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  • Disputas: 2019-04-26 10:00 F3, Stockholm
    Bessegato, Luca
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Modeling of Modular Multilevel Converters for Stability Analysis2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Modular multilevel converters (MMCs) have recently become the state-of-the-art solution for various grid-connected applications, such as high-voltage direct current (HVDC) systems and flexible alternating current transmission systems (FACTS). Modularity, scalability, low power losses, and low harmonic distortion are the outstanding properties that make MMCs a key technology for a sustainable future.

     

    The main objective of this thesis is the modeling of grid-connected MMCs for stability analysis. The stability of the interconnected system, formed by the converter and the ac grid, can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. Therefore, a method for the calculation of the ac-side admittance of MMCs is developed. This method overcomes the nonlinearities of the converter dynamics and it can be easily adapted to different applications. Moreover, the effects of different control schemes on the MMC ac-side admittance are studied, showing how the converter admittance can be reshaped. This is a useful tool for system design, because it shows how control parameters can be selected to avoid undesired grid-converter interactions.

     

    This thesis also studies ac/ac MMCs for railway power supplies, which are used in countries with a low-frequency railway grid, such as Germany (16.7 Hz) and Sweden (16 2/3 Hz). A hierarchical control scheme for these converters is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. For computing the insertion indices, an open-loop scheme with sum capacitor voltage estimation is applied to the ac/ac MMC. Lyapunov stability theory is used to prove the asymptotic stability of the converter operated with the proposed control method. This specific open-loop scheme is also adapted to a modular multilevel matrix converter, which performs three-to-three phase direct conversion.

     

    Finally, this thesis presents the design of a down-scaled MMC prototype for experimental verification, rated at 10 kW with 30 full-bridge submodules. The hardware and the software are designed to be easily reconfigurable, which makes the converter suitable for different research projects focused on MMCs. Experiments on this down-scaled MMC are used to support and validate the key results presented throughout the thesis.

  • Disputas: 2019-04-26 10:00 Kollegiesalen, Stockholm
    Zandi Shafagh, Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Thiol-ene Nanostructuring2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Improving the health and well-being of humankind does not only constitute

    part of our moral codes, but is also enlisted as the number three goal of

    the 2030 agenda for sustainable development set by the UN. Fulfilling such

    objective in the regions of resource-poor settings or for age groups with more

    vulnerability to infectious agents demands immediate actions. This has necessitated

    novel ways of rapid and ultra-sensitive diagnostics to provide compact

    and affordable systems, e.g. for an early detection of bacteria and viruses.

    The fields of bio-micro/nanoelectromechanical systems (BioMEMS/NEMS)

    and lab-on-a-chip (LoC) have been founded based on such demands, but

    critically challenged by problems partly associated with manufacturing and

    material domains and biosensing methods. The fabrication methods for the

    miniaturization of features and components are often complicated and expensive,

    the commonly used materials are typically not adaptable to industrial

    settings, and the sensing mechanisms are sometimes not sensitive enough for

    the detection of lowly-concentrated samples.

    In this thesis, new methods of ultra-miniaturization, as well as conventional

    cleanroom-based techniques, for nanopatterning of well-defined topographies

    in off-stoichiometry thiol-ene-(epoxy) polymers are presented. In addition,

    their use for several sensing applications has been demonstrated. The

    first part of the thesis gives an introduction to the field of BioMEMS/NEMS.

    The second part of the thesis presents a technical background about the

    prevalent methods of polymer micro- and nanofabrication, implementation

    of the resulting polymer structures for different sensing applications, along

    with the existing challenges and shortcomings associated with state of the

    art. The third part of the thesis presents e-beam nanostructuring of thiol-ene

    resist, for the first time, achieving the smallest and densest features reported

    in these polymer networks. The thiol-ene-based polymer also represents a

    novel class of e-beam resist resulting in structures with reactive surface nature.

    The fourth part of the thesis demonstrates the use of thiol-ene-epoxy

    systems for nanoimprint lithography and further shows the structuring of

    high-aspect-ratio and hierarchical topologies via single-step UV-NIL. The fifth

    part of the thesis introduces Micro- and NanoRIM platforms for scalable and

    off-cleanroom manufacturing of microfluidic devices and nanostructuring of

    materials in thiol-ene (-epoxy) systems. The sixth part of the thesis exhibits

    the implementation of the noted nanofabrication methods for different

    BioMEMS/NEMS applications including protein nanopatterning, simultaneous

    molding and surface energy patterning, ultra-sensitive digital biosensing,

    and facile quartz crystal microbalance (QCM) sensor packaging.

  • Disputas: 2019-04-26 13:00 D3, Stockholm
    Hungria-Gunnelin, Rosane
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande, Bygg- och fastighetsekonomi.
    Empirical studies of auctions of non-distressed residential real estate2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Real estate auctions have become a popular sales mechanism in Sweden in the past couple of decades when the internet facilitated the marketing of properties for sale. With the possibility to display several exterior and interior pictures of the property rather than the single façade picture style of traditional newspapers advertisements, and a more detailed description of the object, brokers significantly increased the number of potential buyers at the showings of properties for sale. The increase in the number of visitors has, especially in the larger cities in Sweden, increased the frequency of bidding wars, in which the winning bid ends far above the list price. Many auction participants, especially those who are inexperienced, perceive the auction-based sales mechanism as very stressful considering that the purchase of a home is for most buyers the largest investment they will ever make. Therefore, the auction mechanism for selling homes is regularly debated in media, among politicians and by regulatory bodies. The scientific literature analyzing auctions of non-distressed homes is, however, very limited. Hence, the debate and analysis of the Swedish auction-based sales mechanism has little empirical evidence to lean on. A main reason for the lack of scientific work in this area is the difficulty to obtain sufficiently detailed auction data to study how sellers’ list price strategy and auction participants bidding strategies affect the outcome of real estate auction auctions and the occurrence of a winner’s curse.

    The overall aim of this thesis is to study how sellers’ list price strategy and bidding strategies of auction participants affect the outcome of auctions of non-distressed residential homes. The thesis is empirical and comprises four papers that analyze the housing markets in Stockholm and Gothenburg. Papers 1 and 2 analyze sales of condominium apartments in Central Stockholm, while Paper 3 analyzes sales of single-family homes in Stockholm County. Paper 4 analyzes sales of condominium apartments in Gothenburg.

    Papers 1, 2 and 3 contribute to the empirical auction literature by studying how the number of bidders, the seller’s list price strategy and auction participants bidding strategies affect the unfolding of auctions and the resulting transaction price. Using a hedonic model Paper 1 analyzes how the number of bidders affects the transaction price. Paper 2 extends the database in Paper 1 to cover a longer time period and develops the hedonic model in Paper 1 by adding explanatory variables describing the seller’s list price strategy and auction participants bidding strategies. Paper 3 develops the hedonic model in Paper 2 by incorporating a more thorough analysis of possible omitted variable bias and further employs methods used in the previous empirical literature to mitigate omitted variable bias by including as explanatory variable the residuals from a price regression of previous sales, as well as the residuals from a list price regression. Furthermore, the paper estimates how list price and bidding strategies affect the probability of a winner’s curse.

    Paper 4 studies auctions of condominiums in Gothenburg, but with a different focus than Papers 1, 2 and 3 since detailed auction data was not available. The paper instead focuses on how sellers’ list price strategy affect sales price and time-on-market, and how information asymmetry between brokers and sellers, combined with brokers’ commission fee structures, affect the choice of list price.

  • Disputas: 2019-04-26 13:30 Kollegiesalen, Stockholm
    Cao, Le Phuong
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Optimal Transmit Strategies for Multi-antenna Systems with Joint Sum and Per-antenna Power Constraints2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nowadays, wireless communications have become an essential part of our daily life. During the last decade, both the number of users and their demands for wireless data have tremendously increased. Multi-antenna communication is a promising solution to meet this ever-growing traffic demands. In this dissertation, we study the optimal transmit strategies for multi-antenna systems with advanced power constraints, in particular joint sum and per-antenna power constraints. We focus on three different models including multi-antenna point-to-point channels, wiretap channels and massive multiple-input multiple-output (MIMO) setups. The solutions are provided either in closed-form or efficient iterative algorithms, which are ready to be implemented in practical systems.

