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Sökning: LAR1:gu > Doktorsavhandling

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61.
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63.
  • Ahlberg, Daniel, 1982 (författare)
  • Asymptotics and dynamics in first-passage and continuum percolation
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis combines the study of asymptotic properties of percolation processes with various dynamical concepts. First-passage percolation is a model for the spatial propagation of a fluid on a discrete structure; the Shape Theorem describes its almost sure convergence towards an asymptotic shape, when considered on the square (or cubic) lattice. Asking how percolation structures are affected by simple dynamics or small perturbations presents a dynamical aspect. Such questions were previously studied for discrete processes; here, sensitivity to noise is studied in continuum percolation. Paper I studies first-passage percolation on certain 1-dimensional graphs. It is found that when identifying a suitable renewal sequence, its asymptotic behaviour is much better understood compared to higher dimensional cases. Several analogues of classical 1-dimensional limit theorems are derived. Paper II is dedicated to the Shape Theorem itself. It is shown that the convergence, apart from holding almost surely and in L^1, also holds completely. In addition, inspired by dynamical percolation and dynamical versions of classical limit theorems, the almost sure convergence is proved to be dynamically stable. Finally, a third generalization of the Shape Theorem shows that the above conclusions also hold for first-passage percolation on certain cone-like subgraphs of the lattice. Paper III proves that percolation crossings in the Poisson Boolean model, also known as the Gilbert disc model, are noise sensitive. The approach taken generalizes a method introduced by Benjamini, Kalai and Schramm. A key ingredient in the argument is an extremal result on arbitrary hypergraphs, which is used to show that almost no information about the critical process is obtained when conditioning on a denser Poisson process.
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65.
  • Ahlberg, Göran, 1958 (författare)
  • Ageing of Swedage Sludge
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)
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66.
  • Ahlberg Gagnér, Viktor (författare)
  • Electromagnetic Field Induced Out-of-Equilibrium Structural Dynamics in Protein Crystals: From Picoseconds to Milliseconds
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Light-induced interactions in biomolecules are strongly varying over different model systems. Most amino acids and proteins absorb ultraviolet light, but only a few with specialised chromophores or fluorophores, are able to absorb light in the visible spectrum. In the terahertz frequency spectrum, spectroscopy have revealed protein-light interactions which are attributed to low-frequency protein vibrations. Despite the fact that questions regarding a protein’s structure and function are integrally connected, only a small fraction have been answered. With the develop ment of ultra-fast facilities, the possibility to answer these questions at picosecond and sub-picosecond time scales are possible. The aim of this thesis is to demonstrate results from different aspects of the structural dynamics research field. This thesis show induced structural dynamics in the model protein bovine trypsin, while irradiated by a terahertz electromagnetic field at millisecond and at femtosecond timescales, during two different X-ray crystallography experiments. At millisecond timescales, differences in averages over the model parameters B-factors and anisotropy (’ANISO’) reveal structural dynamics which are not attributed to thermal vibrations. A clustering of the individual components of the anisotropic displacement parameter tensor, group atoms which have seemingly no spatial correlation. This indicates long range vibrations, oscillating over the entire protein scaffold. At femtosecond timescales, averages of distances of individual atom positions and individual B-factors, show structural differences which are distributed over the entire protein model, but localised to specific residues, or nearest neighbours. In addition, the structural dynamics in photosyntetic reaction center protein were demonstrated in a femtosecond optical pump-X-ray probe experiment. Average distance ratios of individual Cα atoms from photo-activated and ”dark” datasets were compared. The distances reveal a structural difference upon excitation with infrared light, attributed to an electron charge transfer from the special pair of chlorophyll molecules, to the menaquinone, via the cofactors of the L-subunit. The structural differences are supported by electron difference maps, time-resolved infrared spectroscopy and molecular modelling. Finally, this thesis demonstrate X-ray data, collected at a commissioning beamtime at the FemtoMAX beamline, of the short-pulse facility at MAX IV. Despite technical and practical difficulties, high resolution X-ray diffraction data were collected with good data reduction and refinement statistics. From this data, a satisfactory protein model was obtained
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67.
  • Ahlberg Helgee, Ernst, 1981 (författare)
  • Improving Drug Discovery Decision Making using Machine Learning and Graph Theory in QSAR Modeling
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • During the last decade non-linear machine-learning methods have gained popularity among QSAR modelers. The machine-learning algorithms generate highly accurate models at a cost of increased model complexity where simple interpretations, valid in the entire model domain, are rare. This thesis focuses on maximizing the amount of extracted knowledge from predictive QSAR models and data. This has been achieved by the development of a descriptor importance measure, a method for automated local optimization of compounds and a method for automated extraction of substructural alerts. Furthermore different QSAR modeling strategies have been evaluated with respect to predictivity, risks and information content. To test hypotheses and theories large scale simulations of known relations between activities and descriptors have been conducted. With the simulations it has been possible to study properties of methods,risks, implementations and errors in a controlled manner since the correct answer has been known. Simulation studies have been used in the development of the generally applicable descriptor importance measure and in the analysis of QSAR modeling strategies. The use of simulations is spread in many areas, but not that common in the computational chemistry community. The descriptor importance measure developed can be applied to any machine-learning method and validations using both real data and simulated data show that the descriptor importance measure is very accurate for non-linear methods. An automated method for local optimization of compounds was developed to partly replace manual searches made to optimize compounds. The local optimization of compounds make use of the information in available data and deterministically enumerates new compounds in a space spanned close to the compound of interest. This can be used as a starting point for further compound optimization and aids the chemist in finding new compounds. An other approach to guide chemists in the process of optimizing compounds is through substructural warnings. A fast method for significant substructure extraction has been developed that extracts significant substructures from data with respect to the activity of the compound. The method is at least on par with existing methods in terms of accuracy but is significantly less time consuming. Non-linear machine-learning methods have opened up new possibilities for QSAR modeling that changes the way chemical data can be handled by model algorithms. Therefore properties of Local and Global QSAR modeling strategies have been studied. The results show that Local models come with high risks and are less accurate compared to Global models. In summary this thesis shows that Global QSAR modeling strategies should be applied preferably using methods that are able to handle non-linear relationships. The developed methods can be interpreted easily and an extensive amount of information can be retrieved. For the methods to become easily available to a broader group of users packaging with an open-source chemical platform is needed.
