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1.
ASSESSMENT OF EFFECTIVE DOSES BASED ON VARIOUS RADON MEASURING TECHNIQUES
Nataša Smrekar, 2016, magistrsko delo

Opis: In my master's thesis, I have focused on radon gas in 43 buildings used for different purposes (23 schools, 3 kindergartens, 16 offices and a residential house) in which preliminary measurements had shown higher concentrations of radon gas. I carried out measurements of radon and short-lived radon products whilst simultaneously employing different measurement techniques. In all 43 buildings, I measured the instantaneous concentration of radon by using scintillation cells; in 18 buildings, I additionally measured the average concentration of radon by using solid state nuclear track detectors and in 10 buildings, I measured concentration retrospectively with solid state nuclear track detectors. In four selected buildings (a school, a kindergarten, an office and a residential house), I carried out the measurements by using all of the available equipment. I monitored the daily fluctuations of concentration of radon and short-lived radon products by using continuous monitors in 14 buildings. This is how I obtained the factor of radioactive equilibrium between radon and its short-lived products. Based on the results obtained, I calculated the effective doses. As the basis for calculating the doses, I used the instantaneous and average concentrations of radon and the equilibrium factor taken from literature (0.40) or own measurements. I compared the doses and critically evaluated them. In contrast to the previous research, I researched radon exclusively in areas with increased risk for radon. I studied the influence of the working regime on the concentration of radon in different working environments (i.e. a school, a kindergarten and an office).
Najdeno v: ključnih besedah
Povzetek najdenega: ...the average concentration of radon by using solid state nuclear track detectors and in 10...
Ključne besede: Radon, short-lived radon products, measurement technique, scintillation cell, solid-state nuclear track detector, retrospective detector, equilibrium factor, effective dose, comparison.
Objavljeno: 28.09.2016; Ogledov: 3793; Prenosov: 227
.pdf Polno besedilo (1,86 MB)

2.
Anaerobic digestion of brewery spent grain as a mono-substrate in a two-stage anaerobic digestion using solid-state digestion reactor and granulated biomass reactor
Marina Tišma, Bruno Zelić, Romana Marinšek Logar, Mario Panjicko, Gregor Drago Zupančič, 2016, objavljeni znanstveni prispevek na konferenci (vabljeno predavanje)

Opis: Anaerobic digestion of brewery spent grain as a mono-substrate was studied. Anaerobic digestion was phase separated in solid state anaerobic digestion reactor, where mostly microbiological hydrolysis and acidogenesis and granular biomass reactor where mostly methanogenesis was performed. The overall process exhibited total solids degradation efficiency between 73.6 and 80.4%. Average specific biogas production was 424±36 L/kg, whereas biomethane production was 230±34 L/kg of brewery spent grain total solids. Granular biomass after adaptation exhibited stabile operation at C-N ratios as low as 0.2 – 0.3, which is rare in anaerobic digestion. P-cresol as a degradation product was present in concentrations up to 45 mg/L and during the process successfully degraded. The excellent adaptability of the granular biomass is confirmed by 67% shift in bacterial and a 32% shift in archaeal community structure in granular biomass reactor after 198 days of successful operation.
Najdeno v: ključnih besedah
Ključne besede: Anaerobic digestion, biogas production, brewery spent grain, microbial biomass, p-cresol degradation, solid state anaerobic digestion
Objavljeno: 21.10.2016; Ogledov: 3332; Prenosov: 0
.pdf Polno besedilo (968,03 KB)

3.
Biogas production from brewery spent grain as a mono-substrate in a two-stage process composed of solid-state anaerobic digestion and granular biomass reactors
Mario Panjicko, Gregor Drago Zupančič, Romana Marinšek-Logar, Lijana Fanedl, Marina Tišma, Bruno Zelić, 2017, izvirni znanstveni članek

Opis: Anaerobic digestion of brewery spent grain as a mono-substrate was studied. Brewery spent grain is a substrate consisting largely of cellulose, hemicellulose and lignin, which are difficult to degrade anaerobically, mostly due to the presence of degradation products, such as phenolic compounds, which cause process inhibition. Therefore, a two-stage system was used for anaerobic digestion. Anaerobic digestion was phase separated in a solid-state anaerobic digestion reactor, where microbiological hydrolysis and acidogenesis occurred and in a granular biomass reactor where mostly methanogenesis was performed. The overall process exhibited total solids degradation efficiency between 75.9 and 83.0 %. Average specific biogas production was 414±32 L/kg, whereas biomethane production was 224±34 L/kg of added total solids. Granular biomass after adaptation exhibited stable operation at substrate C/N ratios in range 0.16 – 4.68. p-cresol was present in concentrations up to 45 mg/L and during the process was successfully degraded by granular biomass. The excellent adaptability of granular biomass was confirmed by 68.2 % shift in bacterial and a 31.8 % shift in archaeal community structure in a granular biomass reactor. The structure of the bacterial community from granular biomass reactor and solid-state anaerobic digestion reactor remained 79.4 % similar at the end of the experiment, whereas archaeal community was only 31.6 % similar. The process exhibited stable operation for 198 days, which shows that brewery spent grain can be successfully anaerobically digested and used for biogas production.
Najdeno v: ključnih besedah
Ključne besede: biogas production, brewery spent grain, C/N ratio, dry digestion, microbial biomass, solid-state anaerobic digestion
Objavljeno: 18.08.2017; Ogledov: 2547; Prenosov: 0
.pdf Polno besedilo (2,27 MB)

