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21.
NONDESTRUCTIVE THERMAL, OPTICAL, CHEMICAL AND STRUCTURAL CHARACTERIZATION OF ADVANCED MATERIALS BY OPTOTHERMAL TECHNIQUES
Hanna Budasheva, doktorska disertacija

Opis: Advanced materials are promising ones in application in fields where it is necessary to decrease energy consumption and ensure better performance at a lower cost. They are materials, which have enhanced properties compared to conventional materials in the field of their applications.1 The huge group of them contributes significantly to every aspect of our lives. Among them, chosen for the present study, are resins for passive sampling of iron species in natural water and sediments, anticorrosive coatings, and multilayered polysaccharide aerogels for medical applications. The composition and structure of each material determine its chemical, mechanical and physical properties, consequently their performance.2 The ability to use advanced materials in areas where their impact will be significant is largely dependent on the ability to precisely determine their characteristics to identify their properties that are either unique or has a better value. Therefore, the development of new methods or improvement of already known ones will make a great contribution to the development of the fields of application of the selected materials. The present study is focused on the examination of the chosen materials by determining their optical, chemical, thermal and structural properties for applying them further in the desired applications. To provide the needed characterization, optothermal techniques such as optothermal beam deflection spectrometry (BDS) and thermal lens spectrometry (TLS) are developed and applied. This dissertation is composed of the following chapters: introduction, theoretical background, optothermal techniques, research goal, part I (gels for passive sampling of iron species in natural water and sediments), part II (anticorrosive coatings), part II (polysaccharide aerogels), references. The core of this dissertation is presented in chapters 5 to 7. Each of the chapters separately covers the information about a selected group of advanced materials, including the sections describing sample preparation, developing the required characterization method, results, and conclusion. The connection link of these chapters is the study of the diffusion process of iron into different types of binding gels in passive samplers; external composites through the anticorrosive layers; drugs into the surrounding during the drug delivery process. In Part I, the BDS method for the study was chosen, it was optimized, and a detailed protocol was developed for the determination of iron in passive sampler gels. The iron residues in the initial solutions were checked by a suitably tuned TLS method. The developed technique was applied to get the iron species distribution in the gel samples deposited in the sediments in the Vrtojbica River. The method was applied to the gels applied on ice from Antarctica in order to obtain the iron species distribution on its surface as well. The obtained results were validated using the TLS, UV-Vis and ICP-MS methods. The chapter contains the analysis of the Fe diffusion depth into the resin sampler, which is presented for the first time. The information is obtained by using the mathematical model and applying it to the obtained practical results by frequency scanning of the gels. The crucial information about the thermal properties of their layers containing Fe-ions from the fitting procedure was extracted. On the basis of these results, information about the diffusion depth of Fe inside the gels was obtained, which has not been previously described in the literature. In Part II, the porosity in the anticorrosion coatings on the basis of their thermal parameters was determined. For the first time, the opened porosity was extracted from the total one. The analysis of Si/Zr-based hybrid sol-gel coatings has shown that the addition of cerium salts into the sol-gel matrix produces changes in its physical, chemical and corrosion properties. And it was found that the sample with the biggest amount of incorporated zirconium and loaded with cerium has the lowest values of porosity and, hence, the best barrier properties of the coating. The obtained thermal parameters of the Si/Zr-based hybrid sol-gel coatings by BDS were validated by the use of the photothermal radiometry method. On the other hand, the analysis of siloxane methacrylate coating has shown that the sol-gel hybrid methodology offers an important route for modification of thermal properties by a combination of inorganic to organic contents where the former than as an integral part of the coating network affects the thermal properties without the need for introducing fillers or nanoparticles. In Part III, the multilayered structure of the samples, containing hyaluronic acid, amoxicillin and fucoidan layers deposited on stainless support has been analyzed by the use of the BDS technique. The thermal parameters of each layer were determined, as well as their thickness. The results revealed the diffusion between neighboring layers and followed changes in the properties of the whole sample, which is reflected in its thermal properties. Such data for multilayered materials, which potentially can be used for drug delivery systems, are presented for the first time. Presented results indicated the ability of the BDS system for the chemical characterisation of the solid materials, the detection of their thermal parameters; investigation of total, opened and closed porosity; determining the thickness of layers in multilayered structures. The TLS method served as the validating one for the purpose of getting comprehensive information in liquid samples about their chemical composition. In summary, this dissertation explores alternative ways to apply optothermal methods to various areas of advanced materials to characterize them in order to improve their initial properties.
Ključne besede: optothermal beam deflection spectrometry, thermal lens spectrometry, diffusive gradients in thin films, iron species, anticorrosive layers, porosity, polysaccharide aerogels, multilayered structures
Objavljeno v RUNG: 29.08.2022; Ogledov: 1885; Prenosov: 55
.pdf Celotno besedilo (5,46 MB)

