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71.
OXYGEN-EXCESS RELATED DEFECTS IN SiO2-BASED MATERIALS: COUPLING THEORY AND EXPERIMENTS
Blaž Winkler, doktorska disertacija

Opis: This work is primarily focused on application of standard first-principle computational approaches to model oxygen excess related point defects in amorphous silica. Atomic models with their respective electronic and optical properties are explored together with some conversion mechanisms between defect models. The first chapter overviews extensive literature about the already known properties of oxygen related defects. Second chapter briefly introduces main methods that have been used in this research, in particular Density Functional Theory (DFT) as energy and force engine with short description of minimal energy path (MEP) algorithm used for modeling chemical/migration reactions, GW approximation for charged electronic excitations (band structure) and Bethe-Salpeter Equation (BSE) for neutral excitations (optical absorption and excitonic structure including electron hole interaction). The third chapter is devoted to the presentation of results. Thanks to the calculation of optical properties of peroxy bridge (POL), a correlation has been found between structural disorder, specifically dihedral angle dispersion, and low coupling with light, which has been identified as main reason why no clear absorption bands have been assigned to the POL. Structure and stability of some other defects, like interstitial ozone molecule (ozonyl) and dioxasilirane (silicon analogy of dioxirane), have been studied. These defects are usually not considered as most important species, however their calculated formation energies are lower compared to some known defects, which indicates they might be present in silica. From a detailed study on possible reaction mechanisms, it has been found that ozonyl might be one of the most important intermediate steps for oxygen exchange reactions. Results also show that dioxasilirane can be spontaneously created during the interaction of oxygen with lone pair defects. By exploring different reactions between oxygen and pre-existing oxygen deficiency centers (ODCs), calculations predict two kinds of passivation behaviors: single-barrier reversible mechanisms with the formation of dioxasilirane-like groups, for which the network keeps the memory of the precursory lone pair defects, and single or multiple-barrier mechanisms, for which the network loses its memory, either because of the high reverse barrier or because of a reconstruction. Final part of this research has been devoted to experimental characterization of the response and tolerance of optical fibers loaded with oxygen under irradiation. These include experiments on commercial fiber along with canonical samples (Optical fibers developed with the intention of studying correlations between different fabrication parameters, dopant/impurity concentration and doping concentrations). Studied fibers also include rare-earth doped fibers.
Ključne besede: Silica, DFT, GW-approximation, Bethe-Salpeter equation, NEB, defect, oxygen, oxygen excess centers, oxygen deficiency centers, optical absorption, optical fibers, radiation induced attenuation.
Objavljeno: 07.05.2019; Ogledov: 133; Prenosov: 11
.pdf Polno besedilo (13,18 MB)

72.
Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser
Giovanni De Ninno, Primož Rebernik Ribič, 2019, izvirni znanstveni članek

Opis: X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. We show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.
Ključne besede: free electron laser, coherence, x-rays
Objavljeno: 07.05.2019; Ogledov: 66; Prenosov: 0
.pdf Polno besedilo (6,89 MB)

73.
New Insights into Manganese Local Environment in MnS-1Nanocrystals
Alenka Ristić, Matjaž Mazaj, Iztok Arčon, Nina Daneu, Nataša Zabukovec Logar, Roger Glaser, Nataša Novak Tušar, 2019, izvirni znanstveni članek

Opis: Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).
Ključne besede: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Objavljeno: 06.05.2019; Ogledov: 60; Prenosov: 0
.pdf Polno besedilo (9,33 MB)

74.
Frnikola je padla
Barbara Pregelj, 2019, samostojni strokovni sestavek ali poglavje v monografski publikaciji

Ključne besede: Juan José Millás, mladinska književnost, prevodi, španska mladinska književnost, večnaslovniškost
Objavljeno: 06.05.2019; Ogledov: 68; Prenosov: 0
.pdf Polno besedilo (380,64 KB)

75.
A Biogenerated Polymetallic Catalyst from Society's Wastes
Oreste Piccolo, Stefano Paganelli, Petro Zanatta, Sebastiano Tieuli, Laura Sperni, Franco Baldi, Iztok Arčon, Michele Gallo, Katarina Vogel-Mikuš, 2019, izvirni znanstveni članek

Opis: Aims:Preparation of the new metals - polymeric composite, Met x-EPS (I), to be used as a green catalyst in water or in two-phase aqueous conditions. Study Design: Recovery and valorization of polymetallic wastes to obtain directly new catalysts using a microorganism to explore their application in removal of difficult and dangerous chemical pollutants present in aqueous environment
Ključne besede: Metals - polymeric composite, biogenerated polymetallic exopolysaccharide, new catalyst from metallic wastes, hydrodechlorination of PCBs in water
Objavljeno: 06.05.2019; Ogledov: 75; Prenosov: 0
.pdf Polno besedilo (373,55 KB)

76.
Sodobna baskovska poezija
Barbara Pregelj, 2019, umetniško delo

Opis: prevod in izbor prevedenih avtorjev
Ključne besede: Ibon Egana, Juan Kruz Igerabide, Benat Sarasola, Itxaro Borda, Angel Erro, Miren Agur Meabe, Leire Bilbao, Jon Benito, prevodi v slovenščino, poezija, baskovska poezija
Objavljeno: 06.05.2019; Ogledov: 79; Prenosov: 0
.pdf Polno besedilo (333,95 KB)

77.
El lenguaje universal de la poesía
Barbara Pregelj, Alenka Jovanovski, Gašper Malej, predavanje na tuji univerzi

Opis: Branje prevodov na literarnem večeru, moderiranje in tolmačenje pogovora s pesnikoma Gašperjem Malejem in Alenko Jovanovski.
Ključne besede: prevajanje v španščino, branje, španščina, slovenska poezija
Objavljeno: 06.05.2019; Ogledov: 45; Prenosov: 0
.pdf Polno besedilo (659,22 KB)

78.
79.
Sestavimo Grizeldo
Barbara Pregelj, druga izvedena dela

Ključne besede: motiviranje za branje, zgodnje poučevanje španščine, Lepa Grizelda
Objavljeno: 06.05.2019; Ogledov: 37; Prenosov: 0
.pdf Polno besedilo (224,72 KB)

80.
Kako dober je lahko prevod, vnovič
Barbara Pregelj, 2019, strokovni članek

Ključne besede: Bela knjiga o prevajanju, delovne razmere, predstavitve, Slovenija
Objavljeno: 06.05.2019; Ogledov: 33; Prenosov: 0
.pdf Polno besedilo (328,72 KB)

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