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Current Trends in computer Science (ENC), Mexican International Conference on

作者： Athanasios Papagelis Christos Zaroliagis Department of Computer Engineering and Informatics Patras Greece Department of Computer Engineering and Informatics Research Academic Computer Technology Institute Patras Greece

Searchius is a collaborative search engine that produces search results based solely on user provided web-related data. We discuss the architecture of this system and how it compares to current state-of-the-art search engines. We show that the global users' preference over pages can be efficiently used as a metric of page quality, and that the inherent organization of the collected data can be used to discover related URLs. We also conduct an extensive experimental study, based on the web related data of 36483 users, to analyze the qualitative and quantitative characteristics of user collected URL collections, to investigate how well the users URL collections cover the web and discover the characteristics that affect the quality of the search results under the proposed setting.

关键词： Search engines Uniform resource locators informatics History Web pages Catalogs computer science International collaboration Data engineering computer architecture

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MBMS Power Planning in Macro and Micro Cell Environments

MBMS Power Planning in Macro and Micro Cell Environments

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IEEE Symposium on computers and Communications (ISCC)

作者： Antonios Alexiou Christos Bouras Vasileios Kokkinos Evangelos Rekkas Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Greece Research Academic Computer Technology Institute Greece and Computer Engineering and Informatics Department University of Patras Greece

Multimedia Broadcast Multicast Services (MBMS), introduced in Third Generation Partnership Project (3GPP) Release 6, is a point-to-multipoint downlink bearer service that addresses the need for the efficient usage of the expensive radio resources. Power control is one of the most important aspects in MBMS due to the fact that Node B's transmission power is a limited resource and must be shared among all MBMS users in a cell. Consequently, the analysis of transmitted power plays a fundamental role in the planning and optimization process of Universal Mobile Telecommunications System (UMTS) radio access networks. This paper investigates several factors affecting Node B's transmission power levels such as, cell deployment, propagation models, Quality of Service (QoS) requirements, users' distributions and mobility issues. Finally, different transport channels for the transmission of the multicast data over the UTRAN interfaces are considered.

关键词： Quality of service Digital multimedia broadcasting Multimedia communication Radio broadcasting Downlink Power control Power system planning Process planning 3G mobile communication Radio access networks

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Agent-based distributed group key establishment in wireless sensor networks

Agent-based distributed group key establishment in wireless ...

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2007 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks, WOWMOM

作者： Chatzigiannakis, Ioannis Konstantinou, Elisavet Liagkou, Vasiliki Spirakis, Paul Computer Technology Institute P.O. Box 1122 26110 Patras Greece Department of Computer Engineering and Informatics University of Patras 26500 Patras Greece Dep. of Information and Communication Systems Engineering University of the Aegean 83200 Samos Greece

ISBN: (纸本)1424409926

Wireless sensor networks are comprised of a vast number of ultra-small autonomous computing, communication and sensing devices, with restricted energy and computing capabilities, that co-operate to accomplish a large sensing task. Such networks can be very useful in practice, e.g. in the local monitoring of ambient conditions and reporting them to a control center. In this paper we propose a distributed group key establishment protocol that uses mobile agents (software) and is particularly suitable for energy constrained, dynamically evolving ad-hoc networks. Our approach totally avoids the construction and the maintenance of a distributed structure that reflects the topology of the network. Moreover, it trades-off complex message exchanges by performing some amount of additional local computations in order to be applicable at dense and dynamic sensor networks. The extra computations are simple for the devices to implement and are evenly distributed across the participants of the network leading to good energy balance. We evaluate the performance of our protocol in a simulated environment and compare our results with existing group key establishment protocols. The security of the protocol is based on the Diffie-Hellman problem and we used in our experiments its elliptic curve analog. Our findings basically indicate the feasibility of implementing our protocol in real sensor network devices and highlight the advantages and disadvantages of each approach given the available technology and the corresponding efficiency (energy, time) criteria. ©2007 IEEE.

关键词： Wireless sensor networks

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Implementing replica placements: Feasibility and cost minimization

Implementing replica placements: Feasibility and cost minimi...

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21st International Parallel and Distributed Processing Symposium, IPDPS 2007

作者： Loukopoulos, Thanasis Tziritas, Nikos Lampsas, Petros Lalis, Spyros Department of Computer and Communications Engineering University of Thessaly Glavani 37 38221 Volos Greece Department of Informatics and Computer Technology Technological Educational Institute of Lamia 3rd km Old Ntl. Rd. 35100 Lamia Greece

ISBN: (纸本)1424409101

Given two replication schemes Xold and Xnew, the Replica Transfer Scheduling Problem (RTSP) aims at reaching Xnew, starting from Xold, with minimal implementation cost. In this paper we generalize the problem description to include special cases, where deadlocks can occur while in the process of implementing Xnew. We address this impediment by introducing artificial (dummy) transfers. We then prove that RTSP-decision is NP-complete and propose two kinds of heuristics. The first attempts to replace dummy transfers with valid ones, while the second minimizes the implementation cost. Experimental evaluation of the algorithms illustrates the merits of our approach. ©2007 IEEE.

关键词： Scheduling

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Load Distribution Fairness in P2P Data Management Systems

Load Distribution Fairness in P2P Data Management Systems

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International Conference on Data engineering

作者： Theoni Pitoura Peter Triantafillou Research Academic Computer Technology Institute and Computer Engineering and Informatics Department University of Patras Greece

ISBN: (纸本)1424408024

We address the issue of measuring storage, or query load distribution fairness in peer-to-peer data management systems. Existing metrics may look promising from the point of view of specific peers, while in reality being far from optimal from a global perspective. Thus, first we define the requirements and study the appropriateness of various statistical metrics for measuring load distribution fairness towards these requirements. The metric proposed as most appropriate is the Gini coefficient (G). Second, we develop novel distributed sampling algorithms to compute G on-line, with high precision, efficiently, and scalably. Third, we show how G can readily be utilized on-line by higher-level algorithms which can now know when to best intervene to correct load imbalances. Our analysis and experiments testify for the efficiency and accuracy of these algorithms, permitting the online use of a rich and reliable metric, conveying a global perspective of the distribution.

