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21.
Airborne Microalgae: Insights, Opportunities, and Challenges
Sylvie V. M. Tesson, Carsten Ambelas Skjøth, Tina Šantl Temkiv, Jakob Löndahl, 2016, review article

Found in: ključnih besedah
Summary of found: ...Airborne microalgae, health effects, ice-nucleation activity, microalgae dispersal...
Keywords: Airborne microalgae, health effects, ice-nucleation activity, microalgae dispersal
Published: 04.01.2021; Views: 552; Downloads: 0
.pdf Fulltext (448,77 KB)

22.
Aeolian dispersal of bacteria in southwest Greenland: their sources, abundance, diversity and physiological states
Tina Šantl Temkiv, Ulrich Gosewinkel, Piotr Starnawski, Mark Lever, Kai Finster, 2018, original scientific article

Found in: ključnih besedah
Summary of found: ...dispersal, community assembly, 16S ribosomal RNA, microbial activity, atmospheric processes...
Keywords: arctic microbial communities, aeolian dispersal, community assembly, 16S ribosomal RNA, microbial activity, atmospheric processes
Published: 04.01.2021; Views: 578; Downloads: 0
.pdf Fulltext (1,51 MB)

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Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles
Leonard Moriau, Marjan Bele, Živa Marinko, Francisco Ruiz-Zepeda, Gorazd Koderman, Martin Šala, Angelija Kjara Šurca, Janez Kovač, Iztok Arčon, Primož Jovanovič, Nejc Hodnik, Luka Suhadolnik, 2021, original scientific article

Abstract: The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiONx) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by various state-of-the-art materials’ characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO2 benchmarks as well as the Ir-supported samples on morphologically different TiONx from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.
Found in: ključnih besedah
Summary of found: ...is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by...
Keywords: electrocatalysis, oxygen-evolution reaction, TiONx-Ir powder catalyst, iridium nanoparticles, anodic oxidation, morphology−activity correlation
Published: 04.01.2021; Views: 666; Downloads: 0
.pdf Fulltext (6,36 MB)

26.
Antibacterial activity of seed extracts of Okra (Abelmoschus esculentus) against selected pathogen
Sandra Oloketuyi, 2017, original scientific article

Abstract: 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.
Found in: ključnih besedah
Keywords: Abelmoschus esculentus, antibacterial activity, foodborne pathogens, extracts, inhibition
Published: 14.01.2021; Views: 514; Downloads: 0
.pdf Fulltext (547,28 KB)

27.
Reconstruction of the coupling between solar proxies
M. Shnirman, Anton Savostianov, Alexander Shapoval, 2020, original scientific article

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...relate the reconstruction of characteristics of solar activity inferred by Blanter et al [Sol. Phys....
Keywords: coupled oscillators, synchronization, solar activity
Published: 22.03.2021; Views: 480; Downloads: 0
.pdf Fulltext (1,31 MB)

28.
Two regimes in the regularity of sunspot number
M. Shnirman, Vincent Courtillot, Alexander Shapoval, Jean-Louis Le Mouël, 2013, original scientific article

Abstract: 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.
Found in: ključnih besedah
Keywords: Lyapunov exponent, solar activity, solar cycle
Published: 19.04.2021; Views: 344; Downloads: 14
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29.
Stochastic description of the high-frequency content of daily sunspots and evidence for regime changes
Vincent Courtillot, Alexander Shapoval, Jean-Louis Le Mouël, M. Shnirman, 2015, original scientific article

Found in: ključnih besedah
Summary of found: ...chaos, solar activity, sunspots...
Keywords: chaos, solar activity, sunspots
Published: 19.04.2021; Views: 304; Downloads: 16
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30.
Sn-modified TiO[sub]2 thin film photocatalysts prepared by low-temperature sol-gel processing
Ksenija Maver, 2021, doctoral dissertation

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by...
Keywords: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Published: 09.06.2021; Views: 594; Downloads: 42
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