| 1. |
- Nilforoush, Rasoul
(författare)
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Anchorage in Concrete Structures : Numerical and Experimental Evaluations of Load-Carrying Capacity of Cast-in-Place Headed Anchors and Post-Installed Adhesive Anchors
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Various anchorage systems including both cast-in-place and post-installed anchors have been developed for fastening both non-structural and structural components to concrete structures. The need for increased flexibility in the design of new structures and strengthening of existing concrete structures has led to increased use of various metallic anchors in practice. Although millions of fasteners are used each year in the construction industry around the world, knowledge of the fastening technology remains poor. In a sustainable society, buildings and structures must, from time to time, be adjusted to meet new demands. Loads on structures must, in general, be increased to comply with new demands, and the structural components and the structural connections must also be upgraded. From the structural connection point of view, the adequacy of the current fastenings for the intended increased load must be determined, and inadequate fastenings must either be replaced or upgraded. The current design models are generally believed to be conservative, although the extent of this behavior is not very clear. To address these issues, the current models must be refined to allow the design of new fastenings and also the assessment of current anchorage systems in practice.The research presented in this thesis consists of numerical and experimental studies of the load-carrying capacity of anchors in concrete structures. Two different types of anchors were studied: (I) cast-in-place headed anchors, and (II) post-installed adhesive anchors. This research focused particularly on the tensile load-carrying capacity of cast-in-place headed anchors and also on the sustained tension loading performance of post-installed adhesive anchors. The overall objective of this research was to provide knowledge for the development of improved methods of designing new fastening systems and assessing the current anchorage systems in practice.For the cast-in-place headed anchors (I), the influence of various parameters including the size of anchor head, thickness of concrete member, amount of orthogonal surface reinforcement, presence of concrete cracks, concrete compressive strength, and addition of steel fibers to concrete were studied. Among these parameters, the influence of the anchor head size, member thickness, surface reinforcement, and cracked concrete was initially evaluated via numerical analysis of headed anchors at various embedment depths. Although these parameters have considerable influence on the anchorage capacity and performance, this influence is not explicitly considered by the current design models. The numerical results showed that the tensile breakout capacity of headed anchors increases with increasing member thickness and/or increasing size of the anchor head or the use of orthogonal surface reinforcement. However, their capacity decreased considerably in cracked concrete. Based on the numerical results, the current theoretical model for the tensile breakout capacity of headed anchors was extended by incorporating several modification factors that take the influence of the investigated parameters into account. In addition, a supplementary experimental study was performed to verify the numerically obtained findings and the proposed refined model. The experimental results corresponded closely to the numerical results, both in terms of failure load and failure pattern, thereby confirming the validity of the proposed model. The validity of the model was further confirmed through experimental results reported in the literature.Additional experiments were performed to determine the influence of the concrete compressive strength and the addition of steel fiber to concrete on the anchorage capacity and performance. These experiments showed that the anchorage capacity and stiffness increase considerably with increasing concrete compressive strength, but the ductility of the anchor decreases. However, the anchorage capacity and ductility increased significantly with the addition of steel fibers to the concrete mixture. The test results also revealed that the tensile breakout capacity of headed anchors in steel fiber-reinforced concrete is significantly underestimated by the current design model.The long-term performance and creep behavior of the post-installed headed anchors (II) was evaluated from the results of long-time tests on adhesive anchors under sustained loads. In this experimental study, adhesive anchors of various sizes were subjected to various sustained load levels for up to 28 years. The anchors were also exposed to several in-service conditions including indoor temperature, variations in the outdoor temperature and humidity, wetness (i.e., water on the surface of concrete), and the presence of salt (setting accelerant) additives in the concrete. Among the tested in-service conditions, variations in the outdoor temperature and humidity had the most adverse effect on the long-term sustained loading performance of the anchors. Based on the test results, recommendations were proposed for maximum sustained load levels under various conditions. The anchors tested under indoor conditions could carry sustained loads of up to 47% of their mean ultimate short-term capacities. However, compared with these anchors, the anchors tested under outdoor conditions exhibited larger creep deformation and failure occurred at sustained loads higher than 23% of their mean ultimate short-term capacities. Salt additives in concrete and wet conditions had negligible influence on the long-term performance of the anchors, although the wet condition resulted in progressive corrosion of the steel. Based on the experimental results, the suitability of the current testing and approval provisions for qualifying adhesive anchors subjected to long-term sustained tensile loads was evaluated. The evaluations revealed that the current approval provisions are not necessarily reliable for qualifying adhesive anchors for long-term sustained loading applications. Recommendations were given for modifying the current provisions to ensure safe long-term performance of adhesive anchors under sustained loads.
