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- Johnsen, Pernilla
(författare)
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Homogenization of Partial Differential Equations using Multiscale Convergence Methods
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis is the theory of periodic homogenization of partial differential equations and some applicable concepts of convergence. More precisely, we study parabolic problems exhibiting both spatial and temporal microscopic oscillations and a vanishing volumetric heat capacity type of coefficient. We also consider a hyperbolic-parabolic problem with two spatial microscopic scales. The tools used are evolution settings of multiscale and very weak multiscale convergence, which are extensions of, or closely related to, the classical method of two-scale convergence. The novelty of the research in the thesis is the homogenization results and, for the studied parabolic problems, adapted compactness results of multiscale convergence type.
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| 2. |
- Persson, Anders J., 1975-
(författare)
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Ethical problems in work and working environment contexts
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis identifies and systematizes two categories ofpractical problems that stem from work and working environmentcontexts: workplace privacy and occupational health risks. Thefocus of the discussion is on ethical justification. Do we havereason to accept a certain level of (potential) harm toemployees by virtue of the fact that they are employees, and ifso, under what circumstances? The thesis consists of a briefintroduction and three essays. InEssayI, it is argued that employees have a prima facieright to privacy, but that this right can be overridden bycompeting moral principles that follow, explicitly orimplicitly, from the contract of employment. Three types ofjustification are specified: those that refer to the employer'sinterests, those that refer to the interests of the employee,and those that refer to the interests of third parties. A setof ethical criteria is developed and used in the subsequentessay to determine the moral status of infringement ofworkplace privacy. InEssayII, these criteria are applied to three broadcategories of intrusive workplace practices: (1) monitoring andsurveillance, (2) genetic testing, and (3) drug testing.Scenarios are used to show that such practical ethical problemscan be handled systematically using proposed guidelines. It isalso shown that some practices are dubious and at least some ofthem can be replaced by less intrusive means of ensuring thedesired outcome, for instance efficiency or safety in aworkplace. EssayIII deals with the fact that health and safetystandards for employees are less protective than those thatapply to the public. Emphasis is put on the distinction betweenexposure and risk, and this distinction is claimed to be a keyfactor in the relevance of arguments in favour of such doublestandards. The analysis of 'double standards' for public andoccupational exposure to risk aims to show that a justificationof such standards is closely linked to two separate types ofissues, namely empirical and normative issues. It is claimedthat this kind of differentiation seems to be supported neitherby a reasonable conception of the contract of employment nor byany obvious ethical principle that is applicable to workplacesor work situations in general. Key words:Contract of employment, double standards,drug testing, ethics, ethical justification, exposure, genetictesting, health and safety standards, privacy, surveillance,risks, work, work environment
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| 6. |
- Persson, Anders, 1972
(författare)
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Towards a Functional Programming Language for Baseband Signal Processing
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developing software for resource constrained embedded systems is a daunting task. In addition to getting the functionality right, a programmer must consider several non-functional properties, including data layout, the target memory hierarchy, concurrency and parallelism. The programmer has to decide on a specific and reasonable solution on these properties upfront during development However, these decisions are necessarily based on incomplete information, since the optimial solution depends on the actual deployment on the target hardware.In this thesis we explore a generative approach, with a staged functional domain specific language, to postpone many of these decisions to a much later stage of the development process.The staged approach gives the progammer explicit control over much of the code generation by using combinators to build the application from reusable components and skeletons.Currently, Feldspar is focused on the data processing part of signal processing in embedded systems. The Feldspar compiler generates single C functions that can be integrated into existing systems. The Feldspar language is based on a combination of shallow and deep embedding, which makes it modular both for the language developer and the end user. This modularity made it easy to add monadic expressions to support mutable updates and deterministic parallelism. Future work includes generation, deployment and orchestration of systems of data processing functions and control processing.Additionally, this thesis presents a technique, and supporting library that allows the programmer to test, profile and analyze compiled Feldspar programs from the host language environment.
