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Coming theses from other universities

Please note that the date and time given on these pages is the time of electronic publication, and not the date of the public defense. To find the time and venue of the public defense, please follow the link to DiVA of the thesis in question.
  • A journey towards complete structure determination of zeolites by electron crystallography methods

    Author: Elina Kapaca
    Publication date: 2020-02-05 08:00

    Electron crystallography has recently become very successful for structural studies of materials with sub-micrometer sized crystals. In this thesis two major techniques have been applied for structure elucidation – 3-dimensional electron diffraction (3D ED) and high-resolution transmission electron microscopy (HRTEM) imaging. Both can provide information about the structure at the atomic level and have been used for structure determination. During the last decade, two 3D ED methods have been used in our group; the stepwise rotation electron diffraction (RED) method developed in our lab and continuous rotation electron diffraction (cRED) where improvements on the already existing RED method were implemented. Both 3D ED methods can be used for fast structure determination of ordered crystalline materials. HRTEM imaging is very useful for structure determination of more complex and severely disordered materials. For complex structures it is often necessary to combine several methods including powder X-ray diffraction (PXRD).

       Zeolites are microporous crystalline materials. They have complex structures and often synthesized as polycrystalline powders. The aforementioned electron crystallography methods have unique advantages in elucidation of atomic structures of such zeolites. In this thesis, the development of 3D ED methods, especially from RED to cRED, is described through the journey of structure determination of four zeolites; a known pure silicate silicalite-1 for testing the RED method, and three new zeolites. The new zeolites include two extra-large pore germanosilicates ITQ-56 and SYSU-3 and one small-pore aluminosilicate EMM-37. The thesis shows the limitations and advantages of the RED and cRED methods and how different challenges in the structure determination of zeolites are tackled by the advances of 3D ED methods. Finally the thesis presents a detailed structural study of disorders in an aluminosilicate zeolite ITQ-39 by combining HRTEM, RED with sample preparation by ultramicrotomy. The structure of ITQ-39 was determined in 2012 by our group. Here three new zeolite polytypes of ITQ-39 were identified from the HRTEM images and their structure models are proposed.

       A complete structure determination of zeolites includes elucidation of the framework structure, guest species such as structure directing agent (SDA) molecules and ions in the pores, and any structural disorder in the crystal. This thesis reflects to all of these structural characteristics of zeolites, presenting the power of electron crystallography.

  • GNSS hardware biases in code and carrier phase observables

    Author: Martin Håkansson
    Publication date: 2020-02-04 16:31

    GNSS hardware biases appear in code and phase observations, and originates both from the receiver and satellite hardware. The presence of biases in GNSS observations might affect the accuracy in precise GNSS positioning applications, and might also be of relevance in other GNSS applications. They may also be a cause of incompatibility between different receiver types or GNSS constellations.

    In this thesis, which is based on four papers, the biases in GNSS code and carrier phase observables are investigated. This is done by: characterizing and analyzing some selected biases; revealing some previously unknown biases; developing new methods to estimate some of the biases; and compiling and presenting information about biases in a new and comprehensive way.

    Paper 1 gives a full review of how various kinds of biases affect various applications of precise GNSS positioning, including multi-GNSS positioning and ambiguity resolved PPP.

    In Paper 2, two cases of relative phase biases, that potentially could degrade the positioning accuracy in precise positioning applications, are investigated. Fortunately, these biases turns out to be small in size with negligible effect on the positioning accuracy in both cases, which involves relative between-receivers biases for receivers of different type and between-signals biases for carrier phase observations of different signals associated with the same carrier frequency.

    Paper 3 characterizes GNSS observations from a Nexus 9 Android tablet. By doing this, it reveals a number of earlier unknown biases. A drift between the code and phase observable of -3 and 2 mm/s is revealed for GPS and GLONASS, respectively. Additionally, an unexpected variation in the GLONASS phase observable, which seems to be dependent on the topocentric range rate of the satellite, is discovered.

    In Paper 4, the existence of nadir dependent code biases is confirmed for GNSS observations from BeiDou-2 satellites of the BeiDou constellation by analyzing the residuals of 2-D and 3-D ionosphere modeling. This a new method to derive this kind of bias, independent of the earlier employed approach based on the multipath linear combination. The estimated effect is, however, too small to infer a similar nadir dependence for GPS and Galileo as well.

