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3rd International Conference on Networking and Services, ICNS 2007

作者： Christodoulopoulos, K. Gkamas, V. Varvarigos, E.A. Computer Engineering and Informatics Dept. Research Academic Computer Technology Institute University of Patras Patras Greece

The existence of good probabilistic models for the job arrival process and the delay components introduced at the different stages of job processing in a Grid environment is important for the improved understanding of the computing concept envisioned by the Grid. In this study, we present a thorough analysis of the job arrival process in the EGEE infrastructure and the time durations a job spends at different states in the EGEE environment. We define four delay components of the total job delay and model each component separately. We observe that the job inter-arrival times at the Grid level can be adequately modeled by a rounded exponential distribution, while the total job delay (from the time it is generated until the time it completes execution) is dominated by the Computing Element's queuing and Worker Node's execution times. © 2007 IEEE.

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Challenges in cross layer adaptation for multimedia transmission

Challenges in cross layer adaptation for multimedia transmis...

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2007 IADIS International Conference on Telecommunications, Networks and Systems, TNS 2007, part of the 1st IADIS Multi Conference on computer Science and Information Systems, MCCSIS 2007

作者： Bouras, Christos Gkamas, Apostolos Kioumourtzis, Georgios Research Academic Computer Technology Institute Computer Engineering and Informatics Department University of Patras N. University of Patras Kazantzaki Str. Rion 26500 Greece Computer Engineering and Informatics Department University of Patras 26500 Greece

ISBN: (纸本)9789728924409

Over the last years a number of new protocols have been developed for multimedia applications in the whole OSI layer's scale. In order to support better wireless user the cross layer design paradigm has been proposed. This paper presents the challenges in design and implementation of cross layer adaptation schemes for multimedia transmission over wired and wireless networks. In addition, the paper proposes the basic aspects of a cross-layer adaptation framework for multimedia transmission over wired and wireless networks. The main concept is based on a "holistic approach" in which all layers participate to the adaptation process and make its own contributions. Finally, the proposed framework can support both wired and wireless receivers in one platform. © MCCSIS 2007 .All right reserved.

关键词： Wireless networks

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engineering and optimization of the miR-106b cluster for ectopic expression of multiplexed anti-HIV RNAs (vol 15, pg 1536, 2008)

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GENE THERAPY 2008年第23期15卷 1566-1566页

作者： Aagaard, L. Zhang, J. von Eije, K. J. Li, H. Saetrom, P. Amarzguioui, M. Rossi, J. J. Division of Molecular Biology Beckman Research Institute of City of Hope Duarte CA USA. City of Hope Graduate School of Biological Sciences City of Hope National Medical Center Duarte CA USA. Department of Medical Microbiology Academic Medical Center of University of Amsterdam Amsterdam The Netherlands. Department of Computer and Information Science Norwegian University of Science and Technology Trondheim Norway. Biotechnology Centre of Oslo University of Oslo Gaustadallé Oslo Norway.

The article presents a study on the optimization of the miR-106b cluster for ectopic expression of multiplexed anti-HIV RNAs. It states that stable expression systems can be delivered to mammalian cells by viral vectors in cell culture and in vivo that result in long-term silencing of the target gene. With the aim of generating a siRNA multiplexing expression system within a single transcript, the researchers used a naturally occurring polycistronic miRNA as a scaffold.

关键词： GENE expression AIDS (Disease) CULTURES (Biology) CYTOLOGY -- Technique RNA research

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Index-based most similar trajectory search

Index-based most similar trajectory search

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23rd International Conference on Data engineering, ICDE 2007

作者： Frentzos, Elias Gratsias, Kostas Theodoridis, Yannis Dept. of Informatics University of Piraeus Research Academic Computer Technology Institute Greece

ISBN: (纸本)1424408032

The problem of trajectory similarity in moving object databases is a relatively new topic in the spatial and spatiotemporal database literature. Existing work focuses on the spatial notion of similarity ignoring the temporal dimension of trajectories and disregarding the presence of a general-purpose spatiotemporal index. In this work, we address the issue of spatiotemporal trajectory similarity search by defining a similarity metric, proposing an efficient approximation method to reduce its calculation cost, and developing novel metrics and heuristics to support k-most-similar-trajectory search in spatiotemporal databases exploiting on existing R-treelike structures that are already found there to support more traditional queries. Our experimental study, based on real and synthetic datasets, verifies that the proposed similarity metric efficiently retrieves spatiotemporally similar trajectories in cases where related work fails, while at the same time the proposed algorithm is shown to be efficient and highly scalable. © 2007 IEEE.

关键词： Online searching

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An efficient mechanism for adaptive multimedia transmission in 3G networks

An efficient mechanism for adaptive multimedia transmission ...

