University of Žilina
  • Žilina, Slovakia
Recent publications
We measure the impact of the bank credit disbursement on Micro, Small and Medium Enterprises (MSME) growth, incorporating the role of regional governors' characteristics in the case of 84 regions of the Russian Federation. Given the considerable heterogeneity across regions, time and reverse causality, we applied the Panel Quantile Regression via Moments (MM-QR) approach to analyze monthly frequency big data (2016M1-2021M1). Our empirical investigation demonstrates that bank credit disbursement and MSME growth follow a non-monotonic relation, implying that up to the specific size of the credit is detrimental, but after surpassing the threshold size, it is supportive to MSME growth under each quantile. Regional governors' political and economic liaison with the federal government impede MSME growth under different quantiles of MSME growth. Our findings further infer that credit market deepening along with firms' individual characteristics are crucial for enterprise performance in the current time of digital transformation. We provide several policy implications.
The article provides an overview of regional economic indicators of the Slovak-Ukrainian borderlands in the period 2010-2020, following the Regional economic performance index ranking. It focuses on economic performance, socioeconomic characteristics, mutual trade, foreign direct investment, and labour migration in the analysed regions. The impacts of the gradual DCFTA implementation are reflected and discussed. Abstract: The article provides an overview of regional economic indicators of the Slovak-Ukrainian borderlands in the period 2010-2020, following the Regional economic performance index ranking. It focuses on economic performance, socioeconomic characteristics, mutual trade, foreign direct investment, and labour migration in the analysed regions. The impacts of the gradual DCFTA implementation are reflected and discussed.
Plasma electrolytic polishing (PEP) is an environment-friendly alternative to the conventional electrochemical polishing (EP), giving optimal surface properties and improved corrosion resistance with minimum energy and time consumption, which leads to both economic and environmental benefits. This paper is focused on the corrosion behavior of PEP treated AISI 316L stainless steel widely used as a biomaterial. Corrosion resistance of plasma electrolytic polished surfaces without/with chemical pretreatment (acid cleaning) is evaluated and compared with original non-treated (as received) surfaces by three independent test methods: electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP), and exposure immersion test. All corrosion tests are carried out in the 0.9 wt.% NaCl solution at a temperature of 37 ± 0.5 °C to simulate the internal environment of a human body. The quality of tested surfaces is also characterized by optical microscopy and by the surface roughness parameters. The results obtained indicated high corrosion resistance of PEP treated surfaces also without chemical pretreatment, which increases the ecological benefits of PEP technology.
3D printing allows controlled deposition of composite components, which the user defines by the modification of the printing parameters. The article demonstrates that all observed printing parameters (infill type, infill orientation) influence the tensile test results of nylon reinforced with chopped carbon fiber. The highest tensile strength obtains specimens with the maximum number of walls around the circumference. The plastic region of the tensile diagram differs significantly with the change of material orientation in the structure, as the specimens with material deposited 45/−45 to the load axis have four times greater tensile strains and 20% higher tensile stresses than 0/90. The assessment of results reveals the significant difference between deformations at break and permanent deformations. In addition, the permanent lateral strain reaches up to 20%. Finally, the article consists of a brief assessment of the printing parameters (printing time, weight) of individual series. The future modelling in FEA software requires additional experiments to verify the viscoelastic properties of the material.
The power system is undergoing significant changes so as to accommodate an increasing amount of renewably generated electricity. In order to facilitate these changes, a shift from the currently employed zonal pricing to nodal pricing is a topic that is receiving increasing interest. To explore alternative pricing mechanisms for the European electricity market, one needs to solve large-scale nodal optimization problems. These are computationally intensive to solve, and a parallelization or sequencing of the models can become necessary. The seasonality of hydro inflows and the issue of myopic foresight that does not display the value in storing water today and utilizing it in the future is a known problem in power system modeling. This work proposes a heuristic step-wise methodology to obtain state of charge profiles for hydro storage units for large-scale nodal and zonal models. Profiles obtained from solving an aggregated model serve as guidance for a nodal model with high spatial and temporal resolution that is solved in sequences. The sequenced problem is guided through soft constraints that are enforced with different sets of penalty factors. The proposed methodology allows for adjustments to congestions on short timescales and proves to perform well in comparison to other approaches to this issue suggested in the literature. Following the input profile closely on a long timescale renders good results for the nodal model.
Spiral plate heat exchangers (SPHEs) are used in industrial applications due to their enhanced thermal performance and tolerance to a soiled stream. The coupling of several SPHEs in series might further improve performance in terms of the effectiveness parameter. In the present study, a compact connection of several SPHE modules is proposed and investigated. For this purpose, a numerical model for the prediction of the effectiveness parameter of a modular SPHE was developed. The model predicted a 2.9% increase in the maximal effectiveness for a two-module SPHE in comparison to a conventional single module SPHE. The temperature profiles of particular streams within the two-module SPHE were predicted. The improved thermal performance and compactness of the modular SPHE configuration observed is advantageous for space-constrained applications.