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| 2. |
- Kentson, Magnus
(författare)
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Fatigue and Peripheral Muscle Dysfunction: Studies on Vitamin D Status, Muscle Metabolism and Systemic Inflammation in Patients with COPD : Aspects of COPD severity beyond FEV1 and exacerbations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundThe severity of Chronic Obstructive Pulmonary Disease (COPD) is usually described in terms of forced expiratory volume in one second (FEV1) and number of exacerbations. However, COPD is a complex disease with different ways of expression, involving pulmonary symptoms, extra pulmonal manifestations and comorbidities, which altogether affect the patient by contributing to reduced functional capacity, increased shortness of breath, reduced health-related quality of life and increased mortality. Systemic inflammation is common in COPD and can potentially constitute a link between the lungs and other organs. The aim of this thesis was to broaden the aspects of COPD severity beyond FEV1 and exacerbations by studying fatigue, the role of vitamin D, nutritional factors, systemic inflammation and peripheral muscle function in patients with COPD. Methods and ResultsIn paper I, we included 101 patients with COPD, and 34 control subjects. Assessment of experience of fatigue, functional limitation due to fatigue, and the relationships to physiological, psychological and situational variables and quality of life (QoL) were evaluated. We found that experience of fatigue was highly prevalent (72% versus 56% in control subjects) and a troublesome symptom in COPD. Patients with COPD and fatigue had lower lung function, shorter walking distance, more dyspnoea, anxiety and depressive symptoms and poorer health status compared to patients without fatigue (all p < 0.01). Several contributing factors were identified to experience of fatigue and functional limitations of fatigue with dyspnoea, depressive symptoms and insomnia as the most prominent factors. No clear association with systemic inflammation was found. Paper II evaluated vitamin D status in 66 patients with advanced COPD (28 with long-term oxygen therapy (LTOT)) and 47 control subjects. 25-hydroxyvitamin 25(OH)D were deter-mined in early fall in a short period of seven weeks. Questionnaires about COPD symptoms, general health, lifestyle, dietary habits and QoL were answered. Lung function tests and blood sampling including systemic inflammatory markers, carotenoids and protein carbonylation (PC) were assessed. The peak annual 25(OH)D of COPD patients was significantly lower than in the control subjects, but there was no significant difference between COPD patients with and without LTOT. Among vitamin D-deficient COPD patients, 25(OH)D correlated positively with lung function, blood oxygenation, food portion size, Mediterranean Diet Score and Ultra-violet Score and negatively with dyspnoea and DOSE-index, a composite index for COPD se-verity. Ongoing vitamin D supplementation was the single most important intervention to maintain 25(OH)D levels <50 nmol/L. In paper III, we evaluated in the same cohort as paper II oxidative damage and levels of carotenoids. Patients with COPD (±LTOT) did not demonstrate increased oxidative damage. Com-pared with the control group, levels of several carotenoids were significantly lower in COPD, and the diet contained significantly less fruit and vegetables. Lycopene correlated positively with saturation and lutein correlated positively with some inflammatory markers but negatively with IL-6, an important marker for systemic inflammation. The study highlights the importance of dietary factors in COPD. In paper IV, 32 patients with COPD answered questionnaires, and were subjected to lung function tests and blood analysis including systemic inflammatory markers. Magnetic resonance imaging (MRI) for analysis of whole-body and thigh muscle composition was performed. Bioenergetics in the resting thigh muscle, (PCr/Pi ratio), were analysed using 31phosphorus magnetic resonance spectroscopy (31P-MRS). We found that adverse muscle composition was common in the COPD group. Clinical characteristics reflecting COPD severity were all associated with a raise of the PCr/Pi ratio in the thigh muscle. Increased MFIa correlated positively to systemic inflammatory markers, negative to physical activity and PCr/Pi ratio. We compared the COPD group with a virtual control group from UK Biobank (n= 3200). ConclusionsSevere COPD is much more than airway obstruction and exacerbations. The presence of fatigue is associated, as well as vitamin D status and nutritional factors, with important clinical out-comes reflecting COPD severity. Adverse muscle composition is common in COPD and there seems to be a link between systemic inflammation, muscle fat infiltration and bioenergetics.
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| 3. |
- Engström, Gunnar, et al.
