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Coming dissertations at TekNat

  • Bright Needles in a Haystack : A Search for Magnetic Monopoles Using the IceCube Neutrino Observatory

    Author: Alexander Burgman
    Publication date: 2021-01-12 13:47

    The IceCube Neutrino Observatory at the geographic South Pole is designed to detect the light produced by the daughter-particles of in-ice neutrino-nucleon interactions, using one cubic kilometer of ice instrumented with more than 5000 optical sensors.

    Magnetic monopoles are hypothetical particles with non-zero magnetic charge, predicted to exist in many extensions of the Standard Model of particle physics. The monopole mass is allowed within a wide range, depending on the production mechanism. A cosmic flux of magnetic monopoles would be accelerated by extraterrestrial magnetic fields to a broad final velocity distribution that depends on the monopole mass.

    The analysis presented in this thesis constitutes a search for magnetic monopoles with a speed in the range [0.750;0.995] in units of the speed of light. A monopole within this speed range would produce Cherenkov light when traversing the IceCube detector, with a smooth and elongated light signature, and a high brightness.

    This analysis is divided into two main steps. Step I is based on a previous IceCube analysis, developed for a cosmogenic neutrino search, with similar signal event characteristics as in...

  • Microfluidics for High-Pressure Inertial Focusing : Focusing, Separation and Concentration of Micro and Sub-micron Particles

    Author: Javier Cruz
    Publication date: 2021-01-12 13:34

    The birth of microsystems set the ground for technologies never imagined before, for it is not only the small size what characterizes the miniaturized systems, but unique phenomena arise in the micro scale. This thesis relates to one such unique phenomenon, inertial focusing, a phenomenon that occurs in microfluidic systems if very special conditions are met and that allows for fine manipulation of particles in fluid samples. This ability is key in a bigger picture: the analysis of complex fluids, where rare particles of interest may be present in very few numbers amongst a myriad of others, making the task difficult – if not impossible. A system exploiting inertial focusing allows, for instance, to focus, separate, isolate and concentrate such rare particles of interest, and even to transfer them to another fluid, thereby enabling/facilitating their detection and analysis. Examples of rare particles of interest in complex fluids are circulating tumor cells in blood, that give away the presence of cancer, extracellular vesicles also in blood, that contain biomarkers with physiological and pathological information about the patient, or bacteria in natural water, where the...

  • Amorphous Magnetic Materials : A Versatile Foundation for Tomorrow’s Applications

    Author: Sebastian George
    Publication date: 2021-01-12 09:33

    Amorphous magnetic materials exhibit a number of key differentiating properties with respect to crystalline magnets. In some cases, the differences may simply be in the values of macroscopic properties such as saturation magnetization, coercivity, Curie temperature, and electrical conductivity. Other cases are more fundamental, such as the possibility for many amorphous alloys to be produced with nearly arbitrary composition, something that is not always possible in crystal structures that may only be stable for certain specific compositions.

    Fundamentally, these properties arise due to the disordered arrangement of atoms in amorphous materials. However, this structure is challenging to probe and characterize, either experimentally or theoretically. A significant contribution of this thesis is the development of a new approach for studying the local atomic structure of amorphous materials, specifically amorphous SmCo and FeZr alloys. The strategy combines extended x-ray absorption spectroscopy (EXAFS) measurements with stochastic quenching (SQ) simulations in a way that provides more information than either method can offer alone. Additionally, this approach offers the...

  • On Solving String Constraints

    Author: Phi Diep Bui
    Publication date: 2021-01-11 13:21

    Software systems are deeply involved in diverse human activities as everyone uses a variety of software systems on a daily basis. It is essential to guarantee that software systems all work correctly. Two popular methods for finding failures of software systems are testing and model checking. Various efficient testing and model checking approaches are satisfiability-based, where the core of the approaches is Satisfiability Modulo Theories (SMT) solvers for solving the path feasibility and/or reachability problems. The significant growth of string manipulating programs in modern programming languages, including Python and JavaScript, demands SMT solvers being capable of analysing string constraints. This thesis proposes two frameworks for checking the satisfiability of extensive classes of string constraints, discovers a new decidable fragment of string constraints, and introduces efficient solvers for solving string constraints.

    The first framework for checking the satisfiability of string constraints is based on Counter-Example Guided Abstract Refinement (Cegar) procedure, and applicable to diverse classes of string constraints. It is worth mentioning that the framework...

  • Criticality of fast failures in the High Luminosity Large Hadron Collider

    Author: Björn Lindström
    Publication date: 2021-01-05 10:38

    Each of the two Large Hadron Collider (LHC) beams contain 362 MJ of energy. This will be further increased to 678 MJ in the upcoming upgrade to the High Luminosity LHC (HL-LHC). In the event of an uncontrolled beam loss, a significant hazard occurs, that can damage the machine components. This thesis is focused on failures that can lead to a fast increase of beam losses, with a focus on the new optics and equipment in the HL-LHC. The criticality for a number of failure scenarios is studied, under different optics configurations of the machine. Mitigation strategies, involving dedicated interlocking and a reduction of the impact that the failures have on the beam are proposed for the most critical scenarios. For a number of less critical failures it is determined that current interlock strategies are sufficient.

    Failures involving the magnet protection and the crab cavities constitute the most severe hazards. The former consists of quench heaters and a new system known as coupling loss induced quench (CLIQ). A new connection scheme is proposed for these, in order to limit their effect on the beam. Dedicated interlocks for detecting spurious discharges of these systems are...

