| 1. |
- Abrahamsson, Olle, 1988-
(författare)
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On Aggregation and Dynamics of Opinions in Complex Networks
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies two problems defined on complex networks, of which the first explores a conceivable extension of structural balance theory and the other concerns convergence issues in opinion dynamics. In the first half of the thesis we discuss possible definitions of structural balance conditions in a network with preference orderings as node attributes. The main result is that for the case with three alternatives (A, B, C) we reduce the (3!)3 = 216 possible configurations of triangles to 10 equivalence classes, and use these as measures of balance of a triangle towards possible extensions of structural balance theory. Moreover, we derive a general formula for the number of equivalent classes for preferences on n alternatives. Finally, we analyze a real-world data set and compare its empirical distribution of triangle equivalence classes to a null hypothesis in which preferences are randomly assigned to the nodes. The second half of the thesis concerns an opinion dynamics model in which each agent takes a random Bernoulli distributed action whose probability is updated at each discrete time step, and we prove that this model converges almost surely to consensus. We also provide a detailed critique of a claimed proof of this result in the literature. We generalize the result by proving that the assumption of irreducibility in the original model is not necessary. Furthermore, we prove as a corollary of the generalized result that the almost sure convergence to consensus holds also in the presence of a fully stubborn agent which never changes its opinion. In addition, we show that the model, in both the original and generalized cases, converges to consensus also in rth moment.
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| 2. |
- Achieng, Pauline, 1990-
(författare)
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Analysis of the Robin-Dirichlet iterative procedure for solving the Cauchy problem for elliptic equations with extension to unbounded domains
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we study the Cauchy problem for elliptic equations. It arises in many areas of application in science and engineering as a problem of reconstruction of solutions to elliptic equations in a domain from boundary measurements taken on a part of the boundary of this domain. The Cauchy problem for elliptic equations is known to be ill-posed.We use an iterative regularization method based on alternatively solving a sequence of well-posed mixed boundary value problems for the same elliptic equation. This method, based on iterations between Dirichlet-Neumann and Neumann-Dirichlet mixed boundary value problems was first proposed by Kozlov and Maz’ya [13] for Laplace equation and Lame’ system but not Helmholtz-type equations. As a result different modifications of this original regularization method have been proposed in literature. We consider the Robin-Dirichlet iterative method proposed by Mpinganzima et.al [3] for the Cauchy problem for the Helmholtz equation in bounded domains.We demonstrate that the Robin-Dirichlet iterative procedure is convergent for second order elliptic equations with variable coefficients provided the parameter in the Robin condition is appropriately chosen. We further investigate the convergence of the Robin-Dirichlet iterative procedure for the Cauchy problem for the Helmholtz equation in a an unbounded domain. We derive and analyse the necessary conditions needed for the convergence of the procedure.In the numerical experiments, the precise behaviour of the procedure for different values of k2 in the Helmholtz equation is investigated and the results show that the speed of convergence depends on the choice of the Robin parameters, μ0 and μ1. In the unbounded domain case, the numerical experiments demonstrate that the procedure is convergent provided that the domain is truncated appropriately and the Robin parameters, μ0 and μ1 are also chosen appropriately.
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| 3. |
- Alijan Farzad Lahiji, Faezeh
(författare)
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Epitaxy of oxide and nitride thin films grown by magnetron sputtering
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need for electronic devices with new functionalities has caused research to move in a way to design and utilize materials with high-performance thermoelectricity, widely used in batteries, sensors, and electronic devices. Two-dimensional materials (2D) with unique structures and remarkable properties have been identified to fabricate oxide heteroepitaxy. The growth of heteroepitaxy has been focused on the growth of high-quality films on single crystalline substrates. The preferred orientation and the crystallization of the materials with thin or two-dimensional structures require an understanding of epitaxy. In epitaxial growth, using a specific, well- defined substrate with lattice constants close to that film is decisive in controlling the film orientation with high epitaxial quality. The electrical, optical, magnetic, and structural properties of the film are strongly determined by the texture and its epitaxial alignment. The majority of studies report epitaxial growth on Si and sapphire with different crystallographic orientations. The family of NaCl-structured materials covers a variety of nitrides and oxides broadly used in science and technology that have been epitaxially grown on monocrystalline Si and sapphire (Al2O3). In this thesis, the structure and optical properties of NiO are investigated as functions of oxygen content on Si(100) and c-Al2O3 using pulsed dc reactive magnetron sputtering. It is found that NiO with cubic structure is a single phase with predominant orientation along (111) on both substrates. It is fiber textured on Si(100), while twin domain epitaxy is achieved on c-Al2O3. The growth of two cases of metal oxide and nitride films (NiO and CrN) with rock-salt (NaCl) structure is also demonstrated on r-plane sapphire. It is revealed that the NaCl-structured materials NiO and CrN grow with a tilted orientation relative to the substrate. This characterization and analysis of the epitaxy, crystallography, and growth modes yield a single and identical epitaxial relationship of these two cubic materials on r-plane sapphire, in contrast to earlier studies on NaCl-structured materials on r-plane sapphire, indicating several different orientation relationships. The results advance the understanding of growth modes and unusual epitaxial relationships of two cases of metal oxide and nitride films with rock-salt (NaCl) structure broadly used in science and technology on r-plane sapphire.
