| 1. |
- Adewumi, Oluwatosin, 1978-
(författare)
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Vector Representations of Idioms in Data-Driven Chatbots for Robust Assistance
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents resources capable of enhancing solutions of some Natural Language Processing (NLP) tasks, demonstrates the learning of abstractions by deep models through cross-lingual transferability, and shows how deep learning models trained on idioms can enhance open-domain conversational systems. The challenges of open-domain conversational systems are many and include bland repetitive utterances, lack of utterance diversity, lack of training data for low-resource languages, shallow world-knowledge and non-empathetic responses, among others. These challenges contribute to the non-human-like utterances that open-domain conversational systems suffer from. They, hence,have motivated the active research in Natural Language Understanding (NLU) and Natural Language Generation (NLG), considering the very important role conversations (or dialogues) play in human lives. The methodology employed in this thesis involves an iterative set of scientific methods. First, it conducts a systematic literature review to identify the state-of-the-art (SoTA) and gaps, such as the challenges mentioned earlier, in current research. Subsequently, it follows the seven stages of the Machine Learning (ML) life-cycle, which are data gathering (or acquisition), data preparation, model selection, training, evaluation with hyperparameter tuning, prediction and model deployment. For data acquisition, relevant datasets are acquired or created, using benchmark datasets as references, and their data statements are included. Specific contributions of this thesis are the creation of the Swedish analogy test set for evaluating word embeddings and the Potential Idiomatic Expression (PIE)-English idioms corpus for training models in idiom identification and classification. In order to create a benchmark, this thesis performs human evaluation on the generated predictions of some SoTA ML models, including DialoGPT. As different individuals may not agree on all the predictions, the Inter-Annotator Agreement (IAA) is measured. A typical method for measuring IAA is Fleiss Kappa, however, it has a number of shortcomings, including high sensitivity to the number of categories being evaluated. Therefore, this thesis introduces the credibility unanimous score (CUS), which is more intuitive, easier to calculate and seemingly less sensitive to changes in the number of categories being evaluated. The results of human evaluation and comments from evaluators provide valuable feedback on the existing challenges within the models. These create the opportunity for addressing such challenges in future work. The experiments in this thesis test two hypothesis; 1) an open-domain conversational system that is idiom-aware generates more fitting responses to prompts containing idioms, and 2) deep monolingual models learn some abstractions that generalise across languages. To investigate the first hypothesis, this thesis trains English models on the PIE-English idioms corpus for classification and generation. For the second hypothesis, it explores cross-lingual transferability from English models to Swedish, Yorùbá, Swahili, Wolof, Hausa, Nigerian Pidgin English and Kinyarwanda. From the results, the thesis’ additional contributions mainly lie in 1) confirmation of the hypothesis that an open-domain conversational system that is idiom-aware generates more fitting responses to prompts containing idioms, 2) confirmation of the hypothesis that deep monolingual models learn some abstractions that generalise across languages, 3) introduction of CUS and its benefits, 4) insight into the energy-saving and time-saving benefits of more optimal embeddings from relatively smaller corpora, and 5) provision of public access to the model checkpoints that were developed from this work. We further discuss the ethical issues involved in developing robust, open-domain conversational systems. Parts of this thesis are already published in the form of peer-reviewed journal and conference articles.
