Bereketidou O.A.,Technological Educational Institute of West Macedonia |
Bereketidou O.A.,University of Western Macedonia |
Goula M.A.,Technological Educational Institute of West Macedonia
Catalysis Today | Year: 2012
A series of 8 wt% nickel catalysts supported on alumina and alumina-modified with different amounts of ceria were prepared. The effect of the supporting ceria loading at the catalytic performance for the biogas reforming reaction was investigated. The physicochemical properties of the final catalysts were determined by using different techniques: N 2 adsorption-desorption isotherms, X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and transmission electron microscopy (TEM). Catalytic performance was evaluated for the biogas reforming reaction using a feed gas mixture of CH 4/CO 2 = 1.5, simulating a clean model of biogas. It was shown that nickel catalysts supported on ceria-alumina exhibit slightly higher conversion values, compared to the one supported on alumina above 800 °C, which can be mainly attributed to the redox properties of ceria. In particular, the 8 wt% nickel catalyst supported on 20 wt% ceria-alumina was proven to have the best catalytic performance with a highest H 2/CO ratio of about 1.3. The biogas reforming reaction catalyzed by nickel-alumina doped with ceria catalysts seems to be an appropriate process in order to produce syngas suitable for methanol or Fischer-Tropsch synthesis reactions, which require H 2/CO ratio values between one and two (1 to 2). © 2012 Elsevier B.V.
Theodoulidis T.,University of Western Macedonia |
Poulakis N.,Technological Educational Institute of West Macedonia |
Dragogias A.,Technological Educational Institute of West Macedonia
NDT and E International | Year: 2010
An existing boundary element method model for eddy current inspection of ideal or narrow cracks is revised. Using some lately devised concepts on efficiently and rapidly simulating canonical eddy current geometries, we show how this model can be made easier to implement and faster to calculate. The approach is largely based on a novel method for rapidly calculating the Green's function and reducing the matrix fill-time, and also on a similar method for rapidly computing the incident electric field. As a result, the model has been made an order of magnitude faster than the existing one without sacrificing accuracy. We pay attention to numerical analysis details and analyze issues that so far have not been clarified. The validity of our approach is also verified by the experiment. Although we have tested the model against published data, we have also produced our own precision measurements for surface and through-the-thickness slots in plates with the coils performing scans along and across the slots at various frequencies. © 2009 Elsevier Ltd. All rights reserved.
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.
Christaki E.,Aristotle University of Thessaloniki |
Bonos E.,Technological Educational Institute of West Macedonia |
Giannenasa I.,Aristotle University of Thessaloniki |
Florou-Paneria P.,Aristotle University of Thessaloniki
Journal of the Science of Food and Agriculture | Year: 2013
Carotenoids are isoprenoid molecules which are synthesised de novo by photosynthetic plants, fungi and algae and are responsible for the orange, yellow and some red colours of various fruits and vegetables. Carotenoids are lipophilic compounds, some of which act as provitamins A. These compounds can be divided into xanthophylls and carotenes. Many macroalgae and microalgae are rich in carotenoids,where these compounds aid in the absorption of sunlight. Industrially, these carotenoids are used as food pigments (in dairy products, beverages, etc.), as feed additives, in cosmetics and in pharmaceuticals, especially nowadays when there is an increasing demand by consumers for natural products. Production of carotenoids from algae has many advantages compared to other sources; for example, their production is cheap, easy and environmentally friendly; their extraction is easier, with higher yields, and there is no lack of raw materials or limited seasonal variation. Recently, there has been considerable interest in dietary carotenoids with respect to their antioxidant properties and their ability to reduce the incidence of some chronic diseases where free radicals are involved. Possibly, carotenoids protect cells from oxidative stress by quenching singlet oxygen damage with various mechanisms. Therefore, carotenoids derived from algae could be a leading natural resource in the research for potential functional ingredients. © 2012 Society of Chemical Industry.
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.
Amina M.,University of Westminster |
Kodogiannis V.S.,University of Westminster |
Petrounias I.,University of Manchester |
Tomtsis D.,Technological Educational Institute of West Macedonia
International Journal of Electrical Power and Energy Systems | Year: 2012
Power load forecasting is an essential tool for energy management systems. Accurate load forecasting supports power companies to make unit commitment decisions and schedule maintenance plans appropriately. In addition to minimizing the power generation costs, it is also important for the reliability of energy systems. This research study presents the implementation of a novel fuzzy wavelet neural network model on an hourly basis, and validates its performance on the prediction of electricity consumption of the power system of the Greek Island of Crete. In the proposed framework, a multiplication wavelet neural network has replaced the classic linear model, which usually appears in the consequent part of a neurofuzzy scheme, while subtractive clustering with the aid of the Expectation-Maximization algorithm is being utilized in the definition of fuzzy rules. The results related to the minimum and maximum load using metered data obtained from the power system of the Greek Island of Crete indicate that the proposed forecasting model provides significantly better forecasts, compared to conventional neural networks models applied on the same dataset. © 2012 Elsevier Ltd. All rights reserved.
Caralis G.,National Technical University of Athens |
Rados K.,Technological Educational Institute of West Macedonia |
Zervos A.,National Technical University of Athens
Renewable and Sustainable Energy Reviews | Year: 2010
In autonomous islands, the wind penetration is restricted due to technical reasons related with the safe operation of the electrical systems. The combined use of wind energy with pumped storage (WPS) is considered as a mean to exploit the abundant wind potential, increase the wind installed capacity and substitute conventional peak supply. In this paper, the experience gained from the analysis of WPS in three specific islands is used towards the estimation of the WPS market in autonomous Greek islands. Parameterized diagrams and a methodology towards the pre-dimensioning and initial design of the WPS are proposed and used towards the estimation of the market in autonomous Greek islands. The objective is to make an initial general prefeasibility study of WPS prospects in the autonomous Greek islands. Results show that there is a significant market for WPS in Greece and the development cost of WPS is competitive to the fuel cost of local power stations in autonomous islands. © 2010 Elsevier Ltd.
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.
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.