(författare)
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Pulmonary function and atherosclerosis in the general population : causal associations and clinical implications
- 2024
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Ingår i: European Journal of Epidemiology. - : Springer Nature. - 0393-2990 .- 1573-7284. ; 39:1, s. 35-49
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Tidskriftsartikel (refereegranskat)abstract
- Reduced lung function is associated with cardiovascular mortality, but the relationships with atherosclerosis are unclear. The population-based Swedish CArdioPulmonary BioImage study measured lung function, emphysema, coronary CT angiography, coronary calcium, carotid plaques and ankle-brachial index in 29,593 men and women aged 50–64 years. The results were confirmed using 2-sample Mendelian randomization. Lower lung function and emphysema were associated with more atherosclerosis, but these relationships were attenuated after adjustment for cardiovascular risk factors. Lung function was not associated with coronary atherosclerosis in 14,524 never-smokers. No potentially causal effect of lung function on atherosclerosis, or vice versa, was found in the 2-sample Mendelian randomization analysis. Here we show that reduced lung function and atherosclerosis are correlated in the population, but probably not causally related. Assessing lung function in addition to conventional cardiovascular risk factors to gauge risk of subclinical atherosclerosis is probably not meaningful, but low lung function found by chance should alert for atherosclerosis.
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| 4. |
- Reichstein, Birte, 1983-
(författare)
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Ontogenetic bottlenecks : effects on intraguild predation systems and ecosystem efficiency
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Size-dependent differences between individuals in size-structured organisms have fundamental effect on population and community dynamics. Intraguild predation (IGP) is one specifically interesting constellation that often arises when two size-structured populations interact. Ontogenetic bottlenecks that determine population size-structure are affected by both population intrinsic as well as population extrinsic factors, and are therefore context-dependent. Surprisingly, size-structured IGP systems have mainly been investigated theoretically and especially long-term empirical studies are widely lacking. In this thesis I investigate empirically how habitat complexity, interaction strength, and stage-specific resource availabilities affect population processes and their effects on the dynamics of a size-structured IGP system. I conducted multi-generation experiments in a size-structured IGP system, with the Least Killifish (Heterandria formosa) as IG prey and the Common Guppy (Poecilia reticulata) as IG predator. With no alternative resource next to the shared resource, IG predator and IG prey could not coexist. Weak interactions only increased IG prey and IG predator persistence times and observed exclusion patterns depended on habitat complexity. An alternative resource for either the juvenile IG predator or the juvenile IG prey on the other hand promoted coexistence. However, this coexistence was context-dependent. Ontogenetic bottlenecks played a central role in the dynamics of the size-structured IGP system in general. In the final study I show that an ontogenetic bottleneck can, through changes in stage-specific resource availabilities, be affected in a way that leads to increased trophic transfer efficiency with potential effects on higher trophic levels.Overall, the results emphasize importance of the broader context in which size-structured communities are embedded. Especially, when managing natural communities it is important to account for the combined effects of size-structure, stage-specific resource availabilities, and habitat structure. Specifically, when managing species that connect habitats or ecosystems all life-stages’ environmental conditions must be consider in order to ensure strong predictive power of tools used for ecosystem management planning.
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| 5. |
- Uszko, Wojciech, 1985-
(författare)
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Effects of warming and nutrient enrichment on feeding behavior, population stability and persistence of consumers and their resources
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Consumer-resource interactions are the basic building blocks of every food web. In spite of being a central research theme of longstanding interest in ecology, the mechanisms governing the stability and persistence of consumer-resource interactions are still not entirely understood. In particular, theoretical predictions on consumer-resource stability along gradients of temperature and nutrient enrichment diverge widely and are sometimes in conflict with empirical results. In this thesis I address these issues from the angle of the functional response, which describes a consumer’s feeding rate as a function of resource density. Specifically, I explore mechanistic, nutrient-based consumer-resource interaction models with respect to the influence of feeding behavior (the shape of the functional response), environmental temperature, nutrient enrichment, and resource quality on consumer-resource stability and persistence. In order to parameterize these models I performed extensive laboratory experiments with pairs of freshwater pelagic algae and grazers of the genus Daphnia, which are widespread, ecologically important model organisms.I found a sigmoidal type III functional response in every studied Daphnia-algae species pair. The exact form of its shape is described by an exponent b which is determined by fitting functional response models to the experimental data. A high value of b can stabilize consumer-resource systems under the otherwise destabilizing influence of nutrient enrichment, as predicted by a novel stability criterion relating b to the consumer’s prey handling time, food conversion efficiency and mortality. Estimated parameter values and, consequently, stability predictions are sensitive to the method of parameter estimation, and I propose a new estimation procedure that minimizes parameter uncertainty. Because many consumers’ feeding rates depend on temperature, warming is expected to strongly affect food web stability. In functional response experiments over a broad temperature gradient, I found that the attack rate coefficient and the maximum ingestion rate of Daphnia are hump-shaped functions of temperature. Moreover, the functional response exponent increases with warming towards stronger type III responses. Plugging these findings into a nutrient-based consumer-resource model, I found that predator persistence is a U-shaped function of temperature in nutrient enrichment-temperature space. Enrichment easily turns the system unstable when the consumer has a type II response, whereas a type III response opens up a large region of stability at intermediate, for the consumer optimal, temperatures. These findings reconcile seemingly conflicting results of earlier studies of temperature effects on consumer-resource dynamics, which can be mapped as special cases onto the enrichment-temperature space. I finally demonstrate the utility of three key model ingredients - temperature dependence of rate parameters, a mechanistic description of the dynamics of algal resources, and a type III functional response in Daphnia - by successfully implementing them in the description and explanation of phytoplankton-Daphnia dynamics in a mesocosm experiment exploring effects of warming on the spring succession of the plankton.
