Technological Education Institute of Central Macedonia
Serres, Greece
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Kleidis K.,Technological Education Institute of Central Macedonia | Oikonomou V.K.,Technological Education Institute of Central Macedonia
Astrophysics and Space Science | Year: 2017

In this work we shall investigate how to realize a cosmological evolution which describes all the evolution eras of our Universe, by using scalar-tensor theories. Particularly, we shall use single scalar and two-scalar theories, and by employing several well known reconstruction schemes, we shall investigate which scalar-tensor theories can realize the unification cosmology. For both the single and two-scalar theories, we find the kinetic terms and the potential of the theory and we also address the issue of the stability of the solutions towards linear perturbations. As we show, in the two-scalar description no instabilities occur, but in the single scalar description, certain solutions are unstable. Also we demonstrate that in the single scalar case, the power spectrum corresponding to early times is nearly scale invariant and compatible with the latest observational data. Finally, we perform an analysis of the effective equation of state, and we show that the EoS describes in a unified way early and late-time acceleration, and in addition it also describes the radiation and matter domination era between the acceleration eras. © 2017, Springer Science+Business Media Dordrecht.

Kuiroukidis A.,Technological Education Institute of Central Macedonia | Throumoulopoulos G.N.,University of Ioannina
Physics of Plasmas | Year: 2016

Extending previous work [R. L. White and R. D. Hazeltine, Phys. Plasmas 16, 123101 (2009)] to the case of a generalized Grad-Shafranov equation (GGSE) with incompressible flow of arbitrary direction, we obtain new classes of exact solutions on the basis of Lie-point symmetries. This is done by using a previously found exact generalized Solovév solution to the GGSE. The new solutions containing five free parameters describe D-shaped toroidal configurations with plasma flow non-parallel to the magnetic field. In addition, the full symmetry group is obtained and new group-invariant solutions to the GGSE are presented. © 2016 EURATOM.

Kuiroukidis A.,Technological Education Institute of Central Macedonia | Throumoulopoulos G.N.,University of Ioannina
Physics of Plasmas | Year: 2016

An alternative method based on an inverse aspect ratio (Ïμ ) expansion which reduces the axisymmetric equilibrium problem to a set of ODEs containing terms of arbitrary order in Ïμ is employed to solve a generalized Grad-Shafranov equation with incompressible sheared flow nonparallel to the magnetic field. The method is applied to construct equilibria with either circular magnetic surfaces and reversed magnetic shear or D-shaped magnetic surfaces and normal magnetic shear. From the former equilibrium, it turns out that the electric field results in an increase of the reversed magnetic shear, thus indicating potential synergetic effects of the sheared flow and the magnetic shear in the formation of an internal transport barrier in consistent with experimental evidence. © 2016 EURATOM.

Karayannis V.G.,Technological Education Institute of Central Macedonia
IOP Conference Series: Materials Science and Engineering | Year: 2016

In the present study, the potential of microwave irradiation as an innovative energy- efficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration. © Published under licence by IOP Publishing Ltd.

Panapakidis I.P.,Aristotle University of Thessaloniki | Papadopoulos T.A.,Aristotle University of Thessaloniki | Christoforidis G.C.,Technological Education Institute of Central Macedonia | Papagiannis G.K.,Aristotle University of Thessaloniki
Energy and Buildings | Year: 2014

Buildings consume 40% of the total primary energy and 30% of the annual electricity, contributing significantly to greenhouse gas emissions. Naturally, therefore, building energy efficiency and notions like the nearly zero energy buildings are continuously gaining importance and popularity as means to reduce carbon emissions and the strong dependence on fossil fuels. A step towards this direction is the incorporation of smart grid technologies, mainly through the widespread of automatic meter reading and smart meters. This enables automatic collection of in depth information of the customer's behavior along with the building's performance and, thus, introduces new opportunities for energy saving and efficient management. However, the recorded amassing ream of data requires efficient processing and interpretation, so as to provide for meaningful information. In order to tackle this problem, this paper proposes a comprehensive methodology for the investigation of the electricity behavior of buildings, using clustering techniques. Utilizing a university campus as a case study, the proposed methodology is applied to the load curves of different buildings leading to the determination of an optimum clustering procedure. The methodology may be generalized for any type of building. © 2014 Elsevier B.V.

Tsanaktsidis C.G.,Technological Education Institute of Central Macedonia
Chemistry and Technology of Fuels and Oils | Year: 2011

The effect of TPA polymer (thermal polyaspartate anion) on the physical-chemical properties of diesel fuel - density, kinematic viscosity at 40 °C, moisture content, total acid number, thermal combustion, 90 vol.% distill-off temperature, and cetane number - is studied. It is shown that the moisture content and total acid number decrease considerably when TPA is introduced, while the heat of combustion and cetane number increase considerably, which improves fuel quality. © 2011 Springer Science+Business Media, Inc.

