| 1. |
- Anttila, Sara
(författare)
-
Power control strategies for renewable energy systems : The inverter's role in future power systems
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Connecting more non-dispatchable renewable energy sources (RESs) will result in a higher power variability and a lower system inertia when the synchronous generators are replaced by inverter-connected RES. Inverter control can be divided in three categories: grid-following, grid-forming (GFM) and grid-supporting. A literature review of inverter control strategies identifies the GFM control as having an important role in maintaining system stability assuming near 100 % inverter-connected RES. Critical aspects of the inverter control are also identified; the control need to function autonomously, be able to remain connected during transient events and be insensitive to grid topology.Combining various RES is also shown to improve system stability. The combination of RES that has been investigated in most studies is wind, solar and wave power. Wave power is still a young technology compared to solar and wind power. It generates higher power fluctuations over short time periods with a significant difference between average and maximum power. Additionally, wave power parks (WPPs) are often connected via long cables which contribute reactive power to the grid. These challenges has to be considered to maintain system stability and power quality when connecting a WPP to the grid.In a Power Hardware-In-the-Loop study of how a WPP affects the power quality at the point of common coupling (PCC), it is found that the impact is highest for WPPs with fewer generators as the variability is reduced when several generators are excited at different times. Energy storage is also shown to have a significant impact on the power quality at the PCC with reduced flicker, total harmonic distortion and power and voltage variability. A simulation study also shows the positive impact of energy storage on power variability and the role of inverter control in reactive power compensation.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Bergman, Sandra, 1985-
(författare)
-
The Dynamics of Developing Leadership Communication in Organisations
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Leadership development is an area which is a top priority for organisations. While communication has historically been viewed as one of many leadership activities, it has recently been suggested to be more central to, even constitutive of, leadership. It has also been put forth that communication researchers may provide a means to develop new theoretical frameworks from which to develop leadership.The purpose of this thesis is to further the theoretical understanding of communicative leadership development, specifically in the form of training efforts. Furthermore, the goal is to provide a new understanding to practitioners who are working with the development of communicative leadership.This is a compilation thesis that consists of three papers. An initial literature review shows that the development of leadership communication receives interest from fields related to health, for instance, from nursing teams, businesses, the military and construction. On the other hand, the subject doesn’t receive as much attention from the field of communication studies. The results of the thesis are based on interviews with managers and communication professionals in two organisations. The findings show several benefits from having communication professionals take on a role as communication trainers, such as increased visibility of the communication department within the organisation and the opportunity to continue to support the leaders after the trainings. Additionally, a framework of adult learning is used to analyse the interviews, which highlights several points of adult learning that are relevant to the development of leadership communication.Based on the empirical data and the literature review, a model of communicative leadership development is suggested. This model is an amalgamation of what was learned from the three papers and summarises the understanding that was gained. Moreover, the model should provide practitioners with a basis for developing communicative leadership trainings as well as for developing the theory of communicative leadership.
|
|
| 5. |
|
|
| 6. |
- Ekelund, Maria, 1970-
(författare)
-
Psoriasis and Temporomandibular Joint Involvement in Juvenile Idiopathic Arthritis (JIA) : A Longitudinal Study of the Nordic JIA Cohort
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Juvenile idiopathic arthritis, JIA, is used as an umbrella term covering a heterogeneous group of chronic arthritis forms in children, many of which have important differences compared to adult arthritis, while others possibly represent similar diseases among children and adults. Classification aims to give a better understanding of the pathogenesis, patterns, disease trajectories and treatment responses. For the juvenile psoriatic arthritis, JPsA, the classification criteria are currently being debated. The distribution of affected joints in JIA differs greatly and it is unknown why some joints appear to be more affected than others. The temporomandibular joint (TMJ) can be affected early in the course of the disease and often the symptoms are mild and without obvious swelling.This thesis has its origin in the Nordic Study Group of Paediatric Rheumatology and the population-based prospective study of 510 children with newly diagnosed JIA included between 1997 and 1999. Totally 440 children were included in the eight-year follow-up, and in the TMJ study 265 patients were examined and underwent cone-beam computed tomography, CBCT, 17 years after onset.After eight years a considerable proportion of the children with definite psoriasis were classified as undifferentiated JIA based on the exclusion criteria in the ILAR classification. Our data also presents the heterogenicity of JPsA and the development over time of clinical variables supporting a psoriatic diathesis, as well as the overlap between JPsA and enthesitis-related arthritis in a group of patients. We found that extensive symptoms and dysfunctions of the TMJ are seen in JIA 17 years after disease onset, even in patients registered with inactive disease or remission. Individuals with substantial condylar damage on CBCT were found in all JIA categories. The deeper understanding of a chronic disease over time is crucial for research initiatives to improve care as well as for clinical decisions and planning of the health care.Our findings suggest a need for a more appropriate classification of JPsA and also that aspects of TMJ involvement should be included in the general health assessment in JIA.