    The first part is concerned with the optimal transmit strategies for point-to-point multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) channels with joint sum and per-antenna power constraints. For the Gaussian MISO channels, a closed-form characterization of an optimal beamforming strategy is derived. It is shown that we can always find an optimal beamforming transmit strategy that allocates the maximal sum power with phases matched to the complex channel coefficients. An interesting property of the optimal power allocation is that whenever the optimal power allocation of the corresponding problem with sum power constraint only exceeds per-antenna power constraints, it is optimal to allocate maximal per-antenna power to those antennas to satisfy the per-antenna power constraints. The remaining power is distributed among the other antennas whose optimal allocation follows from a reduced joint sum and per-antenna power constraints problem with fewer channel coefficients and a reduced sum power constraint. For the Gaussian MIMO channels, it is shown that if an unconstraint optimal power allocation for an antenna exceeds a per-antenna power constraint, then the maximal power for this antenna is used in the constraint optimal transmit strategy. This observation is then used in an iterative algorithm to compute the optimal transmit strategy in closed-form.

    In the second part of the thesis, we investigate the optimal transmit strategies for Gaussian MISO wiretap channels. Motivated by the fact that the non-secure capacity of the MISO wiretap channels is usually larger than the secrecy capacity, we study the optimal trade-off between those two rates with different power constraint settings, in particular, sum power constraint only, per-antenna power constraints only, and joint sum and per-antenna power constraints. To characterize the boundary of the optimal rate region, which describes the optimal trade-off between non-secure transmission and secrecy rates, related problems to find optimal transmit strategies that maximize the weighted rate sum with different power constraints are derived. Since these problems are not necessarily convex, equivalent problem formulation is used to derive optimal transmit strategies. A closed-formsolution is provided for sum power constraint only problem. Under per-antenna power constraints, necessary conditions to find the optimal power allocation are provided. Sufficient conditions, however, are available for the case of two transmit antennas only. For the special case of parallel channels, the optimal transmit strategies can deduced from an equivalent point-to-point channel problem. In this case, there is no trade-off between secrecy and non-secrecy rate, i.e., there is onlya transmit strategy that maximizes both rates.

    Finally, the optimal transmit strategies for large-scale MISO and massive MIMO systems with sub-connected hybrid analog-digital beamforming architecture, RF chain and per-antenna power constraints are studied. The system is configured such that each RF chain serves a group of antennas. For the large-scale MISO system, necessary and sufficient conditions to design the optimal digital and analog precoders are provided. It is optimal that the phase at each antenna is matched tothe channel so that we have constructive alignment. Unfortunately, for the massive MIMO system, only necessary conditions are provided. The necessary conditions to design the digital precoder are established based on a generalized water-filling and joint sum and per-antenna optimal power allocation solution, while the analog precoder is based on a per-antenna power allocation solution only. Further, we provide the optimal power allocation for sub-connected setups based on two properties: (i) Each RF chain uses full power and (ii) if the optimal power allocation of the unconstraint problem violates a per-antenna power constraint then it is optimal to allocate the maximal power for that antenna. The results in the dissertation demonstrate that future wireless networks can achieved higher data rates with less power consumption. The designs of optimal transmit strategies provided in this dissertation are valuable for ongoing implementations in future wireless networks. The insights offered through the analysis and design of the optimal transmit strategies in the dissertation also provide the understanding of the optimal power allocation on practical multi-antenna systems.

  • Disputas: 2019-04-26 14:00 F3, Stockholm
    Ihrner, Niklas
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Ytbehandlingsteknik.
    Structural Lithium Ion Battery Electrolytes2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A major challenge in the electrification of vehicles in the transport industry is that batteries are heavy, which reduces their effectiveness in mobile applications. A solution to this is structural batteries, which are batteries that can carry mechanical load while simultaneously storing energy. This can potentially lead to large weight savings on a systems level, since they may allow replacement of load bearing structures with structural batteries. Carbon fibers are suitable for structural batteries because they have superb mechanical properties and readily intercalate lithium ions, i.e. they can be used as electrodes in a lithium ion battery. However, to utilize carbon fibers in structural batteries, a polymer (matrix) is needed to form a composite battery. The polymer is required to have high modulus and high ion transport properties, which are inversely related, to function as an electrolyte. This thesis focuses on the development and characterization of such polymer electrolytes.

    The first study was performed on a homogenous polymer electrolyte based on plasticized polyethylene glycol-methacrylate. The influence of crosslink density, salt concentration and plasticizer concentration on the mechanical and electrochemical properties were investigated. Increases in both ionic conductivity and storage modulus were obtained when, compared to non-plasticized systems. However, at high storage modulus (E’>500 MPa) the ionic conductivity (𝜎<10-7 S cm-1) is far from good enough for the realization of structural batteries.

    In a second study, phase separated systems were therefore investigated. Polymerization induced phase separation (PIPS) via UV-curing was utilized to the produce structural battery electrolytes (SBE), consisting of liquid electrolyte and a stiff vinyl ester thermoset. The effect of monomer structure and volume fraction of liquid electrolyte on the morphology, electrochemical and mechanical properties were investigated. High storage modulus (750 MPa) in combination with high ionic conductivity (1.5 x 10-4 S cm-1) were obtained at ambient temperature. A SBE carbon fiber lamina half-cell was prepared via vacuum infusion and electrochemically cycled vs lithium metal. The results showed that both ion transport and load transfer was enabled through the SBE matrix.

    In the third study the mechanical and electrochemical properties of the SBE-carbon fiber lamina were investigated and the multifunctional performance was evaluated. A new formulation of SBE, with a small addition of thiol monomer, were prepared with improved electrochemical and mechanical properties. The mechanical properties of the SBE carbon fiber lamina did not deteriorate after electrochemical cycling. The capacity of the SBE carbon fiber lamina half-cell was 232 ± 26 mAh g-1, at a C/20 charge rate. Furthermore, the lamina displayed multifunctional performance, compared to the monofunctional properties of its constituents.

    In the final study, a new curing method was investigated, since UV-curing cannot be used to prepare full-cell carbon fiber composite structural batteries. Thermal curing was investigated to prepare the SBE. The PIPS was not adversely affected by the change in curing method, and the length scale of the phase separation in the SBE was slightly larger compared to UV-cured SBEs. The thermally cured SBEs exhibited improved thermomechanical properties without a reduction in the electrochemical properties. Thermal curing did not affect the electrochemical properties of the SBE carbon fiber lamina, however the type of carbon fiber utilized was found to negatively affect the cycling performance.

    Fulltekst tilgjengelig fra 2020-03-25 10:42
  • Disputas: 2019-04-26 18:22 FA32, Stockholm
    Bergstrand, Jan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Super resolution fluorescence imaging: analyses, simulations and applications2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Fluorescence methods offer extraordinary sensitivity and specificity, and are extensively used in the life sciences. In recent years, super resolution fluorescence imaging techniques have developed strongly, uniquely combining ~10 nm sub diffraction resolution and specific labeling with high efficiency. This thesis explores this potential, with a major focus on Stimulated Emission Depletion, STED, microscopy, applications thereof, image analyses and simulation studies. An additional theme in this thesis is development and use of single molecule fluorescence correlation spectroscopy, FCS, and related techniques, as tools to study dynamic processes at the molecular level. In paper I the proteins cytochrome-bo3 and ATP-synthase are studied with fluorescence cross-correlation spectroscopy, FCCS. These two proteins are a part of the energy conversion process in E. coli, converting ADP into ATP. We found that an increased interaction between these proteins, detected by FCCS, correlates with an increase in the ATP production. In paper II an FCS-based imaging method is developed, capable to determine absolute sizes of objects, smaller than the resolution limit of the microscope used. Combined with STED, this may open for studies of membrane nano-domains, such as those investigated by simulations in paper VII. In paper III and paper IV super resolution STED imaging was applied on Streptococcus Pneumoniae, revealing information about function and distribution of proteins involved in the defense mechanism of the bacteria, as well as their role in bacterial meningitis. In paper V, we used STED imaging to investigate protein distributions in platelets. We then found that the adhesion protein P-selectin changes its distribution pattern in platelets incubated with tumor cells, and with machine learning algorithms and classical image analysis of the STED images it is possible to automatically distinguish such platelets from platelets activated by other means. This could provide a strategy for minimally invasive diagnostics of early cancer development, and deeper understanding of the role of platelets in cancer development. Finally, this thesis presents Monte-Carlo simulations of biological processes and their monitoring by FCS. In paper VI, a combination of FCCS and simulations was applied to resolve the interactions between a transcription factor (p53) and an oncoprotein (MDM2) inside live cells. In paper VII, the feasibility of FCS techniques for studying nano-domains in membranes is investigated purely by simulations, identifying the conditions under which such nano-domains would be possible to detect by FCS. In paper VIII, proton exchange dynamics at biological membranes were simulated in a model, verifying experimental FCS data and identifying fundamental mechanisms by which membranes mediate proton exchange on a local (~10nm) scale.

