| 1. |
- Choudhary, Vipin
(author)
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Nondestructive testing and antenna measurements using UWB radar in industrial applications
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Many industries are rapidly substituting the manual test operations and move towards automated operations using modern technologies.Modern technologies such as digital cameras, sonic sensors, infrared sensors, and radar and lidar systems are used for non-destructive testingoperations. Among all the different sensors, radar systems have theability to penetrate built structures (dielectric materials), which makes them flexible and suitable for a wide range of industrial and military applications in non-destructive sensing. Such examples are the detection of damages in goods manufacturing, monitoring the health of manystructures, object detection through the wall for security purposes, etc.In particular, ultra-wide-band (UWB) radar systems are beneficial inproviding high measurement accuracy and simultaneously reduced sensitivityto passive interference (such as rain, smoke, mist etc.), immunity to external radiation and noise.The objectives of this thesis are: I) to investigate electrically small concealed structures using synthetic aperture radar (SAR), II) to determinethe complex refractive index of objects using an UWB radar system,and III) to answer to the question how we can reduce the mutual coupling (cross talk) in an UWB radar system with collocated transmitand receive antennae. In objective I, the aim is non-destructive testing of built structures, such as in concrete slab manufacturing or for use in the renovation process. In addition electrically small periodic meshes,and their orientation, could not be distinguished in conventional SAR images. The proposed polarimetric analysis method demonstrates the usefulness of the singular value decomposition (SVD) using back projection algorithm (BPA) in extracting information about shape and for classifying an electrically small object. Further in this thesis for objective II, a new method for determining the complex refractive index (or equivalently the complex relative permittivity) of objects with planar interfaces is presented. The proposed method is relatively insensitive to hardware-impairments such as frequency-dependence of antennas and analog front end. The objects can be finite in size and at a finite distance. The limits in size and distance for the method to be valid are experimentally investigated. Hence, the method is designed for industrial in-line measurements onobjects on conveyor belts. Furthermore, in the following parts of this thesis −objective III− we investigate and show how a microwave metamaterial based absorber can be used to improve the performance of aradar system for short range applications, when positioned between the transmit and receive antennas. As results, the error in estimated target distance is reduced and clutter reduction is improved.
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| 2. |
- Sundin, Martin, 1983-
(author)
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Bayesian methods for sparse and low-rank matrix problems
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Many scientific and engineering problems require us to process measurements and data in order to extract information. Since we base decisions on information,it is important to design accurate and efficient processing algorithms. This is often done by modeling the signal of interest and the noise in the problem. One type ofmodeling is Compressed Sensing, where the signal has a sparse or low-rank representation. In this thesis we study different approaches to designing algorithms for sparse and low-rank problems.Greedy methods are fast methods for sparse problems which iteratively detects and estimates the non-zero components. By modeling the detection problem as an array processing problem and a Bayesian filtering problem, we improve the detection accuracy. Bayesian methods approximate the sparsity by probability distributions which are iteratively modified. We show one approach to making the Bayesian method the Relevance Vector Machine robust against sparse noise.Bayesian methods for low-rank matrix estimation typically use probability distributions which only depends on the singular values or a factorization approach. Here we introduce a new method, the Relevance Singular Vector Machine, which uses precision matrices with prior distributions to promote low-rank. The method is also applied to the robust Principal Component Analysis (PCA) problem, where a low-rank matrix is contaminated by sparse noise.In many estimation problems, there exists theoretical lower bounds on how well an algorithm can perform. When the performance of an algorithm matches a lowerbound, we know that the algorithm has optimal performance and that the lower bound is tight. When no algorithm matches a lower bound, there exists room for better algorithms and/or tighter bounds. In this thesis we derive lower bounds for three different Bayesian low-rank matrix models.In some problems, only the amplitudes of the measurements are recorded. Despitebeing non-linear, some problems can be transformed to linear problems. Earlier works have shown how sparsity can be utilized in the problem, here we show how the low-rank can be used.In some situations, the number of measurements and/or the number of parametersis very large. Such Big Data problems require us to design new algorithms. We show how the Basis Pursuit algorithm can be modified for problems with a very large number of parameters.