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Structural, morphological and chemical properties of metal/topological insulator interfaces
Katja Ferfolja, 2021, doktorska disertacija

Opis: Topological insulators (TIs) represent a new state of matter that possess a different band structure than regular insulators or conductors. They are characterized with a band gap in the bulk and conductive topological states on the surface, which are spin polarized and robust toward contamination or deformation of the surface. Since the intriguing properties of the TIs are localized at the surface, it is important to obtain knowledge of the possible phenomena happening at the interface between TIs and other materials. This is especially true in the case of metals, due to the fact that such interfaces will be present in the majority of foreseen TI applications. The presented study combines microscopy and spectroscopy techniques for characterization of morphology, stability and chemical interaction at the interface between TI and metals deposited by means of physical vapor deposition. Our research is based on the interface of Bi2Se3 topological insulator with Ag, Ti and Pt – metals that can be encountered in devices or applications predicted to utilize the special properties of topological insulators. STM and SEM imaging of Ag/Bi2Se3 interface showed that Ag atoms arrange on the surface in the form of islands, whereas significantly bigger agglomerates are found at the surface steps. The interface was found to be unstable in time and resulted in the absorption of the metal into the crystal at room temperature. Evidences of a chemical reaction at the Ag/Bi2Se3 interface are presented, showing that new phases (Ag2Se, AgBiSe2 and metallic Bi) are formed. Deposition of Ti on Bi2Se3 resulted in different morphologies depending on the film thickness. At a very low coverage (<1 Å) islands are formed. However, the islands growth is hindered before the completion of a full layer due to the occurrence of a chemical reaction. No surface features could be detected by SEM for Ti coverage up to 20 nm. In contrary, when Ti thickness reached 40 nm, compressive stress triggered buckling of the deposited film. XPS analysis revealed that a redox solid-state reaction occurs at the Ti/Bi2Se3 interface at room temperature forming titanium selenides and metallic Bi. The reaction has significant kinetics even at cryogenic temperature of 130 K. Pt forms a homogenous film over the whole substrate surface, which is stable in time at room temperature. Although the interface of Pt with Bi2Se3 was found to be i less reactive compared to Ag and Ti, an interfacial phase formed upon annealing to ∼90 °C was detected by TEM cross section experiment. A model for prediction of interfacial reactions between a metal and Bi2Se3 based on the standard reduction potential of the metals and Gibbs free energy for a model reaction is presented. Based on these two values the reaction can be expected to result in the formation of binary and/or ternary selenides and Bi. Presented work shows on the importance of metal/topological insulator interfaces characterization taking into account the possibility of a chemical reaction with all of its consequences. Results should be considered for future theoretical and applicative studies involving such interfaces as well as for the possible engineering of 2D TI heterostructures.
Najdeno v: ključnih besedah
Povzetek najdenega: ...film. XPS analysis revealed that a redox solid-state reaction occurs at the Ti/Bi2Se3 interface at...
Ključne besede: topological insulators, topological surface states, Bi2Se3, thin films, Ag, Ti, Pt, morphology, interfaces, solid-state reaction, metal selenides, reactivity, stability, electron microscopy, dissertations
Objavljeno: 09.06.2021; Ogledov: 487; Prenosov: 32
URL Polno besedilo (0,00 KB)
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6.
Room-temperature solid-state reaction at the Ag/Bi[sub]2Se[sub]3 interface
Matjaž Valant, Iuliia Mikulska, Sandra Gardonio, Katja Ferfolja, Mattia Fanetti, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Topological insulators (TI) are materials that, while having a forbidden bandgap in bulk, are conductors at their surface due to presence of surface-localized electronic states crossing the band gap. [1] TIs are possible because of a time reversal symmetry and spin-orbit coupling, which invert bulk band states in their energy positions and make the bulk band structure non trivial. Consequently, the topological surface states (TSS) emerge on the surface of these materials. Unlike ordinary surface states, TSS cannot be destroyed by contamination or defects on the surface. Additionally, TSS are also spin polarized, which means that when applying current to TI, the current will have a well defined direction of the electron spins. The topological insulators - a relatively new class of materials - are being widely studied not only from fundamental aspects, but also from their applicative perspectives. It has been predicted that TIs could be used in fields of spintronics, electronics and catalysis. [2,3] Interestingly, only a few studies about metal/TI interfaces have been reported. This is surprising since integration of TI in the applications will often necessitate an interface with the metal, therefore, detailed knowledge on chemistry and electrical conditions at the interface will be required. In this contribution results on research on the chemistry of the Ag/Bi2Se interface will be presented, in particularonthesolid-statereactionbetweennanoparticles.IthasbeenobservedthatwhenBi2Se3 andAgare put in contact a chemical reaction occurs at the interface, producing AgBiSe2 and Ag2Se. Interestingly, the reaction already occurs at room temperature, which is not usual for solid-state reactions. In literature this reaction has not been properly described. The authors rather described it as intercalation of the silver atoms, which we have disproved and showed that recrystallization of the new phases occurs. [3,4,5] The results will alsobediscussedincomparisonwithothertwoAg/Bi2Se3 systemsunderourinvestigation:i)Agdepositedby achemicalrouteonBi2Se3 nanoflakesandii)AgdepositedfromavapourphaseinvacuumonaBi2Se3.single crystal
Najdeno v: ključnih besedah
Ključne besede: topological insulators, topological surface states, solid-state reaction, TI/metal interface
Objavljeno: 20.08.2021; Ogledov: 114; Prenosov: 0
.pdf Polno besedilo (1,11 MB)

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