31. Noise-guided evolution within cyclical interactionsMatjaž Perc, Attila Szolnoki, 2007, original scientific article Abstract: We study a stochastic predator-prey model on a square lattice, where each of the six species has two superior and two inferior partners. The invasion probabilities between species depend on the predator-prey pair and are supplemented by Gaussian noise. Conditions are identified that warrant the largest impact of noise on the evolutionary process, and the results of Monte Carlo simulations are qualitatively reproduced by a four-point cluster dynamical mean-field approximation. The observed noise-guided evolution is deeply routed in short-range spatial correlations, which is supported by simulations on other host lattice topologies. Our findings are conceptually related to the coherence resonance phenomenon in dynamical systems via the mechanism of threshold duality. We also show that the introduced concept of noise-guided evolution via the exploitation of threshold duality is not limited to predator-prey cyclical interactions, but may apply to models of evolutionary game theory as well, thus indicating its applicability in several different fields of research.
Keywords: dynamic systems, stochastic processes, cyclical interactions, evolutionary rules, flow simulations, Monte Carlo simulations
Published in DKUM: 07.06.2012; Views: 2353; Downloads: 411
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32. Spatio-temporal modelling explains the effect of reduced plasma membrane Ca[sup]2+[/sup] efflux on intracellular Ca[sup]2+[/sup] oscillations in hepatocytesMarko Marhl, Marko Gosak, Matjaž Perc, C. Jane Dixon, Anne K. Green, 2008, original scientific article Abstract: In many non-excitable eukaryotic cells, including hepatocytes, ▫$Ca^{2+}$▫ oscillations play a key role in intra- and intercellular signalling, thus regulating many cellular processes from fertilisation to death. Therefore, understanding the mechanisms underlying these oscillations, and consequently understanding how they may be regulated, is of great interest. In this paper, we study the influence of reduced ▫$Ca^{2+}$▫ plasma membrane efflux on ▫$Ca^{2+}$▫ oscillations in hepatocytes. Our previous experiments with carboxyeosin show that a reduced plasma membrane ▫$Ca^{2+}$▫ efflux increases the frequency of ▫$Ca^{2+}$▫ oscillations, but does not affect the duration of individual transients. This phenomenon can be best explained by taking into account not only the temporal,but also the spatial dynamics underlying the generation of ▫$Ca^{2+}$▫ oscillations in the cell. Here we divide the cell into a grid of elements and treat the ▫$Ca^{2+}$▫ dynamics as a spatio-temporal phenomenon. By converting an existing temporal model into a spatio-temporal one, we obtain theoretical predictions that are in much better agreement with the experimental observations.
Keywords: cellular signalling, calcium oscillations, intracellular oscilations, spatio-temporal dynamics, hepatocytes, stochastic simulations
Published in DKUM: 07.06.2012; Views: 1651; Downloads: 55
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33. Lower secondary school students' attitudes toward computer-supported laboratory exercisesAndreja Špernjak, Miro Puhek, Andrej Šorgo, 2010, original scientific article Abstract: In Science teaching laboratory work is recognized as one of the cornerstones. In school science laboratory work computers can be used as computer supported laboratory (real) and as virtual laboratory. In the first case "real" laboratories involve bench top experiments utilizing data acquisition systems while "virtual" laboratory entails interactive simulations and animations. Lower secondary school students in age between 11 and 15 performed three laboratory exercises (Activity of yeast, Gas exchange in breathing, Heart rate) as classic, computer-supported and virtual laboratory. As a result of testing we know that all three methods are suitable even for younger students. When they were asked which method they liked the most, their first choice was computer-supported laboratory, followed by classic laboratory, and virtual laboratory at the end. Additionally recognized weak and strong sides of used methods are discussed.
Keywords: education, biology, computer-supported laboratory, simulations, secondary schools
Published in DKUM: 07.06.2012; Views: 2345; Downloads: 107
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35. Computational model for the analysis of bending fatigue in gearsJanez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, original scientific article Abstract: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4.
Keywords: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics
Published in DKUM: 01.06.2012; Views: 3343; Downloads: 99
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36. Mathematical model of IRIS replication mechanism for the simulation of tactical networksJože Mohorko, Matjaž Fras, 2009, original scientific article Abstract: The Multilateral Interoperability Programme (MIP) was established to promote more successful and better harmonized operational functions for international peace-keeping forces. The C2IEDM/JC3IEDM (Command and Control Information Exchange Data Model) ensures the interconnection of Command and Control Information Systems (C2ISs) throughout all levels, from the corps down to the lower ranks. The usability of C2ISs highly correlates with the capacities of data information carriers, and the need is growing for greater capacity and reliability of transmission media and cryptographic message security. Simulation of tactical networks is an important task in planning military missions. Such methodologies assure a higher probability of success during critical tactical operations. This article focuses on a new radio network modeling method for the C2IS, which is verified by the OPNET simulation environment. This modeling method can be used in tactical radio network planning and optimization processes.
