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.
Burnetas A.,National and Kapodistrian University of Athens |
Economou A.,National and Kapodistrian University of Athens |
Vasiliadis G.,Technological Education Institute of Central Macedonia
Queueing Systems | Year: 2017
We consider the single-server Markovian queue with infinite waiting space and assume that there exists a certain reward-cost structure that reflects the customers’ desire for service and their dislike for waiting. The system is unobservable for the customers at their arrival instants, but the administrator provides them with periodic announcements of their current positions at rate (Formula presented.), so that they may renege if it is preferable for them to do so. The customers are strategic, and their decision problem is whether to join or not the system upon arrival and whether to stay or renege later. Their strategies are specified by a join probability q and a reneging threshold n. We determine the equilibrium strategies (Formula presented.) and study the socially optimal strategies (Formula presented.). Extensive numerical experiments provide interesting qualitative insight about the model. In particular, the equilibrium throughput of the system is a unimodal function of (Formula presented.). Moreover, despite the fact that we have an avoid-the-crowd situation, it is possible that (Formula presented.), in contrast to the classical unobservable model. © 2017 Springer Science+Business Media New York
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.
Tsakstara V.,Technological Education Institute of Central Macedonia |
Tsakstara V.,University of Ioannina
Advances in High Energy Physics | Year: 2015
At first, we evaluate scattering cross sections of low, and intermediate-energy neutrinos scattered off the 114Cd isotope, the most abundant Cd isotope present also in the COBRA detector (CdTe and CdZnTe materials) which aims to search for double beta decay events and neutrino observations at Gran Sasso laboratory (LNGS). The coherent ν-nucleus channel addressed here is the dominant reaction channel of the neutral current ν-nucleus scattering. Our ν-nucleus cross sections (calculated with a refinement of the quasiparticle random-phase approximation, QRPA) refer to the g s → g s transitions for ν-energies εν ≤ 100 MeV. Subsequently, simulated ν-signals on 114Cd isotope are derived. Towards this purpose, the required folded cross section comes out of simulation techniques by employing several low, and intermediate-energy neutrino distributions of the astrophysical ν-sources, like the solar, supernova, and Earth neutrinos, as well as the laboratory neutrinos, the reactor neutrinos, the pion-muon stopped neutrinos, and the β-beam neutrinos. © 2015 Vaitsa Tsakstara.
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.
Tokatlidis I.S.,Democritus University of Thrace |
Papadopoulos I.I.,Technological Education Institute of Central Macedonia |
Baxevanos D.,41 Palaiologou |
Koutita O.,Dep. of Plant Breeding
Crop Science | Year: 2010
Breeders ought to consider the confounding effects of the environment and genotype × environment (G × E) interaction on response to early generation selection. To meet this requirement, honeycomb breeding was performed at a low density within two dry bean populations (Phaseolus vulgaris L.) under typical open-fi eld conditions and in an adjacent greenhouse. Nineteen progeny lines were formed through selection of nine and ten of the highest-yielding plants in the greenhouse and the fi eld, respectively. Honeycomb progeny testing at the low density in the two distinct environments showed up to 75% improvement in plant-yield potential. Under farming-density conditions in fi ve environments, six of the lines outyielded the respective original population by 12 to 38% and exhibited the greatest stability according to the genotype and genotype × environment (GGE) biplot model. At low density, the greenhouse evaluation demonstrated less acquired variance than the field evaluation and was especially useful for selection and progeny evaluation. Three of the six outstanding lines originated from the greenhouse. Honeycomb progeny estimation on a single-plant yield basis in the greenhouse, rather than in the field, gave a better prediction of yield potential on an area basis. The results showed that honeycomb breeding performed in two environments to address the G × E interaction may be successful for developing varieties that exhibit both high and stable productivity. © Crop Science Society of America.