| 31. |
- Balliu, Enkeleda, PhD student
(författare)
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Power Scaling of Highly Compact Single-Frequency Yb-Doped Fiber Amplifiers
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Both scientific interests and industrial applications have stimulated the advance of single-frequency laser technology. The high spatial and temporal coherence of this technology has facilitated many applications such as gravitational wave detection, high-precision fiber sensors, high-resolution spectroscopy, holography, and nonlinear optical conversion. However, this is currently achieved through large footprint lasers with limited portability and mobility. Therefore, there is a need to reduce the size of these lasers into a compact format. Power performance of hundreds of watts in the near-infrared spectrum and tens of watts in the visible and UV spectra for continuous (CW) operation mode and pulse energies up to several tens of mJ in pulsed operation mode are needed. An amplification structure for single-frequency lasers that meets these requirements is the master oscillator power amplifier (MOPA). However, compactness imposes several constraints on the MOPA design. The main challenge is the limited output power of the single-frequency fiber MOPA due to the onset of stimulated Brillouin scattering (SBS) in the amplifier fiber. SBS arises from the interaction of acoustic phonons with the propagating signal wave and is converted into a frequency-shifted, backward-propagating wave. SBS is manifested through high-intensity pulses propagating in the backward direction, which can be very harmful for optical components and the seed laser itself. Hence, the suppression of SBS is crucial to the power optimization of the MOPA. This thesis therefore focuses on investigating different SBS suppression techniques that fit a compact MOPA design. More specifically, this is implemented by studying the efficiency of the strain distribution technique applied to the amplifier fiber and the use of custom and commercial highly Yb- doped fibers both in CW and pulse operating MOPAs. Using highly Yb-doped fibers presents challenges with respect to the composition of the fiber material and in high- power operation that can have undesirable degradational effects, such as photodarkening and thermal load generation, and these have been investigated and discussed in this thesis. As a result of the different mitigation approaches, output power approaching 100 W in CW mode operation and pulse energies near mJ in pulse mode operation are demonstrated in only one amplification stage, showing the feasibility of a MOPA design with high performance and a small footprint. This may facilitate many applications in the visible and UV spectral ranges that require mobility and portability.
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| 32. |
- Barac, Filip
(författare)
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Error mitigation in industrial wireless sensor networks : Corrupted packet forensics and recovery
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless sensor networks (WSN) are gradually penetrating the industrial automation domain. This process is, however, inhibited by a number of challenges that need to be considered and addressed before WSN can serve the most demanding industrial applications. In the context of process automation, existing technology can only serve the three least critical application classes related to non-critical monitoring of slowly-changing physical variables. The main issue in that respect is the insufficient communication timeliness and reliability, caused by the influence of harsh radio environment and the infeasibility of applying advanced communication techniques, due to the poor computational power of low-cost specialized hardware. The goal of this work is to improve wireless communication reliability in industrial environments, where the proposed solutions are generally applicable to other WSN domains as well as radio environments. This research is based on the notion that corrupt packets contain valuable channel state information that can be leveraged to improve communication robustness. The research methodology used in this work is rather unconventional, compared to existing research, but also highly intuitive, bearing in mind that counteracting a phenomenon requires a thorough knowledge of its properties. In order to rectify the aforementioned challenges, this work makes the following three contributions. The first contribution is a comprehensive analysis of communication errors recorded in practically relevant scenarios in a number of industrial environments. The related literature is seemingly rich, but essentially poor, due to inadequate measurement objectives, environments, and scenarios. The main research outcome of this measurement campaign is a set of practically relevant conclusions, which can be used for the design of coding, interleaving and packet recovery schemes. The second contribution is the design of two packet recovery schemes, based on the knowledge about error patterns obtained in the industrial measurement campaign. The first scheme is a proposal for redefinition of the IEEE 802.15.4 physical layer, where digital errors are counteracted at the earliest stage in the receiver chain. The second scheme exploits the determinism in packet structure inherent to industrial communication. Both schemes significantly improve the correctability of corrupted packets received. The third contribution is a channel diagnostics algorithm that determines whether a packet was corrupt by multipath fading and attenuation or by wireless local area network interference. The algorithm is derived from the error traces collected in three industrial environments and tested at a fourth, previously unused, industrial site. The results of live tests verify the ability of the proposed algorithm to promptly reestablish communication after a sudden deterioration of channel quality.
