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  • Public defence: 2020-06-02 09:00 Registrera dig här: https://kth-se.zoom.us/webinar/register/WN_vZiy4PpORU2GrLe-nbAwaw
    Lundberg, Joacim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI - Statens Väg- och Transportforskningsinstitut.
    Road Surface and Tyre Interaction: Functional Properties affecting Road Dust Load Dynamics and Storage2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Particulate matter is a problem for human health, where several relationships between negative health effects and air pollution has been found, including, but not limited to, respiratory diseases, lung cancer and cardiovascular diseases. In countries where studded tyres are used, for example Sweden, Norway and Finland, and where traction sanding is used, particles from abrasion wear of pavements and crushing of traction sand contribute significantly to PM10.

    The thesis has several objectives, where a broader aim is to investigate the complex road surface and tyre system regarding abrasion wear of pavements and the impact on abrasion wear particles and road dust. The thesis also aims to put these aspects in relation to other, equally complex, aspects coming from or affected by the road surface and tyre interaction which include noise, rolling resistance and friction. This is done through some more specific objectives and limitations described in the thesis. The thesis also has the fundamental aim to act as a starting point to reach a more holistic approach to understand the functional performance of the road surface and tyre interaction which has been done in cooperation with Vieira and the results he publishes in his thesis.

    The road surface and tyre interaction consist of a complex contact system which is affected by both tyre properties and the road surface course properties, including both its inherent material properties and the road surface characteristics, as well as the surrounding environment and any interface consisting of for example water, slush, snow, ice or sand and so on.

    The surface wear course has several functions which is dependent on the inherent material properties. The wear course must resist several degradation processes, including chipping, different types of deformation, different types of cracking as well as abrasion wear due to studded tyres to mention some.

    The surface course construction and the traffic characteristics affect the particle generation, where the surface course properties that govern the resistance against abrasion wear also affect the generation of wear particles.

    Other aspects which are affected by the road surface and tyre interaction is the generation of noise and the rolling resistance. Noise has, as for particles, an negative impact on health and the road surface and tyre interaction is the dominating source from about 15 km/h to 25 km/h for light traffic and from about 30 to 35 km/h for heavy traffic. Several mechanisms generate or amplifies the noise and is connected to the surface characteristics such as the macrotexture. Rolling resistance is the conversion of mechanical energy to heat for a rolling tyre and is affected by both the road surface and tyre deflections and deformations and are affected by the surface characteristics such as unevenness and the macrotexture. The rolling resistance is linked to fuel consumption and in extension to exhaust emissions. Another functional property is the friction which is affected by the road surface characteristics by the micro- and macrotexture.

    There are several measures to reduce road dust loads and PM10. The measures can be either preventive or mitigative. Measures aimed at changing the traffic situation and the tyre usage, changing of the road surface wear course, cleaning of the road surface and dust binding are described.

    Several methods has been used in the studies discussed in the thesis and consist of a large-scale road simulator, the usage of laser measurement systems for determination of road abrasion wear and texture respectively, a prediction model for studded tyre abrasion wear and the NORTRIP model for modelling of non-exhaust particle emissions from road traffic. Also used was a commercial system for traffic measurements and a method for determining the proportion of studded tyre usage. Road dust was sampled and quantified using the WDS (Wet Dust Sampler) method and the collected dust was quantified and characterised using a laboratory method and by using laser granulometry.  Turbidity was used as an approximation of the road dust load.

    Five papers are appended to the thesis. The first paper describes the calibration of the Swedish studded tyre abrasion wear prediction model and the effect it has on the NORTRIP model, in which the abrasion wear model is implemented. The second paper describes the macrotexture of different surface wear courses and how different texture measures could be used to describe the potential dust storage capability. The third paper investigate the WDS-method regarding its performance regarding water and how the water performance theoretically affects potential dust losses. The fourth paper describe the spatial and temporal variation of road dust for six winter and spring seasons in Stockholm, Sweden, for several streets with SMA (Stone Mastic Asphalt) pavements. The fifth paper describe a similar investigation performed in Linköping, Sweden, during one winter and spring season for a double layered porous asphalt and for an SMA which acted as a reference. When applicable, the results from Linköping was compared to those from Stockholm.

    The results showed that the abrasion wear modelling overestimated the abrasion wear by approximately 50% which caused the NORTRIP model to overestimate the contribution from the abrasion wear to the particle emissions, which was not surprising. However, it is not likely that the NORTRIP model gets a decrease of the emissions 50% since the road surface and tyre interaction is complex and several aspects affects the abrasion wear and the resulting generation and storage of road dust, including, but not limited to, polishing of the road surface, increased abrasion wear for wet surfaces.

    The results from the WDS investigation showed that the method seems to function well, given the limitations of the study. The largest water loss was the water retained on the road surface. It also seems like most of the dust is collected. The discussions also consider how the WDS method uses water and the strengths and weaknesses this has compared to dry sampling methods.

    The results from the spatial and temporal variation of the road dust loads in Stockholm showed that there are differences between seasons and there is a difference between the dust loads in the wheeltracks and between wheeltracks. In some cases, differences were seen between the streets with large variations, which could be expected since the road dust load is dependent on the traffic characterization, road operation, deposition of material on the surface and the meteorology.  Another result was that an increasing macrotexture seemed to result in an increase in dust loads. The macrotexture was, generally, lower between the wheeltracks and higher in the wheeltracks, which was not surprising due to the traffic impact on the texture development. The macrotexture was, however, only measured at a single occasion. The repaving of a SMA surface course to a more abrasion resistant SMA surface course resulted in a higher dust load compared the before the repaving, while visual observation of the road surface implied a rougher macrotexture. This could, however, have been affected by an increased abrasion wear which occur during the first winter season due to a higher initial abrasion wear. The results in Linköping showed similar temporal and spatial variations as in Stockholm for the investigated SMA surface course. It was also discussed how the double layered porous pavements construction affect the particle transport processes. In the comparison between Stockholm and Linköping, it was suggested that the dust binding and cleaning in Stockholm affect the dust load since these measures are not performed in Linköping which is possibly reflected in the dust loads in and between wheeltracks.

    How different texture measures could be used to characterize the road surface texture and its connection to the dust load storage was also discussed, including a discussion of which measures that could be used. It is, however, also noted that the measures discussed the measure that should be used is not necessarily discovered yet.

    The discussion also mention the lack of a holistic approach regarding the road surface and tyre interaction which simultaneously consider effect such as abrasion wear particles, noise and rolling resistance. Some measures seem to be of interest to improve at least two aspects simultaneously, for example the usage of a double layered porous pavement or texture optimisation. Different strength and weaknesses are discussed for the different mechanisms affecting the different aspects as well as how some mechanisms should be further studies from other perspectives, for example noise mechanisms which may be interesting from a particle perspective.

    The thesis ends with giving some suggestions for continued research to increase the knowledge. This concern abrasion wear modelling and road dust emission modelling where the road surface texture should be considered. Also suggested is that mechanisms from other aspects of the road surface and tyre interaction, for example those affecting noise, also should be investigated and be used to explain mechanisms related to road dust generation and suspension. Several combined investigations are suggested for studying several aspects from or affecting the road surface tyre interaction simultaneously, including noise, rolling resistance, the road surface characteristics, road abrasion wear, abrasion nwear particles, the road dust loads, the suspension of particles and friction which is required to finally achieve the holistic knowledge required to at least minimise conflicts of interest between different functional properties for road surface courses.

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    Road Surface and Tyre Interaction Functional Properties affecting Road Dust Load Dynamics and Storage - Kappa
  • Public defence: 2020-06-02 09:00 Online: https://kth-se.zoom.us/webinar/register/WN_94cOBU56TluzJktLxD9ZAQ, Stockholm
    Mattila, Robert
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Hidden Markov Models: Identification, Inverse Filtering and Applications2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A hidden Markov model (HMM) comprises a state with Markovian dynamics that is hidden in the sense that it can only be observed via a noisy sensor. This thesis considers three themes in relation to HMMs, namely, identification, inverse filtering and applications.

    In order to employ an HMM, its parameters have first to be identified (or, estimated) from data. Traditional maximum-likelihood estimation procedures may, in practice, suffer from convergence to bad local optima and high computational cost. Recently proposed methods of moments address these shortcomings, but are less accurate. We explore how such methods can be extended to incorporate non-consecutive correlations in data so as to improve their accuracy (while still retaining their attractive properties).

    Motivated by applications in the design of counter-adversarial autonomous (CAA) systems, we then ask the question: Is it possible to estimate the parameters of an HMM from other data sources than just raw measurements from its sensor? To answer this question, we consider a number of inverse filtering problems. First, we demonstrate how HMM parameters and sensor measurements can be reconstructed from posterior distributions from an HMM filter. Next, we show how to estimate such posterior distributions from actions taken by a rational agent. Finally, we bridge our results to provide a solution to the CAA problem of remotely estimating the accuracy of an adversary’s sensor based on its actions.

    Throughout the thesis, we motivate our results with applications in various domains. A real-world application that we investigate in particular detail is how the treatment of abdominal aortic aneurysms can be modeled in the Markovian framework. Our findings suggest that the structural properties of the optimal treatment policy are different than those recommended by current clinical guidelines – in particular, that younger patients could benefit from earlier surgery. This indicates an opportunity for improved care of patients with the disease.

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  • Public defence: 2020-06-02 13:00 Registrera dig här: https://kth-se.zoom.us/webinar/register/WN_98c2Sup3Szqrj9925SfXZg, Stockholm
    Valisena, Daniele
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    Coal Lives: Italians and the Metabolism of Coal in Wallonia, Belgium, 1945-19802020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This manuscript focuses on the relationship between coal and the history of the over 300,000 Italian miners who moved to Wallonia, Belgium, from 1946 onwards, in accordance to the State agreement between Italy and Belgium known as “men in exchange for coal.” Notably, I use environmental history of migration to analyze what I define as “the metabolism of coal.” The socio-ecological metabolism of coal still defines Wallonia’s built and natural environment. The three main drivers of the metabolism of coal have been coal extraction, exercised mainly by immigrant labor; the material processing and transformation of coal into energy and other commodities; and the circulation of those coal byproducts within and outside of Belgium.

