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Coming dissertations at TekNat

  • Contacts and Interconnects for Germanium-based Monolithic 3D Integrated Circuits

    Author: Lukas Jablonka
    Publication date: 2019-07-15 11:30

    Three-dimensional integrated circuits have great potential for further increasing the number of transistors per area by stacking several device tiers on top of each other and without the need to continue the evermore complicated and expensive down-scaling of transistor dimensions. Among the different approaches towards the realization of such circuits, the monolithic approach, i.e. the tier-by-tier fabrication on a single substrate, is the most promising one in terms of integration density. Germanium is chosen as a substrate material instead of silicon in order to take advantage of its low fabrication temperatures as well as its high carrier mobilities. In this thesis, the work on two key components for the realization of such germanium-based three-dimensional integrated circuits is presented:the source/drain contacts to germanium the interconnects.

    As a potential source/drain contact material, nickel germanide is investigated.In particular, the process temperature windows for the fabrication of morphologically stable nickel germanide layers formed from initial nickel layers below 10 nm are identified and the reaction between nickel and germanium is further studied by...

  • The Extremes of Neutrino Astronomy : From Fermi Bubbles with IceCube to Ice Studies with ARIANNA

    Author: Elisabeth Unger
    Publication date: 2019-07-02 14:16

    The Fermi bubbles are extended regions of hard gamma-ray emission which were discovered with Fermi-LAT data to exist above and below the Galactic Center. In order to explain the origin of the gamma-rays, different theories are proposed. In particular, within hadronic models, highly-accelerated cosmic rays interact with interstellar matter and create the observed gamma-rays and in addition neutrinos. Data from the neutrino detector IceCube was analyzed using a maximum likelihood method. An upper limit on the possible neutrino flux from the Fermi bubbles at energies between 10 GeV and 200 GeV was determined.

    While this analysis is performed with the lowest energies IceCube can reach, the ARIANNA (Antarctic Ross Ice-shelf ANtenna Neutrino Array) experiment has the goal to detect the highest energy neutrinos by measuring radio wave radiation produced by their interaction products in the ice. With ARIANNA the propagation of radio waves in the firn (packed snow) of the Ross Ice Shelf was investigated. According to the classical approach the radio waves, produced in the firn, are supposed to bend down because of the changing density, and therefore changing refractive index, an...

  • Leveraging Existing Microarchitectural Structures to Improve First-Level Caching Efficiency

    Author: Ricardo Alves
    Publication date: 2019-06-11 13:49

    Low-latency data access is essential for performance. To achieve this, processors use fast first-level caches combined with out-of-order execution, to decrease and hide memory access latency respectively. While these approaches are effective for performance, they cost significant energy, leading to the development of many techniques that require designers to trade-off performance and efficiency.

    Way-prediction and filter caches are two of the most common strategies for improving first-level cache energy efficiency while still minimizing latency. They both have compromises as way-prediction trades off some latency for better energy efficiency, while filter caches trade off some energy efficiency for lower latency. However, these strategies are not mutually exclusive. By borrowing elements from both, and taking into account SRAM memory layout limitations, we proposed a novel MRU-L0 cache that mitigates many of their shortcomings while preserving their benefits. Moreover, while first-level caches are tightly integrated into the cpu pipeline, existing work on these techniques largely ignores the impact they have on instruction scheduling. We show that the variable hit latency...

  • Trans-crustal magma storage in contrasting tectonic settings

    Author: Harri Geiger
    Publication date: 2019-06-10 11:06

    Magmatic plumbing systems comprise magma chambers, sheet intrusions, and conduits which link the Earth’s deep interior with the Earth’s surface. As such, they are the structural framework of magma transport and storage that is governed by complex physical and chemical processes in magma reservoirs and through the interaction of magma bodies with surrounding crustal rocks over timescales from hours to millions of years. These geological processes, in turn, play a vital role in controlling eruptive behaviour and the magnitude of associated volcanic eruptions that impact the environment as well as human society. Our understanding of the nature and location of magmatic processes and plumbing system architecture remains, however, fragmentary. This lack of knowledge can partly be attributed to limits regarding the spatial resolution of geophysical methods and partly to geochemical uncertainties and errors in associated models. Ongoing advances in analytical techniques increase spatial, temporal, and chemical resolution, hence enabling us to gather more detailed knowledge on the structure and dynamics of magmatic systems, especially for individual volcanoes, but also in respect to the...

  • Electrochemical Characterizations of Conducting Redox Polymers : Electron Transport in PEDOT/Quinone Systems

    Author: Mia Sterby
    Publication date: 2019-06-10 10:28

    Organic electrode materials for rechargeable batteries have caught increasing attention since they can be used in new innovative applications such as flexible electronics and smart fabrics. They can provide safer and more environmentally friendly devices than traditional batteries made from metals. Conducting polymers constitute an interesting class of organic electrode materials that have been thoroughly studied for battery applications. They have high conductivity but are heavy relative to their energy storage ability and will hence form batteries with low weight capacity. Quinones, on the other hand, are low weight molecules that participate in electron transport in both animals and plants. They could provide batteries with high capacity but are easily dissolved in the electrolyte and have low conductivity. These two constituents can be combined into a conducting redox polymer that has both high conductivity and high capacity. In the present work, the conducting polymer PEDOT and the simplest quinone, benzoquinone, are covalently attached and form the conducting redox polymer used for most studies in this thesis. The charge transport mechanism is investigated by in situ...

  • Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations

    Author: Andreas Ekstedt
    Publication date: 2019-06-04 13:42

    The Higgs particle was first predicted in 1964, and was discovered in the summer of 2012 at the Large Hadron Collider (LHC). This discovery was the latest in a long list of successful Standard Model predictions spanning the last fifty years. However, some of the Standard Models predictions, such as massless neutrinos, are not in agreement with experiment. Thus, extensions of the Standard Model should be considered. Furthermore, some issues, such as how quarks are bound within the proton, are difficult to study from first principles.

    In paper I and II of this thesis, a class of models that contains a new TeV scale neutral vector boson is studied. The parameter space of this class of models is constrained using electroweak precision constraints and 13 TeV LHC data. Gauge anomalies are cancelled both by choosing appropriate fermion charges, and by adding Green-Schwarz terms.

    The Higgs mechanism is often studied at leading order, but there are also important radiative corrections. These radiative corrections, which change the ground state energy, can both be IR divergent and gauge dependent. In paper III it is shown how to solve both of these problems. In particular, IR...

  • Designing grinding tools to control and understand fibre release in groundwood pulping

    Author: Magnus Heldin
    Publication date: 2019-05-29 11:00

    Mechanical pulping is a very energy demanding process in which only a fraction of the energy is used for the actual separation of wood fibres. The rest of the energy is lost, partly in damaging already separated fibres and partly as heat during viscoelastic deformation of the wood. Groundwood pulping is one of the major mechanical pulping processes. In this process, a piece of wood is pressed against a rotating grinding stone. The stone surface has traditionally been made of grinding particles fused to a vitrified matrix. Though the process is close to 200 years old, the detailed mechanisms of the interactions between the grinding particles and the wood surface are still not fully understood. The random nature of the grinding stones combined with the heterogeneous nature of wood creates a stochastic process that is difficult to study in detail. This work utilizes well-defined tools, that facilitate testing and analysis, to increase the understanding of the tool-wood-interaction. In-situ tomography experiments were performed with such well-defined tools, to study the deformations and strains induced in the wood as the tool asperities engage the wood surface. Numerical...

  • Hybrid observers for systems with intrinsic pulse-modulated feedback

    Author: Diana Yamalova
    Publication date: 2019-05-27 11:07

    Dynamical processes resulting from the interaction of continuous and discrete dynamics are often encountered in living organisms. Time evolutions of such processes constitute continuous variables that are subject to instant changes at discrete points of time. Usually, these discrete events cannot be observed directly and have to be reconstructed from the accessible for measurement continuous variables.

    Thus, the problem of hybrid state estimation from measurements of continuous outputs is important to and naturally arises in life sciences but, so far, scarcely covered in the existing literature.

    This thesis deals with a special class of hybrid systems, where the continuous linear part is controlled by an intrinsic impulsive feedback that contributes discrete dynamics. The impacting pulsatile feedback signal is not available for measurement and, therefore, has to be reconstructed. To estimate all the elements of the hybrid state vector, an observation problem is considered.

    The focus of the work is on a state observation problem for an analytically tractable example of a hybrid oscillator with rich nonlinear dynamics including, e.g.,...

  • Carbon in Boreal Streams : Isotopic Tracing of Terrestrial Sources

    Author: Audrey Campeau
    Publication date: 2019-05-24 14:13

    The boreal biome comprises vast areas of coniferous forests, dotted with millions of peatlands. Plants harbouring these ecosystems fix CO2 from the atmosphere, which is later incorporated into the vegetation biomass and subsequently buried in soils. Over the course of millennia, this process has led to the formation of a large repository of organic C, currently stored in boreal soils. Streams draining this landscape are typically enriched with carbon dioxide (CO2), methane (CH4) and dissolved organic carbon (DOC). As a consequence, streams tend to emit CO2 and CH4 to the atmosphere, two potent greenhouse gases, and thus contribute positively to radiative climate forcing. The sources fuelling C to boreal streams are not well understood. This thesis aims to unravel these sources, and promote a better consolidation of terrestrial and aquatic C biogeochemical processes. The work is largely based on stable and radiogenic C isotope characterization of various dissolved C forms in stream and groundwater, within contrasting ecosystem types across Sweden.

    This thesis identifies boreal soils as the main source of CO2 in streams. Soil respiration (i.e. biogenic sources)...

  • Studies of Giardia-host interactions: role of cysteine-rich surface proteins.

    Author: Dimitra Peirasmaki
    Publication date: 2019-05-24 09:17

    Giardia intestinalis is a eukaryotic parasite that colonizes the small intestine of humans and animals causing the diarrheal disease known as giardiasis. This parasite is not invasive and does not internalize into host cells but it rather attaches to the brush border surface of the small intestine disrupting the epithelial barrier. Giardia causes around 280 million symptomatic infections in humans every year, while it can also cause chronic and asymptomatic infections. Giardiasis is a multifactorial disease but only few factors that directly contribute in the pathogenesis and virulence of the disease have been identified. G. intestinalis has eight genetic groups, but only two of them (A and B) are known to infect humans.

    In this thesis, whole genome sequencing was performed for two human assemblage A isolates (AS175 and AS98) and were compared to assemblage A isolate WB genome (Paper I). Genome-wide variations were identified among the three isolates including isolate-specific coding sequences and high level of nucleotide diversity of multi-gene families such as VSPs and HCMPs.

    We further used an in vitro model for parasite...