  • Deactivation of emission control catalysts for heavy-duty vehicles : Impact of biofuel and lube oil-derived contaminants

    Author: Sandra Dahlin
    Publication date: 2020-02-04 12:58

    Catalytic emission control is used to reduce the negative impact of pollutants from diesel exhausts on our health and on the environment. For a heavy-duty truck, such a system consists of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a selective catalytic reduction (SCR) catalyst, and an ammonia slip catalyst (ASC). Due to greenhouse-gas induced global warming, it is necessary to decrease the emissions of such gases. Two strategies for this reduction are: 1) to produce engines that are more fuel efficient, 2) to use sustainably produced renewable fuels such as biodiesel and HVO. However, both these strategies may pose additional challenges for the emission control system: a colder exhaust due to the higher fuel-efficiency requires the use of highly active catalysts; catalyst deactivation related to impurities in biofuels, which requires very robust catalysts.   The objective of this thesis was to study the impact of biofuel as well as lubrication oil-related contaminants on the performance of emission control catalysts (DOC and SCR catalysts) for heavy-duty diesel engines. The main focus has been on the low-temperature performance of V2O5-WO3/TiO2 (VWTi) and Cu-SSZ-13 SCR catalysts.    Results from the project have shown that both Cu-SSZ-13 and VWTi catalysts capture and can be deactivated by phosphorus (P), while only the Cu-SSZ-13 is deactivated by sulfur (S). The degree of the P-related deactivation depends on the concentration in the catalyst, which depends on content of P in the exhaust and the exposure time, as well as the type of catalyst. S-deactivation of Cu-SSZ-13 is observed at low temperatures, where un-poisoned Cu-SSZ-13 are significantly more active than VWTi catalysts. As a contrast, the VWTi-performance can even be improved by sulfur; but alkali metals are severe poisons to VWTi catalysts. Partial performance-recovery of S-poisoned Cu-SSZ-13 can be obtained by exposing it to sulfur-free exhausts at elevated temperatures. The use of an upstream DOC, providing fast SCR conditions to the SCR catalyst, considerably improves the low-temperature performance of the VWTi, as well as sulfur-poisoned Cu-SSZ-13 catalysts. An upstream DOC also protects the SCR catalysts from phosphorus deactivation, as it can trap large amounts of P. However, if too much phosphorus is captured by the DOC, severe deactivation of this catalyst results, which lowers the overall performance of the exhaust treatment system.  Insights from this project will guide the development of robust exhaust treatment systems for various applications. Additionally, it could aid in developing more durable emission control catalysts.

  • The role of deep hydrocarbons in the global hydrocarbon budget

    Author: Daniil Kudryavtsev
    Publication date: 2020-02-03 10:19

    Nowadays, the issue of global warming and related environmental problems got widespread awareness among scientific society, politics, the industry as well as it has affected our everyday life. The reason for such a negative impact on the atmosphere is attributed mainly to human activities. It is thought that one of the most dangerous greenhouse gases is carbon dioxide (CO2). Nevertheless, the problem of hydrocarbon emissions began to receive particular attention due to the exponential growth of methane emissions in the atmosphere. What is the reason for such behaviour and what about other hydrocarbons, first of all, ethane, propane and butane isomers? In this work, it was proposed that geological emissions, mainly the emission from the dissociation of natural gas hydrates is one of the main reasons for the dramatic rise in hydrocarbon emissions to the atmosphere. Natural gas hydrates are not only composed of methane and water cages but have in their structure a broad range of hydrocarbons, including ethane, propane, butanes and some others. 

    The purpose of this thesis is to investigate the sources of non-methane volatile hydrocarbons in the atmosphere, examine their impact on the environment and explore the correlation of hydrocarbon emissions with CO2 emissions. 

    To reveal the impact of natural gas hydrates to the hydrocarbon budget it was assumed, that hydrocarbons that are contributing to the natural gas hydrate formation have deep mantle origin. To confirm this hypotheses high-pressure high temperature investigation of propane and butanes were conducted. The results of this investigation are presented in this thesis. To model extreme thermobaric conditions the diamond-anvil cell technique with two-sided laser heating was used. The method of Raman spectroscopy was applied for the analysis. 

