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Coming dissertations at TekNat

  • Seismic structure of the central Svecofennian lithosphere

    Author: Sebastian Buntin
    Publication date: 2021-11-26 07:42

    Lithospheric structures in the Fennoscandian Shield in Sweden have been studied by a number of large-scale wide-angle seismic reflection/refraction (WARR) and normal-incidence reflection profiles since the 1960s. Among these were the over 2000 km long Fennoscandian Long Range (FENNOLORA) project in 1979 and the Baltic and Bothnian Echoes from the Lithosphere (BABEL) in 1989, which provided valuable images of the subsurface down to over 60 km depth including the Moho. Additionally, the 550 km long WARR profile, UPPLAND, was acquired in 2017, transecting across the Uppland and Ljusdal Batholiths from south to north. 

    Due to the computational progress in the last 25 years, improved seismic images and velocity models could be obtained by reprocessing the recovered BABEL data set. The main finding of the reprocessed BABEL profiles is the presence of large-scale saucer-shaped intrusions of around 100 km diameter connected to an up-domed lower crust and sub-Moho reflectors. These interpreted offshore saucer-shaped intrusions together with those observed onshore suggest a nested interconnected emplacement model, implying that the deeper saucer-shaped intrusions fed the shallower...

  • Spin Current Generation in Magnetic Heterostructures and its Impact on Terahertz Emission : A Spin Dynamics Perspective

    Author: Rahul Gupta
    Publication date: 2021-11-25 09:36

    The transfer of knowledge from one generation to another is key to the intellectualness of mankind. In the present information age, digital technology provides easy access to knowledge and information. However people across the globe simultaneously generate an enormous digital footprint, which demands to store and process the information in a modish way. Spin-based electronics is being considered a prospective candidate beyond complementary metal-oxide-semiconductor technology with several applications in data storage and data communication. The key concept of this technology is the generation, transportation, and detection of spin currents in magnetic heterostructures consisting of ferromagnetic (FM) and non-ferromagnetic (NFM) bilayer thin films.

    In this thesis, I describe the concepts of spin dynamics at the nano- to femtosecond timescales and experimental techniques used to extract the spin dynamics properties of magnetic heterostructures. In this regard, we have shown that the Gilbert damping parameter and the number of quantum conductance channels (QCCs) can be enhanced by doping the FM layer with Re in the Ru/Fe65Co35/Ru heterostructure. The same heterostructure...

  • Prediction horizon requirement  in control and extreme load analyses for survivability : Advancements to improve the performance of wave energy technologies

    Author: Zahra Shahroozi
    Publication date: 2021-11-25 09:23

    The main objective of wave energy converters (WECs) is to ensure reliable electricity production at a competitive cost. Two challenges to achieving this are ensuring an efficient energy conversion and offshore survivability.        

    This thesis work is structured in three different sections: Control and maximum power optimization, forces and dynamics analysis in extreme wave conditions, and statistical modeling of extreme loads in reliability analysis.       

    The need for prediction and future knowledge of waves and wave forces is essential due to the non-causality of the optimal velocity relation for wave energy converters. Using generic concepts and modes of motion, the sensitivity of the prediction horizon to various parameters encountered in a real system is elaborated. The results show that through a realistic assumption of the dissipative losses, only a few seconds to about half a wave cycle is sufficient to predict the required future knowledge for the aim of maximizing the power absorption.         

    The results of a 1:30 scaled wave tank experiment are used to assess the line force and dynamic behaviour of a WEC during extreme wave events. Within the...

  • Rethinking Speculative Execution from a Security Perspective

    Author: Christos Sakalis
    Publication date: 2021-11-25 07:25

    Speculative out-of-order execution is one of the fundamental building blocks of modern, high-performance processors. To maximize the utilization of the system's resources, hardware and software security checks in the speculative domain can be temporarily ignored, without affecting the correctness of the application, as long as no architectural changes are made before transitioning to the non-speculative domain. Similarly, the microarchitectural state of the system, which is by necessity modified for every single operation (speculative or otherwise) also does not affect the correctness of the application, as such state is meant to be invisible on the architectural level. Unfortunately, while the microarchitectural state of the system is indeed separate from the architectural state and is typically hidden from the users, it can still be observed indirectly through its side-effects, through the use of "side-channels". Starting with Meltdown and Spectre, speculative execution, combined with existing side-channel attacks, can be abused to bypass both hardware and software security barriers and illegally gain access to data that would not be accessible otherwise.

    Embroiled in a...

  • Optimal Scheduling for Timely Information in Communication Systems

    Author: Ghafour Ahani
    Publication date: 2021-11-24 10:19

    The explosive growth of data in information society poses significant challenges in the timely delivery of information in the context of communication networks. Hence, optimal utilization of scarce network resources is crucial. This dissertation contributes to several aspects related to the timely delivery of information, including scheduling of data flows between sources and destinations in a network, scheduling of content caching in a base station of mobile networks, and scheduling of information collection. Two important metrics, namely, delivery deadline and information freshness, are accounted for. Mathematical models and tailored solution approaches are developed via tools from optimization.

    Five research papers are included in the dissertation. Paper I studies a flow routing and scheduling problem with delivery deadline. This type of problem arises in many applications such as data exchange in scientific projects or data replication in data centers where large amounts of data need to be timely distributed across the globe. Papers II, III, and IV inves­tigate content caching along time in a base station. Content caching at the network’s edge has recently been...

