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Structure optimisation of biopigment prodigiosin from Serratia marcescens ATCC 27117 and antimicrobial and anticancer properties of novel halogenated derivatives
Jelena Lazić, 2022, doktorska disertacija

Opis: Prodigiosins (PGs) are a class of bacterial secondary metabolites with remarkable biological activities and colour. In this study, optimised fermentative production of prodigiosin (PG) using waste processed meat as a substrate has been achieved to levels of 83.1 ± 3.0 mg/L from a commercially available Serratia marcescens ATCC 27117 strain within 12 h. Methods were established for the reliable PG extraction from both the bacterial cell pellet and the culture supernatant, while gravitation column chromatography was used to obtain pure bacterial PG. The structure of the isolated PG was optimised by environmentally acceptable oxidative bromination reactions, obtaining mono- and dibrominated derivatives (PG-Br and PG-Br2). Chemical structures were confirmed by structural characterisation using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS), showing that PG-Br is a mixture of two monobrominated isomers in approximately equal ratios, while PG-Br2 was afforded as a pure derivative. PG and its brominated derivatives (Br-derivatives) showed anticancer potential with half-maximal inhibitory concentration (IC50) values ranging from 0.62 to 17.00 μg/mL on four tested cancer cell lines (A549 lung, A375 skin, MDA-MB-231 breast, HCT116 colon) and an induction of early apoptosis, but low selectivity against healthy cell lines (MRC-5 lung fibroblasts and HaCaT skin keratinocytes). All three PG, PG-Br and PG-Br2 compounds did not affect roundworms (Caenorhabditis elegans) at concentrations up to 50 μg/mL. However, an improved toxicity profile of Br-derivatives in comparison to the parent PG was observed in vivo using zebrafish (Danio rerio) model system, when 10 μg/mL applied at 6 h post fertilisation caused death rate of 100, 30 and 0% by PG, PG-Br and PG-Br2, respectively, which is a significant finding for further structural optimisations of bacterial PGs.
Ključne besede: prodigiosin, Serratia marcescens, meat waste, halogenation, novel derivatives, anticancer activity, apoptosis, zebrafish embryotoxicity
Objavljeno v RUNG: 21.10.2022; Ogledov: 1706; Prenosov: 32
.pdf Celotno besedilo (3,39 MB)

3.
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: 2328; Prenosov: 164
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4.
Improved photocatalytic activity of SnO[sub]2-TiO[sub]2 nanocomposite thin films prepared by low-temperature sol-gel method
Ksenija Maver, Iztok Arčon, Mattia Fanetti, Samar Al Jitan, Giovanni Palmisano, Matjaž Valant, Urška Lavrenčič Štangar, 2021, izvirni znanstveni članek

Opis: The objective of this research was to investigate how the photocatalytic activity of pure TiO2 can be improved by SnO2 modification. Different molar ratios of tin to titanium were prepared. The correlation between tin concentration and structural properties was investigated to explain the mechanism of photocatalytic efficiency and to optimize the synthesis conditions to obtain enhanced activity of the SnO2-modified TiO2 photocatalysts under UV-irradiation. The SnO2-modified TiO2 photocatalysts were prepared by a low-temperature sol-gel method based on organic tin and titanium precursors. The precursors underwent sol-gel reactions separately to form SnO2-TiO2 sol. The sol-gels were deposited on a glass substrate by a dip-coating technique and dried at 150 ◦C to obtain the photocatalysts in the form of a thin film. To test the thermal stability of the material, an additional set of photocatalysts was prepared by calcining the dried samples in air at 500 ◦C. The photocatalytic activity of the samples was determined by measuring the degradation rate of an azo dye. An increase of up to 30% in the photocatalytic activity of the air-dried samples was obtained when the TiO2 was modified with the SnO2 in a concentration range of 0.1–1 mol.%. At higher SnO2 loadings, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. The calcined samples showed an overall reduced photocatalytic activity compared to the air-dried samples. Various characterization techniques (UV-Vis, XRD, N2-physisorption, TEM, EDX, SEM, XAS and photoelectrochemical characterization) were used to explain the mechanism for the enhanced and hindered photocatalytic performances of the SnO2-modified TiO2 photocatalysts. The results showed that the nanocrystalline cassiterite SnO2 is attached to the TiO2 nanocrystallites through the Sn-O-Ti bonds. In this way, the coupling of two semiconductors, SnO2 and TiO2, was demonstrated. Compared to single-phase photocatalysts, the coupling of semiconductors has a beneficial effect on the separation of charge carriers, which prolongs their lifetime for accessibility to participate in the redox reactions. The maximum increase in activity of the thin films was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases is achieved for the given physical parameters such as particle size, shape and specific surface area of the catalyst.
Ključne besede: photocatalytic activity, Sn-modified TiO2, low-temperature, thin films, XAS analysis
Objavljeno v RUNG: 05.07.2021; Ogledov: 2623; Prenosov: 0
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5.
Sn-modified TiO[sub]2 thin film photocatalysts prepared by low-temperature sol-gel processing : dissertation
Ksenija Maver, 2021, doktorska disertacija

