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Coming dissertations at TekNat

  • Exploring Dye-Sensitized Mesoporous NiO Photocathodes : from Mechanism to Applications

    Author: Lei Tian
    Publication date: 2020-02-11 06:40

    Increasing attention has been paid on solar energy conversion since the abundant solar energy possesses the potential to solve the problems on energy crisis and climate change. Dye-sensitized mesoporous NiO film was developed as one of the attractive photocathodes to fabricate p-type dye-sensitized solar cells (p-DSCs) and dye-sensitized photoelectrosynthetic cells (p-DSPECs) for electricity and chemical fuels generation, respectively. In this thesis, we designed a well-structured NiO-dye-TiO2 configuration by an atomic layer deposition (ALD) technique, with an organic dye PB6 as the photosensitizer. From kinetic studies of charge separation, ultrafast hole injection (< 200 fs) was observed from the excited state of PB6 dye into the valence band of NiO; dye regeneration (electron injection) was in t1/2 ≤ 500 fs, which is the fastest reported in any DSCs. On the basis of NiO-dye-TiO2 configuration, we successfully fabricated solid-state p-type DSCs (p-ssDSCs). Insertion of an Al2O3 layer was adopted to reduce charge recombination, i.e. NiO-dye-Al2O3-TiO2. Theoretically, such a configuration is possible to maintain efficient charge separation and depressed charge recombination...

  • Exploring the Merits and Challenges of Hyperon Physics : with PANDA at FAIR

    Author: Walter Ikegami Andersson
    Publication date: 2020-02-07 11:01

    Binary hyperon production in antiproton-proton annihilations will be carried out with the PANDA experiment at FAIR, and probes the strong interaction in the non-perturbative regime where the relevant degrees of freedom are unclear. The self-analyzing decays of hyperons provide a straightforward way to study reaction dynamics via the measurement of spin observables. However, since weakly decaying hyperons can travel several centimeters before decaying, they are challenging to reconstruct. Conventional track reconstruction algorithms assume that charge particles originate in the experiment interaction point.

    In this thesis, software tools are developed for the reconstruction and fitting of charged particles in the collaboration-wide software package PandaRoot. Pattern recognition algorithms are developed for the reconstruction of charged particle tracks with displaced vertices. Three algorithms that reconstruct the longitudinal momentum in the Straw Tube Tracker (STT) of PANDA are developed. They are based on a combinatorial approach, a Hough Transform, and a recursive annealing fit. The implementation and performance of these algorithms are presented. The track fitting scheme...

  • Stolen genes, a shortcut to success : Evolution of metabolic and detoxification capacities in Diplomonads

    Author: Alejandro Jimenez-Gonzalez
    Publication date: 2020-02-07 08:59

    Parasites do not represent a single evolutionary lineage meaning that they have evolved several times. The changes that parasites have undergone to adapt to such a lifestyle are not entirely understood. This thesis focuses on the study of diplomonads (Fornicata, Metamonada), a group of host-associated or free-living protists, to better understand how they adapted to different environments and hosts.

    Diplomonads, and close relatives, are found in low-oxygen environments. However, some species can withstand fluctuating levels of oxygen. In a first study, we reconstructed the oxygen detoxification pathway of Fornicata and study its evolution. Comparative genomics showed that Fornicata shares a common pathway with lineage-specific modifications. Phylogenetic analyses showed a pathway in a constant change where proteins have been gained and lost.

    In a second study, the Giardia muris genome was sequenced and compared to the genome of G. intestinalis WB. We reconstructed the metabolic capacities of both species. Our analyses showed that the observed differences are the result of gene acquisitions or differential losses that can be explained based on...

  • Interrogating Diffusional Mass and Charge Transport in Catalytic Metal-Organic Frameworks

    Author: Ben A. Johnson
    Publication date: 2020-02-06 13:30

    Molecular catalysts are efficient and selective for the electrochemical conversion of small molecules for energy conversion. Application of molecular species in a large-scale industrial setting requires stabilization in a heterogeneous support material. Metal-organic frameworks (MOFs), having high surface areas for increased active site density, have shown promise as potential platforms in which to incorporate molecular catalysts. However, moving from a homogenous environment to catalysis in porous media, necessitates efficient mass and charge transport to the imbedded catalysts. Either diffusional charge transport or diffusion of substrate have the potential to limit the overall observed rate of product formation, if they are slower than the intrinsic rate of the catalytic reaction. This thesis seeks to examine the effect of diffusional mass and charge transport on molecular catalysis in MOFs.

    First, chemically driven water oxidation is examined using a molecular ruthenium catalyst covalently grafted in MIL(Cr)-101 (MIL = Materials Institute Lavoisier) (Chapter 3). A formal kinetic analysis using a steady-state reaction-diffusion model revealed the limitations incurred...

