Technological Educational Institute of Western Macedonia

About: Technological Educational Institute of Western Macedonia is a based out in . It is known for research contribution in the topics: Catalysis & Symplectic geometry. The organization has 291 authors who have published 522 publications receiving 7682 citations. The organization is also known as: TEI of West Macedonia & TEI of Western Macedonia.

Investigating the impact of decentralized energy storage systems in active low-voltage distribution networks

Abstract: Photovoltaic (PV) penetration in Low-Voltage (LV) networks is expected to increase in the following years, posing a series of problems in the operation pf low-voltage networks. Among the most important challenges imposed, is the reverse power flow caused by high injected energy from distributed PVs during peak irradiation hours. This is the reason of voltage rises above the permissible limits. Amongst other solutions, such as active power curtailment and reactive power absorption, the installation of distributed Energy Storage Systems (ESS) seems to be an attractive solution since it can absorb surplus power locally, avoiding curtailment methods, power flow losses on the feeder and grid reinforcements. As the cost of storage is decreasing, ESS are expected to be increasingly adopted by prosumers. This work evaluates the influence of such systems on the voltage profile of LV feeders and on the self-consumed energy of prosumers. Intensive simulations on a benchmark feeder assess the conflicted benefits of power system operators and ESS owners.

An effective spectrum handoff scheme for Cognitive Radio Ad hoc Networks

Abstract: Cognitive Radio Networks (CRNs) is the key technology to overcome the disadvantages of static spectrum allocation and enhance spectrum utilization through Dynamic Spectrum Access (DSA) techniques. One important topic of the development of CRNs is spectrum handoff, which ensures the uninterrupted communication of Secondary Users (SUs). Two types of spectrum handoff approaches exist, namely the proactive and the reactive spectrum handoff. When the Primary User (PU) traffic is high the proactive spectrum handoff approach is more suitable whereas the reactive handoff on light PU traffic achieves better performance. In this paper we evaluate the use of proactive and reactive spectrum handoff policies in CRNs. Simulations are conducted using NS-3 simulator. To the extent of our knowledge, an extensive CRN simulation regarding spectrum handoff on NS-3 simulator has not been carried out. Furthermore, we implemented a hybrid spectrum handoff scheme that selectively uses either reactive or proactive handoffs, based on PU traffic intensity. Additionally our scheme adjusts dynamically the SU frame size throughout SU communications, to minimize collisions. Simulations show that the proposed hybrid scheme performs better than the proactive and reactive handoff types. Moreover, the dynamic adjustment of the frame size on cognitive nodes enhances performance noticeably in certain scenarios.

Exploring Student Viewing Behaviors in Online Educational Videos

Abstract: Online video use in education is an expanding trend and research that focuses on how students view educational videos becomes of particular interest. In our previous work, we argued that in order to conduct a detailed analysis of the learner viewing behavior we have to deploy tools that log the learner activity and assist statistical analysis and data mining. Working towards this direction, a framework for recording and analyzing learner behavior was presented. This paper presents findings of applying this framework into educational settings.

Free (open) boundary condition: some experiences with viscous flow simulations

Abstract: SUMMARY The free (or open) boundary condition (FBC, OBC) was proposed by Papanastasiou et al. (A new outflow boundary condition, International Journal for Numerical Methods in Fluids, 1992; 14:587–608) to handle truncated domains with synthetic boundaries where the outflow conditions are unknown. In the present work, implementation of the FBC has been tested in several benchmark problems of viscous flow in fluid mechanics. The FEM is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal or non-isothermal, steady-state conditions, for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure dependence of the viscosity, slip at the wall, and surface tension are all considered individually in the extrudate-swell benchmark problem for a wide range of the relevant parameters. The present results extend previous ones regarding the applicability of the FBC and show cases where the FBC is inappropriate, namely in the extrudate-swell problem with gravity or surface-tension effects. Particular emphasis has been given to the pressure at the outflow, which is the most sensitive quantity of the computations. In all cases where FBC is appropriate, excellent agreement has been found in comparisons with results from very long domains. The formulation for Picard-type iterations is given in some detail, and the differences with the Newton–Raphson formulation are highlighted regarding some computational aspects. Copyright © 2011 John Wiley & Sons, Ltd.