    The technocratic organization of such an ecology –– enacted by the capitalistic rationale behind the metabolism of coal –– permeates in a totalitarian way the socio-ecological ordering of Wallonia, encompassing and traversing wastelands, liminal and semi-rural zones, as well as memories.  This process is still evident today even when coal production has entirely ceased. These now liminal spaces attracted capitals, workers, material cultures, and different living species, which all contributed to co-producing hybrid ecologies that still live, inhabit, and resist on the edges of Belgian industrial metabolism. But what happens when such an all-encompassing order of things crumbles down? How is the geo-history of such a place re-signified in the everyday life of those who inhabit Wallonia? What is the material and historical heritage of post-industrial areas such as Wallonia?

    Using environmental history of migration and environmental humanities as methodological and epistemological standpoints I want to stress the ecological continuities and shifts within the metabolism of coal. Using a transdisciplinary approach, I analyze workscapes, post-industrial spaces, heritage sites, as well as memorial and socio-environmental transformation and relationalities through time and space. In doing that, I employ what I define as a geo-historical approach.  Each of the six chapters of my thesis is built around a geo-historical correspondence between a place and a key concept which forms a series of threads stretched within the landscape. Those threads all follow a socio-ecological pattern, linking the three major Walloon rivers (Meuse, Haine, Sambre) and the Walloon coal basins, which are almost perfectly juxtaposing in a geographical, geological and historical meshwork.

  • Public defence: 2020-06-03 10:00 Stockholm
    Zhou, Yang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Modeling Kinetics of Protein-Ligand Systems2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Protein-ligand interactions dominate many life activities and are crucial for thedevelopment of tracers for diagnosing diseases and drugs for treating diseases.For protein-ligand interactions, the binding affinity is conventionally believedto be the most important indicator. However, there is increasing evidencethat the binding affinity alone is not sufficient for providing comprehensiveinformation about protein-ligand interactions. Kinetics, which describes theduration of the interactions and is closely related to the interaction mechanism,is considered as important as, or even more important than, the binding affinityin the study of the mechanisms of protein-ligand interactions.Although kinetics parameters of a protein-ligand system can be measuredexperimentally, the underlying molecular mechanism for the kinetics is difficultto reveal by experiment, which is, however, essential for understanding theorigin of the kinetics and for the rational design of drugs or tracers. In the lastdecade, computer simulations have emerged as a powerful tool for studying biomolecularsystems. Computer simulation methods have also been developedfor modeling kinetics of protein-ligand systems.In this thesis, I explored computer simulations for modeling kinetics propertiesof four different protein-ligand systems. In paper I, I studied the relationshipbetween the ligand binding and conformational changes of the ATAD2-BRD protein. In paper II, I investigated the free energy profile for the coupledfolding and binding of the intrinsically disordered protein p53 with MDM2and calculated the rate constants for the binding and unbinding processes. Inpaper III, I revealed the unbinding paths of the PET tracer ASEM from the  a7-nAChR, calculated the unbinding rate, and explored a way of how to findthe key protein conformational changes strongly coupled to the ligand unbindingprocess. In paper IV, I further refined our methodology for finding theunbinding paths and clarified the unbinding mechanism of the metabolite ofraloxifene from the enzyme CYP3A4.

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    Thesis
  • Public defence: 2020-06-03 10:00 https://kth-se.zoom.us/webinar/register/WN_eJweiFa5T-ik_eYrkrR-gg, Stockholm
    Li, Xiaojie
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Materials for advanced energy technology from quantum-mechanical modeling2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present thesis addresses promising material solutions for fusion reactors from a theoretical point of view. We focus on two specific systems: W-based alloys used as plasma-facing materials and reduced activation ferritic/martensitic (RAFM, Ferich) steels used as structural materials of breeding-blanket. We aim to systematically investigate the alloying effects on the micro-mechanical properties of these body-centered cubic (bcc) solid solutions. The all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA) is the main tool for our theoretical studies. The knowledge of the elastic parameters and their solute-induced changes is important for alloy design and for a multi-scale modeling approach to the mechanical properties. We also explore the planar faults in the present Fe-based alloys.In part one, the effect of neutron transmutation elements on the elastic properties of the W-based alloys are calculated. Under intensive radiation, W transforms to Re/Os and thus there is a certain degree of Re/Os doping in the base alloy. Both Re and Os solute atoms shrink the lattice constant, which lead to increasing bulk modulus as the amount of Re or Os increases. The polycrystalline shear and Young’s moduli of W1−xyRexOsy (0 ≤ xy ≤0.06) enhance with the addition of Re but decrease with increasing Os level. From the variations of the Cauchy pressure, Poisson’s ratio, Pugh ratio B/G, and the ratio of cleavage energy to shear modulus for the dominant slip system, we conclude that the intrinsic ductility of the alloy increases with increasing Re and Os content. We use the energy difference between the face-centered cubic (fcc) and bcc structures to estimate the alloying effect on the ideal tensile strength in the [001] direction.In part two, we choose three RAFM steels: CLAM/CLF-1, F82H, and EUROFER97 and investigate the micro-mechanical properties of the main alloy phases at low temperature (0 K). Being the main building blocks of the RAFM steels, first the lattice parameters, elastic properties, surface energy and unstable stacking fault energy of ferromagnetic α-Fe and Fe91Cr9 are calculated for reference. For quantitative understanding, we present a detailed analysis of the calculated individual alloying effects of V, Cr, Mn, and W on the elastic properties of Fe91Cr9. A linear superposition of these individual rates on the elastic properties of RAFM steels is shown to reproduce well the values from ab initio calculations. The composition dependence of the elastic constants is decomposed into electronic and volumetric contributions and they are analyzed separately. Finally, the intrinsic ductility is evaluated through Rice’s phenomenological theory by using the ratio of surface and unstable stacking fault energies. The results are consistent with those obtained by the common empirical criteria.In part three, the temperature dependence (T ≤ 1120 K) of the isothermal singlecrystal and polycrystalline elastic parameters of α-Fe and CLAM are reported by using a first-principles based modeling approach. The effect of temperature on the strongly temperature-dependent elastic constants C11 T and CT' is reproduced, as well as that on derived isotropic elastic moduli. Weak changes in C12 T and C44 T with temperature are obtained. The approach is applied to predict the temperature effect on the elastic parameters of three RAFM steels. Contributions due to loss of longrange magnetic order and the combined effect of volume expansion and entropy are found to be important in determining the temperature dependence of the elastic parameters in all the materials investigated.In part four, the (100) and (110) surface energies and surface segregation energies of Fe1−xbCrxb binary alloys, xb ≤ 15 at.%, are computed. These alloys form the basic building blocks of RAFM steels and thus their surface properties are of fundamental importance for the modeling the mechanical behavior. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < xb < 9 at.%. In contrast, a nearly homogeneous Cr concentration profile is energetically favorable in Fe-Cr(110) surface. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The surface electronic structures are used to explain the stability of the Cr surface magnetic moments against bulk Cr content.

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  • Public defence: 2020-06-03 14:00 Live-streaming: https://kth-se.zoom.us/j/64148260640 If you lack computer or computer skills, contact Dan Zenkert, danz@kth.se, Stockholm
    Johannisson, Wilhelm
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Exploring structural carbon fiber composites for mass-less energy and actuation2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The energy consumption in transport is today a large contributor to global greenhouse emissions. One way of reducing these emissions is by electrification, which is an ongoing journey for the vehicle industry. The aeronautical industry has started investigations but are limited by the relatively low specific energy of batteries.

    One way to improve the specific energy of batteries is by making them multifunctional by combining them with other functions of the vehicle. When the battery is combined with a structural material, the resulting material is referred to as a structural battery. This structural battery ultimately performs the fundamental function of mechanical rigidity and the battery function provides almost mass-less energy. The idea of structural batteries has been around for a while, but its actual construction has not yet been understood.

    This thesis is focused on exploring the design and implications of structural batteries made from carbon fiber composites. The first section is focused on the construction of the structural battery. Specifically investigating a structural carbon fiber negative electrode with regards to its manufacturing, electrochemical properties and mechanical properties. The results show that the construction of a negative electrode for structural batteries is achievable. The next section is using the findings from the first section in exploring the implications of implementing a structural battery into vehicles with regards to weight saving and life cycle characteristics. The findings show that the structural batteries have the potential to decrease both weight and life cycle burdens. The last section presents the use of the structural carbon fiber negative electrodes as a morphing material controlled by applied electrical power. The morphing deformations are large and stationary when power is removed but the morphing rate of the material is limited. Additionally, it is solid state, lightweight and has an elastic modulus higher than aluminum with large morphing deformations.

    The long-term outcomes of a thesis are hard to predict, but the findings herein conclude that the technology of structural batteries have the potential to disrupt energy storage in transportation, as well as traditional actuation and morphing technologies.

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  • Public defence: 2020-06-04 10:00 Registrera dig här: https://kth-se.zoom.us/webinar/register/WN_Bp8dzpcbQMKNNOGyj51R2g, Stockholm
    Sjölander, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Structural behaviour of shotcrete in hard rock tunnels2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tunnels in hard and jointed rock are normally excavated in an arch shape to enable the rock mass to support its weight. Since the beginning of the 1980's, fibre reinforced shotcrete (FRS) in combination with rock bolts have been the dominating support method for hard rock tunnels. This type of rock support is a complex composite structure in which the structural behaviour depends on interaction between shotcrete, rock and bolts. The design is commonly based on a rock mass classification system in combination with analytical solutions or finite element (FE) modelling. However, the in-situ variations of important properties of the shotcrete are normally neglected.