关键词： Peer to peer computing Distributed computing Load management Sampling methods technology management engineering management Testing Data engineering informatics Algorithm design and analysis

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Substring Matching in P2P Publish/Subscribe Data Management Networks

Substring Matching in P2P Publish/Subscribe Data Management ...

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International Conference on Data engineering

作者： Ioannis Aekaterinidis Peter Triantafillou R&A Computer Technology Institute and Department Computer Engineering and Informatics University of Patras Greece

ISBN: (纸本)1424408024

The content-based publish/subscribe (pub/sub) paradigm for system design is becoming increasingly popular, offering unique benefits for a large number of data-intensive applications. Coupled with the peer-to-peer technology, it can serve as a central building block for such applications deployed over a large-scale network infrastructure. A key problem toward the creation of large-scale content-based pub/sub infrastructures relates to dealing efficiently with continuous queries (subscriptions) with rich predicates on string attributes; in this work we study the problem of efficiently and accurately matching substring queries to incoming events.

关键词： Routing Large-scale systems Subscriptions informatics Application software Data structures Intrusion detection computer network management technology management computer networks

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Multicost Routing in Wireless AD-HOC Networks with Variable Transmission Power

Multicost Routing in Wireless AD-HOC Networks with Variable ...

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IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)

作者： N. M. Karagiorgas P. C. Kokkinos C. A. Papageorgiou E. A. Varvarigos Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Department of Computer Engineering and Informatics University of Patras Patras Greece

In this work we study the combination of multicost routing and variable transmission power in wireless ad-hoc networks. In multicost routing, each link is assigned a cost vector consisting of several parameters. These parameters are treated separately and are combined at the end of the algorithm using various optimization functions, corresponding to different routing schemes, for selecting the optimal path. The cost parameters we use are the hop count, the interference caused, the node residual energies, and the node transmission powers. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multicost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.

关键词： Routing Ad hoc networks Interference Power control computer networks Power engineering computing Energy consumption Cost function Power engineering and energy informatics

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Scalable Data Collection Protocols for Wireless Sensor Networks with Multiple Mobile Sinks

Scalable Data Collection Protocols for Wireless Sensor Netwo...

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Annual Symposium on Simulation

作者： Athanasios Kinalis Sotiris Nikoletseas Department of Computer Engineering and Informatics University of Patras Patras Greece Computer Technology Institute Patras Greece

Data propagation in wireless sensor networks is usually performed as a multihop process. To deliver a single message, the resources of many sensor nodes are used and a lot of energy is spent. Recently, a novel approach is catching momentum because of important applications; that of having a mobile sink move inside the network area and collects the data with low energy cost. Here we extend this line of research by proposing and evaluating three new protocols. Our protocols are novel in a) investigating the impact of having many mobile sinks; b) in weak models with restricted mobility, proposing and evaluating a mix of static and mobile sinks; and c) proposing a distributed protocol that tends to equally spread the sinks in the network to further improve performance. Our protocols are simple, based on randomization and assume locally obtainable information. We perform an extensive evaluation via simulation; our findings demonstrate that our solutions scale very well with respect to the number of sinks and significantly reduce energy consumption and delivery delay

关键词： Wireless application protocol Wireless sensor networks Intelligent sensors Costs Monitoring Sensor phenomena and characterization Spread spectrum communication Energy consumption Contracts Batteries

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Parametric surface-source modeling and estimation with electroencephalography

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International Congress Series 2007年 1300卷 117-120页

作者： Cao, N. Yetik, I.S. Nehorai, A. Muravchik, C.H. Haueisen, J. Department of Electrical and Systems Engineering Washington University in St. Louis United States Department of Electrical and Computer Engineering Illinois Institute of Technology United States Departamento de Electrotecnia Universidad Nacional de La Plata Argentina Institute of Biomedical Engineering and Informatics TU-Ilmenau Germany

We develop four parametric EEG models to estimate current sources that are spatially distributed on a surface. Such sources exist for example in studies of epilepsy or induced spreading depression. We provide forward and inverse solutions and compute the Cramér-Rao bounds on the unknown source parameters. We validate our solutions using electric measurements from a body phantom. © 2007 Elsevier B.V. All rights reserved.

关键词： Cramér-Rao bounds EEG Extended source modeling

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Evolution of web applications with aspect-oriented design patterns

Evolution of web applications with aspect-oriented design pa...

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2nd International Workshop on Adaptation and Evolution in Web Systems engineering, AEWSE 2007

作者： Bebjak, Michal Vranić, Valentino Dolog, Peter Institute of Informatics and Software Engineering Faculty of Informatics and Information Technology Slovak University of Technology Ilkovičova 3 84216 Bratislava 4 Slovakia Department of Computer Science Aalborg University Fredrik Bajers Vej 7 DK-9220 Aalborg EAST Denmark

It is more convenient to talk about changes in a domainspecific way than to formulate them at the programming construct level or-even worse-purely lexical level. Using aspect-oriented programming, changes can be modularized and made reapplicable. In this paper, selected change types in web applications are analyzed. They are expressed in terms of general change types which, in turn, are implemented using aspect-oriented programming. Some of general change types match aspect-oriented design patterns or their combinations.

关键词： Aspect oriented programming

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