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| 4. |
- Alkusaibati, Wael, 1990-
(författare)
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Digitalized Co-production of Emergency Response : Using Volunteers as First Responders
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Contemporary global challenges like global warming, rapid urban development, and the current unstable security situation, lead to an increase in large-scale crises (e.g., forest fires) alongside frequent smaller emergencies (e.g., house fires and traffic accidents). The increase in emergencies strains professional response organizations, necessitating additional resources. Civilian volunteers are therefore increasingly being integrated into the response system. The development is mediated by information and communication technologies (ICTs) which enable communication between professional responders (e.g., the municipal rescue services, the emergency medical services, the Public Swedish Answering Point) and citizens. While many studies focus on spontaneous volunteer activities emerging on social media, fewer examine organized volunteerism initiatives at the local emergency response level. Over a decade ago, a municipal rescue service in northern Sweden established an initiative recruiting volunteers as first responders and equipping them with basic response tools. The volunteers undergo training in tasks such as cardiopulmonary resuscitation (CPR) and fire extinguishing. They are dispatched to predefined response tasks using simple ICT applications like SMS lists or mobile apps. This initiative has expanded to other areas due to perceived benefits such as shorter response times and reduced casualties and material damage. The phenomenon can be labelled as an emerging form of ICT-enabled or digitalized co-production of public services. However, previous research indicates a research gap in understanding, describing, and defining this type of co-production. The overall aim of the thesis is to describe how these ICT-enabled initiatives emerge and develop over time and identify the related effects on the response system. This is expected to provide recommendations on how they can be developed and supported. This aim is divided into three specific objectives, where each has been addressed through a research paper: 1- identifying how the existing literature describes ICT-enabled/digitalized volunteerism in large- and small-scale emergencies, 2- identifying how these initiatives emerge and operate, and can be maintained in small-scale emergencies, introducing more systematized knowledge on this concept, 3- initially evaluating the contributions of volunteers in the initiatives. Leaning on a case study approach inspired by action research, a combination of data collection methods has been adopted, e.g., a literature review, interviews, and incident reports filled out by volunteers. For the data analysis, the theoretical lens of ICT-enabled/digitalized co-production of public services has been applied. The first paper is a literature review study that examines digitally enabled volunteering activities in crises and small-scale emergencies. It highlights the prevalence of studies on volunteers using social media for crowdsourcing in crises, often termed digitalized volunteerism which entails virtual and, or physical contributions by volunteers to the response efforts. In contrast, fewer studies focus on volunteers' role in local small-scale emergencies, labelled as "hybrid" ICT-enabled or digitalized coproduction. The term hybrid here refers to the loose affiliation of the volunteers where they collaborate with the rescue services but are not officially associated through binding contracts. Hence, they are in between spontaneous and organized volunteerism. Both volunteering modes support professional response systems and display similar needs for steering, financial support, coordination, and integration of ICT artifacts. However, crises require increased coordination to manage uncertainties, risks, and data overload effectively. The second paper presents three models describing the emergence of hybrid digitalized co-production initiatives in urban and rural areas, as defined in Paper 1, along with how national authorities can support them. These models i.e., Rural, Urban, and National consist of three phases: Recruitment, Response, and Maintenance. Each model exhibits distinct characteristics. In rural areas for example, there is a need for more regular training due to low alerting frequency, and the possibility of using simple dispatch ICTs as cost-effective solutions. Conversely, urban areas have more alerts, necessitating more advanced ICTs, with less emphasis on regular training compared to rural areas. At the macro-level, the national model highlights roles that national actors can play such as facilitating a joint Application Programming