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1.
The development of a “drive-in” filters dewatering system in the Velenje coal mine using finite-element modelling
Goran Vižintin, Miran Veselič, Andrej Bombač, Evgen Dervarič, Jakob Likar, Đorđe Vukelič, 2009, original scientific article

Abstract: During the mining operations at the Velenje coal mine, groundwater has been presenting a constant threat to underground works. The hydrogeological setup is so complex that a lot of structural drilling and well-logging operations were needed in the past to clarify it. Above the lignite seam is a Pliocene and Pleisticene multilayer aquifer system, composed mainly of permeable sand layers and impermeable clay layers. In 1981 the Pliocene aquifers were divided into three packages. Based on the water-table data of each aquifer, pumping tests, chemical analyses of the groundwater and the geophysical properties the Pliocene aquifers directly above the seam, together with impermeable layers, were divided into: a) the first water-bearing sands (Pl1), b) the aquifers 2080 m above the coal seam (Pl2) and c) the upper Pliocene aquifers (Pl3). For the mining operations the most important aquifer of saturated sands is Pl1. The hydraulic pressure of the groundwater in these sands directly affects the safety of the mining. These aquifers are mostly affected by the dewatering activities, too. However, the dewatering wells are constructed in such a way as to capture the whole Pl2 and, somewhere, even a part of the Pl3 complex, too. The water pressure in this multilayer aquifer can reach over 35 bars, so a massive program of drawdown activities has been needed and is still in place to decrease the water table in the area related to the mining operations. Special, multilevel observation wells are used to monitor the water level. A number of 3D finite-difference models (FDMs) were used to estimate the regional groundwater drawdown. It was observed that the FDMs performed well when predicting the regional situation, but the model-predicted drawdown was lower than the observed values at observation points in the area where the dewatering operations using “drive-in” filters have taken place in the past. This is a well-known problem of the FDM: the drawdown being rather a function of the cell size than of the flow net. The risk of water inrushes will increase, especially after 2012 and 2017, when a series of surface-drilled wells, connected into the mine’s pumping-line batteries, will be abandoned due to excavation works and mining-subsidence effects. Consequently, the dewatering schemes had to be completely reviewed. The destroyed, first-order dewatering structures will have to be replaced by a series of “drive-in” filters, drilled from the mine roadways in the area of the planned longwall face operations. For the drive-in filter-system design the FDM does not seem to be appropriate. This is especially so if the error in the drawdown and pumping flow prediction is taken into account. That led, in 2007, to the selection of the finite-element method (FEM) for the prediction of the groundwater drawdown and the water pumping rates in the areas were the underground works will encounter the risk of a water inrush. Based on the FEM prediction the sizing and the layout pattern of the “drive-in” filters were made.
Keywords: drive-in filters, groundwater, mining water, mining hydrology, geophysical well login, mathematical modelling
Published: 06.06.2018; Views: 331; Downloads: 40
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2.
The architecture of a school system according to the theory of dynamical systems
Boris Aberšek, Janez Bregant, 2012, original scientific article

Abstract: From the experience of recent years it seems clear that the existing educational system, as a whole, is perceived as an ailing system that fails to meet the needs of a major portion of the society it serves. Every aspect of the educational process must be studied and reconsidered in the light of new and different societal expectations. In the last decades we started with one school reform after the other, but it looks now that these changes had no positive impact whatsoever. Even worse, the school system was damaged afterwards. In this paper we will explore some possibilities how to improve it without facing these consequences. The main idea is, as a result of our latest research, that mathematical methods for describing and simulating could be very useful for predicting and simulating school systems without using a long term and complex empirical experimentation. The paper introduces the correlation between the dynamical mathematical calculus and the educational school system and elaborates to some extent the basic idea of using the former to predict the latter.
Keywords: architecture, mathematical modelling, school systems, dynamical systems
Published: 19.12.2017; Views: 613; Downloads: 51
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3.
Computer-supported modelling of multimodal transportation networks rationalization
Ratko Zelenika, Slavomir Vukmirović, Hilmija Mujić, 2007, short scientific article

