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Coming dissertations at TekNat

  • Uncertainty and correlation modeling for load flow analysis of future electricity distribution systems : Probabilistic modeling of low voltage networks with residential photovoltaic generation and electric vehicle charging

    Author: Umar Hanif Ramadhani
    Publication date: 2021-03-05 06:37

    The penetration of photovoltaic (PV) and electric vehicles (EVs) continues to grow and is predicted to claim a vital share of the future energy mix. It poses new challenges in the built environment, as both PV systems and EVs are widely dispersed in the electricity distribution system. One of the vital tools for analyzing these challenges is load flow analysis, which provides insights on power system performance. Traditionally, for simplicity, load flow analysis utilizes deterministic approaches and neglecting  correlation between units in the system. However, the growth of distributed PV systems and EVs increases the uncertainties and correlations in the power system and, hence, probabilistic methods are more appropriate.

    This thesis contributes to the knowledge of how uncertainty and correlation models can improve the quality of load flow analysis for electricity distribution systems with large numbers of residential PV systems and EVs. The thesis starts with an introduction to probabilistic load flow analysis of future electricity distribution systems. Uncertainties and correlation models are explained, as well as two energy management system strategies: EV smart...

  • X-ray Absorption and Fragmentationas Initial Steps of Radiation Damage in Free Organic Molecules and Nanoparticles

    Author: Abdul Rahman Abid
    Publication date: 2021-03-03 14:01

    Understanding the molecular radiation damage is crucial in radiobiology, molecular physics, and atmospheric science. In this thesis, the initial steps of radiation damage of anhydrous gas-phase molecules and hydrated nanoparticles were studied using synchrotron radiation based electron-ion coincidence spectroscopy and X-ray absorption spectroscopy under vacuum conditions. Electron - ion coincidence spectroscopy was used to study the photofragmentation and molecular dynamics of the isolated gas-phase molecules. In addition to the photofragmentation of the gas-phase molecules, the effect of the initial ionization site, initial molecular geometry, and the intramolecular chemical environment has been studied. In avobenzone, core ionization leads to massive fragmentation, with a slight site-selectivity concerning fragment production. In ortho-aminobenzoic acid, core ionization leads to the production of a hydronium ion, indicating that the importance of functional group's position for double intramolecular hydrogen transfer. X-ray absorption spectroscopy was used to probe hydrated nanoparticles prepared at different relative humidities. In hydrated inorganic and mixed inorganic-...

  • Capturing Air Pollutants : Photochemical Adsorption and Degradation of SO2, NO2 and CO2 on Titanium Dioxide

    Author: David Michael Langhammer
    Publication date: 2021-03-02 13:09

    Titanium dioxide (TiO2) is a material with many useful properties. It is used most widely as a pigment in white paint, although in technological research it is better known for its ability to catalyze chemical reactions during light absorption. This process is referred to as photocatalysis, where the energy of the light is used to power the chemical reactions. This has enabled several interesting applications of TiO2, where it can for instance be applied to windows or façade walls to make their surfaces self-cleaning. Another implementation that has received much attention lately is artificial photosynthesis, where the light energy is used to transform CO2 and H2O into synthetic fuels. This thesis work contributes to the development of both these applications, although the main ambition is to show how three of the most common ambient air pollutant molecules, SO2, NO2 and CO2, can be captured at the surface of TiO2 by means of photocatalysis. 

    Specifically, infrared (IR) spectroscopy and density functional theory (DFT) has been used as complementary tools of analysis to study the photocatalytic reactions that enable transformation of SO2, NO2 and CO2 into strongly bound...

  • Molecular simulations of G protein-coupled receptors : A journey into structure-based ligand design and receptor function

    Author: Pierre Matricon
    Publication date: 2021-03-02 12:44

    The superfamily of G protein-coupled receptors (GPCRs) contains a large number of important drug targets. These cell surface receptors recognize extracellular signaling molecules, which stimulates intracellular pathways that play major roles in human physiology. Breakthroughs in structural biology have led to an exponentially increasing number of atomic resolution GPCR structures, which have provided insights into the molecular basis of ligand binding and receptor activation. However, in order to use these structures in rational drug design, computational methods able to predict ligand binding modes and affinities are required. In the first part of this thesis, molecular simulations were used to explore the potential of using structure-based approaches to discover and optimize GPCR ligands. In paper I, molecular dynamics (MD) simulations in combination with free energy perturbation (FEP) guided improvements of binding affinities for fragment-like ligands of the A2A adenosine receptor (A2AAR), which is a target for Parkinson’s disease and cancer. Two computational approaches were then explored to design selective GPCR ligands. MD/FEP was first used to guide the optimization of a...

  • Evolutionary consequences of sex-specific selection

    Author: Josefine Stångberg
    Publication date: 2021-03-02 12:30

    Sex-specific selection is widespread, evident by the evolution of sexual dimorphism in many traits in sexually reproducing taxa. The reason why the sexes may experience selection that differs in direction or magnitude is often linked to the reproductive strategies associated with the sex-specific reproductive physiology. Competition for mates or fertilisations creates conditions where selection is sex-specific and may overall be stronger on the sex experiencing more competition. However, the sexes share a majority of their genome and consequently many traits may be genetically correlated between the sexes, constraining sex-specific adaptation. In paper I, II and III, I investigate the consequences of exposure to altered strength of sex-specific selection in the laboratory through 30 generations of experimental evolution with skewed sex ratios, using the sexually reproducing nematode Caenorhabditis remanei as a model organism. I created female-biased (FB) and male-biased (MB) treatments. In paper I, I investigated the phenotypic response to selection in three life history traits (body size, fitness and...