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| 7. |
- Persson, Fredrik, 1971-
(författare)
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A Study of Factors Affecting the Particle Size for Water Atomised Metal Powders
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of metal powders by water atomisation is a well established process, which can be used to produce a wide range of particle sizes. A careful control of the particle size distribution is necessary, to atomise powders with a high quality and at a low production cost. Therefore, it is necessary to have a substantial knowledge of the relation between operational parameters and the particle size, to be able to produce water atomised metal powders with consistent and high yields. The main purpose with this thesis was to increase the knowledge about factors which affect the mass median particle size (d50) for water atomised metal powders. The specific objectives with the study were to develop a theoretical d50 model and to investigate the relation between the particle size and the physical properties of the liquid metal. Pilot scale experiments for liquid iron showed that alloy additions of carbon and sulphur decreased the d50 value, at a maintained liquid steel temperature before atomisation. Moreover, it was indicated that the reduced particle size at increased %C and %S contents may be related to a decreased viscosity and surface tension of the liquid metal, respectively. An alternative explanation could be that raised superheats at increased carbon contents increased the total available time for atomisation, which may have contributed to a reduction of the d50 value. The theoretical d50 model developed in this work showed a very good correlation to the current experimental data. The model considers the influence of surface tension, viscosity, melt stream diameter, water pressure, water jet angle and water to metal ratio. This model was further used to analyse how the d50 value was influenced by the viscosity and the surface tension. A reduced viscosity from 4∙9 to 2∙1 mPa s decreased the d50 value with 33%. In addition, the particle size was estimated to decrease with 21% by decreasing the surface tension from 1840 to 900 mN m-1.
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| 9. |
- Persson, Jens, 1978-
(författare)
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Homogenization of Some Selected Elliptic and Parabolic Problems Employing Suitable Generalized Modes of Two-Scale Convergence
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis is devoted to the homogenization of certain elliptic and parabolic partial differential equations by means of appropriate generalizations of the notion of two-scale convergence. Since homogenization is defined in terms of H-convergence, we desire to find the H-limits of sequences of periodic monotone parabolic operators with two spatial scales and an arbitrary number of temporal scales and the H-limits of sequences of two-dimensional possibly non-periodic linear elliptic operators by utilizing the theories for evolution-multiscale convergence and λ-scale convergence, respectively, which are generalizations of the classical two-scale convergence mode and custom-made to treat homogenization problems of the prescribed kinds. Concerning the multiscaled parabolic problems, we find that the result of the homogenization depends on the behavior of the temporal scale functions. The temporal scale functions considered in the thesis may, in the sense explained in the text, be slow or rapid and in resonance or not in resonance with respect to the spatial scale function. The homogenization for the possibly non-periodic elliptic problems gives the same result as for the corresponding periodic problems but with the exception that the local gradient operator is everywhere substituted by a differential operator consisting of a product of the local gradient operator and matrix describing the geometry and which depends, effectively, parametrically on the global variable.
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| 10. |
- Wang, Chunliang, 1980-
(författare)
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Computer Assisted Coronary CT Angiography Analysis : Disease-centered Software Development
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The substantial advances of coronary CTA have resulted in a boost of use of this new technique in the last several years, which brings a big challenge to radiologists by the increasing number of exams and the large amount of data for each patient. The main goal of this study was to develop a computer tool to facilitate coronary CTA analysis by combining knowledge of medicine and image processing.Firstly, a competing fuzzy connectedness tree algorithm was developed to segment the coronary arteries and extract centerlines for each branch. The new algorithm, which is an extension of the “virtual contrast injection” method, preserves the low density soft tissue around the coronary, which reduces the possibility of introducing false positive stenoses during segmentation.Secondly, this algorithm was implemented in open source software in which multiple visualization techniques were integrated into an intuitive user interface to facilitate user interaction and provide good over¬views of the processing results. Considerable efforts were put on optimizing the computa¬tional speed of the algorithm to meet the clinical requirements.Thirdly, an automatic seeding method, that can automatically remove rib cage and recognize the aortic root, was introduced into the interactive segmentation workflow to further minimize the requirement of user interactivity during post-processing. The automatic procedure is carried out right after the images are received, which saves users time after they open the data. Vessel enhance¬ment and quantitative 2D vessel contour analysis are also included in this new version of the software. In our preliminary experience, visually accurate segmentation results of major branches have been achieved in 74 cases (42 cases reported in paper II and 32 cases in paper III) using our software with limited user interaction. On 128 branches of 32 patients, the average overlap between the centerline created in our software and the manually created reference standard was 96.0%. The average distance between them was 0.38 mm, lower than the mean voxel size. The automatic procedure ran for 3-5 min as a single-thread application in the background. Interactive processing took 3 min in average with the latest version of software. In conclusion, the presented software provides fast and automatic coron¬ary artery segmentation and visualization. The accuracy of the centerline tracking was found to be acceptable when compared to manually created centerlines.
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