Abstract: This paper deals with issues of shaping and functioning of computer programs in the modelling and solving of multimodal transportation network problems. A methodology of an integrated use of a programming language for mathematical modelling is defined, as well as spreadsheets for the solving of complex multimodal transportation network problems. The paper contains a comparison of the partial and integral methods of solving multimodal transportation networks. The basic hypothesis set forth in this paper is that the integral method results in better multimodal transportation network rationalization effects, whereas a multimodal transportation network model based on the integral method, once built, can be used as the basis for all kinds of transportation problems within multimodal transport. As opposed to linear transport problems, multimodal transport network can assume very complex shapes. This paper contains a comparison of the partial and integral approach to transportation network solving. In the partial approach, a straight forward model of a transportation network, which can be solved through the use of the Solver computer tool within the Excel spreadsheet interface, is quite sufficient. In the solving of a multimodal transportation problem through the integral method it is necessary to apply sophisticated mathematical modelling programming languages which support the use of complex matrix functions and the processing of a vast amount of variables and limitations. The LINGO programming language is more abstract than the Excel spreadsheet, and it requires a certain programming knowledge. The definition and presentation of a problem logic within Excel, in a manner which is acceptable to computer software, is an ideal basis, for modelling in the LINGO programming language, as well as a faster and more effective implementation of the mathematical model. This paper provides proof for the fact that it is more rational to solve the problem of multimodal transportation networks by using the integral, rather than the partial method.
Keywords: intermodal transportation, transportation networks, spreadsheets, mathematical modelling, programming languages, Lingo, Solver
Published: 01.06.2017; Views: 537; Downloads: 66
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4.
SWITCHED CAPACITOR-BOOST CONVERTER FOR THERMOELECTRIC SYSTEM
Leon Maruša, 2015, master's thesis

Abstract: The purpose of this work was to develop and test the switched capacitors-boost converter (SC-BC), which can be used for stepping up voltage by a factor of at least ten driving energy harvesting applications. Extensive mathematical modelling of SC-BC was done for obtaining its nonlinear model and equations of multiple static characteristics. Simulations of SC-BC and its simplified models were done within a PSIM environment. The choice was made for closed-loop to use the combination of a PI controller and sliding mode control due to the robustness requirements and excellent closed-loop dynamics. Control was implemented on digital signal processor TMS320F28335 within a MATLAB/SIMULINK environment. Lastly the open and closed-loop experiments were done on a real SC-BC prototype.
Keywords: switched capacitors, boost converter, sliding mode control, energy harvesting, mathematical modelling
Published: 14.10.2015; Views: 1236; Downloads: 148
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6.
Mathematical models for the simulation of pumps systems
Mitja Kastrevc, Edvard Detiček, 2012, original scientific article

Abstract: This paper presents the influence of a mathematical model in the simulation of pumping systems; specifically, a model of an induction motor is presented; the paper also covers a comparison between commonly used mathematical models of AC motors. For verification of the simulated data, a practical pump system was tested.
Keywords: induction motors, mathematical modelling, hydraulic pump systems
Published: 10.07.2015; Views: 787; Downloads: 40
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8.
Modeling of molecular and cellular mechanisms involved in [Ca sup 2+] signal encoding in airway myocytes
Marko Marhl, Denis Noble, Etienne Roux, 2006, review article