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| 2. |
- Ahmed, Mukhtiar
(författare)
-
Fluorine-Free Ionic Liquids and Electrolytes : From Synthesis to Energy Storage Applications
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since their introduction by Sony in 1990, lithium-ion batteries (LIBs) have acquired a sizable market share. They have the best energy densities, a high open circuit voltage, a low self-discharge rate, no memory effect, and a slow loss of charge when not in use. These properties make them the most popular rechargeable batteries for portable gadgets, electric vehicles and aerospace applications. They do, however, pose major safety issues since the conventional electrolytes are made of fluorinated salts dissolved in volatile organic solvents, the former being meta-stable at ambient temperature and the latter being flammable with a high vapour pressure. Thus, there is an urge to develop thermally and electrochemically stable non-fluorinated electrolytes to improve the safety and performance of batteries. Electrolytes based on ionic liquids (ILs) offer a range of advantages over traditional electrolytes including low volatility and high thermal and electrochemical stabilities, and can additionally be made fluorine-free and task-specific. In addition, the transport properties of ILs can be controlled by structural design of chemical functionalities to reduce the ionic interactions and enhance the ion mobilities.This thesis is focussed on the development of new fluorine-free ILs and electrolytes for safer energy storage applications. An overview of synthesis, physicochemical and electrochemical characterizations of six different families of ILs and their structurally analogous electrolytes based on the aromatic heterocyclic rings, oligoether based aromatic and aliphatic carboxylates, oligoether phosphates and aromatic sulfonyl anions coupled with n- tetrabutylphosphonium-, imidazolium-, pyrrolidinium-based and alkali metal cations is presented. The structures and purity of the new anions, their intermediate products and the ILs are characterized by using multinuclear NMR, FTIR and mass spectrometry. These studies are further complemented by using NMR diffusometry to investigate the relative anion and anion mobilities and understand the possible interaction mechanisms between the oppositely charged ions within the ILs and the electrolytes, and especially, the influence of Li+ addition in the IL-based electrolytes. Among the synthesized ILs, the sulfonyl-based ILs revealed highest thermal stabilities, aromatic oligoether-based ILs showed the best electrochemical stabilities and aromatic sulfonyl -based ILs exhibited highest ionic conductivities. Some of the synthesized salts displayed promising performance as electrolytes in energy storage devices.
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| 3. |
- Ahmer, Muhammad
(författare)
-
Intelligent fault diagnosis and predictive maintenance for a bearing ring grinder
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Predicting the failure of any structure is a difficult task in a mechanical system. However complicated and difficult the prediction might be, the first step is to know the actual condition of the system. Given the complexity of any machine tool, where a number of subsystems of electro-mechanical structures interact to perform the machining operation, failure diagnostics become more challenging due to the high demand for performance and reliability. In a production environment, this results in maintenance costs that the management always strives to reduce. Condition-based machine maintenance (CBM) is considered to be the maintenance strategy that can lead to failure prediction and reducing the maintenance cost by knowing the actual condition of the asset and planning the maintenance activities in advance.Grinding machines and grinding processes have come a long way since the inception of the centuries old grinding technique. However, we still have a number of challenges to overcome before a completely monitored and controlled machine and process can be claimed. One such challenge is to achieve a machine level CBM and predictive maintenance (PdM) setup which is addressed in this thesis. A CBM implementation framework has been proposed which combines the information sampled from sensors installed for the purpose of the process as well as condition monitoring. Accessing the machine's controller information allows the data to be processed with respect to different machine states and process stages. The successful implementation is achieved through a real-time and synchronized data acquisition setup that allows data from multiple sources to be acquired, stored, and consolidated. The dataset thus generated is used in a significant part of this project and is also published in Swedish National Data Service (SND).The thesis also presents the failure diagnostic model based on two step classification approach using benchmarked random forest models. The binary classifier predicts if there is a fault present in the machine based on crucial sensors data from the Idle segment of the grinding cycle. Multi-class random forest classifier diagnosis the fault condition. PdM, knowing when to trigger maintenance action, is achieved through predicting the overall quality of the produced parts from the feature set extracted from sensor data of the Spark-out segment of the grinding cycle. Combining fault diagnosis with the predicted quality information resulted in reliable and actionable maintenance decisions for the bearing ring grinder. The demonstrated setup, based on a production bearing ring grinder, is adaptable to similar machines in production.
