71. Mass composition of ultra-high energy cosmic rays at the Pierre Auger ObservatoryGašper Kukec Mezek, 2019, doctoral dissertation Abstract: Cosmic rays with energies above 10^18 eV, usually referred to as ultra-high energy cosmic rays (UHECR), have been a mystery from the moment they have been discovered. Although we have now more information on their extragalactic origin, their direct sources still remain hidden due to deviations caused by galactic magnetic fields. Another mystery, apart from their production sites, is their nature. Their mass composition, still uncertain at these energies, would give us a better understanding on their production, acceleration, propagation and capacity to produce extensive air showers in the Earth's atmosphere. Mass composition studies of UHECR try to determine their nature from the difference in development of their extensive air showers.
In this work, observational parameters from the hybrid detection system of the Pierre Auger Observatory are used in a multivariate analysis to obtain the mass composition of UHECR. The multivariate analysis (MVA) approach combines a number of mass composition sensitive variables and tries to improve the separation between different UHECR particle masses. Simulated distributions of different primary particles are fitted to measured observable distributions in order to determine individual elemental fractions of the composition. When including observables from the surface detector, we find a discrepancy in the estimated mass composition between a mixed simulation sample and the Pierre Auger data. Our analysis results from the Pierre Auger data are to a great degree independent on hadronic interaction models. Although they differ at higher primary masses, the different models are more consistent, when combining fractions of oxygen and iron. Compared to previously published results, the systematic uncertainty from hadronic interaction models is roughly four times smaller. Our analysis reports a predominantly heavy composition of UHECR, with more than a 50% fraction of oxygen and iron at low energies. The composition is then becoming heavier with increasing energy, with a fraction of oxygen and iron above 80% at the highest energies.
Keywords: astroparticle physics, ultra-high energy cosmic rays, extensive air showers, mass composition, Pierre Auger Observatory, machine learning, multivariate analysis
Published in RUNG: 03.04.2019; Views: 4889; Downloads: 186
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72. Cu and Zr surface sites in photocatalytic activity of TiO [sub] 2 nanoparticles : the effect of Zr distributionOlena Pliekhova, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2019, original scientific article Abstract: The present work is focused on the role of ZrO2 modification in the performance of CuO modified TiO2. Zirconia
loading leads to formation of more resistant photocatalytic layers compared to samples modified with only
copper containing species. Surface modification of mixed phase TiO2 with CuO/ZrO2 improves the degradation
of Reactive blue 19 dye under simulated solar irradiation. An in-depth investigation of the catalysts showed that
in case of CuO/ZrO2 modification, the covering of the TiO2 surface with zirconium containing species prevents
morphological and harmful energetic changes induced by copper species formed on the rutile TiO2 phase at a
higher copper loading.
Keywords: titanium dioxide, surface modification, XAS analysis, surface acidity, Hammett indicators
Published in RUNG: 26.03.2019; Views: 3166; Downloads: 0
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76. IETI, Isogeometric Tearing and InterconnectingStefan K. Kleiss, Clemens Pechstein, Bert Jüttler, Satyendra Tomar, 2012, original scientific article Keywords: isogeometric analysis, NURBS, domain decomposition, FETI, IETI
Published in RUNG: 13.11.2018; Views: 3123; Downloads: 0
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77. Volatile and sensory profiling of Shiraz wine in response to alcohol management: comparison of harvest timing versus technological approachesRocco Longo, John W. Blackman, Guillaume Antalick, Peter J. Torley, Suzy Y. Rogers, Leigh Schmidtke, 2018, original scientific article Keywords: Common Component Specific Weights Analysis, polypropylene membrane, sensory descriptive analysis, sequential harvest, volatiles, wine alcohol-reduction
Published in RUNG: 17.09.2018; Views: 3381; Downloads: 0
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78. A comparative study of partial dealcoholisation versus early harvest: Effects on wine volatile and sensory profilesRocco Longo, John.W Blackman, Guillaume Antalick, Peter J. Torley, Suzy.Y Rogers, Leigh Schmidtke, 2018, original scientific article Keywords: Common component and specific weights analysis, Dealcoholisation, Early harvest, Evaporative perstraction, Lower alcohol wine, Reverse osmosis, Sensory descriptive analysis, Wine
Published in RUNG: 17.09.2018; Views: 3442; Downloads: 0
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80. Amorphous nanocomposite of polycarbosilanes and aluminum oxideAndraž Mavrič, 2018, doctoral dissertation Abstract: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous.
The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer.
The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm.
The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects.
In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Keywords: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Published in RUNG: 19.07.2018; Views: 6066; Downloads: 210
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