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Sökning: WFRF:(Eriksson S.) > Doktorsavhandling

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1.
  • Carpman, Nicole (författare)
  • Resource characterization and variability studies for marine current power
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.
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2.
  • Eriksson, Arne S., 1961 (författare)
  • Elastic Wave Scattering by Closed Cracks and Thin Flaws - Multiple Scattering and Resonances
  • 1992
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis we study elastic wave scattering by thin flaws and closed cracks, which finds applications in ultrasonic testing and evaluation of materials. First we consider the scattering of an SH-wave by a thin finite elastic layer between two elastic half-spaces. The layer, thin compared to the wavelengths involved, is modelled by spring boundary conditions extended with terms accounting for inertia forces. A direct integral equation method is used, with the discontinuity of displacement and traction over the thin layer as the unknowns. Numerical results are given for the scattered energy and the far field amplitude. We also investigate the elastodynamic scattering by two penny-shaped cracks with spring boundary conditions in the fully three-dimensional case. The transition matrix of a single crack is first determined by a direct integral equation method which gives the crack-opening displacement (COD) and the integral representation which subsequently gives the scattered field expanded in spherical waves. Two cracks are considered by a multi-centered T matrix approach where the matrix inverses are expanded in Neumann series. Rotation matrices are employed so that the cracks may have an arbitrary orientation. The numerical procedures are very stable and it has been possible to go to quite high frequencies. The back-scattered longitudinal far field amplitude is computed both in the frequency and time domain in a few cases and the effects due to multiple scattering are in particular explored. The natural frequencies of one partially closed penny-shaped crack are calculated for the symmetric part of the problem. The natural frequencies are given as the complex SEM (singularity expansion method) poles of the symmetric part of the T matrix. A clear correlation is shown between the migration of the poles, as the crack gets more closed, and the frequencies at which the scattering cross section has its peaks.
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3.
  • Eriksson, Anna S. (författare)
  • Syndecan - Regulation and Function of its Glycosaminoglycan Chains
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The cell surface is an active area where extracellular molecules meet their receptors and affect the cellular fate by inducing for example cell proliferation and adhesion. Syndecans and integrins are two transmembrane molecules that have been suggested to fine-tune these activities, possibly in cooperation. Syndecans are proteoglycans, i.e. proteins with specific types of carbohydrate chains attached. These chains are glycosaminoglycans and either heparan sulfate (HS) or chondroitin sulfate (CS). Syndecans are known to influence cell adhesion and signaling. Integrins in turn, are important adhesion molecules that connect the extracellular matrix with the cytoskeleton, and hence can regulate cell motility. In an attempt to study how the two types of glycosaminoglycans attached to syndecan-1 can interact with integrins, a cell based model system was used and functional motility assays were performed. The results showed that HS, but not CS, on the cell surface was capable of regulating integrin-mediated cell motility.Regulation of intracellular signaling is crucial to prevent abnormal cellular behavior. In the second part of this thesis, the aim was to see how the presentation of glycosaminoglycan chains to the FGF signaling complex could affect the cellular response. When attached to the plasma membrane via syndecan-1, CS chains could support the intracellular signaling, although not promoting as strong signals as HS. When glycosaminoglycans were attached to free ectodomains of syndecan-1, both types of chains sequestered FGF2 from the receptors to the same extent, pointing towards functional overlap between CS and HS.To further study the interplay between HS and CS, their roles in the formation of pharyngeal cartilage in zebrafish were established. HS was important during chondrocyte intercalation and CS in the formation of the surrounding extracellular matrix. Further, the balance between the biosynthetic enzymes determined the ratio of HS and CS, and HS biosynthesis was prioritized over CS biosynthesis.The results presented in this thesis provide further insight into the regulation of HS biosynthesis, as well as the roles of both HS and CS on the cell surface. It is evident, that in certain situations there is a strict requirement for a certain HS structure, albeit in other situations there is a functional overlap between HS and CS.
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5.
