| 1. |
- Saarimäki, Jonas
(författare)
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Effect of Dwell-times on Crack Propagation in Superalloys
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas turbines are widely used in industry for power generation and as a power source at "hard to reach" locations where other possibilities for electrical supply are insufficient. There is a strong need for greener energy, considering the effect that pollution has had on global warming, and we need to come up with ways of producing cleaner electricity. A way to achieve this is by increasing the combustion temperature in gas turbines. This increases the demand on the high temperature performance of the materials used e.g. superalloys in the turbine. These high combustion temperatures can lead to detrimental degradation of critical components. These components are commonly subjected to cyclic loading of different types e.g. combined with dwell-times and overloads at elevated temperatures, which influence the crack growth. Dwell-times have shown to accelerate crack growth and change the cracking behaviour in both Inconel 718 and Haynes 282. Overloads at the beginning of the dwell-time cycle have shown to retard the dwell time effect on crack growth in Inconel 718. To understand these effects more microstructural investigations are needed.The work presented in this licentiate thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", concentrating on fatigue crack growth mechanisms in superalloys during dwell-times, which have shown to have a devastating effect on the crack propagation behaviour. Mechanical testing was performed under operation-like conditions in order to achieve representative microstructures and material data for the subsequent microstructural work. The microstructures were microscopically investigated in a scanning electron microscope (SEM) using electron channeling contrast imaging (ECCI) as well as using light optical microscopy.The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at the maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. When an overload is applied prior to the dwell-time, the crack growth rate decreases with increasing overload levels in Inconel 718. At high temperature crack growth in Inconel 718 took place as intergranular crack growth along grain boundaries due to oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along phase boundaries with subsequent severe oxidation of the phase.This thesis comprises two parts. The first giving an introduction to the field of superalloys and the acting microstructural mechanisms that influence fatigue during dwell times. The second part consists of two appended papers, which report the work completed so far in the project.
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| 2. |
- Carlsson, Magnus
(författare)
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Methods for Early Model Validation : Applied on Simulation Models of Aircraft Vehicle Systems
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Simulation models of physical systems, with or without control software, are widely used in the aeronautic industry in applications ranging from system development to verification and end-user training. With the main drivers of reducing the cost of physical testing and in general enhancing the ability to take early model-based design decisions, there is an ongoing trend of further increasing the portion of modeling and simulation.The work presented in this thesis is focused on development of methodology for model validation, which is a key enabler for successfully reducing the amount of physical testing without compromising safety. Reducing the amount of physical testing is especially interesting in the aeronautic industry, where each physical test commonly represents a significant cost. Besides the cost aspect, it may also be difficult or hazardous to carry out physical testing. Specific to the aeronautic industry are also the relatively long development cycles, implying long periods of uncertainty during product development. In both industry and academia a common viewpoint is that verification, validation, and uncertainty quantification of simulation models are critical activities for a successful deployment of model-based systems engineering. However, quantification of simulation results uncertainty commonly requires a large amount of certain information, and for industrial applications available methods often seem too detailed or tedious to even try. This in total constitutes more than sufficient reason to invest in research on methodology for model validation, with special focus on simplified methods for use in early development phases when system measurement data are scarce.Results from the work include a method supporting early model validation. When sufficient system level measurement data for validation purposes is unavailable, this method provides a means to use knowledge of component level uncertainty for assessment of model top level uncertainty. Also, the common situation of lacking data for characterization of parameter uncertainties is to some degree mitigated. A novel concept has been developed for integrating uncertainty information obtained from component level validation directly into components, enabling assessment of model level uncertainty. In this way, the level of abstraction is raised from uncertainty of component input parameters to uncertainty of component output characteristics. The method is integrated in a Modelica component library for modeling and simulation of aircraft vehicle systems, and is evaluated in both deterministic and probabilistic frameworks using an industrial application example. Results also include an industrial applicable process for model development, validation, and export, and the concept of virtual testing and virtual certification is discussed.
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| 3. |
- Ehn, Micael, 1983-
(författare)
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On the causes and effects of specialization : A mathematical approach
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Division of labor and division of knowledge are so important andcommon in society today that it is almost impossible to imagine asociety where everyone knows the same things and perform the sametasks. This would be a society where everyone grows, or gathers, andprepares their own food, makes their own tools, builds their ownhouse, and so on. Cultural evolution is the field of research that studies the creationand diffusion of ideas and societies. It is very uncommon for thesestudies to take into account the effects of specialization. Thisthesis will show that specialization is of great importance tocultural evolution. The thesis is divided into three parts: one introduction and two papers. The introduction covers the mathematical models used byeconomists to study the relation between the market and division oflabor. The first paper is an interdisciplinary survey of the researchon division of labor and specialization, including both theoretic andempirical studies. The second paper is a mathematical model of howspecialization of knowledge (i.e. higher education) leads to socialstratification. The model is tested against statistical data fromseveral countries and found to be a good predictor of the differencesin income between people of high and low education.
