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- Ek, Gustav, 1992-
(författare)
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Hunting Hydrogen : Structure-property relations in High Entropy Alloy-based metal hydrides
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal hydrides have many uses when switching the energy system from fossil fuels to renewable sources, such as rechargeable batteries, hydrogen storage, hydrogen compression and thermal storage. State of the art materials for these applications such as LaNi5 and TiFe, however, suffer certain limitations such as degradation during repeated hydrogen cycling and harsh activation conditions for initial hydrogen uptake, promoting the need for novel materials. One class of materials that are interesting options are High Entropy Alloys (HEA), which are solid solutions where typically four or more different elements occupy a single crystallographic site in a simple structure such as body centered cubic (bcc) or cubic close packed (ccp). Due to the random distribution of the elements, there is a large variety of local environments for hydrogen, potentially unlocking sites that are unavailable in conventional transition metal hydrides. There is also the possibility of vast chemical tunability when using this many principal elements. It is therefore imperative to establish design rules to enable tuning of the hydrogen sorption properties of these materials by changing the composition. The effect of having many differently sized metals on the crystal structure is also not fully understood, and is believed to have a high impact on the bulk properties such as hydrogen sorption in these materials.This thesis covers the experimental synthesis of a wide range of HEAs and subsequent evaluation of their structural and hydrogen sorption properties. Several new design rules have been established, such as that the atomic size mismatch between the constituent metals has no effect on the maximum hydrogen capacity, that the addition of large elements like Zr leads to phase separation and that controlling the valence electron concentration, VEC, destabilizes the HEA-based metal hydrides. Based on these findings, the material TiVCrNbH8 has been identified as a candidate with properties rivaling that of TiFeH2.
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| 2. |
- Gustafsson, Gabriel
(författare)
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Alpha-Synuclein Oligomers : Cellular Mechanisms and Aspects of Antibody Treatment
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Parkinson’s disease (PD) and dementia with Lewy bodies (DLB), aggregated α-synuclein deposit inside cells within the brain. Smaller soluble α-synuclein aggregates, oligomers, are present both intra- and extracellularly. The α-synuclein oligomers are known to be particularly harmful, although the underlying neurotoxic mechanisms are not fully understood. The aim of this thesis was to investigate the pathogenic roles of α-synuclein oligomers and the possibility to target such species with antibody treatment.Passive immunotherapy with α-synuclein antibodies can lead to reduced pathology and ameliorated symptoms in transgenic mice. However, it remains unknown whether the antibodies are taken up by cells or whether they act extracellularly. In Paper I, we assessed cellular internalization of various α-synuclein monoclonal antibodies. The oligomer selective mAb47 displayed the highest uptake, which was promoted by the extracellular presence of α-synuclein.Alpha-synuclein aggregates can be found in both neurons and glial cells, but the pathogenic role of glial deposits has only been sparsely investigated. In Paper II, co-cultures of neurons and glia were exposed to α-synuclein oligomers. The astrocytes in the cultures rapidly accumulated oligomers, which were only partially degraded by lysosomes. The sustained intracellular α-synuclein deposits were associated with mitochondrial stress reactions in the astrocytes. In Paper III, we sought to explore whether the astrocytic pathology induced by α-synuclein oligomers could be ameliorated by antibody treatment. Pre-incubation of oligomers with mAb47 promoted α-synuclein clearance, reduced astrocytic accumulation and rescued cells from mitochondrial stress. We could demonstrate that binding of the antibody to its antigen in the extracellular space was crucial for these effects to occur.The progressive pathology in PD is believed to be driven by cell-to-cell spreading of α-synuclein aggregates, potentially via exosomes and other extracellular vesicles (EVs). In Paper IV, we found that either fusing α-synuclein to a non-physiological protein tag or introducing the PD-causing A53T mutation directed α-synuclein towards EV secretion. Also, EV-associated α-synuclein was particularly prone to induce toxicity in recipient cells.In conclusion, this thesis sheds new light on the cellular dysfunction related to α-synuclein pathology and on how the underlying pathogenic processes may be targeted by antibody treatment.
