| 1501. |
- Sjöberg, Jonas, 1964-
(författare)
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Non-Linear System Identification with Neural Networks
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses the non-linear system identification problem, and in particular, investigates the use of neural networks in system identification. An overview of different possible mode! structures is given in a common framework. A nonlinear structure is described as the concatenation of a map from the observed data to the regressor, and a map from the regressor to the output space. This divides the model structure selection problem into two problems with lower complexity: that of choosing the regressor and that of choosing the non-linear map.The possible choices for the regressors consists of past inputs and outputs, and filtered versions of them. The dynamics of the mode! depends on the choice of regressor, and families of different mode! structures are suggested based on analogies to linear black-box models. State-space models are also described within this common framework by a special choice of regressor. It is shown that state-space models which have no parameters in the state update function can be viewed as an input-output mode! preceded by a pre-filter. A parameterized state update function, on the other hand, can be seen as a data driven regressor selector. The second step of the nonlinear identification is the mapping from the regressor to the output space. It is often advantageous to try some intermediate mappings between the linear and the general non-linear mapping. Such non-linear black-box mappings are discussed and motivated by considering different noise assumptions.The validation of a linear mode! should contain a test for non-linearities and it is shown that, in general, it is easy to detect non-linearities. This implies that it is not worth spending too much energy searching for optimal non-linear validation methods for a specific problem. lnstead the validation method should be chosen so that it is easy to apply. Two such methods, based on polynomials and neural nets, are suggested. Further, two validation methods, the correlation-test and the parametric F-test, are investigated. It is shown that under certain conditions these methodscoincide.Parameter estimates are usually based on criterion minimization. In connection with neural nets it has been noted that it is not always optimal to try to find the absolute minimum point of the criterion. Instead a better estimate can be obtained if the numerical search for the minimum is prematurely stopped. A forma! connection between this stopped search and regularization is given. It is shown that the numerical minimization of the criterion can be view as a regularization term which is gradually turned to zero. This closely connects to, and explains, what is called overtraining in the neural net literature.
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| 1502. |
- Sjöberg, Johan, 1978-
(författare)
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Optimal Control and Model Reduction of Nonlinear DAE Models
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, different topics for models that consist of both differential and algebraic equations are studied. The interest in such models, denoted DAE models, have increased substantially during the last years. One of the major reasons is that several modern object-oriented modeling tools used to model large physical systems yield models in this form. The DAE models will, at least locally, be assumed to be described by a decoupled set of ordinary differential equations and purely algebraic equations. In theory, this assumption is not very restrictive because index reduction techniques can be used to rewrite rather general DAE models to satisfy this assumption.One of the topics considered in this thesis is optimal feedback control. For state-space models, it is well-known that the Hamilton-Jacobi-Bellman equation (HJB) can be used to calculate the optimal solution. For DAE models, a similar result exists where a Hamilton-Jacobi-Bellman-like equation is solved. This equation has an extra term in order to incorporate the algebraic equations, and it is investigated how the extra term must be chosen in order to obtain the same solution from the different equations.A problem when using the HJB to find the optimal feedback law is that it involves solving a nonlinear partial differential equation. Often, this equation cannot be solved explicitly. An easier problem is to compute a locally optimal feedback law. For analytic nonlinear time-invariant state-space models, this problem was solved in the 1960's, and in the 1970's the time-varying case was solved as well. In both cases, the optimal solution is described by convergent power series. In this thesis, both of these results are extended to analytic DAE models.Usually, the power series solution of the optimal feedback control problem consists of an infinite number of terms. In practice, an approximation with a finite number of terms is used. A problem is that for certain problems, the region in which the approximate solution is accurate may be small. Therefore, another parametrization of the optimal solution, namely rational functions, is studied. It is shown that for some problems, this parametrization gives a substantially better result than the power series approximation in terms of approximating the optimal cost over a larger region.A problem with the power series method is that the computational complexity grows rapidly both in the number of states and in the order of approximation. However, for DAE models where the underlying state-space model is control-affine, the computations can be simplified. Therefore, conditions under which this property holds are derived.Another major topic considered is how to include stochastic processes in nonlinear DAE models. Stochastic processes are used to model uncertainties and noise in physical processes, and are often an important part in for example state estimation. Therefore, conditions are presented under which noise can be introduced in a DAE model such that it becomes well-posed. For well-posed models, it is then discussed how particle filters can be implemented for estimating the time-varying variables in the model.The final topic in the thesis is model reduction of nonlinear DAE models. The objective with model reduction is to reduce the number of states, while not affecting the input-output behavior too much. Three different approaches are studied, namely balanced truncation, balanced truncation using minimization of the co-observability function and balanced residualization. To compute the reduced model for the different approaches, a method originally derived for nonlinear state-space models is extended to DAE models.