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| 4. |
- Al-Madhlom, Qais
(författare)
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Potential Use of Aquifer Thermal Energy Storage System in Arid Regions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After the Oil Crises in 1973, which meant higher energy costs, the world started to look for other sources of energy. This led to the development of renewable energy techniques. Because of the intermittent nature of renewable energy, storage systems were also developed. Underground Thermal Energy Storage (UTES) systems spread and are now globally well known. In these systems, excess thermal energy (heat or cold) is stored (short term and/or long term) from the surplus period to periods of higher demand. The storage media in such systems are underground materials, e.g. rock, soil, and/or groundwater. The current study aims to examine the use of underground thermal energy storage systems in arid regions, in order to increase the efficiency of both cooling and heating systems in these regions, such that CO2 emissions and consumed electricity for these purposes are reduced. Three main parameters determine which type of Underground Thermal Energy Storage (UTES) systemis most suitable. These are site, design, and operation parameters. The site-specific parametersinclude soil properties and all geo-hydrological, environmental, geological, metrologicalconditions. Therefore, the site parameters cannot be changed after installing the storage system,since they majorly depend on the location, while the other parameters (design and operation) canbe changed after construction. The first primary goal of this study is to find how and what site parameters involved to specify the most suitable type of UTES systems in arid regions. Thus, the suitable type of UTES systems can be decided. The second primary goal is to answer how and where to select the best location to install the adopted system. To achieve the goals of the study, two arid regions within Iraq were used as case studies. They are Babylon and Karbala, where the former is characterized by its shallow aquifer, while the latter is characterized by a relatively deeper aquifer. The ArcMap-GIS software was used to prepare the relevant digital maps, e.g. maps of hydraulic conductivity, population, type of soil, aquifers, groundwater elevation, transmissivity, and slope. Then, the vulnerability (readiness for being polluted by the surface contaminants) maps of the available aquifers were determined, followed by finding the seepage velocity of the groundwater. Depending on the outputs of the vulnerability and the seepage velocity, the most suitable type of Underground Thermal Energy Storage (UTES) systems can be decided. This study, also, includes developing/inventing a general methodology that can be used to determine the best location to install Underground Thermal Energy Storage (UTES) systems, including Aquifer Thermal Energy Storage (ATES) systems. The last part of this study includes applying the suggested methodology to determine the best location to install the suitable type of Underground Thermal Energy Storage (UTES) system in the study area. The first study was in the Babylon Province. Here, groundwater table is very shallow (less than 2 m depth in some regions). The crystalline bedrock is at a depth of 9-12 km below the ground surface, overlaid by 9-12 km of sedimentary rocks on which there is a 2-50 m thick layer of alluvial silty clay sediments. The groundwater moves slowly in this aquifer (2.12*10-6 - 1.85*10-1) m/d, and it is brackish having salinity of 5000-10000 mg/l. The susceptibility (vulnerability) of the aquifer in northern part of Babylon province is low to very low having ranges from 80 to 120 on Drastic model scale, which has the overall range of 26 – 226 (i.e. 0.27- 0.47 on normalized vulnerability). The second study area was a part of Karbala Province. This area can be divided into two regions based on the geology and geo-hydrological conditions. An eastern part is located on the Mesopotamian plain, and a western part is located in Western Desert. In both parts, the groundwater table is relatively deeper than the Babylon province. In the eastern part, it is generally more than 4 mbgs (meter below ground surface). While, in the western part it is deeper and reaches to 48 mbgs in depth. The soil in the eastern part is alluvial silty clay, while the western part consists of gypcrete sandy deposits. The groundwater, which flows towards the east, has a seepage velocity range from 0 to 0.27 m/d. The salinity of the groundwater changes from slightly brackish (1000-3000) mg/l in the western parts to highly brackish (5000-10000) mg/l in the Mesopotamian parts of the province. By comparing the site parameters of each province with the different UTES systems, the type of thermal energy storage system was decided. The most important site parameters are the depth of the water table and the aquifer characteristics. For Babylon Province, the expected suitable underground thermal energy storage system is an aquifer thermal energy storage system in silty clay. For Karbala Province, two systems are suggested: for the eastern part, aquifer thermal energy storage system in silty clay is recommended, while for the western part, a deep (10-30 m depth) sandy aquifer thermal energy storage system is recommended. After that, a methodology was developed and used to determine the suitable location in which to install the Aquifer Thermal Energy Storage (ATES) system. For Babylon province, the site selection index ranges between 2.9 and 5.3 on 1 to 10 scale. About 71% of the region has a site selection index ranges between 4.71 and 5.3. Concerning Karbala study area, the site selection index ranges between 3.1 and 9.1. About 15% of the region has a site selection index between 8.1 and 9.1.The energy saving in neighboring countries to Iraq by using the Aquifer Thermal Energy Storage (ATES) system ranges from 55% to 72%. It is also expected that using a ground sink heat pump instead of a conventional air-to-air heat pump increases the COP (Coefficient Of Performance) of roughly (10) to (-17). The negative sign means that the heat is injected into the ground. More theoretical and field studies are required to cover the different aspects of the subject of potential use of Aquifer Thermal Energy Storage (ATES) system in an arid region, and to verify the improvement of COP (Coefficient Of Performance) due to using these systems.
