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Coming dissertations at TekNat

  • Power control strategies for renewable energy systems : The inverter's role in future power systems

    Author: Sara Anttila
    Publication date: 2020-10-15 10:46

    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...

  • The role of freshwater phytoplankton in the global carbon cycle

    Author: Fabian Engel
    Publication date: 2020-10-14 09:48

    Water flowing through the landscape transports chemical substances including carbon. Along the way from upland soils to the ocean, carbon is transformed from organic carbon into inorganic carbon and vice versa. One such carbon transformation process is the uptake of carbon dioxide (CO2) from the water phase by phytoplankton. For some inland waters, it has been shown that phytoplankton can significantly reduce the amount of CO2 (measured as partial pressure of CO2, pCO2) in the water phase. However, the importance of this process for carbon budgets on a regional and global scale is not yet known.

    The aim of this thesis was to investigate the importance of CO2 uptake by phytoplankton for CO2 dynamics in lakes and rivers on a regional and global scale, and to explain its spatial variation. Conceptual models and the analysis of monitoring data together with statistical modeling and meta-analyses were used.

    Combining a conceptual lake model for carbon transformation with a mass balance approach showed that gross primary production in lakes is an important flux in the global dissolved inorganic carbon budget of inland waters. In a next step, a simple proxy to...

  • Dimensions of Professionalism : A Study of Computer Science Teaching in Saudi Arabia

    Author: Fayiq Alghamdi
    Publication date: 2020-10-12 09:00

    In Saudi Arabia, new computing education programs have been introduced in alignment with the Saudi Vision 2030, which is a plan launched in 2017 to reduce Saudi Arabia's reliance on oil, diversify its economy, and develop its health, education, recreation, infrastructure and tourism. Computer science is a rapidly changing area, which places high demands on teachers in the subject to develop both their subject and pedagogical competence. This thesis explores computer science teachers’ perspectives on professional development from three viewpoints—the Saudi Teaching Competencies Standard, engagement in teachers’ awards and self-directed learning. The thesis examines the efforts of computer science teachers as they develop new pedagogies during their teaching careers as a result of the new regulations. The main question is ‘How do Saudi Arabian computer science teachers develop their teaching professionalism?’ Conclusions draw on the outcomes of four sub-studies. A mixed-methods approach consisting of interviews and questionnaires was used to collect data. The participants comprised 389 computer science teachers from different Saudi Arabian cities with different demographics and...

  • World oil supply in the 21st century : A bottom-up perspective

    Author: Henrik Wachtmeister
    Publication date: 2020-10-08 14:37

    Oil-fuelled progress was a defining feature of the 20th century, and still today, oil remains the world’s largest primary energy source. Yet, oil is a non-renewable and carbon-intensive resource, either depletion or resulting carbon emissions will ultimately limit its use. This thesis investigates the potential and dynamics of world oil supply in order to increase the understanding of this defining dilemma of the 21st century. Specifically, it focusses on the different characteristics of conventional oil and the recently emerged unconventional tight oil, and their associated implications. It does so from a bottom-up perspective by combining physical and economic dynamics on the individual field and well levels.               

    The thesis is based on six papers. The first examines the usefulness of bottom-up modelling by a retrospective analysis of past oil projections. The second investigates how unconventional tight oil can be modelled on the well level using decline curve analysis. The third derives typical production parameters for conventional offshore oil fields. The fourth compares the production dynamics of conventional oil and tight oil and discusses possible oil...

  • Pair production of Higgs bosons in the final state with bottom quarks and τ leptons in the ATLAS experiment : Search results using LHC Run 2 data and prospect studies at the HL-LHC

    Author: Petar Bokan
    Publication date: 2020-10-08 13:11

    After the discovery of the Higgs boson, the ultimate test of the electroweak symmetry breaking and the Standard Model (SM) of particle physics is to establish evidence of Higgs boson self-coupling, which can be achieved by searching for pair production of Higgs bosons. In addition, many theories beyond the SM predict heavy resonances that could decay into pairs of Higgs bosons. A search for non-resonant and resonant pair production of Higgs bosons in the final state with two bottom quarks and two τ leptons (bb̄τ+ τ) is presented for 36.1 fb-1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider (LHC). The observed (expected) 95% confidence level (CL) upper limit on the non-resonant Higgs boson pair production cross-section times the bτ+τ- branching ratio corresponds to 12.7 (14.8) times the SM prediction. The ratio of the Higgs boson self-coupling to its SM expectation, κλ, is observed (expected) to be...

