| 1. |
- Cedervall, Johan
(författare)
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Structure-Magnetism Relations in Selected Iron-based Alloys : A New Base for Rare Earth Free Magnetic Materials
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Materials for energy applications are of great importance for a sustainable future society. Among these, stronger, lighter and more efficient magnetic materials will be able to aid mankind in many applications for energy conversion, for example generators for energy production, electric vehicles and magnetic refrigerators. Another requirement for the materials is that they should be made from cheap and abundant elements. For these reasons temperature induced magnetic transitions for three materials were studied in this work; one for permanent magnet applications and two magnetocaloric materials.Fe5SiB2 has a high Curie temperature and orders ferromagnetically at 760 K, providing possible application as a permanent magnet material. The ordering of the magnetic moments were studied and found to be aligned along the tetragonal c-axis and Fe5SiB2 undergoes a spin transition on cooling through a transition temperature (172 K), where the spins reorient along the a-axis in an easy plane.AlFe2B2 orders ferromagnetically at 285 K, making it a candidate for the active material in a magnetic refrigerator. The order of the magnetic transition has been studied as well as the magnetic structure. It was found that the magnetic moments are aligned along the crystallographic a-axis and that the magnetic transition is of second order.FeMnP0.75Si0.25 undergoes a first order magnetic transition around 200 K and the transition temperatures on cooling are different for the first cooling/heating cycle than for following cycles. This so called ”virgin effect” has been studied and found to originate from an irreversible structure change on the first cooling cycle through the ferromagnetic transition temperature.
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| 2. |
- Gebrewahid, Essayas, 1984-
(författare)
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Compiling Concurrent Programs for Manycores
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The arrival of manycore systems enforces new approaches for developing applications in order to exploit the available hardware resources. Developing applications for manycores requires programmers to partition the application into subtasks, consider the dependence between the subtasks, understand the underlying hardware and select an appropriate programming model. This is complex, time-consuming and prone to error.In this thesis, we identify and implement abstraction layers in compilation tools to decrease the burden of the programmer, increase programming productivity and program portability for manycores and to analyze their impact on performance and efficiency. We present compilation frameworks for two concurrent programming languages, occam-pi and CAL Actor Language, and demonstrate the applicability of the approach with application case-studies targeting these different manycore architectures: STHorm, Epiphany and Ambric.For occam-pi, we have extended the Tock compiler and added a backend for STHorm. We evaluate the approach using a fault tolerance model for a four stage 1D-DCT algorithm implemented by using occam-pi’s constructs for dynamic reconfiguration, and the FAST corner detection algorithm which demonstrates the suitability of occam-pi and the compilation framework for data-intensive applications. We also present a new CAL compilation framework which has a front end, two intermediate representations and three backends: for a uniprocessor, Epiphany, and Ambric. We show the feasibility of our approach by compiling a CAL implementation of the 2D-IDCT for the three backends. We also present an evaluation and optimization of code generation for Epiphany by comparing the code generated from CAL with a hand-written C code implementation of 2D-IDCT.
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| 3. |
- Glorieux, Emile
(författare)
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Constructive cooperative coevolution for optimising interacting production stations
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Engineering problems have characteristics such as a large number of variables, non-linear, computationally expensive, complex and black-box (i.e. unknown internal structure). These characteristics prompt difficulties for existing optimisation techniques. A consequence of this is that the required optimisation time rapidly increases beyond what is practical. There is a needfor dedicated techniques to exploit the power of mathematical optimisation tosolve engineering problems. The objective of this thesis is to investigate thisneed within the field of automation, specifically for control optimisation ofautomated systems.The thesis proposes an optimisation algorithm for optimising the controlof automated interacting production stations (i.e. independent stations thatinteract by for example material handling robots). The objective of the optimisation is to increase the production rate of such systems. The non-separable nature of these problems due to the interactions, makes them hard to optimise.The proposed algorithm is called the Constructive Cooperative CoevolutionAlgorithm (C3). The thesis presents the experimental evaluation of C3, bothon theoretical and real-world problems. For the theoretical problems, C3 istested on a set of standard benchmark functions. The performance, robustness and convergence speed of C3 is compared with the algorithms. This shows that C3 is a competitive optimisation algorithm for large-scale non-separable problems.C3 is also evaluated on real-world industrial problems, concerning thecontrol of interacting production stations, and compared with other optimisation algorithms on these problems. This shows that C3 is very well-suited for these problems. The importance of considering the energy consumption and equipment wear, next to the production rate, in the objective function is also investigated. This shows that it is crucial that these are considered to optimise the overall performance of interacting production stations.