  • Linear models for multiscale materials simulations : Towards a seamless linking of electronic and atomistic models for complex metal oxides

    Author: Akshay Krishna Ammothum Kandy
    Publication date: 2021-03-02 10:35

    Multiscale modelling approaches, connecting data from electronic structure calculations all the way towards engineering continuum models, have become an important ingredient in modern materials science. Materials modelling in a broader sense is already amply used to address complex chemical problems in academic science, but also in many industrial sectors. As far as multiscale modelling is concerned, however, many challenges remain, in particular when it comes to coupling and linking the various levels along the multiscale ladder in a seamless and efficient fashion.        

    This thesis focusses on the development of new and efficient linear models to improve the quality and parameterisation processes of the two-body potentials used in empirical and semi-empirical methods within a multiscale materials modelling framework. In this regard, a machinery called curvature constrained splines (CCS) based on cubic splines to approximate general two-body potentials has been developed. The method is linear, and parameters can be easily solved in a least-square sense using a quadratic programming approach. Moreover, the objective function is  convex, implying that global minima can...

  • Engineering Surfaces of Solid-State Nanopores for Biomolecule Sensing

    Author: Shiyu Li
    Publication date: 2021-03-01 13:56

    Nanopores have emerged as a special class of single-molecule analytical tool that offers immense potential for sensing and characterizing biomolecules such as nucleic acids and proteins. As an alternative to biological nanopores, solid-state nanopores present remarkable versatility due to their wide-range tunability in pore geometry and dimension as well as their excellent mechanical robustness and stability. However, being intrinsically incompatible with biomolecules, surfaces of inorganic solids need be modified to provide desired functionalities for real-life sensing purposes. In this thesis, we presented an exploration of various surface engineering strategies and an examination of several surface associated phenomena pertaining specifically to solid-state nanopores. Based on the parallel sensing concept using arrayed pores, optical readout is mainly employed throughout the whole study.

    For the surface engineering aspect, a list of approaches was explored. A versatile surface patterning strategy for immobilization of biomolecules was developed based on selective poly(vinylphosphonic acid) passivation and electron beam induced deposition technique. This scheme was then...

  • Allosteric control of ALC1-catalyzed nucleosome remodeling

    Author: Laura C. Lehmann
    Publication date: 2021-03-01 10:00

    The genetic information of eukaryotic cells is packaged inside the nucleus as chromatin. This packaging restricts access to the DNA and therefore represents a barrier for processes such as DNA replication, repair, and gene expression. Specialized enzymes, termed ATP-dependent chromatin remodelers (remodelers), are involved in regulating the chromatin landscape by repositioning, ejecting, and altering the composition of nucleosomes, the smallest building blocks of chromatin. Remodelers are tightly regulated by post-translational modifications, nucleosomal features, as well as by their own domains and subunits. Dysregulation of remodeling activity has been implicated in severe disease states such as various types of cancer.

    ALC1/CHD1L (Amplified in Liver Cancer 1/Chromodomain-Helicase-DNA-binding protein 1-Like) is an oncogenic remodeler involved in DNA damage repair. This thesis investigates the molecular basis of ALC1 regulation, the role of the nucleosome and its features in ALC1 activation, as well as the role of this remodeler in DNA damage repair. 

    The results presented in this thesis show that, without DNA damage, the catalytic domain of ALC1 adopts an inactive...

  • Voltage Transients in the Field Winding of Salient Pole Wound Synchronous Machines : Implications from fast switching power electronics

    Author: Roberto Felicetti
    Publication date: 2021-02-26 10:24

    Wound Field Synchronous Generators provide more than 95% of the electricity need worldwide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding.

    This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage...

  • Materials analysis using MeV-ions: fundamental challenges and in-situ applications

    Author: Karim-Alexandros Kantre
    Publication date: 2021-02-25 10:43

    The interaction of energetic ions with matter is highly relevant for a wide range of applications. Amongst them, material characterization employing ion beams is widely used due to its capability of high-resolution composition depth profiling. The non-destructive nature of these techniques makes them appealing, although there are still several aspects  which can be improved and thus deserve attention. For example, better understanding of energy deposition of ions in matter, can improve simultaneous depth profiling of light and heavy atomic species in a single target. Also, the synthesis of advanced material systems requires complex, multi-step protocols. This situation creates an increased demand for in-situ material characterization, keeping the benefits of ion beam analysis. The present thesis addresses the above mentioned open aspects which are of both fundamental and applied character.

    First, the energy loss of heavy ions in solid matter, at energies relevant for recoil spectrometry, is investigated. The contribution of inelastic and elastic collisions of heavy ions to the total energy loss as well as the validity of the single scattering assumption  are assessed....