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| 33. |
- Bayat, Nazlin
(författare)
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Investigation of Surface Formation in As-Cast and Homogenized 6xxx Aluminium Billets
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The direct chill (DC) casting technique to produce billets for extrusion and ingots for rollingwas developed in the 1930s. The principle, which is still valid, is a two-stage cooling with a primary cooling at a mould surface followed by water spraying directly on the surface. Improvements of this technique have mainly focused on changes to the primary cooling, where a water-cooled metal mould has been replaced by different techniques to minimize cooling at this stage. The drive for development comes from the extrusion industry, which can increase the productivity and quality of extruded profiles by improving the billet surface appearance and structure. Hot top casting supported by airflow against the casting surface during the primary cooling is currently the standard procedure to achieve acceptable billet surfaces. The goal is to minimize the depth of the surface segregation zone, which is the governing factor for the appearance of different phases in the surface region. Billet surface quality is evaluated by quantifying surface appearance, segregation zone thickness, and occurrence of large Mg2Si and β-particles near the surface. The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality the as-cast billets are heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases.In this research the formation of the surface segregation for smooth defect-free surfaces in both as-cast and homogenized billets was studied. In addition, the surfaces with defects such as wavy, spot and vertical drag defects were investigated and possible mechanisms for initiation of those defects were explained. Moreover, for a better understanding of the homogenization process in-situ studies of the heat treatment of 6082, 6005, 6060 and 6063 Al alloys were carried out by using a transmission electron microscope (TEM). Based on the observations, an explanation of the probable mechanisms taking place during transformation from β-to α-phase was presented.
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| 34. |
- Bellman, Lina
(författare)
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In the mind of the property appraiser : Studies of commercial property valuation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A transparent market provides participants with as much information as possible. In Sweden, where the environment of commercial properties is highly transparent various actors still need to minimise some continuing information asymmetry, and one possibility is to hire property appraisers.Transparent commercial property markets are often regulated by governments and professional institutions. The combination of regulation and socialisation through memberships in professional associations and shared educational backgrounds, training, work experience, and institutional frameworks serve to produce and reproduce professional values and identities. The overall aim of this thesis is to describe and analyse the Swedish profession of property appraisers as expressed through members’ perceptions and use of various standards and methods, ways of gathering information gathering, assessments of value-influencing factors, and their confidence in their own assessments when valuing commercial properties.The repertory grid technique was used to collect and analyse empirical data and to map the thought patterns of respondents in two main samples. The repertory grid interviews in 2010/2011 included about half of the appraisers in Sweden (67 of 138), and in 2015 just over half (81 of 145).This thesis concludes that Swedish authorised property appraisers use country dependent valuation standards and methods, but there are signs of their increased adoption internationally. Swedish appraisers gather and assess information in a similar way. Their aggregated thought patterns demonstrate relatively strong homogeneity and moderate complexity. However, the findings also reveal that appraisers’ thought patterns differ depending on the university from which they graduated. The appraisers graduated from the highest ranked university simplify their valuation judgements more than do other appraisers.During the valuation process, property appraisers gather and assess a large amount of information considered relevant for estimations of a property object’s market value. Four types of information (local environment, location, rental income, and discount rate) seem to have the greatest impact on the estimated market value. The appraisers further perceive that these information types is common in that the decisions in the information gathering stage is critical to the entire valuation process when using clients as information sources. This seems to affect their perceived confidence at the assessment stage and, in turn, the final estimated market value. In situations where the appraisers have low confidence, they are left dependent on the clients, which risks reducing their independence.
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| 35. |
- Berg, Jan-Erik, 1957-
(författare)
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Wood and fibre mechanics related to the thermomechanical pulping process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.