  • Year-round production of forest seedlings under LED lamps : Biological and energetic implications of indoor cultivation

    Author: Marco Hernandez Velasco
    Publication date: 2021-11-23 08:53

    Year-round cultivation of forest seedlings under light emitting diodes (LED) is a technology receiving increased attention from nurseries in the boreal forest regions. In these areas, the climate is characterized by strong seasonal fluctuations, resulting in short vegetation periods with narrow time windows for seedling transplanting and outdoor growth. An indoor pre-cultivation phase under LEDs would offer nurseries the possibility to extend their production throughout the year.

    LED lamps present several advantages compared to traditional light sources such as higher efficacies, longer lifetimes and advanced controls. In order to test their feasibility for seedling cultivation, three different LED lamps were compared against fluorescent lights. Biological effects of the light quality were studied through pre-cultivating seedlings of Picea abies (L.) Karst. and Pinus sylvestris L. under each spectrum in a growth room with controlled conditions. LEDs showed equal or better results than the control also after a forest field trial.

    Effects of light quantity were studied for both species using the most promising LED spectrum. Unlike the energy input,...

  • Ceramic Materials as Drug Delivery Systems

    Author: Amina Vazda
    Publication date: 2021-11-19 12:17

    The aim of this thesis is to evaluate ceramic materials for drug delivery drugs applications. Three delivery routes were investigated; abuse-deterrent oral formulation, inhalation, and novel ceramic crystals with drug entrapped. 

    A geopolymer matrix was developed in order to withstand non-medical abuse such as crushing, snorting, extraction etc. An in vivo study was performed, where oral administration of zolpidem loaded geopolymer pellets was evaluated. The results showed a higher plasma concentration for immediate release formulations compared to the geopolymer, however the geopolymer formulation showed a prolonged release compared to the immediate release control group.  

    Pulmonary drug delivery offers a fast and non-invasive drug delivery. Releasing fentanyl from calcium sulfate for pulmonary drug delivery were investigated by applying the drug onto the ceramic and heating to 230-250°C for 1-10 minutes. The evaporated drug was collected and quantified which resulted in a total amount of 1.2µg released fentanyl. 

    Synthesis of ceramic materials containing drugs within the crystal structure has been investigated, both calcium carbonate and hydroxyapatite were...

  • Morphological changes in mycobacteria

    Author: Malavika Ramesh
    Publication date: 2021-11-19 10:41

    Morphological variations at different stages and conditions of growth has been observed frequently in various mycobacteria. Despite years of research, the molecular basis of such variations is still not clear and requires further elucidation. Owing to the pathogenic significance of mycobacteria, currently, mycobacterial research emphasizes on understanding responses to oxygen deprivation, starvation, various antibiotic treatments, latency and dormancy.

    In this thesis, change in cell shape from rod to coccoid, occurrence of refractive spore-like phase grey, phase bright bodies and branching are some of the morphological variations discussed. Further, this thesis also discusses microaerobic condition (oxygen deprivation) and the localisation pattern of the stressosome complex. 

  • Getting Work Done : The Significance of the Human in Complex Socio-Technical Systems

    Author: Rebecca Cort
    Publication date: 2021-11-19 09:30

    This thesis aims to deepen the understanding of the role and relevance of the worker in the functioning of complex socio-technical systems. The perspective adopted is profoundly human-centred and the worker is considered as a resource. This stands in stark contrast to the performance-related measurements and accident investigations which have typically formed much research on work in complex safety-critical systems and conveyed a perspective of the human as merely a system cog. The empirical material in this thesis is based on ethnographic fieldwork in the shape of workplace studies conducted across two distinct work domains: manufacturing and operational train traffic. The studies are informed by distributed cognition (DCog) and activity theory (AT) as prominent theoretical approaches for developing in-depth understandings of how work activities are accomplished in situations where the interplay between humans and their socio-cultural and material environment is of interest. The findings are illustrated by empirical work that provides detailed accounts of work practices derived from a total of four work settings. It is illustrated how acquired experiences and skills allow the...

  • Band gap engineering in Cu2ZnGexSn1-xS4 thin film solar cells

    Author: Nishant Saini
    Publication date: 2021-11-18 10:22

    Photovoltaics based on kesterite Cu2ZnSnS4 (CZTS) has attracted interest as a sustainable alternative to other thin film technologies due to their tunable material properties and earth-abundance. However, the efficiency is limited to 12.6 % for selenium-containing CZTS, with a large voltage-deficit due to tail states, deep defects, secondary phases etc.

    In this thesis, Ge incorporation in kesterite solar cells was utilized to reduce Sn-related deep defects and tune the band gap. CZTS, Cu2ZnGeS4 (CZGS), and mixed Cu2ZnGexSn1-xS4 (CZGTS) films, and solar cells were investigated. CZGS showed wurtzite-like phases when sputter-deposited in a sulfur-rich atmosphere using GeS target. The mixture of phases could not recrystallize to kesterite phase after annealing, so, metallic Ge target was utilized for CZGTS absorber fabrication. From varying the Ge content in CZGTS, it could be concluded that CZTS grain growth increased at a low concentration of Ge.

    Sulfurization of CZTS layers deposited on top of CZGS was done to achieve band gap grading. Glow Discharge Optical Emission Spectroscopy showed smooth grading while Scanning Tunneling Microscopy/Energy Dispersive Spectroscopy...

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