| 1. |
- Berginström, Nils, 1984-
(författare)
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Fatigue after traumatic brain injury : exploring novel methods for diagnosis and treatment
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Traumatic brain injury (TBI) is one of the most common causes of disability and mortality. While some patients recover quickly, especially at the mild side of the injury severity continuum, many will experience symptoms for years to come. In this chronic phase, patients report a wide array of symptoms, where fatigue is one the most common. This fatigue makes huge impact in several areas of these patients’ lives. Despite the prevalence of fatigue after TBI, the underlying mechanisms are unclear. Further, there are no standardized way for assessment and diagnosis, and there are no treatments with satisfying empirical support. The aim of this thesis was to examine the effects of the novel compound OSU6162 on fatigue in patients with TBI, and to explore functional and structural brain imaging correlates of fatigue after TBI.Methods: Studies I and III were based on a placebo-controlled, double-blinded clinical trial examining the effects of the monoaminergic stabilizer OSU6162 on fatigue in patients in the chronic phase of traumatic brain injury. In study I, self-assessment scales of fatigue and neuropsychological tests were used as outcomes, while functional magnetic resonance imaging (fMRI) blood-oxygen-level dependent (BOLD) signal was the primary outcome in study III. Studies II and IV used cross-sectional designs, comparing patients with TBI with age- and gender matched healthy controls. Study II examined whether fMRI BOLD signal could be used to detect and diagnose fatigue in patients with TBI, and study IV whether white matter hyperintensities (WMH) contribute to lower cognitive functioning and presence of fatigue after TBI.Results: Study I revealed no effects of OSU6162 during 28 days of treatment at maximum doses of 15 mg twice daily on measures of fatigue or any other outcome. The results from study II indicated that fatigue after TBI is linked to alterations in striato-thalamic-cortical loops, and suggested that fMRI could be a promising technique to use in the diagnosis of fatigue after TBI. In study III the results revealed effects of treatment in the right occipitotemporal and orbitofrontal cortex. In these areas, the BOLD response was normalized in the OSU6162 group as compared to healthy controls, while the placebo group showed a steady low activity in these areas. The regional effects were located outside the network shown to be linked to fatigue in study II, which might explain why there were no effects on fatigue after treatment with OSU6162 in study I. Study IV showed that WMH lesions increased with increased TBI severity, but the presence and extent of lesions did not explain lower neuropsychological functioning or fatigue in subjects with previous TBI.Conclusions: In summary, although no effects on fatigue after treatment with OSU6162 were seen, the results provide support to the theory that fatigue after TBI is linked to alterations in striato-thalamic-cortical loops, and on how fatigue after TBI could be assessed or diagnosed using fMRI. Structural damage within white matter was however not related to fatigue.
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| 2. |
- Franke, Ulrik, 1981-
(författare)
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Analysis of enterprise IT service availability : Enterprise architecture modeling for assessment, prediction, and decision-making
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Information technology has become increasingly important to individuals and organizations alike. Not only does IT allow us to do what we always did faster and more effectively, but it also allows us to do new things, organize ourselves differently, and work in ways previously unimaginable. However, these advantages come at a cost: as we become increasingly dependent upon IT services, we also demand that they are continuously and uninterruptedly available for use. Despite advances in reliability engineering, the complexity of today's increasingly integrated systems offers a non-trivial challenge in this respect. How can high availability of enterprise IT services be maintained in the face of constant additions and upgrades, decade-long life-cycles, dependencies upon third-parties and the ever-present business-imposed requirement of flexible and agile IT services?The contribution of this thesis includes (i) an enterprise architecture framework that offers a unique and action-guiding way to analyze service availability, (ii) identification of causal factors that affect the availability of enterprise IT services, (iii) a study of the use of fault trees for enterprise architecture availability analysis, and (iv) principles for how to think about availability management.This thesis is a composite thesis of five papers. Paper 1 offers a framework for thinking about enterprise IT service availability management, highlighting the importance of variance of outage costs. Paper 2 shows how enterprise architecture (EA) frameworks for dependency analysis can be extended with Fault Tree Analysis (FTA) and Bayesian networks (BN) techniques. FTA and BN are proven formal methods for reliability and availability modeling. Paper 3 describes a Bayesian prediction model for systems availability, based on expert elicitation from 50 experts. Paper 4 combines FTA and constructs from the ArchiMate EA language into a method for availability analysis on the enterprise level. The method is validated by five case studies, where annual downtime estimates were always within eight hours from the actual values. Paper 5 extends the Bayesian prediction model from paper 3 and the modeling method from paper 4 into a full-blown enterprise architecture framework, expressed in a probabilistic version of the Object Constraint Language. The resulting modeling framework is tested in nine case studies of enterprise information systems.
