of web-based education by preparing a lesson or program according to this model.On the other hand, a survey has been conducted in Turkey in some of the universities either offering web-based education or are interested in studies in this field.The aim of this survey is to analyze from system design point of view the studies carried out in our universities on this matter and to get a picture of the existing situation.The directed questions aiming this were prepared by taking into consideration of the three stages of system design subsystem, i.e. administrative design, educational design, and technological design. It is intended for the result of this survey to shed light to the new-coming institutions in this field. As a matter of fact, each stage of this subsystem is a survey item itself and should be researched one by one in other studies.Furthermore, for individuals interested in distance education and web-based distance education and for people newly involved in this matter, this thesis is intended to be a reference material and to serve this purpose the sections are prepared containing the basic information accordingly. Nevertheless, since most of the information regarding system design are prepared without taking into consideration the disabled people, the relevant information are not complete. In another study, the offering of the web-based education to the disabled people, especially for deaf, hard of hearing or speech impaired, and blind students, has to be investigated.Finally, in this thesis the proposed model for the Web-Based Distance Education, as being a basic and conceptual model, has a flexible structure; i.e., suitable for all the institutions and establishments intending to offer the web-based education.What is important here, is to exploit the potential sources within the institution that will display the required systematic approach

    Overlapping communication and computation by using a hybrid MPI/SMPSs approach

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    A previous version of this document was submitted for publication by october 2008.Communication overhead is one of the dominant factors that affect performance in high-performance computing systems. To reduce the negative impact of communication, programmers overlap communication and computation by using asynchronous communication primitives. This increases code complexity, requiring more effort to write parallel code and making less readable code. This paper presents the hybrid use of MPI and SMPSs (SMP superscalar), a task-based shared-memory programming model, enhanced with a restart mechanism allowing the programmer to introduce the asynchronism that is necessary to enable the effective communication/computation overlap in a productive way. We demonstrate the hybrid use of MPI/SMPSs with the high-performance LINPACK benchmark, which uses the lookahead technique to overlap communication and computation. MPI/SMPSs improves the performance of a pure MPI with look-ahead by 7,6% on a 1024 processors machine. In addition to better performance, hybrid MPI/SMPSs substantially reduces code complexity, it is less sensitive to network bandwidth and operating system noise, and improves the use of main memory.Postprint (published version

    A study of System Interface Sets (SIS) for the host, target and integration environments of the Space Station Program (SSP)

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    System interface sets (SIS) for large, complex, non-stop, distributed systems are examined. The SIS of the Space Station Program (SSP) was selected as the focus of this study because an appropriate virtual interface specification of the SIS is believed to have the most potential to free the project from four life cycle tyrannies which are rooted in a dependance on either a proprietary or particular instance of: operating systems, data management systems, communications systems, and instruction set architectures. The static perspective of the common Ada programming support environment interface set (CAIS) and the portable common execution environment (PCEE) activities are discussed. Also, the dynamic perspective of the PCEE is addressed

    Evaluation of Job Queuing/Scheduling Software: Phase I Report

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    The recent proliferation of high performance work stations and the increased reliability of parallel systems have illustrated the need for robust job management systems to support parallel applications. To address this issue, the national Aerodynamic Simulation (NAS) supercomputer facility compiled a requirements checklist for job queuing/scheduling software. Next, NAS began an evaluation of the leading job management system (JMS) software packages against the checklist. This report describes the three-phase evaluation process, and presents the results of Phase 1: Capabilities versus Requirements. We show that JMS support for running parallel applications on clusters of workstations and parallel systems is still insufficient, even in the leading JMS's. However, by ranking each JMS evaluated against the requirements, we provide data that will be useful to other sites in selecting a JMS
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