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

作者： Vasilis S. Gkamas Emmanouel A. Varvarigos Computer Engineering and Informatics Research Academic Computer Technology Institute University of Patras Rio-Patras Greece

We propose a MAC protocol for mobile ad hoc networks that uses power control for the RTS/CTS and DATA frame transmissions in order to improve energy and capacity utilization efficiency. Unlike IEEE 802.11, in our scheme the RTS frames are not sent using the maximum transmission power to silence neighbouring nodes, and the CTS frames do not silence all receiving nodes to the same degree. In contrast, the transmission power of the RTS frames follows a slow start principle, while the CTS frames, which are sent at maximum transmission power, prevent the neighbouring nodes from transmitting their DATA frames with power more than a computed threshold, while allowing them to transmit at power levels less than that threshold. This is done by including in the RTS and the CTS frames additional information, such as the power of the transmissions, and the interference tolerance of the nodes. Moreover the DATA frames are sent at the minimum required transmission power increased by a small margin to ensure connectivity with the intended receiver, so as to cause minimal interference to neighbouring nodes and allow for future interference to be added to the receiver of the DATA frames. The power to be used by the transmitter is computed by the recipient of the RTS frame and is included in the CTS frame. It is expected that a network with such a power management scheme would achieve a better throughput performance and more power savings than a network without such a scheme

关键词： Power control Media Access Protocol Mobile ad hoc networks Interference computer networks Power engineering computing Design engineering Power engineering and energy informatics Throughput

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Evaluating different one to many packet delivery schemes for UMTS

Evaluating different one to many packet delivery schemes for...

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IEEE International Symposium on World of Wireless Mobile and Multimedia Networks (WoWMoM)

作者： A. Alexiou D. Antonellis C. Bouras Computer Engineering and Informatics Department University of Patras Greece Research Academic Computer Technology Institute Greece

It is known that multicasting is an efficient method of supporting group communication as it allows the transmission of packets to multiple destinations using fewer network resources. Thus, service providers are increasingly interested in supporting multicast communications over wireless networks and in particular over UMTS. Multicasting is a more efficient method of supporting group communication than unicasting or broadcasting, as it allows transmission and routing of packets to multiple destinations using fewer network resources. In this paper the three above mentioned methods of supporting group communication are analyzed in terms of their performance

关键词： 3G mobile communication Performance analysis Multicast protocols Ground penetrating radar computer networks Wireless networks Routing Circuits Multimedia communication Costs

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A method for personalized clustering in data intensive web applications

A method for personalized clustering in data intensive web a...

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Joint International Workshop on Adaptivity, Personalization and the Semantic Web, APS'06

作者： Rigou, Maria Sirmakessis, Spiros Tzimas, Giannis Computer Engineering and Informatics Department University of Patras Rio GR-26504 Department of Applied Informatics in Administration and Economy TEI of Messolonghi Nea Ktiria Messolonghi GR-30200 Research Academic Computer Technology Institute Patras University N. Kazantzaki Str. Rio GR-26500

ISBN: (纸本)1595934537

The paper introduces an algorithm for personalized clustering based on a range tree structure, used for identifying all web documents satisfying a set of predefined personal user preferences. The returned documents go through a clustering phase before reaching the end user, thus allowing more effective manipulation and supporting the decision making process. The proposed algorithm demonstrates increased applicability in semantic web settings, since they offer the infrastructure for the explicit declaration of web document attributes and their respective values, thus allowing for more automated retrieval. The proposed algorithm improves the k-means range algorithm, as it uses the already constructed range tree (i.e. during the personalized filtering phase) as the basic structure on which the clustering step is based, applying instead of the k-means, the k-windows algorithm. The total number of parameters used for modeling the web documents dictates the number of dimensions of the Euclidean space representation. The time complexity of the algorithm is O(log d-2n+v), where d is the number of dimensions, n is the total number of web documents and v is the size of the answer. Copyright 2006 ACM.

