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Kozáni, Greece

Mitsoulis E.,National Technical University of Athens | Malamataris N.A.,TEI of Western Macedonia | Malamataris N.A.,George Mason University
Journal of Non-Newtonian Fluid Mechanics | Year: 2012

The free (or open) boundary condition (FBC, OBC) was proposed by Papanastasiou et al. (A new outflow boundary condition, Int. J. Numer. Methods Fluids 14 (1992) 587-608) to handle truncated domains with synthetic boundaries where the outflow conditions are unknown. In the present work, implementation of the FBC has been extended to viscoelastic fluids governed by integral constitutive equations. As such we consider here the K-BKZ/PSM model, which also reduces to the upper-convected Maxwell fluid (UCM) for a single relaxation time and an appropriate choice of material parameters. The Finite Element Method (FEM) is used to provide numerical results in simple test cases, such as planar flow at an angle and Poiseuille flow in a tube where analytical solutions exist for checking purposes. Then previous numerical results obtained with the differential UCM model are checked in highly viscoelastic flows in a 4:1 contraction. Finally, the FBC is used with the K-BKZ/PSM model with data corresponding to a benchmark polymer melt (the IUPAC-LDPE melt). Particular emphasis is based on a non-zero second normal-stress difference, which has been reported in the literature to cause problems and seems responsible for earlier loss of convergence. The results with the FBC in short domains are in excellent agreement with those obtained from long domains used until now to accommodate the highly convective nature of the stresses in viscoelastic flows, for which the FBC seems most appropriate. © 2012 Elsevier B.V. Source


Dossis M.F.,TEI of Western Macedonia
Proceedings - IEEE Annual Symposium on VLSI, ISVLSI 2010 | Year: 2010

High-level synthesis has been envisaged as a suitable methodology to design and deliver on time, at least large parts of today's complex IC systems. This paper describes a unified and integrated HLS framework, to automatically produce custom and massively-parallel hardware, including its memory and system interfaces from high-level sequential program code. Using compiler-generators and logic programming techniques, provably-correct hardware compilation flow is achieved. The utilized hardware optimization inference engine is driven by a set of resource constraints, which limit to a certain boundary the number of available hardware operators to function in parallel during each control step. This optimization reduces drastically the number of different control steps (states) of the implemented application. The hardware compilation runs are completed in orders-of-magnltude less time than that which would be needed by even very experienced HDL designers to implement the same applications in RTL code. Implementation results from synthesis of a number of control-dominated, linear and repetitive, applications including a MPEG video compression engine with up to a few hundred states, are presented. In all cases the HLS framework delivers quickly provably-correct, implementable RTL code and the optimized schedule is reduced at up to 30% in comparison with the initial schedule. © 2010 IEEE. Source


Danis T.G.,DELCOF SA | Karagiozoglou D.T.,DELCOF SA | Tsakiris I.N.,TEI of Western Macedonia | Alegakis A.K.,University of Crete | Tsatsakis A.M.,University of Crete
Food Chemistry | Year: 2011

The incidence and levels of pesticide residues in peaches grown using Integrated Crop Management (ICM) methods in Pella and Imathia, districts of Macedonia, Northern Greece, are hereby presented. A total of 1150 peach samples were collected pre-harvest (June-September) and were analysed during the period of 2002-2007. Residual levels of selected insecticides, fungicides and acaricides were determined by Gas Chromatography-Mass Spectrometry following solid phase extraction. The monitoring program is extended up to 31 pesticides. Twenty-two of them were measured above detection limit, and 8 of them were found present every year. Insecticides represent the highest incidence amongst pesticide categories (654 positive samples, 56.9%) while chlorpyrifos is the most frequent within the category (491 positive samples). The incidence of pyrethrins was the highest in 2007 (26.8%) while bifenthrin was detected most frequently within this category (67 positive samples in 2007). Traceable levels of pesticides were lower than the Maximum Residues Limits (MRLs) in all peach samples. Variances in incidence and levels of pesticides are attributed to some extent to the weather conditions as well as due to abidance by the guidelines of agronomists during blowing and harvest period. Monitoring in agricultural products could be employed as the first step in a chain of biomonitoring studies in humans, and may also be proven to be a good and ample indicator of exposure. © 2010 Elsevier Ltd. All rights reserved. Source


Achilias D.S.,Aristotle University of Thessaloniki | Panayotidou E.,Aristotle University of Thessaloniki | Zuburtikudis I.,TEI of Western Macedonia
Thermochimica Acta | Year: 2011

Poly(3-hydroxybutyrate) (PHB)/organically modified clay nanocomposites were prepared by the melt mixing method and were characterized using wide-angle X-ray diffraction. Their thermal degradation kinetics was investigated using thermogravimetric analysis at various heating rates. Further kinetic analysis was performed using isoconversional methods and the invariant kinetic parameters method was used to estimate the so-called true kinetic parameters, i.e. the pre-exponential factor, A and the activation energy, E, as well as the reaction model. It was found that intercalated structures are formed and the thermal stability of the material is improved by the addition of the nano-filler. From the isoconversional analysis, it was found that the activation energy does not vary significantly with the degree of degradation denoting degradation in one step with similar values for pure PHB and for all nanocomposites. Using the invariant kinetic parameters method, it was found that the model that best describes the experimental data was that of Sestak-Berggrens with f(a) = αn(1 - α)m, where the value of n is always larger than m and is increasing with the amount of the nano-filler. The value of the true activation energy was found to be about 100 kJ mol-1 for all nanocomposites and the pre-exponential factor for PHB was estimated equal to 5.35 × 109 min-1. Finally, the values of the kinetic rate constant k were found to decrease with the amount of the nano-filler up to 3 wt%, while for amounts larger than 3 wt% k increased reaching a value greater than that of pure PHB for the 10 wt% nanocomposites. © 2010 Elsevier B.V. Source


Papadopoulou S.K.,Aristotle University of Thessaloniki | Dritsas G.,Aristotle University of Thessaloniki | Karapanagiotis I.,Art Diagnosis Center | Zuburtikudis I.,TEI of Western Macedonia | Panayiotou C.,Aristotle University of Thessaloniki
European Polymer Journal | Year: 2010

A fluorinated methacrylic homopolymer, poly(2,2,3,3,3-pentafluoropropyl methacrylate) (PPFPMA) was synthesized by a free radical polymerization reaction. The dispersive component of the surface energy (γsd) of PPFPMA was determined by contact angle measurements and inverse gas chromatography (IGC). An extensive surface characterization was conducted by means of IGC. Surface characterization demonstrated that PPFPMA has low γsd value, even at 35 °C and is a Lewis amphoteric polymer with predominantly basic character, as confirmed by the Lewis acidity and basicity constants KA and KB, respectively. The values of γsd obtained by IGC are slightly higher than those obtained by the contact angle method. This trend can be attributed to the fact that IGC evaluates, primarily, high energy sites of a surface. © 2009 Elsevier Ltd. All rights reserved. Source

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