    The aim of this thesis is to describe and explain how the variations in shotcrete thickness and bond strength affect the structural behaviour and capacity for a shotcrete lining. Especially, the influence of local variations in shotcrete thickness and bond strength has been studied in detail. For this purpose, a numerical framework capable of simulating bond failure, cracking of FRS and pull-out failure of grouted rock bolts have been developed. Moreover, in-situ data for shotcrete thickness and bond strength have been collected and analysed to characterize  the variations in important shotcrete parameters.

    The results in this thesis show that when shotcrete is subjected to shrinkage, local variations in shotcrete thickness affects the crack pattern. However, the number and width of the cracks are similar to the case with uniform thickness. Most importantly, a pattern of fine and narrow cracks develops in unreinforced shotcrete subjected to shrinkage when a continuous bond to the rock exists. When shotcrete is subjected to the load from a loose block, the force is transferred to the surrounding rock through bond stresses distributed over a narrow band. Simulations have shown that the structural capacity, with respect to bond failure, depends on the shotcrete thickness. Moreover, a strong linear correlation was found between the mean value of the bond strength and shotcrete thickness around the perimeter of the block and the structural capacity. Local weak areas, i.e. with low bond strength or thickness, may exist around the perimeter without having a significant effect on the structural capacity. Design of bolt-anchored shotcrete linings is based on failure modes previously derived from experimental testing. This thesis has contributed to an increased understanding of the failure mechanisms of the lining and has confirmed that the design can be based on individual failure mechanisms.

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    Sjölander_Thesis
  • Public defence: 2020-06-04 10:00 https://kth-se.zoom.us/webinar/register/WN_E0ALwYOFS-mP-vAFhp2QQw, Stockholm
    Liu, Qingyun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Royal Institute of Technology.
    Studies of optical properties of lanthanide upconversion nanoparticles for emerging applications.2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    YTTERBY, a small village very close to Stockholm where I live, is the place in the world which has lent its name to the largest number of elements in the periodic table, namely four - YTTRIUM, YTTERBIUM, ERBIUM and TERBIUM. Three more lanthanide elements were discovered from the now empty quarry located in this village. By the time of their discoveries in the 19th century little could be known about their fantastic properties, the versatility of their use and functionality in what we now call nanotechnology. This is a circumstance that motivated me to rather recently enter lanthanide research, in particular studies of their outstanding optical properties for the purpose of information technology and energy harvesting.

    So far, upconversion nanoparticles (UCNPs) have been much explored as unique spectral converters for various applications, like biotechnology, information technology and photovoltaic devices due to properties like sharp emission profiles, low autofluorescence and large anti-Stoke shifts. Still, there is much to explore and to understand in order to fully utilize the very unique properties of UCNPs. The kinetic dynamics of the upconversion process is one such aspect that is not well understood, and a deeper understanding of the kinetic dynamics of lanthanide upconversion systems could thus broaden their applications. Therefore, the work of this thesis is focused on investigating the kinetic dynamics of upconversion processes mainly based on systems with NaYF4 as host material, and Yb3+/Er3+ or Yb3+/Tm3+ embedded as sensitizer/activator. Through rate equation models, the kinetic dynamics of upconversion are comparatively investigated with numerical simulations and analytical derivation. The temporal response regarding upconverted luminescence and quantum yield power density dependence, excitation duration response and excitation frequency response of the upconversion systems are investigated and the corresponding applications for multicolor imaging, optical encoding, photovoltaics, IR photodetectors are explored and analyzed in the thesis, taking advantage of the kinetic properties.

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    PhD thesis summary
  • Public defence: 2020-06-04 10:00 Live-streaming: https://kth-se.zoom.us/j/62627066334 If you lack computer or computer skills, contact Luca Brandt, brandtl@kth.se, Stockholm
    Morra, Pierluigi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Modelling and control of turbulent and transitional flows2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The dynamics of fluid motion can accurately be described by the Navier– Stokes equations. Manipulating these equations to reduce their complexity but preserving their main characteristics has always been a key research activity in the field of fluid mechanics. Effort has been made to provide high-fidelity models for wall-bounded turbulent flows or reduced-order models for applications such as drag reduction, lift enhancement, or noise suppression. Model order reduction has also been employed for studying the dynamics of the Navier-Stokes equations. In this PhD thesis, the emphasis is on providing computationally inexpensive methods for industrial applications.

    Numerical simulations are performed to tackle model order reduction for flow control of transitional boundary-layer flows for drag reduction. It is assumed that localized wall sensors and actuators are available, and that only the time signals accessible in experiments are provided. Thus, a method to include unknown high-dimensional input disturbances in a reduced-order model of a transitional boundary-layer flow is presented. The method is applied for the design of an optimal controller for drag reduction through delay of transition. Moreover, the role of the actuator is discussed and a comparison between realistic actuators and actuators computed using optimization methods is presented. Here, the emphasis is on the effectiveness of the actuators for the studied flow control cases.

    Numerical simulations are also performed to tackle high-fidelity modeling in wall-bounded turbulent flows. The accuracy of the resolvent analysis in predicting the most energetic flow structures in a wall-bounded turbulent flow is quantified for different temporal frequencies. A direct comparison between the predictions from the resolvent analysis and the flow structures identified in DNS data is presented. Moreover, the beneficial effects attained with the inclusion of the Reynolds-stresses via an eddy-viscosity model are clarified for flows with friction Reynolds number up to 1007.

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  • Public defence: 2020-06-04 10:00 https://kth-se.zoom.us/webinar/register/WN_ZGfpgdfbTaWDGBGKrV9tcQ, Stockholm
    Sun, Xun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio Investigation of Face-centered cubic High-Entropy Alloys2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High-entropy alloys (HEAs) represent a special group of solid solutions containing five or more principal elements. The new design strategy has attracted extensive attention from the materials science community. The design and development of HEAs with desired properties have become an important subject in materials science and technology. Herein this case, I investigate the basic properties of paramagnetic (PM) HEAs, including the magnetic properties, Curie temperatures, electronic structures, phase stabilities, and elastic properties using the first-principles exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA) for dealing with the chemical and magnetic disorder. To understand and model the mechanical properties of face-centered cubic (fcc) HEAs, I also study the generalized stacking fault energy (GSFE), negative stacking fault energy (SFE) and twinning mechanism of various HEAs. Thesis focuses mainly on AlxCrMnFeCoNi (0 ≤ x ≤ 5, in molar fraction) and related HEAs.Whenever possible, I compare the theoretical predictions to the available experimental data in order to verify the employed ab initio methodology. I make use of the previous theoretical investigations carried out on AlxCrFeCoNi HEAs to reveal and understand the role of Mn in AlxCrMnFeCoNi HEAs. The theoretical lattice constants are found to increase with increasing x, which is in good agreement with the available experimental data. The magnetic transition temperature for the body-centered cubic (bcc) structure strongly decreases with x, whereas that for the fcc structure shows a weak composition dependence. Within their own stability fields, both structures are predicted to be PM at ambient conditions. Upon Al addition, the crystal structure changes from fcc to bcc with a broad two-phase field region, in line with the observations. Bain path calculations suggest that within the duplex region both phases are dynamically stable.Comparison with available experimental data demonstrates that the employed approach describes accurately the elastic moduli of the present HEAs. The elastic parameters exhibit complex composition dependences and the elastic anisotropy is unusually high for both cubic phases. The brittle/ductile transitions formulated in terms of Cauchy pressure and Pugh ratio become consistent only when the strong elastic anisotropy is accounted for. The negative Cauchy pressure of CrMnFeCoNi is found to be due to the relatively low bulk modulus and C12 elastic constant, which in turn are consistent with the relatively low cohesive energy. Our findings in combination with the experimental data suggest anomalous metallic character for the present HEAs system.The negative SFE of fcc medium-entropy alloys (MEAs) and HEAs originate from the metastable character of the fcc phase. I argue that the common models underlying the experimental measurements of SFE fail in metastable alloys. Considering various metals including concentrated solid solutions, I demonstrate that in contrast to the experimentally measured SFEs, the SFEs obtained by DFT calculations correlate well with the primary deformation mechanisms observed experimentally in these alloys. In the case of negative SFE (or in metastable fcc alloys), the transformation-mediated twinning (TMT) is the predominant mechanism instead of the layer-by-layer twinning mechanism. It provides a continuous avenue for strain accommodation and strain hardening, realizing the joint transformation-induced plasticity and twinning-induced plasticity in the same system, and thus enabling the simultaneous improvement of strength and ductility. For the fcc CrMnFeCoNi HEA, upon Al addition or temperature increase, the intrinsic and extrinsic stacking fault energies increase, whereas the hexagonal close packed (hcp)/fcc interfacial energy stays almost constant.The work and results presented in this thesis give a good background to go further and study the plasticity of fcc HEAs as a function of chemistry and temperature. This is a very challenging task and only a very careful pre-study concerning the phase stability, magnetism, elasticity and GSFE can provide enough information to turn my plan regarding ab initio description of the thermo-plastic deformation mechanisms in fcc HEAs into a successful research. The novel TMT mechanism disclosed for the first time by myself and my colleagues advances our knowledge in plasticity and paves the road to design novel alloys with outstanding mechanical properties using quantum metallurgy.

    The full text will be freely available from 2020-10-01 15:01
  • Public defence: 2020-06-04 15:00 https://kth-se.zoom.us/j/67302879470, Stockholm
    Zhang, Liang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Industrial Biotechnology. AdBIOPRO, VINNOVA Competence Centre for Advanced Bioproduction by Continuous Processing.
    Development of mathematical modelling for the glycosylation of IgG in CHO cell cultures2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chinese hamster ovary (CHO) cells are the most popular expression system for the production of biopharmaceuticals. More than 80% of the approved monoclonal antibodies (mAbs) or immunoglobulin G (IgG) are produced with these cells. Glycosylation is a usual post- translational modification important for therapeutic mAbs. It affects their stability, half-life and immunological activities. Substantial studies have shown that glycosylation can be affected by the culture conditions in manufacturing, e.g. pH, temperature and media components. To achieve a good control of the glycosylation, a number of mathematical models have been developed. However, most of them have been developed for the cell line engineering, while very few can be used to design the media components for matching a given glycoprofile.