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| 5. |
- Al-Maqdasi, Zainab, 1986-
(författare)
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Multifunctionality and Durability of Cellulosic Fiber Reinforced Polymer Composites
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall objective of this thesis is to develop and evaluate cellulose-based fiber composites with added multifunctionality for advanced applications. In the strive towards sustainable societies and industries, materials as well as production processes need to be assessed against the sustainability criteria and selected accordingly. Cellulosic fibers reinforced polymer composites are being increasingly used in applications where weight saving, and environmental friendliness is as important as structural performance. Nonetheless, these materials have their limitations regarding durability and stability of the properties, but their potential in use for advanced applications can be expanded if functionalized and considered beyond their structural performance. Such multi-functionality of composites can be achieved by the coating of fibers and/or modifying the matrix with functional reinforcement, or by both of these routes combined. Coating of fibers and modifying the matrix with nano-reinforcement are two selected approaches for imparting functionality to the cellulosic fiber composites in the current study. Conductive Regenerated Cellulose Fibers (RCFs) were produced by coating commercial RCFs with copper via electroless plating process. Electrical conductivity and mechanical performance were evaluated, and the coated fibers were transformed into an embedded strains sensor-like assembly that could be used as structural health monitoring system in composites structures. A noticeable degradation in the mechanical strength of fibers was realized and it was attributed to the influence of the chemicals of the final plating step of process on the chains of cellulose as well as the loss of crystalline order in the RCF. In order to obtain modified matrix (nanocomposites) for multifunctional wood polymer composites (WPC), the commercial masterbatches based on Graphene Nanoplatelets (GNPs) were utilized by melt extrusion process. Effect of the processing parameters in terms of change in screw configurations and the change in composition of the constituents on the structure and mechanical performance of the nanocomposites was studied. Results showed that there is insignificant effect of the change in the screw configuration in comparison with the effect of increasing the content of the GNPs. Stronger shear forces did not result in better dispersion of the nanoparticles. Addition of the compatibilizer, on the other hand, resulted in an adverse effect on the properties compared to the formulations where it is absent. The use of GNPs with larger aspect ratio resulted in much better improvement in the mechanical performance. Addition of the nanoparticles did not only improve mechanical performance but also resulted in increased thermal conductivity and diffusivity, especially when micro-scale reinforcement was added because of synergy between wood fibers and the GNPs. This synergy was reflected also in the significant 99% improved wear resistance and the >80% reduction in the creep strains of wood and graphene reinforced composites. During the design and selection of materials, quasi-static properties are often used as a selection criterion. However, in reality structures in use are often loaded during lengthy periods of time which are followed by multiple steps of unloading/reloading, depending on the service conditions. In such cases their time-dependent response becomes more crucial than instantaneous mechanical response. Typically, characterization of these properties requires a lot of time, but it may be significantly shortened if proper modeling and analysis are employed. The effect of addition of GNPs to the polymer and wood composites has been studied experimentally by short term creep tests. The materials showed highly nonlinear response even at very low loading stresses, but the addition of the nanoparticles resulted in a decrease in the nonlinearity and in the irreversible strains due to plasticity. Modelling approaches have been used to extract parameters from experimental data that could be used in predicting long term performance using Zapas model for viscoplasticity and Schapery’s model for nonlinear viscoelasticity. Overall, the results of the performed work contribute to enriching the research field with the potential the bio-based composites have to offer in the advanced application and how nano-scale reinforcement can interact synergistically with the micro-sized fibers to improve the overall performance of WPC and under different loading scenarios.