22.
Synthesis and application of transition metal phosphide nanomaterials as electrocatalysts for water splitting and chemical transformations : dissertation
Takwa Chouki, 2022, doktorska disertacija

Opis: In this thesis, we will focus on the solvothermal synthesis of iron phosphides (FeP, Fe2P) using triphenylphosphine (TPP) as an inexpensive and stable phosphorus source. The obtained iron phosphides were applied as electrocatalysts in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), Rhodamine B (RhB) degradation, Escherichia coli (E. coli) inactivation, nitrates reduction reaction (NO3RR) to ammonia (NH3), and as counter electrodes in dye-sensitized solar cells (DSSCs). Detailed characterizations of catalysts were carried out to investigate the correlations between the material structure and catalytic activity. The first part of the thesis gives an introduction to the topic which cover overview of literature about the use of transition metal phosphide as efficient electrocatalysts in water splitting studies, NO3RR to NH3 and DSSCs. The second part is a description of the experimental methods. The third part discusses the solvothermal synthesis of FeP and Fe2P catalysts using TPP precursor. The phase conversion of iron phosphides at elevated temperatures under reductive atmosphere was reported. Structural characterizations of the obtained materials were achieved using multiple techniques. The electrocatalytic activities of heat-treated iron phosphide films for HER were studied in acidic environment. The fourth part discusses the use of Fe2P nanoparticles (NPs) for OER. The fifth part outlines the use of Fe2P precatalyst in water treatment studies. Using a thin film of Fe2P precatalyst, RhB degradation and E. coli inactivation in the presence of in-situ generated reactive chlorine species were reported. Characterization of Fe2P electrocatalysts before and after the test was carried out using different techniques. The sixth part shows for the first time the use of FeP and Fe2P as a noble metal-free electrocatalysts for NO3RR to NH3. In this chapter we will emphasize the nitrate reaction pathways, which are highly complex and poorly understood. The seventh part demonstrates the use of FeP and Fe2P catalysts as robust and efficient counter electrodes in DSSCs.
Ključne besede: solvothermal synthesis, iron phosphides, electrocatalysis, HER, OER, RhB degradation, E. coli inactivation, NO3RR to NH3, DSSCs, dissertations
Objavljeno v RUNG: 29.08.2022; Ogledov: 1747; Prenosov: 95
.pdf Celotno besedilo (6,35 MB)
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23.
Exploration of yeast biodiversity potential for development of alternative biofungicides in viticulture : dissertation
Rowland Adesida, 2022, doktorska disertacija