    This thesis presents developments of mathematical modelling for glycosylation prediction and experimental design of feeding different combinations of carbon sources in CHO cell cultures. The first study investigates the impacts of mannose, galactose, fructose and fucose to the IgG glycoprofile. Specifically, we look at intracellular nucleotide sugars in fed-batch cultures, where glucose is absent and lactate is used as complementary carbon source. The second study is based on the concept of elementary flux mode (EFM) and the mass balance of the glycan residues. A mathematical model named Glycan Residue Balance Analysis (GReBA) is developed for the prediction of the glycosylation profiles of IgG in pseudo perfusion cultures by feeding combinations of glucose, mannose, galactose and lactate. The model is further optimized for a feeding strategy design of perfusion cell cultures to obtain a desired glycoprofile. In the last study, a probabilistic graphic model based on Bayesian network (BN) is developed for glycosylation prediction in cultures under different multiple variable factors affecting the glycosylation.

    The results show that the manipulation of different sugars in the media can be used to control the glycosylation. Both the GReBA and PGM models exhibit abilities for glycosylation prediction and experimental design.

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  • Public defence: 2020-06-05 09:00 Kollegiesalen, Stockholm
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Correlation spectroscopy with epitaxial quantum dots: Single-photons alone in the dark2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The advent of quantum computation promises exciting advances, not only in fields like medicine and metrology, but many industries that rely on parameter-heavy calculations or simulation of molecular interaction. At the same time Shor's algorithm for quantum computers presents a threat to current asymmetric encryption protocols used in everyday communication. Flying qubits, i.e. single-photons, can help mitigate this problem via quantum key distribution, which is insusceptible to an increase in computational power. In addition, they can link quantum computers, forming a quantum network, so that quantum states can be transmitted between them. Sources of flying qubits need good performance in key metrics like single--photon purity, repetition rate, indistinguishability and brightness to become useful in these applications. They should ideally emit strongly entangled pairs of photons and be matched to other quantum technologies in bandwidth and emission energy.

    In this thesis the emission characteristics of single epitaxial quantum dots, the single-photon source of our choice, are investigated. Strongly entangled photon-pair emission is demonstrated for three different quantum-dot systems:

    • InAsP quantum dots embedded in nanowire waveguides, suitable for integration into photonic circuits, show emission of single photons and entangled photon pairs under non-resonant and quasi-resonant excitation. Violation of Bell's inequality is demonstrated using the traditional set of polarization angles.
    • GaAs quantum dots grown in droplet--etched nanoholes are tested with two resonant excitation methods: Using resonance fluorescence, near-unity indistinguishability and re-excitation limited single-photon purity, albeit not simultaneously with laser-inherited bandwidth, are measured. Using two-photon resonant excitation we set a new standard for single-photon purity, can generate pairs of entangled photons but suffer from reduced indistinguishability. In addition, nanofabrication of paraboloid shaped reflectors for enhanced extraction efficiency of photons and strain-tuning of the emission energy into resonance with the 87Rb D1-line are demonstrated.
    • Strain-tunable InAs quantum dots emitting in the telecom C-band are investigated under above-band excitation and two different resonant two-photon excitation techniques, all of which cause pure single-photon emission. Using the robust phonon-assisted two-photon excitation technique, close-to ideal entangled photon-pair emission is demonstrated.

    For many of these findings photon arrival times were recorded over many hours with temporal precision on the order of 10 ps. We have developed a user-friendly, yet versatile piece of software in order to extract as much information as possible from this vast amount of data.

    These results will facilitate integration of quantum dot based single- and entangled-photon sources into future quantum networks and quantum key distribution systems.

    The full text will be freely available from 2020-06-05 09:00
  • Public defence: 2020-06-05 10:00 Stockholm
    von Witting, Emma
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Technology.
    The ADAPT scaffold as a tool for diagnostic imaging and targeted therapy2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Molecular recognition, or the specific interactions between a protein and its ligand, is central to biology and a key factor for many different clinical and technical applications. Despite antibodies being only one of many different affinity proteins, it has by far been the most successful. However, their large size and complex structure can be limiting in terms of cost and stability. Furthermore, their effector functions can sometimes be undesired or even detrimental. Over the past decades, many alternative affinity proteins have emerged to overcome some of these limitations.

    The Albumin Binding Domain (ABD), originally present on the surface of certain bacterial cells, has previously been subjected to combinatorial protein engineering for the generation of ADAPTs (ABD Derived Affinity ProTeins) that bind to different targets. One of these, the ADAPT6, targets HER2 and has shown great promise as a tracer for radionuclide molecular imaging for diagnosis and stratification of HER2 positive patients. The work in this thesis has aimed to optimise the ADAPT6 tracer further and also describes the first-inhuman clinical trial for imaging of HER2-overexpressing breast cancer. The results establish that ADAPT6 is safe and well-tolerated by patients and able to detect primary tumours as well as metastases with very high contrast already 2 hours after injection. However, the high kidney uptake associated with its fast blood clearance prevents further use of ADAPT6 also in a therapeutic setting. By engineering the ADAPT6 to prolong its circulatory half-life and reduce the kidney uptake, this thesis has also aimed to explore the therapeutic potential of this molecule. As a first step towards this goal, the ADAPT6 was genetically fused to an ABD to allow for binding to a patient’s own serum albumin and hence avoid the same extent of renal filtration. Indeed, when evaluated in mice, fusion to ABD increased the retention in circulation by more than 200-fold and exhibited a dramatically decreased renal activity. Treatment of tumour-bearing mice with the ABD-fused ADAPT6 conjugated to a cytotoxic radionuclide significantly prolonged survival by more than two-fold and was not associated with any observable toxicity. Finally, this thesis also describes a novel combinatorial library from which several bispecific ADAPTs have been identified, binding to both albumin and other clinically relevant targets simultaneously. This miniature bispecific scaffold offers an opportunity to combine the benefits associated with small size such as good tissue extravasation and alternative administration routes while still maintaining a sufficient in vivo half-life.

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  • Public defence: 2020-06-05 10:00 Publikt via ZOOM, Stockholm
    Ternstedt, Patrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A Study of Parameters that Influence the Kinetics of the AOD Decarburisation Process2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on the AOD process, which is an important metallurgical reactor in stainless steel production. To be more specific, the thesis is limited to study the decarburisation step, which is the first of three process steps in the AOD converter. The main research questions is to increase the knowledge of reasons for random differences in decarburisation rates during the process. In the first part of the study, physical modeling is used to study the mixing in AOD converters. Parameters that were studied included, bath heights, gas flow rates and chemical reactions. The results showed that the mixing time decreased with an increased gas flow rate or an increased bath height. In addition, the influence of the top slag on the fluid flow and mixing time was studied. The results showed that the flow field was influenced by the slag phase and that it is of importance to account for the solid slag fractions to simulate the fluid flow and mixing time to resemble AOD converters. However, the results from this first part of the thesis illustrates that mixing is not the rate-limiting step for decarburisation in AOD converters. Instead, the focus was shifted to study if the slag was the cause for random differences in the decarburistaion rate. Slag samples were collected from an industrial AOD reactor. These slags are quite unique since they contain mainly solids and a small liquid fraction. Thus, petrography was used to study the samples and a new methodology was developed to characterize the slag samples. Methods for characterising the top slag samples from the AOD process were established, including combinations of different techniques. The common slag phases in decarburisation slag were identified. The results showed good agreement with samples analysed with SEM and EDS compared to calulations made in Thermo-Calc. Overall, it was shown that the slag characteristics changes during the decarburization period and that these changes can be determined using the new methodology. In the last part of the thesis, the commercial AOD process control model TimeAOD2 was used in combination with Thermo-Calc calculations to study how the process could be improved so that the slag composition became most beneficial for improving the kinetics of the decarburisation part of the AOD converter process. The results show that it is possible to predict the slag composition and especially the amount of liquid slag in the sample. This in turn, makes it possible to better estimate the optimal lime addition depending on the silicon content in steel and the amount of carry-over slag from the electric arc furnace.  Furthermore, it is shown that to large lime additions will lead to an increased heating time while not improving the decarburization rate.

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  • Public defence: 2020-06-05 10:00 https://kth-se.zoom.us/s/68861340458
    Berglund, Emelie
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology.
    Molecular and Spatial Profiling of Prostate Tumors2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Every cancer tumor is unique, with characteristics that change over time. The evolution of a full-blown malignancy from a single cell that gives rise to a heterogeneous population of cancer cells is a complex process. The use of spatial information makes a big contribution to understanding the progression of tumors and how patients respond to treatment. Currently, the scientific community is taking a step further in order to understand gene expression heterogeneity in the context of tissue spatial organization to shed light on cell- to-cell interactions. Technological advances in recent years have increased the resolution at which heterogeneity can be observed. Spatial transcriptomics (ST) is an in situ capturing technique that uses a glass slide containing oligonucleotides to capture mRNAs while maintaining the spatial information of histological tissue sections. It combines histology and Illumina sequencing to detect and visualize the whole transcriptome information of tissue sections. In Paper I, an AI method was developed to create a computerized tissue anatomy. The rich source of information enables the AI method to identify genetic patterns that cannot be seen by the naked eye. This study also provided insights into gene expression in the environment surrounding the tumor, the tumor microenvironment, which interacts with tumor cells for cancer growth and progression. In Paper II, we investigate the cellular response of treatment. It is well known that virtually all patients with hormone naïve prostate cancer treated with GnRH agonists will relapse over time and that the cancer will transform into a castration-resistant form denoted castration-resistant prostate cancer. This study shows that by characterizing the non-responding cell populations, it may be possible to find an alternative way to target them in the early stages and thereby decrease the risk of relapse. In Paper III, we deal with scalability limitations, which in the ST method are represented by time- consuming workflow in the library preparation. This study introduces an automated library preparation protocol on the Agilent Bravo Automated Liquid Handling Platform to enable rapid and robust preparation of ST libraries. Finally, Paper IV expands on the first work and illustrates the utility of the ST technology by constructing, for the first time, a molecular view of a cross-section of a prostate organ.