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| 6. |
- Al-Ramahi, Nawres Jabar, 1980-
(författare)
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Comprehensive numerical analysis of stress state in adhesive layer of joint including thermal residual stress and material non-linearity
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this work is to improve understanding of the stress state in the adhesive layer of bonded joints and identify key parameters which govern performance of adhesive joints. This information is crucial for the prediction of the failure initiation and propagation with the further estimation of the durability and strength of adhesively bonded structures.A systematic numerical analysis of stress state in the adhesive layer of a single-lap and double- lap joint under various loading conditions (thermal and mechanical loading) and an alternative methodology to predict the direction for crack propagation within adhesive layer are presented in this thesis. To identification of the most important parameters of joints is done based on the assessment of the peel and shear stress distributions in the adhesive layer. The thermal residual stresses arising after assembling of joints at elevated temperature are accounted for in the analysis.Initially, accurate, realistic 3D finite element model with novel boundary conditions (displacement coupling) was developed and validated. The employed boundary conditions allow to eliminate the edge effect and simulate the behavior of an infinite plate of composite laminate with off-axis layers (monoclinic materials). It is also possible to decouple the edge effects induced by the finite specimen width from the interaction with ends of the joint overlap region. Due to these advanced setting it is possible to eliminate influence of some of the parameters as well as to reduce geometry of the model without losing precision. Thus, the model is optimized with respect to the number of elements as well as element size distribution and does not require excessive computational power to obtain accurate stress distributions even near to the possible sites with stress perturbations (e.g. corners, cracks, etc). Additionally to the geometrical parameters, various material models have been employed in simulations of adhesive joints. A linear and non-linear material models (adherend and adhesive) was used for the single-lap joint, while a linear material behavior was considered for double-lap joint. The geometrical non-linearity was also included in the analysis whenever required. To make results more general and applicable to a wide range of different joints the normalized (with respect to the thickness of adhesive layer) dimensions of joints were used. Depending on the analyzed type of joint (single- or double- lap), combination of similar and dissimilar (hybrid) materials for adherends are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of the composite adherend (carbon and/or glass fibers) different laminate lay-ups were selected: uni-directional ([08]T and [908]T) and quasi-isotropic ([0/45/90/-45]S and [90/45/0/-45]S). In general, discussion and conclusions concerning the importance of various joint parameters are based on the magnitude of the peel and shear stress concentration at the ends of the overlap. In order to identify general trends with respect to the influence of mechanical properties of adherends the master curves for shear and peel stresses are constructed and analyzed. To simulate effect of the residual thermal stresses on the behavior of joints different methods for assembly of joints were considered (using dedicated adhesive or employing co-curing method). The results of this investigation lead to the conclusions that the one of the most important factors affecting the simulation results is the sequences of application of thermo-mechanical loading for different assembly methods. It is shown that simple superposition of thermal and mechanical stresses (most common approach) in the adhesive layer works properly only for linear material but it gives inaccurate results if non-linear material is considered. The thesis demonstrates the appropriate way to combine thermal and mechanical loads to obtain correct stress distributions for any material (linear and non-linear). The analysis of the influence of residual thermal stresses has shown that the peel and shear stress concentration at the ends of overlap joint and the shear stress within the over-lap region are reduced due to thermal effect. In case of composite adherend the co-curing assembly method is more favorable (in terms of reducing stress concentrations) than using adhesive for joining the materials.Finally, the simulation of the crack propagation within the adhesive layer for the bi-material (steel and composite) DCB sample with thick adhesive layer was carried out. The alternative to traditional fracture mechanics approach is proposed for the prediction of the crack path in the adhesive layer: a maximum hoop stress criterion. The hoop stress on the perimeters of a relatively large circle around the crack tip is evaluated to predict the direction of the crack extension with respect to the existing crack. The fracture mechanics is used to validate this approach and it is proved that if the Mode I is dominant for the crack propagation the hoop stress criterion be successfully used to predict crack path in the adhesive layer. This methodology is much more effective (in terms of required time and resources) than energy release based criterion or even X-FEM.The main result of this thesis is a tool to obtain accurate stress distributions in the adhesive layer of joints. This tool provided better understanding of the behavior of adhesive joints and allowed to develop new approach for prediction of crack propagation in the adhesive layer. This is definitely a development in the design of stronger, more durable adhesive joints for lighter structural components.
