1. Engineering Materials and Process Technologies : 2nd Conference of Programme Groups of the Faculty of Mechanical Engineering University of Maribor, Book of Abstracts2025 Abstract: The publication presents an overview of the research achievements of Programm Groups of the Faculty of Mechanical Engineering: P2-0424 Design of Novel Properties of (Nano)Materials & Applications, P2-0063 Design of Cellular Structures, P2-0120 Technologies of Metastable Materials, P2-0118 Textile Chemistry and Advanced Textile Materials, and P2-0196 Research in Power, Process, and Environmental Engineering from 2024 to 2025. Members of the program group present their research innovations and progress achieved within the framework of the program group's activities.
Keywords: advanced textile materials, composites, nanomaterials, biotechnology, surface functionalization and modification, cellular structures, metastable materials, power, process and environmental engineering
Published in DKUM: 03.11.2025; Views: 0; Downloads: 2
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2. Non-equilibrium plasma methods for tailoring surface properties of polyvinylidene fluoride : review and challengesAlenka Vesel, Rok Zaplotnik, Gregor Primc, Miran Mozetič, Tadeja Katan, Rupert Kargl, Tamilselvan Mohan, Karin Stana-Kleinschek, 2021, review article Abstract: Modification and functionalization of polymer surface properties is desired in numerous
applications, and a standard technique is a treatment with non-equilibrium gaseous plasma. Fluorinated polymers exhibit specific properties and are regarded as difficult to functionalize with polar
functional groups. Plasma methods for functionalization of polyvinylidene fluoride (PVDF) are
reviewed and different mechanisms involved in the surface modification are presented and explained
by the interaction of various reactive species and far ultraviolet radiation. Most authors used argon
plasma but reported various results. The discrepancy between the reported results is explained
by peculiarities of the experimental systems and illustrated by three mechanisms. More versatile
reaction mechanisms were reported by authors who used oxygen plasma for surface modification
of PVDF, while plasma sustained in other gases was rarely used. The results reported by various
authors are analyzed, and correlations are drawn where feasible. The processing parameters reported
by different authors were the gas pressure and purity, the discharge configuration and power, while
the surface finish was predominantly determined by X-ray photoelectron spectroscopy (XPS) and
static water contact angle (WCA). A reasonably good correlation was found between the surface
wettability as probed by WCA and the oxygen concentration as probed by XPS, but there is hardly
any correlation between the discharge parameters and the wettability.
Keywords: polyvinylidene fluoride, gaseous plasma, surface modification, wettability, functionalization, activation plazma
Published in DKUM: 16.06.2025; Views: 0; Downloads: 8
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3. Efficient modification of the CRAFT algorithm for layout optimisationBorut Buchmeister, Aljaž Javernik, Robert Ojsteršek, Iztok Palčič, 2025, original scientific article Abstract: Every combination of product mix and production volume requires a suitable layout of workplaces (functional units). An optimised layout is of utmost importance to achieve global competitiveness of companies and to build an efficient, sustainable production. We plan the layout mainly with heuristic methods; constructive, improvement and combined methods are available. In this paper, a modification of the established improvement algorithm CRAFT (exchange method) is presented, which provides much better and more accurate results at a slightly higher computational cost. The most important change is the immediate precise determination of the centroids of the areas of workplaces (or departments) that are exchanged. The distance between any two workplaces is represented by the orthogonal distance between the centroids. In the example given, which is based on a pairwise exchange, the difference is 22 % in favour of the modified algorithm.