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  • Public defence: 2020-06-05 10:00 https://kth-se.zoom.us/webinar/register/WN_uqGMc4x8QwWk4TPfSb5TFA, Stockholm
    Xie, Ruiwen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Defects in Austenitic Steels and Hard Metals - A DFT-based Study2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Materials are never 100% pure due to the limitation of purification method or manufacturing process. Nor are they perfect, especially under deformation. The present work aims to explore different roles played by the defects in austenitic steels and hard metals.

    The first focus is iron-manganese (Fe-Mn) based twinning induced plasticity(TWIP) steels which are a category of austenitic materials showing a good combination of high strength and ductility. The planar fault is fundamental for the TWIP mechanism. First, the γ-surface of pure γ-Fe (fcc-Fe) is calculated for different magnetic states. Next, the effects of alloying elements, including Mn,interstitial carbon (C) and nitrogen (N), are addressed. The γ-surface includes several prominent stacking fault energies that are fundamental for, e.g, predicting critical twinning stress and twinnability. The present work compares the γ-surface obtained at different magnetic states, including nonmagnetic (NM), paramagnetic(PM), antiferromagnetic single-layer (AFMI) and double-layer (AFMD) states. The local magnetism significantly influences the γ-surface. In addition, the existing antiferromagnetic (AFM) order results in two different deformation paths inγ-Fe, leading to the generations of superlattice intrinsic stacking fault (SISF) and complex stacking fault (CSF), respectively. The intrinsic stacking fault energy corresponding to SISF is relatively low while its corresponding unstable stacking fault energy is relatively high. The magnetic structures are investigated in the unstable stacking fault and the intrinsic stacking fault configurations via Monte Carlo (MC) simulations. The MC results show that only SISF configuration is favourable, and the two distinctive unstable stacking fault configurations may coexist.

    The Mn effect on the γ-surface of γ-Fe is studied at AFMI state and the crystal tetragonality is considered. The comparison with experimentally measured stacking fault energy (SFE) dependence on Mn composition shows that the AFMI results reproduce better the experimental trend in high-Mn Fe-Mn alloys than the PM results. Further, the interstitial alloying effects of C and N on the γ-surface of γ-Fe are investigated and no remarkable difference is observed betweenthe C and N impacts. The interaction between dislocation and interstitial atoms, which is fundamental to understand the phenomenon like dynamic strain ageing (DSA), is studied using the generalized stacking fault as an approximation of the partial dislocation core. The minimum migration energy path (MEP) and migration energy surface (MES) of C in the dislocation core of AFMD γ-Fe are calculated. In contrast to the common assumption that the interstitial atoms are stationary during the passage of fast-moving dislocations, the present work suggests that a pair of dislocation partials are capable of moving C atoms forward on the slip plane by one full Burgers vector. Moreover, at the stacking fault ribbon and especially near the dislocation core, the in-plane diffusion energy barriers of C are significantly reduced compared to that in the bulk, rendering a fast diffusion channel for C. The proposed mechanisms for C transport and diffusion are not decided by local magnetic order and can be used to explain the strain rate dependent formation kinetics of twinning or hexagonal close-packed (hcp) martensite in C-alloyed TWIP steels or high entropy alloys. Similarly, the ab initio results show that the diffusion energy barrier of N in the dislocation core is approximately 14.9% of that in the bulk. According to experimental observations, carbon promotes while N suppresses the DSA. However, the different C and N effects on the DSA cannot be understood from current thermodynamic investigations.

    The defects in the binder phase of hard metals (cemented carbides) are another important topic in this thesis. The interstitial tungsten (W) and C defects in hard metals come from the sintering process during industrial manufacturing. The cemented carbides are composite materials made of tungsten carbide (WC) grains glued together by a binder phase. Typically, the binder phase consists of ductile cobalt (Co) and some amount of dissolved W and C. The measurement ofthe magnetic saturation is one method employed for quality control of cemented carbides. Despite the great success of Co, a substitute of Co is needed due to its rising price and health threats. The substitution of a material in production processes can be complex. Ideally, manufacturing processes and quality controls should be used as usual or at least new ones have to be devised in a simpleway. The present work selects 85Ni-15Fe (85 at.% of Ni and 15 at.% of Fe) to demonstrate the relation between the magnetic saturation and the components of the binder phase of cemented carbides using ab initio method, which providesa non-destructive quality control method in cemented carbides.

    The full text will be freely available from 2020-12-31 12:23
  • Public defence: 2020-06-05 13:00 https://kth-se.zoom.us/webinar/register/WN_0MG9EB_dSuuhnvezU1O1aw - http://Vid fysisk närvaro eller Du som saknar dator/ datorvana kan kontakta service@itm.kth.se, Stockholm
    Fagrell, Per
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Change and inertia in the development of Swedish engineering education: The industrial stakeholder perspective2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates higher education development in Sweden from an external stakeholder perspective, with a particular focus on engineering education. Industry has long been a major external stakeholder in the development of profession-oriented higher education, not least in the context of engineering education. Representatives of industry and other employers have continuously called for developments in the curriculum to prepare students for an evolving profession. Scholars of higher education have gone so far as to depict employers as the definitive stakeholder in higher education today. However, it has also been claimed that engineering education and its institutions are, and always have been, rather unresponsive to external calls for changes. These partly contrasting views call for a study of the role of industry vis-à-vis the different strategies that higher education institutions can draw upon to respond to external calls for change. Thus, the following overarching research question is posed: What kind of role does an external stakeholder such as industry have in the development of engineering education?

    The conceptual framework for the thesis is based on literature on organisational continuity and change, response strategies to external calls for change, university–business collaboration, and curriculum development and quality. The main theoretical concept presented in the thesis, however, is stakeholder theory and stakeholder analysis. A model for stakeholder analysis is chosen and presented in which the assessment of the attributes power, legitimacy and urgency form the basis for the analysis of the stakeholders’ salience.

    Empirically, the thesis is based on three studies, which have yielded four appended papers. The studies represent different situations in which external stakeholders have had the possibility of impacting higher education. All three studies have an interpretative and qualitative methodological approach, with semi-structured interviews as the main source for data collection, combined in the second study with historical document studies. In order to frame these studies in their historical context, an overview of the development of engineering education in Sweden is presented as a background. In this overview, the development of relationships between industry and engineering education institutions are depicted with reference to a series of milestone events.

    The results show that, from a historical perspective, industry has indeed been an influential stakeholder to engineering education. It is argued that while industry still is an important stakeholder, higher education institutions today have to attend to the interests of a broader range of stakeholders, including students, government and others. Claims in the international literature that employers are the definitive stakeholder in higher education does not seem to fit well with the Swedish context, as analysed in this thesis. This may be partly understood as a consequence of a shift away from national-level decision-making regarding higher education development, leaving previous structures for active stakeholder influence less potent.

    Important decisions about engineering education have in Sweden moved from a national and centralised level to an international level, exemplified by the Bologna Process and the global quality assurance and enhancement scheme called the CDIO[1] Initiative, and at the same time to a local level due to an ambitious autonomy scheme for higher education institutions in Sweden. This can be seen as a divergent trend compared to an international setting, specifically in Anglophone countries where the Washington Accord acts as the basis for curriculum development. This accreditation agreement is heavily influenced by the accreditation scheme for engineering education in the United States, the ABET criteria, in whose formulation employer representatives have a major impact. It may be questioned whether industry representatives have fully recognised this shift in the decision-making process in the engineering curriculum in Sweden. With regard to earlier claims that engineering education and its institutions are unresponsive to external calls for change, the thesis concludes that higher education institutions respond and act, but not always in the way external stakeholders expect or want. External stakeholders have to persist in their eternal quest for progress and development in engineering education, but they may have to adjust and divert their attention to both an international and local context at the same time.

    [1] CDIO: Conceive-Design-Implement-Operate

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  • Public defence: 2020-06-05 14:00 Publikt via ZOOM, Stockholm
    Törnblom, Oskar
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Organizational Design and Leadership Development: The Role of Increasing Complexity​2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Many organizations need to adapt to increasingly complex environments. New forms of organizational design and leadership are called for and, under some circumstances, more collective leadership practices are needed. Furthermore, values and beliefs in some societal contexts foster a general positive bias for collective leadership. Paradoxically, many investment decisions regarding leadership development activities do not pay off. At the same time, the research fields of collective leadership development and on-the-job leader development are underutilized. The research field of leadership is in need of consolidation and integration within and between research areas. There has been much less research done on collective leadership development compared with leader development, and research on leadership development has been focused more on individual and collective change rather than on contextual facilitating factors such as organizational design.

    To address these theoretical and practical challenges, the aim of the thesis was to explore organizational design and leadership development in terms of increasing complexity in the empirical context of technology-, knowledge-, and project-intensive organizations. The research design was centered around two studies that were part of a larger interactive research project and two conceptual studies that jointly investigated (1) organizational design and increasing complexity, (2) leadership development and increasing complexity, (3) how increasingly complex organizational design can foster leadership development. The interactive research project had four goals in terms of creating common learning for the project partners involved, new academic knowledge, and organizational development not only for the participating organizations but also for organizations in general.

    The thesis contributes to the research fields of organizational design and leadership development as well as their intersection. It adds to theory by providing a more fine-grained definition of ways of understanding leadership development according to increasing complexity. Furthermore, it adds to the understanding of how increasingly complex organizational design can foster leadership development, especially collective leadership, thus demonstrating empirical examples of leadership development without traditional leadership development investments.

