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Coming dissertations at TekNat

  • Ceramic Core–Shell Particles : Synthesis and Use within Dentistry

    Author: Camilla Berg
    Publication date: 2021-04-15 14:51

    Dentin hypersensitivity is one of the most prevalent conditions related to oral health, affecting a large share of the adult population. Shortcomings with the available treatment options are related to non-ideal particle sizes and degradation properties. An improved clinical outcome could possibly be obtained using a bioactive occluding agent that can offer a high, continuous release of ions, as well as having a particle size that allows for penetration into the dentin tubules. 

    The work in this thesis focused on the development and investigation of a synthesis approach for calcium phosphate core–shell particles and the use of those in the treatment of dentin hypersensitivity. The overall aim was to increase the knowledge about the synthesis and to evaluate the in vitro performance of amorphous calcium magnesium phosphate (ACMP) particles when used as an occluding agent. 

    The synthesis of the core-shell particles was based on precipitation reactions in aqueous solutions and the synthesized materials were studied in terms of morphological, structural, and compositional aspects. Resulting particles had diameters ranging from 400 nm–1. 5 µm (depending on...

  • An experimental approach on linear synthetic inertia

    Author: Martin Fregelius
    Publication date: 2021-04-06 14:13

    The interest in renewable energy has significantly increased in the last decades which has led to an increased amount of renewable energy sources in the grid. In the Nordic grid, the major contribution to renewable energy is hydro power and wind power and an increase in the amount of wind power is expected in the future. The increase in wind power and decommissioning of nuclear power is expected to decrease the mechanical inertia in the system which helps to stabilise the electrical grid frequency. The inertia is expected to decrease by a factor of two within 20 years and other solutions for frequency stability must be implemented to assure a stable power system. At Uppsala University several projects are investigating how grid-connected energy storages can increase the frequency stability with a high penetration of intermittent renewable energy sources. In this thesis, a linear synthetic inertia control algorithm is implemented on a national Instruments FPGA for controlling the power flow from a supercapacitor energy storage via a two-level three-phase inverter. The control strategy is evaluated both via simulations and experimental tests in a nano grid. The results of the...

  • From Declarative Models to Local Search

    Author: Gustav Björdal
    Publication date: 2021-03-30 11:49

    A solver is a general-purpose software for solving optimisation problems. It takes as input a description of a problem, called a model, and uses a collection of algorithms, called its solving technology, to ideally produce an optimal solution as output. Most solvers have a modelling language that cannot be processed by other solvers. This means that there is a risk of making an early commitment to a solver and its technology when writing a model. To address this risk, and to increase the accessibility of solvers, there has been a push for technology-independent modelling languages, a notable one being MiniZinc.

    A model written in MiniZinc is transformed by the MiniZinc toolchain in order to suit a targeted solver and its technology. However, for a solver to process a MiniZinc model, it also requires what is called a backend for MiniZinc. A backend translates the transformed MiniZinc model into the solver’s own modelling language and synthesises any components not in a MiniZinc model that the solver (or its technology) requires.

    The solving technology called constraint-based local search (CBLS) is based on the popular algorithm design methodology called local search...

  • Lichens in Mountain Rainforests of Tanzania : Studies of Usnea and Calicioids

    Author: Stella Gilbert Temu
    Publication date: 2021-03-29 14:09

    Lichens occur in various habitats. They often have narrow niches and are sensitive to environmental changes leading to their use as bioindicators of environmental disturbances and conditions; air and heavy metal pollution, agricultural toxins, assessing forest continuity and drought tolerance. Lichenological studies in Africa, particularly in Tanzania, have been scarce, and those available have been mainly based on morphology and chemistry data.   The aim of my doctorate was to investigate lichens, in particular Usnea and calicioid lichens in mountain rain forests in Tanzania, using both traditional and molecular approaches.

    Paper I and II explored Usnea subgenus Eumitria. In paper I, molecular, morphological and chemical methods were utilized. A phylogeny of Eumitria from Tanzania based on a four-markers data set supported monophyly of Eumitria, where sixty-two new sequences were reported. In paper II additional specimens of the Usnea pectinata aggregate from Tanzania and São Tomé and Príncipe were studied, and forty-two...

