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Sökning: swepub > Karlstads universitet > Licentiatavhandling

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1.
  • Ekengren, Jens, 1976- (författare)
  • Estimating inclusion content in high performance steels
  • 2008
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Non-metallic inclusions in steel pose a major problem for the fatigue resistance, especially regarding fatigue at very long lives corresponding to low cyclic stress levels, as well as being detrimental to material toughness and polishability.The largest inclusions are quite rare, which makes conventional detection methods timeconsuming if reliable results are to be obtained. Based on surface scanning using light or electron microscopes, these methods provide results that have to be converted to reflect the statistical volume distribution of inclusions.Very high cycle fatigue (in the order of 109 cycles or more) using ultrasonic fatigue at 20 kHz has been found efficient at finding the largest inclusions in volumes of about 300 mm3 per specimen. The inclusions found at the fatigue initiation site can then been used to estimate the distribution of large inclusions using extreme value statistics.In this work, a new method for estimating the volume distribution of large inclusions is presented as well as a suggested ranking variable based on the volume distribution.Results from fatigue fractography and area scanning methods are compared to the endurance limit at 109 cycles for a number of batches from two high performance steels.In addition, the extreme value distributions of fatigue initiating inclusions in six high performace steels, produced by different routes, are presented. It is shown that all modes of the Generalized Extreme Values distribution can be found in different materials. This result shows that the assumption of mode I distribution, also known as Gumbel or Largest Extreme Value distribution, must be substantiated.
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  • Haas, Jan, Ph.D, 1983- (författare)
  • Remote Sensing of Urbanization and Environmental Impacts
  • 2013
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The unprecedented growth of urban areas all over the globe is nowadays maybe most apparent in China having undergone rapid urbanization since the late 1970s. The need for new residential, commercial and industrial areas leads to new urban regions challenging sustainable development and the maintenance and creation of a high living standard as well as the preservation of ecological functionality. Therefore, timely and reliable information on land-cover changes and their consequent environmental impacts are needed to support sustainable urban development.The objective of this research is the analysis of land-cover changes, especially the development of urban areas in terms of speed, magnitude and resulting implications for the natural and rural environment using satellite imagery and the quantification of environmental impacts with the concepts of ecosystem services and landscape metrics. The study areas are the cities of Shanghai and Stockholm and the three highly-urbanized Chinese regions Jing-Jin-Ji, the Yangtze River Delta and the Pearl River Delta. The analyses are based on classification of optical satellite imagery (Landsat TM/ETM+ and HJ-1A/B) over the past two decades. The images were first co-registered and mosaicked, whereupon GLCM texture features were generated and tasseled cap transformations performed to improve class separabilities. The mosaics were classified with a pixel-based SVM and a random forest decision tree ensemble classifier. Based on the classification results, two urbanization indices were derived that indicate both the absolute amount of urban land and the speed of urban development. The spatial composition and configuration of the landscape was analysed by landscape metrics. Environmental impacts were quantified by attributing ecosystem service values to the classifications and the observation of value changes over time.ivThe results from the comparative study between Shanghai and Stockholm show a decrease in all natural land-cover classes and agricultural areas, whereas urban areas increased by approximately 120% in Shanghai, nearly ten times as much as in Stockholm where no significant land-cover changes other than a 12% urban expansion could be observed. From the landscape metrics analysis results, it appears that fragmentation in both study regions occurred mainly due to the growth of high density built-up areas in previously more natural environments, while the expansion of low density built-up areas was for the most part in conjunction with pre-existing patches. Urban growth resulted in ecosystem service value losses of ca. 445 million US dollars in Shanghai, mostly due to a decrease in natural coastal wetlands. In Stockholm, a 4 million US dollar increase in ecosystem service values could be observed that can be explained by the maintenance and development of urban green spaces. Total urban growth in Shanghai was 1,768 km2 compared to 100 km2 in Stockholm. Regarding the comparative study of urbanization in the three Chinese regions, a total increase in urban land of about 28,000 km2 could be detected with a simultaneous decrease in ecosystem service values corresponding to ca. 18.5 billion Chinese Yuan Renminbi. The speed and relative urban growth in Jing-Jin-Ji was highest, followed by the Yangtze River Delta and the Pearl River Delta. The increase in urban land occurred predominately at the expense of cropland. Wetlands decreased due to land reclamation in all study areas. An increase in landscape complexity in terms of land-cover composition and configuration could be detected. Urban growth in Jing-Jin-Ji contributed most to the decrease in ecosystem service values, closely followed by the Yangtze River Delta and the Pearl River Delta.
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4.