Interface (API), joint insurance solutions, and an ICT system that can register incoming and active volunteers. The third paper is an initial evaluation of these initiatives at emergency sites, focusing on ICT-enabled dispatch, estimated response times, tasks performed, and collaboration with professionals, to assess the effects of using volunteers. This approach contrasts with previous studies that took an overall perspective and only used qualitative data. A total of 53 incident reports were collected from volunteers, revealing that volunteers arrived before professionals in twothirds of incidents, contributing to an average gain of 5 minutes. Additionally, volunteers performed a broader range of tasks than previously described, and often continued collaboration with professionals on-site, despite the initial expectation of handing over tasks upon the arrival of professional response actors. Also, comparing this data with the rural model from Paper 2, similarities and differences emerged. For instance, there was a higher number of alerts, and the basic ICTs used for dispatch were deemed insufficient, contrary to the model's perception. The thesis’ scientific contribution is a clearer conception of digitalized co-production of, above all, local emergency response as an emerging phenomenon. In the three papers, the ICT dispatch was identified as central and needs further development to enhance this co-production form. The thesis also sheds light on the need to integrate the initiatives into the official governmental frameworks. Furthermore, the thesis provides a primary understanding of how the concept works on the ground and provides an initial evaluation of the effects. In the practical field, the thesis offers insights into the importance of volunteers as additional resources to the official response systems, highlights challenges, hindrances, and enablers, and suggests potential solutions and improvements. Future work will include a further collection of incident reports for more reliable assessments and complementary interviews with volunteers. Also, the potential role of volunteers in larger crises, for example, as part of civil preparedness, will be further explored.
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| 5. |
- Andersson, Angelica
(författare)
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Mode choice modelling of long-distance passenger transport based on mobile phone network data
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reliable forecasting models are needed to achieve the climate related goals in the face of increasing transport demand. Such models can predict the long-term behavioural response to policy interventions, including infrastructure investments, and thus provide valuable pre-dictions for decision makers. Contemporary forecasting models are mainly based on national travel surveys. Unfortunately, the response rates of such surveys have steadily declined, implying that the respondents become less representative of the whole population. A particular weakness is that it is likely that respondents with a high valuation of time are less willing to respond to surveys (because they have less time available for such), and therefore there is a high chance that they are underrepresented among the respondents. The valuation of time plays an important role for the cost benefit analyses of public policies including transport investments, and there is no reliable way of controlling for this uneven sampling of time preferences. Fortunately, there is simultaneously an increase in the number of signals sent between mobile phones and network antennae, and research has now reached the point where it is possible to determine not only the travel destination but also the travel mode based on mobile phone network antennae connections. The aim of this thesis is to investigate if and how mobile phone network data can be used to estimate transportation mode choice demand models that can be used for forecasting and planning. Key challenges with using this data source in the context of mode choice models are identified and met. The identified challenges include uncertainty in the choice variable, the difficulty to distinguish car and bus trips, and the lack of information about the trip purpose. In the first paper we propose three possible model formulations and analyse how the uncertainty in the choice outcome variable would play a role in the different model formulations. We also conclude that it is indeed possible to estimate mode choice demand models based on mobile phone network data, with good results in terms of behavioural interpretability and significance. In the second paper we estimate models using a nested logit structure to account for the difficulty in separating bus and car, and a latent class model specification to meet the challenge of having an unknown trip purpose.
