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Coming dissertations at TekNat

  • Power transfer in the air gap of linear generators for wave power

    Author: Anna E. Frost
    Publication date: 2019-05-13 10:35

    An increased need for electric energy and share of renewable energy is important for a more sustainable future, to which wave power can contribute. Some concepts for wave power use linear generators, and the studies presented here focus on the power transfer and forces in the air gap of linear generators.

    Based on Poynting's theorem, analytical expressions were derived for how much power is transmitted in the air gap of linear electric machines. The equations were derived for flat linear generators as well as for cylindrical linear generators, and for both the radial and the longitudinal power flows. The radial power flow contributes to the electricity that can be taken from the generator, while the longitudinal contributes to unwanted effects such as vibration. The equations show that for flat linear electric machines, vibrations and other unwanted power transmissions can be reduced by increasing the number of poles in the machine, without decreasing the desired power transfer. Otherwise, the same factors that increase the desired power transfer also increase the unwanted.

    By studying the generator as a damping force and a lumped circuit, it was derived that the...

  • Learning based Word Search and Visualisation for Historical Manuscript Images

    Author: Tomas Wilkinson
    Publication date: 2019-05-13 09:35

    Today, work with historical manuscripts is nearly exclusively done manually, by researchers in the humanities as well as laypeople mapping out their personal genealogy. This is a highly time consuming endeavour as it is not uncommon to spend months with the same volume of a few hundred pages. The last few decades have seen an ongoing effort to digitise manuscripts, both preservation purposes and to increase accessibility. This has the added effect of enabling the use methods and algorithms from Image Analysis and Machine Learning that have great potential in both making existing work more efficient and creating new methodologies for manuscript-based research.

    The first part of this thesis focuses on Word Spotting, the task of searching for a given text query in a manuscript collection. This can be broken down into two tasks, detecting where the words are located on the page, and then ranking the words according to their similarity to a search query. We propose Deep Learning models to do both, separately and then simultaneously, and successfully search through a large manuscript collection consisting of over a hundred thousand pages.

    A limiting factor in applying...

  • Constructions in higher-dimensional Auslander-Reiten theory

    Author: Andrea Pasquali
    Publication date: 2019-05-13 09:02

    This thesis consists of an introduction and five research articles about representation theory of algebras.

    Papers I and II focus on the tensor product of algebras from the point of view of higher-dimensional Auslander-Reiten theory. In Paper I we consider the tensor product Λ of two algebras which are n- respectively m-representation finite. In the case when Λ itself is (n+m)-representation finite, we construct its (n+m)-almost split sequences explicitly in function of the n- and m-almost split sequences of the factors. In Paper II we use the constructions of Paper I to prove the following result: the tensor product of an n- and an m-complete acyclic algebras (in the sense of Iyama) is (n+m)-complete and acyclic.

    Papers III and IV deal with the combinatorics of Postnikov diagrams, or equivalently of the Grassmannian cluster category. This is motivated by 2-dimensional Auslander-Reiten theory: we are interested in constructing self-injective Jacobian algebras as they are the 3-preprojective algebras of 2-representation finite algebras. In Paper III we investigate when the stable...

  • Accuracy of protein synthesis and its tuning by mRNA modifications

    Author: Gabriele Indrisiunaite
    Publication date: 2019-05-10 14:40

    The ribosome is a large macromolecular complex that synthesizes all proteins in the cell in all kingdoms of life. Proteins perform many vital functions, ranging from catalysis of biochemical reactions to muscle movement. It is essential for cells and organisms that proteins are synthesized rapidly and accurately.

    This thesis addresses two questions regarding the accuracy of protein synthesis. How do bacterial and eukaryotic release factors ensure accurate termination? How do mRNA modifications affect the accuracy of bacterial protein synthesis?

    Bacterial release factors 1 (RF1) and 2 (RF2) are proteins that recognize the stop codons of mRNA and catalyze the release of a synthesized protein chain from the ribosome. It has been proposed that RFs ensure accurate termination by binding to the ribosome in an inactive, compact conformation and acquire a catalytically active, extended conformation only after recognizing a correct stop codon. However, the native compact conformation was too short-lived to be captured by conventional structural methods. We have developed a fast-kinetics approach for determining when the RFs are in a compact conformation on the ribosome and...

  • Oxygen Storage Chemistry of Nanoceria

    Author: Dou Du
    Publication date: 2019-05-10 13:44

    The versatile redox chemistry of ceria (CeO2) originates from its Ce4f electron, which plays the key role in changing the oxidation state of Ce between +IV and +III. Ceria is, among other things, a material that can act as a powerful oxygen buffer with a high oxygen storage capacity (OSC). This is used in many technical applications, such as the three-way catalyst, cleaning exhausts from gasoline vehicles. This thesis is concerned with the dramatic OSC effect observed experimentally in the literature for very small ceria nanoparticles (NPs) at lower temperatures, where the effect was found to be accompanied by the formation of superoxide ions (O2–).

    The main aim of the thesis work was to develop strategies to allow us to discover the origin of the OSC phenomenon, and to simulate temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) experiments and collect useful mechanistic insight about these processes. Quantum-mechanical (DFT) calculations, partly with modified DFT functionals, and later augmented by microkinetic (MK) modelling building on the DFT-results, made it possible to model the large and complex NP systems needed to make...

  • Development of Nanoporous Inorganic Carbonates for Pharmaceutical and Environmental Applications

    Author: Maria Vall
    Publication date: 2019-05-10 09:12

    Mesoporous magnesium carbonate (MMC) is a highly porous, anhydrous material which can be synthesized without the use of templates. This thesis shows how post- and in synthesis modification of MMC can create porous inorganic carbonates suitable for different pharmaceutical and environmental applications. 