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| 1503. |
- Sjödin, Jörgen, 1970-
(författare)
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Swedish district heating systems and a harmonised European energy market : means to reduce global carbon emissions
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy systems in Europe are becoming more harmonised and the European Union is working to establish a single market for energy. In this thesis, it is therefore regarded as a system failing to consider a separate and isolated Swedish energy system. Extending the system boundaries enables increased resource efficiency. System failings involve a discrepancy between institutional conditions and the motives for economy, when rationality for the individual actors is not rational to society.It is important to reduce the anthropogenic emissions of climate gases, carbon dioxide in particular. Climate changes with severe negative consequences can be expected unless radical measures are taken to reduce emissions.The aim of this thesis is to examine the possibilities to reduce carbon emissions in a harmonised EU energy market, and to identify system failings. In the thesis, it is shown how combined heat and power (CHP) generation in Sweden is able to reduce the global emissions of carbon dioxide and improve resource utilisation. Because combustion of biofuels is not considered to release any net amounts of carbon dioxide to the atmosphere, using biofuels in combined generation can displace carbon emissions from other power generation.In Sweden, where electric power supply is dominated by hydropower and nuclear power, increased use of electricity may cause emissions of carbon dioxide in another country. Inversely, decreased use of electricity can reduce total carbon emissions. Accordingly, electricity conservation measures undertaken in Sweden can reduce global carbon emissions. This occurs when the export of electricity from Sweden displaces power production involving fossil fuels, for example coal condensing power generation. Analogously, when decreased import of electricity to Sweden reduces fossil fuel generation in for example Denmark, total carbon emissions will decrease.System failings illustrated in the thesis include pricing of district heating that is not based on the marginal costs of the producer, but rather on the customers' willingness to pay. Another example of a system failing is the absence of prices for various kinds of environmental pollution, which could be introduced through, for example, uniform taxation schemes.