The current paper provides a review and meta-analysis of the practical implications of disaster risk management related to the ventilated improved latrines in South Africa. This technology is evaluated through its legacy and novel challenges of disaster risk reduction. In the current article, the methodology adopted was a literature review and meta-analyses. The results indicate that the in-situ treatment and breakdown of faecal sludge in the ventilated improved pit latrines is not always taking place and that anaerobic digestion might not always be feasible. New strategies are proposed to manage the sanitation-related risks in South Africa by specifying more exact dimensions for the newly built ventilated improved pit latrines by suggesting the use of novel sanitation additives such as fly ash to enhance on-site and in situ treatment, as well as ex situ treatment of the pit latrine faecal sludge. Regular maintenance can lead to prevention of the dysfunctional character of the ventilated improved pit latrines as a functional sanitation technology and a user-friendly hygiene barrier to the spread of sanitation/WASH-related epidemics or infectious diseases. The implementation of the novel strategies should be enhanced by the application of the (Environ-mental) Technology Assessment in sanitation service delivery in South Africa.
The manufacture of photovoltaic panels for the production of sustainable energy also involves the stage of electrical connection of the cells in the panel structure. This electrical connection is made by soldering of copper strips on the negative electrode of the cell. During the bonding process, due to the temperature of approximately 220-240°C at which the connecting strip is continuously heated, cracking processes of the upper layer of glass from the cell surface were identified. For this reason, it is necessary either to heat to lower temperatures, a solution that is not viable due to the melting temperature of the solder alloy which usually exceeds 210°C, or a different dosing of the heat flux. The solution proposed in the paper is to create a variable heat flux that allows the melting of the solder alloy, but at the same time to reduce the thermal load of the glass support layer. Through the proposed variant, the energy dosing is done with the help of a heating system consisting of two sources, an ultra-acoustic energy source and a classical resistive source. The resistive source provides an amount of energy to ensure a temperature in the range of 60-140°C, the difference to the melting point of the solder alloy being transferred locally by ultrasonic pulses. Research has highlighted the need to limit the range of values of the pressure of the circular sonotrode, which positively influences the mechanical stress of the photovoltaic cell, but also leads to a reduction in the joining speed. The dosing of the two components of the total energy, the one coming from the resistive source and the one coming from the ultra-acoustic vibration source is decisive for the efficiency of the joining process and for the quality of the soldered joint. Microscopic analyses revealed micro-cracks of the glass surface layer at forces higher than 100 N. Areas with lack of soldering for resistive heating at temperatures lower than 130oC were highlighted, the difference of 90-110°C being achieved by the contribution of ultra-acoustic energy.
Sustainable development requires green energy and low carbon footprint in manufacturing sector of photovoltaic systems. The electrical connections of photovoltaic cells need to have low electrical resistance in order to reduce the electrical losses and therefore to improve the performance of the photovoltaic panels. This paper aims to present researches related to bonding of wires that connect solar cells by using microwave technology. The microwave bonding has the main advantage that offers fast bonding but, in the same time, this technology does not offer stability of the thermal heating. Two different unwanted phenomena like thermal runaway and plasma arc discharge often lead to the damaging of copper and aluminum wires used in electrical connection. The study presented in this paper is focused on simulation of the thermal field developed in copper wires in order to optimize the bonding process and increase the quality of products. The simulation of the thermal field has been done using Fourier equations for conducting heating in copper materials and eutectic alloys. The simulation model has been validated through experimental heating using a 6 kW water-cooled microwave generator controlled by a matching load auto-tuner for best transfer of the power from generator to copper wires. The temperature has been measured in real time using an infrared pyrometer for metals with 2.3 μm spectral range and measurement range between 0o C and 7000 C. The study is finalized with elaboration of mathematical model for microwave-injected power as function for temperature developed in copper wires that can be applied with success in further microwave bonding applications of copper wires. In addition, the electrical resistance of bonded wires was measured in order to collect feedback for improving the microwave bonding process.
Capturing particulate matter (PM) is an important issue due to the protection of human health and the quality of their life. This paper describes the innovation of an affordable particulate matter capture device for small heat sources to reduce particulate matter emissions. The design of two investigated variants of the device is based on the principle of a tubular electrostatic precipitator with one charging electrode placed in the chimney. The design of the precipitators is aimed at increasing the area of the collecting electrodes by elements dividing precipitation space, with a simultaneously increased number of charging electrodes. The influence of the elements’ application on the pressure drop and the gas flow velocity through the devices is analyzed by computational fluid dynamics (CFD). The work is further focused on the economic evaluation of precipitators and design adjustments for lower energy consumption. The achieved results show the right direction of efforts to improve the equipment designed to capture PM emissions.