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| 36. |
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| 37. |
- Bergstrand, Ulrika
(författare)
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Styrning och re-kontextualisering av värden i utbildningspolicy på nationell och lokal nivå
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study, governing as re-contextualization of values in Swedish educational policy has been described and analyzed. Two levels have been central to the study: the national level, in the form of the Swedish Schools Inspectorate's (SSI) survey to school personnel, and the municipal level, examined by interviews with superintendents in sparsely populated and rural areas. Three qualitative content analyses were performed, in two of which Rokeach’s theory of values as desirable actions and goals was used. The results presented that the dominant policy goal and the value expressed was that schools should promote students' knowledge, which is in line with the values underlying the PISA survey. The SSI survey expressed that schools should be quality assured to enhance students' knowledge development. Desirable actions to achieve this were: the principals evaluating, the teachers adapting to individual students, strengthening an environment conducive to learning with codes of conduct, and the guardians being informed about their children’s development. However, the superintendents expressed a lack of competence and qualified teachers for equivalent assessments, a need to upskill teachers, and that the information to the guardians did not always reach them. The study also showed an expressed value to include all students in teaching, which is in line with the values underlying the Salamanca statement. The SSI survey expressed this value as the students' participation in individualized teaching, an increased efficiency in special support, a socialization through codes of conduct, and that the students should know their rights. The superintendents expressed this value as motivating students, particularly boys, to study, adapting education for students in need of special support, preventing violations of newcomers, addressing girls' mental health, and the strengthening of democratic attitudes. In summary, the study shows that the values at the national level promoted increased individual rights, while at the local level, the values were expressed as a need to increase democratic values. Nonetheless, the values underlying the education of democratic citizens in sparsely populated and rural areas cannot be considered a closed chapter, even though policies at the national level continue to emphasize the values of promoting students' development of knowledge and their individual rights.
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| 38. |
- Billmayer, Jakob, 1983-
(författare)
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Ska dörren vara öppen? : Disciplin i klassrummet i Sverige och Tyskland
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study is to investigate discipline in German and Swedish classrooms and describe its cultural contexts. In countries with compulsory education, it must be assumed that not all students voluntarily attend classes. The mandatory presence of students combined with the ban on corporal punishment in schools means that classroom interaction has to be organized according to certain manners and rules (Luhmann, 2002a:108a). These rules are understood here as discipline meaning the organization and control of individuals and their actions over space and time (Foucault, 1987/1975). This study assumes similarities in the fundamental disciplinary mechanisms, although different contexts (here Germany and Sweden) will create different concrete manifestations of the phenomenon. Since the observation of cultural contexts is not as self-evident and direct as the observation of classroom interactions of teachers and students, the theoretical considerations here include a detailed discussion of methodology for observing culture. Starting with Alfred Schütz’ concept of ideal types and Niklas Luhmann’s theory on massmedia, it is argued that culture can be observed through the products of mass media. The empirical data for this study consists of field studies in the form of observations in German and Swedish classrooms as well as the examination of Germanand Swedish films and television series about teachers and students. The classroom observations were used to create ideal typical descriptions of different implementations of disciplinary procedure. Based on the analysis of teacher figures in various German and Swedish films and television series, several “good” and “bad” teacher types were initially identified. Combining the two results allowed conclusions tobe made about correlations between disciplinary order and whether a teacher is considered “good” or “bad”. This review of the various types of order is the basis for the description of cultural contexts. The results of classroom observations and film studies and their discussion in relation to prior Swedish research, gives the picture of a cultural context in which various forms of classroom order are avail-able, in which they are critically discussed and also can exist in parallel to each other. On the other hand, the German context seems to allow only one form of classroom order, both in actual school operations as well as in the mass media representation and scientific reflection.
