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Coming dissertations at TekNat

  • Cladophora Cellulose-based Separators for Lithium Batteries

    Author: Ruijun Pan
    Publication date: 2019-01-16 10:00

    The development of lithium-ion batteries (LIBs) has been focused on exploring and improving the electrode materials and electrolytes in the past decades. An indispensable component, the separator, is however not studied as extensively. In general, a separator has two functions, i.e. preventing the direct contact between the cathode and anode and providing the ionic transport pathways. Commercial separators for LIBs are usually made of polyolefin materials, which often have low thermal stabilities and poor electrolyte wettabilities.

    In this thesis, a new type of material, i.e. Cladophora cellulose, is used to manufacture separators for LIBs and lithium-metal batteries (LMBs). The separators, made with Cladophora cellulose fibers via a straightforward paper making method, possess several advantages compared to conventional polyolefin separators regarding, e.g. ionic conductivity, thermal stability, electrolyte wettability and pore distribution, providing promising alternatives for battery separators.

    Apart from studying the two basic functions mentioned above, two types of advanced separator functionalities have been studied, i.e. redox-...

  • Flood Prediction in data-scarce basins : Maximising the value of limited hydro-meteorological data

    Author: José Eduardo Reynolds Puga
    Publication date: 2019-01-14 10:39

    Floods pose a threat to society that can cause large socio-economic damages and loss of life in many parts of the world. Flood-forecasting models are required to provide simulations at temporal resolutions higher than a day in basins with concentration times smaller than 24 h. However, data at such resolutions are commonly limited or not available, especially in developing or low-income countries. This thesis covers issues related to the scarcity and lack of high temporal-resolution hydro-meteorological data and explores methods where the value of existing data is maximised to improve flood prediction.

    By varying the starting time of daily records (the day definition), it was shown that this definition had large implications on model calibration and runoff simulation and therefore, should be considered in regionalisation and flood-forecasting applications. A method was developed to treat empirically model-parameter dependencies on the temporal resolution of data. Model parameters seemed to become independent of the temporal resolution of data when the modelling time-step was sufficiently small. Thus, if sub-daily forcing data can be secured, flood forecasting in basins...

  • Dynamics of Magnetic Molecules under Electrical Control

    Author: Henning Hammar
    Publication date: 2019-01-09 09:31

    This thesis theoretically studies the dynamics of molecular magnets under electrical control. Molecular magnets are nanoscale magnets that can, e.g., consist of single-molecules or single-atoms. In these magnets, the electronically mediated exchange and transport can be controlled by external fields. In this thesis, we study the effect of electrical control and voltage pulses on the transport properties, spin dynamics and the exchange of the molecular magnets.

    Nonequilibrium Green's functions is the method used to describe the underlying electronic structure of the magnetic molecule. The studied systems consists of single-molecule magnets in a tunnel junction between metallic leads. Here, the transport characteristics are derived for charge, spin and heat currents in the system for time-dependent voltage pulses. Furthermore, a generalized spin equation of motion is derived for the molecular spin moment, using nonequilibrium field theory. The equation of motion incorporates nonequilibrium conditions and is of nonadiabatic character. The effective model for the spin moment can be decomposed into effective magnetic field, isotropic Heisenberg interaction, and anisotropic...

  • Adapting sonar systems for monitoring ocean energy technologies

    Author: Francisco Francisco
    Publication date: 2019-01-08 14:10

    The global energy sector is under profound reforms aiming towards renewable energy sources, clean technologies and expansion of smart grids, all with the additional aim of providing affordable and dependable electricity for everyone. A reduction of carbon dioxide emissions is a priority on the global agenda, and to achieve that, cleaner energy technologies has to be more integrated into the energy mix. This thesis focus on a sustainable implementation of wave, tidal and offshore wind power, wherefore there is a need to investigate more about the prerequisites and consequences ocean energy can have on the marine environment. For that, reliable, cost effective and continuous environmental monitoring framework is necessary in order to support and safeguard ocean energy operations.

    The main objectives of the research presented in this thesis are to develop a multifunctional environmental monitoring platform based on sonar systems for ocean energy applications, by adapting high resolution multibeam, dual beam and split beam sonar systems and also underwater cameras; Propose data acquisition and processing protocols capable of decipher sonar data in order to provide continuous...

  • Ion dynamics and structure of collisionless shocks in space

    Author: Andreas Johlander
    Publication date: 2019-01-07 13:30

    Shock waves form when supersonic flows encounter an obstacle. Like in regular gases, shock waves can form in a plasma - a gas of electrically charged particles. Shock waves in plasmas where collisions between particles are very rare are referred to as collisionless shock waves. Collisionless shocks are some of the most energetic plasma phenomena in the universe. They are found for example around exploded supernova remnants and in our solar system where the supersonic solar wind encounters obstacles like planets and the interstellar medium. Shock waves in plasmas are very efficient particle accelerators though a process known as diffusive shock acceleration. An example of particles accelerated in shock waves are the extremely energetic galactic cosmic rays that permeate the galaxy. This thesis addresses the physics of collisionless shocks using spacecraft observations of the Earth's bow shock, particularly understanding the ion dynamics and shock structure for different shock conditions. For this we have used data from ESA's four Cluster satellites and NASA's four Magnetospheric Multiscale (MMS) satellites. The first study presents Cluster measurements from the quasi-parallel...