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| 6. |
- Ask, Per, 1978-
(författare)
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Invasion of top and intermediate consumers in a size structured fish community
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I have investigated the effects of invading top and intermediate consumers in a size-structured fish community, using a combination of field studies, a lake invasion experiment and smaller scale pond and aquaria experiments. The lake invasion experiment was based on introductions of an intermediate consumer, ninespine stickleback (Pungitius pungitius L.), in to allopatric populations of an omnivorous top predator, Arctic char (Salvelinus alpinus L.). The invasion experiment was performed in two tundra lakes and in two birch forest lakes to investigate the effect of climate on the invasion success. I found that the effect of sticklebacks on char was size dependent. Small char suffered reduced growth from resource competition with sticklebacks whereas the maximum size of adult char increased from the addition of a larger prey resource, stickleback. The negative effect of sticklebacks on the growth of small char suggests that sticklebacks may be a better resource competitor than char, which was also supported by the pond and aquaria experiments. The pond experiments also suggested that char were more efficient cannibals than interspecific predators on sticklebacks. Cannibalism in char may limit the recruitment of char and decrease both their predatory and competitive effect on coexisting species and thereby also promote the coexistence of char and sticklebacks. The successful invasion by sticklebacks and their subsequent increases in density suggest that the absence of sticklebacks in char lakes in this region is not caused by biotic interactions with char. Instead, it may be suggested that co-occurrence of sticklebacks and char in the region is limited by dispersal. The char – stickleback system resembles an intraguild predation system with char as the top consumer and stickleback as the intermediate consumer. The effects of the stickleback invasion is also contrasted with a field study of a northern pike (Esox lucius L.) invasion into a system with coexisting char and stickleback, where pike can be viewed as the top consumer and char as the intermediate consumer both feeding on sticklebacks. In this case pike excluded char. The identity of the invading species and the relative strength of the predatory and competitive interactions in the two contrasting systems are discussed in relation to coexistence in intraguild predation systems. I found that the identity of the invading species is of crucial importance for the response at the ecosystem level, and that the inherent size dependency of competitive and predatory interactions in fish communities is important for attaining a mechanistical understanding of the effects of invasive species in lake ecosystems.
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| 7. |
- Lindh, Magnus, 1973-
(författare)
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Evolution of Plants : a mathematical perspective
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Earth harbors around 300 000 plant species. The rich and complex environment provided by plants is considered a key factor for the extraordinary diversity of the terrestrial fauna by, for example, providing food and shelter. This thesis contributes to the understanding of these questions by investigating how the interplay of physiology, demography, and evolution gives rise to variation and diversity in fundamental plant traits. This will help us answer questions such as: How has this amazing diversity of plant species emerged? Which mechanisms maintain diversity? How are plant strategies and plant diversity influenced by variations in the environment?A plant faces multiple problems to survive and reproduce successfully. These problems can be modeled by considering traits, trade-offs and a fitness measure. For example: How to maximize growth rate, while maximizing structural stability? I will investigate four plant models in order to understand the function of plants, and mechanisms promoting diversity. Paper I: We study how annual plants with and without growth constraints should optimize their flowering time when productivity or season length changes. With a dynamic ontogenetic growth model and optimal control theory we prove that a bang-bang reproductive control is optimal under constrained growth and constant mortality rate. We find that growth constraints can flip the direction of optimal phenological response for increasing productivity. The reason is that the growth rate of vegetative mass saturates at high productivity and therefore it is better to flower earlier and take advantage of a longer reproductive period. If season length extends equally both in the beginning and the end of the season, growth constraints control the direction of the optimal response as well. Our theory can help explaining phenological patterns along productivity gradients, and can be linked to empirical observations made on a calendar scale.Paper II: We introduce a new measure of tree crown-rise efficiency based on the loss of biomass of the tree during growth. The more mass the tree looses during growth, the less crown-rise efficient it is. Top-heavy shapes loose more biomass than bottom-heavy shapes. Light-use efficiency is defined as the mean light assimilation of the leaves in the crown times the ratio of leaf mass and total mass. We then study the trade-off between light-use efficiency to crown-rise