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Coming dissertations at TekNat

  • Enabling Sustainable Networked Embedded Systems

    Author: Ambuj Varshney
    Publication date: 2018-04-18 10:27

    Networked Embedded Systems (NES) are small energy-constrained devices typically with sensors, radio and some form of energy storage. The past several years have seen a rapid growth of applications of NES, with several predictions stating billions of devices deployed in the near future. As NES are deployed at large scale, a growing challenge is to support NES for long periods of time without negatively impacting their physical or the radio environment, i.e., in a sustainable manner. In this dissertation, we identify intertwined challenges that affect the sustainability of NES systems: co-existence on the shared wireless spectrum; energy consumption; and the cost of the deployment and maintenance. We identify research directions to overcome these challenges and address them through the six research papers.

    Firstly, NES have to co-exist with other wireless devices that operate on the shared wireless spectrum. A growing number of devices contending for the spectrum is challenging and leads to increased interference among them. To enable NES to co-exist with other wireless devices, we investigate the use of electronically steerable directional antennas (ESD). ESD antennas...

  • Oxidized Cladophora nanocellulose derivatives : Functionalization towards biocompatible materials

    Author: Igor Rocha
    Publication date: 2018-04-17 11:32

    Nanocellulose is a promising candidate for biomedical applications because of its enhanced mechanical properties, increased surface area and greater porosity compared to bulk cellulose.

    This thesis investigates the functionalization of Cladophora nanocellulose and evaluates the influence of these modifications on physicochemical properties and biocompatibility of the material.

    An electrochemically assisted TEMPO-mediated oxidation setup produced cellulose materials with varying degrees of carboxyl groups. This approach allowed control of the charge applied during the process and adjustment of the carboxylation. Carboxylated nanocellulose membranes had smaller surface area and total pore volume and a more compact structure than the membranes of the unmodified material. Moreover, the introduction of carboxyl groups resulted in membranes with an aligned fiber pattern; the alignment and aggregation of the fibers tended to increase with higher degrees of oxidation.

    Cytocompatibility studies using fibroblasts and osteoblastic cells have shown that the bioinert Cladophora nanocellulose membranes can be rendered bioactive by the introduction of...

  • Magnetic Nanoparticle Based Biosensors for Pathogen Detection and Cancer Diagnostics

    Author: Bo Tian
    Publication date: 2018-04-13 10:56

    This thesis describes several magnetic nanoparticle (MNP)-based biosensing strategies which take advantage of different magnetic sensors, molecular tools and nanotechnologies. Proposed biosensors can be classified into three groups, i.e., immunoassay-based, molecular amplification-based, and nanoparticle assembly-based. The principal motivation is to develop and optimize biosensors for out-of-lab and point-of-care testing.

    Immunoassay-based biosensors described in this thesis employ antibodies as the bio-recognition element for the detection of bacteria cells/fragments or proteins. Two typical immunoassay formats, i.e., direct and competitive format, are studied and compared for bacteria detection. In addition, in the protein biomarker detection, MNP chains are formed in the presence of target analytes as well as in the external rotating magnetic field. The high shape/magnetic anisotropy of the chains provides better optomagnetic performance.

    Two different molecular amplification methods, i.e., rolling circle amplification (RCA) and loop-mediated isothermal amplification (LAMP), are described under the topic of molecular amplification-...

  • Shining Light on Molecules : Electron Transfer Processes in Model Systems for Solar Energy Conversion Investigated by Transient Absorption Spectroscopy

    Author: Jens Föhlinger
    Publication date: 2018-04-13 09:01

    In the recent years, solar energy conversion has attracted a huge research interest due to the potential application for limiting the greenhouse effect. In many solar cells and solar fuel cells, understanding of charge transfer (CT) and recombination is important for future improvement of the overall efficiency. One important tool for that is transient absorption spectroscopy (TAS).

    Mesoporous nickel oxide films were investigated due to their potential application in p-type dye-sensitized solar cells (DSSCs), tandem DSSCs and dye sensitized solar fuel cells (DSSFC:s). Firstly, it was found that the hole generated by band gap excitation is trapped on an ultrafast time scale by Ni3+ states. It was possible to observe a direct signal from the holes by transient mid-IR absorption spectroscopy allowing for direct detection of hole injection and trapping. On a ns time scale, the trapped holes relaxed to much less reactive holes which favored long lived NiO-dye charge separation (CS).

    A series of perylene monoimide (PMI) dyes with different anchoring groups was studied. Differences in binding affinity and stability were found. Nevertheless, all PMIs showed ultrafast charge...

  • Luminescence of Silicon Nanoparticles Synthesized by Ion Implantation

    Author: Thawatchart Chulapakorn
    Publication date: 2018-04-12 09:34

    Silicon nanoparticles (SiNPs) have been shown to display luminescence in the visible range with a peak wavelength depending on the nanoparticle size. This finding is of potential interest for integration of optoelectronic devices in semiconductor technology. In this thesis, silicon nanoparticles are formed in thermally grown SiO2 films by implantation of Si-ions. Implantation parameters such as energy, fluence, and target temperature, as well as post-implantation annealing (PIA) conditions are studied in order to optimize the luminescence properties of the nanoparticles. Ion energies between 15 and 70 keV, fluences up to 1017 atoms/cm2, and target temperatures ranging from room temperature to 600 ºC are employed. The PIA process is carried out at temperatures between 1000 and 1200 °C in ambient nitrogen, or argon gas. In addition, dangling bonds, which reduce the total luminescence of SiNPs, are passivated, using forming gas annealing (FGA). Quantification of hydrogen content induced by FGA process is performed by ion beam analysis (IBA) techniques. Furthermore, irradiations with swift heavy ions (SHIs) with several tens of MeV kinetic energy are performed as a possible way to...