  • Disputas: 2019-05-03 09:00 Air & Fire, Solna
    Jess, David Unnersjö
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biofysik.
    High-resolution Imaging of Cleared and Expanded Kidney Tissue Samples2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The kidney is one of the most important and complex organs in the humanbody with the task of filtering hundreds of litres of blood daily. It is responsiblefor the salt and acid/base balance in the body, as well as secretinghormones important for red blood cell production and blood pressure regulation. Kidney disease is one of the fastest growing causes of death in the modern world, and this motivates extensive research for better understandingthe function of the kidney in both health and disease. Kidney failure or end stage renal disease (ESRD) is irreversible and requires treatment with dialysisor transplantation. Some of the most important cellular structures for blood filtration in the kidney are of very small dimensions (below 200 nanometers), and thus electron microscopy has previously been the only method with high enough resolution to study the morphology and topology of these minute structures. In three studies included in this thesis, we show that the finest elements of the kidney can now be resolved using different light microscopy techniques. In study 1, we show that by combining optical clearing with STED microscopy, protein localizations in the slit diaphragm of the kidney can be resolved, with widths around 75 nanometers. In study 3, a novel sample preparation method, expansion microscopy, is utilized to isotropically expand kidney tissue samples in space. Expansion improves the effective resolution by a factor of 5, making it possible to resolve podocyte foot processes and the slit diaphragmusing diffraction-limited confocal microscopy. We also show that by combining expansion microscopy and STED microscopy, the effective resolution can be improved even further (<20 nm). In our most recent work, study 5, we apply a simplified, moderate tissue swelling protocol which together with optimization of the confocal imaging provides sufficient resolution to resolve foot processes and parts of the filtration barrier. This new protocol is fast and technically simple, making it ideal for routine use, such as for future clinical pathology. In collaboration with kidney researchers, we have applied both STED microscopy and expansion microscopy to various disease models, showing that these tools can be used to both visualize and quantify pathologies occurring in different parts of the glomerular filtration barrier (GFB). In study 2, STED microscopy in combination with optical clearing is used to study the localization of Coro2b in secondary foot processes in both mouse and human tissue. In two ongoing studies with preliminary results presented in the thesis, we use STED microscopy and optical clearing to study the pathogenesis of focal segmental glomerulosclerosis (FSGS) by the use of genetic mouse models. Based on STED images, we extract different morphological parameters from foot processes and the glomerular filtration barrier (GFB) at different stages of the disease. In study 4, we apply a tissue expansion protocol to answer questions about the phenotype seen in podocytes where the mediator complex subunit 22 (Med22) is inactivated. By inactivating Med22 in a transgenic mouse line with cytosolic expression of tdTomato in podocytes, we saw strong indications that the vesicle-like structures seen in EM micrographs were indeed intracellular vesicles and not dilated sub-podocyte space. In summary, the work presented in this thesis has contributed to the development of a new toolbox for imaging renal ultra-structure using light microscopy, a field previously reserved for electron microscopy.

  • Disputas: 2019-05-03 10:00 Sal F3, Stockholm
    Tomé Torquemada, Silvia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Studies of some thermodynamic aspects related to the production of silicon and ferrosilicon2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis presents a fundamental study on some thermodynamic aspects regarding the silicon and ferrosilicon production. The purity requirements for silicon and ferrosilicon alloys are stringent. In order to achieve a successful and efficient refining of the silicon and ferrosilicon produced by carbothermic reduction, it is of great importance to know the phase relations in the system and to have reliable thermodynamic, kinetic and other physical data for the elements involved.

    The first part of the thesis includes a study of different phase relationships of the SrO-SiO2 and SiO2-SrO-Al2O3 systems. Experiments were performed to determine the phase relationships at temperatures between 1300 °C and 1625 °C in the binary system and at 1450 °C, 1500 °C and 1600 °C in the ternary system. The present result would be valuable when determining the compositions of the refining slags. A fully liquid slag would ensure favorable kinetic conditions in the refining process.

    The activities of some metallic elements in the silicon melt were determined in the second part of the thesis. The activities of Sr, Al, Zr and Ca in silicon were experimentally determined at temperatures that varied between 1450 °C and 1600 °C. These activities would provide useful information regarding the process temperature and the design of refining slags.

    The third part of the thesis covers the study of the activities in a ferrosilicon alloy. The activity coefficients for Al and Ca in FeSi50 were experimentally determined by equilibrating SiO2-Al2O3-CaO slags with ferrosilicon at 1550 °C. The activities obtained would be very useful information for the optimization of the refining process.

  • Disputas: 2019-05-03 10:00 Ka-Sal B (Sal Peter Weissglas), Kista
    Hou, Shuoben
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektronik.
    Silicon Carbide High Temperature Photodetectors and Image Sensor2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Silicon Carbide (SiC) has the advantages of ultraviolet (UV) sensing and high temperature characteristics because of its wide band gap. Both merits make SiC photodetectors very attractive in astronomy, oil drilling, combustion detection, biology and medical applications. Driven by the objective of probing the high temperature surface of Venus (460 °C), this thesis develops SiC photodetectors and an image sensor for extremely high temperature functions. The devices and circuits are demonstrated through the procedure of layout design, in-house processing and characterizations on two batches.

    The process flow has been optimized to be suitable for large scale integration (LSI) of SiC bipolar integrated circuits (IC). The improved processing steps are SiC dry etching, ohmic contacts and two-level metal interconnect with chemical-mechanical polishing (CMP). The optimized process flow is applied in the fabrication of discrete devices, a transistor-transistor logic (TTL) process design kit (PDK) and LSI circuits.

    The photodetectors developed in this thesis, including photodiodes with various mesa areas, a phototransistor and a phototransistor Darlington pair have stable characteristics in a wide temperature range (25 °C ~ 500 °C). The maximum operational temperature of the p-i-n photodiode (550 °C) is the highest recorded temperature accomplished ever by a photodiode. The optical responsivity of the photodetectors covers the spectrum from 220 nm to 380 nm, which is UV-only.

    The SiC pixel sensor and image sensor developed in this thesis are pioneer works. The pixel sensor overcomes the challenge of monolithic integration of SiC photodiode and transistors by sharing the same epitaxial layers and topside contacts. The pixel sensor is characterized from 25 °C to 500 °C. The whole image sensor circuit has 256 (16 ×16) pixel sensors and one 8-bit counter together with two 4-to-16 decoders for row/column selection. The digital circuits are built by the standard logic gates selected from the TTL PDK. The image sensor has 1959 transistors in total. The function of the image sensor up to 400 °C is verified by taking basic photos of nonuniform UV illumination on the pixel sensor array.

    This thesis makes an important attempt on the demonstration of SiC opto-electronic on-chip integration. The results lay a foundation on the development of future high temperature high resolution UV image sensors.

  • Disputas: 2019-05-07 10:00 Kollegiesalen, Stockholm
    Nikouie, Mojgan
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Design, Construction and Evaluation of a StackedPolyphase Bridges Converter for Integrated ElectricDrive Systems in Automotive ApplicationsMOJGAN NIKOUIEDoctoral ThesisStockholm, Sweden2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis presents a new concept for integration of the electricdrive system, specifically for electric and hybrid electric vehicle applications.The topology introduces an integration between the so-calledstacked polyphase bridges (SPB) converter and fractional-slot concentratedpermanent-magnet synchronous machine. The SPB converter iscomprised of an arbitrary number of submodules that are connected inseries to a dc-source voltage. A very compact integrated electric drivesystem is gained by the integration. Several advantages are potentiallygained from the concept, such as considerably shortening the powercables interconnecting the converter with the machine and as well asreduction in terms of electromagnetic interference, weight, and size.The principal focus of the thesis is on the design, construction, andcontrol of the SPB converter. Three different generations for the SPBconverter, all with four submodules, have been developed within theproject. In the first two generations, a submodule consists of a two-layerprinted circuit board (PCB) including both power and control circuits,whereas in the third generation, each submodule has separate powerand control boards. The power circuit is a conventional two-level threephaseconverter. In the third generation, the power PCBs can handlean rms current of 100 A and a dc-link voltage of 100 V.Along with the design of the converter, control algorithms have beendeveloped. A conventional proportional–integral (PI) current controlleris implemented on the microprocessor of each control board, on whichouter control loops are added. One important contribution concerningthe control is the stability analysis and balancing controller designresulting thereof. Since the submodules are series connected to the dcsourcevoltage, it is essential to ensure that the total voltage is sharedequally among the submodules.Secondly, a study of the SPB converter under fault is made. It is assumedthat one submodule is facing a short- or open-circuited powertransistor and the behavior of the converter is studied. A proposal fora safe way of short circuiting the faulty submodule is presented.Finally, torque ripple minimization is discussed. It is shown that usingan estimator for the flux linkage harmonics in the machine as well asadding a resonant part to the PI current controller can be an efficientmethod to suppress the ripple.