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| 4. |
- Eriksson, Emelie, 1987-
(författare)
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Patterns of corporate visual selfrepresentation in accounting narratives
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation deals with firms’ visual and pre-visual self-representations in accounting narratives. Self-representations are those descriptions about the company that firms include in accounting narratives to convey the current standings and their identity. External stakeholders increasingly expect non-numerical information about firms to be disclosed, and accounting narratives are a key medium for firms to account for their activities and maintain legitimacy as social actors. The question of which reporting conventions exist for legitimating selfrepresentations, especially from a visual perspective, remains unexplored. The purpose of this study is therefore to explore the empirical phenomenon of self-representations in accounting narratives in relation to legitimation rhetoric.The study is based on three research papers dealing with different patterns of self-representations in accounting-related narratives, including corporate reporting and business model diagrams. The examples are viewed through the theoretical lenses of semiotics and institutional theory, particularly legitimation theory. The study combines visual methods (visual content analysis and visual taxonomy) with other methods (interviews, text analysis) to conceptualize and exemplify what is meant by self-representations in accounting narratives. The study finds that there may be multiple parallel pre-visual self-representations at play to influence representations of the self, that visual self-representations are becoming more common in accounting narratives, and that several rhetorical strategies for legitimation are observable in these representations. By showing how diagrams can serve a legitimating purpose in accounting narratives, it is argued that diagrams should be considered on par with graphs and photographs as visual rhetorical devices in accounting narratives, and that they could be used as key communicative elements in the accounting process.Second, based on the longitudinal and comparative examples of self-representations, it is suggested that self-representations increasingly refer to abstract rather than concrete referents. This change is discussed in terms of the increasingly digital and service-based knowledge economy, where material referents give way to “amaterial” values. The contribution of this study is to describe selfrepresentations through several empirical examples, and to thereby increase awareness among practitioners and researchers of how visuals serve as communicative resources with legitimating functions in accounting narratives. Four concepts are proposed as tools for explaining the observed developments, and for improving visual literacy with regard to accounting narratives: inclusive perspective on accounting narratives, amateriality, self-representation, and diagrams.
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| 5. |
- Eriksson, Johan, 1987
(författare)
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Atom probe tomography of Zircaloy-2 exposed to boiling water reactor operation
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zirconium alloys are used as cladding tubes for the fuel in nuclear reactors. In boiling water reactors (BWRs), the alloy Zircaloy-2, which contains the alloying elements Sn, Fe, Cr, Ni, and O, is commonly used. In this thesis, results from atom probe tomography studies of Zircaloy-2 exposed to three and nine annual cycles of BWR operation are presented. The alloying elements were observed to be redistributed after reactor exposure. Clusters of Fe and Cr or Fe and Ni were observed at expected positions of radiation-induced type dislocation loops. Regions containing mainly Fe–Cr clusters were much more common than regions containing mainly Fe–Ni clusters. The Fe–Cr clusters appeared dense and spheroidal, whereas the Fe–Ni clusters appeared dilute and disc-shaped. The Fe–Ni discs occupied planes that correspond to all three families of first-order prismatic planes but with deviation from perfect axis alignment. Many grain boundaries were observed, and there were large grain-to-grain variations in cluster number density and cluster composition. Regarding cluster number density, there was on average no difference between three cycles and nine cycles. After nine cycles the clusters were on average larger and contained more Cr. Sn was observed to cluster in regions where there were no Fe–Cr or Fe–Ni clusters. Enrichment of Sn and Fe and small amounts of Cr and Ni was observed at grain boundaries. After nine cycles, but not after three cycles, enrichment of Sn, Fe, and Ni at ring-shaped features interpreted to be radiation-induced component loops was observed. Hydrogen was observed to be preferentially located outside a partially dissolved Zr(Fe,Cr)2 second phase particle that also contained Ni and Si. The present work demonstrates that the well-known dislocation loops have a chemistry, in the form of clusters of different types and shapes, that might substantially affect mechanisms degrading the cladding tubes, e.g. irradiation growth, corrosion, and hydrogen pickup.