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| 1504. |
- Sjögren, Torsten, 1969-
(författare)
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Influences of the Graphite Phase on Elastic and Plastic Deformation Behaviour of Cast Irons
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The amount and morphology of the graphite phase largely controls the resulting properties of cast iron. For instance, in flake graphite cast irons the mechanical properties are low while the thermal conductivity is high. This is in contrast with spheroidal graphite cast irons where the mechanical properties are high and the thermal conductivity is low. These differences are due to the different graphite morphologies and must be accounted for in the design work and material selection of cast iron components. In this work the influence of the graphite phase on the elastic and plastic deformation behaviour of cast irons has been studied.The material grades studied originate from castings for marine diesel engine piston rings with different chemical analyses. Two groups of pearlitic cast iron materials were studied; one with differences in graphite morphology and one with grey irons that differed in graphite content. For these different material grades the mechanical properties were correlated to microstructural parameters. In addition to standard uniaxial tensile tests, acoustic emission measurements were used for the study of deformation.When studying the modulus of elasticity of the cast iron it was found that the modulus of elasticity of the inherent graphite phase depends on the roundness of the graphite particles and is due to the strong anisotropy of the graphite phase. A linear correlation between nodularity and the modulus of elasticity of the graphite phase was derived. This correlation made it possible to account for the anisotropy of the graphite phase in the model used. By applying the linear function when modelling the effective modulus of elasticity, a high accuracy between experimental and theoretical values was achieved.Another factor affecting the elastic response when subjecting a cast iron component to tensile load was found to be the plastic deformation that actually occurs at very low strains for all of the studied cast iron grades. It was observed that the plastic deformation in the low strain elastic region, quantified by using acoustic emission measurements, increased linearly with decreasing modulus of elasticity. These measurements showed that the amount of plastic deformation in the elastic region was largely controlled by the graphite morphology. It was concluded that as the roundness of the graphite particles increases, the plastic deformation activity in the elastic region decreases.The plastic deformation activity continued linearly into the pronounced plastic region of the tensile tests. A decrease in roundness or increase in graphite fraction resulted in an increase of the amount of plastic deformation and the strain hardening exponent. Adependence between strength coefficient and graphite fraction was observed. Models for the flow curves for pearlitic cast irons were developed and shown to accurately reproduce the observed experimental curves.The surveys performed and conclusions from this thesis will be helpful in the design of new cast iron materials.
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| 1505. |
- Sjölander, Daniel
(författare)
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Luminescent molecular recognition of pathognomonic and aging associated protein aggregates
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Various protein inclusions have been recognized to be associated with aging and pathogenic conditions, such as in Alzheimer’s disease, Parkinson’s disease, Type 2 diabetes, and the prionoses Creutzfeldt-Jakob disease, Chronic wasting disease (CWD), and Mad cow disease. The causative transition of protein aggregation is the alteration in the conformation of the protein that renders the protein susceptible towards self-assembly. Variations in the physico-chemical ultrastructure of the protein deposit, i.e. the conformation and the chemical nature of the fibril constituent protein monomers, translate into specific structure-property phenotype, hence clinicopathology. Upon transmission and/or propagation this phenomenon gives rise to specific protein aggregate strains. Today most potential treatments of the protein conformational diseases have been a huge failure, effectively due to late diagnosis and subsequent therapeutic intervention. An imperative for efficient treatment is early detection and accurate identification for proper clinical diagnosis.The purpose of the studies in this thesis was to develop highly sensitive methods for detection and discrimination of age- and disease associated protein deposits both for in vitro and ex vivo utilization.Herein we have shown that, for in vitro usage, Nile red will bind to amyloid-like protein aggregates derived from a plethora of precursor proteins. It was also found that the fluorescence was insensitive to acidic assay conditions in contrast to the standard in vitro dye Thioflavin T (ThT). Further, Nile red was shown to discriminate between conformational isoforms thus enabling conformational typing of amyloid structures.For the development of ex vivo detection methods we employed luminescent conjugated oligothiophenes (LCOs) and utilized the structure-conformation induced optical properties of this class of protein aggregate ligands. The heptameric oligothiophene h-FTAA was successfully used to detect, with high sensitivity, protein deposits from various systemic amyloidoses (ATTR, AA, AL-λ/κ, and the local amyloidosis AIAPP) derived from biopsy specimens. Also aging-associated protein deposits were detected which was found promising for early detection of potentially pathogenic protein inclusions. Further, LCO staining of tissue sections was found compatible with immunolabeling enabling subtyping of involved proteins. Early detection of amyloidosis also requires relatively non-invasive methods, why h-FTAA staining was directed towards fine-needle-aspirated (FNA) abdominal fat tissue smears. Staining of protein deposits and detection with high sensitivity was also found in the fat tissue smears.In addition to the relatively rare prionoses it has lately been shown that Alzheimer’s, Parkinson’s diseases share similar properties as the prion pathologies. Hence the urgent need for ligands that will recognize specific disease specific strain aggregates. Using an established murine model for prion strain propagation we were able to discriminate two different prion strains, murine adapted Sheep Scrapie (mSS) and murine adapted Chronic wasting disease (mCWD) from each other by using multimodal fluorescence microscopy entailing emission/excitation spectral imaging and fluorescent lifetime imaging (FLIM).In conclusion we have shown that the LCOs will recognize protein aggregates with high sensitivity and selectivity. In addition we have shown that the LCOs detect protein aggregates that Congo red failed to recognize thus allowing potentially early diagnosis. Last, we show that the LCOs will recognize and discriminate between different protein aggregate strains which potentially will allow disease specific therapeutic targeting.