Opis: Botrytis cinerea Pers., the fungal plant pathogen and the causal agent of gray mould diseases in grapevine, is vastly responsible for substantial economic losses in table and wine grapes production worldwide by negatively affecting plant growth and causing the reduction of grape and wine quality. The conventional approach for pathogen control has been up to date based on synthetic fungicides with good effectiveness against pathogens but a negative impact on the environment. The growing level of harmful residues in the environment and some also detected in wines have led the European Union and many winemakers to limit the application of synthetic fungicides to earlier season. However, with a high risk of disease also late in the season, the need for other solutions is clear. Consequently, more and more research is focused on finding potential alternatives in the form of effective biological control agents. Although there are several reports of yeast’s biocontrol activity, they are up to date still poorly commercialized for such purposes. As the yeasts represent an important part of the grape microflora, competing with other microorganisms (including pathogens) for nutrients and space, we decided to examine the potential of autochthonous yeasts as "green" alternatives in fighting against phytopathogens such as B. cinerea in viticulture. With this aim, we tested the biocontrol activity of 119 different indigenous yeasts belonging to 30 different species of 17 genera against filamentous fungus B. cinerea, the causal agent of grey mould or botrytis bunch rot in grape. The yeasts were screened for putative multidimensional modes of action such as antifungal volatiles (VOC), in vitro inhibition of fungal mycelial growth, competition for nutrients, hydrolytic enzyme activities, and yeast tolerance to fungicides like copper, iprodione and cyprodinil/fludioxonil combination. With a qualitative detection of the hydrolysis activity by using screening methods based on solid medium with chitin or βD-glucosides as substrates, we found that many tested yeasts were capable of producing lytic enzymes with the ability to degrade the cell wall of phytopathogenic fungi and are potentially also able to produce VOCs via hydrolysis of grape glycosides as a result of β-glucosidase presence. Furthermore, we observed the capability of tested yeast to inhibit fungal mycelia growth on plate and assimilation of a wide variety of carbon sources; however, no siderophore producers were detected. In general, the yeasts under observation were tolerant to the tested fungicides. Their fungicide resistance can indeed be regarded as a beneficial trait for potential biofungicide agent (PBA) candidates due to open possibilities of applications and combinations within low input pest management strategies in the vineyard. Finally, a field experiment in Pinot noir and Pinot gris vineyards was designed to study different combinations of optimized canopy microclimate manipulation (CMM) techniques and potential biocontrol agent (PBA) application. In experimental conditions, the ability of PBA’s to maintain appropriate population density for disease prevention was observed. In addition, the grape and wine quality parameters were analysed to observe the possible impact of implemented biocontrol yeast on final products. The biocontrol yeast Pichia guilliermondii ZIM 624 was selected and applied in experimental vineyards based on yeast testing results. We were able to detect and confirm PBA yeast’s suitable density on grapes until harvest. In the case of early defoliation for both varieties lower grape compactness was observed together with lower yield/ plant, regardless of PBA yeast/ no yeast application. Among grape basic quality parameters, the optimized techniques showed a positive effect on sugar content. Still, unexpectedly, in the treatments with biocontrol yeasts some trends toward higher acidity were noticed in Pinot gris.
Ključne besede: sustainable viticulture, Botrytis cinerea, gray mould, yeasts, biocontrol, canopy microclimate manipulation, grapevine metabolite, dissertations
Objavljeno v RUNG: 07.07.2022; Ogledov: 1712; Prenosov: 132
.pdf Celotno besedilo (4,17 MB)
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24.
CO2 dynamics and dissolutional processes in the karst vadose zone
Lovel Kukuljan, 2022, doktorska disertacija