Sariannidis N.,Technological Education Institute of Central Macedonia | Zafeiriou E.,Democritus University of Thrace | Giannarakis G.,University of Aegean | Arabatzis G.,Democritus University of Thrace
Business Strategy and the Environment | Year: 2013

A firm's financial performance is closely related to its environmental behavior. This result is valid especially in the case of socially responsible firms. In the present study a data econometric analysis is conducted based on a GARCH model for socially responsible and conventional firms. According to our findings, the performance of socially responsible firms is negatively related to an increase of global CO2 emissions. The firms' costs for implementing environmental policies and the investors' attitude towards the aforementioned firms may account for our results. © 2012 John Wiley & Sons, Ltd and ERP Environment.

Kleidis K.,Technological Education Institute of Central Macedonia | Spyrou N.K.,Aristotle University of Thessaloniki
Astronomy and Astrophysics | Year: 2015

Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent. We find this model particularly interesting, because for ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of, which is eventually settled down to the range -0.089 < ≤ 0. This cosmological model does not suffer either from the age problem or from the coincidence problem. At the same time, this model reproduces to high accuracy the distance measurements performed with the aid of the supernovae (SNe) Type Ia standard candles, and most naturally interprets, not only when, but also why the Universe transits from deceleration to acceleration, thus arising as a mighty contestant for a DE model. © ESO, 2015.

Karayannis V.G.,Technological Education Institute of Central Macedonia
Journal of Building Engineering | Year: 2016

In the present research, the development of building bricks is examined, using steel industry electric arc furnace dust (EAFD) as admixture into standard clayey raw materials typically used by ceramic industries, and employing a pilot-plant simulation of industrial processes for red brick manufacturing,. The recycling of solid residues, which are derived in massive quantities from steel production plants, as alternative raw materials towards circular economy, is of increasing importance. In particular, steel dust recovered from EAF gas treatment, contains several oxides and, thus, can be considered as secondary material for substituting clays in traditional brick manufacturing. Possible economic benefits for the energy intensive industrial ceramic sector from energy savings upon firing along with a high potential for environmentally safe management of steel dust should be emphasized. For that purpose, various clay/EAFD mixtures were prepared and mixed with water to form a plastic mass for brick specimen shaping by extrusion. The green specimens were dried, and then fired at different peak temperatures (850, 950 and 1050 °C) in a controlled laboratory chamber furnace for sintering and consolidation. The effect of the by-product content (%) and of the firing temperature on brick shrinkage, bulk density, water absorption capability, mechanical strength and thermal conductivity was investigated. According to the results, the development of extruded and fired bricks with up to 15 wt% recycled steel industry byproduct is feasible without significant variations in their technological properties. © 2016 Elsevier Ltd

Tsanaktsidis C.G.,Technological Education Institute of Central Macedonia | Christidis S.G.,Technological Education Institute of Central Macedonia | Favvas E.P.,Greek National Center For Scientific Research
Fuel | Year: 2013

Thermal Polyaspartate Anion, a derivative biopolymer of aspartic acid, was used to remove water residues of both diesel and jet liquid hydrocarbons fuels. In this work a novel and simple method for improving the properties of fuel is reported. Different masses of TPA polymer have been mixed with a constant volume of fuel and the humidity concentration, the heat of combustion, the flash point as well the cetane index were measured according to the ASTM standard protocols. For the evaluation of the effect of the polymer additive in the physicochemical properties of the fuel, a number of ASTM standard measurements were followed. In addition, Fourier transform infrared spectroscopy (FTIR), temperature-modulated differential scanning calorimetry (TM-DSC) and thermogravimetric analysis (TGA) were used in order to evaluate the interactions between water and polymer. The removal of the humidity/water is requisite in fuel technology because of the numerous problems related to the presence of water, such as: corrosion of engine parts, pipelines and storage reservoirs, ice formation at very low temperatures and turbidity growth due to impurities. Water removal improved the physicochemical properties of both studied fuels, diesel and jet, up to 463 j/g and 1040 j/g for the heat of combustion, 28.2% and 71.4% for the total acid number and up to 39.4% and 25.7% for humidity, for diesel fuel and jet fuel respectively. Overall, the proposed method can be used in a simple fuel cleaning process using a metal mesh vessel of Thermal Polyaspartate Anion (TPA) polymer. The polymer can be replaced and re-generated as often needed. © 2010 Elsevier Ltd. All rights reserved.

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