    The results received show that propane and butane isomers stable in the pressure  up to 40 GPa at ambient temperature. Propane remains stable at temperatures up to 900 K. At temperatures >900 K chemical transformations of propane are starting to occur producing mixture of light alkanes.

  • Responsive Molecular Systems through Dynamic Covalent Chemistry

    Author: Antanas Karalius
    Publication date: 2020-02-03 10:13

    Nature tends to inspire research in chemistry. Systems that emerge from molecules interacting via reaction networks is something that life has mastered over the course of evolution in order to produce complexity. Dynamic reactions are key in systems chemistry, where reaction networks give rise to complex, emergent behavior. This thesis aims to harness a special feature of selected dynamic reaction systems – responsiveness.The first chapter of this thesis introduces dynamic covalent chemistry and a general approach to create simple reaction networks by connecting dynamic covalent reactions. Concepts in systems chemistry are introduced in terms of network topology, responsiveness and non-equilibrium processes, while drawing parallels to natural systems.The second chapter explores the potential of the nitroaldol reaction for dynamic systems. Nitroaldol reactions are demonstrated for dynamic polymerization as well as formaldehyde-responsive breakdown of dynamic polymers. The simultaneous formation and breakdown of polymers create emergent non-equilibrium behavior. Furthermore, nitroaldol produced-diols are used in boronate ester formation. This reactivity produces interdependence over two reactions. Combining nitroaldol and boronate building blocks enabled boronate dynamers of different topology.The third chapter explores metal coordination effects in dynamic reaction networks. Novel base-free nitroaldol reactivity is exploited in reaction networks with hemiacetals. A systemic response to metals is demonstrated by hemiacetal-metal coordination. In the second half of the chapter, a biomimetic dynamic imine complex is shown to produce emergent, π-π-interactions resembling a “draw-bridge”. Variation of metal charge, effective electrostatic character of substituent and ligands gives control over the system and its emergent π-π-interactions.

  • Towards computational materials design and upscaling of alternative binder cemented carbides

    Author: David Linder
    Publication date: 2020-01-31 09:45

    Increasing demands on economic, social and environmental sustainability throughout society is putting pressure on the development of new and improved materials for resource efficiency, improved component life-time and substitution of toxic or rare elements. For the cemented carbide industry, as a major provider of tools for e.g. mining and metal cutting which are integral parts of many production chains, this may require complete or partial substitution of cobalt. Cobalt ore is primarily mined in conflict regions and cobalt powder has been shown to be carcinogenic upon inhalation. Substitution of this element could therefore have significant impact on several aspects of society. However, it is far from trivial to substitute this critical element in cemented carbide production. Nearly a century of materials and product development has made state-of-the-art cemented carbides with cobalt binder phase one of the most successful engineering materials. Over the years, accumulated investments throughout the supply chain has made these materials indispensable in industrial production. When envisioning cobalt substitution, it is therefore critical to generate new methods for accelerated materials development and standardised materials qualification. This will enable faster and more reliable development of new materials with the potential to substitute cobalt throughout the industry.

    The present thesis is focused on the continued development of an integrated computational materials engineering framework for materials design as well as the development of quality control methods for alternative binder cemented carbides. The existing computational framework is here extended with a model for fracture toughness which allows for property trade-off between hardness and toughness. The extended framework is shown to replicate experimentally well-established property combinations and is thereby applicable for computational design of cemented carbides for specific applications. Furthermore, conventional quality control methods based on magnetic properties are evaluated and further developed for alternative binder cemented carbides. Combining these results on computational materials design and the steps towards standardised quality control has the potential to greatly accelerate future development of cemented carbides, both for cobalt substitution and for improved component life-time.