  • Aiming at Moving Targets : Applying Cognitive Work Analysis to Work Domains in Transition

    Author: Ida Löscher
    Publication date: 2020-02-06 10:44

    The design of IT systems for complex work environments is essential for workers to be able to operate more effectively and efficiently. To design a system that supports the workers' specific tasks we need to understand the work demands and the context in which the system operates. However, this is a difficult task because of the dynamic nature of complex systems. The thesis investigates how the cognitive work analysis (CWA) framework (Vicente, 1999) can be applied to understand a domain under transformation by (1) developing methods to manage challenges associated with applying CWA to real-world complex systems and (2) investigating how models from the CWA framework can be used to contend with the moving target for development. The studies are carried out within two quite different application domains: long-haul driving and health care. An activity prioritization method was suggested as a useful technique to focus the analyzing efforts during the analysis of tasks and strategies. However, adaption to practical constraints has to be done thoughtfully in order not to lose the value of the analysis. Moreover, workshops were proposed as a means to bridge the gap between the...

  • Stelar Performance Under Drought : Regulation of Developmental Robustness and Plasticity of the Arabidopsis Root Xylem

    Author: Prashanth Ramachandran
    Publication date: 2020-02-06 08:14

    Plants have evolved genetic mechanisms to sense, modulate and modify developmental programs in response to the changing environment. This brings forth challenges in stably generating tissue patterns while simultaneously allowing amenability. Gene perturbation studies have identified molecular regulators that control fate specification and differentiation of various tissues. However, we lack a complete understanding of how these processes are influenced by the environment. In this thesis, using Arabidopsis xylem as a model, I show that developmental regulators that function in maintaining a stable growth pattern are also involved in the manifestation of phenotypic plasticity. We found that the generation of a robust xylem developmental program is dependent on a feed forward loop between components of the auxin signalling pathway and the master regulators of xylem development, class III Homeodomain Leucine-Zipper (HD-ZIP III) transcription factors (TFs). By directly activating an auxin signalling activator (MP) and repressor (IAA20), the HD-ZIP III TFs facilitate stable xylem patterning and development. We also show that alterations to the HD-ZIP III mediated...

  • Solid-state nanopores : fabrication and applications

    Author: Shuangshuang Zeng
    Publication date: 2020-01-31 10:13

    Nanopores are of great interest in study of DNA sequencing, protein profiling and power generation. Among them, solid-state nanopores show obvious advantages over their biological counterparts in terms of high chemical stability and reusability as well as compatibility with the existing CMOS fabrication techniques. Nanopore sensing is most frequently based on measuring ionic current through a nanopore while applying a voltage across it. When an analyte passes through the pore, the ionic current temporarily changes, providing information of the analyte such as its size, shape and surface charge. Although many magnificent reports on using solid-state nanopores have appeared in the literature, several challenges still remain for their wider applications, which include improvement of fabrication reproducibility for mass production of ultra-small nanopores and minimization of measurement instability as well as control of translocation speed and reduction of background noise. This thesis work explores different techniques to achieve robust and high throughput fabrication of sub-10 nm nanopores for different applications.

    The thesis starts with presenting various fabrication...

  • Too close for comfort : The role of Contact-Dependent growth Inhibition (CDI) in interbacterial competition and cooperation

    Author: Marcus Wäneskog
    Publication date: 2020-01-31 06:21

    Contact-Dependent growth inhibition (CDI) was discovered in 2005 in the E. coli isolate EC93. Since then our knowledge of CDI systems and their impact on bacterial communities have increased exponentially. Yet many biological aspects of CDI systems are still unknown and their impact on complex microbial communities have only just begun to be studied. CDI systems require the function of three proteins; CdiBAI. The outer-membrane transport protein, CdiB, allows for the transportation of the toxin delivery protein CdiA to the cell surface of an inhibitor cell. Through a contact- and receptor-dependent interaction with a target cell the toxic C-terminal domain of CdiA is cleaved off and delivered into the target cell were it mediates a growth arrest. Different CdiA-CT domains encodes for diverse toxic activities, such as nucleases and membrane ionophore toxins. Each unique CdiA-CT toxin has a cognate immunity protein (CdiI) that binds and neutralize against its toxic activity, thus preventing a possible self-inhibition.

    In this thesis I have studied the effect of CDI system(s) on both single cell and population level, within both intra- and interspecies bacterial...

  • Fiber Floer cohomology and conormal stops

    Author: Johan Asplund
    Publication date: 2020-01-30 09:10
  • New Paradigms in GPCR Drug Discovery : Structure Prediction and Design of Ligands with Tailored Properties

    Author: Mariama Jaiteh
    Publication date: 2020-01-24 08:43

    G protein-coupled receptors (GPCRs) constitute a large superfamily of membrane proteins with key roles in cellular signaling. Upon activation by a ligand, GPCRs transduce signals from the extracellular to the intracellular environment. GPCRs are important drug targets and are associated with diseases such as central nervous system (CNS) disorders, cardiovascular diseases, cancer, and diabetes. Currently, 34% of FDA-approved drugs mediate their effects via modulation of GPCRs. Research during the past decades has resulted in a deeper understanding of GPCR structure and function. Moreover, recent breakthroughs in structural biology allowed the determination of several atomic resolution GPCR structures. New paradigms in GPCR pharmacology have also emerged that can lead to improved drugs. Together, these advances provide new avenues for structure-based drug discovery. The work in this thesis focused on how the large amount of structural data gathered over the last decades can be used to model GPCR targets for which no experimental structures are available, and the use of structure-based virtual screening (SBVS) campaigns to identify ligands with tailored pharmacological properties...