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Dopamine-assisted modification of polypropylene film to attain hydrophilic mineral-rich surfaces
Alenka Ojstršek, Angela Chemelli, Azra Osmić, Selestina Gorgieva, 2023, izvirni znanstveni članek

Opis: 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.
Ključne besede: polypropylene film, dopamine-assisted modification, hydrophilicity, mineralization
Objavljeno v DKUM: 15.03.2024; Ogledov: 236; Prenosov: 4
.pdf Celotno besedilo (3,72 MB)
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Efficiency of laser-shaped photovoltaic cells
Ewa Korzeniewska, Mariusz Tomczyk, Łukasz Pietrzak, Miralem Hadžiselimović, Bojan Štumberger, Klemen Sredenšek, Sebastijan Seme, 2020, izvirni znanstveni članek

Opis: 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.
Ključne besede: photovoltaic cells, efficiency, photovoltaic cell modification, laser modification, silicon cells
Objavljeno v DKUM: 15.11.2023; Ogledov: 338; Prenosov: 15
.pdf Celotno besedilo (16,82 MB)
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Contrasting responses of alien and ancient forest indicator plant species to fragmentation process in the temperate lowland forests
Mirjana Šipek, Lado Kutnar, Aleksander Marinšek, Nina Šajna, 2022, izvirni znanstveni članek

Opis: 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.
Ključne besede: forest fragment, indicator plants, invasion, diversity, habitat modification, habitat conservation
Objavljeno v DKUM: 12.07.2023; Ogledov: 257; Prenosov: 32
.pdf Celotno besedilo (2,16 MB)
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Three-Phase load current reconstruction using singleshunt current measurement and modified vector modulation for three-level DC-AC converter : doctoral dissertation
Haris Kovačević, 2022, doktorska disertacija

Opis: 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.
Ključne besede: single-shunt, three-level inverter, SVM modification, current reconstruction, vector injection
Objavljeno v DKUM: 09.03.2023; Ogledov: 346; Prenosov: 42
.pdf Celotno besedilo (12,21 MB)

Modification of polyamide knitted fabric using different zeolites
Alenka Ojstršek, Tomaž Fakin, Karin Stana-Kleinschek, Darinka Fakin, 2017, izvirni znanstveni članek

Opis: The aim of this research was to apply three different types of zeolites and the combination thereof in the form of a very fine powder, together with different chemicals and additives on polyamide knitted fabric according to an industrially acceptable exhaustion procedure in order to study changes in the morphology, optical properties and wettability of surfaces. Zeolites were analysed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and gas physiosorption. Additionally, the morphology of zeolite-coated surfaces was examined closely using SEM, while changes in molecular-chemical level were examined by means of IR spectroscopy. Optical properties were studied using CIE colour measurement and diff use reflectance profi le determination, while the hydrophilic/hydrophobic character was examined using goniometry. The obtained results show the suitability of the employed exhaustion procedure, depending on the type of zeolite and the composition of the treatment bath. The results also provided evidence of the enhanced wettability of PA fabrics using 4A and 13X zeolites in combination with selected additives.
Ključne besede: zeolites, polyamide fibres, exhaustion, surface modification, wettability
Objavljeno v DKUM: 31.08.2017; Ogledov: 2280; Prenosov: 414
.pdf Celotno besedilo (577,72 KB)
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Chemical modification and characterization of the surface of polysulfone membranes
Irena Kukovičič, Robert Šoster, Milan Brumen, Volker Ribitsch, D. Wiegel, K. Arnold, Črtomir Stropnik, 2000, izvirni znanstveni članek