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| 6. |
- Andreasson, Martin, 1993-
(författare)
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The process of executing digital transformation strategies : Case studies in established Swedish manufacturing firms
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence of digital technologies has forced established firms to engage in a digital transformation. Digital transformations are complex and time-consuming processes, and therefore, they require unique strategies for coordinating and prioritizing activities. Existing research provides some examples of established Swedish firms engaging in digital transformations to keep up with competition. Responding to the need to better understand how these firms approach their digital transformation, this thesis explores how digital transformation strategies have been executed by established Swedish manufacturing firms and why some digital transformation strategies are realized whereas others are not.This thesis builds on digital transformation and digital transformation strategy literature. The term "digital transformation" primarily refers to firms’ incorporation of digital technologies into products and services, the development of new digital business models, and new organizational setups. The term "digital transformation strategy," likewise, refers to the process of executing the digital transformation.To answer the research questions presented in this thesis, I conducted two studies at two different firms. Study 1 was an embedded longitudinal single-case study conducted at the corporate unit and two business units of one firm and includes 30 interviews. Study 2 was a multiple-case study conducted at two firms and included six cases and a total of nine interviews.This thesis’ examination of digital transformation strategies demonstrates how the firms incorporated both basic- and advanced-level digital technologies into existing and new products and created new digital services. The firms also implemented new business models, such as e-commerce channels and pay-per-use payment schemes. Further, the firms also introduced new organizational setups, such as cross-functional teams and departments specializing in digital technologies and their potential applications. The execution of the digital transformation strategies was dynamic, and the firms regularly reformulated their strategies throughout the process. Furthermore, this study’s analysis of the execution of digital transformation strategies highlighted how managers interpreted the firm’s intentions and created emergent strategic responses to adapt to new digital technologies and customer demands. The firms measured the outcomes of the digital transformation strategy by considering both traditional measurements, such as return on investment, and new measurements, such as positive brand image and customer engagement.The thesis identified three key elements that impact whether or not a firm is able to realize its digital transformation strategy. First, new digital products and services must be aligned with market demands and customer needs. Second, internal and external collaboration support digital product and service development. Third, all dimensions of the digital transformation must be managed to avoid creating a misalignment between the firm’s digital transformation strategy and current business strategy.The execution of a digital transformation strategy requires managers to constantly reevaluate the strategy and respond to changing customer demands and available digital technologies. The lessons of this thesis can provide managers within digitally transforming firms with useful tools to improve the execution process of their digital transformation strategy.
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| 7. |
- Arnström, Daniel, 1994-
(författare)
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On Complexity Certification of Active-Set QP Methods with Applications to Linear MPC
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In model predictive control (MPC) an optimization problem has to be solved at each time step, which in real-time applications makes it important to solve these efficiently and to have good upper bounds on worst-case solution time. Often for linear MPC problems, the optimization problem in question is a quadratic program (QP) that depends on parameters such as system states and reference signals. A popular class of methods for solving such QPs is active-set methods, where a sequence of linear systems of equations is solved. The primary contribution of this thesis is a method which determines which sequence of subproblems a popular class of such active-set algorithms need to solve, for every possible QP instance that might arise from a given linear MPC problem (i.e, for every possible state and reference signal). By knowing these sequences, worst-case bounds on how many iterations, floating-point operations and, ultimately, the maximum solution time, these active-set algorithms require to compute a solution can be determined, which is of importance when, e.g, linear MPC is used in safety-critical applications. After establishing this complexity certification method, its applicability is extended by showing how it can be used indirectly to certify the complexity of another, efficient, type of active-set QP algorithm which reformulates the QP as a nonnegative least-squares method. Finally, the proposed complexity certification method is extended further to situations when enhancements to the active-set algorithms are used, namely, when they are terminated early (to save computations) and when outer proximal-point iterations are performed (to improve numerical stability).
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| 8. |
- Balachandran, Arvind, 1994-
(författare)
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Battery Integrated Modular Multilevel Converter Topologies for Automotive Applications
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electric vehicles are rapidly developing in response to the need for increasing sustainable energy sources. The range and lifetime of an electric vehicle are limited by the battery pack. A pack comprises modules with several parallel and/or series-connected cells. Differences in leakage currents and cell in-homogeneities cause individual cell voltage and state-of-charge distribution among the cells to be non-homogeneous. As a result, over time, some cells discharge faster than other cells, thus limiting the total energy delivered by the pack. In order to maximize the energy delivered by the pack, individual cell control is desirable. As a solution, battery-integrated modular multi-level converter (BI-MMC) topologies are proposed, presented, and evaluated. BI-MMC topology consists of either one or two arms per phase, and each arm comprises several cascaded stages of DC–AC converters and is commonly referred to as submodules. BI-MMCs provide increased controllability and potential improvement in the lifetime of the battery pack. Furthermore, BI-MMCs have low output total harmonic distortion, further improving the powertrain efficiency.The first contribution is the design and evaluation of 3-phase and 6-phase BI-MMCs; comparisons are made against a conventional 2-level inverter for a 40-ton 400 kW commercial vehicle. The evaluation considers the total number of submodules, energy rating of the DC-link capacitors, battery losses, capacitor losses, and semiconductor losses. The evaluation showed that the BI-MMCs have lower semiconductor losses than the conventional 2-level inverter. However, the BI-MMCs have higher capacitor and battery losses. The second contribution is the investigation of the impact that the number of series connected cells per submodule has on the total losses of the BI-MMC. The study showed that 5- to 6-series connected cells have the lowest losses. The third contribution is the design principles for optimization of the DC-link capacitors and the MOSFET switching frequency; this is supported by experimental validation for the loss distribution within a submodule. The fourth contribution is a methodology for determining the battery impedance using the full-load converter current. In a conventional battery pack, the battery is connected directly to the fast charger’s DC supply. However, in a BI-MMC, the battery and the inverter are integrated, potentially increasing the DC charging capabilities because higher voltages can be achieved during charging than during operation. The fifth contribution is thus the derivation and investigation of the maximum DC charging power of BI-MMCs assuming the same submodule semiconductor losses during traction. The analysis showed that most BI-MMCs have a maximum DC charging power of about 1MW.
