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Coming dissertations at TekNat

  • Micro-grids supplied by renewable energy : Improving technical and social feasibility

    Author: Caroline Bastholm
    Publication date: 2019-03-08 14:06

    Universal access to electricity stands high on the global agenda and is regarded as essential for positive development in sectors such as health care, education, poverty reduction, food production and climate change. Decentralized, off-grid electrification is deemed an important complement to centralized grid extension. By utilizing a renewable energy source, solar technology for the generation of electricity, photovoltaics (PV) is being considered as a way forward to minimize the environmental problems related to energy use.

    This thesis aims to contribute to improving the technical and social feasibility of PV and PV-diesel hybrid micro-grids for the purpose of providing access to electricity to people in rural areas of countries with low level access to electricity. In line with these general aims, the focus has been to address three questions related to challenges in three phases of rural electrification. The work has a multi-disciplinary approach, addressing mainly technical and social aspects of long-term sustainability of micro-grids, in a local context, and the changes these are intended to generate. One specific micro-grid in Tanzania has been used as a major case...

  • Toward fully automatic earthquake detection and processing for tomography in the Hengill area

    Author: Frederic Wagner
    Publication date: 2019-03-05 09:38

    This thesis focuses on the automation of seismic data analysis, in particular, event detection, quality assessment of detected events, and preparation of an earthquake catalogue for seismic tomography.

    The developed event detector uses back-propagation and stacking of a seismic trace attribute with a known velocity model to detect and locate events. A four-dimensional volume in space and time is probed for local maxima of coherently stacking signals. These local maxima define event location and origin time. Application of the detection algorithm to data from a dense 26-station 3-component seismic network in the Hengill area, SW Iceland, produced an increased true-to-false detection ratio compared to the local detection routine.

    The detected events were analysed using inter-event cross-correlation with a manually picked reference catalogue to determine their similarity with real events. Automatic P- and S-phase picks were derived using the time delay information from highly correlated events. Relocation with the determined phase picks improves hypocentre uncertainty. A multi-stage selection process is implemented to categorise the detected events into different...

  • Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden

    Author: Silvia Salas Romero
    Publication date: 2019-03-05 09:37

    Quick-clay landslides are considered one of the most important geohazards in Sweden, Norway, and Canada. The deposits involved are glacial and postglacial clays and silty clays, which are very sensitive to increased stress that may collapse their structure and cause liquefaction.

    A multidisciplinary approach was adopted in this study of quick clays in an area of southwest Sweden that is prone to landslides. It was mainly based on geophysical methods, but was complemented and validated with geotechnical, geological, and hydrological data. Downhole geophysics, land and river reflection seismics, radio magnetotellurics, P-wave refraction tomography, magnetics, and multichannel analysis of surface waves comprised the main geophysical methods used in this research. Laboratory measurements of core samples, such as grain size analysis, mineral magnetic properties, fossil content, X-ray fluorescence, cation exchange capacity, X-ray powder diffraction, electrical conductivity, and pH were also taken. Hydrological modelling was used to obtain information on the properties of groundwater within a coarse-grained layer, given the importance of this information in the formation of...

  • Moisture-Induced Strains and Stresses in Wood

    Author: Sabina Huč
    Publication date: 2019-02-27 11:57

    To design safe, reliable and durable timber structures subjected to varying natural outdoor or indoor climates, understanding the long-term behavior of wood when mechanically loaded or restrained to deform is crucial. The present thesis focuses on the numerical modeling of the long-term mechanical behavior of wood. The numerical analysis is divided in the moisture transport and the mechanical analyses. In the moisture analysis, the multi-Fickian moisture transport model is used to determine spatial and temporal moisture content fields over the analyzed domain due to changing relative humidity (RH) of the ambient air. The obtained moisture contents are taken into the mechanical analysis where a new mechanical model is applied for predicting rheological response of wood in three orthotropic directions simultaneously. Experimental results of different authors are used to support numerous numerical analyses performed for various wood species, deformation and loading modes in constant or changing RH conditions. The performed analyses show that the new mechanical model adequately predicts the viscoelastic behavior of hardwood and softwood species in two orthotropic...

  • Problematizing Sustainable ICT

    Author: Per Fors
    Publication date: 2019-02-26 09:20

    How should we understand the relationship between information and communication technology (ICT) and sustainability? Generally, it is assumed that while ICT products contribute to many environmental and social problems as they are produced and disposed of, the potential of using ICT to achieve a more sustainable society is immense. However, despite the fact that such a discourse is favored not only in the industrial but also in the political and academic spheres, we have yet to see this presumed sustainability-related potential of ICT fully exploited.

    This thesis argues that conventional assumptions and understandings related to three abstractions in sustainable ICT research and practice – namely the technological, the social, and the sustainable – contribute to an overly optimistic discourse of sustainable ICT, which favors certain research approaches and practical applications. Adhering to such a discourse risks reinforcing, rather than breaking loose from, an unsustainable status quo. Through problematization, this thesis aims to unveil and challenge such underlying assumptions and understandings, based on insights from the social...

