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Coming dissertations at TekNat

  • Combinatorial and analytical problems for fractals and their graph approximations

    Author: Konstantinos Tsougkas
    Publication date: 2019-01-23 12:36

    The recent field of analysis on fractals has been studied under a probabilistic and analytic point of view. In this present work, we will focus on the analytic part developed by Kigami. The fractals we will be studying are finitely ramified self-similar sets, with emphasis on the post-critically finite ones. A prototype of the theory is the Sierpinski gasket. We can approximate the finitely ramified self-similar sets via a sequence of approximating graphs which allows us to use notions from discrete mathematics such as the combinatorial and probabilistic graph Laplacian on finite graphs. Through that approach or via Dirichlet forms, we can define the Laplace operator on the continuous fractal object itself via either a weak definition or as a renormalized limit of the discrete graph Laplacians on the graphs.

    The aim of this present work is to study the graphs approximating the fractal and determine connections between the Laplace operator on the discrete graphs and the continuous object, the fractal itself.

    In paper I, we study the number of spanning trees on the sequence of graphs approximating a self-similar set admitting spectral decimation.

    In paper II, we...

  • Efficient Memory Modeling During Simulation and Native Execution

    Author: Nikos Nikoleris
    Publication date: 2019-01-23 12:06

    Application performance on computer processors depends on a number of complex architectural and microarchitectural design decisions. Consequently, computer architects rely on performance modeling to improve future processors without building prototypes. This thesis focuses on performance modeling and proposes methods that quantify the impact of the memory system on application performance.

    Detailed architectural simulation, a common approach to performance modeling, can be five orders of magnitude slower than execution on the actual processor. At this rate, simulating realistic workloads requires years of CPU time. Prior research uses sampling to speed up simulation. Using sampled simulation, only a number of small but representative portions of the workload are evaluated in detail. To fully exploit the speed potential of sampled simulation, the simulation method has to efficiently reconstruct the architectural and microarchitectural state prior to the simulation samples. Practical approaches to sampled simulation use either functional simulation at the expense of performance or checkpoints at the expense of flexibility. This thesis proposes three approaches that use...

  • Bridging McMurry and Wittig in One-Pot : Olefins from Stereoselective, Reductive Couplings of Two Aldehydes via Phosphaalkenes

    Author: Juri Mai
    Publication date: 2019-01-23 08:52

    The formation of C=C bonds is of great importance for fundamental and industrial synthetic organic chemistry. There are many different methodologies for the construction of C=C bonds in the literature, but currently only the McMurry reaction allows the reductive coupling of two carbonyl compounds to form alkenes. This thesis contributes to the field of carbonyl olefinations and presents the development of a new synthetic protocol for a one-pot reductive coupling of two aldehydes to alkenes based on organophosphorus chemistry. The coupling reagent, a phosphanylphosphonate, reacts with an aldehyde to yield a phosphaalkene intermediate which upon activation with a base undergoes an olefination with a second aldehyde.

    A general overview of synthetic methods for carbonyl olefinations and the chemistry of phosphaalkenes is given in the background chapter. The Wittig reaction and its variations are discussed in detail. The synthesis, reactivity, properties and applications of phosphaalkenes are highlighted with particular focus on strategies to stabilize these otherwise reactive species.

    The third chapter describes a novel method for the reductive coupling of aldehydes....

  • Regulating Gene Expression to Promote Osteoblastic Differentiation of Stem Cells

    Author: Maruthibabu Paidikondala
    Publication date: 2019-01-23 08:42

    Bone is a tissue that heals by itself, unless the defect is too large (critical size). Today, novel regenerative medicine approaches have emerged as an alternative to treat such defects. This thesis explores alternative therapeutic strategies for bone tissue engineering which are biocompatible and clinically translatable. Many types of scaffolds that can act as reservoirs for growth factors such as rh-BMP-2 have been developed for bone tissue engineering in the past. However, the role of cross-linking chemistries that are employed to make hydrogels on the integrity and function of the loaded growth factors is not well understood. In this thesis, we have explored the influence of cross-linking chemistry on rh-BMP-2 integrity and bioactivity both in-vitro and in-vivo. These studies have demonstrated that thiol-Michael addition cross-linking chemistry greatly affects the integrity and bio-functionality of the loaded protein BMP-2 and leads to poor bone formation in an in-vivo rat model. On the other hand, hydrogels employing hydrazone chemistry did not significantly affect the integrity and bioactivity of BMP-2, which lead to a superior bone formation ...

  • Neuromolecular and behavioural profile of teleosts : - effects of boldness, agonistic behaviour and reproductive status

    Author: Arshi Mustafa
    Publication date: 2019-01-23 07:35

    This thesis investigates if boldness is reflected in the function of brain histaminergic system in zebrafish (Danio rerio). Moreover, behavioural differences in AB line, spiegeldanio (spd) line and wild caught strain of zebrafish have also been explored apart from the winner-loser effect in AB and spd fish. This thesis also includes studies on the effect of progestins on reproductive behaviour in zebrafish and regulation of leptinergic system on sexual maturation in male Atlantic salmon (Salmo salar L.).

    Boldness is reflected in higher expression of histamine receptor 1 (hrh1) in the telencephalon and diencephalon of male zebrafish and dominance by an elevated expression of hrh1 in the optic tectum. In female zebrafish boldness is also associated with lower expression of histamine receptor 3 (hrh3) in the optic tectum and dominance by lower expression of hrh3 in the telencephalon. Comparison of behavioural traits of zebrafish of AB, spd and wild type shows that wild type strain is most shy and shows no gender difference. AB is bolder than spd in the open field test while spd is bolder AB in the novel tank dive test....