efficiency for tree crown shapes. We assume that the total tree mass is constant, and a constant vertical light gradient represent the shading from a surrounding forest. We find large differences in crown shapes at intermediate vertical light gradient, when both self-shading and mean-field shading are important, suggesting light-use vs crown-rise efficiency as a new trade-off that can explain tree diversity. Our crown-rise efficiency measure could easily be integrated into existing forest models.Paper III: We extend an evolutionary tree crown model, where trees with different heights compete for light, with drought-induced mortality rates depending on ground-water availability and the depth of an optional taproot. The model does not include competition for ground water. Our model explains how ground-water availability can shape plant communities, when taproot and non-taproot strategies can coexist, and when only one of these strategies can persist. We investigate how emerging plant diversity varies with water table depth, soil water gradient and drought-induced mortality rate. The taproot enables plants to reach deep water, thus reducing mortality, but also carries a construction cost, thus inducing a trade-off. We find that taproots maintain plant diversity under increasing drought mortality, and that taproots evolve when groundwater is accessible at low depths. There are no viable strategies at high drought mortality and deep water table. Red Queen evolutionary dynamics appear at intermediate drought mortality in mixed communities with and without taproots, as the community never reaches a final evolutionarily stable composition.Paper IV: We extend a size-structured plant model, with self-shading and two evolving traits, crown top-heaviness and crown width-to-height ratio. The model allows us to identify salient trade-offs for the crown shape. The most important trade-off for top-heaviness is light-use efficiency vs crownrise efficiency, and the most important trade-off for width-to-height ratio is self-shading vs branch costs. We find that when the two traits coevolve; the outcome is a single common evolutionarily stable strategy (ESS), far away from the highest net primary production (NPP). When only sun angle is decreasing with increasing latitude both the crown width-to-height ratio and crown top-heaviness decrease. However, when light response in addition to the sun angle decreases with increasing latitude, the crown width-to-height ratio is nearly invariant of latitude except at low site productivity when the ratio decreases with latitude. Top-heaviness is always decreasing with increasing latitude. Finally, we find that crown top-heaviness increases with the NPP or leaf-area index (LAI) at ESS, but crown width-to-height ratio is maximal at an intermediate NPP or LAI.
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| 8. |
- Persson, Magnus, 1972-
(författare)
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Utbildningskontraktets villkor : Utbildningsförlopp på en förändrad gymnasielärarutbildning
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For the last decades the social position of the Swedish upper secondary schoolteacher programme has fallen dramatically in the field of higher education. The once social homogeneity among students has transformed into heterogeneity. This study investigates what educational action students take while studying, and making experiences from the programme and how this relates to their individual educational and social resources, and to the overall changes in the higher education sector. A centrepiece in the study is the relation between what students expect of the programme, on the one hand, and what the programme actually delivers on the other. This is understood as an educational contract. This contract is divided into a labour-market contract and a teaching-contract where the former regulates how teaching content connects with the future labour-market expectations held by the students, and the latter how demands from the programme connect to students’ expectations of what it is to be a university student. In this case it produces educational action that can’t be understood without knowledge about the social disposition of the individual student (elaborated as habitus in this study), as well as knowledge about the social position of the educational programme. The study draws on a longitudinal series of in-depth interviews, supplemented by survey data and historical material. Three courses of education were identified. First the completed course, second the drop-out course and finally the changed course where students finished their academic degree but used it to get a higher social position in the labour-market than a position as upper secondary schoolteachers would have given them. The different courses of education exhibit a social pattern that can be understood both in relation to the expanded availability of higher education and to the social dispositions of the students; a key in the understanding of how conditions of the educational contract are formed both socially and historically. Some major findings can be formulated from this. First: Choice of courses of education mainly reproduced already existing internal social differences among the students but were revealed in new arrangements related to the altered field of higher education. Second: Expectations and choice of courses of education can in different ways, be traced to the social genealogy of teacher education. Third: Social pattern contributed to strengthen the on-going falling social position of the upper secondary schoolteacher programme.
