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Coming dissertations at TekNat

  • Dynamic Modelling of Physical Processes in Magmatic Systems: Dyke Emplacement and Flow-Induced Crystal Rotations

    Author: Rémi Vachon
    Publication date: 2018-11-09 12:11

    The main motivation for this thesis is to develop and improve numerical tools and methods that help further our comprehension of the volcanic plumbing system and its dynamics.

    The commonly used standard elastic model predicts solutions of dyke shape, thickness, over-pressure and fracturing criteria that do not always fit natural observations. In the first part of the thesis, we want to test whether other host-rock rheologies leads to more realistic dykes. We examine three different rheologies: 1) elasticity with pressure dependent elastic moduli, 2) elastoplasticity with plastic failure in regions of high shear stresses and 3) viscoelasticity to describe ductile flow of rocks by creeping mechanisms in regions of high temperature. Solu-tions from the three tested models give dykes with more rectangular shapes relative to solutions computed from the model of linear elasticity. In addition, the calculated magma pressure for an intrusion of a given thickness is reduced for all tested rheologies. Greatest differences with the linear elastic solution are given by the elastoplastic model, in which computed magma over-pressures are lower than elastic solutions by a factor of 2 to 10...

  • Ion-Crosslinked Nanocellulose Hydrogels for Advanced Wound Care Applications

    Author: Alex Basu
    Publication date: 2018-11-09 09:39

    A current trend in the field of wound care is the development of wound healing materials that are designed to address specific types of wounds or underlying pathologies to achieve improved healing. At the same time, there is a societal drive to replace synthetic materials with renewable alternatives. The work presented in this thesis was therefore carried out to investigate the use of wood nanocellulose, produced from the world’s most abundant biopolymer, cellulose, in advanced wound care applications.

    Wood-based nanofibrillated cellulose (NFC) was chemically functionalized and crosslinked using calcium to obtain a self-standing hydrogel. The NFC hydrogel was evaluated in terms of its physicochemical properties, biocompatibility, blood interactions, bacterial interactions, in vivo wound healing ability and, finally, as a protein carrier. Parallel with the assessment of the NFC hydrogel, modified versions of the material were tested to investigate the tunability of the above-mentioned characteristics.

    The ability of the hydrogel to maintain a moist wound bed was demonstrated. Evaluation of the biocompatibility showed that the material was cytocompatible and...

  • Carboligation using the aldol reaction : A comparison of stereoselectivity and methods

    Author: Derar Al-Smadi
    Publication date: 2018-11-07 07:55

    The research summarized in this thesis focuses on synthesizing aldehyde and aldol compounds as substrates and products for the enzyme D-fructose-6-aldolase (FSA). Aldolases are important enzymes for the formation of carbon-carbon bonds in nature. In biological systems, aldol reactions, both cleavage and formation play central roles in sugar metabolism. Aldolases exhibit high degrees of stereoselectivity and can steer the product configurations to a given enantiomeric and diastereomeric form. To become truly useful synthetic tools, the substrate scope of these enzymes needs to become broadened.

    In the first project, phenylacetaldehyde derivatives were synthesized for the use as test substrates for E. coli FSA. Different methods were discussed to prepare phenylacetaldehyde derivatives, the addition of a one carbon unit to benzaldehyde derivatives using a homologation reaction was successful and was proven efficient and non-sensitive to the moisture. The analogues were prepared through two steps with 75-80 % yields for both meta- and para-substituted compounds.

    The second project focuses on synthesizing aldol compound using FSA enzymes, both...

  • Self-Consumption of Photovoltaic Electricity in Residential Buildings

    Author: Rasmus Luthander
    Publication date: 2018-11-06 07:59

    Worldwide installations of photovoltaics (PV) have increased rapidly due to national subsidies and decreasing prices. One important market segment is building-applied PV systems, for which the generated electricity can be self-consumed. Self-consumption is likely to become important both for the profitability and to facilitate integration of high shares of PV in the power system. The purpose of this doctoral thesis is to examine opportunities and challenges with distributed PV in the power system on four system levels: detached houses, communities, distribution systems and national level. This was done through literature studies and computer simulations. Previous research has shown a larger potential to increase the PV self-consumption in detached houses by using battery storage rather than shifting the household appliance loads. This thesis shows that, on the community level, the self-consumption increased more when sharing one large storage instead of individual storages in each house. On the distribution system level, PV power curtailment was identified as an effective solution to reduce the risk of overvoltage due to high PV penetration levels. However, the curtailment...

  • Application of Uncertainty Quantification Techniques to Studies of Wall-Bounded Turbulent Flows

    Author: Saleh Rezaeiravesh
    Publication date: 2018-11-01 10:22

    Wall-bounded turbulent flows occur in many engineering applications. The quantities of interest (QoIs) of these flows can be accurately obtained through experimental measurements and scale-resolving numerical approaches, such as large eddy simulation (LES). However, due to the prohibitive computational costs imposed by the turbulent boundary layers (TBL) involved in these flows, the use of a standard wall-resolving (WR)LES is limited to low Reynolds (Re-) numbers. As an alternative, wall-modeled (WM)LES can be employed, in which the near-wall region of the TBL is modeled.