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| 3. |
- Borpatra Gohain, Prakash
(author)
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The Quest for Robust Model Selection Methods in Linear Regression
- 2022
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Doctoral thesis (other academic/artistic)abstract
- A fundamental requirement in data analysis is fitting the data to a model that can be used for the purpose of prediction and knowledge discovery. A typical and favored approach is using a linear model that explains the relationship between the response and the independent variables. Linear models are simple, mathematically tractable, and have sound explainable attributes that make them widely ubiquitous in many different fields of applications. Nonetheless, finding the best model (or true model if it exists) is a challenging task that requires meticulous attention. In this PhD thesis, we consider the problem of model selection (MS) in linear regression with a greater focus on the high-dimensional setting when the parameter dimension is quite large compared to the number of available observations. Most of the existing methods of MS struggle in two major areas, viz., consistency and scale-invariance. Consistency refers to the property of the MS method to be able to pick the true model as the sample size grows large or/and when the signal-to-noise-ratio (SNR) increases. Scale-invariance indicates that the performance of the MS method is invariant and stable to any kind of data scaling. These two properties are very crucial for any MS method. In the field of MS employing information criteria, the BayesianInformation Criterion (BIC) is undoubtedly the most popular and widely-used method. However, the new BIC forms including the extended versions designed for the high-SNR scenarios are not invariant to data-scaling and our results indicate that their performance is quite unstable under different scaling scenarios. To eradicate this problem we proposed improved versions of the BIC criterion viz., BICR and EBICR where the subscript ‘R’ stands for robust. BICR is based on the classical setting of order selection, whereas EBICR is the extended version of BICR to handle MS in the high-dimensional setting where it is quite possible that the parameter dimension p also grows with the sample size N. We analyze their performance as N grows large as well as when the noise variance diminishes towards zero, and provide detailed analytical proofs to guarantee their consistency in both cases. Simulation results indicate that the performance of the proposed MS criteria is robust to any data scaling and offers significant improvement in correctly picking the true model. Additionally, we generalize EBICR to handle the problem of MS in block-sparse high-dimensional general linear regression. Block-sparsity is a phenomenon that is seen in many applications. Nevertheless, the existing MS methods based on information criteria are not designed to handle the block structure of the linear model. The proposed generalization handles the block structure effortlessly and can be employed for MS in any type of linear regression framework.
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| 4. |
- Byhamre, Marja Lisa, 1981-
(author)
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Snus use and mortality : associations, potential mechanisms, and socioeconomic aspects
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Snus is a smokeless tobacco product made of a moist powder of ground tobacco. It is used mainly in the Nordic countries, although increasingly popular internationally. The Swedish snus tradition dates back to the seventeenth century, and it is now used daily by about 23% of the male and 6% of the female population. Snus contains high levels of nicotine as well as carcinogenic substances and microorganisms that could potentially cause adverse health effects. The physiological effects of snus use include acutely raised blood pressure and heart rate, and increased cardiac oxygen demand, while the psychological response results in alertness and anxiety reduction. The high nicotine content causes rapid onset of addiction. Previous research on snus use and health is largely inconclusive, but indicates increased risks of all-cause, cardiovascular and cancer mortality. This thesis aimed to further investigate the health effects of snus use, with a focus on mortality, potential underlying mechanisms, and the impact of socioeconomic factors. Four original papers form the base of this thesis. The first study was performed on a pooled dataset of eight Swedish cohorts (The Swedish Collaboration on Health Effects of Snus use), including over 169 000 men. We found an increased risk of all-cause (HR 1.28, 95% CI 1.20; 1.35), cardiovascular, and other cause mortality, and indications of raised cancer mortality. The second study was set within an interventional program in northern Sweden (Västerbotten Intervention Programme) and included 46 000 men and women. It showed increased mortality overall (estimates similar to first study), from cardiovascular diseases, and external causes (e.g., accidents and suicide) that remained after controlling for socioeconomic status. We found these associations in groups of varying socioeconomic background (e.g., both basic education and high-income groups), suggesting that increased mortality risks among snus users are not restricted to certain socioeconomic groups. Studies