Opis: The dynamics and distribution of carbon dioxide (CO2) in karst systems are crucial for understanding fundamental karst processes, namely precipitation and dissolution, which drive karst development both at the surface and underground. The study of CO2 transport provides valuable insights into the role of karst systems in the global carbon cycle and the impact on present climate, but also into the growth of speleothems, which are one of the most reliable terrestrial archives for palaeoclimate reconstruction. Due to the complexity of karst systems, long-term monitoring and high-resolution analyses of cave air and water geochemistry are essential to better understand the controlling factors that affect these processes and their outcomes. In the framework of this dissertation, cave climate and water hydrochemistry monitoring was established in a side-passages of the renowned Postojna Cave in Slovenia during 2017–2021. In the Pisani Passage, high CO2 concentrations, large temporal variations and a heterogeneous distribution of CO2, as well as extreme dissolution features, have already been detected in previous studies. The aim of the present study was to investigate these observations in depth and to find the reasons for their occurrence. This led to creating of a conceptual model for CO2 transport in karst systems that would be valid not only in this case but in karst areas worldwide. The first focus of the study is dedicated to understanding the spatio-temporal dynamics of the partial pressure of CO2 (pCO2) in the Pisani Passage, which is mainly transported by advection (i.e., cave ventilation). Continuous measurements of airflow velocity, air temperature and pCO2 showed (1) that airflow through the karst massif is driven by both the action of the chimney effect and external winds, and (2) that the relationship between the direction of airflow, the configuration of airflow pathways and the connection to the outside explains the observed variations in pCO2. Due to the particular configuration of the airflow pathways, the terminal chamber of Pisani Passage accumulates high levels of CO2 (>10,000 ppm) and forms high vertical gradients of up to 1000 ppm/m. The pCO2 is low and uniform during updraft when outside air flows into the cave chamber through open, unobstructed passages (i.e., high-flow, low-pCO2 pathways). When the airflow reverses direction to downdraft, the chamber is fed by low-flow, high-pCO2 pathways that enter the cave passage through a CO2-rich fracture network embedded in a vadose zone. The spatial distribution of inlets and outlets results in minimal mixing between the low and high pCO2 pathways, leading to high and persistent pCO2 gradients. In addition to the chimney effect driving the seasonal ventilation of the cave, the specific signs of a secondary wind-driven effect were also found; which is the second focus of this study. Wind flow over irregular topography leads to near-surface air pressure variations, and thus, pressure differences between cave entrances at different locations. Pressure differences depend on wind speed and direction and their relationship to surface topography and the location of cave entrances. Winds can act in the same or opposite direction as the chimney effect, either enhancing, diminishing or even reversing the direction of density-driven airflows. In the case of Postojna Cave, north and northeast winds enhance the downdraft and limit updraft, while the opposite is true for south winds, which enhance the updraft and limit downdraft. To investigate the importance of wind-driven flow, a computational fluid dynamics model was used to calculate the wind pressure field over Postojna Cave and the pressure differences between selected points for different configurations of wind speed and direction. These values were compared with those obtained from airflow measurements in the cave and from simple theoretical considerations. Despite the simplicity of the approach and the complexity of the ca
Ključne besede: cave climate, cave ventilation, carbon dioxide, dripwater geochemistry, speleothem corrosion, Postojna Cave, Slovenia
Objavljeno v RUNG: 22.06.2022; Ogledov: 1681; Prenosov: 66
.pdf Celotno besedilo (8,45 MB)

25.
Reducibility in algebraic hyperstructures : PhD thesis
Milica Kankaras, 2022, doktorska disertacija

Objavljeno v RUNG: 05.05.2022; Ogledov: 1380; Prenosov: 0

26.
Unravelling the molecular basis of hydroxyapatite weathering driven by the ectomycorrhizal fungus Paxillus involutus
Christina Paparokidou, 2018, doktorska disertacija

