University of Aegean

Mytilini, Greece

University of Aegean

Mytilini, Greece
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Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2009.1.1 | Award Amount: 5.57M | Year: 2010

The complete transition from analogue to the digital TV is planned in Europe for 2012. This will release significant amount of valuable spectrum in VHF/UHF bands. In fact, the Digital TV Switchover provides a once in a lifetime opportunity for the development of innovative services and the introduction sophisticated new technologies into the VHF/UHF bands.\n\nHowever, despite the grand words about opening up a new band to support low cost, low power, ubiquitous access and innovative new providers, there are many obstacles to TV white spaces systems. The creation of workable devices that clearly demonstrate and prove that no harmful interference is caused to broadcasters or other licensed systems is one of those challenges as is the completion of standards.\n\nThe CogEU proposal aims to take advantage of the transition to digital TV by developing cognitive radio systems that leverage the favourable propagation characteristics of the TVWS through the introduction and promotion of real-time secondary spectrum trading and the creation of new spectrum commons in the upper band of the cleared spectrum. CogEU will also define new methodologies for TVWS equipment certification and compliance addressing coexistence with the DVB-T/H European standard.\n\nThree main application scenarios with good market potential will be investigated:\n\tCellular, WiFi and WiMax network extension over TV white spaces\n\tMobile TV over TV white spaces\n\tPublic safety applications over TVWS\n\nAs a consequence the project should help the European decision makers and standards to move the TV spectrum management paradigm towards a more liberal and efficient method, by providing sufficient evidence on the technology and economic viability of its deployment. In fact the project timeframe perfectly matches the TV Digital switchover roadmap planned for most of the European countries.

Gizelis C.A.,University of Aegean | Vergados D.D.,University of Piraeus
IEEE Communications Surveys and Tutorials | Year: 2011

The expansion of new technologies is expected to offer economic growth in the wired and wireless technological networking environment, while at the same time, it will offer a wide variety of services and give the possibility for utilizing technologies for the benefit of many subscribers. The Pricing Schemes are designed to offer profitable business to the Wireless Service Providers (WSPs), as well as, to create favorable services for the mobile subscribers and eventually to get charged according to their services usage. In this paper, the Pricing Schemes are classified, based on their ability to adapt to the needs of the WSPs and their subscribers during the entire service period, into Static-based Pricing and Dynamic-based Pricing Schemes. The Pricing Schemes are also analyzed in detail and are further classified according to the factors involved in the price calculation of a service, i.e. the Service Level Agreement (SLA), the subscription type, the negotiation capabilities between WSPs and their subscribers, the network capacity, the available bandwidth and frequency spectrum, the network hops, and the Base Stations (BSs). The affected elements by the pricing network are also discussed, together with the performance evaluation of the presented pricing schemes. © 2005 IEEE.

Agency: European Commission | Branch: FP7 | Program: CPCSA | Phase: INFRA-2011-1.2.2. | Award Amount: 2.57M | Year: 2011

Information and Communication Technologies have an unprecedented potential to improve the responsiveness of governments to the needs of citizens and have long been recognized as a key strategic tool to enable reforms in the public sector. During the last years, this potential of ICT has started to be dealt with in a multi-disciplinary way, giving birth to new research communities dealing with governance and policy modelling, modelling and simulation of complex systems, public administration information systems, open governance and social media. However, this potential is to this day non-systematically exploited, as there are significant barriers that hinder the effective exploration, management and distribution of the vast amounts of available public sector data towards the research communities.The main goal of ENGAGE project is the deployment and use of an advanced service infrastructure, incorporating distributed and diverse public sector information resources as well as data curation, semantic annotation and visualisation tools, capable of supporting scientific collaboration and governance-related research from multi-disciplinary scientific communities, while also empowering the deployment of open governmental data towards citizens. The ENGAGE consortium comprises of 9 partners from Belgium, Germany, Greece, Israel, the Netherlands and the United Kingdom, with an excellent track record both in the eInfrastructures and the Governance domain (NTUA, FOKUS, STFC, Uni. Aegean, TU DELFT) including world-leaders in cloud infrastructures (IBM, Microsoft and INTRASOFT International) and a large network of scientific data diffusion (EUROCris).Following on Open Data initiatives throughout Europe, ENGAGE has established links with numerous National and International public sector organisations, research communities, open data experts and standardisation fora. The proposal is supported by the Greek NREN and NGI node GRNET, providing the infrastructure for service provision.

Agency: European Commission | Branch: FP7 | Program: CPCSA | Phase: INFRA-2010-1.2.1 | Award Amount: 8.31M | Year: 2010

Several research communities in Europe exploit e-Infrastructures, sharing data and computing resources with Grid and Supercomputing technology. However the inherent complexity of these technologies has limited their wider adoption and their long term sustainability: designing, developing and operating a computing infrastructure for an e-Science community remains challenging and costly.\nVENUS-C will develop and deploy an industrial-quality service-oriented platform based on virtualisation technologies to serve research and industrial user communities, leveraging previous experiences and competences of grids & supercomputing, while investigating new sustainable business models.\nFor Europe to remain at an international competitive edge, it needs to continue investing aggressively in new computing technologies such as those proposed by VENUS-C. These could develop into an essential infrastructure of the information economy.\nVENUS-C will foster the development of Cloud Computing service offerings taking advantage of existing international opportunities and European industrial potential. Ten years ago, Europe successfully applied a similar approach with Grid computing, importing key technology from the US to quickly become a world-wide leader.\nBy exploiting commercial solutions, but avoiding vendor lock-in with effective interoperability, VENUS-C will provide an easy way to deploy end-user services, dynamically extending e-infrastructures capabilities, addressing all aspects of a sustainable infrastructure.\nVENUS-C is a Europe-driven industry-led consortium with skilled partners and a strong, international advisory committee formed by worldwide experts in distributed computing and scientific applications. The user communities involved are: Bioinformatics, System Biology, Drug discovery, Civil Protection, Civil Engineering, and Digital Libraries. Twenty short-term experiments will be supported in the second year of VENUS-C through a competitive selection process.