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| 9. |
- Becirovic, Ema, 1992-
(författare)
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On Massive MIMO for Massive Machine-Type Communications
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To cover all the needs and requirements of mobile networks in the future, the predicted usage of the mobile networks has been split into three use-cases: enhanced mobile broadband, ultra-reliable low-latency communication, and massive machine-type communication. In this thesis we focus on the massive machine-type communication use-case which is intended to facilitate the ever increasing number of smart devices and sensors.In the massive machine-type communication use-case, the main challenges are to accommodate a huge number of devices while keeping the battery lives of the devices long, and allowing them to be placed in far-away locations. However, these devices are not concerned about other features such as latency, high data rate, or mobility.In this thesis we study the application of massive MIMO (multiple-input multiple-output) technology for the massive machine-type communication use-case. Massive MIMO has been on the radar as an enabler for future communication networks in the last decade and is now firmly rooted in both academia and industry. The main idea of massive MIMO is to utilize a base station with a massive number of antennas which gives the ability to spatially direct signals and serve multiple devices in the same time- and frequency resource.More specifically, in this thesis we study A) a scenario where the base station takes advantage of a device's low mobility to improve its channel estimate, B) a random access scheme for massive machine-type communication which can accommodate a huge number of devices, and C) a case study where the benefits of massive MIMO for long range devices are quantified. The results are that the base station can significantly improve the channel estimates for a low mobility user such that it can tolerate lower SNR while still achieving the same rate. Additionally, the properties of massive MIMO greatly helps to detect users in random access scenarios and increase link-budgets compared to single-antenna base stations.
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| 10. |
- Bergman, Filip, 1992-
(författare)
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Sustainability performance of multi-utility tunnels : Sustainability assessments for furthering knowledge and understanding
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The multi-utility tunnel has received increased attention as an alternative method for the installation of subsurface infrastructure for the distribution of electricity, water, sewage and district heating. In previous research, the multi-utility tunnel (MUT) has been described as a more sustainable technology compared to the conventionally used technique where the cables and pipes are placed with open-cut excavation (OCE), especially when the entire life cycle is taken into account. This thesis aims to contribute to an improved understanding of MUT's sustainability performance in relation to conventional installation using open-cut excavation. This is done by using literature study, interview study and quantitative sustainability assessments to gain an understanding of the current state of knowledge. Furthermore, this thesis also focuses on how knowledge can be deepened with the help of quantitative sustainability assessments and the challenges of conducting this type of assessment. This thesis shows that the state of knowledge regarding MUT's sustainability performance is low and scattered, with a lack of a holistic approach. Direct economic performance has gained the most attention, followed by indirect and social impact, and the environmental impact has so far barely been assessed. The sustainability performance depends to a large extent on the conditions of the specific case, and these should be considered when assessing the technology. Quantitative assessments have the potential to help deepen the knowledge of the sustainability implications of using MUT. The characteristics of MUT have some similarities with other types of physical infrastructure. Similarities are that the systems are long-lived, have project conditions that affect sustainability performance, and impact a broad spectrum of actors. One difference to typical infrastructure systems is that the owner and management structure of MUT is, by design, more complex as several types of utility systems are in use. The characteristics of MUT give some practical considerations that need to be addressed: data availability, including practitioners; detailed data; transparency; and flexibility. This thesis highlights the complexity of assessing MUT´s sustainability performance and advocates that future studies should have a learning-oriented approach so that the knowledge level can collectively and gradually improve over time rather than focusing on decision-oriented studies.
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