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| 4. |
- Lindmark, Johan
(författare)
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The wet fermentation biogas process : Limitations and possibilities for efficiency improvements
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The biogas process is known as an environmental friendly and sustainable way of producing energy and fuel but to be fully commercially competitive with other types of processes, efficiency improvements are needed. By doing a case study at the Växtkraft biogas plant in Västerås, Sweden, three specific limitations were identified and studied. Firstly, to improve the capacity of the plant, pre-treatments of the different substrates are needed to disintegrate the substrate and by doing so increasing the gas yield and the speed in which it is produced. Secondly, to improve the fermentation process itself more knowledge is needed around the mixing inside the digester. To be able to create an optimal and stable environment for the microorganisms the mixing is the key, because the mixing affects the mass transfer of all solids, nutrients, gases and other substances in the digester. Thirdly, the water treatment of the recirculated process water cannot reach the desired separation of dry matter (DM) and this is affecting the capacity of the plant negatively. The feed for the digester is produced by mixing the process water and the substrate to get a pumpable slurry with a DM content of 8-10 %. When there is too much DM in the process water to begin with, the mixing ratio between the substrate and the liquid changes, decreasing the amount of substrate that can be added to the mixture and later on fed to the digester. The full biogas potential of most organic materials cannot be extracted during the relatively short retention time of most digesters because of their complex structures. The organic materials are broken down too slowly and the nutrients cannot become biologically available in that time span. This means that a lot of the bound energy in the organic material leaves the biogas plant with the liquid digestate. The efficiency of the process can be improved by pre-treating the material before digestion. Pre-treatment experiments to disintegrate ley crop silage using electroporation, a treatment using electrical fields, were conducted to study its effect on the biogas yield. The experiments resulted in up to twice the amount of biogas being produced from the pre-treated material compared to untreated material. Numerical simulations of the mixing inside a digester were carried out to understand the effect that a gas lift mixing configuration has on the mass transfer in the system. The mixing dynamics were evaluated by testing five different flow rates of the injected gas and the effect that the liquid recirculation system has. The results indicate that there are large unmixed zones and that changing the gas flow rate only has a marginal effect on these areas. The simulation also suggests that the outlet of the liquid recirculation system is situated too close to the gas injectors, resulting in energy losses in form of diminished mixing of the digester. Experiments to reduce the DM content of the recirculated process water were carried out using a ceramic ultrafiltration membrane. The flux through the membrane and the separation efficiency were investigated at different operation temperatures, 70°C, 90°C and 110°C. The results show that 59-63 % of the DM was separated in this temperature interval and that the flux/flow through the membrane increased with the temperature. These results correspond to a 29 % increase in the capacity to add new substrate. The energy required to heat the membrane, if heat recovery is used, is small in comparison to the increased methane yield. In the best case scenario these above identified improvements could increase the methane yield by up to 40%.
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| 5. |
- Svensson, Johan, 1983-
(författare)
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Androgenic Effects of the Progestin Levonorgestrel in Three-spined Stickleback (Gasterosteus aculatus)
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The extensive use of pharmaceuticals and their poor removal by wastewater treatment plants has led to the emergence of pharmaceutical compounds as global aquatic contaminants. Progestins, the synthetic analogues to progesterone, are receiving increasing attention as contaminants and have been shown to impair reproduction in fish and amphibians at low ng L-1 concentrations. Certain progestins, like levonorgestrel (LNG), have androgenic properties and are several orders of magnitude more potent in terms of reproductive impairment in fish than non-androgenic progestins. We exposed three-spined stickleback (Gasterosteus aculeatus) to LNG to investigate its androgenic effects in fish. Male stickleback kidneys produce spiggin, a glue-like glycoprotein used in nest building. Spiggin production is directly and specifically governed by androgens and its induction in females serves as the best known biomarker for androgen exposure in fish. In the present project females were exposed to LNG for 21 days after which effects on spiggin biomarkers and vitellogenesis were evaluated. Male sticklebacks that were in the final stage of a breeding period were exposed to various concentrations of LNG for six weeks under winter conditions, after which reproductive status was evaluated from gross morphology, histology and key gene transcript levels. In female sticklebacks, LNG induced spiggin production in the kidneys and suppressed vitellogenesis in the liver. In males, LNG inhibited the post-breeding regression of secondary sex characters and spiggin production, as well as the resumption of spermatogenesis; thus LNG functionally inhibits the natural transition from breeding into non-breeding condition. Suppression of vitellogenesis in females and disruption of the male reproductive cycle as shown in this thesis could entail severe fitness costs and severely affect natural stickleback populations. Some of the present effects occurred at 6.5 ng L-1, well within the range of environmental LNG levels, and may therefore occur in progestin-contaminated waters. In conclusion, the present results establish LNG as a highly potent androgenic pollutant of environmental concern, and support the contention that the reproductive impairment in fish caused by progestins could to a significant degree be mediated by their androgenic properties.