three and four investigated potential underlying mechanisms that might contribute to increased mortality among snus users, including established cardiometabolic risk factors in study three (the metabolic syndrome and its components: obesity, hypertension, type 2-diabetes and abnormal blood lipids) and more novel risk factors in study four (low-grade inflammation, low vitamin D-concentrations, and altered iii testosterone levels). The analytical samples were drawn from a long- term follow-up study of around 900 16-year-olds in a municipality in northern Sweden (Northern Sweden Cohort, study three) and more than 6 000 participants in another population-based cohort (the Northern Sweden MONICA study, study four). We found no associations between snus use and established cardiometabolic risk factors, but there was evidence of lower concentrations of inflammatory and vitamin D-status biomarkers in both men and women, and higher testosterone concentrations in men who were currently using snus. We conclude that snus use is associated with increased all-cause and cardiovascular mortality, and to death by other causes, that may be restricted to external causes. Cancer mortality may also be increased among snus users. The associations cannot be fully explained by differences in socioeconomic status among snus users and non-users. Established cardiometabolic risk factors do not seem to be the main mechanisms behind these associations. Lower inflammatory biomarker levels among snus users may serve as a protective factor, while lower vitamin D-concentrations and increased testosterone levels may be part of an underlying mechanism linking snus use to increased mortality. Future research should focus on the health consequences of snus use among women, on other possible links between snus use and death, and on mortality in different cancers among users of snus. The health consequences of dual use of snus and cigarettes should also be assessed.
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| 5. |
- Champati, Jaya Prakash, et al.
(author)
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Detecting State Transitions of a Markov Source : Sampling Frequency and Age Trade-off
- 2022
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In: IEEE Transactions on Communications. - New York : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 70:5, s. 3081-3095
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Journal article (peer-reviewed)abstract
- We consider a finite-state Discrete-Time Markov Chain (DTMC) source that can be sampled for detecting the events when the DTMC transits to a new state. Our goal is to study the trade-off between sampling frequency and staleness in detecting the events. We argue that, for the problem at hand, using Age of Information (AoI) for quantifying the staleness of a sample is conservative and therefore, study another freshness metric age penalty, which is defined as the time elapsed since the first transition out of the most recently observed state. We study two optimization problems: minimize average age penalty subject to an average sampling frequency constraint, and minimize average sampling frequency subject to an average age penalty constraint; both are Constrained Markov Decision Problems. We solve them using the Lagrangian MDP approach, where we also provide structural results that reduce the search space. Our numerical results demonstrate that the computed Markov policies not only outperform optimal periodic sampling policies, but also achieve sampling frequencies close to or lower than that of an optimal clairvoyant (non-causal) sampling policy, if a small age penalty is allowed.
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| 6. |
- Irshad, Yasir, 1977-
(author)
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On some continuous-time modeling and estimation problems for control and communication
- 2013
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Doctoral thesis (other academic/artistic)abstract
- The scope of the thesis is to estimate the parameters of continuous-time models used within control and communication from sampled data with high accuracy and in a computationally efficient way.In the thesis, continuous-time models of systems controlled in a networked environment, errors-in-variables systems, stochastic closed-loop systems, and wireless channels are considered. The parameters of a transfer function based model for the process in a networked control system are estimated by a covariance function based approach relying upon the second order statistical properties of input and output signals. Some other approaches for estimating the parameters of continuous-time models for processes in networked environments are also considered. The multiple input multiple output errors-in-variables problem is solved by means of a covariance matching algorithm. An analysis of a covariance matching method for single input single output errors-in-variables system identification is also presented. The parameters of continuous-time autoregressive exogenous models are estimated from closed-loop filtered data, where the controllers in the closed-loop are of proportional and proportional integral type, and where the closed-loop also contains a time-delay. A stochastic differential equation is derived for Jakes's wireless channel model, describing the dynamics of a scattered electric field with the moving receiver incorporating a Doppler shift.