  • Eriksson, Jonna S., 1989 (författare)
  • Polyploid Phylogenetics in Plants: Insights on non-model organisms in Fabaceae and Malvaceae
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Genome duplication is a common phenomenon in angiosperms and advances in sequencing technologies and bioinformatics is now revealing its prevalence and significance. In a polyploidization event all genes in a genome are doubled. Duplicated genes can take one of three paths, either both of the duplicated are maintained or one of them may be randomly lost or selected against. Polyploid species are challenging for resolving species relationships because of the number of duplicated genes and the different processes leading to genome reduction. In this thesis I investigate the mode of polyploid origin (i.e. auto- and allopolyploidy) and the role of ancient genome duplication in plant speciation. Here, two families were studied because of their numerous rounds of polyploidization events, Fabaceae and Malvaceae. To discern between the complex processes involving polyploidy, large amounts of data were generated from several nuclear genes using target gene capture and Illumina sequencing. In Medicago (Fabaceae) two modes of polyploidy (autopolyploidy and allopolyploidy) were discovered. In the first case, an autopolyploid mode was identified, because gene comparisons showed two independently evolving species, a cryptic tetraploid species derived from a diploid progenitor. In the second case, two woody tetraploids were found to be hybrids. Since the closest parental lineages associated with the hybridization only have woody roots, the genome duplication for genes related to woodiness may be an instance of transgressive phenotype (extreme morphological character) in the hybrids. Evidence of genome duplication appears not only in recently formed polyploids, but may also be present through genes that were duplicated in a lineage’s history. The traces of ancient genome duplication events may be scarce owing to random mutations and gene losses. Hibiscus (Malvaceae) is a plant genus which possesses diverse chromosome numbers among species, indicative of potential polyploidization events. By studying the number of gene copies in diploid species, two ancient genome duplications were identified in Hibiscus. Additionally, numerous polyploidization events following the ancient duplications were detected among the extant species, indicating a complex reticulate history. Hibisceae consists of five major clades: /Calyphylli, /Euhibiscus, /Furcaria, /Trionum and /Megistohibiscus but with inconsistent genus naming conventions (e.g. Hibiscus occurs across all of the clades). In this study, phylogenetic analysis of HTS data supported the classification of the group into the major clades; all were found to be monophyletic and no hybrid polyploidization events were found to have occurred between them. Additionally, each major clade's taxa were found to have common base chromosome numbers. Given the results, a taxonomic renaming, based on base chromosome number, of the major clade's genera is recommended. This thesis demonstrates a rich history of polyploidizations both recent and ancient – highlighting the important role this phenomenon has played in the evolution of two distantly-related plant families. Polyploidy may explain the underlying causes of when classical taxonomy (classification before DNA sequences) is not enough and may potentially lead to underestimation of the true number of species. Due to the unique patterns across lineages, polyploidizations allows for no generalizations; despite its ubiquity, it remains mysterious. Polyploidy is, at least in part, reversible and leads to a smaller genome size over time.
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6.
  • Eriksson Lundström, Jenny S. Z., 1973- (författare)
  • On the Formal Modeling of Games of Language and Adversarial Argumentation : A Logic-Based Artificial Intelligence Approach
  • 2009
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Argumentation is a highly dynamical and dialectical process drawing on human cognition. Successful argumentation is ubiquitous to human interaction. Comprehensive formal modeling and analysis of argumentation presupposes a dynamical approach to the following phenomena: the deductive logic notion, the dialectical notion and the cognitive notion of justified belief. For each step of an argumentation these phenomena form networks of rules which determine the propositions to be allowed to make sense as admissible, acceptable, and accepted. We present a formal logic framework for a computational account of formal modeling and systematical analysis of the dynamical, exhaustive and dialectical aspects of adversarial argumentation and dispute. Our approach addresses the mechanisms of admissibility, acceptability and acceptance of arguments in adversarial argumentation by use of metalogic representation and Artificial Intelligence-techniques for dynamical problem solving by exhaustive search. We elaborate on a common framework of board games and argumentation games for pursuing the alternatives facing the adversaries in the argumentation process conceived as a game. The analogy to chess is beneficial as it incorporates strategic and tactical operations just as argumentation. Drawing on an analogy to board games like chess, the state space representation, well researched in Artificial Intelligence, allows for a treatment of all possible arguments as paths in a directed state space graph. It will render a game leading to the most wins and fewest losses, identifying the most effective game strategy. As an alternate visualization, the traversal of the state space graph unravels and collates knowledge about the given situation/case under dispute. Including the private knowledge of the two parties, the traversal results in an increased knowledge of the case and the perspectives and arguments of the participants. As we adopt metalogic as formal basis, arguments used in the argumentation, expressed in a non-monotonic defeasible logic, are encoded as terms in the logical argumentation analysis system. The advantage of a logical formalization of argumentation is that it provides a symbolic knowledge representation with a formally well-formed semantics, making the represented knowledge as well as the behavior of knowledge representation systems reasoning comprehensible. Computational logic as represented in Horn Clauses allows for expression of substantive propositions in a logical structure. The non-monotonic nature of defeasible logic stresses the representational issues, i.e. what is possible to capture in non-monotonic reasoning, while from the (meta)logic program, the sound computation on what it is possible to compute, and how to regard the semantics of this computation, are established.