While the widespread acceptance of social virtual words is being increased in the last years, little are known about how students' personal factors can affect their engagement in online learning courses. The current study proposed and empirically examined a conceptual model that aimed to fill this gap. The main purpose is to present an extensive empirical data of 305 novice or expert students (153 graduates and 152 postgraduates) who enrolled in online courses at university level which were held in Second Life. On this occasion it was tried to be investigated, measured and finally verified the effects of computer self-efficacy, metacognitive self-regulation and self-esteem that can predict the students' engagement as an overall multidimensional construct of factors (cognitive, emotional and behavioral). The results from the three-step hierarchical regression analysis revealed that computer self-efficacy, metacognitive self-regulation, and self-esteem in online courses were not only positively correlated with student's cognitive and emotional engagement factors, but were also negatively correlated with behavioral factors. Educational implications from these results can provide a more expedient and meritorious instructional quality format aimed at reinforcing users' engagement in Second Life for sequencing and pacing future-driven online courses. © 2014 Elsevier Ltd. All rights reserved.

Rizomiliotis P.,University of Aegean
IEEE Transactions on Information Theory | Year: 2010

In the past few years, algebraic attacks against stream ciphers with linear feedback function have been significantly improved. As a response to the new attacks, the notion of algebraic immunity of a Boolean function f was introduced, defined as the minimum degree of the annihilators of f and f + 1. An annihilator of f is a nonzero Boolean function g, such that f · g=0. While several constructions of Boolean functions with optimal algebraic immunity have been proposed, there is no significant progress concerning the resistance against the so-called fast algebraic attacks. In this paper, we provide a framework to assess the resistance of Boolean functions against the new algebraic attacks, including fast algebraic attacks. The analysis is based on the univariate polynomial representation of Boolean functions and necessary and sufficient conditions are presented for a Boolean function to have optimal behavior against all the new algebraic attacks. Finally, we introduce a new infinite family of balanced Boolean functions described by their univariate polynomial representation. By applying the new framework, we prove that all the members of the family have optimal algebraic immunity and we efficiently evaluate their behavior against fast algebraic attacks. © 2006 IEEE.

Glykas M.,University of Aegean
Expert Systems with Applications | Year: 2013

This paper elaborates on the application of Fuzzy Cognitive Maps (FCMs) in strategy maps (SMs). The limitations of the Balanced Scorecards (BSCs) and SMs are first discussed and analyzed. The need for simulated scenario based SMs is discussed and the use of FCMs as one of the best alternatives is presented. A software tool for the development, simulation and analysis of FCM based SMs is also presented. The effectiveness of the resulting software tool and FCM theory in SMs is experimented in two case studies in Banking. © 2012 Elsevier Ltd. All rights reserved.

Zissis D.,University of Aegean | Lekkas D.,University of Aegean
Future Generation Computer Systems | Year: 2012

The recent emergence of cloud computing has drastically altered everyone's perception of infrastructure architectures, software delivery and development models. Projecting as an evolutionary step, following the transition from mainframe computers to client/server deployment models, cloud computing encompasses elements from grid computing, utility computing and autonomic computing, into an innovative deployment architecture. This rapid transition towards the clouds, has fuelled concerns on a critical issue for the success of information systems, communication and information security. From a security perspective, a number of unchartered risks and challenges have been introduced from this relocation to the clouds, deteriorating much of the effectiveness of traditional protection mechanisms. As a result the aim of this paper is twofold; firstly to evaluate cloud security by identifying unique security requirements and secondly to attempt to present a viable solution that eliminates these potential threats. This paper proposes introducing a Trusted Third Party, tasked with assuring specific security characteristics within a cloud environment. The proposed solution calls upon cryptography, specifically Public Key Infrastructure operating in concert with SSO and LDAP, to ensure the authentication, integrity and confidentiality of involved data and communications. The solution, presents a horizontal level of service, available to all implicated entities, that realizes a security mesh, within which essential trust is maintained. © 2011 Elsevier B.V. All rights reserved.

Kofinas G.,University of Aegean
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study a gravity theory where a scalar field with potential, beyond its minimal coupling, is also coupled through a nonminimal derivative coupling with the torsion scalar which is the teleparallel equivalent of Einstein gravity. This theory provides second order equations of motion and we find large-distance, nonperturbative, static, spherically symmetric four-dimensional solutions. Among them a general class of black hole solutions is found for some range of the parameters/integration constants with asymptotics of the form of hyperscaling violating Lifshitz spacetime with spherical horizon topology. Although the scalar field diverges at the horizon, its energy density and pressures are finite there. From the astrophysical point of view, this solution provides extra deflection of light compared to the Newtonian deflection. © 2015 American Physical Society.

Stamatatos E.,University of Aegean
Journal of the American Society for Information Science and Technology | Year: 2011

In this paper a novel method for detecting plagiarized passages in document collections is presented. In contrast to previous work in this field that uses content terms to represent documents, the proposed method is based on a small list of stopwords (i.e., very frequent words). We show that stopword n-grams reveal important information for plagiarism detection since they are able to capture syntactic similarities between suspicious and original documents and they can be used to detect the exact plagiarized passage boundaries. Experimental results on a publicly available corpus demonstrate that the performance of the proposed approach is competitive when compared with the best reported results. More importantly, it achieves significantly better results when dealing with difficult plagiarism cases where the plagiarized passages are highly modified and most of the words or phrases have been replaced with synonyms. © 2011 ASIS&T.

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