    Controlled release of IBU was achieved by loading IBU onto amine modified MMC (aMMC). The amine coverage was varied and there was a clear correlation between the release rate of IBU and the amine coverage, the higher the amine coverage the slower the release rate. aMMC was also used to load salicylic acid (SA). SA was then released within 15 minutes in a phosphate buffer (pH 6.8). The cytotoxicity of aMMC was evaluated and it was found non-toxic for human dermal fibroblast cells with particle concentration up to 1000 µg/mL for 48 h of exposure.  aMMC also showed a high adsorption capacity for three different types of anionic azo dyes;  acid red 183, amaranth and reactive black 5. The addition of amine groups to the surface of MMC significantly increased the uptake of the three dyes tested. Composite materials were synthesized by combining the synthesis of MMC and the...

  • Plants as Sources of Natural and Effective Acaricides : Against Ixodes ricinus  (Acari: Ixodidae)

    Author: Fawzeia Elmhalli
    Publication date: 2019-05-02 14:02

    Ticks and tick-borne diseases are major health hazards worldwide, with increasing numbers of cases of Lyme disease and tick-borne encephalitis reported yearly. Meanwhile, concerns about the environmental impact and safety of chemical acaricides are driving research into alternative control methods, such as plant-based acaricides. I evaluated eight plant species for their toxicity and repellency against nymphs of Ixodes ricinus (Acari: Ixodidae), the most important life cycle stage of tick-borne infection of humans.

    Paper I examines the toxicity of the principal active component of the essential oil (EO) of lemon eucalyptus (Corymbia citriodora), p-menthane-3,8-diol (PMD). At 4 h of exposure time (ET), lethal PMD concentrations for 50% mortality (LC50) were 0.035–0.037 mg/cm² and for 95% mortality (LC95) were 0.095-0.097 mg/cm². For 0.1 mg/cm², lethal times for 50% mortality (LT50) were 2.1-2.8 h and for 95% mortality (LT95) were 3.9-4.2 h. An open filter assay gave the most consistent results of five methods tried. Paper II investigated the toxicity of ylang-ylang oil (YYO) and star anise oil (SAO), two naturally occurring, commercially...

  • Silicon Nanowire Field-Effect Devices as Low-Noise Sensors

    Author: Xi Chen
    Publication date: 2019-05-02 12:54

    In the past decades, silicon nanowire field-effect transistors (SiNWFETs) have been explored for label-free, highly sensitive, and real-time detections of chemical and biological species. The SiNWFETs are anticipated for sensing analyte at ultralow concentrations, even at single-molecule level, owing to their significantly improved charge sensitivity over large-area FETs. In a SiNWFET sensor, a change in electrical potential associated with biomolecular interactions in close proximity to the SiNW gate terminal can effectively control the underlying channel and modulate the drain-to-source current (IDS) of the SiNWFET. A readout signal is therefore generated. This signal is primarily determined by the surface properties of the sensing layer on the gate terminal, with sensitivity close up to the Nernstian limit widely demonstrated. To achieve a high signal-to-noise ratio (SNR), it is essential for the SiNWFETs to possess low noise of which intrinsic device noise is one of the major components. In metal-oxide-semiconductor (MOS)-type FETs, the intrinsic noise mainly results from carrier trapping/detrapping at the gate oxide/semiconductor interface and it is inversely...

  • Alexandria: A General Drude Polarizable Force Field with Spherical Charge Density

    Author: Mohammad Mehdi Ghahremanpour
    Publication date: 2019-05-02 10:37

    Molecular-mechanical (MM) force fields are mathematical functions that map the geometry of a molecule to its associated energy. MM force fields have been extensively used for an atomistic view into the dynamic and thermodynamics of large molecular systems in their condensed phase. Nevertheless, the grand challenge in force field development—which remains to be addressed—is to predict­­­­ properties of materials with different chemistries and in all their physical phases. 

    Force fields are, in principle, derived through supervised machine learning methods. Therefore, the first step toward more accurate force fields is to provide high-quality reference data from which the force fields can learn. Thus, we benchmarked quantum-mechanical methods—at different levels of theory—in predicting of molecular energetics and electrostatic properties. As the result, the Alexandria library was released as an open access database of molecular properties.  

    The second step is to use potential functions describing interactions between molecules accurately. For this, we incorporated electronic polarization and charge penetration effects into the Alexandria force field. The Drude model...

  • Transition Metal-Based Electrocatalysts for Alkaline Water Splitting and CO2 Reduction

    Author: Zhen Qiu
    Publication date: 2019-04-29 14:39

    With excessive usage of fossil fuels and ever-increasing environmental issues, numerous efforts have been devoted to the development of renewable energies for the replacement of traditional fossil fuels to reduce greenhouse gas emission and realize the rapidly growing demand for global energy. Renewable energies, however, often show diurnal and seasonal variations in power output, forming a need for energy storage to meet people’s continuous energy supply. One approach is to use electrolysis and produce a fuel that can be used on demand at a later stage. A full realization of effective electricity-to-fuel conversion, however, is still limited by the large overpotential requirements as well as concerns with the usage of scarce platinum group elements. This thesis presents studies on transition metal-based electrocatalysts for alkaline water splitting and CO2 reduction, which are two technologies to produce a chemical fuel from renewable electricity. Our aim is to develop efficient, inexpensive, and robust electrocatalysts based on earth-abundant elements with high energy conversion efficiencies.

    In the first part, we develop and investigate three different electrocatalysts...