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Coming dissertations at TekNat

  • Cells and 2-representations of bimodules over Nakayama algebras

    Author: Helena Jonsson
    Publication date: 2020-05-28 15:50
  • Developmental exposure to mixtures of environmental pollutants : Studies on metabolism, developmental processes, and reproductive organs in zebrafish and chicken embryos

    Author: Anna Mentor
    Publication date: 2020-05-19 13:35

    Humans and wildlife are continuously exposed to mixtures of environmental pollutants. Mixture toxicity can be challenging to predict due to interactions between chemicals and thus whole-mixture approaches are crucial in toxicology. Developing organisms are generally more sensitive to chemical insult than adults and early exposure has been linked to metabolic and reproductive disorders later in life. It is thus imperative to clarify how mixtures of environmental pollutants affect early development.

    Within this thesis, consequences of early exposure to human-relevant chemical mixtures have been demonstrated using zebrafish and chicken embryos. The mixtures were designed previously based on negative associations with birth weight (mixture G) or anogenital distance (mixture S) in Swedish children. Mixture G consist of phthalate monoesters, perfluoroalkyl acids, and triclosan (TCS). It was assessed for effects on developmental processes (apoptosis and wnt/β-catenin signaling) and lipid metabolism in zebrafish. Two components of mixture G were assessed as single compounds: perfluorooctane sulfonate (PFOS) and TCS. Exposure to mixture G induced apoptosis, reduced wnt/β-catenin...

  • Mechanisms controlling air-sea gas exchange in the Baltic Sea

    Author: Lucía Gutiérrez-Loza
    Publication date: 2020-05-19 10:45

    Carbon plays a major role in physical and biogeochemical processes in the atmosphere, the biosphere, and the ocean. CO2 and CH4 are two of the most common carbon-containing compounds in the atmosphere, also recognized as major greenhouse gases. The exchange of CO2 and CH4 between the ocean and the atmosphere is an essential part of the global carbon cycle. The exchange is controlled by the air–sea concentration gradient and by the efficiency of the transfer processes. The lack of knowledge about the forcing mechanisms affecting the exchange of these climate-relevant gases is a major source of uncertainty in the estimation of the global oceanic contributions. Quantifying and understanding the air–sea exchange processes is essential to constrain the estimates and to improve our knowledge about the current and future climate. In this thesis, the mechanisms controlling the air–sea gas exchange in the Baltic Sea are investigated.

    The viability of micrometeorological techniques for CH4 monitoring in a coastal environment is evaluated. One year of semi-continuous measurements of air–sea CH4 fluxes using eddy covariance measurements suggests that the method is useful for CH4 flux...

  • Distributed Detection and Its Applications with Energy Harvesting Wireless Networks

    Author: Sinchan Biswas
    Publication date: 2020-05-15 12:58

    With the advent and widespread applications of high data-rate wireless services and devices, two of the fundamental resources in wireless communication have become extremely important and are scarce. These two resources are bandwidth and energy respectively. To tackle the problem of the ever-growing requirements of bandwidth, the paradigm of cognitive radio has been proposed in the literature where the users without any license are capable of utilizing the wireless radio spectrum allocated to the licensed user when it is idle. The performance of such a dynamic spectrum allocation policy depends heavily on the unlicensed users' ability to detect the vacancy in a licensed user's radio spectrum. Different types of detection algorithms have been investigated in the literature for this purpose. Some classic detection techniques like energy detection, matched filter detection, cyclo-stationary detector, generalized likelihood ratio test detector have found significant applications in sensing the licensed spectrum. These group of detection techniques focuses on collecting samples and performing the detection in a non-sequential fashion. The sequential counterpart of such techniques...

  • Functional Aspects of Cranial Implants : Mechanical and Regenerative Properties

    Author: Susanne Lewin
    Publication date: 2020-05-15 08:19

    In several neurosurgical procedures, the skull must be temporarily opened. The resulting bone defect can subsequently be reconstructed with a cranial implant. However, the complication rate of this surgical procedure is high (~20%). The most common complication for cranial implants is infection. Currently, the most frequently used implant materials are titanium alloys, PMMA or PEEK. An improved clinical outcome – in terms of increased bone regeneration, vascularization and soft tissue compatibility – could possibly be obtained through the use of bioactive and osteoconductive materials such as calcium phosphates (CaP).

    This thesis focuses on CaP–titanium composite (CaP–Ti) implants. This recently developed implant type is increasingly used with a promising outcome. However, a thorough understanding of its functional properties is lacking, something that is of high importance for their clinical use, but also for future biomaterial development. The overall aim of this thesis is to increase the knowledge of the in vivo functional aspects of CaP–Ti composite implants, with a specific focus on the mechanical and regenerative properties.

    The mechanical properties...

  • Seismic investigations and physical property studies of natural resources in Finland and Sweden : Efficient exploration of groundwater and mineral resources

    Author: Georgiana Maries
    Publication date: 2020-05-14 09:23

    Natural resources, such as mineral deposits and groundwater in particular, are crucial for our society, as the world prepares itself for a smooth transition towards green technologies and decarbonization. Apart from extraction and use, innovative mineral exploration solutions are needed to complete the full value chain and to achieve the sustainable development goals.  

