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Coming dissertations at TekNat

  • Learning based segmentation and generation methods for handwritten document images

    Author: Kalyan Ram Ayyalasomayajula
    Publication date: 2019-04-15 11:34

    Computerized analysis of handwritten documents is an active research area in image analysis and computer vision. The goal is to create tools that can be available for use at university libraries and for researchers in the humanities. Working with large collections of handwritten documents is very time consuming and many old books and letters remain unread for centuries. Efficient computerized methods could help researchers in history, philology and computer linguistics to cost-effectively conduct a whole new type of research based on large collections of documents. The thesis makes a contribution to this area through the development of methods based on machine learning. The passage of time degrades historical documents. Humidity, stains, heat, mold and natural aging of the materials for hundreds of years make the documents increasingly difficult to interpret. The first half of the dissertation is therefore focused on cleaning the visual information in these documents by image segmentation methods based on energy minimization and machine learning. However, machine learning algorithms learn by imitating what is expected of them. One prerequisite for these methods to work is that...

  • Structural Studies of Mn-X (X=Al, Bi): Permanent Magnetic Materials without Rare Earth Metals

    Author: Hailiang Fang
    Publication date: 2019-04-08 14:03

    How to generate and use electricity in a more efficient way is a major challenge for humankind. In this context, permanent magnets play an important role within a very broad range of electric power applications. The strongest magnets used today are mainly based on alloys that contain rare-earth metals, which are neither economical nor sustainable. The search for new alternative alloys with satisfactory magnetic properties is the major motivation for the investigations summarized in this thesis. Interesting candidates for alternative rare-earth free alloys were selected with τ-MnAl as the basis. Theoretical studies suggest that such alloys may show good magnetic properties after chemical modifications to optimize them. Another compound with promising magnetic properties is MnBi, included in this study.

    MnAl-Z (Z= C, B, Ga as doping elements) and MnBi compounds were synthesized through carefully devised high-temperature methods, followed by various milling and annealing steps. The structural phase analysis of the samples was based on X-ray and neutron diffraction. A systematic microstructural investigation was also performed for selected samples. The phase transitions of...

  • Avian Malaria and Interspecific Interactions in Ficedula Flycatchers

    Author: William Jones
    Publication date: 2019-04-02 14:16

    Parasitism is a core theme in ecological and evolutionary studies. Despite this, there are still gaps in our knowledge regarding host-parasite interactions in nature. Furthermore, in an era of human-induced, global climatic and environmental change revealing the roles that parasites play in host life-histories, interspecific interactions and host distributions is of the utmost importance. In this thesis, I explore avian malaria parasites (haemosporidians) in two species of passerine birds: the collared flycatcher Ficedula albicollis and the pied flycatcher F. hypoleuca. In Paper I, I show that an increase in spring temperature has led to rapid divergence in breeding times for the two flycatcher species, with collared flycatchers breeding significantly earlier than pied flycatchers. This has facilitated regional coexistence through the build up of temporal isolation. In Paper II, I explore how malaria assemblages across the breeding ranges of collared and pied flycatchers vary. I find that pied flycatcher populations have significantly higher infection prevalence than collared flycatchers, but collared flycatchers have a higher...

  • Biosensing platforms using graphene based bioreactive nanostructures with various dimensions

    Author: Yuanyuan Han
    Publication date: 2019-04-01 13:44

    Nanomaterials have brought new aspects and improvements to the biosensing field due to their unique physical and chemical properties that are not shown in the bulk state. This thesis focuses on concepting, developing and testing of biosensors where nanomaterials including graphene gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs) constitute the biosensors. The motivation is to improve the properties of biosensors for protein and nucleic acids by using the nanomaterials’ high surface volume ratio, their unique electrical properties, their good stability and biocompatibility.

    The synthesis of well controlled hybrid materials was essential to obtain well performing nucleic acids sensors, whereas a protein sensor contained mainly graphene and organic molecules. The nanomechanical measurements were applied on pyrene-maltose functionalized graphene surfaces after incubating them with the protein. When the Concanavalin A was captured by the pyrene-maltose, the adhesion force of biosensor surface increased significantly. This detection principle was employed to quantify the Concanavalin A attachment to the surface sensitively.

    In the development of the...

  • Graphene Based Inks for Printed Electronics

    Author: Man Song
    Publication date: 2019-04-01 13:43

    The outstanding properties of graphene make it attractive ink filler for conductive inks which plays an important role in printed electronics. This thesis focuses on the ink formulation based on graphene and graphene oxide (GO).

    Liquid phase exfoliation of graphite is employed to prepare graphene dispersions, i.e., shear- and electrochemical exfoliation. High concentration graphene dispersions with small size, few-layer graphene platelets are obtained by both methods. With the addition of ethyl cellulose stabilizer, shear-exfoliated graphene platelets in NMP were successfully inkjet printed on different substrates. The printed graphene film with electrical conductivity of ~3^104 S/m was obtained after annealing at 350 °C for one hour. Alternatively, the electrochemically exfoliated graphene nano-platelets were collected and redispersed in DMF to form inks. The printed film of conductivity ~2.5^103 S/m was obtained after annealing at 300 °C for one hour.

    Water based GO/Ag hybrid inks were developed for screen printing. When high concentration GO aqueous dispersion was mixed with reactive silver ink, the viscosity of the mixture increased instantly to above 1000 cP as...