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| 9. |
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| 10. |
- Fröjd, Camilla, 1967-
(författare)
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Cancer Patients’ Satisfaction with Doctors’ Care : Consequences and Contributing Conditions
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main aims were to: explore whether there is a relation between doctors’ ability to identify patients’ worry and wish for information and self-efficacy with regard to communicating with patients about difficult matters; describe which cues doctors consider when estimating patients’ worry and wish for information, and investigate whether there is a relation between patients’ satisfaction with doctors’ care and patients’ psychosocial function. Eleven doctors and 69 patients (of which 36 patients participated in the longitudinal study) with carcinoid tumours participated. Doctors’ self-efficacy, and ability to identify patients’ worry/wish for information were investigated at patients’ first admission. Doctors were interviewed about which cues they considered when estimating patients worry/wish for information. Patients’ satisfaction with care (CASC SF 4.0) and psychosocial function (EORTC QLQ-C30, HADS) were measured longitudinally, during the first year after diagnosis. Doctors reported higher self-efficacy when showing good ability to identify patients’ wish for information, than when showing less good ability, overestimated patients’ worry and underestimated patients’ wish for information. Doctors considered patients’ verbal behaviour and body language together with knowledge and experience when estimating patients worry and wish for information. Patients who met doctors showing good ability to identify their wish for information, reported a higher cognitive function than patients who met doctors showing less good ability. At all assessments patients expressed high satisfaction with doctor’ care and patients’ satisfaction did not change over time. Patients’ satisfaction with doctors’ care were related to their psychosocial function shortly after the first three admissions to specialist care. Patients with carcinoid tumours in some respects reported a worse HRQoL than the general Swedish population. Fatigue, diarrhoea, limited possibilities to work/pursue daily activities, and worry that the illness will get worse were among the most prevalent, and worst, aspects of disease- and treatment related distress.
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| 11. |
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| 12. |
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| 13. |
- Persson, Jonas, 1969-
(författare)
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Bandwidth-reduced Linear Models of Non-continuous Power System Components
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Denna avhandling är fokuserad på modellering av elkraftsystemkomponenter och deras representation vid simuleringar av elkraftsystem. Avhandlingen jämför olika linjäriseringstekniker. Dessa tekniker är såväl numeriska som analytiska och används vid linjärisering av ett dynamiskt system. Efter en linjärisering är det möjligt att beräkna egenvärdena av det linjäriserade systemet samt använda andra verktyg ämnade för studier av linjära system. I avhandlingen visas hur olika linjäriseringtekniker influerar egenvärdesberäkningen av det linjära systemet. I avhandlingen tas fram bandviddsreducerade linjära modeller av en kraftsystemkomponent med hjälp av två tekniker. Senare görs simuleringar med de linjära modellerna tillsammans med ett introducerat gränssnitt. Den studerade kraftsystemkomponenten är en tyristorstyrd seriekondensator (TCSC). En fördel med att använda en linjär representation av en kraftsystemkomponent är att det förenklar simuleringarna. Storleken på komplexiteten av en simulering vid lösandet av ekvationerna minskar och den konsumerade fysiska tiden att simulera minskar. En nackdel med en linjär modell är att dess giltighet kan vara begränsad. Behovet av att bygga linjära modeller av kraftsystemkomponenter torde även finnas i framtiden. Med dagens horisont (år 2006) finns behov av att bygga linjära modeller utgående från detaljerade modeller av bl a högspända likströmslänkar (HVDC-länkar), reaktiva effektkompensatorer (SVC) samt tyristorstyrda seriekondensatorer (TCSC). Hur skall dessa representeras när vi vill studera dynamiken av ett helt kraftsystem och det då är nödvändigt att reducera deras komplexitet? Denna frågeställning uppkommer när vi vill genomföra tidsdomänsimuleringar på en inte alltför detaljerad nivå av de individuella kraftsystemkomponenterna eller när vi vill linjärisera kraftsystemet för att studera dess stabilitet med hjälp av småsignalanalys.
