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Sökning: WFRF:(Eriksson Johan) > Doktorsavhandling

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  • Bejhed, Johan, 1973- (författare)
  • Fluidic Microsystems for Micropropulsion Applications in Space
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission.Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work.Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified.A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve.The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements.For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine.A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar.The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility.
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  • Dahlgren, Johan Petter, 1978- (författare)
  • Linking plant population dynamics to the local environment and forest succession
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Linking environmental variation to population dynamics is necessary to understand and predict how the environment influences species abundances and distributions. I used demographic, environmental and trait data of forest herbs to study effects of spatial variation in environmental factors on populations as well as environmental change in terms of effects of forest succession on field layer plants. The results show that abundances of field layer species during forest succession are correlated with their functional traits; species with high specific leaf area increased more in abundance. I also found that soil nutrients affect vegetative and flowering phenology of the forest herb Actaea spicata. The effect of nutrients shows that a wider range of environmental factors than usually assumed can influence plant phenology. Moreover, local environmental factors affected also the demography of A. spicata through effects on vital rates. An abiotic factor, soil potassium affecting individual growth rate, was more important for population growth rate than seed predation, the most conspicuous biotic interaction in this system. Density independent changes in soil potassium during forest succession, and to a lesser extent plant population size dependent seed predation, were predicted to alter population growth rate, and thereby the abundance, of A. spicata over time. Because these environmental factors had effects on population projections, they can potentially influence the occupancy pattern of this species along successional gradients. I conclude that including deterministic, as opposed to stochastic, environmental change in demographic models enables assessments of the effects of processes such as succession, altered land-use, and climate change on population dynamics. Models explicitly incorporating environmental factors are useful for studying population dynamics in a realistic context, and to guide management of threatened species in changing environments.
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4.
  • Eriksson, Johan, 1956- (författare)
  • Polybrominated diphenyl ethers and Tetrabromobisphenol A : Chemical synthesis, X-ray crystallography and Photochemical degradation
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In the 1960s’ several manmade chemicals were detected in the environment, far from their sources. The most well known, and most likely those with the largest impact on the society, were DDT and its related compounds, and PCBs. These anthropogenic compounds were characterised as persistent organic pollutants (POPs). Following these POPs, several other chemicals have found their way to the environment. Over the last two decades, brominated flame retardants (BFRs) have become a matter of concern. Among all BFRs being commercially produced, tetrabromobisphenol A (TBBPA) and polybrominated diphenyl ethers (PBDEs) are the ones with the largest annual production. TBBPA is a very well defined compound while PBDEs consist of a large number of isomers and homologues (congeners). TBBPA does not seem to accumulate in biota as the PBDEs do, but is still of concern since it is found in e.g. sediments. The PBDEs can reach accumulation levels up in the ppm range. Still there is a lack of basic data for both TBBPA and PBDEs. Hence the present thesis is aimed to fill some of the data gaps by pursuing work on 1) photochemical degradation of TBBPA, some related compounds, and PBDEs; 2) synthesis of PBDE congeners and of TBBPA degradation products and 3) structural identifications of a selected set of BFRs by X-ray crystallography.An apparatus was designed for carrying out photochemical degradation test of chemicals in general but in particular for BFRs. Quantum yield, rate of degradation and to some extent, identification of degradation products were performed on TBBPA, the corresponding chlorinated compound and a number of TBBPA degradation products and on 15 single PBDE congeners. In order to make this work possible all three nonaBDE isomers were synthesised via a reductive pathway applying sodium borohydride as a reducing agent. The three nona-BDEs were all characterised by X-ray crystallography. The results of the photochemical degradation of TBBPA in water show a rapidly degradable compound also at pH’s that are environmentally relevant. Hence it is likely that TBBPA is not transported long distances, when exposed to sunlight, without undergoing photochemical degradation. It is notable that the TBBPA is degraded through cleavage between the two phenol rings. When the method was applied to study quantum yields and rate constants for the reaction of PBDE congeners it is evident that the decabromodiphenyl ether (BDE-209) is rapidly transformed. The reaction rate differ drastically from PBDEs with four or five bromine substituents that have very long half-lives when subjected to UV-light under the same conditions as for BDE-209. Lower brominated diphenyl ethers and polybrominated dibenzofurans were identified as PBDE degradation products. The synthesis of PBDEs and of TBBPA degradation products expanded the study as did the X-ray structure identifications.