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| 3. |
- Holmberg, Karolina, 1965-
(författare)
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Empirical Essays in Macroeconomics and Finance
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Derivation and Estimation of a New Keynesian Phillips Curve in a Small Open Economy This paper explores how well Swedish inflation is explained by a New Keynesian Phillips Curve. As the real driving variable in the Phillips Curve, a measure of firms' real marginal cost is compared to the traditional output gap. The results show that, with real marginal cost in the Phillips Curve equation, the point estimates generally have the expected positive sign, which is less frequently the case with the output gap. However, with both real marginal cost and the output gap, it is difficult to pin down a statistically significant relationship with inflation. Firm-Level Evidence of Shifts in the Supply of Credit This paper examines empirically whether firms are subject to shifts in credit supply over the business cycle. Shifts in the supply of credit are identified by exploring how firms substitute between commitment credit -- lines of credit -- and non-commitment credit. The results show that firms on average rely more on commitment credits when monetary policy is tight and when the financial health of banks is weaker. The results are consistent with a bank lending channel of monetary policy and with shifts in the supply of credit following deteriorations in banks' balance sheets. Lines of Credit and Investment: Firm-Level Evidence of Real Effects of the Financial Crisis This paper studies how the 2008 financial crisis affected corporate investment in Sweden through its effect on credit availability. The approach is to compare investments of firms before and after the onset of the crisis as a function of their ex ante sensitivity to a credit supply shock, controlling for fundamental determinants of investments. Sensitivity to a credit supply shock is measured as credit reserves, defined as unused credit on lines of credit. The results indicate that the decline in investment following the crisis was not exacerbated by a contraction in the supply of credit.
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| 4. |
- Pontiller, Benjamin, MSc, 1985-
(författare)
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Molecular mechanisms involved in prokaryotic cycling of labile dissolved organic matter in the sea
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Roughly half of the global primary production originates from microscopic phytoplankton in marine ecosystems, converting carbon dioxide into organic matter. This organic matter pool consists of a myriad of compounds that fuel heterotrophic bacterioplankton. However, knowledge of the molecular mechanisms – particularly the metabolic pathways involved in the degradation and utilization of dissolved organic matter (DOM) – and transcriptional dynamics over spatiotemporal gradients are still scarce. Therefore, we studied the molecular mechanisms of bacterioplankton communities, including archaea, involved in the cycling of DOM, over different spatiotemporal scales in experiments and through field observations.In seawater experiments, we found a divergence of bacterioplankton transcriptional responses to different organic matter compound classes (carbohydrates, nucleic acids, and proteins) and condensation states (monomers or polymers). These responses were associated with distinct bacterial taxa, suggesting pronounced functional partitioning of these compounds in the Sea. Baltic Proper mesocosms amended with two different river loadings (forest versus agriculture river water) revealed a divergence in gene expression patterns between treatments during bloom decay. This was particularly true for genes in phosphorus and nitrogen metabolism, highlighting the importance and sensitivity of interaction effects between river- and phytoplankton-derived DOM in regulating bacterial activity responses to changes in precipitation-induced riverine runoff.In shipboard mesocosms in an Atlantic coastal upwelling system, we found significant changes in bacterioplankton transcription of hydrolyzing enzymes and membrane transporters from phytoplankton bloom development to senescence, primarily driven by phytoplankton-derived DOM and dissolved organic carbon dynamics. These responses differed substantially between bacterial orders, suggesting that functional resource partitioning is dynamically structured by temporal changes in DOM quantity and quality. Further analysis of these gene systems in a stratified fjord revealed pronounced divergence in transcription with depth and between bacterial taxa; moreover, transcription was more variable in the surface waters. This highlights the interplay between functional and physical partitioning of biogeochemical cycles. Collectively, the findings in this thesis contribute novel insights into the interdependency between prokaryotes and DOM by shedding light on the mechanisms involved in DOM cycling over ecologically relevant spatiotemporal scales.
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