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| 7. |
- Albertsson, Kim
(författare)
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Machine Learning in High-Energy Physics: Displaced Event Detection and Developments in ROOT/TMVA
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many proposed extensions to the Standard Model of particle physics predict long-lived particles, which can decay at a significant distance from the primary interaction point. Such events produce displaced vertices with distinct detector signatures when compared to standard model processes. The Large Hadron Collider (LHC) operates at a collision rate where it is not feasible to record all generated data—a problem that will be exac-erbated in the coming high-luminosity upgrade—necessitating an online trigger system to decide which events to keep based on partial information. However, the trigger is not directly sensitive to signatures with displaced vertices from Long-lived particles (LLPs). Current LLP detection approaches require a computationally expensive reconstruction step, or rely on auxiliary signatures such as energetic particles or missing energy. An improved trigger sensitivity increases the reach of searches for extensions to the standard model.This thesis explores the possibility to apply machine learning methods directly on low-level tracking features, such as detector hits and hit-pairs to identify displaced high-mass decays while avoiding a full vertex and track reconstruction step.A dataset is developed where modelled displaced signatures from novel and known physics processes are mixed in a custom simulation environment, which models the in-ner detector of a general purpose particle detector. Two machine learning models are evaluated using the dataset: a multi-layer dense Artificial Neural Network (ANN), and a Graph Neural Network (GNN). Two case studies suggest that dense ANNs have difficulty capturing relational information in low-level data, while GNNs can feasibily discriminate heavy displaced decay signatures from a Standard Model background. Furthermore it was found that GNNs can perform at a background rejection factor of 103 and a signal efficiency of 20% in collision environments with moderate levels of pile-up interactions, i.e. low-energy particle collisions simultaneous with the primary hard scatter. Further work is required to integrate the approach into a trigger environment. In particular, detector material and measurement resolution effects should be included in the simulation, which should be scaled to model the High-Luminosity Large Hadron Collider (HL-LHC) with its more complicated geometry and its high levels of pile-up.In parallel, the machine learning landscape is quickly evolving and concentrating into large software frameworks with expanding scope, while the High-Energy Physics (HEP) community maintains its own set of tools and frameworks, one example being the Toolkit for Multivariate Analysis (TMVA) which is part of the ROOT framework. This thesis discusses the long- and short-term evolution of these tools, both current trends and some relations to parallel developments in Industry 4.0.
