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Coming dissertations at TekNat

  • The evolution of sex chromosomes and sex-linked sequences in birds

    Author: Homa Papoli Yazdi
    Publication date: 2019-04-23 10:44

    Identifying the processes involved in the evolution of suppressed recombination between sex chromosomes and understanding their consequences for the evolutionary dynamics of sex-linked loci have been major topics of research during the last century. In this thesis, I used the avian ZW system, where females are the heterogametic sex, to investigate the underlying processes in sex chromosome evolution in birds. I identified the gametologous genes between the largely recombining Z and W chromosomes of ostrich and dated the timing of the cessation of recombination to prior to the split of modern birds. I then constructed a genetic map of the ostrich Z chromosome and corrected its assembly in order to obtain the ancestral organization of the Z chromosome in a basal clade of birds. By analyzing the inversion events across the avian phylogeny, I concluded that a combination of Z- and possibly W-linked inversions might have been responsible for the evolution of suppressed recombination in avian sex chromosomes. To understand the determinants of levels of genetic diversity on Z chromosome compared to autosomes, I calculated Z to autosome (Z:A) genetic diversity across 32 avian species....

  • Probing Catalytic Reaction Mechanisms of Biomimetic Diiron Complexes through Time-resolved Absorption Spectroscopy

    Author: Shihuai Wang
    Publication date: 2019-04-23 10:10

    Directed design of improved molecular catalysts for hydrogen evolution reactions relies on rational benchmarking based on a detailed understanding about the mechanism of catalysis. Specifically, investigation of multi-electron redox catalysis, with structural characterization of catalytic intermediates, combined with the kinetics of their transformations, can reveal the rate-limiting step of the overall reaction, possible degradation pathways and the function of structural motives. However, direct spectroscopic observation of catalytic intermediates is in most cases not available due to the rapid turnover of efficient catalysts.

    In this thesis, time-resolved absorption spectroscopy with UV-Vis and mid-IR detection was used to identify catalytic reaction intermediates and account for kinetics relevant to elementary reactions steps of H2 formation on a nanosecond to second time scale. For a class of FeIFeI (S-R-S)(CO)6-n(PMe3)n complexes (R = propyl, benzyl or azapropyl), inspired by the active site of FeFe-hydrogenase, the key intermediates formed in different catalytic pathways have been characterized. These complexes typically feature very similar coordination geometry,...

  • Pathogenesis and Cell Biology of the Salmon Parasite Spironucleus salmonicida

    Author: Ásgeir Ástvaldsson
    Publication date: 2019-04-17 11:59

    Spironucleus species are classified as diplomonad organisms, diverse eukaryotic flagellates found in oxygen-deprived environments. Members of Spironucleus are parasitic and can infect a variety of hosts, such as mice and birds, while the majority are found to infect fish. Massive outbreaks of severe systemic infection caused by a Spironucleus member, Spironucleus salmonicida (salmonicida = salmon killer), have been reported in farmed salmonids resulting in large economic impacts for aquaculture.

    In this thesis, the S. salmonicida genome was sequenced and compared to the genome of its diplomonad relative, the mammalian pathogen G. intestinalis (Paper I). Our analyses revealed large genomic differences between the two parasites that collectively suggests that S. salmonicida is more capable of adapting to different environments. As S. salmonicida can infiltrate different host tissues, we provide molecular evidence for how the parasite can tolerate oxygenated environments and suggest oxygen as a potential regulator of virulence factors (Paper III). To further investigate the molecular responses...

  • Wind Turbine Sound in Cold Climates

    Author: Kristina Conrady
    Publication date: 2019-04-15 14:33

    The increase in the number of wind turbines (WTs) in populated areas in cold climates increases the number of people potentially being affected by WT sound. Outdoor sound propagation is strongly dependent on meteorological conditions, however, limitations in the knowledge exist regarding the implications of meteorological conditions in cold climates. Long-term acoustic and meteorological measurements were conducted in the vicinity of two wind farms in northern Sweden, to investigate the effect of snow and low-level wind maxima on WT sound, to analyse the occurrence of amplitude modulation and to evaluate selection methods for WT sound measurements. Different selection methodologies were applied to the acoustical data. The simplest method only includes a minimum rotational frequency of the WTs, while the most comprehensive method additionally includes criteria based on spectral resemblance, temporal variation of the sound level, amplitude modulation and wind speed. The effect of snow on WT sound depends on the snow quality. Snow on trees lowers the sound level by ca. 2 dBA. Low-level wind maxima below hub height reduce the sound level near the surface. Since this effect is...

  • 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...