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Boundary domain integral method for the study of double diffusive natural convection in porous media
Janja Kramer Stajnko, Renata Jecl, Leopold Škerget, 2007, original scientific article

Abstract: The main purpose of this paper is to present a boundary domain integral method(BDIM) for the solution of natural convection in porous media driven by combining thermal and solutal buoyancy forces. The Brinkman extension of the classical Darcy equation is used for the momentum conservation equation. The numerical scheme was tested on a natural convection problem within a square porous cavity, where different temperature and concentration values are applied on the vertical walls, while the horizontal walls are adiabatic and impermeable. The results for different governing parameters (Rayleigh number, Darcy number, buoyancy ratio and Lewis number) are presented and compared withpublished work. There is a good agreement between those results obtained using the presented numerical scheme and reported studies using other numerical methods.
Keywords: double diffusive natural convection, porous medium, velocity-vorticity formulation, Brinkman extended Darcy formulation, boundary domain integrated method
Published: 31.05.2012; Views: 1098; Downloads: 54
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Evaluating the impact of environmental factors on the international competitiveness of Small and Medium sized Enterprises in the Western Balkans
Goran Andzelic, Vladimir Dzakovic, Bojan Lalić, Danica Zrnic, Iztok Palčič, 2011, original scientific article

Abstract: Small and Medium-sized Enterprises (SMEs) with an export potential face significant obstacles in gaining international competitiveness, due to the highly dynamic environment in which they operate. This study evaluates the impact of environmental factors on international competitiveness of the Western Balkans SMEs by identifying the key pairs of environmental factors and factors of international competitiveness, which facilitate an increase in international competitiveness of these firms. The paper also studies the importance of strategic planning and decision making process in the Western Balkans SMEs. Research is based on a questionnaire conducted on the representative sample of SMEs in Serbia, Montenegro and Bosnia and Herzegovina in the period September 2008 to March 2009. The findings of the research indicate which significant environmental factors have an impact on gaining the international competitiveness of the Western Balkans SMEs, therefore offering sound basis for strategic positioning and further gaining of competitive advantage.
Keywords: international competitiveness, small and medium enterprises, strategic positioning, environmental factors, Western Balkans
Published: 01.06.2012; Views: 1565; Downloads: 19
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Experimental models of medium break loss of coolant accidents with and without steam generator tube rupture
Jure Marn, Marjan Delić, Leopold Škerget, 2003, original scientific article

Abstract: This paper reports model experiments simulating medium break loss of coolant accidents, with and without steam generator tube rupture (SGTR), in pressurized water reactors. Apart from a significant influence on the pressure in the reactor coolant system in the early parts of the accident, SGTR generally has only a small effect on the pressures and temperatures during the accident. The initial reactor conditions are found to be more significant. Some results of preliminary numerical models are briefly presented and these are broadly in agreement with the experimental measurements.
Keywords: nuclear engineering, nuclear accidents, steam generator tube rupture, loss of coolant, medium break loss of coolant accident, computer program, Melcor, MELCOR computer code, integral test facility
Published: 01.06.2012; Views: 849; Downloads: 67
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Boundary element method for natural convection in non-Newtonian fluid saturated square porous cavity
Renata Jecl, Leopold Škerget, 2003, original scientific article

Abstract: The main purpose of this work is to present the use of the Boundary Element Method (BEM) in the analysis of the natural convection in the square porous cavity saturated by the non-Newtonian fluid. The results of hydrodynamic and heat transfer evaluations are reported for the configuration in which the enclosure is heated from a side wall while the horizontal walls are insulated.The flow in the porous medium is modelled using the modified Brinkman extended Darcy model taking into account the non-Darcy viscous effects. The governing equations are transformed by the velocity-vorticity variables formulation enabling the computation scheme to be partitioned into kinematic and kinetic parts. To analyse the effects of the available non-Newtonian viscosity and to evaluate the presented approach, the power law model for shear thinning fluids (n<1), for shear thickening fluids (n>1) and in the limit for the Newtonian fluids (n=1) is considered. Numerical model is tested also for the Carreau model adequate for many non-Newtonian fluids. Solutions for the flow and temperature fields and Nusselt numbers are obtainedin terms of a modified Rayleigh number Ra*, Darcy number Da, and the non-Newtonian model parameters. The agreement between the results obtained with finite difference method is very good indicating that BEM can be efficiently used for solving transport phenomena in saturated porous medium.
Keywords: natural convection, non-Newtonian fluid, porous medium, cavity flow, boundary element method, boundary domain integral method
Published: 01.06.2012; Views: 965; Downloads: 55
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The impact of market knowledge and institutional incentives on the internationalization of small and medium-sized enterprises in Slovenia
Nuša Basle, 2015, master's thesis

Abstract: The internationalization of firms is an important part of globalization. Firms are looking for their opportunities in foreign markets. For this reason, they need to have specific market knowledge. They can create it themselves by primary market research and/or gain it from available secondary sources. Companies need to be aware that market knowledge is crucial for the internationalization process. Small and medium-sized enterprises (SMEs) are the most valuable part of both European and Slovenian economy. SMEs substantially contribute to economic growth and job creation and are considered the present and future backbone of the European and Slovenian economy. Because of the importance of SMEs, various programs and mechanisms for SMEs support were developed at the level of the European Union (EU) and Slovenia. These constitute Institutional Support and contain, among other things, financial and non-financial mechanisms to support the internationalization of SMEs.
Keywords: Internationalization, Small and medium-sized enterprises (SMEs), Entrepreneurship, Market knowledge, Institutional Support, Slovenia
Published: 20.11.2015; Views: 832; Downloads: 70
.pdf Full text (5,73 MB)

Modelling medium access control in IEEE 802.15.4 nonbeacon-enabled networks with probabilistic timed automata
Tatjana Kapus, original scientific article

Abstract: This paper concerns the formal modelling of medium access control in nonbeacon-enabled IEEE 802.15.4 wireless personal area networks with probabilistic timed automata supported by the PRISM probabilistic model checker. In these networks, the devices contend for the medium by executing an unslotted carrier sense multiple access with collision avoidance algorithm. In the literature, a model of a network which consists of two stations sending data to two different destination stations is introduced. We have improved this model and, based on it, we propose two ways of modelling a network with an arbitrary number of sending stations, each having its own destination. We show that the same models are valid representations of a star-shaped network with an arbitrary number of stations which send data to the same destination station. We also propose how to model such a network if some of the sending stations are not within radio range of the others, i.e. if they are hidden. We present some results obtained for these models by probabilistic model checking using PRISM.
Keywords: wireless personal area network, medium access control, hidden station, formal specification, probabilistic model checking
Published: 15.06.2017; Views: 303; Downloads: 169
.pdf Full text (2,25 MB)
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