|
|
| 7. |
- Ersson, Lisa, 1985-
(författare)
-
β-N-methylamino-L-alanine (BMAA)-induced neurotoxicity : Studies in vitro and in vivo
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- β-N-methylamino-L-alanine (BMAA) is a neurotoxic non-proteinogenic amino acid produced naturally by cyanobacteria, diatoms and dinoflagellates and it has been detected in samples from fresh and marine water from all over the world. It can bioaccumulate in fish and shellfish, and has a potential to biomagnify in a terrestrial food chain. BMAA was first discovered in the search for a neurotoxin related to the amyotrophic lateral sclerosis/Parkinsonism-dementia complex (ALS/PDC) found among the Chamorro people in Guam. This non-proteinogenic amino acid has also been suggested to contribute to sporadic neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD). BMAA can induce neurotoxicity via multiple mechanisms. It can act as an excitotoxin by activating glutamate receptors and to induce oxidative stress. It has also been suggested to be misincorporated into proteins leading to misfolded protein aggregates. Previous studies have demonstrated a specific damage in the hippocampus, including intracellular fibril formation, in adult rats following neonatal exposure to BMAA. In this thesis both in vitro and in vivo models were used to characterize the uptake, transport and effects of BMAA in cultured cell lines and in neonatal rodent brain tissue. The uptake of radiolabeled BMAA, as well as the effects of various amino acids and transporter antagonists on the uptake were studied in human mammary epithelial cells, intestinal epithelial cells, glioblastoma and neuroblastoma cells. Based on the obtained results a potential human mother-to-infant transfer of BMAA was suggested. BMAA-induced metabolic changes in a differentiated human neuroblastoma cell line were also characterized. The results revealed a plentitude of altered metabolites, many of them involved in amino acid metabolism and the TCA cycle. Of special interest were the perturbations in alanine, aspartate and glutamate metabolism as this pathway is involved in neurotransmission. The results revealed that BMAA can interfere with fundamental metabolic and neurotransmission pathways. Finally, the levels of free and protein-associated BMAA in the brain and peripheral tissues in neonatal rats exposed to BMAA were analysed. The results revealed high levels of free BMAA in some brain regions, thus demonstrating that the neonatal brain is not protected from BMAA by the blood-brain barrier. The results also revealed a protein-association of BMAA in the neonatal hypothalamus and hippocampus. Although the total amount of BMAA in the hippocampus was not high compared to other brain regions, the percentage of protein-associated BMAA was significantly higher. The results suggest that the protein-association of BMAA may play a role in the long-term effects in the hippocampus following neonatal exposure to BMAA. The studies in this thesis have demonstrated 1) a potential transfer of BMAA via breast milk to the brain of the nursing infant, 2) BMAA-induced metabolic alterations related to neurotransmission in human neuroblastoma cells and 3) that both free and protein-associated BMAA can be detected in the neonatal rat brain.
