| 30571. |
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| 30572. |
- Lörstad, Daniel
(författare)
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Numerical modeling of deforming bubble transport related to cavitating hydraulic turbines
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cavitation is a problem in many hydroelectric power plants since it can cause adverse effects on performance and damage to nearby solid surfaces. The concerns of this thesis are the numerical aspects of flow simulations in cavitating hydraulic turbines which contain several difficulties: turbulent and complex flows, steady and moving parts of the geometry, bubble transport and cavitation development. The focus is on the accuracy and reliability of several different aspects of these difficulties, namely the study of bubble transport without phase change. Two main strategies are chosen. Firstly the investigation of the turbulent bubble-flow interaction in a turbine geometry and secondly the investigation of the bubble deformation and the bubble-flow interaction. Consequently, different methods in order to handling these types of three dimensional multi-phase flows are presented. Volume of Fluid (VOF) is used for immersed fluid-fluid flows and improved methods are presented and evaluated for the phase transport and the interface treatment. This includes the Direction Averaged Normal model (DAN) and the Direction Averaged Curvature model (DAC). The Volume of Solid (VOS) method is also presented and evaluated. VOS is built on VOF and is a second order accurate boundary treatment method in Cartesian grids for both stationary and moving geometries of complex shape. All the methods are tested using different three dimensional cases which leads to a confirmation of the high accuracy. The high accuracy of the VOF model is verified by comparing it with the experimental data for both rising wobbling bubbles and the bubble formation for air injection in the bottom of a water channel. The real advantage of the VOS method is demonstrated for a turbulent flow past a rotating propeller placed in a square channel, where the turbulence and the bubble transport are simulated using Large Eddy Simulation (LES) and Lagrangian Particle Tracking (LPT) respectively.
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| 30573. |
- Lötmarker, Lena
(författare)
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Krian i förvandling : uppsatsämnen och skrivanvisningar för läroverkets svenska uppsatsskrivning
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation is about the goals that existed for Swedish essay writing in grammar schools from the start of the nineteenth century to the 1960s. The point of departure is the contrast between the negative image often painted of this essay writing and the positive picture painted of writing tuition before this period (classical rhetoric) and after it (process-oriented writing with the emphasis on genres outside the world of school). My aim is to study whether there are similarities to the earlier and later ideals during the grammar-school era.The material used consists of curricula, essay topics from the final examination, and textbooks on essay writing. On a number of points the analysis reveals an aspiration for extensive and varied training in writing, and shows that the ideals display a large measure of continuity. These ideals concern both the set essay topics and the instructions for writing presented in curricula and textbooks. The essay topics were largely linked to the specialist subjects taught in grammar school. Within this main category, however, a series of different essay types were distinguished. Throughout the period letter writing was recommended, and certain other genres occur which have clear counterparts outside school. To a large extent the instructions concern correct language and style. Right up to the end of the period, however, we find textbooks stating instructions for topic analysis, collection of material, and disposition, that is to say, the stages in the rhetorical process.
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| 30574. |
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| 30575. |
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| 30576. |
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| 30577. |
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| 30578. |
- Lövdahl, Cecilia
(författare)
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Injury-induced activation of vascular smooth muscle cells. Role of specific gene expression and intracellular signalling pathways
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Migration and proliferation of smooth muscle cells (SMC) are important events in the development of atherosclerosis and restenosis following angioplastic surgery. It is important to gain further knowledge about the mechanisms regulating SMC form and function in order to understand the underlying disease process. In this thesis I have used cultured rat aortic SMC and analysed how these cells respond to either a mechanical or enzymatic injury. The objective has been to identify the molecular mechanisms involved in injury-induced activation of SMC. I have focused my studies on the role of molecules regulating migration and proliferation. These include metalloproteinases and the intracellular signalling molecule ERK1/2. Increased expression of the migration-related stromelysin gene as well as early and transient expression of the transcription factor Ets-1 were detected when primary SMC were established in culture. Up-regulated Ets-1 expression was also seen in the rat carotid artery following balloon-injury. Since Ets-1 regulates the stromelysin gene, the role of stromelysin in injury-induced SMC activation was further investigated using antisense oligonucleotides directed towards the stromelysin translation initiation site. Treatment with antisense oligos inhibited phenotypic change as well as decreased the migration and proliferation of SMC after injury in vitro. Furthermore, these antisense oligos reduced neointimal thickening after balloon-injury in rat carotid arteries. Injury-induced ERK1/2 phosphorylation could be coupled to altered SMC function by the use of the MEK1-inhibitor PD98059. In addition, the synthetic metalloproteinase inhibitor Batimastat (BB94) reduced ERK1/2 activation as well as SMC migration and proliferation. Further studies demonstrated that Ca2+, calmodulin, tyrosine kinases, G-proteins and Src all appear to be involved in injury-induced ERK1/2 activation, migration and proliferation in SMC. In conclusion, these results suggest (1) a role for Ets-1 and metalloproteinases such as stromelysin in the SMC response to injury, (2) that the ERK1/2 is a key signalling molecule in the alteration of SMC function, (3) that release of Ca2+ is necessary for optimal ERK1/2 activation, and (4) that SMC activation due to injury is a result of signal transmission via several converging ERK1/2 connected pathways.