    The application of seismic methods for both near-surface environmental and deep mineral exploration investigations is known, but high costs are associated with data acquisition and processing. In order to illustrate the potential of the seismic methods for efficient exploration of groundwater and mineral resources, cost-effective seismic surveys were acquired within two locations in Finland and Sweden, for aquifer delineation and imaging of iron-oxide mineralization in a hardrock environment, respectively. Physical properties, obtained from geophysical downhole logging and laboratory measurements, were analyzed for a complete characterization of the mineralization and its host rocks. 3D ray-tracing and 2D finite-difference forward modeling were carried out for better assessing the seismic response of the...

  • The Arctic Ocean Palaeomagnetic Record : A Stratigraphic Approach

    Author: Steffen Wiers
    Publication date: 2020-05-13 13:23

    The Arctic Ocean is an essential component of the global climate system, yet understanding of its geological archives is hampered by difficulties in age modelling. In addition to the scarcity of dateable microfossils, the palaeomagnetic record of Arctic sediments is unusual. Palaeomagnetic inclination sequences from Arctic sediments display numerous changes from steep positive to steep negative values that do not match the established geomagnetic polarity timescale. Independent age constraints suggest that most changes in the upper few meters below the sea-floor took place within the Brunhes normal chron. It has been suggested that zones of reversed inclination contain reversed titanomaghemite, formed by sea-floor oxidation of titanomagnetite. Until now, self-reversed components of Arctic records have not been studied in the context of regional stratigraphic frameworks, which could elucidate the relative timing of significant diagenetic changes, or their synchronicity between different records.

    This thesis examines marine sediments from three different areas of the Arctic. All records were evaluated within their regional stratigraphic frameworks and cross-correlated with...

  • The origin and fate of sediment organic carbon in tropical reservoirs

    Author: Anastasija Isidorova
    Publication date: 2020-05-13 13:15

    Recently, the construction of reservoirs has boomed, particularly in the tropics, but the impact of reservoirs on the global carbon cycle is not evident. Reservoirs accumulate sediments that simultaneously bury organic carbon (OC) and thus act as a C sink, and also produce methane (CH4) and thus emit a strong greenhouse gas. High temperature, internal production and sedimentation rates in tropical reservoirs may enhance both OC burial and CH4 production, however to a currently unknown extent. This thesis investigates the efficiency of the OC sink as well as the OC sources that feed into OC burial and CH4 production in four contrasting tropical reservoirs in Brazil. 

    The results demonstrate that reservoir sediments receive both terrestrial and aquatic OC, and that terrestrial OC is more prevalent in reservoirs with low internal production, and in river inflow bays. Aquatic OC is present in the sediments of all studied reservoirs, particularly in the reservoirs with high internal production and at sites that are closer to the dam. Reservoirs that experience anoxic conditions or high sediment deposition rates are likely to bury terrestrial OC at higher efficiency than oxic...

  • All Roads Lead to the Non-Coding RNome : Evolution of Multicellularity and Host Response to Bacterial Infection

    Author: Jonas Kjellin
    Publication date: 2020-05-13 08:54

    The ability to control gene expression is fundamental for all living organisms. Therefore, a large variety of regulatory mechanisms exist in each cell which are essential for e.g. developmental processes and to quickly adapt to different cellular stresses such as infection. Today we know that much of this regulation depends on non-coding (nc)RNAs. However, the function and evolutionary origin of many ncRNAs remains to be understood.

    The work presented in this thesis revolves around the evolutionary group of Dictyostelia. These social amoebae grow as single cells but initiate a multicellular development program when food runs low. The evolutionary position of Dictyostelia within Amoebozoa together with their multicellular development make these organisms relevant for investigating the evolution of ncRNAs and their association with multicellularity. Furthermore, the dictyostelid Dictyostelium discoideum is one of few organisms besides plants and animals were miRNAs have been identified. It is also an established model organism, well-adapted for laboratory growth and detailed molecular work.

    In this thesis, we investigate the biogenesis of miRNAs in D....

  • Antibiotic Resistance and the Cellular Currency S-adenosyl-methionine : Modification of aminoglycosides and nucleic acids

    Author: Sandesh Kanchugal P
    Publication date: 2020-05-11 14:16

    Streptomycin and spectinomycin are antibiotics that bind to ribosomes and inhibit protein synthesis. Common resistance mechanisms involve enzymatic modification of the two drugs by aminoglycoside nucleotidyltransferases (ANTs). The first part of this thesis covers the structural mechanism of two ANT enzymes. The first is the dual-specificity AadA, belonging to the ANT(3")(9) family, which modifies the 3" position of streptomycin and position 9 of spectinomycin. The second is ANT(9) that only modifies spectinomycin at position 9.

    We solved crystal structures of both enzymes, AadA in complex with ATP and streptomycin and ANT(9) with ATP and spectinomycin. The two enzymes show overall structural similarity and both consist of an N-terminal nucleotidyltransferase domain and a C-terminal helical domain. The binding of ATP between the two domains induces a conformational change that allows the drug to bind. The modified hydroxyl groups of both drugs align at similar positions in the active site, even though the drugs are chemically distinct. Comparison of the ANT(9) and AadA structures shows that spectinomycin specificity is explained by the straight α5 helix followed by a...

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