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Sökning: WFRF:(Persson J) > Doktorsavhandling

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1.
  • Lagerstedt, Jens, 1975- (författare)
  • Regulatory and Structural Properties of the High-Affinity Phosphate Acquisition System in Saccharomyces cerevisiae
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Inorganic phosphate is an essential nutrient required for the synthesis of many cellular components (e.g., nucleic acids, proteins, lipids and sugars), as well as for meeting metabolic needs (e.g., energy production and translocation). In the case of the unicellular yeast Saccharomyces cerevisiae, the presence of both high- and low-affinity phosphate transporters in the plasma membrane provides for adaptation to environmental variations. Of these systems, the high-affinity Pho84 transport system is the major phosphate transporter activated when the cells have limited access to external phosphate. This integral membrane protein belongs to the major facilitator superfamily (MFS) and possesses 12 predicted transmembrane domains. Activation of this and other proteins (e.g., extracellular phosphatases) involved in maintaining cellular phosphate homeostasis under conditions of limited availability of external phosphate is controlled primarily by transcriptional regulation. However, the presence of proteins indirectly or directly involved in phosphate transport by Pho84, including Gtr1, has been reported. The Gtr1 protein binds guanine nucleotides and probably functions as a molecular switch. The present thesis describes the regulated intracellular trafficking and degradation of Pho84 in response to phosphate, as well as to its non-hydrolysable and non-utilizable analog methylphosphonate. The involvement of the Gtr1 protein in high-affinity phosphate uptake has also been examined. Moreover, in vitro and in silico analyses of structural and functional aspects of both the Pho84 and Gtr1 proteins are presented and discussed.
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2.
  • Lundqvist, Maria J., 1973- (författare)
  • Quantum Chemical Modeling of Dye-Sensitized Titanium Dioxide : Ruthenium Polypyridyl and Perylene Dyes, TiO2 Nanoparticles, and Their Interfaces
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Quantum chemical calculations have been used to model dye-sensitized nanostructured titanium dioxide systems that can be used in solar cells for solar energy to electricity conversion. Structural, electronic and spectral properties of isolated dyes and both bare and dye-sensitized TiO2 have been calculated with density functional theory, providing detailed information about both the separate parts and the dye-TiO2 interface.The connection between the geometry, the ligand field splitting and the lifetime of the triplet metal-to-ligand charge transfer (MLCT) excited state has been explored for a series of ruthenium polypyridyl dyes. Moreover, the relative energetics of MLCT and metal centered triplet excited states have been studied for a number of such systems. It was found that small alterations of the polypyridyl ligands can result in significant changes in ligand field splitting and in the energetics of the triplet states.Attachment of the dyes to the TiO2 surface is achieved via anchor and spacer groups. The influence of such groups on various properties of the dye and their ability to act as mediators of photo-induced surface electron transfer has been studied. Delocalization of the lowest unoccupied dye orbital onto the spacer and/or anchor group indicates that certain unsaturated groups can mediate electron transfer.With a combination of methods that enables efficient computations and a scheme for construction of metal oxide clusters, chemical models for bare TiO2 nanocrystals in the 1-2 nm size range have been developed. The electronic structures show well-developed band structures with essentially no electronic band gap defect states.Atomistic models of the interface between TiO2 nanocrystals and Ru(II)-bis-terpyridine dyes, the so-called N3 dye as well as perylene dyes are reported. Electronic coupling strengths, which provide estimates for the electron injection times, are extracted from the interfacial electronic structure and the lowest electronic excitations are calculated.
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3.