Opis: Ectomycorrhizal fungi (EMF) form symbiotic partnerships with tree roots and are able to chemically weather inorganic phosphorus (Pi)-rich minerals, supplying Pi to their host in return for photosynthates. The fungal-driven nutrient cycling from mineral weathering plays a pivotal role in ecosystems and crops productivity, as well as geochemical cycles. The aim of the study presented in this thesis is to unravel the molecular mechanisms by which the EM fungus Paxillus involutus weathers the Pi-rich mineral hydroxyapatite (HAP), either non-symbiotically or in symbiosis with its host tree Pinus sylvestris. Development of an artificial system to study P. involutus responses to varying concentration of Pi led to the identification of five high-affinity Pi transporter genes, of which the expression varies in an inversely proportional manner to Pi availability. Using the same system, whole-transcriptomic data from fungal hyphae unravelled the molecular basis of the EMF ability in Pi uptake at the global gene scale, revealing that EM symbiosis can directly affect Pi-responsive fungal genes such as the Pi transporter PiPT4. A second artificial system was used to study HAP solubilisation driven by P. involutus, which was confirmed by EDX spectroscopy data showing depletion of Pi from the HAP crystals, along with secondary minerals formation. Whole-transcriptomic analysis revealed that EM symbiosis induces a different set of HAP weathering genes in P. involutus hyphae, compared to the fungus growing non-symbiotically, including the specific expression of organic acid metabolic genes, which resulted in enhanced HAP solubilisation. Metabolomic analysis led to the identification of multiple secreted metabolites enriched in the presence of HAP in P. involutus systems grown non-symbiotically or in symbiosis with P. sylvestris seedlings. The analysis also led to the identification of putative novel fungal weathering agents. Results from transcriptomic and metabolomic analyses were ultimately combined in a model of HAP weathering by P. involutus.
Ključne besede: Paxillus involutus, Pinus sylvestris, ectomycorrhizal symbiosis, hydroxyapatite, SEM-EDX, fungal mineral weathering, fungal weathering metabolites, RNA-seq, UPLC-Q-TOF-MS
Objavljeno v RUNG: 03.05.2022; Ogledov: 1382; Prenosov: 0
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28.
Characterization of a karst aquifer in the recharge area of Malenščica and Unica springs based on spatial and temporal variations of natural tracers
Blaž Kogovšek, 2022, doktorska disertacija

Opis: The aim of the present study is to characterize and improve the still insufficient knowledge of the recharge processes that have an important influence on the flow and solute transport in karst aquifers and thus also on the quantity and quality of karst water sources. A binary karst aquifer in the recharge area of the Malenščica and Unica springs, which covers an area of about 820 km2 in SW Slovenia, was selected as the study area. A dense monitoring network was established at 20 observation points (six springs, four ponors, seven water-active caves and three surface streams) for simultaneous monitoring of the hydrological characteristics and the physicochemical properties of the water, the so-called natural tracers. Data-loggers were installed to measure water pressure, temperature and conductivity. During selected storm events, samples were taken for chemical and microbiological analyses and discharge measurements were made. The meteorological and hydrological data of the Slovenian Environment Agency complemented the extensive dataset. Collected data allowed the analysis and comparison of the spatial and temporal variations of the natural tracers under different hydrological conditions. Frequent discharge measurements allowed the generation of rating curves and proved to be a crucial element for understanding the hydraulic processes that determine the functioning of this system. The calculation of the water budget allowed an assessment of the proportion of autogenic and allogenic recharge of the springs and a quantitative estimate of autogenic recharge under different hydrological conditions. The hydrological analysis, i.e. the flow duration curve, the hydrograph separation techniques and the recession analysis, revealed that the Malenščica spring has a higher storage capacity, a greater proportion of autogenic recharge, especially at low-flow, and a slower recession than the Unica spring. This was also confirmed by correlation and spectral analyses, which were also used to investigate the relationships between discharges at ponors and springs. However, the results of the cross-correlation analysis showed hardly any difference between the two springs and in this case proved to be unsuitable for studying the influence of allogenic recharge. Instead, partial cross-correlation analysis was used to control the input parameters of effective precipitation and discharge of one of the sinking streams to determine the contribution of the other sinking stream to the observed spring. The results confirmed differences in allogenic recharge of the Unica and Malenščica springs. Hysteresis analysis has been applied as a complementary method to time series analysis and represents an improved approach to the characterization of the karst hydrological system. The hydraulic approach to the construction of hysteresis enabled a detailed analysis of allogenic and autogenic water interaction and its influence on the Malenščica and Unica springs under different hydrological conditions. Narrow shapes of the hysteresis indicate a direct hydraulic connection between the ponor and the spring and thus a well-developed drainage system. Any deviation towards a convex or concave shape indicates a less developed, more matrix-related drainage system or the influence of other recharge sources. Analysis of physicochemical hysteretic function of individual locations confirmed the differences in the recharge characteristics of the two springs. Compared to the Unica spring, the Malenščica spring has specific recharge characteristics that result in lower vulnerability to the effects of the sinking streams. A greater proportion of autogenic recharge in the initial phase of the storm event is important, as it allows for a time delay of the possible negative effects of the sinking stream. However, possible pollution from the area of autogenic recharge can have strong negative effects, as in this initial phase with low discharges the dilution effect is negligible.
Ključne besede: karst aquifer, dynamics of natural tracers, storm events, discharge measurements, time series analysis, hysteresis, Unica spring, Malenščica spring
Objavljeno v RUNG: 01.03.2022; Ogledov: 2078; Prenosov: 94
.pdf Celotno besedilo (18,38 MB)