  • Disputas: 2019-05-07 13:00 F3, Stockholm
    Sabel, Linda
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande, Fastighetsvetenskap.
    Samhällets styrning av fastighetsindelningen: Dåtid, nutid och framtid2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [sv]

    Markens indelning i fastigheter utgör en grundläggande beståndsdel i samhällsbyggandet. De krav som ställs på fastighetsindelningen får konse­kven­ser för vilka fastigheter som får bildas, registreras och ägas vilket i sin tur påverkar samhälls­utvecklingen i ett bredare perspektiv genom att ange förut­sättningarna för var människor kan bo och bedriva olika verksamheter. I Sverige har staten sedan hundra­­tals år tillbaka på olika sätt reglerat fastigheters utformning och inne­håll. Genom skiftesrefor­mer och förbud har lagstiftaren strävat efter att komma till rätta med uppsplittring av jord i små och olönsamma enheter. Till en början var orsak­erna främst skatte­mässiga men med tiden förflyttades fokus så att national­eko­nomiska och sociala skäl kom att ligga bakom styrningen.

    Många önskemål om förändringar i fastighetsindelningen kan med dagens regel­verk inte tillmötesgås. Syftet med avhandlingen är att undersöka om det nuvarande regelverket kan liberaliseras. Även om de aktuella bestämmelserna har genomgått vissa förändringar för att anpassas till gällande jordpolitik, har bedöm­nings­grunderna som används för att avgöra om en fastighet är lämplig för sitt ändamål (t.ex. bostad, industri, infrastruktur, jordbruk eller skogsbruk) varit i stort sett oförändrade sedan fastighetsbildningslagens tillkomst för snart femtio år sedan.

    Avhandlingen är uppdelad i tre delar. Den första delen beskriver historiken och motiven bakom regel­verkets tillkomst (Del I, Dåtid). Den andra delen inne­håller en studie av den gällande rätts­tillämpningen (Del II, Nutid). I den tredje och sista delen undersöks möjlig­heten att liberalisera regelverket genom att införa vissa lättnader (Del III, Fram­tid). Till stöd för utvärderingen i Del III används rättseko­nomiska och rätts­filosofiska teorier.

    I den historiska översikten (Del I) framträder tre bärande argument för att fastighetsindelningen bör styras med hjälp av allmänna fastig­hets­­bildningsvillkor, nämligen att åstadkomma: stabilitet, rätts­säkerhet och en effektiv markanvänd­ning. I fråga om rättssäkerhetsaspekten framhålls särskilt fastighetens betydelse som kredit­objekt. Granskningen av gällande rätt (Del II) visar att det nuvarande systemet är komplext och svårt att tillämpa samt att det i vissa fall brister i rättssäkerhetshänseende. Av utvär­deringen (Del III) framgår att systemet även kan ifrågasättas ur effektivitets­­­synpunkt. De befarade riskerna med ett mer liberalt synsätt har inte kunnat verifieras. Ett förslag till liberalisering presenteras med utgångs­punkt från två huvudprinciper:

    • Styrning av fastighetsindelningen kan separeras från beslut om mark­an­vändningen, förutom inom områden med bindande planer.
    • Fastighetsbildning som bygger på frivillighet bör tillåtas.
  • Disputas: 2019-05-09 10:00 Kollegiesalen, Stockholm
    Sophonrat, Nanta
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Pyrolysis of mixed plastics and paper to produce fuels and other chemicals2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    As the world population and economy grow, higher consumption results in higher waste packaging, plastics and paper residues. Pyrolysis offers a way to recover fuels and other chemicals from this waste fraction. By applying heat to these materials in the absence of oxygen, pyrolysis process can convert these feedstocks into more valuable products in the forms of gas, liquid and char.

    One important issue in the pyrolysis process which requires an investigation is the interactions between the feedstocks which consist of cellulose as the main component of paper and different types of plastics. Regarding this topic, 3 subtopics were investigated which are: the effect of mixing methods on the co-pyrolysis products, the interactions between the plastics and cellulose, and the formation of H, OH and water during cellulose pyrolysis. All these experimental investigations were based on microscale pyrolysis experiments using Py-GC/MS technique.

    In the first work, polyethylene and cellulose were mixed by melting and by putting side-by-side. It was found that some interactions occurred during co-pyrolysis of these materials which slightly altered the yields of some anhydrosugars, aldehydes and ketones when the two feedstocks were mixed together by melting. Nevertheless, the main pyrolysis products from each feedstock were not affected. 

    In the second study, the investigation continues on the interactions between different types of plastics (PE, PP, PS, PET) and cellulose. By using Py-GC×GC/MS, a good separation of the mixed pyrolysis products could be achieved, thus assisting the analysis. It was found that although the main pyrolysis products from each feedstock were not affected by the co-pyrolysis, small interactions occurred such that the interactions between different plastics were more pronounced than the interactions between plastics and cellulose. Nevertheless, some hydrogen transfer reactions occurred when PS was co-pyrolyzed with cellulose. However, the source of hydrogen was not clear.

    Therefore, the investigation on the formation of H and OH radicals during cellulose pyrolysis was performed. This work combined first-principle calculations with experimental investigations. The author of the thesis was responsible for the experimental part. It was found from the first-principle calculations that it is energetically more favorable for the generation of a pair of H and OH radicals with subsequence formation of water than to generate a single radical because the formation of a double bond on the resulting cellulose helps stabilize the structure. With Gibbs free energy calculations, it was predicted that the water would be released at 280 °C. This agree well with the experimental findings from multistep pyrolysis of cellulose in Py-GC/MS which showed that water was generated at two different temperature ranges with the first peak around 280 °C.

    As the interactions between the feedstocks during co-pyrolysis do not much improve the liquid products’ properties, and the nature of the products produced from plastics and paper pyrolysis are significantly different; it might be more beneficial to separate the pyrolysis products from the two feedstocks. Moreover, the hydrocarbons produced from plastics pyrolysis and the oxygenated products from paper pyrolysis require different upgradation methods. Stepwise pyrolysis was then proposed to produce and collect these two products separately. With simulated feedstock mixtures (PE, PS, cellulose) and real waste fractions which are paper rejects, it was successfully demonstrated that the stepwise pyrolysis with a temperature of the first step of 300-350 °C and a temperature of the second step of 500 °C could be used to produce two products streams as previously described. However, an optimization of the process and further investigations on product properties and upgradation are still required.

    As a continuation on the investigation of the stepwise pyrolysis, an upgradation of the products from the first pyrolysis step was studied. When PVC plastic is present in the feedstock, dehydrochlorination of PVC occurs in the temperature range of the first pyrolysis step together with the pyrolysis of cellulose. Calcium oxide (CaO) was then tested for the simultaneous adsorption of HCl and reforming of cellulose pyrolysis products. The experiments were performed in a two-stage reactor system which was a pyrolysis reactor connected in series to a catalytic reactor containing CaO. It was found that the catalytic temperature should be between 300-350 °C because the desorption of HCl occurred when the temperature was higher than 400 °C. This was partly due to a reaction between water and CaCl2 which caused the desorption of HCl.

    From all the studies, stepwise pyrolysis has a great potential to produce fuels and other chemicals from mixed plastics and paper. Further investigations are needed to develop, evaluate and realize this promising process.

