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A system dynamics model for improving primary education enrollment in a developing country
Chandra Sekhar Pedamallu, Linet Ozdamar, LS Ganesh, Gerhard-Wilhelm Weber, Erik Kropat, 2010, izvirni znanstveni članek

Opis: The system dynamics approach is a holistic way of solving problems in real-time scenarios. This is a powerful methodology and computer simulation modeling technique for framing, analyzing, and discussing complex issues and problems. System dynamics modeling is often the background of a systemic thinking approach and has become a management and organizational development paradigm. This paper proposes a system dynamics approach for studying the importance of infrastructure facilities on the quality of primary education system in a developing nation. The model is built using the Cross Impact Analysis (CIA) method of relating entities and attributes relevant to the primary education system in any given community. The CIA model enables us to predict the effects of infrastructural facilities on the community's access of primary education. This may support policy makers to take more effective actions in campaigns that attempt to improve literacy.
Ključne besede: developing countries, system modeling, cross impact analysis, simulation, system dynamics, primary education
Objavljeno: 28.11.2017; Ogledov: 577; Prenosov: 247
.pdf Celotno besedilo (1,03 MB)
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Robust clustering of languages across Wikipedia growth
Kristina Ban, Matjaž Perc, Zoran Levnajić, 2017, izvirni znanstveni članek

Opis: Wikipedia is the largest existing knowledge repository that is growing on a genuine crowdsourcing support. While the English Wikipedia is the most extensive and the most researched one with over 5 million articles, comparatively little is known about the behaviour and growth of the remaining 283 smaller Wikipedias, the smallest of which, Afar, has only one article. Here, we use a subset of these data, consisting of 14 962 different articles, each of which exists in 26 different languages, from Arabic to Ukrainian. We study the growth of Wikipedias in these languages over a time span of 15 years. We show that, while an average article follows a random path from one language to another, there exist six well-defined clusters of Wikipedias that share common growth patterns. The make-up of these clusters is remarkably robust against the method used for their determination, as we verify via four different clustering methods. Interestingly, the identified Wikipedia clusters have little correlation with language families and groups. Rather, the growth of Wikipedia across different languages is governed by different factors, ranging from similarities in culture to information literacy.
Ključne besede: Wikipedia, language, growth dynamics, data analysis, clustering
Objavljeno: 13.11.2017; Ogledov: 763; Prenosov: 315
.pdf Celotno besedilo (1004,06 KB)
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Rigid body dynamics in optimization of the machine tool vibroisolation
Radomir Slavković, Aleksandar Veg, Nedeljko Dučić, Nikola Slavković, Jelena Baralić, Ivan Milićević, 2015, izvirni znanstveni članek

Opis: Modern design of the machine tool treats the suspending parts as a crucial element of the effective vibration isolation. Therefore the suspending items are specifically developed and subjected to extensive tests before being applied on real objects. These elements ensure accurate levelling and appropriate vibration damping. Usually selection of inadequate support element causes intensive disturbing effects in machining. The paper presents dynamics analysis of the machine tool suspended on flexible mountings. The overall analysis is conceived on a rigid body dynamics. This method enables selection of an optimal supporting configuration. Further on such an effective suspension design prevents a need for expensive monitoring of the dynamic characteristics of the mechanical system, i.e. machine tool and supports. The paper explores dynamics of a real, flexibly supported machine tool. Results are obtained with the assistance of the "SUPPORT" software. Finally the theoretical and computational statements are approved throughout extensive site measurements on the machine tool body with appropriate instrumentation.
Ključne besede: dynamics analysis, experiment, machine tool, software, transfer function
Objavljeno: 12.07.2017; Ogledov: 537; Prenosov: 312
.pdf Celotno besedilo (2,13 MB)
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Raziskave interakcij med celicami in biopolimernimi materiali z naprednimi eksperimentalnimi metodami kot osnova za študij biokompatibilnosti polimerov
Rok Podlipec, 2015, doktorska disertacija