  • Structured Data

    Author: Stephan Brandauer
    Publication date: 2018-12-20 08:33

    References are a programming language construct that lets a programmer access a datum invariant of its location.

    References permit aliasing -- several references to the same object, effectively making a single object accessible through different names (or paths). Aliasing, especially of mutable data, is both a blessing and a curse: when used correctly, it can make a programmer's life easier; when used incorrectly, for example through accidental aliases that the programmer is unaware of, aliasing can lead to hard to find bugs, and hard to verify programs.

    Aliases allow us to build efficient data structures by connecting objects together, making them immediately reachable. Aliases are at the heart of many useful programming idioms. But with great power comes great responsibility: unless a programmer carefully manages aliases in a program, aliases propagate changes and make parts of a program's memory change seemingly for no reason. Additionally, such bugs are very easy to make but very hard to track down.

    This thesis presents an overview of techniques for controlling how, when and if data can be aliased, as well as how and if data can be mutated. Additionally,...

  • Design of Rare Earth Free Permanent Magnet Generators

    Author: Petter Eklund
    Publication date: 2018-12-19 07:41

    Low speed permanent magnet (PM) synchronous generators (SGs) are commonly used in renewable energy. Rare earth (RE) PMs such as neodymium-iron-boron are a popular choice due to their high performance. In 2011 supply and cost issues were added to the previously existing environmental concerns regarding REPM raw materials as the world's major producer China imposed export restrictions. This thesis aims to investigate and propose design solutions for PMSGs that do not use REPMs. Two approaches are used: to design generators using the cheaper and more abundant ferrite PM materials, and to investigate how properties of new PM materials influence SG design.

    A ferrite PM rotor is designed to replace a REPM rotor in an experimental 12 kW wind power generator. The new design employs a flux concentrating spoke type rotor to achieve performance similar to the old REPM rotor while using ferrite PMs. The ferrite PM rotor design is built. The air gap length, magnetic flux density in the air gap, PM remanence, and voltage at both load and no load are measured. The generator has lower no load voltage than expected, which is mainly explained by lower than specified remanence of the...

  • Model Checking of Software Systems under Weak Memory Models

    Author: Tuan-Phong Ngo
    Publication date: 2018-12-17 09:08

    When a program is compiled and run on a modern architecture, different optimizations may be applied to gain in efficiency. In particular, the access operations (e.g., read and write) to the shared memory may be performed in an out-of-order manner, i.e., in a different order than the order in which the operations have been issued by the program. The reordering of memory access operations leads to efficient use of instruction pipelines and thus an improvement in program execution times. However, the gain in this efficiency comes at a price. More precisely, programs running under modern architectures may exhibit unexpected behaviors by programmers. The out-of-order execution has led to the invention of new program semantics, called weak memory model (WMM). One crucial problem is to ensure the correctness of concurrent programs running under weak memory models.

    The thesis proposes three techniques for reasoning and analyzing concurrent programs running under WMMs. The first one is a sound and complete analysis technique for finite-state programs running under the TSO semantics (Paper II). This technique is based on a novel and equivalent semantics for TSO, called Dual TSO...

  • Of spiders, bugs, and men : Structural and functional studies of proteins involved in assembly

    Author: Wangshu Jiang
    Publication date: 2018-12-14 13:44

    Protein assembly enables complex machineries while being economical with genetic information. However, protein assembly also constitutes a potential threat to the host, and needs to be carefully regulated.

    Sulfate is a common source of sulfur for cysteine synthesis in bacteria. A putative sulfate permease CysZ from Escherichia coli appears much larger than its apparent molecular mass when analyzed by chromatography and native gel. Clearly CysZ undergoes homo-oligomerization. Using isothermal titration calorimetry, we confirmed that CysZ binds to its putative substrate sulfate, and also sulfite with higher affinity. CysZ-mediated sulfate transport—in both E. coli whole cells and proteoliposomes—was inhibited in the presence of sulfite, indicating a feedback inhibition mechanism.

    Proteus mirabilis is a Gram-negative bacterium causing urinary tract infections. Its simultaneous expression of multiple fimbriae enables colonization and biofilm formation. Fimbriae are surface appendages assembled from protein subunits, with distal adhesins specifically recognizing host-cell receptors. We present the first three structures of P. mirabilis...

  • The Importance of Being Promiscuous : Understanding enzyme function, specificity, and evolution through structure

    Author: Annika Söderholm
    Publication date: 2018-12-14 13:41

    Enzymes are known to be amazingly specific and efficient catalysts. However, many enzymes also have so-called promiscuous functions, i.e., they are able to catalyze other reactions than their main one. The promiscuous activities are often low, serendipitous, and under neutral selection but if conditions arise that make them beneficial, they can play an important role in the evolution of new enzymes. In this thesis, I present three studies where we have characterized different enzyme families by structural and biochemical methods. The studies demonstrate the occurrence of enzyme promiscuity and its potential role in evolution and organismal adaptation.

    In the first study, I describe the characterization of wild type and mutant HisA enzymes from Salmonella enterica. In the first part of this study, we could clarify the mechanistic cycle of HisA by solving crystal structures that showed different conformations of wild type HisA in complex with its labile substrate ProFAR (N´-[(5´-phosphoribosyl)formimino]-5-aminoimidazole-4-carboxamide ribonucleotide). In the second part of this study, structures of mutant enzymes from a real-time evolution study provided us with an...