    The thesis proposes future research on emerging technology as an accelerator for leadership development and interactive research in partnership with organizations in order to further integrate the research fields of organizational design and leadership development. In terms of managerial contributions, a number of suggestions are offered to support better knowledge creation and decision-making regarding organizational design, on-the-job leader development, and especially collective leadership development. Furthermore, a shift from a psychology-centered leadership development approach toward more of a systemic and organizational design-centered leadership development approach that includes both individual and collective dimensions is called for. This shift will potentially change the leadership development industry, making many of the contemporary investments in leadership development obsolete.

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    Appendix 6 Key theoretical definitions in brief
  • Public defence: 2020-06-08 10:00 144 28, Stockholm
    Wahlström, Niklas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.
    Polysaccharides from red and green seaweed: Extraction, characterisation and applications2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cultivation of seaweed has been conducted for centuries in Asia, but is largely undeveloped in Sweden even though there is potential for this industry. Seaweed offers benefits compared with land-based biomass cultivation. Cultivation of seaweed does not occupy land areas and does not require irrigation or fertilizers, which contributes to avoid coastal eutrophication. Seaweed contains polysaccharides and is a potential feedstock for production of bio-based materials. The aim of this thesis was to extract and map the chemical structure of polysaccharides from macroalgae collected along the Swedish west coast. Another aim was to use the extracted polysaccharides to design new bio-based materials. In the first study, a fractionation strategy was developed to sequentially extract proteins and polysaccharides from the red macroalgae Porphyra. The fractionation yielded one protein fraction and three polysaccharide fractions. In the second study, the polysaccharide ulvan was extracted from two species of the green macroalgae Ulva. Two different extraction protocols were tested. Parameters such as the yield, molecular weight and monosaccharide composition of the extracted ulvan depended on the extraction protocol and the specie of Ulva used for the extraction. In the third study, ulvan extracted from Ulva was used to prepare hydrogels, which were tested as an adsorbent for heavy metals and the dye methylene blue. Ulvan was first oxidized into ulvan dialdehyde and mixed with gelatin, yielding hydrogels. The hydrogels showed high water-uptake capacity and a high adsorption capacity of methylene blue. The hydrogels also adsorbed heavy metal ions. In the fourth study, cellulose was extracted from Ulva and further used to prepare cellulose nanofibrils (CNF). Chemical analysis of the CNF showed that it contains mostly cellulose but also a smaller amount of a xylose-glucose copolymer. The CNF had a crystallinity index of 48% and showed typical peaks for the cellulose I allomorph.

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  • Public defence: 2020-06-08 13:00
    Gallinaro, Julia
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science. Bernstein Center Freiburg and Faculty of Biology, University of Freiburg, Germany.
    Neuronal assembly formation and non-random recurrent connectivity induced by homeostatic structural plasticity2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Plasticity is usually classified into two distinct categories: Hebbian or homeostatic. Hebbian is driven by correlation in the activity of neurons, while homeostatic relies on a negative feedback signal to control neuronal activity. Since correlated activity leads to strengthened synaptic contacts and formation of cell assemblies, Hebbian plasticity is considered to be the basis of learning and memory. Stronger synapses, on the other hand, promote stronger correlation. This positive feedback loop can lead to instability and homeostatic plasticity is thought to play a role of stabilization. The experimentally observed time scales of homeostatic plasticity, however, are too slow to compensate for the fast Hebbian changes. Therefore, the exact way multiple types of plasticity interact in the brain remains to be elucidated. In this thesis, we will show that homeostatic plasticity can also have interesting effects on network structure. We will show that homeostatic structural plasticity has a Hebbian effect on the network level, and it comprises two separate time scales, a faster for learning and a slower for forgetting. Using a model of classical conditioning task, we will show that this rule can perform pattern completion, and that network response upon stimulation is gradual, reflecting the strength of the memory. Furthermore, we will show that networks grown with homeostatic structural plasticity and a broad distribution of target rates exhibit non-random features similar to some of those found in cortical networks. These include a broad distribution of in- and outdegrees, an over-abundance of bidirectional motifs and scaling of synaptic weights with the number of presynaptic partners. Overall, we will use simulations of spiking neural networks and mathematical tools to show that there is more to homeostatic plasticity than just controlling network stability. It remains an open question, however, the extent to which homeostatic plasticity can be accounted for structural features found in the brain.

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  • Public defence: 2020-06-08 13:30 https://kth-se.zoom.us/webinar/register/WN_73LDRd7wTluzgWYizxWIJA, Stockholm
    Taibi, Emanuele
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    A multi-sector framework for accelerating renewable energy deployment in power, transport and industry2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Climate change is the defining issue of our time (United Nations, 2018). Renewable energy, combinedwith energy efficiency, can potentially be the most effective solution to address energy-relatedGreenhouse Gas (GHG) emissions. This work covers global, regional and national strategies to acceleratedeployment of renewable energy in power, transport and industry, using a variety of methodologies toaddress sectoral challenges and account for sectoral specificities. These sectors jointly represented 85%of energy-related emissions in 2016 (IRENA, 2019a).The thesis is structured around four focus areas. Foci 1-3 investigate the key components of an energytransformation jigsaw that looks at key sectors in which renewable energy can be integrated: industry,transport and power. The fourth focus area is informed by the other three and provides key insights forthe necessary institutional setting and changes for the transition to renewable energy to play out.Focus 1: Decarbonising industryIndustry needs a combination of electricity and heat, therefore apart from decarbonising electricity it isalso necessary to decarbonise heat: depending on temperature levels, a combination of solar thermal,heat pumps and most prominently bioenergy can help in decarbonising process heat. In this thesis I focuson the often overlook role of renewable energy in process heat provision. The analysis presented here isglobal in scale and covers all manufacturing sectors, assessing the potential for biomass, as well as solarthermal and heat pumps, to provide the necessary process heat for industry. This, in combination withincreased electrification and the production of hydrogen from renewable power, charts the way in termsof decarbonisation of industry at the global level. Results show that renewables can replace 50% of fossilfuel consumption for industry. In addition to this, decarbonisation of electricity supply can indirectlydecarbonise industry, especially if industrial energy demand is further electrified.Focus 2: Decarbonising transportIn the transport sector, we can replace petroleum fuels with renewable fuels. To date, this has beenachieved mostly with biofuels. In the future, renewables-based hydrogen and its derivatives can also bea significant source of carbon-neutral fuels. Finally, we are witnessing the rise of battery electric vehicles,which can be leveraged to provide flexibility to the power system and integrate more solar and wind,creating a virtuous cycle of more renewables in power and in transport at once. The analysis presentedin this thesis covers both the structural evolution of the automotive sector in Europe, and how the shiftfrom gasoline to diesel in passenger cars would affect the demand for biodiesel as opposed to ethanol,and the impact of battery electric vehicles (EVs) on the power system. In particular, this analysis looks athow EVs can be leveraged to facilitate the integration of large shares of solar and wind into powersystems, with an application to a small island developing state (SIDS) that pledge to go 100% renewableenergy by 2030, Barbados. Sectoral interactions, like the impact of electric vehicles on the power sector,are also crucial in determining a smooth, coordinated transition of the energy sector away from fossilfuels, further improving affordability and reliability of energy services.Focus 3: Transforming the power sector through rapid deployment of solar and windAs the power sector is a fundamental driver for the energy transition, this PhD tackles some of thechallenges related to the use of solar and wind as main sources for power sector decarbonisation. This 

    PhD covers methodological aspects on how to perform the necessary planning studies to transform thepower system using solar and wind generation. This methodological planning framework is applied 1) inthe power generation expansion plan for the Republic of Cyprus, as a key contribution to the developmenton the National Energy Roadmap of Cyprus, 2) to the Pacific Small Island Developing State (SIDS) of Samoa,looking at how different studies can translate policy targets into a renewable-based, reliable andaffordable power system, and 3) to the Caribbean SIDS of Barbados, where the power system analysisshows how to link the power sector to the transportation sector to provide mutual benefits from thedecarbonisation of both sectors.Focus 4: The institutional framework for accelerated renewable energy deploymentFor change to happen, especially at the pace and scale required to meet the objectives of the Parisagreement, the institutional framework for the energy sector requires changes. Increased electrificationaccompanied by decarbonisation of the power sector requires significant changes to how electricity isprocured, regulated, traded and financed. In some regions policies and markets should be adjusted orredesigned. In other regions, the absence of unbundled wholesale electricity markets could be initially achallenge but could be turned into an opportunity for an easier, speedier transition implemented by avertically integrated utility, which is the most common model to date in the majority of countries.Institutional frameworks are very specific for each country or, at best, region, and are difficult to transferfrom one context to another; however, they often remain the largest obstacle to an acceleration inrenewable energy deployment.Beyond the power sector, industry is a sector where change is difficult to achieve at speed, as largeinvestments already in place and global competitiveness of products and services make transitionsparticularly difficult. Additionally, industry requires rapid returns, limiting the spectrum of viableinvestments into new processes, which in turn limits energy efficiency potential and the possibility ofadopting renewable energy to replace fossil fuels.For renewables in transport, a precedent has been set by biofuels, as in many regions and countries theyrepresent an important renewable energy resource for decarbonisation of transport. Moving forward,especially for global sectors like shipping and aviation, a broader framework will be required to introducecarbon-neutral fuels at scale.Overall, the goal of this thesis is to provide policy makers with a set of tools and examples that can supportthe development of effective policies and plans for the increased adoption of renewable energy sourcesat the global, regional and national level and spanning transport, industry and the power sector.