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6.
  • Sundin, Greger, 1977- (författare)
  • A Matter of Amusement : The Material Culture of Philipp Hainhofer’s Games in Early Modern Princely Collections
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Games were important to the Augsburg art agent Philipp Hainhofer (1578-1647), and this ludic category was included in most of his art cabinets, procured over period of thirty years during the first half of the seventeenth century. It offered amusement (Kurzweil) as part of an overall ambition for the cabinets to be of service and use (“nutzen vnd dienst”). Board games, dice, packs of cards and games of both chance and skill represented many of the various game types of their day, while constituting a material taxonomy of games. The encyclopaedic ambition of a Kunstkammer is apparent, and games provide an insight to courtly practices of the early modern period.This thesis investigates Hainhofer’s relationship with games through the materiality of the still extant games of his art cabinets, categorised within a taxonomy of board games, playing cards, miscellaneous games and games paraphernalia. Via a material culture studies framework, it sets their design in a late Renaissance context while also examining how contemporary game practices influenced game design and use. Further, the games, their placements within the cabinets, and other associated material traces are used to reconstruct original, now lost, games and how they would function in intended art cabinet use.It further explores the progression of Hainhofer agency towards games, types and designs over a long period of time, and devises the hypothesis that he, to a certain degree formed, rather than conformed to, the taste of his patrons and clients in terms of games. Games were evidently required by Hainhofer to be at the inventive and artistic forefront, just as important as technical, scientific, natural or colonial discoveries would be to any Kunstkammer owner.
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  • A. Manneh, Ilana, 1970- (författare)
  • Supporting Learning and Teaching of Chemistry in the Undergraduate Classroom
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • There is agreement in research about the need to find better ways of teaching chemistry to enhance students’ understanding. This thesis aims to contribute to the understanding of how we better support teaching and learning of undergraduate chemistry to make it meaningful and intelligible for students from the outset. The thesis is concerned with examining the interactions between student, specific content and teacher in the undergraduate chemistry classroom; that is, the processes making up the three relations of the didactic triangle. The data consists of observations of students and tutors during problem-solving activities in an introductory chemistry course and interviews with graduate students.Systematic analyses of the different interactions between the student, the chemistry content, and the tutor are made using the analytical tool of practical epistemology analysis. The main findings of the thesis include detailed insights into how undergraduate chemistry students deal with newly encountered content together with didactic models and concrete suggestions for improved teaching and for supporting continuity and progression in the undergraduate chemistry classroom. Specifically, I show how students deal with the chemistry content through a complex interaction of knowledge, experiences, and purposes on different levels invoked by both students and tutors as they interact with each other. Whether these interactions have a positive or negative effect on students’ learning depends on the nature of knowledge, experiences and purposes that were invoked. Moreover, the tutor sometimes invoked other purposes than the ones related to the task at hand for connecting the activity to the subject matter in general. These purposes were not always made continuous with the activity which resulting in confusion among students. The results from these analyses were used for producing hypotheses and models that could support continuity and progression during the activity. The suggested models aim to make the content more manageable and meaningful to students, enabling connections to other experiences and purposes, and helping teachers and tutors to analyze and reflect on their teaching. Moreover, a purpose- and activity-based progression is suggested that gives attention to purposes in chemistry education other than providing explanations of chemical phenomena. The aim of this ‘progression in action’ is to engage students in activities were they can see the meaning of chemical concepts and ideas through their use to accomplish different chemical tasks. A general conclusion is that detailed knowledge about the processes of teaching and learning is important for providing adequate support to both undergraduate students and university teachers in the chemistry classroom.
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9.