关键词： Cluster analysis

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A tool for extracting model clones from a conceptual schema

A tool for extracting model clones from a conceptual schema

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IASTED International Conference on Software engineering, as part of the 24th IASTED International Multi-Conference on APPLIED informatics

作者： Faliagka, Evanthia Rigou, Maria Sirmakessis, Spiros Tzimas, Giannis Department of Computer Engineering and Informatics University of Patras Rio Campus 26504 Greece Research Academic Computer Technology Institute Patras University N. Kazantzaki str. Rio Campus 26500 Greece Department of Applied Informatics in Administration and Economy Technological Institution of Messolongi Nea Ktiria 30200 Greece

ISBN: (纸本)0889865744

In this paper the authors present an overview of techniques and tools that enable the effective evaluation and refactoring of a Web application's conceptual schema. Moreover, based on the introduction of the notion of model clones (in a previous work), as partial conceptual schemas that are repeated within a broader application model and the notion of model smells, as certain blocks in the Web applications model that imply the possibility of refactoring, this paper illustrates a methodology and a tool for detecting and evaluating the existence of potential model clones, in order to identify problems in an application's conceptual schema by means of efficiency, consistency, usability and overall quality. The methodology can be deployed either in the process of designing an application or in the process of reengineering it. Evaluation is performed according to a number of inspection steps. At first level the compositions used in the hypertext design are evaluated, followed by a second level evaluation concerning data manipulation and presentation to the user.

关键词： World Wide Web

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Modeling and Simulation of Submicron MOSFETs with Alternative Gate Dielectrics for DRAM Cells

Modeling and Simulation of Submicron MOSFETs with Alternativ...

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International Conference on Microelectronics, MIEL

作者： N. Konofaos G.Ph. Alexiou Computer Engineering & Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

In this study, we designed and simulated MOS devices having alternative gate dielectrics and examined their electrical behaviour as well as their effectiveness on the performance of a DRAM cell containing them. The devices under test had gate dielectrics of SrTiO 3 , (Ba 1-x Sr x )TiO 3 , TiO 2 , Ta 2 O 5 , Y 2 O 3 and (Pb 1 La x )TiO 3 . Equivalent oxide thicknesses were derived between 0.95 and 4 nm. Among the candidate materials, SrTiO 3 was the most promising when data retention is required, while Y 2 O 3 depicted the best I-V behavior. An increased cell capacitance resulted to higher memory refreshing times, improving substantially the device reliability

关键词： MOSFETs Random access memory High-K gate dielectrics Leakage current Circuit testing Dielectric materials High K dielectric materials MOS devices Dielectric devices Inorganic materials

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Pathfinding architectures for interdomain Bandwidth Broker operation

Pathfinding architectures for interdomain Bandwidth Broker o...

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IEEE International Conference on Networks

作者： Christos Bouras Dimitris Primpas Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

ISBN: (纸本)0780397460

This paper deals with bandwidth brokers and their inter-domain operation. The basic issues for inter-domain operation are discussed and we try to approach the most demanding issues as the selection of the best inter domain routing path (pathfinding). Generally, we discuss two models for inter domain routing through bandwidth broker, analyzing their advantages and comparing them. Also, we simulated the second one (generalized distributed pathfinding) trying to evaluate its performance. Finally, we discuss the simulation's results and present how this model should be incorporated in normal operation routing of commercial ISPs or academic networks that works on a federated way

关键词： Bandwidth Quality of service Routing Admission control Diffserv networks computer architecture informatics Spine Communication system control Network topology

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Resubmissions and Partly Defined Requests in an Adaptive Admission Control Algorithm for Bandwidth Brokers

Resubmissions and Partly Defined Requests in an Adaptive Adm...

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International Conference on Systems and International Conference on Mobile Communications and Learning Technologies, (ICN/ICONS/MCL) International Conference on Networking

作者： Ch. Bouras K. Stamos Computer Engineering and Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

The purpose of this paper is to examine the issues related to the efficiency and adaptability of the admission control module of a Bandwidth Broker. The proposed architecture is able to handle situations such as the resubmission of previously rejected requests and offer a fair treatment for requests in an environment where a subset of these requests do not specify their ending time. We describe the proposed mechanisms for such cases which aim at solving the additional problems of fairly prioritizing resubmitted requests and efficiently handle requests which do not specify ending times. We also provide experimental evaluations of the proposed algorithms and the conclusions they lead us to.