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| 39. |
- Bjärtå, Anna, 1974-
(författare)
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FEAR - A process influenced by concurrent processing demands
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fear is a central aspect in mammalian evolution, prompting escape from and avoidance of threat and dangers. Therefore, it is reasonable to believe that we have a well developed system to detect dangers and quickly respond to them. It has been shown that threatening information has an advantage in information processing; it seems to promote a rapid capture of selective attention and puts demand on processing resources. It has been suggested that the elicitation of fear occurs automatically, and that it is independent of and impenetrable to cognition.The idea with the present research is that fear processing is dependent on all concurrent internal or external processing demands. One visual search study (Study II) and two secondary task studies (Study I & III) have been conducted to investigate if external or internal distraction can interfere with fear processing. In order to provoke fear responses, spider or snake fearful individuals have been exposed to pictures of their feared stimulus. The aim of Study II was to investigate if the selective attention to fear stimuli could be influenced by contextual factors, such as the nature of the distracting stimuli in a visual search. Study I and III aimed to investigate manipulation of resources allocated to fear stimuli. In Study I, task demand was used as the manipulation, and in Study III an internal cognitive directive was used. The results from these studies indicate that fear is susceptible to manipulation by both external and internal means. By changing circumstances in the surrounding or in the individuals’ internal states, responses to threatening stimuli can be altered. This means that processing of threatening stimuli is influenced by other concurrent processing demands, suggesting that a fear response is not occurring as an isolated and impenetrable process. In an evolutionary perspective, a fear system that is easily triggered but has access to cognitive evaluation at all times ought to be far more flexible, thus creating a better chance for survival than a modular and impenetrable fear system.
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| 40. |
- Björk, Annette
(författare)
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Stödjande gemenskap : Utveckling och utvärdering av en intervention för livsstilsförändring bland vuxna med adhd
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The entire project revolves around a lifestyle intervention that has been developed, implemented and evaluated. The intervention included adults with ADHD and comorbid mental illness. ADHD (Attention Deficiency Hyperactive Disorder) is a neuropsychiatric diagnosis/disability characterized by attention problems, impulsivity and hyperactivity and can affect education, working life, social relationships and form the basis for impaired lifestyle habits. Previous research shows shortened life expectancy in adults with ADHD, which related to deteriorating lifestyle habits. In the long run, the disability may be the basis for impaired living conditions and lifestyle habits and contribute to the individual's well-being and quality of life. In the field of health sciences, it is important to alleviate suffering, promote health and prevent ill health. Thus, the overall aim of this dissertation is to analyze living conditions among people with ADHD and mental illness, as well as to develop and evaluate a lifestyle intervention for this group.The PhD project includes four sub-studies: Study I, a qualitative interview study (n = 20) of adults with ADHD and mental illness, aimed at describing experiences of everyday suffering in this group. The analysis showed experiences of both suffering and well-being in living with ADHD. The focus of the suffering was the experience of loneliness, both regarding relationships in life, relationships in health care, but also to ADHD diagnosis and mental illness. Well-being was experienced when diagnosed with ADHD but also in relation to supportive social relationships. Study II, a quantitative descriptive and comparative study, aimed to gain more knowledge about people withADHD and their health situation. One group of people with ADHD (n = 48)was compared to the normal population without ADHD (n = 42). The results showed poorer health outcomes regarding self-perceived general health and the group with ADHD was less weekly physical active but nevertheless had no decreased aerobic fitness compared to the normal population. Study III, aquantitative descriptive study (n = 25), aimed to examine the degree of acceptance of the intervention and its impact on lifestyle habits, health and well-being, MBI and physical fitness. The tests before and after completing intervention showed small positive effects regarding weekly physical activity, quality of life and general- and mental health. Study IV, a qualitative study(n = 15), with adults with ADHD and comorbid mental illness aimed to investigate the experience of participating in a nurse-led lifestyle intervention. The analysis, based on material from interviews, showed that the participants perceived the intervention as supportive, which is related to the interpersonal relationships that arose in the intervention. Through supportive kindship with the other participants in the intervention, lifestyle habits and health experience were improved.The conclusion of the thesis is that the lifestyle intervention, based on interpersonal relationships and supported kindship, can be useful for making lifestyle changes in adults with ADHD and mental illness. Such support is important because adults with ADHD and mental illness experience a lack of and a desire for social support and has an increased risk of deteriorating health and unhealthy lifestyles. However, future adjustments to the content of the intervention must be made to improve the lifestyle intervention towards more sustainable lifestyle changes. Above all, the lifestyle intervention ought to be continuous. It is also of great importance for further research that insider perspective is used, that is, investigate the professionals' experiences regarding the intervention.
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