  • Cladophora Cellulose-based Separators for Lithium Batteries

    Author: Ruijun Pan
    Publication date: 2019-01-16 10:00

    The development of lithium-ion batteries (LIBs) has been focused on exploring and improving the electrode materials and electrolytes in the past decades. An indispensable component, the separator, is however not studied as extensively. In general, a separator has two functions, i.e. preventing the direct contact between the cathode and anode and providing the ionic transport pathways. Commercial separators for LIBs are usually made of polyolefin materials, which often have low thermal stabilities and poor electrolyte wettabilities.

    In this thesis, a new type of material, i.e. Cladophora cellulose, is used to manufacture separators for LIBs and lithium-metal batteries (LMBs). The separators, made with Cladophora cellulose fibers via a straightforward paper making method, possess several advantages compared to conventional polyolefin separators regarding, e.g. ionic conductivity, thermal stability, electrolyte wettability and pore distribution, providing promising alternatives for battery separators.

    Apart from studying the two basic functions mentioned above, two types of advanced separator functionalities have been studied, i.e. redox-...

  • Flood Prediction in data-scarce basins : Maximising the value of limited hydro-meteorological data

    Author: José Eduardo Reynolds Puga
    Publication date: 2019-01-14 10:39

    Floods pose a threat to society that can cause large socio-economic damages and loss of life in many parts of the world. Flood-forecasting models are required to provide simulations at temporal resolutions higher than a day in basins with concentration times smaller than 24 h. However, data at such resolutions are commonly limited or not available, especially in developing or low-income countries. This thesis covers issues related to the scarcity and lack of high temporal-resolution hydro-meteorological data and explores methods where the value of existing data is maximised to improve flood prediction.

    By varying the starting time of daily records (the day definition), it was shown that this definition had large implications on model calibration and runoff simulation and therefore, should be considered in regionalisation and flood-forecasting applications. A method was developed to treat empirically model-parameter dependencies on the temporal resolution of data. Model parameters seemed to become independent of the temporal resolution of data when the modelling time-step was sufficiently small. Thus, if sub-daily forcing data can be secured, flood forecasting in basins...

  • Dynamics of Magnetic Molecules under Electrical Control

    Author: Henning Hammar
    Publication date: 2019-01-09 09:31

    This thesis theoretically studies the dynamics of molecular magnets under electrical control. Molecular magnets are nanoscale magnets that can, e.g., consist of single-molecules or single-atoms. In these magnets, the electronically mediated exchange and transport can be controlled by external fields. In this thesis, we study the effect of electrical control and voltage pulses on the transport properties, spin dynamics and the exchange of the molecular magnets.

    Nonequilibrium Green's functions is the method used to describe the underlying electronic structure of the magnetic molecule. The studied systems consists of single-molecule magnets in a tunnel junction between metallic leads. Here, the transport characteristics are derived for charge, spin and heat currents in the system for time-dependent voltage pulses. Furthermore, a generalized spin equation of motion is derived for the molecular spin moment, using nonequilibrium field theory. The equation of motion incorporates nonequilibrium conditions and is of nonadiabatic character. The effective model for the spin moment can be decomposed into effective magnetic field, isotropic Heisenberg interaction, and anisotropic...

  • Adapting sonar systems for monitoring ocean energy technologies

    Author: Francisco Francisco
    Publication date: 2019-01-08 14:10

    The global energy sector is under profound reforms aiming towards renewable energy sources, clean technologies and expansion of smart grids, all with the additional aim of providing affordable and dependable electricity for everyone. A reduction of carbon dioxide emissions is a priority on the global agenda, and to achieve that, cleaner energy technologies has to be more integrated into the energy mix. This thesis focus on a sustainable implementation of wave, tidal and offshore wind power, wherefore there is a need to investigate more about the prerequisites and consequences ocean energy can have on the marine environment. For that, reliable, cost effective and continuous environmental monitoring framework is necessary in order to support and safeguard ocean energy operations.

    The main objectives of the research presented in this thesis are to develop a multifunctional environmental monitoring platform based on sonar systems for ocean energy applications, by adapting high resolution multibeam, dual beam and split beam sonar systems and also underwater cameras; Propose data acquisition and processing protocols capable of decipher sonar data in order to provide continuous...

  • Ion dynamics and structure of collisionless shocks in space

    Author: Andreas Johlander
    Publication date: 2019-01-07 13:30

    Shock waves form when supersonic flows encounter an obstacle. Like in regular gases, shock waves can form in a plasma - a gas of electrically charged particles. Shock waves in plasmas where collisions between particles are very rare are referred to as collisionless shock waves. Collisionless shocks are some of the most energetic plasma phenomena in the universe. They are found for example around exploded supernova remnants and in our solar system where the supersonic solar wind encounters obstacles like planets and the interstellar medium. Shock waves in plasmas are very efficient particle accelerators though a process known as diffusive shock acceleration. An example of particles accelerated in shock waves are the extremely energetic galactic cosmic rays that permeate the galaxy. This thesis addresses the physics of collisionless shocks using spacecraft observations of the Earth's bow shock, particularly understanding the ion dynamics and shock structure for different shock conditions. For this we have used data from ESA's four Cluster satellites and NASA's four Magnetospheric Multiscale (MMS) satellites. The first study presents Cluster measurements from the quasi-parallel...