Opis: The last two decades have been determined by the development in the field of tissue engineering. Beside the constant progress in new biomaterials and scaffold fabrication methods, currently the main focus is to understand scaffolds biocompatibility. In our thesis, physical aspects of scaffold biocompatibility were studied by correlating molecular to macro scale physical properties of scaffolds with cell attachment and cell growth. In order to focus on scaffold physical properties, scaffolds were prepared by the same chemical composition of natural polymer gelatin excluding biochemical effects on the cell response. Scaffold with different physical properties were obtained by changing the temperature, pH and crosslinker degree during the cryogelation and populated by the fibroblast cells. Advanced experimental biophysical methods were applied to determine the polymer mobility via electron paramagnetic resonance (EPR) with spin labelling, the scaffold mechanical properties via rheometry, dynamic mechanical analysis (DMA) and nanoindentation using atomic force microscope (AFM) and the scaffold porosity via confocal fluorescence microscopy (CFM). The anisotropy of the molecular mobility of the side chains of polymers in the crosslinked gelatin structure was found to correlate with the initial cell growth (throughout the first week) the best of all the physical properties measured. About five times less efficient cell growth was measured on the scaffolds with highly mobile, spatially nonrestricted dynamics of the polymer side chains, in comparison with cell growth on the scaffolds with the restricted rotational motion of polymers. The result indicates that cells identify and respond to the degree of polymer mobility, where partially immobile phase is necessary for efficient cell attachment and efficient cell growth. So far, the molecular mobility of polymers constituting tissue engineering materials has never been studied thoroughly with respect to its influence on cell response, and therefore may represent a new experimental approach in understanding biocompatibility. To further understand cell-scaffold interaction, the study focused also on the first events during cell attachment - bond formation between the cell surface proteins and the specific binding sites on the material. In our thesis, cell adhesion dynamics was investigated in real-time on the surfaces of gelatin scaffolds with different physical properties using spatially-controlled cell manipulation by the optical tweezers and the confocal fluorescence microscopy detection. Our goal was to elucidate, if the adhesion dynamics can be correlated with cell growth and if it can be dependent on the scaffold polymer molecular mobility. Quantitative characterization of the optical tweezers force applied during cell-scaffold adhesion analysis was done by viscous drag force calibration and dynamic cell sequential trapping of individual cells. The maximal force on a trapped cell not causing the thermal damage was measured up to 200 pN, with nearly linearly increasing force profile across the cell towards the plasma membrane. By submicron spatial resolution of cell manipulation, we managed to quantify probability of cell adhesion, cell adhesion strength and mechanism of cell attachment, including the formation of the membrane tethers, which slow down the adhesion process. Adhesion strength was classified according to the displacement of the attached cell under the force of optical tweezers measured in the direction of the scaffold surface.Cell adhesion was shown to significantly correlate with cell growth in the first days of culture, while the adhesion itself seems to be dependent on the molecular mobility of surface polymers. The result indicates that the interactions during the first seconds may markedly direct further cell response. The developed methodology for cell adhesion analysis on the surfaces of 3D scaffolds serves as a good tool to forecast scaffold biocompatibility.
Ključne besede: polymer molecular mobility, mechanical response, morphology, scaffold biocompatibility, cell growth, single cell manipulation, cell adhesion dynamics, optical tweezers, electron paramagnetic resonance, dynamical mechanical analysis, nanoindentation, fluorescence microscopy and microspectroscopy
Objavljeno: 06.10.2015; Ogledov: 1549; Prenosov: 99
.pdf Celotno besedilo (5,95 MB)

The impact of economic growth on the dynamics of enterprises
Dijana Močnik, 2010, izvirni znanstveni članek

