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Nikolaidis A.,Technological Educational Institute of West Macedonia
Multimedia Tools and Applications | Year: 2016

The current paper describes a new technique for embedding secret data in JPEG compressed color digital images. Emphasis is given in improving effective payload percentage over file size increase while retaining low distortion levels. The proposed technique is based on modification of non-zero quantized coefficients. In contrast to previously proposed techniques, the present one does not require the use of non-standard Huffman tables. Apart from that, no side information needs to be included in a JPEG header to assist the decoder in extracting the hidden message. The main idea behind the technique is to create zero population bins in the coefficient histogram in order to accommodate the secret message bits. Specifically, all coefficients whose absolute value is L are modified by 1 in the direction of their sign when a bit 1 is to be embedded or are not modified when a bit 0 is to be embedded. Coefficients with absolute values greater than L are also incremented by one in the direction of their sign, so that they are not confused with coefficients where embedding has occurred. At the side of the decoder, both the message bits can be extracted from coefficients with absolute values L and L+1, and the original image can be restored by shifting all coefficients with absolute value greater than L in the opposite direction of their sign. The results show significant improvement in comparison with representative state-of-the-art techniques, in terms of ratio of payload over file size increase. © 2014, Springer Science+Business Media New York.

Asvesta A.,Technological Educational Institute of West Macedonia | Dimitriadis S.,Aristotle University of Thessaloniki
Journal of Volcanology and Geothermal Research | Year: 2010

In northern Greece, along the western edge of the Paleozoic Vertiscos terrane (Serbomacedonian massif) and within the Peonias subzone - the eastern part of the Vardar (Axios) Zone - a Silicic Volcano-Sedimentary (SVS) succession of Permo(?)-Skythian to Mid Triassic age records the development of a faulted continental margin and the formation of rhyolitic volcanoes along a continental shelf fringed by neritic carbonate accumulations. It represents the early rifting extensional stages that eventually led to the opening of the main oceanic basin in the western part of the Vardar (Axios) Zone (the Almopias Oceanic Basin). Even though the SVS succession is deformed, altered, extensively silicified and metamorphosed in the low greenschist facies, primary textures, original contacts and facies relationships are recognized in some places allowing clues for the facies architecture and the depositional environment.Volcanic and sedimentary facies analysis has been carried out at Nea Santa and Kolchida rhyolitic volcanic centres. Pyroclastic facies, mostly composed of gas-supported lapilli tuffs and locally intercalated accretionary lapilli tuffs, built the early cones which were then overridden by rhyolitic aphyric and minor K-feldspar-phyric lava flows. The characteristics of facies, especially the presence of accretionary lapilli, imply subaerial to coastal emplacement at this early stage. The mature and final stages of volcanism are mostly represented by quartz-feldspar porphyry intrusions that probably occupied the vents. At Nea Santa area, the presence of resedimented hyaloclastite facies indicates subaqueous emplacement of rhyolitic lavas and/or lobes. Moreover, quartz-feldspar-phyric sills and a partly extrusive dome featuring peperites at their margins are inferred to have intruded unconsolidated, wet carbonate sediments of the overlying Triassic Neritic Carbonate Formation, in a shallow submarine environment. The dome had probably reached above wave-base as is indicated by the presence of reworked rhyolitic clasts in the younger mixed rhyolite-carbonate epiclastic sedimentary facies. This facies is interpreted as mass- and debris-flow of mixed provenance, deposited below wave-base.The facies architecture of the SVS succession records a change in volcanic activity from explosive to effusive and then to intrusive. The depositional environment changed from subaerial-coastal to shallow submarine as the silicic volcanism evolved and carbonate sedimentation was progressively taking over, probably compensating for the gradual subsidence of the corresponding basin. Silicic magmatism and carbonate sedimentation were contemporaneous and spatially related.The timing of the rifting, the continental crustal elements involved and the accompanying tectonic, magmatic and sedimentary processes are features of the spatially and temporally evolving western peri-Tethyan region. © 2010 Elsevier B.V.

Malamataris N.A.,George Mason University | Malamataris N.A.,Technological Educational Institute of West Macedonia
International Journal for Numerical Methods in Fluids | Year: 2013

The wall effects are investigated in the three-dimensional laminar flow over a backward-facing step. For this purpose, a numerical experiment is designed under actual laboratory conditions. The aspect ratio of the computational domain is 1:40 and the expansion ratio is 1:2. The Reynolds number ranges from 100 to 950. The governing equations are the steady state, isothermal and incompressible Navier-Stokes equations for Newtonian fluids. They are solved with a homemade Galerkin finite element code. The computations are validated with data from available laboratory and numerical experiments. The results focus on the variation of both velocity profiles and lengths of eddies along the lower and upper wall in the spanwise direction. Calculated streamlines in the streamwise and transverse direction show how the flow is distorted near the lateral wall and how it develops up to the plane of symmetry. The study of skin friction lines along the top and bottom wall of the domain reveals a flow that takes place in the spanwise direction. This spanwise component of the flow becomes more dominant with increasing Reynolds number and is impossible to be sustained at steady state for Reynolds numbers higher than 950 for this particular geometry. © 2012 John Wiley & Sons, Ltd.

Kalogiratou Z.,Technological Educational Institution of Western Macedonia at Kastoria | Monovasilis T.,Technological Educational Institute of West Macedonia | Psihoyios G.,University of Peloponnese | Simos T.E.,University of Peloponnese | Simos T.E.,King Saud University
Physics Reports | Year: 2014

In this work we review single step methods of the Runge-Kutta type with special properties. Among them are methods specially tuned to integrate problems that exhibit a pronounced oscillatory character and such problems arise often in celestial mechanics and quantum mechanics. Symplectic methods, exponentially and trigonometrically fitted methods, minimum phase-lag and phase-fitted methods are presented. These are Runge-Kutta, Runge-Kutta-Nyström and Partitioned Runge-Kutta methods. The theory of constructing such methods is given as well as several specific methods. In order to present the performance of the methods we have tested 58 methods from all categories. We consider the two dimensional harmonic oscillator, the two body problem, the pendulum problem and the orbital problem studied by Stiefel and Bettis. Also we have tested the methods on the computation of the eigenvalues of the one dimensional time independent Schrödinger equation with the harmonic oscillator, the doubly anharmonic oscillator and the exponential potentials. © 2013 Elsevier B.V..

Lappas G.,Technological Educational Institute of West Macedonia
Proceedings - 2011 International Conference on Advances in Social Networks Analysis and Mining, ASONAM 2011 | Year: 2011

Web mining is a well established field with many applications. Over the last years we experience a vast and rapidly growing amount of multimedia content that becomes available online. Web 2.0 and online social networks have dramatically influenced the growing amount of multimedia content due to the fact that users become more active producers and distributors of such multimedia context. Web mining techniques and theory need to be expanded in order to include new emerging research trends from mining such heterogeneous new web data. This work conceptualizes and introduces the concept of social multimedia mining as a new emerging research area that combines web mining research, multimedia research and social media research. © 2011 IEEE.

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