  • Conservative Definitions for Higher-order Logic with Ad-hoc Overloading

    Author: Arve Gengelbach
    Publication date: 2021-03-29 09:35

    With an ever growing dependency on computer systems, the need to guarantee their correct behaviour increases. Mathematically rigorous techniques like formal verification offer a way to derive a system's mathematical properties for example with the help of a theorem prover. A theorem prover is a type of software that assists a user in deriving theorems expressed in a formal language. With a theorem prover one should never be able to prove something that is contradictory, as otherwise the proof effort is worthless. This property is called consistency and is essential for formal developments.

    Theorem provers enjoy high confidence, since they often rely on a trusted logical kernel that is enriched with new symbols in a controlled way. Instead of asserting the existence of mathematical objects with their desired properties, new symbols are introduced through definitions. These definitions are checked by this kernel, and expected to act as abbreviations. Any theorem that is expressible without a definition should not need that definition in its proof. A definition satisfying this property is called conservative. Conservative definitions are especially important as they preserve...

  • Finite Difference Methods for Wave Dominated Problems

    Author: Jonatan Werpers
    Publication date: 2021-03-26 12:39

    Wave models are an important class of models that describe many diverse phenomena such as sound waves, fluid flow, and quantum mechanics. These models are often described mathematically as partial differential equations (PDE). Often these equations do not admit solutions on closed-form and then the only option to study them is numerical methods. These numerical methods must be robust, accurate, and efficient. For spatial discretizations, it is known that higher-order finite-difference methods are efficient, but they often complicate achieving robustness.

    In this thesis, we focus on high-order finite-difference methods for solving these wave-dominated PDEs. We use the summation-by-parts (SBP) framework together with simultaneous approximation terms (SAT) for the boundary conditions to prove stability and robustness. This results in efficient numerical methods that are known to converge to the correct solution.

    The work in this thesis aims to broaden the scope of these finite-difference methods in different ways. In Paper I and III the framework is extended to two dispersive wave equations, solving challenges arising in both the spatial discretization as well as the...

  • Structural and Biochemical Characterizations of Three Potential Drug Targets from Pathogens

    Author: Lu Lu
    Publication date: 2021-03-25 12:35

    As antibiotic resistance of various pathogens emerged globally, the need for new effective drugs with novel modes of action became urgent. In this thesis, we focus on infectious diseases, e.g. tuberculosis, malaria, and nosocomial infections, and the corresponding causative pathogens, Mycobacterium tuberculosis, Plasmodium falciparum, and the Gram-negative ESKAPE pathogens that underlie so many healthcare-acquired diseases. Following the same-target-other-pathogen (STOP) strategy, we attempted to comprehensively explore the properties of three promising drug targets.

    Signal peptidase I (SPase I), existing both in Gram-negative and Gram-positive bacteria, as well as in parasites, is vital for cell viability, due to its critical role in signal peptide cleavage, thus, protein maturation, and secreted protein transport. Three factors, comprising essentiality, a unique mode of action, and easy accessibility, make it an attractive drug target. We have established a platform, investigating the protein purification, enzymatic kinetics, and inhibition. A full-length SPase I from E. coli, including two transmembrane segments, was produced and purified in...

  • Toward functional Metal-Organic Frameworks: molecular doping, depth profiling, and surface growth

    Author: Timofey Liseev
    Publication date: 2021-03-19 10:06

    In this thesis, selected synthetic aspects of functional Metal-Organic Frameworks (MOFs) are considered. More specifically, the work is focused on MOFs doped with functional molecules in the role of structural linkers. In the first part, preparation of such MOF/molecular catalyst hybrid materials of two topologies UiO (UiO = Universitet i Oslo) and NU-1000 (NU = Northwestern University) – is investigated and three different synthetic pathways to these materials are studied. In the second part, a novel MOF depth profiling technique – Rutherford Backscattering Spectrometry – is introduced and then used to elucidate depth distribution of molecules post-synthetically introduced into a MOF. In the last part, efficient interfacing of MOFs with electrodes is considered and a methodology for growing surface-mounted layer-pillar-type M2L2P MOFs (SURMOFs, M = metal, L = layer linker, P = pillar linker) with high degree of orientation and thickness control on bare Si substrates is developed.

  • Computational Insights into Atomic Scale Wear Processes in Cemented Carbides

    Author: Emil Edin
    Publication date: 2021-03-08 13:58

    As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar...

  • 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...

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