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Coming dissertations at TekNat

  • Gaussian process models of social change

    Author: Björn Rune Helmer Blomqvist
    Publication date: 2018-11-30 11:01

    Social systems produce complex and nonlinear relationships in the indicator variables that describe them. Traditional statistical regression techniques are commonly used in the social sciences to study such systems. These techniques, such as standard linear regression, can prevent the discovery of the complex underlying mechanisms and rely too much on the expertise and prior beliefs of the data analyst. In this thesis, we present two methodologies that are designed to allow the data to inform us about these complex relations and provide us with interpretable models of the dynamics.

    The first methodology is a Bayesian approach to analysing the relationship between indicator variables by finding the parametric functions that best describe their interactions. The parametric functions with the highest model evidence are found by fitting a large number of potential models to the data using Bayesian linear regression and comparing their respective model evidence. The methodology is computationally fast due to the use of conjugate priors, and this allows for inference on large sets of models. The second methodology is based on a Gaussian processes framework and is designed to...

  • Self-assembly of magnetic particles

    Author: Hauke Carstensen
    Publication date: 2018-11-28 09:58

    Self-assembly is the spontaneous formation of larger structures from small building blocks. This process is driven and determined by the interactions between the constituents. Examples of self assembly are found almost everywhere and, in particular, biological systems in general rely on a hierarchical formation of structures over a range of length scales. Technologically, self-assembly can be used to form mesoscopic structures and artificial crystals. In the case of particles with micrometer size suspended in a liquid phase, it is possible to use optical microscopy for the the investigation of self-assembly.

    In this thesis, the self-assembly of microbeads with tunable magnetic interactions is studied, based on the statistic analysis of microscope images and computer simulations. Magnetic and non-magnetic microbeads are suspended in a ferrofluid, which is a dispersion of magnetic nanoparticles in water. As a result, the magnetic properties of the microbeads in the ferrofluid are altered and can be described by effective magnetic susceptibilities and magnetic dipole moments, which can be tuned continuously. The liquid is confined between glass slides and effectively the...

  • Composite Regenerative Scaffolds

    Author: Elle Edin
    Publication date: 2018-11-27 10:51

    Regenerative medicine and tissue engineering solutions of heavily innervated tissues are at this point lacklustre. This thesis expands our knowledge of appropriate acellular scaffolds for tissue repair in general and nerve regeneration in particular. The optimal surgical procedure for the implantation of artificial extracellular matrix (ECM) was evaluated for recombinant human collagen (RHCIII) implants. Suturing techniques, as well as the usage of human amniotic membrane “bandages” were evaluated. While complete regeneration of corneal tissues occurred, only slight differences in effects of surgical technique could be found.

    The safety and efficacy of clinical trials using mesenchymal stromal cells (MSCs) was evaluated by conducting a systematic review and meta-analysis. MSC therapy was shown to be safe, with no increases mortality, rehospitalization or adverse events. There was also an indication of efficacy, as the overall mortality in the studies included was significantly smaller in the MSC treated group.

    Multicomponent hydrogel capsules encapsulating single cells were developed. Capsules manufactured from gelatin, agarose and fibrinogen were compared to pure...

  • Isomeric yield ratio measurements with JYFLTRAP : In quest of the angular momentum of the primary fragments

    Author: Vasileios Rakopoulos
    Publication date: 2018-11-23 08:54

    In this thesis, isomeric yield ratios of twenty nuclides produced in the fission of natU and 232Th by protons at 25-MeV and natU by high-energy neutrons were studied. The experiments were performed at the IGISOL-JYFLTRAP facility at the University of Jyväskylä. It is the first time that direct ion counting is used for the determination of the intensities of the states of interest, thus avoiding dependency on knowledge of nuclear decay schemes and properties. This was possible due to the superior resolution of a Penning trap which was utilized for this work. Two different techniques were employed, namely the sideband cooling technique and the phase-imaging ion-cyclotron-resonance technique. With the former, a mass resolving power of m/δm = 105 can be routinely achieved, while the latter, which was recently implemented at JYFLTRAP, offers an increase in the mass resolving power by a factor of ten. In addition, isomeric yield ratios were also determined by means of γ-ray spectroscopy.

    From a comparison of the same isomeric pair from two different reactions, a dependency on the fissioning system can be observed. This indicates an effect of the fission mode to the yield ratio...

  • An X-ray Spectroscopic Study of Perovskites Oxides and Halides for Emerging Devices

    Author: Dibya Phuyal
    Publication date: 2018-11-21 10:36

    This thesis investigates the electronic structures on several perovskite oxide and halide materials with a focus on light harvesting applications. The systematic study of the electronic properties of the transition metal oxides and post-transition metal halides is a key point if one is to understand their properties. The element and site selective nature of several x-ray based spectroscopic techniques are given special emphasis in order to obtain a complete picture of the electronic properties of the compounds in question. Much of the experimental studies are accompanied by ab initio calculations that corroborate with our experimental results.

    In the oxide portion of this work, a new class of metallic oxides based on doping of an antiferromagnetic LaFeO3 was synthesized and systematically studied with x-ray absorption, x-ray emission, and photoemission spectroscopies. The compound’s electronic structure is complex, having itinerant as well as localized components that give rise to a unique physical state where antiferromagnetism, metallicity and charge-disproportionation coexist. Our resonant photoemission results establish that the Fe states in both magnetically...