  • Arnell, Matilda, 1987- (författare)
  • Distribution patterns of fleshy-fruited woody plants at local and regional scales
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Fleshy-fruited woody plants share a long history with humans, providing us with food and wood material. Because of this relation, we have actively moved some of these plants across landscapes and continents. In Sweden, these species are often found in open and semi-open habitats such as forest edges, their fruits are most often dispersed by birds and their flowers are, with some exceptions, pollinated by insects.  In this thesis my overall aim was to map and analyse distribution patterns of fleshy-fruited woody plants in Sweden to expand our knowledge on the mechanisms governing their distributions. First, I mapped a population of the early flowering, fleshy-fruited shrub Daphne mezereum (common mezeron, tibast) and surveyed the reproduction and fruit removal of all individuals (chapter I). My main aim was to investigate to what extent reproduction and fruit removal was affected by local distribution patterns. Secondly, I mapped local distribution patterns of fleshy-fruited woody species and analysed spatial associations between life stages and species (chapter II). My main aim was to relate these spatial associations to predictions of how bird dispersal would shape the local distribution patterns and the hypothesis that birds create ‘wild orchards’. Thirdly, I digitized historical maps and surveyed fleshy-fruited woody species along transects across landscapes (chapter III). My aim was to examine the hypothesis that these species accumulate in open and semi open habitats created by human land use. Fourthly, I estimated range filling of woody plants in Sweden at a 1 km2 resolution (chapter IV). My aim was to compare these estimates among species with different dispersal systems to understand the effect of dispersal on the occupancy of woody species at regional scales.I found the distribution patterns of these species to be affected by past and present land use, supporting the hypothesis that these plants accumulate in open habitats. Occurrences of species in this guild in todays’ forest are positively related to past human land use (chapter III) and the density of D. mezereum increases with decreasing distances to forest edges (chapter I). This accumulation may in part be explained by the positive effect of forest edges on reproduction and fruit removal (chapter I). I further found local distribution patterns of this guild and the individual species to be aggregated (chapter I and II), and spatial associations between saplings and reproductive individuals to support the ‘orchard’ hypothesis (chapter II). The aggregated pattern of fruit-bearing individuals was positively related to fruit removal whereas aggregated flowering individuals was negatively related to fruit set (chapter I). On the regional scale, I found these species to occupy climatically suitable areas, or fill their potential ranges, to a less extent that wind dispersed trees and shrubs (chapter IV), which may indicate dispersal limitation.In conclusion, the behaviour of birds and humans have shaped, and still shape the current distribution of fleshy-fruited trees and shrubs in Sweden, resulting in accumulation in open habitats and locally aggregated distribution patterns. Changing land-use practices and potential mismatches between fruit maturation and bird dispersal with a changing climate may thus result in even lower chances of these species to fill their potential ranges, due to habitat losses and dispersal limitations at local and regional scales.  
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10.
  • Awad, Amar, 1988- (författare)
  • Functional brain imaging of sensorimotor dysfunction and restoration : investigations of discomplete spinal cord injury and deep brain stimulation for essential tremor
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The nervous system exists to generate adaptive behaviour by processing sensory input from the body and the environment in order to produce appropriate motor output, and vice versa. Consequently, sensorimotor dysfunction is the basis of disability in most neurological pathologies. In the current thesis, I explore two conditions with different types and degrees of sensorimotor dysfunction by means of functional magnetic resonance imaging (fMRI). In part 1, I assess residual sensory connections to the brain in clinically complete spinal cord injury (SCI) with seemingly complete loss of sensorimotor function below the injury level. In part 2, fMRI is combined with deep brain stimulation (DBS) to investigate interventional mechanisms of restoring dysfunctional sensorimotor control in essential tremor (ET).Part 1: SCI disrupts the communication between the brain and below-injury body parts, but rarely results in complete anatomical transection of the spinal cord. In studies I and II, we demonstrate somatosensory cortex activation due to somatosensory (tactile and nociceptive) stimulation on below-level insensate body parts in clinically complete SCI. The results from studies I and II indicate preserved somatosensory conduction across the spinal lesion in some cases of clinically complete SCI, as classified according to international standards. This subgroup is referred to as sensory discomplete SCI, which represents a distinct injury phenotype with an intermediate degree of injury severity between clinically complete and incomplete SCI.Part 2: ET is effectively treated with DBS in the caudal zona incerta, but the neural mechanisms underlying the treatment effect are poorly understood. By exploring DBS mechanisms with fMRI, DBS was shown to cause modulation in the activity of the sensorimotor cerebello-cerebral regions during motor tasks (study III), but did not modulate the functional connectivity during resting-state (study IV).fMRI is a valuable tool to investigate sensorimotor dysfunction and restoration in SCI and DBS-treated ET. There is evidence for sensory discomplete SCI in about half of the patients with clinically complete SCI. DBS modulates DBS modulation of the activity in the sensorimotor cerebello-cerebral circuit during motor tasks, but not during resting-state, is action-dependent.
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