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| 1506. |
- Sjöqvist, Jonas, 1985-
(författare)
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Light interactions in flexible conjugated dyes
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis methodological developments have been made for the description of flexible conjugated dyes in room temperature spectrum calculations.The methods in question target increased accuracy and efficiency by combining classical molecular dynamics (MD) simulations with time-dependent response theory spectrum calculations. For absorption and fluorescence spectroscopies a form of conformational averaging is used, where the final spectrum is obtained as an average of spectra calculated for geometries extracted from ground and excited state MD simulations. For infrared and Raman spectroscopies averaged spectra are calculated based on individual spectra, obtained for zero-temperature optimized molecular structures, weighted by conformational statistics from MD trajectories. Statistics for structural properties are also used in both cases to gain additional information about the systems, allowing more efficient utilization of computational resources. As it is essential that the molecular mechanics description of the system is highly accurate for methods of this nature to be effective, high quality force field parameters have been derived, describing the molecules of interest in either the MM3 or CHARMM force fields.These methods have been employed in the study of three systems. The first is a platinum(II) actylide chromophore used in optical power limiting materials, for which a ultraviolet/visible absorption spectrum has been calculated. The second is a family of molecular probes called luminescent conjugated oligothiophenes, used to detect and characterize amyloid proteins, for which both absorption and fluorescence spectra have been calculated. Finally, infrared and Raman spectra have been calculated for a group of branched oligothiophenes used in organic solar cells.In addition, solvation effects have been studied for conjugated poly\-eletrolytes in water, resulting in the development of two solvation models suitable for this class of molecules. The first uses a quantum meachanics/molecular mechanics (QM/MM) description, in which the solute mole\-cule is described using accurate quantum mechanical methods while the surrounding water molecules are described using point charges and polarizable point dipoles. The second discards the water entirely and removes the ionic groups of the solute. The QM/MM model provides highly accurate results while the cut-down model gives results of slightly lower quality but at a much reduced computational cost.Finally, a study of protein-dye interactions has been performed, with the goal of explaining changes in the luminescence properties of the LCO chromophores when in the presence of amyloid proteins. Results were less than conclusive.