|
|
| 8. |
- Fachrizal, Reza, 1993-
(författare)
-
Synergy between Residential Electric Vehicle Charging and Photovoltaic Power Generation through Smart Charging Schemes : Models for Self-Consumption and Hosting Capacity Assessments
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The world is now in a transition towards a more sustainable future. Actions to reduce the green-house gases (GHG) emissions have been promoted and implemented globally, including switching to electric vehicles (EVs) and renewable energy technologies, such as solar photovoltaics (PV). This has led to a massive increase of EVs and PV adoption worldwide in the recent decade.However, large integration of EVs and PV in buildings and electricity distribution systems pose new challenges such as increased peak loads, power mismatch, component overloading, and voltage violations, etc. Improved synergy between EVs, PV and other building electricity load can overcome these challenges. Coordinated charging of EVs, or so-called EV smart charging, is believed to a promising solution to improve the synergy.This licentiate thesis investigates the synergy between residential EV charging and PV generation with the application of EV smart charging schemes. The investigation in this thesis was carried out on the individual building, community and distribution grid levels. Smart charging models with an objective to reduce the net-load (load - generation) variability in residential buildings were developed and simulated. Reducing the net-load variability implies both reducing the peak loads and increasing the self-consumption of local generation, which will also lead to improved power grid performance. Combined PV-EV grid hosting capacity was also assessed. Results show that smart charging schemes could improve the PV self-consumption and reduce the peak loads in buildings with EVs and PV systems. The PV self-consumption could be increased up to 8.7% and the peak load could be reduced down to 50%. The limited improvement on self-consumption was due to low EV availability at homes during midday when the solar power peaks. Results also show that EV smart charging could improve the grid performance such as reduce the grid losses and voltage violation occurrences. The smart charging schemes improve the grid hosting capacity for EVs significantly and for PV slightly. It can also be concluded that there was a slight positive correlation between PV and EV hosting capacity in the case of residential electricity distribution grids.
|
|
| 9. |
- Grahn, Lisa
(författare)
-
Kvinnor och moderskap i Sara Lidmans Jernbaneepos
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Licentiatavhandlingen undersöker skildringen av moderskap i Sara Lidmans Jernbaneepos (1977–1999), en romanserie i sju delar. I centrum för sviten står ett stort manligt kodat modernitetsprojekt – att ta järnvägen till Västerbotten. Licentiatavhandlingen fokuserar på de kvinnliga berättelser som också skapar historien, och hur upplevelser av sexualitet, graviditet och modrande arbete skildras. Genom att skilja på moderskap som en patriarkal institution och modrande som en kvinnocentrerad praktik, och genom att använda begreppet matrilinjära narrativ, belyser licentiatavhandlingen modersgestaltens agens och egna berättelse, till skillnad från de narrativ som traditionellt funnits kring moderskap. På så sätt undersöks modrande som en potentiellt frigörande och gränsöverskridande upplevelse, vilket är tidigare ouppmärksammade sidor av Lidmans författarskap.
|
|
| 10. |
- Gupta, Rahul
(författare)
-
Nanoscale spin dynamics in ferromagnetic/normal-metal heterostructures for spin-logic application : Engineering of spin-torque efficiency in Co2FeAl/β-Ta and Ru/FeCo/Ru multi-layers
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present information age, people across the globe generate an enormous digital footprint. Therefore, it is necessary to store and process the information in an elegant way. Spin-logic circuits are being considered potential candidates beyond CMOS integrated computing due to high clock speed, non-volatility, and higher logical efficiency. A basic building block for spin-logic circuits is ferromagnetic (FM) and normal-metal (NM) heterostructures. An example of a spin-logic data processing circuit is the spin-orbit torque (SOT) magnetic random access memory (MRAM). Energy efficient operation of such circuits depends on the interfacial electronic and magnetic properties of the heterostructures. These properties are known as Gilbert damping of the FM layer, spin Hall angle of the NM layer, spin-mixing conductance and spin-memory loss at the interface. To reduce the power consumption of such circuits, we propose two methods; doping and interface engineering. In paper I, we use ultra-low damping Fe65Co35 thin films as the FM layer and Ru as the NM layer. The interfacial parameter, the spin-mixing conductance, of the FeCo/Ru heterostructure is enhanced by 98% with Re doping in the FeCo. In paper II, we use Co2FeAl as the FM layer and β-Ta as the NM layer, and inserting a Cu continuous layer at the interface of Co2FeAl/β-Ta, yielding an enhancement of the spin-mixing conductance. In both cases, the enhancement in spin-mixing conductance can be linked to the increase in number of quantum conductance channels on the NM side, which helps to reduce the power consumption, and may provide a direction towards ultra-fast efficient operation of spin-logic circuits.
|
|