  • Studies on adverse-pressure-gradient turbulent boundary layers on wings

    Author: Alvaro Tanarro
    Publication date: 2020-01-31 06:03

    The present licentiate thesis addresses the use of well-resolved simulations to simulate turbulent boundary layers (TBL) subjected to adverse pressure gradients. Within the thesis a wide variety of analyses are performed, and a method to improve the performance of the simulations is presented. The first aim of the thesis is to assess the effect of adverse pressure gradients and flow history on the development and fundamental characteristics of turbulent boundary layers. With this in mind, well-resolved large-eddy simulations (LES) of the turbulent boundary layers over two wing sections are performed using the spectral-element-method (SEM) code Nek5000. In order to assess the effects of the adverse pressure gradient on turbulent boundary layers, turbulence statistics are computed and time series are collected from the simulations. The turbulence statistics show a significant effect of the adverse pressure gradient on the mean velocity profiles, turbulent fluctuations and turbulent kinetic energy budgets. In addition, the time series are used to compute the power-spectral densities of the turbulent boundary layers and to analyse the effect of the adverse pressure gradient on the turbulent scales across the boundary layer. After having compared both wings at moderate Reynolds number Rec=400,000, the next goal is to perform high-resolution simulations of wings at higher Reynolds numbers in order to study conditions closer to those in reality, and to evaluate the effect of adverse pressure gradient with increasing Reynolds numbers. To achieve this, better and more efficient computational methods are required. In this thesis, the performance of the adaptive mesh refinement method recently implemented in Nek5000 is assessed for the first time on wing simulations. The obtained results show a large potential of this new method (which includes the use of non-conformal meshes) with respect to the previous simulations carried out with conformal meshes. Lastly, we performed a modal decomposition of the TBLs developing around both wing sections. To this end, we consider spectral proper orthogonal decomposition (SPOD), which can be used to identify the most energetic structures of the turbulent boundary layer.

  • A Brave New Workplace: Disclosing the smart and the dark sides of the alternative office spaces

    Author: Claudia Manca
    Publication date: 2020-01-29 15:05

    In recent decades, several knowledge work organizations have introduced alternative workplaces (AWs) that are implemented through flexible and collaborative office models. Their rapid diffusion has been prompted by the deterministic assumption that these may influence workers’ relations and behaviors in the office, in a way that is conducive to greater collaboration and adaptive flexibility. Yet, the scarce empirical fieldwork on alternative workplaces and their multidisciplinary nature limit our understanding of their actual implications for people and organizations.

    This thesis questions the validity of the deterministic assumption guiding the implementation, use, and design of AWs, and identifies a set of approaches that companies and managers can employ to avoid inconsistencies and negative outcomes. To do this, this thesis builds upon a collection of studies that have been designed to address four research questions. The first study identifies a framework for AWs that has been used as a cognitive model to interpret the results and draw the boundaries of the empirical fieldwork (RQ1). The framework has been employed in an exploratory analysis, aimed at a systematic overview of the barriers and enablers that companies encounter when implementing AWs (RQ2). The second study explores how AWs are experienced by individuals and groups of knowledge workers, by bringing new opportunities and challenges that cast themselves as oppositional tensions (RQ3). The third study looks at how knowledge workers interpret the AW and enact its organization, by means of spatial practices that problematize the status of its flexible and permeable boundaries (RQ4). The fourth study develops a systematic approach to identifying the spatial implications of AWs (RQ3, 4).

    Drawing upon these studies, the thesis posits three important contributions. First, it feeds the discussions on AWs by bringing new empirical evidence in a relatively under-researched area. Second, it advances the concept of the AW, by providing a high-level model synthesizing the different organizational areas in which implementation and discourses have taken place. This thesis advocates the need to bring together the discussions on the different aspects of the AW under the same banner, to better investigate the interactional effects between different implementation areas. Third, the thesis contributes to workplace research and sociology of space by shedding some light on the impact of the spatial reconfiguration of work activities and relations brought by AWs to people and companies. From a practical perspective, this thesis identifies some approaches that are available to companies and their managers to handle the tensions and the identity threats that arise in the new office environment.