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| 1507. |
- Skallberg, Andreas, 1983-
(författare)
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Photoemission and Characterization of Neutrophils and Nanoparticles : Energy Mapping and Elemental Composition with sub-µm Resolution
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Imaging and visualization of cells and tissues are important when studying various biological phenomena. The ability to provide spatial information with molecular and chemical specificity may increase our insight and understanding of biological problems within life sciences. There is a need for well suited analytical imaging tools for addressing challenges that can increase our knowledge from the visualization on the cellular and subcellular level. In this thesis, we have focused on the use of surface analytical techniques based on the photoemission process. Synchrotron based surface analytical tools such as mirror electron microscopy, low energy electron microscopy, X-ray photoelectron spectroscopy, X-ray photoemission electron microscopy and near edge X-ray absorption fine structure spectroscopy were used to obtain highly resolved chemical information for both fundamental biological systems and technical innovations.A combined photoemission electron microscopy and imaging X-ray photoelectron spectroscopy instrument have been used for visualization and characterization of neutrophils attached to silicon and gold surfaces. Neutrophils are white blood cells and a major part of our innate immune system. In the body they circulate and scavenge for possible threats, such as pathogens. The neutrophils possess three main defense mechanisms to tackle any possible threat in the body. One of these mechanisms is the release and formation of extracellular traps used for entrapping and capturing. We have visualized the extracellular trap formation in presence of nanoparticles and images of the neutrophils have been obtained with threshold mapping and work function contrast from energy-filtering operations together with element specific imaging and chemical maps. We demonstrated work function variation in imaging mode for the cellular morphology and the characteristic polymorphonuclear morphology of the nucleus. These results demonstrate the potential and extend the use of photoemission electron microscopy and imaging X-ray photoelectron spectroscopy as analytical tools for visualization of biological materials and processes on the cellular level.The use of nanoparticles in recent years have significantly increased. Today, nanoparticles are being used in a wide range of applications, such as in electronics, energy, biology, and medicine. One hot topic in medicine is the development of contrast enhancement agents for magnetic resonance imaging. We report the development of two types of nanoparticles to be used as contrast enhancers for magnetic resonance imaging. The first type is water-dispersible and ultra-small Fe3O4 nanoparticles coated with polyacrylic acid. The Fe3O4 nanoparticles exhibit good magnetic properties, biocompatibility, excellent relaxivity properties and can be employed as a potential dual T1 and T2 weighted contrast agent. The second type is cerium oxide nanoparticles with the integration of gadolinium. Cerium oxide has unique redox properties due to the coexistence of Ce3+ and Ce4+ states making them suitable for scavenging reactive oxygen species. The integration of gadolinium makes these nanoparticles promising contrast agents with both therapeutic and diagnostic properties. We have designed a new technical innovative energy saving process where a reduction in the annealing temperature for oxide removal is obtained, by the presence of europium doped gadolinium oxide nanoparticles in comparison to Eu3+ and Gd3+. A low coverage of nanoparticles and ions revealed a significant reduction in annealing temperature for the oxide removal. These results deliver a promising one step energy saving strategy of producing silicon-based contacts. In summary, this thesis work demonstrates the power of element specific imaging and chemical mapping of bio-related surfaces as well as nanoparticle tracking in the sub-micro and nano region.
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| 1508. |
- Sklyar, Alexey, 1991-
(författare)
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Digital servitization : Organizing the firm and working with the ecosystem
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traditionally, equipment sales were the main source of revenues for manufacturing firms. The situation has changed, and such firms are undergoing servitization when revenues are increasingly derived from services. In parallel, the digitalization of industries brings novel technologies to the forefront of manufacturers’ agendas. With servitization and digitalization converging, many firms are now undergoing digital servitization. Both internal focus and external focus appear important for digital servitization; yet, the extant research remains scarce, explaining the need to further explore the phenomenon’s intra- and inter-organizational sides. To this end, the present thesis aims to describe and analyze how manufacturing firms manage digital servitization internally and externally.Building upon the academic literature in industrial marketing and related disciplines, this thesis leverages five appended papers as its empirical foundation. On the intra-organizational side, the empirical findings concern how firms can organize for digital servitization. Specifically, the findings point toward organizing the structure, where a particular emphasis lies on service and product units, especially alongside the spectrum of central/local and front-end/back-end roles and functions. Furthermore, the empirical evidence suggests that organizing the support for digital servitization requires an internal focus on data (together with relevant digital technologies and software), responsiveness, and agility.On the inter-organizational side, the findings concern how firms can work with their ecosystems. First, working with the vision for digital servitization involves different ecosystem actors, where digitalization-related factors and the timing of relevant initiatives are of importance. Second, working with customers is associated with digital infrastructure for efficient service provision, digital competences of customers, and novel sources and types of value propositions. Third, working with partners requires large-scale, extensive collaboration around digital servitization initiatives, where both commercial and non-commercial actors play an important role. Moreover, the empirical evidence on the inter-organizational side suggests relevant capabilities when working with ecosystems.In terms of theoretical implications, the present thesis contributes to business marketing research and cross-disciplinary servitization research, belonging to the growing stream of literature that studies intra- and inter-organizational sides of digital servitization. Finally, as managerial implications, this thesis offers suggestions for manufacturers on how to organize the structure and the support for digital servitization, as well as how to work with the external business environment.