Opis: Asymmetric porous membranes were prepared from polysulfone by a wet-phase separation procedure. Different chemical modifications were applied to the upper membrane surface, i.e. the surface which was exposed to interaction with nonsolvent (water) in the coagulation bath during the membrane formation. The membrane surface was modified by the series of Friedel-Crafts electrophilic substitutions of aromatic rings in the polysulfone molecules. As a reagent 1-chlorodecane or propylene oxide dissolved in hexane and $AlCl_3$ as a catalyst were used. In the former case a hydrophobic and in the latter one a hydrophilic coating was achieved, respectively. The membrane surface was also modified by sulfonization with sulfuric (VI) acid water solution; in this way negative charges were introduced at the membrane surface. The membranes, unmodified and chemically modified, were characterized by measuring the membrane thickness, the deionized water flux through the membrane, the zeta potential and contact angle. The specific chemical modifications of the membrane surface affect the water flux, the zeta potential and contact angle values whereas the membrane thickness remains unchanged. These effects are interpreted in terms of hydrophilicity and hydrophobicity, changes of the membrane surface charge and the thickness of shear layer at the membrane surface, all with respect to the particular modification applied. Reaction with 1-chlorodecane gave a hydrophobic surface by nonpolar $–(CH_2)_9-CH_3$ groups and reaction with propylene oxide gave a hydrophilic surface with polar group $-CH(CH_3)-CH_2-OH$. The surface of sulfonized polysulfone membranes contained ionizable ($-SO_3H$) functional groups.
Ključne besede: polysulfone, chemical modification, Friedel-Crafts electrophilic substitution, sulfonization, hydrophylicity, hydrophobicity
Objavljeno v DKUM: 17.08.2017; Ogledov: 1439; Prenosov: 119
.pdf Celotno besedilo (82,15 KB)
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Protein adsorption on various plasma-treated polyethylene-terephthalate substrates
Nina Recek, Morana Jaganjac, Metod Kolar, Lidija Milković, Miran Mozetič, Karin Stana-Kleinschek, Alenka Vesel, 2013, izvirni znanstveni članek

Opis: Protein adhesion and cell response to plasma-treated polymer surfaces were studied. The polymer polyethylene terephthalate (PET) was treated in either an oxygen plasma to make the surface hydrophilic, or a tetrafluoromethane CF4 plasma to make the surface hydrophobic. The plasma source was radiofrequency (RF) discharge. The adsorption of albumin and other proteins from a cell-culture medium onto these surfaces was studied using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The cellular response to plasma-treated surfaces was studied as well using an MTT assay and scanning electron microscopy (SEM). The fastest adsorption rate was found on the hydrophilic oxygen plasma-treated sample, and the lowest was found on the pristine untreated sample. Additionally, the amount of adsorbed proteins was higher for the oxygen-plasma-treated surface, and the adsorbed layer was more viscoelastic. In addition, cell adhesion studies support this finding because the best cell adhesion was observed on oxygen-plasma-treated substrates.
Ključne besede: oxygen and fluorine plasma treatment, polymer surface modification, protein adsorption, cell adhesion, quartz crystal microbalance, QCM
Objavljeno v DKUM: 22.06.2017; Ogledov: 1241; Prenosov: 431
.pdf Celotno besedilo (2,39 MB)
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Adapted user-centered design : a strategy for the higher user acceptance of innovative e-health services
Emilija Stojmenova Duh, Bojan Imperl, Tomaž Žohar, Dejan Dinevski, 2012, izvirni znanstveni članek

Opis: Being familiar with all the benefits of e-Health and the strategic plan for the Slovenian health sectors informatization, Telekom Slovenia and the Faculty of Medicine from the University of Maribor, along with other partners, have initiated an e-Health project. The project group is developing various e-Health services that are based on modern ICT (information and communications technology) solutions and will be available on several screens. In order to meet the users needs and expectations and, consequently, achieve the high acceptance of e-Health services, the user-centered design (UCD) approach was employed in the e-Health project. However, during the research it was found that conventional UCD methods are not completely appropriate for older adults: the target population of the e-Health services. That is why the selected UCD methods were modified and adapted for older adults. The modified UCD methods used in the research study are presented in this paper. Using the results of the adapted UCD methods, a prototype for a service named MedReminder was developed. The prototype was evaluated by a group of 12 study participants. The study participants evaluated the MedReminder service as acceptable with a good potential for a high adoption rate among its target population, i.e., older adults.
Ključne besede: ICT, e-Health, MedReminder, user-centered design, modification, adaptation, older adults
Objavljeno v DKUM: 21.06.2017; Ogledov: 1222; Prenosov: 212
.pdf Celotno besedilo (1,04 MB)
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