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| 6. |
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| 7. |
- Svensson, Jennie, 1987-
(författare)
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The Submerged Entry Nozzle : A Study of how to Reduce Decarburization and Clogging
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During continuous casting the submerged entry nozzle (SEN) is one of the critical points. This since sequence casting is favourable, clogging of the SEN results in fever sequences or aborted castings. In this study the preheating of SEN has been evaluated at different steel plants. This since it earlier has been found, preheating resulted in decarburisation of the refractory base material (RBM) which in turn resulted in clogging of the SEN. During the industrial preheating trials it was found that decarburisation of the SEN is possible.The decarburisation results in a higher oxygen potential near the SEN wall. This in turn makes it possible for aluminum in the molten steel to form alumina particles. For low carbon aluminum killed steel grades, accretion of alumina clusters on the SEN internal wall result in clogging which hinder or reduces the steel flow through the SEN. For this reason, laboratory trials were performed to establish the formation of a liquid phase. Thus simulating the formation of liquid inclusions when alumina clusters attaches to the SEN wall, and which can be washed away by the steel flow. Formation of a liquid phase was indicated at the temperatures 1550-1600°C, and plasma coated nozzles were tried in pilot plant trials. The coating contained of 5-9 pct, 99.9 pct pure, calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ).
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| 8. |
- Svensson, Johan, 1974
(författare)
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Tillgänglighet för personer med funktionsnedsättningar
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the design of our cities tends to constrain people with impairments from performing their daily activities, removing barriers and making public space accessible for everyone is becoming a human rights-issue. Due to an ageing population, the number of impaired citizens is expected to increase substantially over the next 50 years. Hence, there is a current demand on urban planners to find a way to adjust their cities, in order to make them usable for every-one, which will grow stronger as the number of elderly in the society increases over the next few decades. However, efficiently improving accessibility requires knowledge about the loca-tion of obstacles in the urban environment and how these affect accessibility.Using GIS-models to map and measure accessibility, this study aims at providing new knowl-edge about the spatial distribution of accessibility and the possibility for impaired persons to travel independently in seven Swedish towns. Furthermore, the study aims at revealing how certain details in the design of the urban environment constrain mobility and restrict accessi-bility for certain groups of impaired citizens. Based on field inventories, detailed digital models of the pedestrian and public transport net-works were created for each town, using traditional digitizing methods. Using GIS for net-work analyses, these models were used to evaluate the possibility for vision and mobility im-paired citizens to reach different destinations. The applied method pays attention to the entire travel chain, starting from any residence in the town, thus analysing the possibility to reach a destination by using a combination of available and usable modes of transport.The results from the study reveal how different types of flaws in the pedestrian network cause interruptions or forces travellers to detours, thus restricting accessibility. The results show where it is possible to live and independently perform daily activities as an impaired citizen, and also how accessibility varies considerably between mobility and vision impaired citizens. The results also reveal how accessibility for impaired citizens is better in densely populated towns and cities. Size and density of urban areas tend to correlate, as does the supply of facili-ties and public transport. Thus, accessibility for impaired citizens appears to be better in cities and larger towns. In conclusion, the study provides new knowledge about accessibility for impaired citizens in Sweden. Furthermore, the study shows how urban planners, by using GIS-models, can easily enhance their knowledge about how flaws in their cities affect accessibility for impaired citi-zens. This study also shows how planners could use these models to simulate potential actions towards improving accessibility. The results from such simulations reveal what effect a cer-tain action would have on accessibility for impaired citizens, thus making it possible to iden-tify and prioritize those actions that would generate the most positive outcome. Keywords: accessibility, disability, functional limitations, GIS, impairment, urban planning.
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