Opis: Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.
Ključne besede: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Objavljeno v RUNG: 09.06.2021; Ogledov: 4732; Prenosov: 163
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6.
Photo-Chemically-Deposited and Industrial Cu/ZnO/Al2O3 Catalyst Material Surface Structures During CO2 Hydrogenation to Methanol: EXAFS, XANES and XPS Analyses of Phases After Oxidation, Reduction, and Reaction
Maja Pori, Iztok Arčon, Venkata Dasireddy, Blaž Likozar, 2021, izvirni znanstveni članek

Opis: Industrial Cu/ZnO/Al2O3 or novel rate catalysts, prepared with a photochemical deposition method, were studied under functional CH3OH synthesis conditions at the set temperature (T) range of 240–350 °C, 20 bar pressure, and stoichiometric carbon dioxide/hydrogen composition. Analytical scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray adsorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methods were systematically utilized to investigate the interfaces, measured local geometry, and chemical state electronics around the structured active sites of commercially available Cu/ZnO/Al2O3 material or synthesized Cu/ZnO. Processed Cu K-edge EXAFS analysis suggested that various Cu atom species, clusters, metallic fcc Cu, Cu oxides (Cu2O or CuO) and the Cu0.7Zn2 alloy with hexagonal crystalline particles are contained after testing. It was proposed that in addition to the model’s Cu surface area, the amount, ratio and dispersion of the mentioned bonded Cu compounds significantly influenced activity. Additionally, XPS revealed that carbon may be deposited on the commercial Cu/ZnO/Al2O3, forming the inactive carbide coating with Cu or/and Zn, which may be the cause of basicity’s severe deactivation during reactions. The selectivity to methanol decreased with increasing T, whereas more Cu0.7Zn2 inhibited the CO formation through reverse water–gas shift (RWGS) CO2 reduction.
Ključne besede: CH3OH synthesis, Cu/ZnO-based catalyst, XPS, XANES, EXAFS analyses, Catalyst selectivity and activity
Objavljeno v RUNG: 03.06.2021; Ogledov: 2375; Prenosov: 0
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8.
Two regimes in the regularity of sunspot number
Alexander Shapoval, Jean-Louis Le Mouël, Vincent Courtillot, M. Shnirman, 2013, izvirni znanstveni članek

