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    Free-Riding and Whitewashing in Peer-to-Peer Systems

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    We devise a simple model to study the phenomenon of free-riding and the effect of free identities on user behavior in peer-to-peer systems. At the heart of our model is a strategic user of a certain type, an intrinsic and private parameter that reflects the user's generosity. The user decides whether to contribute or free-ride based on how the current burden of contributing in the system compares to her type. We derive the emerging cooperation level in equilibrium and quantify the effect of providing free-riders with degraded service on the emerging cooperation. We find that this penalty mechanism is beneficial mostly when the "generosity level" of the society (i.e., the average type) is low. To quantify the social cost of free identities, we extend the model to account for dynamic scenarios with turnover (users joining and leaving) and with whitewashers: users who strategically leave the system and re-join with a new identity. We find that the imposition of penalty on all legitimate newcomers incurs a significant social loss only under high turnover rates in conjunction with intermediate societal generosity levels

    Triage: Performance Isolation and Differentiation for Storage Systems

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    Ensuring performance isolation and differentiation among workloads that share a storage infrastructure is a basic requirement in consolidated data centers. Existing management tools rely on resource provisioning to meet performance goals; they require detailed knowledge of the system characteristics and the workloads. Provisioning is inherently slow to react to system and workload dynamics, and in the general case, it is impossible to provision for the worst case

    Encoding Volumetric Grids For Streaming Isosurface Extraction

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    Gridded volumetric data sets representing simulation or tomography output are commonly visualized by displaying a triangulated isosurface for a particular isovalue. When the grid is stored in a standard format, the entire volume must be loaded from disk, even though only a fraction of the grid cells may intersect the isosurface

    New Horizons: Telecommunications Policy in Israel in the 21st Century

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    The telecommunications industry in Israel has changed significantly in recent years. This paper examines key issues that will arise in Israel as a result of these major changes and argues that the major changes in the telecommunications industry require significant changes in the regulatory structure. The paper first provides important background material on the current structure in the various sectors of the telecommunications industry in Israel. The paper then discusses the current regulatory environment and makes recommendations regarding the future regulatory structure in Israel and the scope for regulation

    Building Polygonal Maps from Laser Range Data

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    This paper presents a new approach to the problem of building a global map from laser range data, utilizing shape based object recognition techniques originally developed for tasks in computer vision. In contrast to classical approaches, the perceived environment is represented by polygonal curves (polylines), possibly containing rich shape information yet consisting of a relatively small number of vertices. The main task, besides segmentation of the raw scan point data into polylines and denoising, is to find corresponding environmental features in consecutive scans to merge the polylinedata to a global map. The correspondence problem is solved using shape similarity between the polylines. The approach does not require any odometry data and is robust to discontinuities in robot position, e.g., when the robot slips. Since higher order objects in the form of polylines and their shape similarity are present in our approach, it provides a link between the necessary low-level and the desired high-level information in robot navigation. The presented integration of spatial arrangement information, illustrates the fact that high level spatial information can be easily integrated in our framework

    Stratum Approaches to Temporal DBMS Implementation

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    Previous approaches to implementing temporal DBMSs have assumed that a temporal DBMS must be built from scratch, employing an integrated architecture and using new temporal implementation techniques such as temporal indexes and join algorithms. However, this is a very large and time-consuming task. This paper explores approaches to implementing a temporal DBMS as a stratum on top of an existing non-temporal DBMS, rendering implementation more feasible by reusing much of the functionality of the underlying conventional DBMS. More specifically, the paper introduces three stratum meta-architectures, each with several specific architectures. Based on a new set of evaluation criteria, advantages and disadvantages of the specific architectures are identified. The paper also classifies all existing temporal DBMS implementations according to the specific architectures they employ. It is concluded that a stratum architecture is the best short, medium, and perhaps even longterm, approach to implementing a temporal DBMS

    Time Patterns in Visual Reception and Written Phrase Production

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    In previous studies we could show that linguistic word structures correlate closely with the time course of written word production. In the present study we investigate whether there are also correlations between the syntactic structures of phrases and the time course of their production

    Almost ASAP Semantics: From Timed Models to Timed Implementations

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    In this paper, we introduce a parametric semantics for timed controllers called the Almost ASAP semantics. This semantics is a relaxation of the usual ASAP semantics (also called the maximal progress semantics) which is a mathematical idealization that can not be implemented by any physical device no matter how fast it is. On the contrary, any correct Almost ASAP controller can be implemented by a program on a hardware if this hardware is fast enough. We study the properties of this semantics, show how it can be analyzed using the tool HyTech, and illustrate its practical use on examples


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