Abstract: In airway myocytes signal transduction via cytosolic calcium plays an important role. In relation with experimental results we review models of basic molecular and cellular mechanisms involved in the signal transduction from the myocyte stimulation to the activation of the contractile apparatus. We concentrate on mechanisms for encoding of input signals into Ca2+ signals and the mechanisms for their decoding. The mechanisms are arranged into a general scheme of cellular signaling, the so-called bow-tie architecture of signaling, in which calcium plays the role of a common media for cellular signals and links the encoding and decoding part. The encoding of calcium signals in airway myocytes is better known and is presented in more detail. Inparticular, we focus on three recent models taking into account the intracellular calcium handling and ion fluxes through the plasma membrane. Themodel of membrane conductances was originally proposed for predicting membrane depolarization and voltage-dependent Ca2+ influx triggered by initialcytosolic Ca2+ increase as observed on cholinergic stimulation. Cellular models of intracellular Ca2+ handling were developed to investigate the role of a mixed population of InsP3 receptor isoforms and the cellular environment in the occurrence of Ca2+ oscillations, and the respective role ofthe sarcoplasmic reticulum, mitochondria, and cytosolic Ca2+-binding proteins in cytosolic Ca2+ clearance. Modeling the mechanisms responsible for the decoding of calcium signals is developed in a lesser extent; however, the most recent theoretical studies are briefly presented in relation with the known experimental results.
Keywords: biophysics, mathematical modelling, modelling, calcium oscillations, contractions, airway smooth muscle cells, muscle cells, smooth muscles, encoding, decoding, bow-tie structures
Published: 07.06.2012; Views: 1282; Downloads: 20
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9.
Theoretical and experimental investigation of calcium-contraction coupling in airway smooth muscle
Prisca Mbikou, Aleš Fajmut, Milan Brumen, Etienne Roux, 2006, original scientific article

Abstract: We investigated theoretically and experimentally the ▫$Ca^{2+}$▫-contraction couplingin rat tracheal smooth muscle. ▫$[Ca^{2+}]_i$▫, isometric contraction and myosin light chain (MLC) phosphorylation were measured in response to 1 mM carbachol. Theoretical modeling consisted in coupling a model of ▫$Ca^{2+}-dependent$▫ MLC kinase (MLCK) activation with a four-state model of smooth muscle contractile apparatus. Stimulation resulted in a short-time contraction obtained within 1 min, followed by a long-time contraction up to the maximal force obtained in 30 min. ML-7 and Wortmannin (MLCK inhibitors) abolished the contraction. Chelerythrine (PKC inhibitor) did not change the short-time, but reduced the long-time contraction. ▫$[Ca^{2+}]_i$▫ responses of isolated myocytes recorded during the first 90 s consisted in a fast peak, followed by a plateau phase and, in 28 % of the cells, superimposed ▫$Ca^{2+}$▫ oscillations. MLC phosphorylation was maximal at 5 s and then decreased, whereas isometric contraction followed a Hill-shaped curve. The model properlypredicts the time course of MLC phosphorylation and force of the short-time response. With oscillating ▫$Ca^{2+}$▫ signal, the predicted force does not oscillate. According to the model, the amplitude of the plateau and the frequency of oscillations encode for the amplitude of force, whereas the peak encodes for force velocity. The long-time phase of the contraction, associated with a second increase in MLC phosphorylation, may be explained, at least partially, by MLC phosphatase (MLCP) inhibition, possibly via PKC inhibition.
Keywords: biophysics, mathematical modelling, modelling, calcium oscillations, contractions, force development, muscle cells, smooth muscles, myosin kinase
Published: 07.06.2012; Views: 1185; Downloads: 71
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10.
Role of cascades in converting oscillatory signals into stationary step-like responses
Marko Marhl, Vladimir Grubelnik, 2007, original scientific article

Abstract: In biological signal transduction pathways intermediates are often oscillatory and need to be converted into smooth output signals at the end. We show by mathematical modelling that protein kinase cascades enable converting oscillatory signals into sharp stationary step-like outputs. The importance of this result is demonstrated for the switch-like protein activation by calcium oscillations, which is of biological importance for regulating different cellular processes. In addition, we found that protein kinase cascades cause memory effects in the protein activation, which might be of a physiological advantage since a smaller amount of calcium transported in the cell is required for an effective activation of cellular processes.
Keywords: physics, calcium oscillations, mathematical modelling, calcium, calcium oscillations, sygnalling cascade, protein kinase cascades, signal transduction, ultrasensitivity, biochemical switch, cellular dynamics
Published: 07.06.2012; Views: 1344; Downloads: 63
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