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| 7. |
- Jansson, Elisabeth, 1968-
(author)
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Paradoxen (s)om entreprenörskap : En romantisk ironisk historia om ett av-vikande entreprenörskapande
- 2008
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Doctoral thesis (other academic/artistic)abstract
- The aim of this thesis is to embrace entrepreneurship as a paradox and to additionally show how an anomaly can be the foundation as well as the energy for the paradoxical, entrepreneurial process. The empirical focus is on the creative industry, in which the intimate connection between entrepreneurship, enterprise, art, culture and creativity has been illustrated and accounted for. The study is conducted with a narrative-rhetorical approach and analyzes and interprets three empirical cases and their stories.The theoretical contribution of the present study is the fact that we enrich our understanding of entrepreneurship as a paradox by grasping it in a romantic ironic-manner. The current study ends in the following significant and illustrative paradoxes that also can be seen as conclusions: Entrepreneurship requires deviance – but also at the same time demands belonging, in the sense that entrepreneurship can be regarded as acting between endogenous self-fulfillment and exogenous purposes. In addition, the basis of the here illustrated phenomenon is to become entrepreneurial. In the name of the romantic irony we have to keep in mind that you can only become an entrepreneur, you can not be one. As soon as one thinks of oneself as an entrepreneur one ceases to be one.The never-ending deviation can be seen as the root-metaphor of entrepreneurship. Conclusively, entrepreneurship is – and will become – a never-ending endeavor. This is an endeavor in which “becoming entrepreneurs” – in the name of the paradox – acts in-between and thereby are limited by, as well as delivered by society’s and discourse’s expectations of economic growth and business creation.
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| 8. |
- Jansson, Magnus, 1973-
(author)
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On Stabilization of Sensorless Synchronous Motor Drives and Traction Converters
- 2005
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Doctoral thesis (other academic/artistic)abstract
- Avhandlingen behandlar först och främst styrning av elmotordrifter, men vi tittar även på styrning av nätomriktare för stabil framdrivning av tåg.Två industriprojekt är rapporterade i avhandlingen, i form av delrapporterna ”Sensorless Control of Electrically Excited Synchronous Machines”, ABB Corporate Research och ”Stable and Passive Traction”, Bombardier Transportation.Beträffande styrning av elektriska motorer, speciellt synkrona växelströmsmotorer, är fokus på området sensorlös reglering. Med sensorlös reglering menas att motorn inte är beskaffad med någon vartalsgivare eller rotorvinkelgivare. Om man kan styra motorn på ett bra sett utan att montera en givare, kan man få ett mindre, billigare och ett mer robust drivsystem. Ökad robusthet erhålls eftersom man inte behöver lita på en givare som eventuellt kan ge felsignal eller i värsta gå sönder.Algoritmen för estimering av rotorvinkel är en vidareutveckling av den så kallade spänningsmodellen; vi kallar den ”Statically Compensated Voltage Model” (SCVM). För drivsystem som innehåller permanentmagnetiserade synkronmotorer, bevisas garanterad synkronisering från godtycklig initialvinkel vid uppstart och dessutom vid reversering.I delprojektet tillsammans med ABB Corporate Research skulle SCVM kunna användas som ett ”backup-system” då ett fel i den ordinarie varvtalsgivaren upptäcks. Detta skulle innebära att drivsystemet kan stoppas på ett lugnt och säkert sätt. I bästa fall skulle man kunna fortsätta köra drivsystemet som om inget hade hänt, utan istället byta varvtalsgivaren vid nästa servicetillfälle.I delprojektet tillsammans med Bombardier Transportation är fokus på styrning av nätomriktare, som indirekt används för framdrivning av tåg. Undersökningen innefattar möjligheten att styra omriktaren på ett sådant sätt att omriktaren uppträder som en passiv komponent. Passivitet gäller då vinkeln mellan inkommande ström och spänning inte överstiger +90° eller understiger -90°. Är inte omriktaren ”passiv” kommer den att interferera med andra tågs omriktare. Nätet kan då bli instabilt och i värsta fall kollapsa. Med hjälp av en annan topologi av strömregulator så utvidgades frekvensområdet då omriktaren uppträder som en passiv komponent.