  • Functional Traits in Sphagnum

    Author: Fia Bengtsson
    Publication date: 2019-02-21 10:04

    Peat mosses (Sphagnum) are ecosystem engineers that largely govern carbon sequestration in northern hemisphere peatlands. I investigated functional traits in Sphagnum species and addressed the questions: (I) Are growth, photosynthesis and decomposition and the trade-offs between these traits related to habitat or phylogeny?, (II) Which are the determinants of decomposition and are there trade-offs between metabolites that affect decomposition?, (III) How do macro-climate and local environment determine growth in Sphagnum across the Holarctic?, (IV) How does N2 fixation vary among different species and habitats?, (V) How do species from different microtopographic niches avoid or tolerate desiccation, and are leaf and structural traits adaptations to growth high above the water table?

    Photosynthetic rate and decomposition in laboratory conditions (innate growth and decay resistance) were related to growth and decomposition in their natural habitats. We found support for a trade-off between growth and decay resistance, but innate qualities translated differently to field responses in different species. There were no trade-offs between production of...

  • Insights into Covalent Chemistry for the Developmen­t of Biomaterials

    Author: Daniel Bermejo-Velasco
    Publication date: 2019-02-21 08:12

    Covalent cross-linking chemistry is currently exploited in the preparation of biomaterial for biomedical applications. Choice of these chemistries for the preparation of biomaterials and bioconjugates strongly influences the biological output of these materials. Therefore, this thesis aims to develop novel bioconjugation strategies understanding their advantages and drawbacks. Our results provide new insight to adapt these chemical transformations for a specific application.

    The first part of this thesis points out the relevance of tuning different properties of biomaterials with specific emphasis on the development of hyaluronic acid (HA) hydrogels. The second part of the thesis describes how different chemical transformations including hydrazone formation (Paper I), thiazolidine formation (Paper II), cross-aldol addition reaction (Paper III) and disulfide formation (Paper IV) dictate material properties.

    This thesis explores both basic organic reaction mechanism and application of these reactions to influence material characteristics. The detailed study of the reaction conditions, kinetics, and...

  • Knowledge elicitation as abstraction of purposive behaviour

    Author: Anton Axelsson
    Publication date: 2019-02-15 08:43

    Researchers use knowledge elicitation methods to document expert knowledge for the primary purpose of understanding cognitive processes and with this understanding, technical solutions to resolve human factors issues can be produced. This dissertation offers a novel perspective on knowledge elicitation as an abstraction process. Such a theoretical framework has emerged by consolidating the ecological approach of Brunswikian psychology with the ideas of tacit and personal knowledge of Polanyian epistemology. Traditionally, knowledge elicitation has been considered an extraction process in which knowledge can be readily transferred from one individual to another. Here, this traditional position is rejected in favour of Polanyi’s premise that much of the knowledge individuals possess is tacit in nature, which implies that it cannot be documented easily, expressed in explicit form or explained. In this dissertation, knowledge is characterised as a personal process of knowing, highlighting context as a subjective knowledge structure of personal experiences that is formulated implicitly and indirectly over time through a dynamic interaction with the environment. Therefore, tacit...

  • Exotic Ribosomal Enzymology

    Author: Josefine Liljeruhm
    Publication date: 2019-02-15 08:42

    This thesis clarifies intriguing enzymology of the ribosome, the multiRNA/multiprotein complex that catalyzes protein synthesis (translation). The large ribosomal RNAs (23S and 16S rRNAs in E. coli) are post-transcriptionally modified by many specific modification enzymes, yet the functions of the modifications remain enigmatic. A deeper insight into two of the 23S rRNA S-adenosyl-methionine-requiring methyltransferase enzymes, RlmM and RlmJ, was given by investigating substrate specificity in vitro. Both enzymes were able to methylate in vitro-transcribed, modification-free, protein-free, 2659-nucleotide-long 23S rRNA. Furthermore, RlmM was able to methylate the 611-nucleotide-long Domain V of the 23S rRNA alone and RlmJ could modify the A2030 with only 25 surrounding nucleotides.

    Translation is evolutionary optimized to incorporate L-amino acids to the exclusion of D-amino acids in the cell. To understand how, and how to engineer around this restriction for pharmacological applications, detailed kinetics of ribosomal dipeptide formation with D- versus L-phenylalanine-tRNA were determined. This was done by varying the concentrations of EF-Tu (...

  • Low-Coordinate Organopnictogens : Synthesis and Optoelectronic properties

    Author: Muhammad Anwar Shameem
    Publication date: 2019-02-13 15:39

    This thesis work is based on the development of novel organopnictogen compounds and the exploration of their potential applications in organic electronics. In particular, incorporation of phosphorus and arsenic into π-conjugated systems is known to modify the optoelectronic properties.

    The first chapter of this thesis is fully devoted to the development of a metal-free synthetic route that allows direct, sequential and stereoselective alkynylation of C,C-dibromophosphaalkenes. The subsequent unusual reactivity of thus synthesized C-mono and C,C-diacetylenicphosphaalkenes with terminal acetylenes afforded highly substituted 1-phoshpha-1,3-butadienes heavier analogue of all carbon 1,3-butadiene motifs. Optimization of the reaction condition favored exclusively the formation of 1-phospha-1,3-butadienes. Unveiling the unique cyclization of the 3-yne 1-phospha-1,3-butadiene gave highly substituted phosphole derivatives. Further, it has been experimentally shown that the P=C unit is essential for this rare cyclization and rearrangement to give π-conjugated phosphole derivatives.

    The second chapter of this thesis work deals with incorporation of...

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