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7.
  • LaForge, Karl Steven, 1957- (författare)
  • Preproenkephalin Gene and mRNA : Studies of Structure, Function, Cocaine Responses in an Animal Model, and Genetic Association with Human Opiate Addiction
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The endogenous opioid enkephalin neuropeptides are mediators of pain perception and have been implicated in human addictions. The preproenkephalin gene and its mRNA have also provided many examples of tissue- and species-specific variations in mRNA structure produced through a variety of transcriptional and post-transcriptional mechanisms. Resultant differences in mRNA structure, in several cases, have impact on translation of enkephalin prepropeptide. The reports and discussion presented herein describe studies of the preproenkephalin gene and mRNA structure in the guinea pig, an animal that may have specific advantages for modeling the human endogenous opioid system. A guinea pig brain cDNA library was constructed and screened for clones of preproenkephalin and preprodynorphin, which were then sequenced. These studies confirmed the predicted mRNA structure that had been previously proposed based on homology with gene sequences and other methods. Multiple transcription initiation sites for each of these prepropeptide genes were also identified. Studies were conducted in the guinea pig to evaluate the effects of the administration of cocaine in a “binge” paradigm for two and seven days on preproenkephalin mRNA levels in several brain regions. “Binge” cocaine administration for seven (but not two) days resulted in differential changes in mRNA levels in different brain regions. Decreases were observed in the nucleus accumbens and hypothalamus, and increases in the frontal cortex, amygdala and hippocampus. These findings differ from those of previous rodent studies and suggest that this species may provide a useful alternative model for the study of the effects of cocaine on preproenkephalin gene expression in the human brain. Human genetic studies were also conducted in opioid-dependent (formerly heroin-addicted) and control subjects to test the hypothesis that the preproenkephalin gene is associated with heroin addiction. In two separate studies, we obtained evidence that this gene may be associated with the development of human heroin addiction.
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8.
  • Lindgren, Åsa, 1973- (författare)
  • Effects of herbivory on arctic and alpine vegetation
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The distribution of plant species and functional traits in alpine and arctic environments are determined by abiotic conditions, but also by biotic interactions. In this thesis, I investigate interactions among plants and herbivory effects on plant community composition and plant functional traits in three different regions: Swedish Lapland, Beringia (USA/Russia) and Finnmark (Norway). Reindeer grazing was found to be extensive in southern Lapland and had limited effects on plant community composition and seedling germination. However, reindeer presence was found to influence plant functional traits, particularly in the subalpine birch forest. Tall herbs were lower and had lower SLA when reindeer were present, while small herbs showed an opposite pattern. The contrasting effects on the two herb groups are probably explained by a competitive release for small herbs when the tall herbs are suppressed by reindeer. Rodents had the largest relative impact on plant community composition in southern Lapland and this is consistent with the study from Finnmark, where rodents heavily affected dwarf shrubs on predator-free islands. With no predators present, vole densities increased profoundly and almost depleted some dwarf shrub species. These results support the idea that small mammals in arctic and alpine tundra are controlled by predators (i.e. top-down). However, a decrease in the nutritional quality in a sedge after defoliation gives support for the idea that small mammals are regulated by plant quality (i.e. bottom-up). In Beringia, small and large herbivores differed in the relation to plant community composition, since large herbivores were related to species richness and small herbivores were related to plant abundance. Plant functional traits were related only to large herbivores and standing crop of vascular plants.
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