Opis: Sunspot numbers WN display quasi-periodical variations that undergo regime changes. These irregularities could indicate a chaotic system and be measured by Lyapunov exponents. We define a functional λ (an "irregularity index") that is close to the (maximal) Lyapunov exponent for dynamical systems and well defined for series with a random component: this allows one to work with sunspot numbers. We compute λ for the daily WN from 1850 to 2012 within 4 yr sliding windows: λ exhibit sharp maxima at solar minima and secondary maxima at solar maxima. This pattern is reflected in the ratio R of the amplitudes of the main versus secondary peaks. Two regimes have alternated in the past 150 yr, R1 from 1850 to 1915 (large λ and R values) and R2 from 1935 to 2005 (shrinking difference between main and secondary maxima, R values between 1 and 2). We build an autoregressive model consisting of Poisson noise plus an 11 yr cycle and compute its irregularity index. The transition from R1 to R2 can be reproduced by strengthening the autocorrelation a of the model series. The features of the two regimes are stable for model and WN with respect to embedding dimension and delay. Near the time of the last solar minimum (~2008), the irregularity index exhibits a peak similar to the peaks observed before 1915. This might signal a regime change back from R2 to R1 and the onset of a significant decrease of solar activity.
Ključne besede: Lyapunov exponent, solar activity, solar cycle
Objavljeno v RUNG: 19.04.2021; Ogledov: 1918; Prenosov: 59
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9.
Reconstruction of the coupling between solar proxies : when approaches based on Kuramoto and Van der Pol models agree with each other
Anton Savostianov, Alexander Shapoval, M. Shnirman, 2020, izvirni znanstveni članek

Opis: The objective of this paper is to establish that algorithms, which reconstruct the coupling between solar proxies based on the properties of the Kuramoto equations, and algorithms, based on the van der Pol equations, might produce similar estimates. To this end, the inverse problem is formulated as follows: reconstruct the coupling based on the solutions of the corresponding equations. For either system of the equations we construct an algorithm solving the inverse problem and establish that there exists a range of moderate values of the correlation such that the algorithms produce practically identical coupling within the established range. The lower boundary of this range is dependent on the half-difference of the oscillators’ frequencies. Then, we apply the two reconstruction algorithms to solar index ISSN and the geomagnetic index aa, which are proxies to the toroidal and poloidal magnetic fields of the Sun respectively. Their correlation belongs within the range that yields the proximity of the coupling reconstructed with all solar cycles from 11 till 23 except 20 and, possibly, 21. Our finding relate the reconstruction of characteristics of solar activity inferred by Blanter et al [Sol. Phys. 2014, 289, 4309; Sol. Phys. 2016, 291, 1003] from the Kuramoto model to the state of the art solar dynamo theory based on the magnetohydrodynamic equations.
Ključne besede: coupled oscillators, synchronization, solar activity
Objavljeno v RUNG: 22.03.2021; Ogledov: 2058; Prenosov: 0
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10.
Antibacterial activity of seed extracts of Okra (Abelmoschus esculentus) against selected pathogen
Sandra Oloketuyi, 2017, izvirni znanstveni članek

Opis: The aim of the study was to determine the antibacterial potency of aqueous and ethanoic extracts of Abelmoschus esculentus seeds. Antibacterial activity of aqueous and ethanoic extracts of A. esculentus seeds were evaluated against selected foodborne pathogens; Listeria monocytogenes, Bacillus cereus, Salmonella enterica, Staphylococcus aureus and Escherichia coli) using agar well diffusion method by measuring the clear zone of inhibition diameter in (mm). It was observed that the aqueous and ethanoic extracts of the four samples of A. esculentus seeds showed broad range of inhibitory activity against the test bacteria especially L. monocytogenes. Thus, A. esculentus seed has a great potential as effective antilisterial and antibacterial activity. Practical Application: Consumption of okra seeds is highly recommended for its nutritive value and antibacterial activity against pathogens, which are most commonly attributed to foodborne diseases such as listeriosis, diarrhea, and salmonellosis. Also, further study could be conducted by isolating and identifying the active ingredient responsible for antibacterial potency for pharmaceutical purpose.
Ključne besede: Abelmoschus esculentus, antibacterial activity, foodborne pathogens, extracts, inhibition
Objavljeno v RUNG: 14.01.2021; Ogledov: 2412; Prenosov: 0
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