  • Disputas: 2019-05-09 10:00 sal F3, Stockholm
    Adolfsson, Karin
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Hydrothermal recycling of natural and synthetic polymers to functional carbon materials2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Utilizing renewable recourses and waste recycling are necessary for reaching a circular resource society. The concept of this thesis was to set up a sustainable recycling route, suitable even for low quality biopolymer and plastic waste for production of functional carbon materials. Carbonaceous materials were prepared by mild hydrothermal carbonizations of cellulose and polypropylene (PP) under acidic conditions. The carbonization of cellulose resulted mainly in micro-/nanometer sized carbon spheres (CS) with polar functionalities. After carbonization of PP, products were found in solid and liquid phase. Completely carbonized solid carbons products were obtained from PP at 250 °C after 60 min. The liquid products from the same process displayed aromatics and exhibited fluorescence properties. In addition, new carbon materials were prepared by acid, base and thermal treatments of the carbonized products at low temperatures. Thermally resistant carbon products and antibacterial CS towards both Staphylococcus aureus and Pseudomonas aeruginosa were demonstrated as possible applications for these products. The minimum inhibitory concentrations of CS were 200-400 µg mL-1 depending on the bacteria strain and reached after only 3 h. Furthermore, nanometer sized carbon nanodots with high oxygenation degree and fluorescence properties were derived together with carbon flakes (CF) from the carbonized products. The CF with flat and micrometer sized morphology and polar groups were utilized for coating of cationized cellulose filters, applied as adsorbents and then subsequently as surfaces for SALDI-MS analysis of environmental contaminants. This work contributes with new routes to and applications for functional carbon materials.

    Fulltekst tilgjengelig fra 2020-04-30 10:30
  • Disputas: 2019-05-10 09:00 Kollegiesalen, Stockholm
    Locke, Ryan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Urbana och regionala studier.
    City Re-Making Approaches in Contemporary Urbanism: “Re-Urbanism” as a Strategy for the Revitalization of Detroit and Declining Cities2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Many cities today are experiencing extreme widespread urban decline, at a time when urban growth and revitalization are prioritized on the agenda. This dissertation examines a number of prominent urban revitalization strategies for declining cities, specifically highlighting the emblematic case of Detroit as a research subject. That city offers many lessons as the epitome of both urban decline and urban revitalization, as evidenced through the media narratives surrounding the “rebirth of Detroit” and its positive improvements over recent years. Through this and other case studies, the dissertation investigates different approaches in the leading contemporary paradigms of urbanism, including the role of place-based and heritage-based strategies for the declining city, and their different structural approaches. These include differences sought in both city structure, and in the collaborative structure of revitalizing institutions. From there, the dissertation draws key lessons together into a synthesis approach called “Re-Urbanism” – an advancement of a model originally developed by Robert Fishman. The model describes strategic partnerships between local government entities, private business leaders, private charitable foundations, small scale grass roots activism, and local entrepreneurship, all aimed at making place-based, heritage-based structural reconnections within the city itself. The dissertation concludes with specific policy and practice recommendations, as well as ideas for further research.

  • Disputas: 2019-05-10 10:00 FA-31, Stockholm
    Kianirad, Hoda
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Studies on Domain Dynamics in Nonlinear Optical Ferroelectric Oxide Crystals2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nonlinear optical frequency conversion is the key technology for modifying laser output radiation, in order to target specific applications. The most powerful technique to obtain tailored second-order nonlinear interactions is the quasi-phasematching (QPM) approach. QPM is based on periodic modulation of the medium’s nonlinearity and allows versatile and efficient frequency conversion in the whole transparency region of the material. QPM is commonly implemented in ferroelectric oxide crystals by periodically inverting the spontaneous polarization, so-called, periodic poling. However, in order to achieve QPM structures of practical relevance, both the optical properties of the material and the domain engineering techniques have to be suitable for the targeted nonlinear interaction.

    Rb-doped KTiOPO4 (RKTP) and vapor-transport-equilibrated stoichiometric LiTaO3 (VTE-SLT) are two of the most promising ferroelectric oxides used for nonlinear optics. The former is suitable for high peak-power applications and for engineering of QPM devices with sub-µm periodicity. The latter shows a short cut-off wavelength with low linear absorption, which makes it very attractive for UV-light generation. However, in order to fully exploit the potential of these two materials, it is of utmost importance to understand the domain dynamics and stability from a fundamental point of view, as well as to investigate ways to overcome their limitations.

    This thesis presents studies on domain dynamics and stability in these two materials. A novel method for periodic poling of RKTP has been investigated. The method, based on using a micro-structured silicon chip as the contact electrode, has been used to fabricate periodically poled RKTP crystals with 9.01 µm period. The samples became well-poled and showed high conversion efficiency for second harmonic generation. The domain dynamics, when the silicon stamp was used as an electrode were studied, showing potential for short-pitch poling and complex patterning.

    Furthermore, the domain stability in RKTP during thermal annealing at high temperatures was investigated. The results show anisotropic domain wall motion, with severe domain contraction along the crystallographic b-axis when the periodicity was reduced. A technique to suppress this domain contraction was developed based on dicing away the edges of the QPM grating so that the domain b-faces terminate in air. This gave excellent results for a broad range of periodicities.

    Studies of the domain stability of periodically poled VTE-SLT during chemical etching were performed by on-line second harmonic generation, and optical microscopy. The results show that wet etching directly after poling leads to domain-wall motion, resulting in back-switching or domain merging. 

    Furthermore, the domain wall motion induced by electron beam irradiation was investigated using a scanning electron microscope. It was found that domain switching strongly depends on the ratio of secondary electrons to incident electrons. These results are discussed in terms of electron beam and screening charges interaction.

  • Disputas: 2019-05-10 10:00 F3, Stockholm
    Ingverud, Tobias
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Ytbehandlingsteknik. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Exploring crosslinked networks of polymers and hybrid cellulose materials2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The field of polymer chemistry has in recent decades had an immense development, resulting in new functional materials with groundbreaking applications. This has been driven partly by strong interdisciplinary alliances between the fields of medicine, biology, chemistry, and materials science. Thermoresponsive block copolymers, have been built for their ability to self-assemble, giving possibility of encapsulation and release of medicine. The dendritic polymer family have been demonstrated as a prime example of highly reactive and interactive functional materials, suitable for biomedical applications. The importance of amines is greatly appreciated in general and especially in polymer chemistry, due to their nucleophilic characteristics in reactions, but also for their ability to interact with other species. There’s also an increase in awareness of standard of living, the effects of climate change and population growth. These are challenges, in need of our outmost focus and knowledge, to direct our path to, towards a more bio based circular economy. This starts, in Sweden, by taking better care of our forest and utilizing its resourceful crop. This thesis seek out spontaneous crosslinking, of various functional polymers, with focus towards hybridizing with nanocellulosic material.

    Initially, interactive permanently charged amine-functional thermoresponsive tri- and star-block copolymers were composed. These were evaluated and used as electrostatic macro-crosslinker of cellulose nanofibrils (CNFs), resulting in thermoresponsive, low dry weight content hydrogels, with notable temperature dependent storage modulus.

    Secondly, reactive and interactive amine-functional dendritic-linear-dendritic (DLD) species were constructed and evaluated in vitro and in vivo. The DLD scaffolds were utilized as fast-degrading, inhibiting surgical site infection (SSIs) antibacterial hydrogel coatings. The crosslinking of the poly(ethylene glycol) (PEG) system was optimized in order to create a two component system, which could be applied with dual syringes. This enabled instantaneous gelation under physiological conditions. The hydrogels moduli could be varied to match various tissues.

    Thirdly, insights and characterizations were provided in the commercial heterofunctional poly(amido amine) carboxylate hyperbranched Helux. Amine post-modifications and intrinsic heterofunctionality alterations of Helux were explored, by increasing the molecular weight and forming Helux self-crosslinked films. Furthermore, two component hydrogels based on Helux and PEG demonstrated curing temperature dependent moduli in the rheometer.

    Finally, utilizing Helux in combination with CNFs to demonstrate the potential to mix on the nanoscale without aggregation. The CNF-Helux could form hydrogels, and wet-stable thermo-crosslinked CNF-Helux composites assemblies such as films and aerogels, with further excess of amines ready for post-modifications of the crosslinked 3D-network.