Opis: The aim of this paper was to test the hypothesized U-shaped relationship between economic development and dynamics of enterprises. The dynamics of enterprises is influenced by the achieved economic development. This paper first analyzed the association between the regional gross value added (GVA) growth rate and different measures of enterprises dynamics from Slovenian data from 2000 to 2005. Our graphical analyses indicated that 1) the rate of gross entry and GVA growth rate were linearly and negatively associated; 2) the association between the rate of gross exit and GVA growth rate is best represented by the downward U-shape function (Ç); and 3) a U-shaped association exists between the rate of net entry and GVA growth rate. The size of the impact was estimated using the regression analysis between the net entries as dependent variable and GVA growth as independent variable that showed the best fit. According to the results, 1) economic growth significantly impacts net entries; 2) the hypothesized U-shaped relationship between net entries and economic growth was confirmed as the Slovenian net entries decrease until the GVA growth rate reaches 10% yet increase when the growth in GVA is higher than 10%; and 3) a ‘natural rate’ of entrepreneurship is to some extent governed by ‘laws’ related to the economic growth rate. The results further indicate that the average net entry rate should be increased by 0.787 units (%) as a result of a region's specific environmental factors. This research confirms the theoretical assumptions that have previously been sparsely tested empirically and even rarely supported by results. Therefore, our results represent a contribution to the robustness of the theoretical as well as empirical clarification of the relationship between entrepreneurship and economic development.
Ključne besede: dynamics of enterprises, firm entries, net entries, economic growth, regression analysis
Objavljeno: 10.07.2015; Ogledov: 910; Prenosov: 69
.pdf Celotno besedilo (525,03 KB)
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Optimal kinematic design of a link-drive mechanism with prescribed velocity characteristics
Bojan Vohar, Karl Gotlih, Jože Flašker, 2003, kratki znanstveni prispevek

Opis: The paper presents an example of a link-drive mechanism for a deep drawing mechanical press. Because of its characteristics such a drive is much more appropriate than conventional crankshaft or eccentric drive. The existing design of the drive has proved unsatisfactory and does not meet all the demands and constraints, which are ideal for deep drawing process. Optimization of the drive is therefore necessary. The intention is to achieve the required velocity characteristics in a defined area of movement. Firstly, the drive is analyzed and a mathematical model is made and prepared for optimization procedure. The process is time-dependent, so it cannot be used directly in the optimization algorithm. Mathematical model is transformed intoa form suitable for the standard non-linear optimization procedure and then optimization is carried out. The method used is sequential quadratic programming. The final objective of the optimization process is to find such dimensions of link-drive members that the given requirements are satisfied in the best possible manner.
Ključne besede: mechanics, dynamics of mechanical systems, closed kinematic chains, mathematical modelling, non-linear optimization, drive optimization, drive dimensioning, kinematic analysis, link-drive mechanism, deep drawing press
Objavljeno: 01.06.2012; Ogledov: 1669; Prenosov: 97
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The complexity of porous structure of building materials
Marko Samec, 2011, doktorska disertacija

Opis: This thesis seeks to establish the link between the structure (in a topological sense) of porous space and charged particle dynamics in porous matter, specifically in constituent elements of sustainable building materials such as clay, cement and soil. The work done is a combination of experimental research and modelling of analysed data using advanced and expanded network models to model pore structure and generalized conductivity model. The main outcome of this doctoral thesis is the demonstration that there is a correlation between the large scale structure of the pore space and the properties of the motion of charged particles through the pore space. This was achieved by conducting two experiments: the structure of pore space of selected porous materials (soil samples, clays, cements, clay-cement mixtures) was investigated using state-of-the-art X-ray computed microtomography, while the dynamics of charged particles in the samples was probed using low-frequency dielectric spectroscopy. The research done and described in the thesis is directed towards the advancement of understanding the transport phenomena and the structure of porous media which is of paramount importance for solving problems in building physics dealing with moist transport in building's envelope, the building-ground interaction, and in transport of contaminants in the vicinity of the repositories where the transfer of moist through soil can be the source of contamination.
Ključne besede: porous matter, clay-water system, hydrating cement, fractional dynamics, dielectric response, X-ray computed tomography, image analysis, complex network
Objavljeno: 11.05.2011; Ogledov: 3913; Prenosov: 184
.pdf Celotno besedilo (34,69 MB)

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