The autonomous movement of the mobile robotic system is a complex problem. If there are dynamic objects in the space when performing this task, the complexity of the solution increases. To avoid collisions, it is necessary to implement a suitable detection algorithm and adjust the trajectory of the robotic system. This work deals with the design of a method for the detection of dynamic objects; based on the outputs of this method, the moving trajectory of the robotic system is modified. The method is based on the SegMatch algorithm, which is based on the scan matching, while the main sensor of the environment is a 2D LiDAR. This method is successfully implemented in an autonomous mobile robotic system, the aim of which is to perform active simultaneous localization and mapping. The result is a collision-free transition through a mapped environment. Matlab is used as the main software tool.
Numerical simulation is a tool used in multiple scientific domains. There is a wide range of simulations where we model a flow of fluid in a specific geometry, for example in simulations of blood flow in microfluidic channels. In such cases, a complex shape of channels has to be defined by describing its boundaries and rigid obstacles. The purpose of this study is develop a method of defining boundaries and obstacle objects with complex and non-trivial shapes in such numerical simulations. The obstacle or a boundary needs to be described only by a cloud of points defining its surface. Based on this point cloud a distance function determining the position and the shape of the obstacle is defined in the whole simulation domain. This general method is presented on a concrete examples involving several simulations performed within a simulation package ESPResSo. The new method of obstacle creation gives excellent results in terms of the accuracy and simulation time consumption.
A driving wheel is a part of a tractor, which transmits forces from a tyre to the ground. Therefore, it affects the tractor movement and the pulling of an implement. The paper is aimed at a tractive performance evaluation of special driving wheels based on drawbar pull at 100%-slip. These wheels consist of steel spikes to be applied in the base or working position. The design is characterized by the spikes placed in a tyre-tread pattern. The rubber lugs of the tyre are higher than spikes, therefore, they are not in contact with the ground in the base position. The spikes in the working position exceed the tyre diameter to be in contact with the ground. Tests were performed on a grass plot at a relatively low soil moisture. The spike tyres were compared with the standard tyres using a sub-compact tractor. An increase in drawbar pull reached a statistically significant value of 15.9% in the 2nd gear and 16.7% in the 1st gear.
In the field of railway operation, it is essential to establish uniform conditions for interconnectivity requirements and compatibility of equipment in the Pan-European railway area to ensure effective interoperability. It also includes, for example, the introduction of a control system with modern and advanced interlocking systems (safety devices). The European Train Control System (ETCS) is a single European train protection system that will increase safety in rail transport. Nevertheless, this system may have an impact on the throughput on those railway lines where it is applied. The main research objective is to determine the impacts and effects of the configuration of track signaling equipment on the operational management of traffic and especially on the creation of a traffic plan. The optimization of transport processes on the railway infrastructure means creating the conditions for achieving higher throughput performance, especially including a higher number of train paths into the train traffic diagram. This paper examines and compares the impacts of ETCS and its levels (in particular ETCS L3) on the practical throughput of the selected national infrastructure manager. A heuristic procedure is used with the application of the analytical methodology of the Railways of the Slovak Republic (ŽSR), which uses the principles of mathematical statistics and probability. Significant comparative indicators are occupancy times and the degree of utilization of practical throughput. These are used in investment decisions in the modernization of line sections to achieve interoperability of the railway system.
The influence of various types of nanoparticle fillers with the same diameter of 20 nm were separately incorporated into a single component impregnating resin based on a polyesterimide (PEI) matrix and its subsequent changes in complex relative permittivity were studied. In this paper, nanoparticles of Al2O3 and ZnO were dispersed into PEI (with 0.5 and 1 wt.%) to prepare nanocomposite polymer. Dielectric frequency spectroscopy was used to measure the dependence of the real and imaginary parts of complex relative permittivity within the frequency range of 1 mHz to 1 MHz at a temperature range from +20 °C to +120 °C. The presence of weight concentration of nanoparticles in the PEI resin has an impact on the segmental dynamics of the polymer chain and changed the charge distribution in the given system. The changes detected in the 1H NMR spectra confirm that dispersed nanoparticles in PEI lead to the formation of loose structures, which results in higher polymer chain mobility. A shift of the local relaxation peaks, corresponding to the α-relaxation process, and higher mobility of the polymer chains in the spectra of imaginary permittivity of the investigated nanocomposites was observed.