  • Liquid scintillators as neutron diagnostic tools for fusion plasmas : System characterization and data analysis

    Author: Federico Binda
    Publication date: 2018-04-11 11:03

    The neutrons produced in fusion devices carry information about various properties of the ions that are reacting in the machine. Measurements of the neutron flux and energy distribution can therefore be used to study the behaviour of the plasma ions under different experimental conditions.

    Several neutron detection techniques are available, each having advantages and disadvantages compared to the others. In this thesis we study neutron measurements performed with NE213 liquid scintillators. One advantage of NE213s compared to other neutron detection techniques is that they are simple to use, small and cheap. On the other hand, their response to neutrons makes the extraction of information about the neutron energy less precise.

    In the thesis we present the development of methods for the characterization and the data analysis of NE213 detectors. The work was performed using two instruments installed at the Joint European Torus (JET) tokamak in the UK: the “Afterburner” detector, which is an NE213 installed on a tangential line of sight, and the neutron camera, which is a system composed of 19 NE213 detectors installed on different lines of sight (10 horizontal and 9...

  • Magnetization Dynamics in Ferromagnetic Thin Films : Evaluation of Different Contributions to Damping in Co2FeAl and FeCo Film Structures

    Author: Serkan Akansel
    Publication date: 2018-04-09 09:11

    Static and dynamic magnetic properties of Co2FeAl and Fe65Co35 alloys have been investigated. Co2FeAl films were deposited at different temperatures and the deposition parameters were optimized with respect to structural and magnetic properties. As a result, a film with B2 crystalline phase was obtained without any post-annealing process. A lowest magnetic damping parameter of  was obtained for the film deposited at 573K. This obtained low value is comparable to the lowest values reported in research literature.  After optimizing the deposition parameters of this alloy, different seed layers and capping layers were added adjacent to the Co2FeAl layer and the effect of these layers on the magnetic relaxation was investigated. In addition to adding nonmagnetic layers to Co2FeAl, the dependence of the magnetic damping parameter with respect to the thickness of Co2FeAl was investigated by depositing films with different thicknesses. A temperature dependent study of the magnetic damping parameter was also performed and the measured damping parameters were compared with theoretically calculated intrinsic Gilbert damping parameters. Different extrinsic contributions to the magnetic...

  • Remediation of mercury contaminated soil and biological mercury methylation in the landscape

    Author: Jingying Xu
    Publication date: 2018-04-06 12:46

    Accumulation of mercury (Hg) in soil originating from both natural and anthropogenic sources poses a major hazard to environmental and human health. Inorganic Hg(II) in soil can be transformed to highly toxic methylmercury (MeHg) mainly via methylating microorganisms. Although MeHg constitutes less than 2% of total Hg in soil, it enters aquatic systems through runoff and can be subsequently bioaccumulated along the food chain, thereby causing severe harm to humans.

    Current major remediation techniques to control soil Hg contamination were reviewed. Organic matter, clay/minerals and complexation ligands within soil are principal factors influencing Hg mobility that is crucial for evaluating and optimising remedial techniques. The potential of soil washing to treat soil Hg contamination was evaluated. The studied soil was fractionated from fine to coarse particles to assess the effectiveness of physical separation. Batch leaching and pH-static titration tests were performed using (1) water, (2) EDTA, (3) NaOH, (4) HCl, (5) acidic leachates from biodegradable wastes, and (6) alkaline leachates from fly/bottom ashes, to estimate the efficiency of chemical extraction. Less...

  • Channel Estimation and Prediction for 5G Applications

    Author: Rikke Apelfröjd
    Publication date: 2018-04-05 13:04

    Accurate channel state information (CSI) is important for many candidate techniques of future wireless communication systems. However, acquiring CSI can sometimes be difficult, especially if the user equipment is mobile in which case the future channel realisations must be estimated/predicted. In realistic settings the predictability of radio channels is limited due to measurement noise, limited model orders and since the fading statistics must be modelled based on a set of limited and noisy training data.

    In this thesis, the limits of predictability for the radio channel are investigated. Results show that the predictability is limited primarily due to limitations in the training data, while the model order provides a second order limitation effect and the measurement noise comes in as a third order effect.

    Then, a Kalman-based linear filter is studied for potential 5G technologies:

    Coherent coordinated multipoint joint transmission, where channel predictions and the covariance matrix of the prediction error are used to design a robust linear precoder, evaluated in a three base station system. Results show that prediction improves the CSI for the...

  • Residual and Solubility trapping during Geological CO2 storage : Numerical and Experimental studies

    Author: Maria Rasmusson
    Publication date: 2018-03-28 13:20

    Geological storage of carbon dioxide (CO2) in deep saline aquifers mitigates atmospheric release of greenhouse gases. To estimate storage capacity and evaluate storage safety, knowledge of the trapping mechanisms that retain CO2 within geological formations, and the factors affecting these is fundamental. The objective of this thesis is to study residual and solubility trapping mechanisms (the latter enhanced by density-driven convective mixing), specifically in regard to their dependency on aquifer characteristics, and to investigate and develop methods for quantification of CO2 trapping in the field. The work includes implementation of existing numerical simulators and inverse modeling, as well as the development of new models and experimental methods for the study and quantification of CO2 trapping.

    A comparison of well-test designs in regard to their abilities to estimate the in-situ residual gas saturation (that determines the residual trapping of CO2) is presented, as well as a novel indicator-tracer approach to obtain residual gas saturation conditions in a formation. The results can aid in the planning of well-tests for estimation of trapping potential during site...