  • Optimal adaptive designs and adaptive randomization techniques for clinical trials

    Author: Yevgen Ryeznik
    Publication date: 2019-04-01 11:06

    In this Ph.D. thesis, we investigate how to optimize the design of clinical trials by constructing optimal adaptive designs, and how to implement the design by adaptive randomization. The results of the thesis are summarized by four research papers preceded by three chapters: an introduction, a short summary of the results obtained, and possible topics for future work.

    In Paper I, we investigate the structure of a D-optimal design for dose-finding studies with censored time-to-event outcomes. We show that the D-optimal design can be much more efficient than uniform allocation design for the parameter estimation. The D-optimal design obtained depends on true parameters of the dose-response model, so it is a locally D-optimal design. We construct two-stage and multi-stage adaptive designs as approximations of  the D-optimal design when prior information about model parameters is not available. Adaptive designs provide very good approximations to the locally D-optimal design, and can potentially reduce total sample size in a study with a pre-specified stopping criterion.

    In Paper II, we investigate statistical properties of several restricted randomization procedures...

  • Adsorption and reactions of sulfur dioxide on TiO2 surfaces : Fundamental studies on single crystals and nanoparticles

    Author: David Langhammer
    Publication date: 2019-03-28 09:43

    Titanium dioxide (TiO2) is a material that is well-known among researchers in environmental science but is perhaps less well-known by the general public. It is commonly used in white paint because of its ability to scatter visible light, and for this reason it is manufactured at a large industrial scale. This is not the reason it has become famous, however, although the large abundance makes it interesting for use in industrial applications. It is famous for its ability to catalyze chemical reactions through the absorption of light. This process is called photocatalysis and it enables both uphill (photosynthetic) and downhill (photocatalytic) reactions since energy is transferred to the reacting molecules during the light absorption. The generation of H2gas from water and the formation of methane or methanol from carbon dioxide and water are two examples of photosynthetic reactions that are possible using TiO2. It can also be used for the degradation of pollutants, toxic compounds and bacteria, as well as for a number of technological applications, such as self-cleaning windows, solar cells and air purification filters.

    This thesis work has primarily been focused on...

  • Evolution of cellular complexity and other remarkable features in Gemmataceae : Complex bacterial lineages defy prokaryotic trends

    Author: Mayank Mahajan
    Publication date: 2019-03-26 10:17

    Bacteria of the family Gemmataceae belong the phylum Planctomycetes and are remarkable because of their complex cellular architectures, previously considered to be traits exclusive to eukaryotes. This thesis provides clues to the atypical cell envelope, the enhanced radiotolerance and the amazing cellular complexity of these bacteria.

    A comparative genomics study of these bacteria revealed massive duplications and new combinations of structural domains that are highly abundant in eukaryotes but rare in bacteria. These domains are known to facilitate signalling and protein interactions. The proteins of these bacteria also contain long regions with no predicted domains. On average, eukaryotic proteins are longer and more disordered than prokaryotic proteins. Intriguingly, the length and fraction of disordered regions in proteins of some bacteria are higher than in many other prokaryotes, and these bacteria also have complex lifestyles. Many bacteria in the Planctomycetes, including the Gemmataceae, are among these few bacteria. This suggests that there is no sharp boundary between prokaryotes and eukaryotes with respect to protein length...

  • Change Point Detection with Applications to Wireless Sensor Networks

    Author: Markus Eriksson
    Publication date: 2019-03-21 14:51

    In this thesis work we develop a new algorithm for detecting joint changes in statistical behavior of multiple, simultaneously recorded, signals. Such signal analysis is commonly known as multivariate change point (CP) detection (CPD) and is of interest in many scientific and engineering applications.

    First we review some of the existing CPD algorithms, where special attention is given to the Bayesian methods. Traditionally, many of the previous works on Bayesian CPD have focused on sampling based methods using Markov Chain Monte Carlo (MCMC). More recent work has shown that it is possible to avoid the computationally expensive MCMC methods by using a technique that is reminiscent of the forward-backward algorithm used for hidden Markov models. We revisit that technique and extend it to a multivariate CPD scenario where subsets of the monitored signals are affected at each CP. The extended algorithm has excellent CPD accuracy, but unfortunately, this fully Bayesian approach quickly becomes intractable when the size of the data set increases.

    For large data sets, we propose a two-stage algorithm which, instead of considering all possible combinations of joint CPs as...

  • Exact Results in Supersymmetric Field Theories : A dissertation on the defect and deformed

    Author: Erik Widen
    Publication date: 2019-03-12 13:45

    Quantum field theories (QFTs) are the most precise descriptions of the physical reality that humanity has found. Yet exact predictions are often missing as most computations are notoriously difficult to carry out. One generally resorts to perturbation theory which immediately limits the regime of validity. The need of better computational techniques and a deeper understanding of quantum field theory is evident.

    The highly symmetric N=4 SYM theory offers guidance in this quest. The theory's maximal supersymmetry and conformal invariance have allowed for the development of several computational techniques, most notably the AdS/CFT correspondence, supersymmetric localization and applications of integrability. These methods provide the rarity of exact results in a fully interacting QFT and shine light on regimes inaccessible by traditional computations.

    The insights drawn from N=4 SYM can be extended into more general settings through deformations and modifications. Three such modifications are the β-deformation, the massive deformation N=2* and N=4 SYM with a defect. This thesis summarizes a number of exact results for these three settings through: i)...