  • Norén, Katarina, 1978- (författare)
  • Coordination Chemistry of Monocarboxylate and Aminocarboxylate Complexes at the Water/Goethite Interface
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis is a summary of five papers with focus on adsorption processes of various monocarboxylates and aminocarboxylates at the water/goethite interface. Interaction of organic acids at the water/mineral interfaces are of importance in biogeochemical processes, since such processes have potential to alter mobility and bioavailability of the acids and metal ions.In order to determine the coordination chemistry of acetate, benzoate, cyclohexanecarboxylate, sarcosine, MIDA (methyliminediacetic acid), EDDA (ethylenediamine-N,N’-diacetic acid) and EDTA (ethylenediamine-N,N’-tetraacetic acid) upon adsorption to the goethite (alpha-FeOOH) surface, a combination of quantitative measurements with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was utilized.Over the pH range studied here (pH 3- 9) all ligands, except for sarcosine, have been found to form surface complexes with goethite. In general, theses were characterized as outer sphere surface complexes i.e. with no direct interaction with surface Fe(III) metal ions. Furthermore, two types of different outer-sphere complexes were identified, the solvent-surface hydration-separated ion pair, and hydration-shared ion pair. For the monocarboxylate surface complexes distinction between these two could be made. At high pH values the solvent-surface hydration-separated ion pair was the predominating complex, while at low pH the surface complex is stabilized through the formation of strong hydrogen bonds with the goethite surface. However, it was not possible to clearly separate between the two outer-sphere complexes for coordination of the aminocarboxylates with the surface of goethite. Additionally, EDDA also formed an inner-sphere surface complex at high pH values. The EDDA molecule was suggested to coordinate to the surface by forming a five membered ring with an iron at the goethite surface, through the amine and carboxylate groups.Contrary to the other ligands studied, EDTA significantly induced dissolution of goethite. Some of the dissolved iron, in the form of the highly stable FeEDTA- solution complex, was indicated to re-adsorb to the mineral surface as a ternary complex. Similar ternary surface complexes were also found in the Ga(III)EDTA/goethite system, and quantitative and spectroscopic studies on adsorption of Ga(III) in presence and absence of EDTA showed that EDTA considerably effects speciation of gallium at goethite surface.The collective results in this thesis show that the affinity of these ligands for the surface of goethite is primarily governed by their chemical composition and structure, and especially important are the types, numbers and relative position of functional groups within the molecular structure.
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4.
  • Persson, Anders J, 1959- (författare)
  • Workplace Ethics : Some practical and foundational problems
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The aim of the present thesis is twofold: first, to analyse some practical ethical problems that stem from the workplace and the working environment and to offer guidelines concerning how such problems can be solved; second, to illuminate how the specific nature of work and the working environment is intimately connected to the relation between the employee and the employing entity, as set forth in an employment contract, and how the form and content of such contracts are, among other things, determined by culturally and socially established ideas. The normative question to be addressed is thus: which of these ideas should be maintained? This can be seen as a second-order, or more fundamental, ethical question whose answer depends on determining which normative principles are right. An additional aim of this thesis is thus to illuminate that the contract relation has relevance to practical ethical problems in the workplace context in this second-order mode. The thesis consists of an Introduction and five papers. In Paper I (written together with Sven Ove Hansson) we argue that employees have a prima facie right to privacy, but that this right can be overridden by competing moral principles that follow, explicitly or implicitly, from the contract of employment. A set of ethical criteria is developed and summarized in the form of a guideline for determining the moral status of infringements into workplace privacy. In Paper II these criteria are applied to three broad classes of privacy-intrusive workplace practices: (1) monitoring and surveillance, (2) genetic testing, and (3) drug testing. In relation to some scenarios on these themes, it is shown that it is possible to handle such practical ethical problems systematically by way of the proposed guideline. Paper III deals with the fact that employees are protected by health and safety standards that are less protective than those that apply to the general public. Emphasis is put on the distinction between exposure and risk, and this distinction is claimed to be a key determinant for the relevance of arguments put forward in support of such double standards. In Paper IV the nature of the contract of employment is explored from an ethical point of view. An argument is developed against the claim that (a) the individual’s freedom of decision and (b) the practice of institutional arrangements are sufficient to justify a contract of employment. Paper V questions the standpoint that the voluntariness of the contracting parties in an employment relationship has substantial value. One overarching issue concerns the meaning of voluntariness in the employment context, another, its normative importance. It is argued that it is indeterminate exactly where the line should be drawn between voluntary and non–voluntary agreements in this context. Concerning the latter issue, it is claimed that even if we were able to draw such a line, this fact does not tell us anything about the normative importance of the voluntariness condition, nor how much normative weight we should assign to the fulfilment of its conditions in the workplace context.
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5.
  • Persson, Jenny J (författare)
  • Streptococcal M protein and human C4BP
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Antigenic variation of surface proteins allows microorganisms to evade the immune system of the infected host. This phenomenon represents an apparent paradox, because the variable protein must retain an important function, while its antigenic properties vary extensively. The surface associated M protein of Streptococcus pyogenes, a common human pathogen, exhibits antigenic variation due to an N-terminal hypervariable region (HVR). The HVRs of many M proteins bind the human complement regulator C4b-binding protein (C4BP), which down-regulates deposition of complement on the bacterial surface and thereby protects the bacteria against complement-mediated phagocytosis. Different immunological, biochemical and structural aspects of this biologically important interaction is the focus of the four papers included in this thesis. C4BP-binding HVRs exhibit remarkable sequence divergence, yet bind the same ligand. In the first study, we found that such HVRs can be studied in isolated form, as synthetic peptides, thus allowing us to directly characterize the HVRs and their interaction with C4BP. Our data indicate that the peptides bind to the same region in C4BP and assume similar folds, although they are antigenically unrelated. In the second study, we show that such a synthetic peptide can be used to purify human C4BP by a simple one-step affinity-chromatography method. The third study was focused on the sequence divergence among C4BP-binding HVRs. Remarkably, analysis of seven HVRs demonstrated that they completely lack residue identities. However, use of site-specific mutagenesis to substitute relatively conserved residues in the M22 protein indicated that the predicted coiled-coil structure of the HVR is crucial for ability to bind C4BP. Interestingly, change of single residues that do not affect C4BP-binding induced major immunological changes. Together, the data in paper III indicate that HVRs of C4BP-binding M proteins have an extraordinary capacity for sequence change and antigenic variability, while retaining a specific ligand-binding function. In paper IV, we studied the three-dimensional structure of C4BP-binding HVRs, using peptides derived from the M4 and M22 proteins. No structure could be obtained, but the data clearly indicate that the central parts of the HVRs are folded as coiled-coils, both in solution and in complex with C4BP, while the termini are flexible. Remarkably, the peptides derived from M4 and M22 appear to adopt similar structures, in spite of a limited number of residue identities.