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| 1509. |
- Skoglar, Per
(författare)
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Tracking and Planning for Surveillance Applications
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vision and infrared sensors are very common in surveillance and security applications, and there are numerous examples where a critical infrastructure, e.g. a harbor, an airport, or a military camp, is monitored by video surveillance systems. There is a need for automatic processing of sensor data and intelligent control of the sensor in order to obtain efficient and high performance solutions that can support a human operator. This thesis considers two subparts of the complex sensor fusion system; namely target tracking and sensor control.The multiple target tracking problem using particle filtering is studied. In particular, applications where road constrained targets are tracked with an airborne video or infrared camera are considered. By utilizing the information about the road network map it is possible to enhance the target tracking and prediction performance. A dynamic model suitable for on-road target tracking with a camera is proposed and the computational load of the particle filter is treated by a Rao-Blackwellized particle filter. Moreover, a pedestrian tracking framework is developed and evaluated in a real world experiment. The exploitation of contextual information, such as road network information, is highly desirable not only to enhance the tracking performance, but also for track analysis, anomaly detection and efficient sensor management. Planning for surveillance and reconnaissance is a broad field with numerous problem definitions and applications. Two types of surveillance and reconnaissance problems are considered in this thesis. The first problem is a multi-target search and tracking problem. Here, the task is to control the trajectory of an aerial sensor platform and the pointing direction of its camera to be able to keep track of discovered targets and at the same time search for new ones. The key to successful planning is a measure that makes it possible to compare different tracking and searching tasks in a unified framework and this thesis suggests one such measure. An algorithm based on this measure is developed and simulation results of a multi-target search and tracking scenario in an urban area are given. The second problem is aerial information exploration for single target estimation and area surveillance. In the single target case the problem is to control the trajectory of a sensor platform with a vision or infrared camera such that the estimation performance of the target is maximized. The problem is treated both from an information filtering and from a particle filtering point of view. In area exploration the task is to gather useful image data of the area of interest by controlling the trajectory of the sensor platform and the pointing direction of the camera. Good exploration of a point of interest is characterized by several images from different viewpoints. A method based on multiple information filters is developed and simulation results from area and road exploration scenarios are presented.
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| 1510. |
- Skoglund, Anders
(författare)
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Multivariate modelling and monitoring for stabilisation of paperboard manufacturing
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many variables are measured on-line in various processes, and this can produce data draining for the operators. One way to extract information from process measurements is to use multivariate methods in monitoring the process. This thesis presents an approach to constructing robust models from historical data, without having to conduct designed experiments. This is achieved by using data from at least one year to cover process variation and by validating the model with external data; objects are selected according to a criteria function.Linear (PLS) and non-linear (ANN) models are compared in terms of their ability to monitor and predict. PLS models were best for monitoring, because they detect process deviations early; on the other hand, ANN models performed better in prediction, due to their ability to handle signal errors.Bearing this in mind, a multivariate model was created and used on-line to monitor paperboard manufacturing, and proved to be a tool much appreciated by operators. A prestudy of how the application could be further improved by augmenting it with a knowledge-based system was also performed.In addition, a study was done in which VIS and NIR spectra were recorded online and used in satisfactorily predicting product properties.Various multivariate methods are briefly described in the thesis. The methods are multivariate data analysis, artificial neural networks, knowledge-based systems,and design of experiments. Various multivariate methods can be used to solve the same type of problems. Since different methods have different advantages, there are no conflicts between the methods. What is important is to choose the right method for a specific problem; often a combination of several methods can perform better than any single method.
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