  • Olefins from carbonyls : Development of new phosphorus-based cross-coupling reactions

    Author: Nicolas Daniele D'Imperio
    Publication date: 2020-10-08 11:24

    Olefins, compounds containing C=C double bonds, are omnipresent in nature and serve as useful starting materials for various chemical modifications. Olefins are of crucial importance in Medicinal Chemistry and are also present in essential objects like dyes, polymers and plastics. Thus, developing methodologies for synthesizing olefins is at the heart of Organic Chemistry.

    In this regard, many reactions have been developed over the years for the production of olefins from different starting materials. To date only one reaction, namely the McMurry coupling, is available for constructing olefins from two carbonyls. This reaction is frequently applied in an academic context, but suffers many drawbacks that limit its wider use. This thesis offers innovative phosphorus-based methodologies for coupling two carbonyls into olefins. All the methods presented herein are based on a one-pot sequence in which a first carbonyl is transformed into a phosphaalkene (P=C double bond containing molecule) which, upon activation, reacts with a second carbonyl with formation of desired alkenes.

    The first two chapters of this thesis give a general overview on literature...

  • Virus retentive filter paper for processing of plasma-derived proteins

    Author: Lulu Wu
    Publication date: 2020-10-07 13:02

    The studies in the present thesis explored the feasibility of using nanocellulose-based filters in virus removal filtration of plasma-derived proteins.


    In Paper I, two-step nanofiltration of commercially available human serum albumin (HSA) product, which was diluted to 10 g L-1 by phosphate buffer saline (PBS) and adjusted pH to 7.4, was performed to remove soluble protein aggregates and reduce filter fouling. The two-step filtration of HSA employed nanocellulose-based filters of varying thickness, i.e. 11 μm and 22 μm filters.  The removal of HSA aggregates during filtration through 11 μm pre-filters dramatically improves the flow properties of the 22 μm filter, enabling high protein throughput and high virus clearance. A distribution of pore sizes between 50 nm and 80 nm, which is present in the 11 μm filter and is absent in the 22 μm filter, plays a crucial part in removing the HSA aggregates. With respect to virus filtration, 1 bar constant trans-membrane pressure filtration shows poor removal ability of ΦX174 bacteriophage (28 nm), i.e., log10 reduction value (LRV) ≤ 3.75, while that at 3 bar and 5 bar achieves LRV[MOU1] [LW2]  > 5 model virus clearance...

  • Image and Data Analysis for Spatially Resolved Transcriptomics : Decrypting fine-scale spatial heterogeneity of tissue's molecular architecture

    Author: Gabriele Partel
    Publication date: 2020-10-06 13:22

    Our understanding of the biological complexity in multicellular organisms has progressed at tremendous pace in the last century and even more in the last decades with the advent of sequencing technologies that make it possible to interrogate the genome and transcriptome of individual cells. It is now possible to even spatially profile the transcriptomic landscape of tissue architectures to study the molecular organization of tissue heterogeneity at subcellular resolution. Newly developed spatially resolved transcriptomic techniques are producing large amounts of high-dimensional image data with increasing throughput, that need to be processed and analysed for extracting biological relevant information that has the potential to lead to new knowledge and discoveries. The work included in this thesis aims to provide image and data analysis tools for serving this new developing field of spatially resolved transcriptomics to fulfill its purpose. First, an image analysis workflow is presented for processing and analysing images acquired with in situ sequencing protocols, aiming to extract and decode molecular features that map the spatial transcriptomic landscape in tissue sections....

  • The Novelty in the Uncanny : Designing Interactions to Change First Impressions

    Author: Maike Paetzel-Prüsmann
    Publication date: 2020-10-01 11:20

    In 1970, Japanese researcher Masahiro Mori published a seminal paper where he hypothesized that robots that appear human-like but are still distinguishable from being human would not attract people towards them, but instead cause an uncanny sensation. This phenomenon, known as the uncanny valley effect, has been widely studied within the social robotics community, and a multitude of experiments have since been conducted supporting Mori's hypothesis. The specifics of a robot's appearance and behavior leading to such an uncanny sensation, however, remain an open research question and require further study. These gaps in the causal relationship between uncanny feelings and a robot's design have lead uncanniness being increasingly used to explain any lack of enthusiasm towards robots, both in the scientific community and the general public. It is then often implicitly assumed that uncanny feelings towards a robot have damaging consequences for long-term human-robot interaction. Most empirical studies on the subject, however, focus on still images or short video clips of robots and participants are only exposed to these stimuli for small frames of time. The current literature on the...

  • Synergy between Residential Electric Vehicle Charging and Photovoltaic Power Generation through Smart Charging Schemes : Models for Self-Consumption and Hosting Capacity Assessments

    Author: Reza Fachrizal
    Publication date: 2020-09-28 13:26

    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...