Keywords: communications, tactical networks, tactical radio networks, traffic modelling, radio network modeling, simulations, C2IS
Published in DKUM: 01.06.2012; Views: 2156; Downloads: 101
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37. Analytical travel time models for multi aisle automated storage and retrieval systemsTone Lerher, Matjaž Šraml, Janez Kramberger, Iztok Potrč, Matej Borovinšek, Blaž Zmazek, 2005, original scientific article Abstract: Multi aisle automated storage and retrieval systems correspond to multiple picking aisles served by a single storage and retrieval machine. These systemsare used in practice when the need for pallet places is high and the throughput capacity is relatively low. Therefore, considerable savings of initial investment costs due to single aisle systems can be achieved using such systems. The objective of the presented study is to develop analytical travel time models for multi aisle automated storage and retrieval systems considering the operating characteristics of the storage and retrieval machine. With the proposed analytical travel time models, average travel time of the storage and retrieval machine, from which the performance of multi aisle automated storage and retrieval systems can be evaluated is determined. A simulation model of multi aisle automated storage and retrieval systems was developed to compare the performances of the proposed analytical travel time models. An example of multi aisle automated storage and retrieval systems withfive picking aisles was presented for the evaluation purpose. The results show that proposed analytical travel time models perform satisfactory according to the results of simulation analysis and could be very useful toolsfor designing of multi aisle automated storage and retrieval systems in real-world applications.
Keywords: warehousing, logistics, high rack storage, simulations, travel time models
Published in DKUM: 01.06.2012; Views: 2425; Downloads: 95
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38. Heat conduction in closed-cell cellular metalsMatej Vesenjak, Zoran Žunič, Andreas Öchsner, Matjaž Hriberšek, Zoran Ren, 2005, original scientific article Abstract: The purpose of this research was to describe the thermal transport properties in closed-cell cellular metals. Influence of cell size variations with different pore gases has been investigated with transient computational simulations. Heat conduction through the base material and gas in pores (cavities) was considered, while the convection and radiation were neglected in the initial stage of this research. First, parametric analysis for definingthe proper mesh density and time step were carried out. Then, two-dimensional computational models of the cellular structure, consisting of the base material and the pore gas, have been solved using ANSYS CFX software within the framework of finite volume elements. The results have confirmed theexpectations that the majority of heat is being transferred through the metallic base material with almost negligible heat conduction through the gas in pores. The heat conduction in closed-cell cellular metals is therefore extremely depended on the relative density but almost insensitive regarding tothe gas inside the pore, unless the relative density is very low.
Keywords: heat transfer, cellular metal materials, porous materials, closed cells, gas fillers, computational simulations
Published in DKUM: 01.06.2012; Views: 2314; Downloads: 103
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39. Coupled simulations of nozzle flow, primary fuel jet breakup, and spray formationEberhard von Berg, Wilfried Edelbauer, Aleš Alajbegović, Reinhard Tatschl, Martin Volmajer, Breda Kegl, Lionel C. Ganippa, 2005, original scientific article Abstract: Presented are two approaches for coupled simulations of the injector flow withspray formation. In the first approach the two-fluid model is used within the injector for the cavitating flow. A primary breakup model is then applied at the nozzle orifice where it is coupled with the standard discrete droplet model. In the second approach the Eulerian multi-fluid model is applied for both the nozzle and spray regions. The developed primary breakup model, used in both approaches, is based on locally resolved properties of the cavitating nozzle flow across the orifice cross section. The model provides the initial droplet size and velocity distribution for the droplet parcels released from the surface of a coherent liquid core. The major feature of the predictions obtained with the model is a remarkable asymmetry of the spray. This asymmetryis in agreement with the recent observations at Chalmers University where they performed experiments using a transparent model scaled-up injector.The described model has been implemented into AVL FIRE computational fluid dynamics code which was used to obtain all the presented results.
Keywords: internal combustion engines, fuel injection, simulations
Published in DKUM: 01.06.2012; Views: 1779; Downloads: 95
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40. Diesel and biodiesel fuel spray simulationsPrimož Pogorevc, Breda Kegl, Leopold Škerget, 2008, original scientific article Abstract: This paper deals with the investigation of the influential parameters of a mathematical spray breakup model using different fuels. Beside injection system measurements, fuel physical properties and injection process characteristics were measured, because they are necessary for the spray simulation input. For validation purposes, spray was injected into motionless air at atmospheric pressure and room temperature and filmed with a high-speed camera. Spray macrocharacteristics have been determined on the recorded images. Using the simulation program, the injection processes for diesel, biodiesel, and their 50% blend B50 have been simulated. Spray mathematical model parameters were tuned based on the experimentally gained results. Primary breakup model parameters showed the biggest impact on the spray characteristics and were therefore expressed using the fuel physical properties, the injection process characteristics, and the working regime parameters. Spray simulations into the combustion chamber were made in the end. All of these results are presented and discussed in this paper.
Keywords: fuel spray, spray breakup, biodiesel fuel, fuels, numerical simulations, mathematical model
Published in DKUM: 31.05.2012; Views: 1952; Downloads: 87
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