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| 3. |
- Nordström, Susanna, 1975-
(författare)
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Configurable Hardware Support for Single Processor Real-Time Systems
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes a further development of a building block for programmable devices in embedded systems handling real-time functionality.Embedded systems are included in a variety of products within different technical areas such as industrial automation, consumer electronics, automotive industry, and communication-, and multimedia systems. Products ranging from trains and airplanes to microwave ovens and washing machines are controlled by embedded systems.Programmable devices constitute a part of these embedded systems. Today, a programmable device can include a complete system containing building blocks connected with each other via programs written using a hardware description language. The programmable devices can be programmed and changed over and over again and this flexibility makes it possible to explore how these building blocks can best be designed in relation to system requirements, before final implementation.This thesis describes a further development of a building block for programmable devices implemented in a non-traditional way, i.e., the implementation is written using both hardware description language and traditional software languages. This new building block handles real-time functionality in a non-traditional way that enables certain benefits, such as increased performance, predictability and less memory consumption. Using a non-traditional implementation also has its drawbacks, and e.g., extensions and adjustments can be hard to handle since modifications are required in both hardware and software programming languages.The new building block was investigated in order to see how it could be facilitated when used for real-time functionality. The configurability of the block was extended which enables further customization of the building block. This leads to the possibility to use the block within a wider spectrumof applications. It is also possible to reduce the size and cost of the final product since resource usage can be optimized.Furthermore, a mathematicalmodel estimating resource usage for real-time functionality has been developed. The model enables distinctive trade-offs comparisons, and guidance for system designers, when considering what type of real-time operating system to use in a certain design.
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| 4. |
- Paridari, Kaveh, 1987-
(författare)
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Hierarchical energy management in smart grids : Flexibility prediction, scheduling and resilient control
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric power industry and society are facing challenges and opportunitiesof transforming the present power grid into a smart grid. Energymanagement systems (EMSs) play an important role in smart grids. A generalhierarchical structure for EMSs is considered here, which is composed ofa lower layer and an upper layer.The first research objective of the thesis is detailed modeling, schedulingand control of flexible loads at the lower layer of EMSs. To do this, a wellstudiedframework has been extended, which focuses on scheduling of staticloads and dynamic loads for home energy management systems (HEMSs).Then, a robust formulation of the framework is proposed, which takes theuser behavior uncertainty into account so that the cost of optimal schedulingof appliances is less sensitive to unpredictable changes in user preferences.Considering that the optimization algorithms in the proposed framework canbe computationally intensive, an efficient plug-and-play policy is proposedand validated through several simulation studies.The second research objective is to predict, plan, and control the aggregatedflexible load at the upper layer. Here, an iterative distributed approachamong aggregator and HEMSs is designed, to maximize the aggregated profitmade out of the shared energy storage system, while technical and operationalconstraints are satisfied. In addition, a strategy is proposed for flexibilityprediction of aggregated heterogeneous thermostatically controlled loads ina single micro-community of households. Then, algorithms are designed forplanning and control of aggregated flexibility in several micro-communities,to be used for bidding in energy and reserve markets.To meet these research objectives, the control systems in the hierarchicalEMSs are connected over IT infrastructures and are in interaction with endusers.While this is done to achieve economical and environmental goals,it also introduces new sources of uncertainty in the control loops. Thus,the third research objective is to design policies to make the EMSs resilientagainst uncertainties and cyber attacks. Here, the user behavior uncertaintyhas been modeled, and a robust formulation is designed so that the optimalsolution for scheduling of appliances is more resilient to the uncertainties. Inaddition, fault-tolerant control techniques have been applied to a hierarchicalEMS to mitigate cyber-physical attacks, with no need for major re-designof the local control loops in already existing EMSs. Moreover, stability andoptimal performance of the proposed attack-resilient control policy have been proven.
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| 5. |
- Stoll, Pia, 1969-
(författare)
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Residential Demand Response in the Context of European Union Energy Policy
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to achieve energy security, reduce global warming and promote the vision of a common electricity market, the European Union (EU) is transforming the EU electricity grid from a large set of independent hierarchical national grids into one meshed EU-wide grid. For the first time in the history of the electric power industry, residential consumers are being integrated into the grid as active consumers and micro-generators of electricity. In the near future, residential buildings in the EU will have to use much less energy and the right source of energy. If residential consumers want to maintain the same level of energy service, buildings will have to use and produce energy differently. Decentralised energy production from renewable energy sources beside or within residential buildingsis required. Distribution grids will receive more locally produced energy and be more autonomous. Suppliers and distribution system operators will have to change business models from quantity-based to service-based. As residential consumers become more active in the EU, residential system developers need to understand what and how system requirements can support EU energy policy. This thesis therefore interprets EU energy policy concerns in terms of factors influencing the residential demand response system design. To test the viability of the influencing factors, system design was constructed and prototyped. One important influencing factor,the “greenness” of electricity information, was concretised as a dynamic CO2 signal and integrated into the system design as a residential demand response signal. The dynamic CO2 signal was not always correlated with the dynamic price of electricity, but there were strong indications that the CO2 intensity signal can and should be used as a supplement to the price signal in the residential demand response system to increase motivation for energy savings. It was found that a CO2 intensity-driven Time-of-Use tariff can be developed, based on forecasts of the hourly wholesale market price and the CO2 intensity, and that this tariff is beneficial for both supplier and household. The thesis thus demonstrates that it is possible to extract system design-influencing factors from EU energy policy and use these for the design and implementation of a residential demand response system.