  • Constraints and symmetries in theories of interacting spin-2 fields

    Author: Anders Lundkvist
    Publication date: 2020-01-29 08:00

    The Hassan-Rosen bimetric theory describes two interacting spin-2 fields, one massless and one massive. In this thesis, a complete canonical analysis of this theory is performed in the metric formulation and all constraints are computed. In particular, a secondary constraint, whose existence was in doubt, is shown to exist and evaluated explicitly, bringing the total number of constraints up to six. This, together with general covariance, is enough to eliminate the Boulware-Deser ghost and ensure that the theory propagates the appropriate seven degrees of freedom. The requirement that the constraints are preserved in time leads to a linear relation between the lapse functions of the two metrics. Knowing the explicit form of the ratio of the lapses is necessary for solving initial value problems. The ratio is computed for the special case where the metrics share the same spherical symmetry.

    Since the bimetric theory is diffeomorphism invariant, it must contain four first class constraints whose Poisson brackets form a certain algebra. In general, it is possible to use this algebra to identify a metric. In this thesis, the four first class constraints of bimetric theory are identified and it is shown that their Poisson brackets indeed forms the algebra required by diffeomorphism invariance. However, the metric identified from the algebra turns out not to be unique, but to depend on a choice of variables. Additionally, it need not coincide with the gravitational metric.

    The candidate nonlinear partially massless bimetric theory is also investigated in this thesis. It is shown that for this theory, the partially massless symmetry cannot be extended beyond cubic order in the action. This result is generalized to the most general two derivative theory of only two interacting spin-2 fields, showing that such a theory cannot possess the partially massless symmetry beyond cubic order.

  • Proton transfer across and along biological membranes

    Author: Johan Berg
    Publication date: 2020-01-29 08:00

    Proton-transfer reactions belong to the most prevalent reactions in the biosphere and make life on Earth possible, as they are central to energy conversion. In most known organisms, protons are translocated from one side of a membrane to the other, which generates an electrochemical gradient that drives ATP synthesis. Both the membranes and the proteins that are involved in these processes are vital components of energy-conversion machineries. This thesis presents and discusses proton transfer at surfaces of membranes and proteins, as well as proton translocation across membranes via enzymes.

    In the first work, we developed a single-enzyme approach to study proton translocation by the proton pump cytochrome bo3 (cyt. bo3). The generated proton gradients were stable as long as substrate (electrons, oxygen) was available. Individual cyt. bo3 could generate proton gradients of ∼2 pH units, which correspond to the measured electrochemical gradient in Escherichia coli cells.

    When acidic and basic amino acids are in close proximity to each other on a protein surface, their individual Coulomb cages can merge to form a proton antenna that enables fast proton transfer to specific groups. To investigate how the function of a proton pump is affected by structural changes in a proton antenna, close to a proton uptake pathway, we characterized the function and structure of genetic variants of cytochrome c oxidase (CytcO). When a Glu, located about 10 Å from the first residue of the D-pathway, was replaced by a non-protonatable residue (Ala) the proton pumping efficiency decreased by more than half compared to the wild-type enzyme. The proton-uptake kinetics was also altered in this variant.

    Cardiolipin (CL) is found in membranes where ATP is generated. This phospholipid alters the membrane structure and binds a variety of proteins including all complexes that take part in oxidative phosphorylation. To investigate the role of CL in proton-transfer reactions on the surface of membranes we used fluorescence correlation spectroscopy to study inner mitochondrial membranes from Saccharomyces cerevisiae. The protonation rate at wild-type membranes was about 50% of that measured with membranes prepared from mitochondria lacking CL. The protonation rate on the surface of small unilamellar vesicles (SUVs) decreased by about a factor of three when DOPC-SUVs were supplemented with 20% CL. Furthermore, phosphate buffer titrations with SUVs showed that CL can act as a local proton buffer in a membrane.

    The respiratory supercomplex factor 1 (Rcf1) has been suggested to facilitate direct electron transfer from the bc1 complex to CytcO by bridging the enzymes and binding cytochrome c (cyt. c) to a flexible domain of Rcf1. We investigated biding of cyt. c to Rcf1 reconstituted into different membrane environments. The apparent KD of the binding between cyt. c and DOPC-liposomes was almost five times lower when Rcf1 was present in the vesicles. Moreover, the apparent KD between cyt. c and liposome reconstituted CytcO was about nine times lower for CytcO isolated from a wild-type strain compared to a Rcf1-lacking strain.

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