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Coming dissertations at TekNat

  • Defect Thermodynamics and Kinetics in Polyanionic Cathodes : A Theoretical Roadmap for Na-ion based Batteries and Hybrid Supercapacitors

    Author: Teeraphat Watcharatharapong
    Publication date: 2019-04-29 14:15

    In this thesis, the framework of the density functional theory is employed to study and predict properties of polyanionic cathodes for Na-ion batteries and hybrid supercapacitors. It consists of three main parts as follows:

    The first part is primarily dedicated to kröhnkite-type Na2Fe(SO4)22H2O cathode. The major goal is to probe diffusion mechanisms of Na+ ions.  The chemical potentials diagrams for the pentrary compound are determined under thermodynamic equilibrium and are used to calculate pH value for solution-based synthesis. We find that the presence of NaFe facilitates a faster migration and reduces the channel blockage issue. Moreover, the defect concentration can be tuned by controlling the pH condition. We conclude that defects and small hole polarons play a role in ionic and electronic conductivity.

    The second part focuses on alluaudite-type Na2+2δFe2-δ(SO4)3 (NFSδ). We unveil the effect of the non-stoichiometry on the thermodynamics, defect nature, and voltage profiles NFSδ with δ = 0, 0.25 and 0.5. The relation between Na ion distribution and energetics is studied and reveals the necessity of using a supercell model. Chemical potential diagrams...

  • Water Splitting Mechanism on 2D Catalytic Materials : DFT based Theoretical Investigations

    Author: John Wärnå
    Publication date: 2019-04-29 14:14

    In this thesis, we have envisaged systematic investigation to predict the water splitting mechanism on ultra-thin two-dimensional (2D) materials using cutting edge computation. Three different families of materials are considered as the case studies - i.MX2 (where M= W and Pt) based transition metal dichalcogenides, ii. lightest 2D material as Boron monolayer and iii. Mg3N2 monolayer. The catalytic reaction mechanism of water dissociation consists of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), both of which are required to be investigated thoroughly in order to perceive the complete picture of water splitting. This is because of the fact that the fundamental understanding of how and why the improved solar hydrogenproduction properties could be developed for such 2D materials is also of great technological importance. We have performed rigorous electronic structure calculations based on density functional theory (DFT) to find the optimum catalytic activity of the considered monolayer nanostructures. Hydrogen and oxygen evolution reaction activity are determined from the surface-adsorbate interaction based on the adsorption energy of the major...

  • Adaptation of wave power plants to regions with high tides

    Author: Mohd Nasir Ayob
    Publication date: 2019-04-26 14:06

    The wave energy converter (WEC) developed at Uppsala University is based on the concept of a heaving point absorber with a linear generator placed on the seafloor. The translator inside the generator oscillates in a linear fashion and is connected via a steel wire to a point absorbing buoy. The power production from this device is optimal when the translator’s oscillations are centered with respect to the stator. However, due to the tides, the mean translator position may shift towards the upper or lower limits of the generator’s stroke length, thereby affecting the power production. This effect will be severe if the WEC operates in an area characterized by a high tidal range. The translator may be stuck at the top or rest at the bottom of the generator for a considerable amount of time daily.

    One of the solutions to this problem is to develop a compensator that is able to adjust the length of the connecting line. With an estimated weight of 10 tonnes of the connecting line and the translator, the use of a pocket wheel wound with steel chain was deemed suitable. Not being connected to an external power supply, the device needs a alternative local power supply to charge...

  • Biogeochemical Processes in Denitrifying Woodchip Bioreactors and their Application in the Mining Industry

    Author: Albin Nordström
    Publication date: 2019-04-24 14:46

    This thesis evaluates passive denitrifying woodchip bioreactors (DWBs) for the removal of nitrate (NO3-) in neutral pH mine drainage, where water is passed through a carbon-rich porous matrix (e.g. woodchips) for the reduction of NO3- to nitrogen gas. DWBs have been used for the removal of NO3- from water in various settings and are expected to operate with little maintenance for at least a decade; however, the processes controlling the emission of greenhouse gases and other undesirable by-products, as well as the magnitude and variability in NO3- removal rates and how these develop over time, are not completely understood and were the focus of this thesis.

    Water treatment in DWBs was investigated in laboratory-scale column tests and in a pilot-scale bioreactor installed at the Kiruna iron ore mine, northern Sweden. Denitrification was the major pathway for NO3- removal in both experimental systems. Incoming NO3- concentrations (up to 30.0 mg N L-1) were removed to below detection limits at temperatures and hydraulic residence times (HRTs) between 5-22°C and ~1.9-2.6 days, respectively, without substantial production of nitrite or ammonium (NH4+). NO3- removal was...

  • Offshore deployments of marine energy converters

    Author: Maria Angeliki Chatzigiannakou
    Publication date: 2019-04-24 11:37

    The depletion warning of non-renewable resources, such as gas, coal and oil, and the imminent effects of climate change turned the attention to clean and fossil fuel-free generated electricity. University research groups worldwide are studying solar, wind, geothermal, biomass and ocean energy harvesting. The focus of this thesis is the wave and marine current energy researched at the division of Electricity at Uppsala University (UU). 

    The main drawbacks that hinder the commercialization of marine energy converter devices is a high installation, operation, maintenance and decommissioning cost. Furthermore, these processes are highly weather dependent and thus, can be time consuming beyond planning. In this thesis, an evaluation of the cost, time and safety efficiency of the devices’ offshore deployment (both wave and marine current), and a comparative evaluation regarding the safety in the use of divers and remotely operated vehicles (ROVs) are conducted. Moreover, a risk analysis study for a common deployment barge while installing an UU wave energy converter (WEC) is presented with the aim to investigate the failure of the crane hoisting system.