    Fulltekst tilgjengelig fra 2020-04-16 12:13
  • Disputas: 2019-05-10 14:00 F3, Stockholm
    Benselfelt, Tobias
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Fiberteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Design of Cellulose-based Materials by Supramolecular Assemblies2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Due to climate change and plastic pollution, there is an increasing demand for bio-based materials with similar properties to those of common plastics yet biodegradable. In this respect, cellulose is a strong candidate that is already being refined on a large industrial scale, but the properties differ significantly from those of common plastics in terms of shapeability and water-resilience.

    This thesis investigates how supramolecular interactions can be used to tailor the properties of cellulose-based materials by modifying cellulose surfaces or control the assembly of cellulose nanofibrils (CNFs). Most of the work is a fundamental study on interactions in aqueous environments, but some material concepts are presented and potential applications are discussed.

    The first part deals with the modification of cellulose by the spontaneous adsorption of xyloglucan or polyelectrolytes. The results indicate that xyloglucan adsorbs to cellulose due to the increased entropy of water released from the surfaces, which is similar to the increased entropy of released counter-ions that drives polyelectrolyte adsorption. The polyelectrolyte adsorption depends on the charge of the cellulose up to a limit after which the charge density affects only the first adsorbed layer in a multilayer formation.

    Latex nanoparticles with polyelectrolyte coronas can be adsorbed onto cellulose in order to prepare hydrophobic cellulose surfaces with strong and ductile wet adhesion, provided the glass transition of the core is below the ambient temperature.

    The second part of the thesis seeks to explain the interactions between different types of cellulose nanofibrils in the presence of different ions, using a model consisting of ion-ion correlation and specific ion effects, which can be employed to rationally design water-resilient and transparent nanocellulose films. The addition of small amounts of alginate also creates interpenetrating double networks, and these networks lead to a synergy which improves both the stiffness and the ductility of the films in water.

    A network model has been developed to understand these materials, with the aim to explain the properties of fibril networks, based on parameters such as the aspect ratio of the fibrils, the solidity of the network, and the ion-induced interactions that increase the friction between fibrils. With the help of this network model and the model for ion-induced interactions, we have created films with wet-strengths surpassing those of common plastics, or a ductility suitable for hygroplastic forming into water-resilient and biodegradable packages. Due to their transparency, water content, and the biocompatibility of cellulose, these materials are also suitable for biomaterial or bioelectronics applications. 

    Fulltekst tilgjengelig fra 2019-12-31 23:59
  • Disputas: 2019-05-10 15:00 D3, Stockholm
    Dastory, Linda
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Nationalekonomi.
    Innovation, Technical Change and the Labour Market2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This doctoral thesis consist of four papers. The two first papers are related to financialeconomics and the other two to labour economics. All four papers deal with microeconomicsanalysis of individuals and firms. Where the first two are from a firms perspectiveand the two second once are from an individual perspective. Moreover, all four papersunderline the importance of innovation for productivity,competitiveness and economicgrowth.In the first essay we use German Community Innovation Survey to identify financiallyconstrained firms. Contrary to previous studies we find that the relationship betweenfinancial constraints and firm size is inverted u-shaped and that it is the group ofmedium sized firms which has the largest funding gaps. This is explained by the factthat these firms have high innovation capabilities but at the same time face high cost ofcapital. Furthermore, we test if financial constraints have an impact on firm productivitygrowth. We find negative effects from funding gaps on productivity, but only for investmentin tangible capital and not for innovation investments.The second essay investigates whether there has been a change in the productivityand funding mix of innovative SMEs post stricter bank regulations. Our result showsthat the likelihood of using bank loans as a funding source has not changed for innovationinvestments nor for tangible investments after stricter capital regulations have beenannounced. On the other hand, sources such as subsidies have increased due to regulatoryprograms that have been implemented in the aftermath of the recent financial crisis.Furthermore, SMEs productivity has not changed post stricter bank regulations. Overall,the impact from different sources of funding on productivity is rather limited.The third essay explores firm formation by migrants with a STEM background. Theresult shows that native born STEM workers have a higher probability to form firmsrelative to migrants. Further categorization of migrants shows that refugees are morelikely to become entrepreneurs than EU-labour migrants. Overall, entrepreneurial migrantshave equal or higher predicted income in comparison to native born STEM entrepreneurs.The fourth essay analysis wage effects from changing work tasks using a tasked-basedapproach where workers are mapped in a two dimensional model classified by their cognitiveand routine task content. The result shows clear signs of wage polarization. switchfrom routine and manual tasks to non routine cognitive task yields an average wage premiumof about 2-6%. More importantly, while the gap was 1-5% in the beginning of theperiod, it increased to 10-13% at the end of the period. The result suggest that adaptingnew production technology and innovations to complement analytical skills has a higherand increasing marginal productivity compared to technologies aimed to replace or complementroutinized and manual work tasks. The period of this study is associated withseveral so-called breakthrough technologies such as, computerization, robotization, digitalizationand the introduction of IT technology.

  • Disputas: 2019-05-16 10:00 Sal F3, Stockholm
    Anton, Nicholas
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Engine Optimized Turbine Design2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The focus on our environment has never been as great as it is today. The impact of global warming and emissions from combustion processes become increasingly more evident with growing concerns among the world’s inhabitants. The consequences of extreme weather events, rising sea levels, urban air quality, etc. create a desperate need for immediate action. A major contributor to the cause of these effects is the transportation sector, a sector that relies heavily on the internal combustion engine and fossil fuels. The heavy-duty segment of the transportation sector is a major consumer of oil and is responsible for a large proportion of emissions.

    The global community has agreed on multiple levels to reduce the effect of man-made emissions into the atmosphere. Legislation for future reductions and, ultimately, a totally fossil-free society is on the agenda for many industrialized countries and an increasing number of emerging economies.

    Improvements of the internal combustion engine will be of importance in order to effectively reduce emissions from the transportation sector both presently and in the future. The primary focus of these improvements is undoubtedly in the field of engine efficiency. The gas exchange system is of major importance in this respect. The inlet and exhaust flows as the cylinder is emptied and filled will significantly influence the pumping work of the engine. At the center of the gas exchange system is the turbocharger. The turbine stage of the turbocharger can utilize the energy in the exhaust flow by expanding the exhaust gases in order to power the compressor stage of the turbocharger.

    If turbocharger components can operate at high efficiency, it is possible to achieve high engine efficiency and low fuel consumption. Low exhaust pressure during the exhaust stroke combined with high pressure at the induction stroke results in favorable pumping work. For the process to work, a systems-based approach is required as the turbocharger is only one component of the engine and gas exchange system.

    In this thesis, the implications of turbocharger turbine stage design with regards to exhaust energy utilization have been extensively studied. Emphasis has been placed on the turbine stage in a systems context with regards to engine performance and the influence of exhaust system components.

    The most commonly used turbine stage in turbochargers, the radial turbine, is associated with inherent limitations in the context of exhaust energy utilization. Primarily, turbine stage design constraints result in low efficiency in the pulsating exhaust flow, which impairs the gas exchange process. Gas stand and numerical evaluation of the common twin scroll radial turbine stage highlighted low efficiency levels at high loadings. For a pulse-turbocharged engine with low exhaust manifold volume, the majority of extracted work by the turbine will occur at high loadings, far from the optimum efficiency point for radial turbines. In order for the relevant conditions to be assessed with regards to turbine operation, the entire exhaust pulse must be considered in detail. Averaged conditions will not capture the variability in energy content of the exhaust pulse important for exhaust energy utilization.

    Modification of the radial turbine stage design in order to improve performance is very difficult to achieve. Typical re-sizing with modifying tip diameter and trim are not adequate for altering turbine operation into high efficiency regions at the energetic exhaust pulse peak.

    The axial turbine type is an alternative as a turbocharger turbine stage for a pulse-turbocharged engine. The axial turbine stage design can allow for high utilization of exhaust energy with minimal pressure interference in the gas exchange process; a combination which has been shown to result in engine efficiency improvements compared to state-of-the-art radial turbine stages.