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    Emanuele Taibi - PhD Thesis
  • Public defence: 2020-06-09 09:00 https://kth-se.zoom.us/webinar/register/WN_qgz5ej_sQVOiEwrSoar3Ew, Stockholm
    Stefanikova, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
    Pedestal structure and stability in JET-ILW and comparison with JET-C2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Controlled thermonuclear fusion offers a promising concept for safe and sustainable production of electrical energy. However, there are still many issues to be investigated on the way to a commercial fusion reactor. An important point for detailed studies is connected to wall materials surrounding hot thermonuclear plasma. The JET tokamak (the largest fusion experiment in the world) in the United Kingdom has completed a major upgrade in 2011 in which the materials of the vessel surrounding the fusion fuel have been changed from a carbon-fibre-composite (or JET-C wall) to Beryllium and Tungsten. These new materials are the same as those that will be used in a next step fusion device International Thermonuclear Experimental Reactor ITER (hence the name ITER-like wall or JET-ILW), designed to demonstrate the feasibility of fusion reactor based on the tokamak concept. One of the goals of JET with the ILW is to act as a test bed for ITER technologies and for ITER operating scenarios.

    The overall purpose of the thesis work is to characterise the effect of the ILW on the structure and stability of edge plasma phenomenon called the pedestal, a steep pressure gradient associated with the H-mode, an operational regime with improved confinement. The aim is to contribute to the understanding of the difference in the pedestal performance between JET-C and JET-ILW.

    The work is focused on experimental characterisation of the pedestal structure in deuterium discharges by analysing the experimental data (radial profiles of electron temperature and density measured in H-mode plasmas) from Thomson scattering diagnostics at JET and on investigating the differences in pedestal stability between JET-ILW and JET-C plasmas in terms of the pedestal modelling. The pedestal structure is determined using a modified hyperbolic tangent fit to the experimental Thomson scattering profiles. The modelling is performed with the pedestal predictive code Europed, based on the EPED model commonly used to predict the pedestal height in JET.

    The experimental analysis has shown several differences in the pedestal structure of comparable JET-ILW and JET-C discharges. One of the key differences introduced in this work is the pedestal relative shift (a separation between the middle of the pedestals of the electron density and temperature) that plays a major role in the difference in the pedestal performance between JET-C and JET-ILW. The work shows that the relative shift can vary significantly from pulse to pulse and that, on average, JET-C plasmas have lower relative shift than JET-ILW plasmas. The pedestal relative shift tends to increase with increase in the gas fuelling and the heating power. Furthermore, the increase in the relative shift has been empirically correlated with the degradation of the experimental normalized pressure gradient αexp.

    To understand the differences in the JET-C and JET-ILW pedestal stability, parameters that affect the pedestal stability and that tend to vary between comparable JET-C and JET-ILW discharges have been identified. These parameters are the pedestal relative shift, pedestal density neped, effective charge number Zeff, pedestal pressure width wpe, and normalized pressure βN. The modelling performed with the predictive Europed code has shown that these five parameters are sufficient to explain the difference in the pedestal performance between JET-C and JET-ILW.

    Furthermore, the modelling has shown that the relative shift and neped play a major role in affecting the critical normalized pressure gradient αcrit (normalized pressure gradient expected by the model comparable to αexp), while the relative shift, wpe and Zeff have a major impact on the pedestal pressure height. Finally, a possible mechanism that has led to the degradation of the pedestal pressure from JET-C to JET-ILW is proposed.

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  • Public defence: 2020-06-09 14:00 https://kth-se.zoom.us/webinar/register/WN_bXnSCrT6Qk-qOk7GYGyIBw, Stockholm
    Doyle, Andrew
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Consolidating concepts of technology education: From rhetoric towards a potential reality2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis focuses on the relationship between international rhetoric and classroom realities in technology education. For some time there has been widespread recognition that the intended goals for learning in the subject area have failed to manifest in enacted practices as envisioned. As the intermediary between rhetoric and reality, the technology teachers and ways of understanding their enacted practices are the focus of this work.

     

    The thesis is based on four research articles which adopt theoretical and empirical approaches to investigating the technology teacher as mediator of enacted practice. In Article I, technology education in the Irish national context is investigated through technology teachers’ reflections on enacted practice. In response to a variety of situational- and systemic- factors which impede classroom practice being identified, Article II and III theorise approaches to investigating enacted practice in technology. In acknowledging the epistemological basis of technology as depicted in the extant literature, a reconceptualisation of how to utilise pedagogical content knowledge research in explaining enacted practice is put forward. Article IV returns to the technology teacher in a transnational context, whereby teachers from the Republic of Ireland, Sweden and New Zealand are interviewed in constructing a grounded theory of teachers’ purposes for teaching technology.

     

    The contributions of the research are twofold. Firstly, following the identification of evidence to support the existence of rhetoric-reality tensions in technology education, an ecologically situated framework of enacted practice is put forward. The framework acknowledges how subject matter is treated in technology education in striving for more comprehensive ways of investigating enacted practice. Secondly, in taking a preliminary step toward understanding enacted practices, a grounded theory of teachers’ purposes for teaching technology is put forward. This grounded theory offers a unified model for articulating the purposes of teaching technology that prevail in classroom realities today.

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  • Public defence: 2020-06-10 10:00 publikt via ZOOM, Stockholm
    Han, Tong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Catalytic pyrolysis of lignin to produce fuels and functional carbon materials 2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Development of renewable energy carriers and green adsorbents is an essential step in creating a fossil-free and toxin-free future of the world. Lignin is the second highest component of biomass and the only renewable resource of aromatics in nature. Currently, around 70 million tons of lignin are produced annually from the pulp and paper industries word-wide, while only 1-2% of them can be upgraded into value-added products. Pyrolysis is one of the most promising technologies for lignin conversion to produce value-added products. After a lignin pyrolysis process, biooil, biogas, and biochar can be produced. Wherein, after upgrading, biogas and biooil can be used as alternatives to fossil based energy carries to produce fuels or chemicals; biochar can be used as carbon source to produce green adsorbents for pollutants removal. 

    This dissertation provides a systematic research focusing on the catalytic pyrolysis of lignin to produce upgraded biofuels and magnetic activated carbons (MACs). First of all, two specific issues i.e. sulfur and melting unique to lignin pyrolysis process are studied to achieve a thorough understanding of the lignin pyrolysis processes. Investigation of sulfur evolution during the lignin pyrolysis process is the study carried out first. Understanding lignin melting characteristics is the study carried out subsequently. Hereafter, in situ catalytic pyrolysis of lignin over low-cost catalysts is studied to produce upgraded biooils. Low-cost catalysts with different textural and acidic properties screening is the study carried out first. Development of a self-sufficient catalytic pyrolysis of lignin process via using activated carbons (ACs) derived from the same lignin pyrolysis process as catalysts is the study carried out subsequently. At last, pyrolysis and subsequent steam gasification of metal dry impregnated lignin is studied to produce MACs and H2-rich syngas. Development of a streamlined process to produce high-quality MACs for phosphorous adsorption is the study carried out first. Pyrolysis and subsequent steam gasification of metal dry impregnated lignin to co-produce MACs and H2-rich syngas is the study carried out subsequently.

    The study of sulfur evolution during the lignin pyrolysis process implies that sulfur-containing radicals are more likely to combine with other small radicals during a fast pyrolysis process. As a result, the main detected sulfur-containing compounds are small molecular gases or liquids with low boiling points and the main compounds in liquid phase are sulfur-free. The study of lignin melting characteristics at pre-pyrolysis temperature implies that the degree of cross-linked of the lignin structure determines its melting characteristics. Lignin extracted from pulping process has a less cross-linked structure. Therefore, it melts and softens to a flow state after a glass transition. Lignin extracted from hydrolysis process has a more cross-linked structure. Therefore, it does not melt but rather decompose after a glass transition.

    The study of low-cost catalysts with different acidic and textural properties screening for in situ catalytic pyrolysis of lignin implies that the use of only commercial AC as a catalyst induces the enhanced yield of monocyclic aromatic hydrocarbons (MAHs) among all low-cost catalysts. Bentonite and red mud catalysts have strong surface acidity but poor porous properties. This determines that produced reactive intermediates are easy to repolymerize to form char or coke without the blocking effect of pore wall. Commercial AC has an abundant porous structure as well as a surface acidity with a certain strength. The produced reactive intermediates could be isolated by pore walls and therefore induce the of MAHs production. A subsequent study of in situ catalytic pyrolysis of lignin over ACs from the same lignin pyrolysis process implies that the use of only AC that has more mesopores than micropores as catalyst could induce a significant decrease of the tarry oil yield and a significant increase of the phenols concentration in aqueous and liquid phase oils. The diffusion efficiency of the reactive intermediates determined by pore size is supposed to be the most crucial parameter that determines the catalytic performance of ACs. The pore sizes of mesopores are much bigger than the sizes of reactive intermediates. Therefore, these pores could allow most of the reactive intermediates to diffuse quickly and to react within their pores.

    The study of the streamlined MACs production process development implies that iron species can be embedded into a carbon matrix via a lignin melting process. After the pyrolysis/carbonization of lignin and FeSO4 mixture under a nitrogen atmosphere, FeSO4 is decomposed and further reduced to form hagg iron carbide, which is buried into carbon matrix of biochars after a lignin melting. During subsequent steam gasification/activation process, iron species are gradually exposed from the carbon via the pore drilling and widening effect of steam. At the same time, the bare part of iron species are oxidized by steam to form magnetite. The maximum phosphorous adsorption capacity of produced MAC sample calculated using the best-fit Langmuir-Freundlich model is estimated to be 21.18 mg P/g. Further study of pyrolysis and subsequent steam gasification of metal dry impregnated lignin to produce MACs and H2-rich syngas implies that during the pyrolysis of FeSO4 impregnated lignin process, H2 is produced via the catalytic cracking of the volatiles. During the subsequent steam gasification of solid residues, H2 was mainly produced via the steam carbon reactions and the steam gas shift reactions. The maximum overall H2 yield of the integrated process is as high as 42.73 mol/kg-lignin. Also, approximately 70% of phosphorous in real domestic wastewater can be adsorbed by MACs produced from the same process after a treatment for 2 hours.