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2007 IADIS International Conference on Wireless Applications and Computing, WAC 2007, part of the 1st IADIS Multi Conference on computer Science and Information Systems, MCCSIS 2007

作者： Alexiou, Antonios Barounis, Konstantinos Bouras, Christos Research Academic Computer Technology Institute and Computer Engineering and Informatics University of Patras N. Kazantzaki str. GR Patras26500 Greece

ISBN: (纸本)9789728924409

This paper proposes a mechanism for the congestion control for video transmission over UMTS. Our scheme is applied when the mobile user experiences real time multimedia content and adopts the theory of a widely accepted rate control method in wired networks, namely equation based rate control. In this approach, the transmission rate of the multimedia data is determined as a function of the packet loss rate, the round trip time and the packet size and the server explicitly adjusts its sending rate as a function of these parameters. Through a number of simulations and experiments we validate the correctness and measure the performance and efficiency of the mechanism. The mechanism at first level is evaluated through simulations that carried out in the ns-2 simulator. At second level, in order to validate the proposed mechanism in real world traffic scenarios we perform some experiments in a commercial UMTS network. © 2007 IADIS

关键词： Video streaming

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Multicast in UMTS: Adopting TCP-Friendliness

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12th IFIP International Conference on Personal Wireless Communications, PWC 2007

作者： Alexiou, Antonios Bouras, Christos Papazois, Andreas Research Academic Computer Technology Institute N. Kazantzaki str. 26500 Patras Greece Computer Engineering and Informatics Department University of Patras 26500 Patras Greece

ISBN: (纸本)9780387741581

In this paper, we present a novel mechanism for the multicast congestion control over UMTS networks. The proposed mechanism is based on the well known TCP-Friendly Multicast Congestion Control (TFMCC) scheme. The key challenge in the design of the new scheme lies in improving the TFMCC mechanism to cope with the packet losses caused by either the temporary or the permanent degradation of the wireless channels. The proposed scheme introduces minor modifications in the UMTS nodes with respect to the computing power of the mobile terminals. Finally, our approach is implemented in the ns-2 network simulator and is evaluated it under various conditions.

关键词： Multicasting

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Mining trajectory databases via a suite of distance operators

Mining trajectory databases via a suite of distance operator...

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IEEE 23rd International Conference on Data engineering Workshop

作者： Pelekis, Nikos Kopanakis, Ioannis Ntoutsi, Irene Marketos, Gerasimos Theodoridis, Yannis Dept. of Informatics Univ. of Piraeus Greece Technological Educational Institute of Crete Greece Research Academic Computer Technology Institute

ISBN: (纸本)9781424408313

With the rapid progress of mobile devices and positioning technologies, Trajectory Databases (TD) have been in the core of database research during the last decade. Analysis and knowledge discovery in TD is an emerging field which has recently gained great interest. Extracting knowledge from TD using certain types of mining techniques, such as clustering and classification, impose that there is a mean to quantify the distance between two trajectories. Having as a main objective the support of effective similarity query processing, existing approaches utilize generic distance metrics that ignore the peculiarities of the trajectories as complex spatiotemporal data types. In this paper, we define a novel set of trajectory distance operators based on primitive (space and time) as well as derived parameters of trajectories (speed and direction). Aiming at providing a powerful toolkit for analysts who require producing distance matrices with different semantics as input to mining tasks, we develop algorithms for each of the proposed operators. The efficiency of our approach is evaluated through an experimental study on classification and clustering tasks using synthetic and real trajectory datasets.

关键词： Trajectories

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Promo: Novel metrics that combine hits and accessibility criteria in order to promote important content and links 07

Promo: Novel metrics that combine hits and accessibility cri...

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2007 Euro American Conference on Telematics and Information Systems, EATIS 2007

作者： Garofalakis, John Giannakou, John Giannakoudi, Theodoula Sakkopoulos, Evangelos Research Academic Computer Technology Institute N. Kazantzaki str. 26500 Greece University of Patras Computer Engineering Informatics Dept 26500 Patras Greece

ISBN: (纸本)9781595935984

In this work, we introduce metrics and a proposed procedure to measure the popularity of a website. We present two novel metrics, Promo and Promo(2) that take advantage of the internal link structure of a website, in order to gain important navigation information. This is indicative of the difficulty the user encounters to access a particular link and can be combined with statistics gained from the log files as a metric of popularity. The two metrics propose a different definition of the popularity of a web object in order to generate a sorted list of promotion values for a website's links. We have delivered a web tool that implements the proposed procedure in order to facilitate a site designer to manipulate his/her web server log data, receive recommendations and popularity results and finally proceed with changes in the structure or position of links. Overall, the experimental study using user-based accesses log data, has been encouraging and it has verified the effectiveness of the Promo metrics.

关键词： Websites

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Enhancing Ns-2 with diffserv QoS features

Enhancing Ns-2 with diffserv QoS features

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10th Communications and Networking Simulation Symposium, CNS 2007, Part of the 2007 Spring Simulation Multiconference, SpringSim 2007

作者： Bouras, Ch. Primpas, D. Stamos, K. Research Academic Computer Technology Institute PO Box 1122 Patras Greece Computer Engineering and Informatics Dept. Univ. of Patras GR-26500 Patras Greece

ISBN: (纸本)1565553128

In this paper, we present work that we have carried out in extending the ns-2 simulator in order to study and validate Quality of Service issues and related architectures. In the case of the DiffServ framework, simulation is valuable since an analytical approach of mechanisms and services is infeasible due to the aggregation and multiplexing of flows. This paper covers work in extending ns-2 functionality towards the direction of realistic traffic generation and a series of mechanisms defined by the DiffServ architecture. We have also extended ns-2 with the functionality of Bandwidth Brokers, which are entities for managing the resources and negotiating end to end resource reservations between domains. The Bandwidth Broker ns-2 implementation is useful for studying the related architectures and admission control procedures.

关键词： Quality of service

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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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