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| 14. |
- Persson, Lennart, 1961-
(författare)
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Prevention of oxidant-induced cell death by intralysosomal iron binding
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The lung is particularly prone to oxidative stress by its exposure to ambient oxygen and inhaled environmental oxidants. Abnormal assimilation and accumulation of iron are found in many lung disorders, which in redox-active form will exacerbate oxidative tissue damage. It may be that the most important cellular pool of redox -active iron exists within lysosomes. As a result, these organelles are very vulnerable to oxidative stress and may burst due to peroxidative membrane destabilization. Support for the importance of intralysosomal iron in cellular oxidant damage includes the observation that the iron chelator, desferrioxamine, which almost exclusively localizes within the lysosomal compartment, will protect cells against oxidati ve challenge. Iron chelators targeted to the lysosomes may therefore be a particularly efficient therapeutic strategy for cells under conditions of substantial oxidative stress.The present study, employing cultures of human respiratory epithelial cells and murine macrophage-like cells, explores the protective effects by iron binding agents upon H202 and gamma radiation-induced lysosomal damage and cell death. Using these in vitro models, the present study shows: (1) that chelation of intralysosomal iron efficiently prevents lysosomal rupture and ensuing cell death induced by either H202 or gamma radiation; (2) that cell permeable lysosomotropic iron-chelators are much more efficient than those being internalized by endocytosis; (3) that intralysosomal iron is the most important cellular pool of redox-active iron for chelation therapy; (4) that ironcatalyzed peroxidative lysosomal destabilization is a decisive and early event in the apoptotic machinery.Although apoferritin and desferrioxarnine suppress the reactivity of lysosomal iron, their efficacy is considerably restrained by their uptake by fluid-phase endocytosis. Apoferritin is digested intralysosomally which further decreases its iron sequestering potential, while desferrioxamine by its intralysosomal retention may disturbe normal cellular functions and cause iron-starvation. Amongst cell permeable iron-binding agents we tested a-lipoic acid, alipoamide, and a synthetic amine derivative of α-lipoarnide, α-lipoic acid-plus (5-[1,2] dithiolan-3-yl-pentanoic acid (2-dimethylamino-ethyl) amide). The large difference in the protective potential of these cell permeant iron-chelators derives from their being localized in different cellular compartments, which lends further support that lysososomes contain the most important pool of chelatable redox-active iron. Indeed, a-lipoic acid-plus by its lysosomotropism was by all means the most efficient iron chelator. On a molar basis α-lipoic acid-plus was 4,000 to 5,000 times more effective than desferrioxamine to prevent lysosomal rupture and cell death induced by H202 or gamma radiation.We conclude that iron chelating therapy targeted to the lysosomes is an efficient strategy to protect oxidatively stressed cells in vitro. A corresponding efficacy of such treatment in vivo, and in iron dependent pulmonary disorders in particular, needs to be explored.
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| 15. |
- Svanbäck, Richard, 1971-
(författare)
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Ecology and Evolution of Adaptive Morphological Variation in Fish Populations
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work in this thesis deals with the ecology and evolution of adaptive individual variation. Ecologists have long used niche theory to describe the ecology of a species as a whole, treating conspecific individuals as ecological equivalent. During recent years, research about individual variation in diet and morphology has gained interest in adaptive radiations and ecological speciation. Such variation among individual niche use may have important conservation implications as well as ecological and evolutionary implications. However, up to date we know very little about the extension of this phenomenon in natural populations and the mechanisms behind it.The results in this thesis show that the extension of individual diet specialization is widely spread throughout the animal kingdom. The variation in diet is mainly correlated to morphological variation but not always. Furthermore, this variation in diet and morphology among individuals could be both genetically determined and environmentally induced and it mainly comes from trade-offs in foraging efficiency between different prey types.The results from a number of studies of perch also show that individual perch differ in morphology and diet depending on habitat, where littoral perch has a deeper body compared to pelagic perch. This difference in morphology corresponds to functional expectations and is related to foraging efficiency trade-offs between foraging in the littoral and pelagic zone of a lake. The variation in morphology in perch is mainly due to phenotypic plasticity but there are also small genetic differences between the littoral and pelagic perch. Two separate studies show that both predation and competition may be important mechanism for the variation in morphology and diet in perch.In conclusion, the results in this thesis show that individual variation in diet and habitat choice is a common phenomenon with lots of ecological and evolutionary implications. However, there are many mechanisms involved in this phenomenon on which we are just about to start learning more about, and only further research in this area will give us the full insight.