    The UU wave energy...

  • Techniques for analyzing digital environments from a security perspective

    Author: Amendra Shrestha
    Publication date: 2019-04-24 11:20

    The development of the Internet and social media has exploded in the last couple of years. Digital environments such as social media and discussion forums provide an effective method of communication and are used by various groups in our societies.  For example, violent extremist groups use social media platforms for recruiting, training, and communicating with their followers, supporters, and donors. Analyzing social media is an important task for law enforcement agencies in order to detect activity and individuals that might pose a threat towards the security of the society.

    In this thesis, a set of different technologies that can be used to analyze digital environments from a security perspective are presented. Due to the nature of the problems that are studied, the research is interdisciplinary, and knowledge from terrorism research, psychology, and computer science are required. The research is divided into three different themes. Each theme summarizes the research that has been done in a specific area.

    The first theme focuses on analyzing digital environments and phenomena. The theme consists of three different studies. The first study is about the...

  • The evolution of sex chromosomes and sex-linked sequences in birds

    Author: Homa Papoli Yazdi
    Publication date: 2019-04-23 10:44

    Identifying the processes involved in the evolution of suppressed recombination between sex chromosomes and understanding their consequences for the evolutionary dynamics of sex-linked loci have been major topics of research during the last century. In this thesis, I used the avian ZW system, where females are the heterogametic sex, to investigate the underlying processes in sex chromosome evolution in birds. I identified the gametologous genes between the largely recombining Z and W chromosomes of ostrich and dated the timing of the cessation of recombination to prior to the split of modern birds. I then constructed a genetic map of the ostrich Z chromosome and corrected its assembly in order to obtain the ancestral organization of the Z chromosome in a basal clade of birds. By analyzing the inversion events across the avian phylogeny, I concluded that a combination of Z- and possibly W-linked inversions might have been responsible for the evolution of suppressed recombination in avian sex chromosomes. To understand the determinants of levels of genetic diversity on Z chromosome compared to autosomes, I calculated Z to autosome (Z:A) genetic diversity across 32 avian species....

  • Probing Catalytic Reaction Mechanisms of Biomimetic Diiron Complexes through Time-resolved Absorption Spectroscopy

    Author: Shihuai Wang
    Publication date: 2019-04-23 10:10

    Directed design of improved molecular catalysts for hydrogen evolution reactions relies on rational benchmarking based on a detailed understanding about the mechanism of catalysis. Specifically, investigation of multi-electron redox catalysis, with structural characterization of catalytic intermediates, combined with the kinetics of their transformations, can reveal the rate-limiting step of the overall reaction, possible degradation pathways and the function of structural motives. However, direct spectroscopic observation of catalytic intermediates is in most cases not available due to the rapid turnover of efficient catalysts.

    In this thesis, time-resolved absorption spectroscopy with UV-Vis and mid-IR detection was used to identify catalytic reaction intermediates and account for kinetics relevant to elementary reactions steps of H2 formation on a nanosecond to second time scale. For a class of FeIFeI (S-R-S)(CO)6-n(PMe3)n complexes (R = propyl, benzyl or azapropyl), inspired by the active site of FeFe-hydrogenase, the key intermediates formed in different catalytic pathways have been characterized. These complexes typically feature very similar coordination geometry,...

  • Pathogenesis and Cell Biology of the Salmon Parasite Spironucleus salmonicida

    Author: Ásgeir Ástvaldsson
    Publication date: 2019-04-17 11:59

    Spironucleus species are classified as diplomonad organisms, diverse eukaryotic flagellates found in oxygen-deprived environments. Members of Spironucleus are parasitic and can infect a variety of hosts, such as mice and birds, while the majority are found to infect fish. Massive outbreaks of severe systemic infection caused by a Spironucleus member, Spironucleus salmonicida (salmonicida = salmon killer), have been reported in farmed salmonids resulting in large economic impacts for aquaculture.

    In this thesis, the S. salmonicida genome was sequenced and compared to the genome of its diplomonad relative, the mammalian pathogen G. intestinalis (Paper I). Our analyses revealed large genomic differences between the two parasites that collectively suggests that S. salmonicida is more capable of adapting to different environments. As S. salmonicida can infiltrate different host tissues, we provide molecular evidence for how the parasite can tolerate oxygenated environments and suggest oxygen as a potential regulator of virulence factors (Paper III). To further investigate the molecular responses...

  • Wind Turbine Sound in Cold Climates

    Author: Kristina Conrady
    Publication date: 2019-04-15 14:33

    The increase in the number of wind turbines (WTs) in populated areas in cold climates increases the number of people potentially being affected by WT sound. Outdoor sound propagation is strongly dependent on meteorological conditions, however, limitations in the knowledge exist regarding the implications of meteorological conditions in cold climates. Long-term acoustic and meteorological measurements were conducted in the vicinity of two wind farms in northern Sweden, to investigate the effect of snow and low-level wind maxima on WT sound, to analyse the occurrence of amplitude modulation and to evaluate selection methods for WT sound measurements. Different selection methodologies were applied to the acoustical data. The simplest method only includes a minimum rotational frequency of the WTs, while the most comprehensive method additionally includes criteria based on spectral resemblance, temporal variation of the sound level, amplitude modulation and wind speed. The effect of snow on WT sound depends on the snow quality. Snow on trees lowers the sound level by ca. 2 dBA. Low-level wind maxima below hub height reduce the sound level near the surface. Since this effect is...

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