Tsekouras G.E.,University of Aegean
Neurocomputing | Year: 2013
In this paper we investigate the implementation of particle swarm optimization in the design of radial basis function neural networks under the framework of input-output fuzzy clustering. The problem being studied concerns the optimal estimation of the basis function centers, provided that the learning process is guided by the information of the output space. The proposed method encompasses a cost function, which is defined by a reformulated version of the fuzzy c-means applied in the product (i.e. input-output) space. The minimization of this function is accomplished by using the particle swarm optimization, where each particle encodes a set of cluster centers associated to a single fuzzy partition. The algorithm is simple and easy to implement, yet very effective. The performance of the resulting network is tested and verified through a number of experimental cases in terms of a 10-fold cross validation analysis. © 2012 Elsevier B.V.
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.
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.
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.
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.