Keywords: algorithm modification, CRAFT method, layout optimisation, pair-wise exchanges, production layout
Published in DKUM: 21.05.2025; Views: 0; Downloads: 11
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4. A method for the immobilization of chitosan onto urinary cathetersAlenka Vesel, Nina Recek, Rok Zaplotnik, Albert Kurinčič, Katja Kuzmič, Lidija Fras Zemljič, 2022, original scientific article Abstract: A method for the immobilization of an antibacterial chitosan coating to polymeric urinary medical catheters is presented. The method comprises a two-step plasma-treatment procedure, followed by the deposition of chitosan from the water solution. In the first plasma step, the urinary catheter is treated with vacuum-ultraviolet radiation to break bonds in the polymer surface film and create dangling bonds, which are occupied by hydrogen atoms. In the second plasma step, polymeric catheters are treated with atomic oxygen to form oxygen-containing surface functional groups acting as binding sites for chitosan. The presence of oxygen functional groups also causes a transformation of the hydrophobic polymer surface to hydrophilic, thus enabling uniform wetting and improved adsorption of the chitosan coating. The wettability was measured by the sessile-drop method, while the surface composition and structure were measured by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Non-treated samples did not exhibit successful chitosan immobilization. The effect of plasma treatment on immobilization was explained by noncovalent interactions such as electrostatic interactions and hydrogen bonds.
Keywords: polymer, chitosan immobilization, adhesion, plasma-surface modification, biopolymers
Published in DKUM: 05.12.2024; Views: 0; Downloads: 13
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5. Multifunctional iron oxide nanoparticles as promising magnetic biomaterials in drug elivery : a ǂreviewKatja Vasić, Željko Knez, Maja Leitgeb, 2024, review article Keywords: multifunctional biomaterials, bio-composites, nanocarriers, magnetic nanoparticles, modification, drug delivery
Published in DKUM: 20.08.2024; Views: 72; Downloads: 17
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7. Dopamine-assisted modification of polypropylene film to attain hydrophilic mineral-rich surfacesAlenka Ojstršek, Angela Chemelli, Azra Osmić, Selestina Gorgieva, 2023, original scientific article Abstract: The presented study focuses on the modification of polypropylene (PP) film with tetraethyl orthosilicate (TEOS) under heterogeneous conditions via polydopamine/polyethylene imine (PDA/PEI) chemistry using a facile dip-coating procedure to attain hydrophilic mineral-rich surfaces. Thus, the resulting PP-based films were further immersed in ion-rich simulated body fluid (SBF) to deposit Ca-based minerals onto the film’s surfaces efficiently. In addition, the chemical reaction mechanism on PP film was proposed, and mineralisation potential inspected by determination of functional groups of deposits, zeta potential, hydrophilicity and surface morphology/topography using Fourier transform infrared (FTIR) spectroscopy, streaming potential, water contact angle (WCA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The obtained results show the improved wettability of samples on account of PDA inclusion (WCA was reduced from 103° for pure PP film to 28° for PDA-modified film), as well as the presence of functional groups, due to the PDA/PEI/TEOS surface functionalisation, increased the ability of minerals to nucleate on the PP film’s surface when it was exposed to an SBF medium. Moreover, the higher surface roughness due to the silica coatings influenced the enhanced anchoring and attachment of calcium phosphate (CaP), revealing the potential of such a facile approach to modify the chemically inert PP films, being of particular interest in different fields, including regenerative medicine.
Keywords: polypropylene film, dopamine-assisted modification, hydrophilicity, mineralization
Published in DKUM: 15.03.2024; Views: 300; Downloads: 9
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8. Efficiency of laser-shaped photovoltaic cellsEwa Korzeniewska, Mariusz Tomczyk, Łukasz Pietrzak, Miralem Hadžiselimović, Bojan Štumberger, Klemen Sredenšek, Sebastijan Seme, 2020, original scientific article Abstract: The main aim of this paper is to analyze the influence of laser shaping of the photovoltaic cell based on its efficiency. The authors described both process of the monocrystalline photovoltaic cell manufacturing, its efficiency, and the possibilities of usage in architecture and the process of creating the photovoltaic cells of unconventional shapes by using laser technology. A method for cutting photovoltaic cells using a fiber laser was presented as well as the parameters of the laser cutting process. The described method allows cutting the massively produced silicon cells according to the predetermined trajectory. Using the proposed process parameters, satisfactory cutting edge quality, and negligible impact of the laser beam on changes in the structure of the photovoltaic cell active layers were achieved. In each cycle of structure cutting, only a small part of the material is removed (from 1 to 2 mikro), and depending on the thickness, the process is repeated from 50 to 300 times. It has been shown that the efficiency of the modified cells depends on the ratio of their surface area to the laser cutting line.