  • Parallelization of dynamic algorithms for electronic structure calculations

    Author: Anton G. Artemov
    Publication date: 2020-12-21 13:18

    The aim of electronic structure calculations is to simulate behavior of complex materials by resolving interactions between electrons and nuclei in atoms at the level of quantum mechanics. Progress in the field allows to reduce the computational complexity of the solution methods to linear so that the computational time scales proportionally to the size of the physical system. To solve large scale problems one uses parallel computers and scalable codes. Often the scalability is limited by the data distribution.

    This thesis focuses on a number of problems arising in electronic structure calculations, such as inverse factorization of Hermitian positive definite matrices, approximate sparse matrix multiplication, and density matrix purification methods. No assumptions are made about the data distribution, instead, it is explored dynamically.

    The thesis consists of an introduction and five papers. Particularly, in Paper I we present a new theoretical framework for localized matrices with exponential decay of elements. We describe a new localized method for inverse factorization of Hermitian positive definite matrices. We show that it has reduced communication costs...

  • Rosetta Observations of Plasma and Dust at Comet 67P

    Author: Fredrik Leffe Johansson
    Publication date: 2020-12-21 13:09

    In-situ observations of cometary plasma are not made because they are easy. The historic ESA Rosetta mission was launched in 2004 and traversed space for ten years before arriving at comet 67P/Churyumov-Gerasimenko, which it studied in unprecedented detail for two years. For the Rosetta Dual Langmuir Probe Experiment (LAP), the challenge was increased by the sensors being situated on short booms near a significantly negatively charged spacecraft, which deflects low-energy charged particles away from our instrument. To disentangle the cometary plasma signature in our signal, we create a charging model for the particular design of the Rosetta spacecraft through 3D Particle-in-Cell/hybrid spacecraft-plasma interaction simulations, which also can be applicable to similarly designed spacecraft in cold plasma environments. By virtue of this model, we find a way to cross-calibrate (with the Mutual Impedance probe, MIP) the LAP spacecraft potential to a plasma density estimate with increased temporal resolution and dynamic range than any single plasma instrument alone.

    To characterise and disentangle the Sun-driven photoelectric current from the positive cometary ion current...

  • Expression and synthetic activation of [FeFe]-hydrogenases in cyanobacteria

    Author: Adam Wegelius
    Publication date: 2020-12-21 07:46

    Photosynthetic microbes can be utilized for hydrogen production, generating a clean, carbon neutral energy carrier from abundant substrates. Cyanobacteria are photosynthetic prokaryotes with large potential for biotechnological energy applications and several strains are capable of hydrogen production. This production is catalysed by a bi-directional [NiFe]-hydrogenase, or by nitrogenase during nitrogen fixation. However, nature’s foremost hydrogen producing enzymes, the [FeFe]-hydrogenases, are not present in these organisms. Many [FeFe]-hydrogenases boast incredible catalytic activities and high bias towards proton reduction. Introduction of a suitable [FeFe]-hydrogenase in a cyanobacterial host could greatly improve the hydrogen production capacity. Unfortunately, generation and characterisation of cyanobacterial strains carrying active [FeFe]-hydrogenases is stalled by the intricate maturation process associated with these enzymes.

    In this thesis, I investigate heterologous expression and artificial maturation of [FeFe]-hydrogenases in cyanobacteria. Genetic tools to reliably express [FeFe]-hydrogenases were developed and tested in the unicellular cyanobacterium ...

  • Abstractions to Control the Future

    Author: Francisco Ramón Fernández Reyes
    Publication date: 2020-12-21 07:36

    Multicore and manycore computers are the norm nowadays, and users have expectations that their programs can do multiple things concurrently. To support that, developers use concur- rency abstractions such as threads, promises, futures, and/or channels to exchange information. All these abstractions introduce trade-offs between the concurrency model and the language guarantees, and developers accept these trade-offs for the benefits of concurrent programming.

    Many concurrent languages are multi-paradigm, e.g., mix the functional and object-oriented paradigms. This is beneficial to developers because they can choose the most suitable approach when solving a problem. From the point of view of concurrency, purely functional programming languages are data-race free since they only support immutable data. Object-oriented languages do not get a free lunch, and neither do multi-paradigm languages that have imperative features.

    The main problem is uncontrolled concurrent access to shared mutable state, which may inadvertently introduce data-races. A data-race happens when two concurrent memory operations target the same location, at least one of them is a write, and there is...

  • Magnetically governed self-assembly of soft matter : A look into interfacial layering, crystallization and percolation

    Author: Apurve Saini
    Publication date: 2020-12-18 13:04

    Self-organisation is the key route for assembling colloidal particles into well-defined structures. Decisive for this are the interactions between the constituents, which are amongst others steric, electrostatic or magnetic. A deep knowledge on the underlying physical processes during self-assembly is crucial for the design and fabrication of well-defined hierarchical architectures from a nanometer scale as well as for realizing smart, functional or stimuli responsive synthetic materials. In this dissertation, the self-assembly of colloidal magnetic particles into organized and multi-layered structures is studied. Particular emphasis is given to solid-liquid boundaries and the response to applied magnetic fields. Particle coatings with specific functional molecules stabilize the nanoparticles (NPs) in the solvent and can simultaneously promote their assembly at a substrate. An example in this context is N-hydroxysuccinimide interacting with (3-aminopropyl)triethoxy silane at the substrate. As a result of this chemical affinity, uniform and densely packed particle wetting layers are seeded which then instate the layering process. As an alternative to chemical binding, the...

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