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| 6. |
- Armendáriz, Mikel
(författare)
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Cost-effective Communication and Control Architectures for Active Low Voltage Grids
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional flow of power. However, nowadays the massive integration of distributed energy resources into distribution grids, such as solar photovoltaics, distributed storage, electric vehicles and demand response programs, presents some challenges. For instance, the unidirectional top-down power flow is being replaced by power flows in any direction: top-down and bottom-up. This paradigm shift adds extra regulatory, economic, and technical complexity for the Distribution System Operators (DSO). Thus to overcome the possible operational constraints, thermal limits, or voltage problems in the grid, an update of the existing electricity infrastructures is required. In response to this new situation, this thesis investigates the cost-effective communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a DSO’s perspective. The solutions include: i) optimal sensor placement configuration to perform low voltage state estimation, ii) optimal metering infrastructure designs for active low voltage monitoring applications, iii) coordinated control strategies to allow the integration of microgrid-like structures into the distribution grids, iv) optimal placement of actuators for operating the control strategies, v) a multiagent-based control solution for self-healing and feeder reconfiguration applications, and vi) a framework model and simulations to assess the reliability of the ICT infrastructure that enables the monitoring and control applications. As concluding remark, since the deployment of technology at low voltage grids is restricted to assets owned by the DSO, the operability of the grid is limited. This condition makes it so that the required communication and control enhancement solutions shall prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analyses of the potential improvement solutions for each grid, because this will allow deploying the right technology only at the necessary locations.
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| 7. |
- Babazadeh, Davood
(författare)
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Distributed Control of HVDC Transmission Grids
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent issues such as priority access of renewable resources recommended by European energy directives and increase the electricity trading among countries lead to new requirements on the operation and expansion of transmission grids. Since AC grid expansions are limited by legislative issues and long distance transmission capacity, there is a considerable attention drawn to application of HVDC transmission grids on top of, or in complement to, existing AC power systems. The secure operation of HVDC grids requires a hierarchical control system. In HVDC grids, the primary control action to deal with power or DC voltage deviations is communication-free and local. In addition to primary control, the higher supervisory control actions are needed to guarantee the optimal operation of HVDC grids. However, the implementation of supervisory control functions is linked to the arrangement of system operators; i.e. an individual HVDC operator (central structure) or sharing tasks among AC system operators (distributed structure).This thesis presents distributed control of an HVDC grid. To this end, three possible supervisory functions are investigated; coordination of power injection set-points, DC slack bus selection and network topology identification. In this thesis, all three functions are first studied for the central structure. For the distributed solution, two algorithms based on Alternating Direction Method of Multipliers (ADMM) and Auxiliary Problem Principle (APP) are adopted to solve the coordination of power injection. For distributed selection of DC slack bus, the choice of parameters for quantitative ranking of converters is important. These parameters should be calculated based on local measurements if distributed decision is desired. To this end, the short circuit capacity of connected AC grid and power margin of converters are considered. To estimate the short circuit capacity as one of the required selection parameters, the result shows that the recursive least square algorithm can be very efficiently used. Besides, it is possible to intelligently use a naturally occurring droop response in HVDC grids as a local measurement for this estimation algorithm. Regarding the network topology, a two-stage distributed algorithm is introduced to use the abstract information about the neighbouring substation topology to determine the grid connectivity.
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| 8. |
- Bultmark, Fredrik, 1973-
(författare)
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Distorted Space and Multipoles in Electronic Structure Calculations
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns methods for electronic structure calculations and some applications of the methods. The augmented planewave (APW) basis set and it’s relatives LAPW (linearised APW) and APW+lo (local orbitals) have been widely used for electronic structure calculations. Here a modification of the APW basis set based on a transformation of the basis functions from a curvilinear coordinate system. Applications to a few test systems show that the modified basis set may speed up electronic structure calculations of sparse systems. The local density approximation (LDA) is used in density functional theory. Although it is the simplest possible approximation possible for the unknown exchange-correlation energy functional, it has proven to give quite accurate results for a wide range of systems. LDA fails in systems where the non-local effects are important. By including non-local effects by adding an orbital dependent term to the energy functional, through for example the LDA+U method, the calculated properties of many materials are closer to experimental observations. In the thesis the most general formulation of the LDA+U method is presented and a new way of interpreting the results of a calculations by formulating the orbital dependent part of the energy functional in terms of multipole momentum tensors. Applications to some early actinide systems leads to a reformulations of Hund’s rules for polarisations associated with the spin and orbital magnetic moment and a suggestion for similar rules, Katt’s rules, valid in the strong spin orbit coupling regime.