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| 30579. |
- Lövdahl, Susanna
(författare)
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Co-morbidity and mortality in Swedish patients with haemophilia - A register study
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Haemophilia is an X-linked inherited recessive disorder affecting males. The increased risk of hemorrhage is explained by the deficiency in either coagulation factor VIII (haemophilia A) or IX (haemophilia B). The severity of haemophilia A and B is characterized by the bleeding pattern. For severe haemophilia bleeding is often spontaneous, mainly in muscles and joints. Since the 1950s the manifestations and treatment of the disease have undergone dramatic changes with, formerly, a median survival of 10-15 years and today a survival comparable to the general population. However, development of the treatment was catastrophically affected by transmission of human immunodeficiency virus (HIV) and viral hepatitis through plasma-derived products until the 1980s. With an increased survival among the haemophilia population other age-related co-morbidities will inevitably become more prevalent. Studies of these co-morbidities are increasingly important, not least since their management may differ among patients with bleeding disorders. The present thesis focuses on incidence, mortality, first degree relatives, and co-morbidities over time, in Swedish persons with haemophilia compared to persons without haemophilia. This was performed by using Swedish national registries and local registries from the three haemophilia centers in Sweden: Malmö, Gothenburg and Stockholm. In Paper I the long-term outcome of haemophilia in terms of incidence, morbidity and mortality was studied. People with haemophilia in Sweden demonstrate higher mortality over time, independent of HIV and viral hepatitis, compared to the control cohort. In Paper II the family structure, focusing on children, siblings and marital status was studied. Having one or more children was less common for persons with haemophilia than the controls, especially for those infected with HIV. With respect to co-morbidities, a special focus was on malignancies and cardiovascular diseases. These were studied in Paper III and IV. Patients with haemophilia showed a higher incidence of malignancies than patients without haemophilia, again, regardless of infection with HIV or viral hepatitis. Hypertension was shown to be elevated, whereas deaths due to cardiovascular diseases were lower when compared to persons without haemophilia.
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| 30580. |
- Löve, Askell
(författare)
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Optimization of image quality and radiation dose in neuroradiological computed tomography
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The goal of clinical computed tomography (CT) is to produce images of diagnostic quality using the lowest possible radiation exposure. Degradation of image quality, with increased image noise and reduced spatial resolution, is a major limitation for radiation dose reduction in CT. This can be counteracted with new post-processing image filters and iterative reconstruction (IR) algorithms that improve image quality and allow for reduced radiation doses. Implementation of new methods in clinical routine requires prior validation in phantoms and clinical feasibility studies including comprehensive evaluation of diagnostic image quality. Aims: The main objectives of this thesis were to assess new methods for improvement of image quality in CT, explore the associated potential for radiation dose reduction, and to outline a comprehensive approach for evaluation of image quality. Methods: Extensive phantom testing was performed and a total of 100 human subjects were included in the clinical studies. Image quality and diagnostic acceptability were assessed in brain CT acquired with 30% reduced radiation dose in combination with post-processing filter (Paper I) and IR (Paper II). The potential of IR for image quality improvement, without concomitant radiation dose reduction, was assessed in craniocervical CT angiography (CTA) (Paper III). The performance of six IR algorithms was evaluated in a brain CT phantom model (Paper IV), using different combinations of radiation dose levels and iterative image optimization levels. Throughout the studies, various approaches for subjective and objective evaluation of image quality were used and assessed. Results: Post-processing image filtering (Paper I) and IR (Paper II) compensated partly or entirely for the loss of image quality caused by 30% reduced radiation dose in brain CT. In both studies, considerable inter-observer variation was seen. In Paper II a discrepancy was seen between results of objective and subjective evaluation of image quality and also between grading and ranking, indicating observer bias. Statistical IR improved image quality in craniocervical CTA (Paper III) with fairly good inter-observer agreement. Despite having different strengths and weaknesses, the six iterative reconstruction algorithms evaluated in Paper IV all improved image quality. Best over-all improvement was seen for one of the model-based IR algorithms, especially at lower radiation doses. Conclusion: All evaluated methods improved image quality and showed potential for radiation dose reduction while maintaining diagnostic quality. Careful study design and comprehensive evaluation of image quality including objective and subjective evaluation steps may reduce observer bias and improve reliability of study results.
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