The total solar energy transmittance (TSET, g - value) is a parameter of transparent system, which can significantly affect the heat demand for cooling of buildings in the summer. A wide range of progressive transparent and shading systems have been developed and applied to a large number of buildings. Their energy performance and efficiency can be determined using simulation tools or measurements. The methodology for accurate g - value determination is described in ISO 19467: 2017. The aim of the study was to derive and verify an alternative methodology for estimating the total solar energy transmittance of selected specimens of transparent systems in case when the standardized equipment is not available or the aim is not to know the exact TSET value. Window specimens were tested under laboratory conditions, which were retrofitted with elements that improve their original properties in terms of heat transfer coefficient and protection against overheating. In total, three methodologies were designed and described, based on A) monitoring of heat fluxes through glazing, B) monitoring of temperature rise in the hotbox and simulation, and C) determination of the difference in heat fluxes of an irradiated specimen and in the absence of radiation. A solar simulator and a heated hotbox were used for the measurements according to the needs of the chosen methodology. The results from the different approaches for determining g - values differ only slightly but are informative. The conclusion from all measurements is the fact that the tested specimens representing type of windows applicable in building retrofitting showed high potential in terms of reducing heat gains from the sun.
Although there are several articles that have carried out a systematic literature review of the analytical hierarchy process (AHP), many of them work with a limited number of analyzed documents. This article presents a computer-aided systematic literature review of articles related to AHP. The objectives are: (i) to identify AHP usage and research impact in different subject areas; (ii) to identify trends in the popularity of the AHP from the first introduction of the method in 1980 to the present; (iii) to identify the most common topics related to AHP and topic development over time. We process 35,430 documents related to AHP, published between 1980 and 2021, retrieved from the Scopus database. We provide detailed statistics about research interest, research impact in particular subject areas over the analyzed time period. We use Latent Dirichlet Allocation (LDA) using Gibbs sampling to perform topic modeling based on the corpus of abstracts. We identify nine topics related to AHP: Ecology & Ecosystems; Multi-criteria decision-making; Production and performance management; Sustainable development; Computer network, optimization and algorithms; Service quality; Fuzzy logic; Systematic evaluation; Risk assessment. We also present the individual topics trends over time and point out the possible future direction of AHP.
To participate fully in society, a person needs to critically evaluate statistical information. To be able to do this, it is appropriate to start developing the statistical literacy of young people in diverse levels in schools. In our article, we present a modified seminar on statistics for prospective humanities teachers. During the seminar, we planned a pedagogical experiment, the aim of which was to statistically verify the students’ own diagnostic competencies as prospective teachers of humanities. The statistical analysis confirmed that the implementation of real research into the course on statistics has a positive impact on the development of statistical literacy but does not change the attitude of students toward statistics and its use in the future teaching practice.
The scientific community in Central Europe often discusses the extent to which temperature changes over the last two decades have contributed to changing the stresses induced in structures. In the field of road and environmental engineering, this question is especially pertinent for pavements. The pavement structure must first be defined methodologically by identifying and defining the types of parameters that change with time. Additionally, it is important to identify the areas of Central Europe that are most affected by climate change. The most important parameters must be described statistically for these areas. Slovakia is one of the countries that may be able to contribute to the solution of this issue due to its location in the middle of Europe. This paper provides a statistical analysis for the period from 1971 to 2020 in Slovakia. A concrete pavement, which is the most commonly used type of pavement, must be used as an example to numerical assess the situation. The conclusions and discussion in this scientific field are directed towards the evaluation of the measurement results in the context of the designed pavement composition and the calculations using the different methods specified in the standards.
This paperwork is focused on the quality of AlSi6Cu4 casting with different wall thicknesses cast into the metal mold. Investigated are structural changes (the morphology, size, and distribution of structural components). The quantitative analysis is used to numerically evaluate the size and area fraction of structural parameters (α-phase, eutectic Si, intermetallic phases) between delivered experimental material and cast with different wall thicknesses. Additionally, the Brinell hardness is performed to obtain the mechanical property benefits of the thin-walled alloys. This research leads to the conclusion, that the AlSi6Cu4 alloy from metal mold has finer structural components, especially in small wall thicknesses, and thus has better mechanical properties (Brinell hardness). These secondary Al-castings have a high potential for use in the automotive industry, due to the thin thicknesses and thus lightweight of the construction
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2,454 members
Martin Klimo
  • Department of Information Networks
Lubos Buzna
  • Department of Mathematical Methods and Operations Research
Michal Frivaldsky
  • Department of Mechatronics and Electronics (DME)
Norbert Tarjányi
  • Department of Physics (DPh)
Mikulas Gintner
  • Department of Physics (DPh)
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Address
Univerzitna 8215/1, 01026, Žilina, Slovakia
Head of institution
prof. Ing. Jozef Jandačka, PhD.
Website
www.uniza.sk