Keywords: photovoltaic cells, efficiency, photovoltaic cell modification, laser modification, silicon cells
Published in DKUM: 15.11.2023; Views: 389; Downloads: 29
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9. Contrasting responses of alien and ancient forest indicator plant species to fragmentation process in the temperate lowland forestsMirjana Šipek, Lado Kutnar, Aleksander Marinšek, Nina Šajna, 2022, original scientific article Abstract: Fragmentation is one of the major threats to biodiversity. In a fragmented landscape, forest specialists are losing suitable forest habitats with specific site and microclimate conditions, which results in their local extinction. Conversely, the invasion of alien species is facilitated by open forest areas and increased boundaries between forest fragments and adjacent land. We studied the effect of fragmentation in terms of fragment size impact on overall plant species richness and on selected ecologically important groups' richness, composition, and diversity. We surveyed vegetation in the interior of 47 fragments of various sizes and one unfragmented reference forest. Our results reveal that the effect of fragmentation is complex and differs for studied plant groups. Decreasing fragment size negatively affects the overall plant richness and richness of native and ancient forest indicator plants as well as their diversity, while the effect is positive for alien plants. The highest proportion of ancient forest indicator plant species and the lowest proportion of alien plants in the unfragmented forest underline the great conservation value of forest fragments. At the same time, our results reveal that large and diverse forest ecosystems are susceptible to biological invasions as well.
Keywords: forest fragment, indicator plants, invasion, diversity, habitat modification, habitat conservation
Published in DKUM: 12.07.2023; Views: 313; Downloads: 60
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10. Three-Phase load current reconstruction using singleshunt current measurement and modified vector modulation for three-level DC-AC converter : doctoral dissertationHaris Kovačević, 2022, doctoral dissertation Abstract: This doctoral thesis focuses on the development of Space Vector Modulation (SVM) techniques adjusted for single-shunt current measurement and applied to the three-level three-phase voltage source inverter. Based on the single-shunt current measurement, three-phase load currents are then reconstructed.
An overview of existing multilevel topologies and their main operating principles is provided within the thesis. To evaluate proposed SVM techniques adjusted for single-shunt current measurement, a three-level three-phase diode clamped voltage source inverter topology is selected. The main advantages of the selected topology are high efficiency, reduced semiconductor stress, the low capacitance of DC-link capacitors, etc. To reconstruct the three-phase load currents, a single-shunt is positioned inside the middle branch of the DC-link.
An overview of existing modulation techniques for two-level and multilevel inverters is provided within the thesis. To reconstruct three-phase load currents, three SVM methods are proposed within the thesis. Due to the lack of a current measurement window, while the voltage vector is positioned near sector or region boundary areas, additional modifications are required. The first SVM method shifts the SVM signals to ensure the minimum current measurement window needed for measurement with minimum additional vector injection. Such an approach ensures the high modulation index values greater than 0.8 with the smallest current ripple due to the SVM signal symmetry. The second method intentionally injects the colinear voltage vector into the existing vector combination to ensure the minimum time window required for current measurement. As a drawback, a smaller modulation index compared to the first method can be achieved. As an advantage, a very low modulation index of less than 0.2 can be achieved. The third method simplifies the second method by using a single SVM pattern. Such a method can be used only for very low modulation indexes and can be applied for two-level and three-level inverters.
The proposed SVM methods are implemented within the Digital Signal Processor (DSP). Experimental results confirm the proper operation of the proposed methods applied to the three-level diode clamped voltage source inverter.
Keywords: single-shunt, three-level inverter, SVM modification, current reconstruction, vector injection
Published in DKUM: 09.03.2023; Views: 396; Downloads: 85
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