  • Studies of a Vertical Axis Turbine for Marine Current Energy Conversion : Electrical system and turbine performance

    Author: Johan Forslund
    Publication date: 2018-11-21 08:17

    Ocean energy is a field of growing interest when it comes to renewable energy thanks to its high density of energy per unit area, and to the high predictability. Conversion of hydrokinetic energy, found in marine currents, is the utilization of the energy in free-flowing water for conversion to electric energy. This thesis presents experimental data from a test site with a marine current converter.

    The converter system features a vertical axis turbine directly connected to a permanent magnet synchronous generator placed on the riverbed. The converter is controlled by an electrical system. The focus of the work is to evaluate power control methods and turbine performance.  

    Results of a simple voltage control system is presented and compared with operation without control. The turbine type in the converter system is not self-starting. The startup power and energy has been investigated through experiments. The converter system has been connected to the local electric utility grid and the first experimental results are presented.  

    The performance of the turbine for a range of water speeds is investigated. The range of experiments are limited by the water...

  • Mille-feuille Filter : A Non-woven Nano-cellulose Based Virus Removal Filter for Bioprocessing

    Author: Simon Gustafsson
    Publication date: 2018-11-20 13:39

    Virus removal filters, produced from synthetic surface-modified polymers or regenerated cellulose by phase inversion, are vital to the production of therapeutic proteins such as monoclonal antibodies and plasma proteins. Use of these filters is also one of the most expensive purification steps in the downstream processing of proteins due to high sales price and being limited to a single use.

    In this thesis, a virus removal filter produced from Cladophora sp. algal nanocellulose has been characterized. The mille-feuille (‘‘a thousand leaves’’) filter paper is the first non-woven, wet-laid filter paper composed of 100% native nanocellulose that is capable of removing the ‘‘worst-case’’ model viruses, the non-enveloped parvoviruses, i.e., minute virus of mice (MVM; 18–20 nm), from water with a log10 reduction value (LRV) ≥5.78 (≥99.9998%). The mille-feuille filter features a unique internal stratified architecture that is the result of nanofiber self-assembly into 2D nanosheets during manufacturing. Such an internal structure has several benefits for achieving highly selective virus removal with high flux.

    The pore size distribution can be tailored to sizes...

  • Structure formation at solid/liquid interfaces : Understanding self-assembly and environmental challenges

    Author: Shirin Nouhi
    Publication date: 2018-11-19 08:04

    The work described in the present dissertation has explored the structure of particles and molecules at solid/liquid interfaces, aiming to understand the physics of self-organizing systems and use this knowledge to address some environmental issues. Surface-sensitive neutron scattering techniques, such as reflectometry and grazing incidence small angle scattering, have been used as the primary tool to investigate structures in proximity to an interface. Some of the challenges in the interpretation of neutron scattering data are discussed, and new methods for analyzing the signal have been proposed.

    It was shown that charged stabilized colloidal particles can self-assemble and form large areas (20 cm2) of crystalline structures, close to a smooth solid surface extending to depths of several micrometers, while orienting themselves into smaller crystallites in the bulk of the suspension. The adsorption of proteins from the seeds of different species of Moringa trees on alumina, silica and polystyrene surfaces was studied, as a means for using proteins from different sources and with different properties, for the water clarification step in the purification process. The seed...

  • Seismicity and crustal structure in Iceland

    Author: Claudia Abril
    Publication date: 2018-11-16 09:50

    The main goal of this Ph.D. thesis is to improve locations of earthquake hypocenters and to resolve heterogeneous crustal structure and its effects on travel times. The data and case studies are drawn from the Icelandic national SIL network and the temporary NICE project deploy-ment in the Tjörnes Fracture Zone. Iceland presents complex tectonics and active volcanism, consequences of its position astride the Mid-Atlantic Ridge between the European and North American plates and on top of a melting anomaly in the mantle below. Studies focused on characterizing the seismicity and the crustal structure are prerequisites for further seismologi-cal studies in Iceland, e.g., on seismic sources, the evolution of volcanic systems, activity on seismic faults and seismic hazard, among others.

    Different methods have been explored. First, we estimated empirically travel-time functions of seismic waves and their uncertainties for 65 stations in the Icelandic permanent network (SIL) using arrival times. The estimated travel-time functions and uncertainties were used to relocate the complete catalog applying a nested-search algorithm to this non-linear problem. The clearest changes in...

  • Understanding Task Parallelism : Providing insight into scheduling, memory, and performance for CPUs and Graphics

    Author: Germán Ceballos
    Publication date: 2018-11-15 10:05

    Maximizing the performance of computer systems while making them more energy efficient is vital for future developments in engineering, medicine, entertainment, etc. However, the increasing complexity of software, hardware, and their interactions makes this task difficult. Software developers have to deal with complex memory architectures such as multilevel caches on modern CPUs and keeping thousands of cores busy in GPUs, which makes the programming process harder.

    Task-based programming provides high-level abstractions to simplify the development process. In this model, independent tasks (functions) are submitted to a runtime system, which orchestrates their execution across hardware resources. This approach has become popular and successful because the runtime can distribute the workload across hardware resources automatically, and has the potential to optimize the execution to minimize data movement (e.g., being aware of the cache hierarchy).

    However, to build better runtime systems, we now need to understand bottlenecks in the performance of current and future multicore architectures. Unfortunately, since most current work was designed for sequential or thread-...

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