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| 16. |
- Tondel, Martin, 1962-
(författare)
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Malignancies in Sweden after the Chernobyl accident in 1986
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- On 26 April 1986 an accident occurred in the Chernobyl nuclear power plant resulting in the release of large amount of radionuclides. Almost five percent of the total released caesium-137 was deposited in Sweden. The incidence of malignancies in the most affected counties in Sweden was investigated in three epidemiological studies.In the first study the incidence of malignancies in children and adolescents was studied for the period 1978-1992. The parishes and their inhabitants were classified according to the ground deposition of caesium-137 on an analogue map provided be the Swedish Radiological Protection Authority. A continuous increase of brain tumour incidence observed during the time of the study had no clear relationship to the Chernobyl fallout. A somewhat decreased relative risk of ALL was observed in areas with increased deposition. Other malignancies showed no changes in incidence over time or with regard to the exposure of caesium-137. In study II and III we enlarged the study base by including adults. We improved the methodology by defining a cohort of subjects who lived in the same parish from 31 December 1985 to 31 December 1987. The inhabitants from seven counties were included. Parishes were classified the same way as in study I. Due to the large number of individuals six exposure categories could be created; <3, 3–29, 30–39, 40–59, 60–79, and 80–120 kBq caesium-137/m2. The inhabitants of the 117 non-affected parishes (<3 kBq/m2) served as reference. During the 1988-1996 followup, 22,409 malignancies were recorded. The MH-IRR in the fully adjusted model was 1.00 (reference), 1.05, 1.03, 1.08, 1.10 and 1.21, respectively. ERR was 0.11 per 100 kBq/m2 (95% CL 0.03;0.20). A more advanced method was used in Study III by ignoring the exposure classification for parishes, and instead matching the dwelling coordinate to a digital map of deposition of casesium-137. In spite of a more valid exposure classification the risk estimates were similar in study II and III. Also, the ERR during the longer follow-up of 1988-1999 was almost identical, 0.10 per 100 kBq/m2 (95% CL 0.00;0.23). The strongest dose-response relationship was seen in the first four years (1988-1991). No obvious excess for leukaemia or thyroid cancer was recognised in either study II or III. The estimated number of exposure related cases was calculated to 849 in study II and 1,278 in study III. Our interpretation is that we have shown an increased incidence of total malignancies with dose-response relationship for caesium-137, only a few years after the Chernobyl accident. In study IV we compared the two different ways of classifying the exposure in study II and III. Out of the 450 parishes 111 got a different classification. The similar risk estimates in study II and III could probably be explained by relatively homogenous exposure in the parishes making the intra-parish difference less influential, especially when included in categories. In study V we examined the urinary excretion of 8-OHdG in Belarussian children from areas with high and low fallout of caesium-137, respectively. We found significantly lower urinary 8-OHdG levels in children from rural contaminated areas compared to urban uncontaminated areas, suggesting an urban, rather than a radiation related, risk factor.Using the Hill criteria for causality there is support for a causal inference between the fallout of caesium-137 from the Chernobyl accident and the increased incidence in total malignancies in Northern Sweden.
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| 17. |
- Åhlfeldt, Emanuel
(författare)
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Hållbart utvecklingsarbete i vård och omsorg : Ett institutionellt perspektiv på projekt i en professionell och byråkratisk kontext
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Det drivs många utvecklingsprojekt inom offentlig sektor, men det saknas kunskap om hur dessa projekt kan bidra till ett hållbart utvecklingsarbete. Syftet med avhandlingen är att förstå och förklara hur resultat och kunskap från utvecklingsprojekt kan integreras i den ordinarie verksamheten i offentliga organisationer och bidra till långsiktiga effekter, som har ett värde för brukarna, organisationen och de anställda.I forskningen saknas en etablerad begreppsapparat för att studera hållbar utveckling i organisationer. En utmaning har därför varit att identifiera och analysera tidigare forskning, för att därigenom definiera begreppet hållbart utvecklingsarbete och viktiga förutsättningar för ett sådant arbete. Den teoretiska referensramen baseras på ett institutionellt perspektiv: nyinstitutionell organisationsteori kombineras med Giddens struktureringsteori och sociologisk professionsteori, som synliggör spänningar mellan konkurrerande styrformer som byråkrati, marknad och professionalism.Avhandlingen utgår från en interaktiv forskningsansats och består av två empiriska delar: en kvantitativ enkätstudie som inkluderar 348 utvecklingsprojekt inom vård och omsorg samt en kvalitativ flerfallstudie av fyra utvecklingsprojekt.Studierna visar att olika faktorer främjade projekten på kort och lång sikt. Tydliga projektmål, styrning och kompetent projektledning hade betydelse för de kortsiktiga projektresultaten, men mycket begränsat påverkan på den långsiktiga hållbarheten. Istället var det ett aktivt ägarskap, och andra faktorer kopplade till ledningen i mottagarorganisationerna, som tydligast främjade ett hållbart utvecklingsarbete. Studierna visar även hur konflikter och motstånd i projekten påverkade förutsättningarna för långsiktig hållbarhet. Det gällde konflikter mellan olika yrkesgrupper, mellan ledning och professionella samt mellan byråkratiska och professionella styrformer. En slutsats är att en analysmodell för hållbart utvecklingsarbete behöver komplettera ett organisatoriskt och institutionellt perspektiv med ett professionsperspektiv.
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