  • Rydstedt Nyman, Monika, 1961- (författare)
  • Managing knowledge sharing of extreme weather induced impacts on land transport infrastructure : Case study of the Swedish Transport Administration
  • 2016
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Extreme weather events and effects of climate change are threats to the transport sector’s functionality and safety. Risk management in this context implies a necessity to focus on the connection between near-term experiences and coping strategies on one hand, and long-term adaptation analyses on the other. How learning from past events and subsequent knowledge sharing can be adopted is a question that needs to be explored, discussed and tested. A systematic approach to lessons learned calls for measures of investigation, reporting, planning, implementation and evaluation. A qualitative case study approach was used in this thesis. In the first paper the practices of accident investigation in operation and maintenance were inventoried within the Swedish Transport Administration (STA). Three accident investigation methods were applied and tested on a cloudburst event, causing flooding in a railway tunnel in Sweden. In the second paper, semi-structured interviews, documents, and archival records were used as means for penetrating deeper into the attitudes and understanding of lessons learned concerning extreme weather events within a procured public-private partnership. The results of the two studies showed weak signals of feedback on lessons learned. Partly, these weak signals could be traced back to weak steering signals. Various obstacles impeded learning curves from lessons learned. The obstacles were of both hard and soft values, e.g. resources in time and equipment, systematic investigation methods, incentives for lessons learned, education and knowledge, values, norms and attitudes towards how and why identified problems should be solved. Successful knowledge sharing requires that close attention is paid to such obstacles and that an adaptive approach is adopted.
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  • Andersson, Ole (författare)
  • Holonomy in Quantum Information Geometry
  • 2018
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis we provide a uniform treatment of the two most popular non-adiabatic geometric phases for dynamical systems of mixed quantum states, namely those of Uhlmann and of Sjöqvist et al. We develop a holonomy theory for the latter which we also relate to the already existing theory for the former. This makes it clear what the similarities and differences between the two geometric phases are. We discuss and motivate constraints on the two phases. Furthermore, we discuss some topological properties of the holonomy of `real' quantum systems, and we introduce higher-order geometric phases for not necessarily cyclic dynamical systems of mixed states. In a final chapter we apply the theory developed for the geometric phase of Sjöqvist et al. to geometric uncertainty relations, including some new "quantum speed limits''.
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  • Asplund, Katarina (författare)
  • Implementation and Experimental Evaluation of a Partially Reliable Transport Protocol
  • 2004
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In the last decade, we have seen an explosive growth in the deployment of multimedia applications on the Internet. However, the transport service provided over the Internet is not always feasible for these applications, since the network was originally designed for other types of applications. One way to better accommodate the service requirements of some of these applications is to provide a partially reliable transport service. A partially reliable transport service does not insist on recovering all, but just some of the packet losses, thus providing a lower transport delay than a reliable transport service. The work in this thesis focuses on the design, implementation, and evaluation of a partially reliable transport protocol called PRTP. PRTP has been designed as an extension to TCP in order to show that such a service could be effectively integrated with current protocol standards. An important feature of PRTP is that all modifications for PRTP are restricted to the receiver side, which means that it could be very easily deployed. The thesis presents performance results from various experiments on a Linux implementation of PRTP. The results suggest that transfer times can be decreased significantly when using PRTP as opposed to TCP in networks in which packet loss occurs. Furthermore, the thesis includes a study that investigates how users perceive an application that is based on a partially reliable service. Specifically, how users select the trade-off between image quality and latency when they download Web pages is explored. The results indicate that many of the users in the study could accept less than perfect image quality if the latency could be shortened.
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10.
  • Berg, Mikael, 1970- (författare)
  • Historielärares historier : Ämnesbiografi och ämnesförståelse hos gymnasielärare i historia
  • 2010
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The overall aim of this study is to analyse history teachers’ understanding of the school subject history. The aim have also been to uncover what factors the history teachers say have affected their understanding of the school subject. Based on survey and interview methods, the question that this study deals with is: in the light of which general understanding of the school subject history, do the teachers make didactic choices on a daily basis?The first theme is biographical. The teachers’ life-history is taken into consideration and several factors in the teachers’ background and the school environment have been identified. It also seems as if the teachers’ understanding of the school subject goes from an elementary and searching approach to one that is more complex and convinced.The second theme is a more structural approach. The results shows three major orientations among the teachers’ general understanding namely, educational (bildung) orientation, critical orientation and identity orientation. Even though a main orientation can be seen among the teachers, an important result is also that the orientation is overall complex.At the most general level some patterns can be seen. First the connection between the teachers’ biography and their general understanding of the school subject. In the understanding of the school subject, it is also notable that teachers relate in different ways to history as science, history as identity and history from an ideological viewpoint. It is also possible to note some signs of change in the school subject history that follows a lager historiographical context.
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