关键词： Programmable control Adaptive control Admission control Bandwidth computer architecture Diffserv networks Routing Quality of service Resource management informatics

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Relaxing Delayed Reservations: An approach for Quality of Service differentiation in Optical Burst Switching networks

Relaxing Delayed Reservations: An approach for Quality of Se...

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International Conference on Broadband Networks (BroadNets)

作者： Kostas Christodoulopoulos Kyriakos Vlachos Kostas Yiannopoulos Emmanuel A. Varvarigos Computer Engineering and Informatics Department (CEID) and Research Academic Computer Technology Institute (RACTI) University of Patras Rio Greece

In this paper we present a signaling protocol for QoS differentiation suitable for optical burst switching networks. The proposed protocol is a two-way reservation scheme that employs delayed and in-advance reservation of resources. In this scheme delayed reservations may be relaxed, introducing a reservation duration parameter that is negotiated during call setup phase. This feature allows bursts to reserve resources beyond their actual size to increase their successful forwarding probability and is used to provide QoS differentiation. The proposed signaling protocol offers a low blocking probability for bursts that can tolerate the round-trip delay required for the reservations. We present the main features of the protocol and describe in detail timing considerations regarding the call setup and the reservation process. We also describe several methods for choosing the protocol parameters so as to optimize performance and present corresponding evaluation results. Furthermore, we compare the performance of the proposed protocol against that of two other typical reservation protocols, a Tell-and-Wait and a Tell-and-Go protocol.

关键词： Quality of service Optical burst switching Protocols Delay Optical buffering Optical fiber networks High speed optical techniques Optical wavelength conversion Switching circuits computer networks

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Discovering regularities in biosequences: Challenges and applications

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Journal of Computational Methods in Sciences and engineering 2006年第3期5卷 189-199页

作者： Makris, C.H. Perdikuri, K. Tsakalidis, A. Computer Engineering and Informatics Department University of Patras 26500 Patras Greece Research Academic Computer Technology Institute 61 Riga Feraiou Street 26221 Patras Greece

Computational methods on molecular sequence data are at the heart of computational molecular biology. Identification of known or unknown DNA and RNA motifs or regions involved in various biological processes such as initiation of transcription, gene expression and translation, or the discovery of various types of repeats are some of the applications of major concern. An accurate identification and localization of such elements will allow biologists to perform deeper studies of the structure, function and evolution of genomes. This requires the development of faster and more complex mathematical models and computer algorithms. In this work we discuss current techniques to cope with string problems in molecular sequence data. We focus on Weighted Sequences and Sequences with “don't care characters”, explaining the open problems and their relevance to biological applications.

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JPEG2000 steganography possibly secure against histogram-based attack

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PCM 2006: 7th Pacific Rim Conference on Multimedia

作者： Noda, Hideki Tsukamizu, Yohsuke Niimi, Michiharu Kyushu Institute of Technology Dept. of Systems Innovation and Informatics 680-4 Kawazu Iizuka 820-8502 Japan Kyushu Institute of Technology Dept. of Electrical Electronic and Computer Engineering 1-1 Sensui-cho Tobata-ku Kitakyushu 804-8550 Japan

ISBN: (纸本)3540487662

This paper presents two steganographic methods for JPEG2000 still images which preserve histograms of discrete wavelet transform (DWT) coefficients. The first one is a histogram quasi-preserving method using quantization index modulation (QIM) with a dead zone in DWT domain. The second one is a histogram preserving method based on histogram matching using two quantizers with a dead zone. Comparing with a conventional JPEG2000 steganography, the two methods show better histogram preservation. The proposed methods are promising candidates for secure JPEG2000 steganography against histogram-based attack. © Springer-Verlag Berlin Heidelberg 2006.

关键词： Image compression

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