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| 8. |
- Alizadeh, Morteza, 1987-
(författare)
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Architectural Aspects of Identification in Decentralized Systems
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-level systems need identification techniques, where higher security and scalability are considered requirements. Identification plays a significant role in systems where smart electronic devices increase in zero trust and open environments like decentralized systems. Also, decentralization has emerged as one of the most exciting domains in recent years, again after the first Internet was invented. Besides, decentralization in identification systems has gained popularity worldwide since cryptocurrencies became part of businesses. Distributed Ledger Technology (DLT) and Distributed Hash Tables (DHT) can be appropriate decentralized solutions that improve identification to be much more secure, scalable, and trustworthy.The decentralized nature of DLT and DHT ensures no single point of failure, making them highly resilient to attacks. Blockchain as a DLT solution can help devices communicate with each other securely and trustably by storing an immutable history of transactions, providing an additional layer of security to identification systems. DHT senable applications to keep files and information immutable in a decentralized manner. DHTs ensure that the data is replicated across multiple nodes, making it highly resilient to data loss. Moreover, mitigating high storage costs without memory limitations is the target of these technologies. In this context, a decentralized system paradigm that combines systems with DLT and DHTs can be highly beneficial.This thesis argues for such a paradigm, and the contributions include introducing the term decentralized networks and architectures and demonstrating the feasibility of using blockchain as a DLT solution in real-world scenarios. These scenarios can be applied to the Internet of Things (IoT) or other Peer to Peer networked systems. We explore different architectures in various systems and analyze the interaction in blockchain. This thesis contributes to developing decentralized identification systems that provide users’ trust in an open environment. It presents the challenges associated with decentralized identification, including registry and storage issues, and proposes solutions using DLT and DHT. The immutability of DLT and DHTs provides fast and secure solutions for decentralized identification systems. In particular, we show that a DHT-based architecture is feasible to maintain decentralization while avoiding memory constraints. However, there is still room for improvement in terms of performance. Our investigation shows that combining DHTs with blockchain in decentralized identifiers improves performance.By concealing blocks in the private blockchain, we show that query performance is better than other DHT and public blockchain-based solutions without concealed information. Moreover, our results show that DHT performs better than the public blockchain for scenarios with many records.These findings highlight the importance of selecting the appropriate technology for decentralized identification systems, considering the specific use case and the number of records to be stored.We also consider different decentralized identification systems and platforms built based on the recommendation of W3C Decentralized Identifiers (DIDs). We found low-efficiency issues using this technology, resulting from leveraging public DLT in the data registry part of DIDs. That model has searching time problems if the DLT grows. Finally, this thesis helps to analyze these issues and find better solutions. By choosing the right technology, we can ensure that decentralized identifiers are efficient, secure, and scalable, which enables users to trust them in an open environment.
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| 9. |
- Almevall, Ariel
(författare)
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Health in later life: A nursing perspective
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ongoing demographic shift towards an older population calls for a corresponding shift to a proactive approach, aiming for health and well-being in old age. This dissertation addresses the need for increased knowledge about health in the context of aging at home. It explores the roles of relationships, home, health, and well-being while examining the various factors influencing health. The disseration also explores how key stakeholders in home care organizations percive a good life for older persons. From a nursing perspective, the disseration explores pathways of change and experiences related to health, guided by the caritative caring theory, which underscores health as wholeness and holiness. By thoroughly examining self-rated health, relationships, and the experiences of older persons receiving home support, along with key stakeholders' perceptions, the dissertation aims to provide valuable insights for nursing practices and the promotion of health in later life.This dissertation aims to explore health in later life, specifically concentrating on widowed women living alone with extensive home care needs. This exploration encompasses both the perspective of older widows and that of key stakeholders. For a comprehensive understanding health, the disseration also study self-rated health among older persons over a 20-year period, exploring its associations to health and well-being factors, including survival. Additionally, the dissertation explores the shared relationship between older women and nurses.This dissertation comprises one quantitative and three qualitative studies, all centred around older persons aged 80 years and older. Paper I is a quantitative, longitudinal study investigating changes in Self-Rated Health (SRH) across the aging spectrum. The study included 1595 participants initially (aged 59-79) and 541 participants at follow-up (age 80-96). Most participants rated their health as "Quite good" (54.5%) at baseline. Over the study period, 42.6% had stable SRH, 40.6% had declined, and 16.8% had improved. Changes in SRH were at follow-up significantly associated with age, pain, nutrition, cognition, walking aid use, self-paced gait speed, lower extremity strength, independence in activities of daily living, weekly physical exercise, outdoor activity, participation in organized activities, visiting others, morale, and depressive symptoms. SRH at baseline was significantly associated with survival (p<0.05). Paper II is a qualitative study about the concept of a good life for single-living older women with extensive care needs. This involved individual interviews with 11 participants aged 82-95, analysed through reflexive thematic analysis. Paper III is a qualitative description of key stakeholders' perceptions regarding a good life for the oldest old persons living at home with extensive care needs. The study utilized qualitative focus groups with 28 participants aged 31-69 (1 man, 27 women), analysed through qualitative content analysis. Paper IV is a qualitative study that aim to explore the meaning of relationship between older women and registered nurses in home care. The research employed qualitative methods, including focus groups and individual interviews, with 11 older women (aged 82-95) and 5 registered nurses (aged 35-47), analysed using qualitative content analysis. In conclusion, health in later life is not merely about avoiding a decline in health; rather, it involves integrating existing aspects into an ever-changing situation. However, challenges such as living alone, experiencing depressive symptoms, and coping with illness and/or functional disability can pose threats, risking overall health and survival. In contrast, for those living with disabilities and illnesses with extensive care needs, the significance of daily life becomes paramount. Simultaneously, the relationship between older women and registered nurse emerges as a recurring connection with the potential not only to enhance daily life but also to serve as a consistent and supportive presence in the home.