    This thesis evaluates the uncertainties involved in the measured QoIs of a set of experiments on TBLs, and also, investigates the predictive accuracy and sensitivity of LES, both wall-resolving and wall-modeled. For these purposes, different uncertainty quantification (UQ) techniques are employed.

    In particular, such techniques are applied to the forward (uncertainty propagation) and inverse (parameter estimation) problems involved in the measurement of mean velocity and wall shear stress using hot-wire anemometry and oil-film interferometry, respectively. The possibility of reducing epistemic...

  • Sources of variability in heterospecific social information use for breeding habitat selection : Role of genetics and personality in collared flycatchers

    Author: Jennifer Morinay
    Publication date: 2018-11-01 07:59

    All their life, individuals have to make decisions that may strongly affect their fitness. To optimize their decisions, they can use personally acquired information but also information obtained from observing other individuals (“social information”). The propensity to gather and use social information and the information meaning might depend on both individual and environmental factors. Studying what drives within- and between-individual differences in social information use should help us understand the evolutionary potential of this supposedly adaptive behaviour. The aim of my PhD was to empirically investigate sources of variability in heterospecific social information use for breeding habitat selection. I worked on a natural population of collared flycatchers (Ficedula albicollis, Gotland Island, Sweden), a passerine species shown to cue on the presence, density, reproductive investment and nest site preference of dominant titmice for settlement decisions. Using both long term and experimental data, I showed that the use of heterospecific social information, measured as the probability to copy tit nest preference, is not heritable but depends on male age and...

  • Infrared spectroscopy studies of adsorption and photochemistry on TiO2 surfaces : From single crystals to nanostructured materials

    Author: Andreas Mattsson
    Publication date: 2018-10-29 09:00

    TiO2 based photocatalysis is a green nanotechnology that can be used for removal of pollutants from water and air, as well as making synthetic fuels from water and carbon dioxide. Said photocatalysis has received major research interests during the last decades. Despite these efforts, many elementary processes that occur on the photocatalyst surface are not fully understood and, therefore, limit our ability to purposefully manufacture more efficient photocatalytic materials. The objective of this thesis is to provide new understanding at a molecular level of important adsorbate species on the TiO2 surfaces.

    Fundamental properties of adsorption and photochemistry of primarily formic acid on different TiO2 surfaces, ranging from single crystals to nanoparticles, have been studied using infrared spectroscopy. A method to simulate IR spectra have been developed and, combined with experimental data, has been proven to be a powerful tool to identify different adsorbate geometries on the surface. In the presence of oxygen, a thermally activated and irreversible reaction between formate and oxygen adatoms takes place on the single crystal rutile (110) surface to yield hydrogen...

  • Cluster Tilting for Representation-Directed Algebras

    Author: Laertis Vaso
    Publication date: 2018-10-25 15:22
  • Effects of Ubiquinone-10 on the Stability and Mechanical Properties of Lipid Membranes

    Author: Emma K. Eriksson
    Publication date: 2018-10-19 11:44

    Ubiquinones are a group of fat-soluble molecules present in many biological membranes. The most abundant version in humans, ubiquinone-10 (Q10), plays an important role in the mitochondrial respiration chain and also functions as a powerful antioxidant. Accumulating evidence suggests that Q10 also could have other functions in the membrane. The aim of this thesis has been to explore Q10’s possible role as a membrane stabilizer.

    To investigate the potential effect of Q10 in membranes, liposomes with compositions of biological relevance were used as models systems. In lipid systems mimicking that of the inner membrane of the mitochondria, Q10 was found to lower the membrane’s permeability to hydrophilic solutes, render the membrane more resistant to rupturing and promote membrane lipid order. In models mimicking the plasma membrane of E.coli, Q10 was observed to decrease the water permeability and increase the elastic resistance against membrane deformation during osmotic shock. All in all, the results suggest a general membrane stabilizing effect of Q10. The results indicate, however, that the extent of, as well as the mechanisms behind, the membrane stabilizing effects of...

  • Spatio-temporal probabilistic forecasting of solar power, electricity consumption and net load

    Author: Dennis van der Meer
    Publication date: 2018-10-18 14:58

    The increasing penetration of renewable energy sources into the electricity generating mix poses challenges to the operational performance of the power system. Similarly, the push for energy efficiency and demand response—i.e., when electricity consumers are encouraged to alter their demand depending by means of a price signal—introduces variability on the consumption side as well.

    Forecasting is generally viewed as a cost-efficient method to mitigate the adverse effects of the aforementioned energy transition because it enables a grid operator to reduce the operational risk by, e.g., unit-commitment or curtailment. However, deterministic—or point—forecasting is currently still the norm.

    This thesis focuses on probabilistic forecasting, a method with which the uncertainty ac- companying the forecast is expressed by means of a probability distribution. In this framework, the thesis contributes to the current state-of-the-art by investigating properties of probabilistic forecasts of PV power production, electricity consumption and net load at the residential and distribution level of the electricity grid.

    The thesis starts with an introduction to probabilistic...