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6.
  • Persson, Mikael J, 1980 (författare)
  • Does education cause participation in politics?
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In most studies of political behavior in Western countries, it is found that individuals with higher education participate to a greater extent in political activities than individuals with lower levels of education. According to the conventional view, education increases skills and knowledge but also affects political interest and political efficacy; factors that all in turn trigger political participation. This dissertation tests two alternative explanations to the conventional view. The first alternative – the relative education model – claims that the social status gained by education drives participation and not the educational experience. According to the second alternative explanation – the pre-adult socialization model – the relationship is largely due to self-selection effects. It suggests that pre-adult factors heavily affect both educational choice as well as political participation in adulthood. The first three papers evaluate the relative education model while the last two papers deal with the pre-adult socialization model. The first paper deals with the research question: Is the relative education model supported in the Swedish context? The second paper deals directly with the causal mechanism: Does social network position mediate the effect of education on political participation? The third article brings the discussion on the relative education model further by providing the first country comparative test of the relative education model, using data from 37 countries. Hence, it deals with the research question: Is the effect of education on political participation absolute or relative in a comparative perspective? The three first articles present evidence in favor of the relative education model. The fourth paper employs matching techniques on data from the UK to mimic an experimental test of the causal effect of higher education. It deals with the question: Is college education a cause or a proxy for political participation? This paper contributes to the discussion by using a more extensive set of pre-adult covariates than previous studies, including important information on childhood cognitive ability. The fifth paper moves from length of education to testing the impact of type of education. It presents a panel study that follows Swedish adolescents over time during the first year in the gymnasium (upper secondary level) in order to answer the question: Does type of education affect political participation? The findings of both paper four and five point in favor of the pre-adult socialization model; education seems to be a proxy rather than a cause for political participation. Taken together, the five papers provide weak evidence that the educational experience directly causes participation. Thus, the dissertation challenges the conventional view on how education is related to participation.
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7.
  • Persson, Urban, 1961- (författare)
  • District heating in future Europe : Modelling expansion potentials and mapping heat synergy regions
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis presents a set of methodologies and approaches to investigate and determine the extent by which district heating can contribute to improved energy system efficiency and reduced carbon dioxide emissions in future Europe. The main motivation for suggesting large-scale implementation of district heating as a structural energy efficiency measure to obtain these objectives originates essentially in the predicament that a majority of European buildings today remain highly dependent on fossil fuels to provide energy needed for space heating and hot water preparation. In parallel, vast annual volumes of rejected excess heat from European power plants and industries are mainly neglected and lost unutilised to the ambient surroundings, why extended recovery and utilisation of such secondary energy assets realistically could replace significant shares of current inefficient supplies by fuel substitution. A prerequisite, however, for the viability of this logical prospect, is that infrastructures by which to facilitate excess heat recovery and subsequent network heat distribution are in place, which by no means is the average case in contemporary Europe.Hereby, the investigation is structured orderly by first establishing whether district heating can be a competitive alternative on current urban European heat markets, facilitated by a distribution capital cost model, where after the energy systemic benefits of expanding district heating are characterised and used to estimate a plausible expansion potential based on comparative analysis. Next, energy system modelling of continental EU27 by the year 2050, with district heating expanded in alignment with this potential, is performed to assess the total energy system cost benefits relative an alternative scenario focusing mainly on individual energy efficiency measures. Finally, spatial mapping to identify current primary target regions from which large-scale implementation of district heating could emanate is conceived and performed by use of a geographical information systems interface.The findings are generally supportive of a realisation of the objectives, mainly so by establishing a three-fold directly feasible expansion potential for district heating in city areas, but recognise also several additional, mainly non-technical, issues and challenges necessary to address in a successful transition to more energy efficient supply structures in future Europe.
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