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| 9. |
- Stenebrand, Agneta
(author)
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Dental anxiety among 15-year-olds : Psychosocial factors and oral health
- 2015
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Doctoral thesis (other academic/artistic)abstract
- AIM: The overall aim of this thesis was to examine the associations between dental anxiety, experiences of dental care, psychosocial factors and oral health among 15-year-olds, and to analyse changes in the prevalence of dental anxiety over time.MATERIALS AND METHODS: The thesis was based on two cross-sectional epidemiological studies in Jönköping, Sweden. Papers I, II, and III were based on a random sample of 15-year-old individuals. The total sample consisted of 221 individuals. Six questionnaires were used, one included items of background data, while the others were psychometric instruments measuring dental anxiety, temperament, general anxiety and depression, general fearfulness and attitudes to dental care. Paper IV was based on the Jönköping studies, a series of epidemiological studies from 1973, 1983, 1993, and 2003 in which random samples of 15-year-old individuals were included. The total sample consisted of 405 individuals. Questionnaires including background data and dental anxiety were used and clinical data were collected.RESULTS: Of the 15-year-old individuals 6.5% were classified as dentally anxious with girls proportionally more fearful than boys (Papers I-III). Dental anxiety correlated significantly with three of the temperament dimensions; emotionality, activity and impulsivity. Reported pain or unpleasant experiences during dental care treatment were clear predictors concerning dental anxiety (Paper I). Both symptoms of general anxiety and depression were significantly correlated with dental anxiety after controlling for other potential risk factors (Paper II). Dental anxiety was associated with both general fearfulness and with attitudes to dental care, where the strongest predictor of dental anxiety was general fearfulness (Paper III). A trend analysis over the 30-year period showed a gradient of statistically significantly decreasing dental anxiety prevalence, from 38.1% in 1973 to 12.8% in 2003. Over the period the 15-year-old individuals with dental anxiety had significantly higher number of filled tooth-surfaces than those with no dental anxiety, and also more caries in 1973. There were no such differences concerning plaque and gingivitis (Paper IV).CONCLUSIONS: Dental anxiety in 15-year-olds correlated with experiences of dental care, psychosocial factors as well as to oral health. Specifically, pain experiences related to dental care, attitudes to dental care and general fearfulness seem to have the strongest impact on dental anxiety. Dental anxiety showed a clear declining change over time. More girls than boys reported dental anxiety. The thesis shows that dental care providers need paying attention on providing a supportive dental care situation, in which the patients should not experience pain. One part may be adequate local anaesthesia during operative dentistry or similar dental treatments. Another part may be a good oral health to prevent negative experiences of dental care. There is a need for the understanding of psychological factors associated with dental care procedures.
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| 10. |
- Ullbrand, Jennifer
(author)
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Phase field modeling of Spinodal decomposition in TiAlN
- 2012
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Licentiate thesis (other academic/artistic)abstract
- TiAlN thin films are used commercially in the cutting tool industry as wear protection of the inserts. During cutting, the inserts are subjected to high temperatures (~ 900 ° C and sometimes higher). The objective of this work is to simulate the material behavior at such high temperatures. TiAlN has been studied experimentally at least for two decades, but no microstructure simulations have so far been performed. In this thesis two models are presented, one based on regular solution and one that takes into account clustering effects on the thermodynamic data. Both models include anisotropic elasticity and lattice parameters deviation from Vegard’s law. The input parameters used in the simulations are ab initio calculations and experimental data.Methods for extracting diffusivities and activation energies as well as Young’s modulus from phase field results are presented. Specifically, strains, von Mises stresses, energies, and microstructure evolution have been studied during the spinodal decomposition of TiAlN. It has been found that strains and stresses are generated during the decomposition i.e. von Mises stresses ranging between 5 and 7.5 GPa are typically seen. The stresses give rise to a strongly composition dependent elastic energy that together with the composition dependent gradient energy determine the decomposed microstructure. Hence, the evolving microstructure depends strongly on the global composition. Morphologies ranging from isotropic, round domains to entangled outstretched domains can be achievedby changing the Al content. Moreover, the compositional wavelength of the evolved domains during decomposition is also composition dependent and it decreases with increasing Al content. Comparing the compositional wavelength evolution extracted from simulations and small angle X-ray scattering experiments show that the decomposition of TiAlN occurs in two stages; first an initial stage of constant wavelength and then a second stage with an increasing wavelength are observed. This finding is characteristic for spinodal decomposition and offers conclusive evidence that an ordering transformation occurs. The Young’s modulus evolution for Ti 0.33 Al 0.67 N shows an increase of 5% to ~398 GPa during the simulated decomposition.
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