29.
Novel analytical approaches in quality and safety control in production of fermented beverages : dissertation
Jelena Topić, 2022, doktorska disertacija

Opis: The exploitation of microorganisms for fermentation goes back centuries. Two types of fermentation are usually used in the winemaking process – alcoholic fermentation and malolactic fermentation. Nowadays, inoculated fermentations with the use of starter cultures are commonly used in order to produce wine with more consistent quality. However, wines can lack in flavour complexity, so scientists and the industry are constantly looking for new and improved starters that can be adapted to different types of wine. In this work we focused on the development and implementation of novel analytical methods for wine quality control. In the course of method development native yeasts and lactic acid bacteria isolates were characterized for wine starter properties. We focused on the determination of biologically active compounds that determine wine quality and safety. Yeasts can influence wine colour through their adsorption capacity and synthesis of stable colour pigments pyranoanthocyanins and lactic acid bacteria can produce biogenic amines which can have adverse detrimental health effects on sensitive consumers when they are present in wines.
Ključne besede: Saccharomyces yeasts, non-Saccharomyces yeasts, pyranoanthocyanins, thermal-lens spectrometry, lactic acid bacteria, biogenic amines, thin layer chromatography, dissertations
Objavljeno v RUNG: 18.02.2022; Ogledov: 2519; Prenosov: 118
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30.
Carniolan savings bank and economic development of Carniola : dissertation
Nataša Hönig, 2021, doktorska disertacija

Opis: The Carniolan Savings Bank was the first financial institution in the Slovenian territory. It was founded in 1820 in Ljubljana, the capital city of Carniola, a province in the Austrian part of the Habsburg Monarchy. This institution collected deposits and managed the credit operations in the country. Even after the basic idea changed due to business development, it continued to play a significant role as a microfinance provider. The thesis covers the period from the establishment of the institution in 1820 to the disintegration of the Austro-Hungarian Monarchy in 1918. Therefore, the study also deals with the main features of the interwar period. It draws attention to some issues faced by the Savings Bank between 1918 and 1945. The dissertation defines the importance and dimensions of innovation in the institutional sense that the Savings Bank acquired. It defines the role that the institution had in an economic, social, political and national context. This has been achieved through in-depth analysis and a classic historical approach. The dissertation provides an original study of the extensive and unexplored historical material. The Carniolan Savings Bank provides an excellent example of the intertwining of politics and nationalism with economic development. It had a significant impact on the changes that were a prerequisite for mobilising the financial resources of social classes that previously had no access to banking services. Therefore, the Savings Bank collected dispersed financial resources on the financial market by allocating capital to various investment opportunities. The most prominent were mortgage loans and the purchase of government securities. However, the rules in place at the state level limited the importance of the Savings Bank to the regional and especially the local level, reflecting its impact on the country’s economic development. Accordingly, it sought ways to get involved, as evidenced by Credit Association that was used by small merchants and craftsmen.
Ključne besede: Carniolan Savings Bank, deposits, credit activity, microfinance, investments, economic nationalism, Habsburg Monarchy, the Province of Carniola
Objavljeno v RUNG: 06.01.2022; Ogledov: 2068; Prenosov: 159
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