  • Disputas: 2019-05-17 10:00 Air & Fire auditorium, Science for Life Laboratory, Solna
    Cengic, Ivana
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Proteinvetenskap, Systembiologi.
    Synthetic biology approaches for improving production of fatty acid-derived compounds in cyanobacteria2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The environmental consequences associated with the use of fossil-sourced fuels and chemicals have brought with it a realization that future development must move in a more sustainable direction. Currently available biofuels or renewably produced chemical, such as bioethanol or biodiesel, are produced from microbial fermentation of sugar-rich crops or by chemical conversion of natural oils or fats. However, these strategies are not sustainable in the long run as fuel and chemical production competes with food supply and arable land usage. Instead of relying on photosynthetic feedstocks that require further conversion, one can engineer photosynthetic cyanobacteria to produce a product of interest directly from CO2 and sunlight. The first part of this thesis aimed to develop new synthetic biology tools for the model cyanobacteria Synechocystis sp. PCC 6803. The second part of the thesis focused on evaluating the regulation of fatty acid synthesis in cyanobacteria, and the production of fatty acid-derived chemicals in Synechocystis.

    In paper I, fusion of small affinity proteins (Affibodies) to the major type IV pili protein was shown to mediate successful surface display of the affibody. This surface display strategy was further shown to allow inter-species binding between Synechocystis and Escherichia coli or Staphylococcus carnosus displaying complementary polymerizing affibodies.

    In paper II, a CRISPR-interference tool was successfully implemented in Synechocystis for inducible gene repression. Further, its multiplexing ability was proven by simultaneous repression of up to four aldehyde reductase/dehydrogenase genes. In paper III, this established CRISPRi tool was used to target and repress native pathways competing with heterologous fatty alcohol production in Synechocystis. Repressing the gene encoding the PlsX phosphate acyltransferase allowed re-direction of carbon-flux from membrane lipids to fatty alcohol production, with a final best strain producing 10.4 mg g-1 DCW octadecanol and hexadecanol.

    In paper IV, the transcriptional response towards perturbations within the fatty acid synthesis pathway was evaluated for the two model cyanobacteria Synechocystis and Synechococcus elongatus PCC 7942. Preliminary results indicate that blocking fatty acid synthesis initiation/elongation causes a transcriptional response of the involved pathway genes only in S. elongatus PCC 7942, indicating differential transcriptional responses in these two strains.

    In paper V, metagenomically sourced aldehyde deformylating oxygenase (Ado) variants were evaluated for their alka(e)ne synthesizing ability. Several of these novel Ado enzymes outperformed the generally well-performing Ado from S. elongatus when relating alka(e)ne production to the soluble enzyme amount.

  • Disputas: 2019-05-17 13:00 Ka-Sal B (Sal Peter Weissglas), Stockholm
    Ivanisevic, Nikola
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektronik, Integrerade komponenter och kretsar.
    Circuit Design Techniques for Implantable Closed-Loop Neural Interfaces2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Implantable neural interfaces are microelectronic systems, which have the potential to enable a wide range of applications, such as diagnosis and treatment of neurological disorders. These applications depend on neural interfaces to accurately record electrical activity from the surface of the brain, referred to as electrocorticography (ECoG), and provide controlled electrical stimulation as feedback. Since the electrical activity in the brain is caused by ionic currents in neurons, the bridge between living tissue and inorganic electronics is achieved via microelectrode arrays. The conversion of the ionic charge into freely moving electrons creates a built-in electrode potential that is several orders of magnitude larger than the ECoG signal, which increases the dynamic range, resolution, and power consumption requirements of neural interfaces. Also, the small surface area of microelectrodes implies a high-impedance contact, which can attenuate the ECoG signal. Moreover, the applied electrical stimulation can also interfere with the recording and ultimately cause irreversible damages to the electrodes or change their impedance. This thesis is devoted to resolving the challenges of high-resolution recording and monitoring the electrode impedance in implantable neural interfaces.

    The first part of this thesis investigates the state-of-the-art neural interfaces for ECoG and identifies their limitations. As a result of the investigation, a high-resolution ADC is proposed and implemented based on a ΔΣ modulator. In order to enhance performance, dynamic biasing and area-efficient switched-capacitor circuits were proposed. The ΔΣ modulator is combined with the analog front-end to provide a complete readout solution for high-resolution ECoG recording. The corresponding chip prototype was fabricated in a 180 nm CMOS process, and the measurement results showed a 14-ENOB over a 300-Hz bandwidth while dissipating 54-μW.

    The second part of this thesis expands upon the well-known methods for impedance measurements and proposes an alternative digital method for monitoring the electrode-tissue interface impedance. The proposed method is based on the system identification technique from adaptive digital filtering, and it is compatible with existing circuitry for neural stimulation. The method is simple to implement and performs wide-band measurements. The system identification was first verified through behavioral simulations and then tested with a board-level prototype in order to validate the functionality under real conditions. The measurement results showed successful identification of the electrode-electrolyte and electrode-skin impedance magnitudes.

  • Disputas: 2019-05-23 10:00 F3, Stockholm
    Zhaoxuan, Feng
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymerteknologi.
    From Polysaccharides to Functional Materials for Trace Pharmaceutical Adsorption2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The transition to bioeconomy will reduce our dependency on fossil fuels as well as contribute to a more sustainable society. Within this framework, exploitation and development of renewable substitutes to petroleum-based products provides feasible roadmap for the material design. Here a perspective is provided to how the natural polysaccharides chitosan (CS) and/or cellulose (CL) could be elaborated and transformed to high-performance materials with the explicit aim of removing trace pharmaceutical contaminants from the wastewater, thus facilitating the sustainable development. In the first part of the thesis, chitosan and cellulose were converted to the carbon spheres (C-sphere) through a microwave-assisted hydrothermal carbonization process, and C-sphere was further broken down to the nanographene oxide (nGO) via a simple oxidation route. On this foundation, a green pathway was developed for fabrication of biobased materials for wastewater purification. First, macroporous chitosan-based composite hydrogels with controllable properties were developed, where chitosan-derived nGO worked as a functional property enhancer. Second, a further development changing from the bulky hydrogels to microgels consisting of CS composite particles in the microscopic size was achieved by a fast one-pot spraying-drying process. The crosslinking reaction occurred in situ during the spray-drying. Last, the C-sphere by-itself was also believed to be a potential adsorbent for wastewater contaminants. In the next step the prepared systems were evaluated for their capacity to adsorb pharmaceutical contaminants. Diclofenac sodium (DCF) was utilized as the model drug, and the three fabricated bio-adsorbents all demonstrated effective DCF adsorption performance, with the adsorption efficiency varying from 65.6 to 100%. Moreover, the DCF adsorption kinetics, isotherms and thermodynamic study were also investigated to reveal the nature of the adsorption process with the different materials. Finally, chitosan-based microspheres were selected for the reusability study, with the adsorption efficiency above 70% retained after six adsorption-desorption cycles, thus further endowing the promising potential of the fabricated bio-adsorbents for commercial applications.

    Fulltekst tilgjengelig fra 2020-04-20 12:12
  • Disputas: 2019-05-24 10:15 F3, Stockholm
    Winroth, Marcus
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Dynamics of Exhaust Valve Flows and Confined Bluff Body Vortex Shedding2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis can be divided into two interconnected topics; engine exhaust-valve flows and confined bluff-body vortex shedding. When optimising engine flow systems it is common to use low order simulation tools that require empirical inputs, for instance with respect to flow losses across the exhaust valves. These are typically obtained from experiments at low pressure ratios and for steady flow, assuming the flow to be insensitive to the pressure ratio and that it can be considered as quasi-steady. Here these two assumptions are challenged by comparing measurements of mass-flow rates under steady and dynamic conditions at realistic pressure ratios. The experiments with a static valve were carried out using a high-pressure flow bench at cylinder pressures up to 500 kPa. For the dynamic-valve experiments the transient flow rate during the blowdown phase of an initially pressurised cylinder was determined. Here a linear motor actuated the valve to obtain equivalent engine speeds in the range 800–1350 rpm. It was shown that neither of the above mentioned assumptions are valid and a new non-dimensional quantification of the steadiness of the process was formulated. Furthermore it was shown through Schlieren visualisation that the shock structures in the exhaust port differ depending on if the system dynamics are included or not. The study shows that reliable results of flow losses past exhaust valves can only be obtained in dynamic experiments at representative pressure ratios. The second topic arose from the need to monitor time-resolved mass-flow rates in conduits. A mass-flow meter based on vortex shedding from bluff bodies was designed where microphones are used to detect the shedding frequency. It consists of a forebody and a downstream mounted tail and the system was shown to be capable of measuring pulsating flow rates. Furthermore, the flow topology associated with different forebody and splitter plates has been characterised, through visualisation of the flow behind the shedder and on the splitter plate. It has been shown that for long splitter plates a “horse shoe” like vortex, which attaches to the tail, is formed. It has also been shown that another energetic mode (denoted mode-II) can interact with and disrupt the primary vortex formation. A hypothesis for the appearance of mode-II has been formulated, linking it to the periodic separation of the boundary layer at the conduit wall.