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68.
  • Ahlberg, Karin, 1965 (författare)
  • Cancer-related fatigue. Experience and outcomes
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Cancer-related fatigue (CRF) is one of the most common and distressing symptoms in cancer patients and it may interfere with everyday aspects of life. Despite the recent significant increase in the literature on CRF it is nevertheless understudied, and several important questions involving experience, aetiology, assessment and interventions remain unanswered. The primary aim of this thesis was to advance the science of cancer-related fatigue and extend prior work by describing CRF over time and the relationship of fatigue to health-related quality of life in patients with uterine cancer who are receiving radiotherapy. Secondary aims were 1) to gain an understanding of the relationships between fatigue, other symptoms and selected physiological mechanisms associated with fatigue, and 2) to identify predictors of fatigue. The Conceptual Model of Symptom Management (Larson et al 1994; Dodd et al 2001) constituted the major theoretical framework for this dissertation. Both quantitative and qualitative methods have been used. In the qualitative study 15 respondents were included before data saturation was achieved. The data collection and data analysis took place in one simultaneous process in accordance with Grounded Theory. In the quantitative studies 60 patients with uterine cancer who were going to receive treatment with radiotherapy were included. Data was collected before start of radiotherapy, during radiotherapy and after completed radiotherapy mainly through self-rating instruments. The quantitative data was analysed with descriptive and non-parametric statistical methods.The results of the studies indicated that fatigue is an experience of the whole person. The patients had a low level of experienced fatigue before starting radiotherapy. The fatigue level increased significantly during the course of radiation therapy and after completed treatment. During the period of treatment, between 77 and 89% experienced fatigue. Other symptoms (loss of appetite, nausea/vomiting, diarrhoea, pain) also increased significantly during treatment and the increases were significantly correlated with general fatigue. The patients psychological distress (anxiety, depression) was low before start of treatment. Although the scores for depression had increased significantly after completed therapy, the levels were still within normal limits. The levels of coping resources, here defined as sense of coherence, were stable throughout the studies. The patients health-related quality of life was high before start of treatment. The scores for global quality of life and social function decreased significantly over time. There was a significant relationship between general fatigue and global quality of life over time when measured at baseline, after 3 weeks of therapy, and after completed therapy. There was also a significant correlation over time between general fatigue and physical function, role function and cognitive function. There was no significant correlation between general fatigue and IL-1, TNF-alpha or haemoglobin. There was a significant negative correlation between the change in IL-6 and general fatigue.The variation in the level of general fatigue after completed therapy was explained mainly by the level of experienced general fatigue at baseline. The knowledge obtained in this thesis should lead to better understanding of the cancer-related fatigue experience, including influencing variables, responses and outcomes, in women with uterine cancer who are receiving radiotherapy. Nursing interventions to help patients with CRF may include careful assessment, identification of patients at risk, and management of problems before the initiation of therapy.
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69.
  • Ahlberg, Kristina, 1954 (författare)
  • Synvändor : universitetsstudenters berättelser om kvalitativa förändringar av sätt att erfara situationers mening under utbildningspraktik
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The main purpose of this study has been to examine the questions: Do people experience view-turns? Can they describe them? What do the processes signify? A narrative method, with an open and dual-focussed interview question to students of medicine, nursing, occupational therapy and physiotherapy in their final term, was used to obtain accounts of university students? experiences of changing ways of experiencing during educational placement. The accounts revealed that all interviewed students except one had found it meaningful and possible to describe experienced processes of changing ways of experiencing. The accounts were analysed phenomenographically and two qualitatively different main categories were discerned, which were drawn directly from the students? descriptions: Addition of Something New, with subcategories Information and Result, and Restructuring of Awareness, with subcategories Figure/Ground, Difference/Similarity, Perspective and Whole/Part. Categorisation of the accounts was verified in a three-stage interjudge reliability test with three independent assessors. Significant difference between placing in the two main categories was found between accounts by students of medicine and those by students of nursing, occupational therapy and physiotherapy. Medical students? accounts were categorised predominantly as addition of something new, whilst accounts from nursing, occupational therapy and physiotherapy students were categorised almost exclusively as restructuring of awareness. This difference was elucidated by theoretical and historical connection to the Natural Attitude and the Philosophical Attitude described within early phenomenology. The described view-turns were theoretically elucidated with phenomenology, pragmatic meaning formation theory and gestalt theory. The theories, which each give a partial understanding of view-turns, all fail however to explain fully the findings of this study. Contradictions amongst the single-dimensional theoretical understandings offered are suggested to be reconciled through the variation theory of learning, by the premise of co-constitution of experiencing and the experienced. An element of contradiction is seen to be integral to dynamic processes of learning. The research question?s simultaneous focussing on two ways of experiencing something appears to have been decisive in revealing dynamic processes of changing ways of experiencing as well as way of experiencing.
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