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| 9. |
- König, Johan, 1983-
(författare)
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Analyzing Substation Automation System Reliability using Probabilistic Relational Models and Enterprise Architecture
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern society is unquestionably heavily reliant on supply of electricity. Hence, the power system is one of the important infrastructures for future growth. However, the power system of today was designed for a stable radial flow of electricity from large power plants to the customers and not for the type of changes it is presently being exposed to, like large scale integration of electric vehicles, wind power plants, residential photovoltaic systems etc. One aspect of power system control particular exposed to these changes is the design of power system control and protection functionality. Problems occur when the flow of electricity changes from a unidirectional radial flow to a bidirectional. Such an implication requires redesign of control and protection functionality as well as introduction of new information and communication technology (ICT). To make matters worse, the closer the interaction between the power system and the ICT systems the more complex the matter becomes from a reliability perspective. This problem is inherently cyber-physical, including everything from system software to power cables and transformers, rather than the traditional reliability concern of only focusing on power system components.The contribution of this thesis is a framework for reliability analysis, utilizing system modeling concepts that supports the industrial engineering issues that follow with the imple-mentation of modern substation automation systems. The framework is based on a Bayesian probabilistic analysis engine represented by Probabilistic Relational Models (PRMs) in com-bination with an Enterprise Architecture (EA) modeling formalism. The gradual development of the framework is demonstrated through a number of application scenarios based on substation automation system configurations.This thesis is a composite thesis consisting of seven papers. Paper 1 presents the framework combining EA, PRMs and Fault Tree Analysis (FTA). Paper 2 adds primary substation equipment as part of the framework. Paper 3 presents a mapping between modeling entities from the EA framework ArchiMate and substation automation system configuration objects from the IEC 61850 standard. Paper 4 introduces object definitions and relations in coherence with EA modeling formalism suitable for the purpose of the analysis framework.Paper 5 describes an extension of the analysis framework by adding logical operators to the probabilistic analysis engine. Paper 6 presents enhanced failure rates for software components by studying failure logs and an application of the framework to a utility substation automation system. Finally, Paper 7 describes the ability to utilize domain standards for coherent modeling of functions and their interrelations and an application of the framework utilizing software-tool support.
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| 10. |
- Lizárraga Jurado, Raquel, 1974-
(författare)
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Non-collinear Magnetism in d- and f-electron Systems
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, non-collinear magnetism has been studied by using density functional theory and the augmented plane wave method with local orbitals (APW+lo). Two conditions for non-collinear instabilities have been identified in this thesis. First, the Fermi energy should cut through both spin up and down states. Secondly, strong nesting between the spin up and spin down Fermi surfaces is needed. The two criteria described here can be fulfilled by tuning the exchange-splitting and/or by modifying the volume. Calculations on several elements; bcc V, bcc and fcc Mn, bcc Fe, bcc and fcc Co, and bcc and fcc Ni show that a non-collinear state can be stabilized provided that the criteria discussed above are met. More complex materials have also been analyzed in terms of these two criteria. The substitutional alloys TlCo2Se2-xSx are found in experiments to possess spin spiral structures for x = {0-1.5} and at a concentration x = 1.75 the alloys become ferromagnetic. As S takes the place of Se in the crystal structure the distance between the Co layers is reduced and the turn angle of the spin spiral becomes smaller until it totally vanishes at x = 1.75. This thesis show that the evolution of the magnetic structure in these alloys is the consequence of a modification of the distance between Co layers, which induces a change in the interlayer exchange coupling. Fermi surfaces have been analyzed in TbNi5 in order to determine nesting features which would be responsible for the magnetic spin spiral observed in this material. The electronic structure of CeRhIn5 is also reported in this thesis. Furthermore, the 3-k magnetic structure of UO2 was investigated and the crystal field levels were calculated. Transition metal systems such as Fe in the superconducting high-pressure hcp phase and in the fcc crystal structure were also studied. The results obtained for fcc Fe are in accordance with previous reports. However the paramagnetic state in hcp Fe is found to be more stable than the antiferromagnetic configurations discussed earlier in the literature as being favored in the volume range where the hcp phase is stable and superconductivity appears (~ 15 GPa). The complex non-collinear magnetic structure in Mn3IrSi was calculated and the results are found to be in good agreement with experiments.
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