  • Disputas: 2019-05-28 13:00 F3, Stockholm
    Parsanezhad, Pouriya
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande, Projektkommunikation.
    Towards a BIM-enabled Facility Management: Promises, Obstacles and Requirements2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A substantial share of the organisations’ annual costs is associated with their facilities. A fundamentalshift from a reactive facility management (FM) practice to a strategically orchestrated FM profession isthus a prerequisite for increased resource efficiency. A coordinated facility management practicecompels, in turn, appropriate information logistics. Building Information Modelling (BIM) is one of themost prominent initiatives frequently addressed by scholars and practitioners as a game-changer inconstruction industry as whole including FM. In order to fully reap the benefits of BIM in FM,however, further research is required. This study aims, therefore, to investigate the challenges againstsuccessful implementation and realizing the benefits of BIM in FM.The primary focus in this study is the FM phase; but the earlier upstream phases have also been studieddue to their implications for a BIM-enabled FM. From a spatial-scale perspective, this study is mainlyfocused on buildings rather than other construction entities. The findings could benefit both academicsand practitioners. Overall, a pragmatic research philosophy has been adopted and the main appliedresearch strategy is case study.The current dissertation is composed of five papers. The focus of the knowledge acquisition throughpapers alternately shifts between the applied and the theoretical. The primary theoretical grounds of thepapers are the built environment management model (BEM2) (Ebinger and Madritsch, 2012) and BIMFramework (Succar, 2009). Further theories from the fields of design methodology and cognitivescience have also been revisited.Paper 1 provides the theoretic basis for more focused studies on existing and desired processes in FMand their associated information transactions. In Paper 2, the current status of the building informationmanagement technologies applied in FM are summarized, the prevailing issues are identified and anumber of technical solutions have been devised. Paper 3 shifts the focus back to the design phase andprovides a knowledge base for developing further theoretical frameworks and conceptual models thatsupport IT-implementation for formalized requirements management. Through Paper 4, it has beeninvestigated how beneficial contemporary design-intent BIM deliverables could be to FM and whatshould be improved. The focus of Paper 5 again shifts back to the FM phase. Here, a methodology hasbeen presented for measuring the benefits of BIM in FM using a proposed benefits realizationassessment framework.Obtaining the full range of the benefits of BIM in FM, however, requires radical organizationalchanges and introducing new roles. Further research is needed for defining new business models thatunderpin and motivate such extensive organizational and procedural changes. More research shouldalso be undertaken for enhancing data interoperability among different actors as well as digitalrepresentations at different spatial scales namely BIM and GIS sources.

  • Disputas: 2019-05-28 15:00 Conference room, Madrid
    Ploussard, Quentin
    KTH, Skolan för elektroteknik och datavetenskap (EECS). Research Technology Institute, Comillas Pontifical University, Spain; Delft University of Technology, the Netherlands.
    Efficient reduction techniques for a large-scale Transmission Expansion Planning problem2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The aim of Transmission Expansion Planning (TEP) studies is to decide which, where, and when new grid elements should be built in order to minimize the total system cost. The lumpiness of the investment decisions, together with the large size of the problem, make the problem very hard to solve. Consequently, methods should be put in place to reduce the size of the problem while providing a similar solution to the one that would be obtained considering the full size problem. Techniques to model the TEP problem in a compact way, also called reduction methods, can reduce the size of the TEP problem and make it tractable. This thesis provides new techniques to reduce the size of the TEP problem in its main three dimensions: the representation made of the grid (spatial dimension), the representation made of the relevant operation situations (temporal representation), and the number of candidate grid elements to consider. In each of the three reduction techniques proposed in this thesis work, the first step consists in solving a linear relaxation of the TEP problem. Then, they make use of information that is relevant to make the network investment decisions to formulate the TEP problem in a compact way for a certain dimension. I use the potential benefits brought by candidate lines to reduce the size of the representation made of the temporal variability in the problem. Besides, I reduce the size of the network by preserving the representation made of the congested lines and partially installed lines while computing an equivalent for other network elements. Lastly, I manage to reduce the set of candidate lines to consider based on the set of expanded corridors and the amount of new capacity built in them. I also compare each of the reduction techniques that I have developed to alternative reduction methods discussed in the literature within various case studies. In each of the three reduction methods proposed, the TEP solution computed solving the TEP problem resulting from applying the proposed reduction methods is more accurate (efficient) than the ones computed applying alternative reduction methods. Besides, this solution is almost as efficient as the solution of the original TEP problem, i.e. the TEP problem that has not been reduced by the proposed reduction method. As a next step, one may explore combining the three reduction methods proposed to maximize the reduction achieved in the size of the TEP problem.

  • Disputas: 2019-06-05 10:00 Q2, Stockholm
    Schillinger, Philipp
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Bosch Center for Artificial Intelligence.
    Specification Decomposition and Formal Behavior Generation in Multi-Robot Systems2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Autonomous robot systems are becoming increasingly common in service applications and industrial scenarios. However, their use is still mostly limited to rather simple tasks. This primarily results from the considerable effort that is required to manually program the execution plans of the robots. In this thesis, we discuss how the behavior of robots can be automatically generated from a given goal specification. This forms the basis for providing formal guarantees regarding optimality and satisfaction of the mission goal specification and creates the opportunity to deploy these robots in increasingly sophisticated scenarios. Well-defined robot capabilities of comparably low complexity can be developed independently from a specific high-level goal and a behavior planner can then automatically compose them to achieve complex goals in a verifiably correct way.

    Intelligent coordination of a robot team can highly improve the performance of a system, but at the same time, considering multiple robots introduces significant additional planning complexity. To address the complexity, a framework is proposed to efficiently plan actions for multi-robot systems. The generated behavior of the robots is guaranteed to fulfill complex, temporally extended, formal mission specifications posed to the team as a whole. To achieve this, several challenges are addressed such as decomposition of a specification into tasks, allocation of tasks to robots, planning of actions to execute the assigned tasks, and coordination of action execution. This enables the combination of heterogeneous robots for automating tasks in a wide range of practically relevant applications.

    The proposed methods determine efficient actions for each robot in the sense that these actions are optimal in the absence of execution uncertainty and otherwise, improve the solution performance over time based on online observations. First, to plan optimal actions, an approach called Simultaneous Task Allocation and Planning is proposed to utilize the interplay of allocation and planning based on automatically identified, independently executable tasks. Second, to improve performance in the presence of stochastic actions, a Hierarchical LTL-Task MDP is proposed to combine auction-based allocation with reinforcement learning to achieve the desired performance with feasible computational effort. Both approaches of the presented framework are evaluated in the considered use case areas of service robotics and factory automation. The results of this thesis enable to plan correct-by-construction behavior from expressive specifications in more complex and realistic scenarios than possible with previous approaches.

  • Disputas: 2019-06-10 13:00 Kollegiesalen, Stockholm
    Ahlin Marceta, Jesper
    Filosofi och historia, KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Filosofi och teknikhistoria, Filosofi.
    Authenticity in Bioethics: Bridging the Gap between Theory and Practice2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of this doctoral thesis is to bridge the gap between theoretical ideals of authenticity and practical authenticity-related problems in healthcare. In this context, authenticity means being "genuine," "real," "true to oneself," or similar, and is assumed to be closely connected to the autonomy of persons. The thesis includes an introduction and four articles related to authenticity. The first article collects various theories intended to explain the distinction between authenticity and inauthenticity in a taxonomy that enables oversight and analysis. It is argued that (in-)authenticity is difficult to observe in others. The second article offers a solution to this difficulty in one theory of authenticity. It is proposed that under certain circumstances, it is morally justified to judge that the desires underlying a person's decisions are inauthentic. The third article incorporates this proposition into an already established theory of personal autonomy. It is argued that the resulting conceptualization of autonomy is fruitful for action-guidance in authenticity-related problems in healthcare. The fourth article collects nine cases of possible authenticity-related problems in healthcare. The theory developed in the third article is applied to the problems, when this is allowed by the case-description, to provide guidance with regard to them. It is argued that there is not one universal authenticity-related problem but many different problems, and that there is thus likely not one universal solution to such problems but various particular solutions.