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| 10. |
- Anandika, Rayendra, 1988-
(författare)
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Non-destructive measurement of near-surface cracks in railheads : with focus on ultrasonic inspections
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Near-surface cracks in railhead that caused by rolling contact fatigue (RCF) is one of a kind rail defects that degrade rail track quality. Dependent on the trail load, the cracks can reach to severe level quickly. From many studies, the crack growth can be summarized as follows: At the first phase, the crack is initiated at the rail surface due to shear stresses created by the interaction between wheel and rail. The crack then propagates at about 30⁰ angle underneath. After a certain period of transition, the cracks starts propagating horizontally, vertically, or branching. If they propagates horizontally, the cracks potentially cause rail spalling. If they propagates vertically, then the cracks become more severe and dangerous.To overcome such defects, the infrastructure manager remove the top of railhead by performing rail grinding periodically. Prior the grinding, rail tracks need to be inspected to figure out how deep the cracks are by performing non-destructive testing (NDT). Eddy current testing (ECT) is one of the common method to estimate rail surface crack depths. Most of the practices in the industry, ECT estimates only the crack depth, without analyzing any other crack parameters, such as crack angle propagation, crack length, crack area, crack branches, etc. It also has no ability to identify multi-leveled cracks, sub surface cracks, dense cracks etc. Since depth is the only crack parameter that can be provided from ECT, the inspector have no knowledge about how severe the surface crack is. Whereas, information of crack phase, that is known from the crack profile (crack angle, crack depth and crack length) is beneficial to determine whether the crack is in initial or severe level. It also helps to decide the right time for grinding and avoid severe cracks remain long in the rails.Motivated by the benefit of knowing crack parameters, in this study, phased array ultrasonic transducer (PAUT) was used to inspect rail surface cracks. Generally, ultrasonic testing is used to inspect defect of rails at the far-field of the surface, such as at the body or bottom of the rails. Ultrasonic testing is not used to inspect near-surface cracks since the existence of dead zone at the few mm front of the transducer that is caused by piezoelectric crystal ringing inside the transducer. In this study, by utilizing wedge, phased array technique, and setting the optimum gain at the calibration process could decrease the existence of the dead zone. Thus the surface cracks can be observed clearly from the breaking surface to the deepest tip. At the measurement result, crack profile (propagation angle, depth and length), crack branches and multi-level cracks could be observed well. To verify the measurement result, the inspected railheads were sliced into pieces with uniform 0.65-mm thickness. From these pieces, 3D cracks networks were reconstructed. Complete information of crack profiles (angle, depth and length) of all cracks under the inspected surfaces were collected and well presented. From the reconstructed crack images, crack tips, multi-level cracks, and crack branches can be seen. These confirms that the measurement results could be used to observe crack profile well. For a brief description about the results, 3.5 mm crack tip depth and 6 mm crack length were estimated well with 8% and 4% error, respectively. Although the measurement system still have lack of detection for crack path that oriented sharply from the horizontal line parallel to the surface, since the ultrasonic waves could not be reflected back by these paths.At the end of this study, assessment about the potential of measurement speed of the used system when be applied to the rail field inspection was presented. The study is based on the state of the art available at this topic. The discussion is provided in order to motivate the application of the system to be chosen by the rail inspector to use it for the real rail field inspection.
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