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| 6. |
- Eriksson, Johan
(författare)
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Embedded real-time software using TinyTimber : reactive objects in C
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Embedded systems are often operating under hard real-time constraints. Such systems are naturally described as time-bound reactions to external events, a point of view made manifest in the high-level programming and systems modeling language Timber. In this licensiate thesis we demonstrate how the Timber semantics for parallel reactive objects translates to embedded real-time programming in C. This is accomplished through the use of a minimalistic Timber Run-Time system, TinyTimber. The TinyTimber kernel ensures state integrity, and performs scheduling of events based on given time-bounds in compliance with the Timber semantics. In this way, we avoid the volatile task of explicitly coding parallelism in terms of traditional processes/threads/semaphores/monitors, and side-step the delicate task to encode time-bounds into process/thread priorities. Moreover, a simulation environment is developed that enables the behaviour of a heterogeous distributed system, consisting of both the hardware and the Timber based embedded software to be observed under a model of the environment. Furthermore, pedagogic issues of reactive objects have been studied in the context of higher education. First results indicate that the use of TinyTimber give students an increased ability to understand and solve embedded programming assignments. Finally, the TinyTimber kernel implementation is discussed. Performance metrics are given for a number of representative platforms, showing the applicability of TinyTimber to small embedded systems. A comparison to a traditional system tick driven, thread based, real-time kernel shows that TinyTimber provides tighter timing and a simpler (yet comprehensive) API. In conclution we find that the use of Reactive Objects in C, realized through TinyTimber is a viable alternative for Embedded Real-Time Programming.
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| 7. |
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| 8. |
- Eriksson, Johan
(författare)
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Neuroimaging Consciousness: What happens in the brain when we become aware of what we percieve?
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although consciousness has been studied since the beginning of the history of psychology, how the brain implements consciousness is seen as one of the last great mysteries. This thesis investigates neural correlates of consciousness by measuring brain activity while specific contents of consciousness are defined and maintained. Study 1 showed that distinct but similar brain regions are activated for the initial creation of a percept and for sustaining that percept over time. Specifically, frontal and parietal regions were activated during both temporal aspects of consciousness. Study 2 investigated the generality of this activation pattern for consciousness in different sensory modalities, and showed that frontal regions were commonly activated for visual and auditory awareness whereas posterior activity was modality specific. However, frontal andparietal regions were jointly activated for both modalities during sustained perception. These results indicate that frontal regions interact with posterior, sensory-specific regions to instantiate a conscious percept. The percept is then maintained by a more general network including frontal and parietal regions.
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| 9. |
- Eriksson, Martin, 1972-
(författare)
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Att ta ställning : Gymnasieelevers argumentation och beslutsfattande om sociovetenskapliga dilemman
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims to explore students’ argumentation and decision-making relating to authentic socioscientific issues (SSI). The ability to make informed decisions about socio scientific issues has been recognized to be an important element in science education to achieve the goal of scientific literacy. However, deliberation on SSIs deals with the fact-value intertwinement and has proven to be a tricky affair, both for students and teachers. In paper I, the focus is on upper secondary students’ use of different reasons in arguing about the existence of wolfs in Sweden. To investigate the students’ ability to find supporting reasons from different subject areas in their informal argumentation, the SEE-SEP model was used as an analytical framework. The results showed that the value aspect dominates students’ informal argumentation on the SSI of wolves in Sweden. In paper II a six-step SSI instructional model is presented, designed to develop students’ ability to argue about complex multi-disciplinary issues. This six-step SSI instructional model aims to create a forum that encourages students to interact with one-another and discuss their arguments dynamically. In paper III students’ argumentation and decision-making upon an authentic SSI relating to environmental toxins in fish from the Baltic Sea, was studied. The students’ argumentation and decision making processes were followed closely and data were collected during multiple stages of the SSI-instructional model. The analysis focused on students’ skills of evaluation and the relationships between the values, knowledge and experiences that they used in their argumentation. The results showed that even though all of the students had access to the same information and agreed on the factual aspects of the issue, they came to different decisions, depending on their background values, knowledge and experiences (i.e. their intellectual baggage). Implications for teaching and research are discussed.
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| 10. |
- Hamrén, Ellinor
(författare)
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A Nationalism of Good Intentions : Dilemmas of inclusion and exclusion
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dissertation analyses ethical aspects of nationalism and criticizes the nation-state paradigm. Based on theories that concern various forms of 'benign' nationalism, the dissertation explores fantasies of inclusion with the help of various 'positions'. The question is: How are national identities, which are able to include ethnic minorities, constructed to be ethically justifiable, and what do the fantasies that sustain these ideas look like? Empirically I have worked with media material and have conducted focus groups with various ethno-political activists in Sweden and Finland. These minority groups are discussed based on the positions they hold in relation to the idea of the nation, and also the positions they would hypothetically end up in if their ethno-political struggle were successful. The dissertation is based on a discourse theoretical approach, with specifically the concept of fantasy being utilised from the discourse theoretical framework. My conclusion is that what I call the 'Fantasy of Inclusion', that is, a fantasy that the discourse of nations has taught us to desire, is based on ignoring the ethnic character of different groups in cases where it becomes "uncomfortable" in order to maintain the idea of inclusion as 'benign'.
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