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- Hulterström, Karolina, 1971-
(författare)
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Ethnic Politics : Voters, Parties and Policies in Kenya and Zambia
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is an investigation of ethnic politics, both as a concept and as an empirical phenomenon. It is based on the propositions that (a) most instances of ethnic politics are non-violent rather than violent and, (b) most scholarly work in the field is explanatory and devoted to violent ethnic conflict. Consequently, it is argued that there is a need to focus on descriptive analysis of non-violent ethnic politics.Hence, the first part of the thesis is devoted to a conceptual discussion of ethnic politics: what does it mean and refer to? The underlying objective of the conceptual investigation is to develop an analytical framework that will improve and facilitate descriptive empirical analysis. It is deemed essential that the framework include several different aspects of both the participatory and policy dimensions of politics, in order to capture accurately the overall impact on ethnicity on politics. In the second part of the study the aptness of the developed framework is tested in a comparison of the nature of, and extent to which, an ethnic cleavage influenced politics in Kenya and Zambia during the 1990s. Voters, parties and distribution policies are examined in order to assess the impact of ethnicity on politics in the two societies. Both objective manifestations, in the form of election data, official statistics etc., and subjective manifestations, i.e. perceptions and attitudes sought through interviews, are employed in the investigation. The analyses reveal a substantial difference between the two countries, with an ethnic cleavage being far more prominent in Kenya than in Zambia. The investigation, however, also shows a considerable variation in the extent to which ethnicity affects the different aspects of politics. This underscores the importance of examining different aspects of politics in order to accurately assess the overall impact of ethnicity on politics.
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- Jonnalagadda, Krishna Praveen, 1988-
(författare)
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Thermal Barrier Coatings : Failure Mechanisms and Life Prediction
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBCs) use in the hot sections of gas turbine engine enables them to run at higher temperatures, and as a consequence, achieve higher thermal efficiency. For full operational exploitation of TBCs, understanding their failure and knowing the service life is essential. The broad objective of the current research is to study the failure mechanisms of new TBC materials and deposition techniques during corrosion and thermal cycling and to develop life models capable of predicting the final failure during thermal cycling.Yttria-stabilized zirconia (YSZ) has constraints such as limited operation temperature, despite being the current industry standard. Pyrochlores of A2B2O7 type have been suggested as a potential replacement for YSZ and were studied in this work. Additionally, improvements to the conventional YSZ in the form of nanostructured YSZ were also explored. The requirement for the new deposition process comes from the fact that the existing low-cost deposition processes, like atmospheric plasma spray (APS), generally exhibit lower strain tolerance. A relatively new technique, suspension plasma spray (SPS), known to be promising with better strain tolerance, has been studied in this work.At the gas turbine operating conditions, TBCs degrade and eventually fail. Common failure observed in gas turbines can be due to corrosion, thermal mismatch between the ceramic and the metallic layers, and bond coat oxidation during thermal cycling. SPS and APS TBCs were subjected to different test conditions to understand their corrosion behavior. A study on the multi-layered SPS TBCs in the presence of V2O5+Na2SO4 showed that YSZ based SPS coatings were less susceptible to corrosion damage compared to Gd2Zr2O7 SPS TBCs. A study on the influence of a sealing layer in multi-layered SPS TBCs in the presence of Na2SO4+NaCl showed that the sealing layer is ineffective if the material used for sealing is inert to the molten salts. A new study on the influence of corrosion, caused by a mixed-gas atmosphere, on the thermal cycling fatigue life of SPS TBCs was conducted. Results showed that corrosive products grew inside the top coat close to the bond coat/top coat interface along with accelerated growth of alumina. These, together, reduced the TCF life of corrosion exposed samples significantly. Finally, a study on the influence of salt concentration and temperature on a thin (dense) and a thick (porous) coating showed that thick and porous coatings have lower corrosion resistance than the thin and dense coatings. Additionally, a combination of low temperature and high salt concentration was observed to cause more damage.Thermal cycling studies were done with the objective of understanding the failure mechanisms and developing a life model. A life model based on fracture mechanics approach has been developed by taking into account different crack growth paths during thermal cycling, sintering of the top coat, oxidation of the bond coat and the thermal mismatch stresses. Validation of such a life model by comparing to the experimental results showed that the model could predict the TCF life reasonably well at temperatures of 1100 °C or below. At higher temperatures, the accuracy of the model became worse. As a further development, a simplified crack growth model was established. This simplified model was shown to be capable of predicting the TCF life as well as the effect of hold times with good accuracy.
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- Zhang, Jun, Dr. 1987-
(författare)
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Synthesis and characterization of fluorescent stilbene-based probes targeting amyloid fibrils
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) is characterized by two main protein aggregate hallmarks in the brain: extracellular deposition of the amyloid-β (Aβ) in senile plaques and intracellular neurofibrillary tangles (NFTs) consisting of hyperphosphorylated tau protein. The past decade has seen great progress in the development of imaging probes for the non-invasive detection of Aβ and tau aggregates. Here positron emission tomography (PET), single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI), are highly promising technologies for clinical diagnostics. However, as a research tool, optical imaging is superior because it is real-time, sensitive, inexpensive, not radioactive and that it in particular affords high-resolution studies both in vitro and in vivo. Fluorescent probes are especially useful for designing novel binding scaffolds for structure investigations of protein aggregates. This thesis describes design, synthesis and evaluation of a series of fluorescent probes for detection of amyloid fibrils, especially Aβ or tau aggregates in vitro.Firstly, trans-stilbenoid vinylbenzene-1,2-diol with benzene, naphthalene, anthracene, and pyrene are investigated with respect to their photophysical properties free in solution and when bound to amyloid fibrils, including time-resolved fluorescence measurements. It is noted that the extended conjugated systems retained the amyloid targeting properties of the probes and both the anthracene and pyrene moieties extensively enhanced the fluorescence intensity and prolonged lifetimes.Secondly, the synthesis of two molecules, Py1SA and Py2SA, based on pyrene linked to salicylic acid via a trans-stilbene C = C bond is presented. The compounds show strikingly different emission spectra when bound to preformed Aβ1-42 fibrils as well as to fibrils from four other distinct proteins. Additionally, excited state intramolecular proton transfer (ESIPT) coupled-charge transfer (ICT) is observed for the anionic form of the probes in polar solvents. This is likely the reason for the spectral differences of the probes when bound to amyloid fibrils.Moreover, the synthesis of a further development of the Congo red analogue X-34 [2,5-bis(4’-hydroxy-3’-carboxy-styryl) benzene] by rational design and synthesis is described. Full photophysical characterization was performed, including recording absorbance and fluorescence spectra, Stokes shift, quantum yield and fluorescence lifetimes. All ligands displayed high affinity towards recombinant amyloid fibrils of Aβ1-42 and tau as well as selectivity towards the corresponding disease-associated protein aggregates in human post mortem AD tissue.Lastly, the synthesis of a set of 2,1,3-benzothiadiazole (BTD)-based ligands with different conjugated spacers and variable patterns of OH substitutions of bis-styryl-BTD prototypes were developed. Aβ binding affinities (Aβ1-42 and Aβ1-40 fibrils) and the specificity towards Aβ plaques of all ligands were determined. These findings extend the structure to activity relationships of BTD-based ligands for Aβ fibril binding.Throughout the studies in this dissertation, new interesting properties of small molecule fluorescence probes have been discovered and analyzed. This knowledge should facilitate the development of noninvasive probes for early detection of Alzheimer's disease and to distinguish different Aβ fibril polymorphs.
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