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  • Public defence: 2020-06-10 10:00 online via Zoom
    Wang, Bochao
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Constitutive models of magneto-sensitive rubber under a continuum mechanics basis and the application in vibration isolation2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to its durability, stretchability, relatively low stiffness and high damping, rubber is widely used in engineering anti-vibration fields. However, a major deficiency is that once installed, the mechanical properties of traditional rubber-based devices are fixed where its adaptability to various loading conditions is poor. An alternative to traditional rubber materials is magneto-sensitive (MS) rubber. The main componentsof MS rubber are a rubber matrix and ferromagnetic particles. Under a magnetic field, the modulus of MS rubber can be altered rapidly and reversibly. Therefore, compared with conventional rubber-based devices, the stiffness of MS rubber-based devices can be adapted to various loading conditions and an enhanced vibration reduction effect can be achieved. Measurement results revealed that the mechanical behavior of MS rubber is not simple. To be specific, the dynamic modulus of MS rubber has a magnetic, frequency,amplitude and temperature dependency. In order to promote the applications of MS rubber in the anti-vibration area, models to depict the above properties are needed. The main goal of this thesis is to model the magnetic, frequency, amplitude and temperature dependence of MS rubber under a continuum mechanics basis. The research results regarding the constitutive modeling consist of three papers (Paper A, C and D). The simulation results show a good agreement with the measurement data, which proves the accuracy and feasibility of the developed model. In addition to the constitutive models of MS rubber, an investigation of MS rubber application in the vibration isolation system under harmonic and random loading cases is numerically conducted (Paper B). In order to achieve an enhanced vibration isolation effect, two control algorithms corresponding to the harmonic and random loading are developed. Numerical results verify that the vibration isolation effect ofMS rubber vibration isolator is better than the traditional rubber-based isolator. In this thesis, the model developed for MS rubber deepens the understanding of how magnetic, frequency, amplitude and temperature affect the mechanical performance of MS rubber. Moreover, the research of MS rubber application in vibration isolators and the corresponding control strategies are helpful for the design of MS rubber-based anti-vibration devices.

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    Constitutive models of magneto-sensitive rubber under a continuum mechanics basis and the application in vibration isolation
  • Public defence: 2020-06-10 10:00 N/A (Via videolink due to Corona virus)
    Tomasson, Egill
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Impact of High Levels of Variable Renewable Energy on Power System Generation Adequacy: Methods for analyzing and ensuring the generation adequacy of modern, multi-area power systems2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The generation adequacy of electricity supply has been an ongoing concern since the restructuring of the industry. Ensuring generation adequacy was a rather straightforward task in the era of natural monopolies. Whose responsibility was it to ensure generation adequacy as the industry became deregulated and more fragmented? Who is willing to finance rarely used generating units? After decades of experience with the competitive electricity market, the question of whether market forces alone are sufficient to ensure generation adequacy still remains.

    Recent energy policies have moreover set a goal of a high share of renewable energy in electricity markets. The presence of high levels of renewable generation makes the supply side of the market more uncertain. This volatility in energy production induces volatility in energy prices which means that the revenue stream of conventional generating technologies is more uncertain than it has traditionally been. This can even deteriorate the economics of some generators to the point where they exit the electricity market. The installed capacity of dispatchable generation can therefore be reduced.

    These developments bring up the question of whether the generation adequacy of modern and future, deregulated and highly variable power systems is ensured. This dissertation focuses on modeling the generation adequacy of modern power systems with a high penetration of variable renewable energy sources. Moreover, the dissertation looks at some solutions with the aim of ensuring the generation adequacy of such systems through various means such as coordinated reserves, energy storage as well as utilizing the flexibility of the demand side of the market.

    The models developed in this dissertation are verified using well-known test systems as well as through large-scale analysis of real-world systems. Aside from focusing on the simulation of power systems, the developed models moreover focus on achieving high computational efficiency. This is done through means such as advanced Monte Carlo simulation and optimization methods that apply decomposition to speed up the simulations.

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  • Public defence: 2020-06-10 10:00
    Li, Junhao
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Theoretical Studies of Drug-Metabolizing Cytochrome P450 Enzymes2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The family of cytochrome P450 enzymes (P450s) belongs to one of the most important enzyme families in the human body. P450s are involved in the synthesis of endogenous compounds and metabolism of exogenous substances. In mammalian species, drug metabolizing P450s are anchored in the bilayer lipid membrane, which allows the enzymes to interact with other proteins and ligand molecules. A wealth of knowledge about the structures, functions, and mechanisms of P450s have been obtained from both experimental and theoretical studies. However, the mechanisms behind some experimental results, such as the regio- and stereoselectivity and structural flexibility are still elusive.

    In this thesis, I present the work done in my doctoral studies, which was focused on the catalytic selectivity and structural flexibility of P450s. Multiple theoretical modeling approaches, such as homology modeling, molecular docking, molecular dynamics, quantum mechanics, and quantum mechanics/molecular mechanics, were applied in the studies. In papers I and II, the regio- and stereoselectivity of CYP4F2, CYP3A4, and CYP19A1 catalyzed C–H hydroxylation of different substrates were studied. The results indicate that the ligand reactivity and accessibility can be decisive for the regio- and stereoselectivity. However, which of them is more important is system-dependent. The quantum mechanics/molecular mechanics calculation results imply that the distribution of spin natural orbitals could be used for discriminating the roles of the reactivity and accessibility. In papers III and IV, the conformational dynamics of the open and closed structures of CYP2B4 and the ligand cooperativity phenomenon of midazolam metabolized by CYP3A4 were investigated using molecular dynamics simulations. From the simulation results, we identified the key residues for the conformational dynamics for the open-to-intermediate transition and found that the ligand cooperativity is also caused by the large flexibility of P450. The results also indicated that the homotropic cooperativity mainly occurs in the large and flexible productive site, rather than in the remote allosteric site.

    The full text will be freely available from 2020-06-15 15:00
  • Public defence: 2020-06-11 10:00 https://kth-se.zoom.us/j/67826970577 , Vid fysisk närvaro eller Du som saknar dator/datorvana kan kontakta service@itm.kth.se
    Arzpeyma, Niloofar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Model Developments to Study Some Aspects of Improving Efficiencies in EAF Plants2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The aim of this thesis is to investigate some aspects of improvements with respect to the energy consumption and raw material selection as well as the understanding of the influence of uncertainties on the performance in electric arc furnace (EAF) plants. The effect of electromagnetic stirring on the scrap melting and post combustion capacity are investigated in two EAFs by using computation fluid dynamic (CFD) models. The results showed that electromagnetic stirring can contribute to a better heat transfer rate at the melt – scrap interface. The Grashof and Nusselt numbers for both electromagnetic stirring and natural convection were estimated, as well as compared to the data from previous studies. Also, the results of the post-combustion in the duct system were used to predict the concentration of uncombusted CO at the possible position to install an off – gas analysis equipment. Also, modeling of the post-combustion in the whole furnace showed that the post-combustion can be improved by increasing the flow rate of the secondary oxygen in a virtual lance burner (VLB) under the meltdown and refining periods of the process. In order to investigate the influence of additions of raw materials on energy, melt composition and slag properties, a static mass and energy balance model is developed. The distribution ratios for metallic elements and dust parameters are calibrated by using process data from an EAF. The model is then applied to investigate the effect of hot briquetted iron (HBI) additions in that particular EAF. The results showed that these additions resulted in an increased electricity consumption and slag amount. The model is then applied to predict how it is possible to adjust the amount of slag formers to reach a desired MgO saturation level. In addition, a statistical model is developed which simulate the melt composition by applying uncertainties in scrap composition, scrap weighing and element distribution factors. The model can estimate the mean and standard deviations in the element concentration of scraps. The results of the model application in an EAF showed that the simulated melt chemical composition is in good agreement with the measured one, when the estimated values for scraps are applied as data in the model.

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  • Public defence: 2020-06-11 13:00 Via Zoom -- https://kth-se.zoom.us/meeting/register/u5Isf--grTguHNPDOGMrkrpy5nka38XCSnZG, Stockholm
    Quino Lima, Israel
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering. Universidad Mayor de San Andres.
    Hydrogeochemistry and spatial variability of arsenic and other trace elements in the Lower Katari Basin around Lake Titicaca, Bolivian Altiplano.: Impact on drinking water quality and groundwater management.2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Arsenic (As) contamination in drinking water is a world-wide problem. Thenatural origin of As, its mobility and transport are of great interest in BolivianAltiplano (Lower Katari Basin: LKB and Sothern Poopó Basin: SPB) due topresence of mineral ore deposits, brines, hot springs and volcanic rocks.Hydrogeochemical spatio-temporal and spatial variability investigations wereapplied to groundwater, surface water and sediments with a statistical approachto better understand the spatial distribution of As, major ions and trace elements,and evaluate the sources of dissolved species and elucidate the processes thatgovern the evolution of natural water in the LKB. The result reveal high levelsof As, boron (B), antimony (Sb), manganese (Mn) and salinity in shallow wells,which exceeds the guideline values of the Bolivian regulation (NB-512) andWorld Health Organization (WHO). The seasonal variation and its impact onthe water quantity, on top of the solids and liquid residual (origin Pallina River)poses significant negative health risk for the community at the banks of theKatari River. The first evaluation of the hydrogeological study indicates that thegroundwater flow was observed in the direction southeast - northwest (SE -NW), and there is an interaction between groundwater and surface water. Thespatial distribution of As varies considerably due to geological characteristics ofthe area as well as due to the heterogeneously distributed evaporites in thesediments (in LKB and SPB). However, the highest concentrations of As arefound in the alluvial sediments of the northern region. Sequential extraction ofsediment along with geochemical modeling (mineral saturation indices) indicatesthat the iron (Fe) and aluminum (Al) oxides as well as their hydroxides are mostimportant adsorbent minerals of As in central and southern region of LKB. Thechemistry of water bodies in LKB and SPB is strongly influenced by theinteraction with the sediment constituents and by the spatial-temporal variations.The results of spatial analysis indicate that despite of the outliers there is a goodautocorrelation for As, B and Sb, since Moran's I values are positive. The globalspatial dependence analysis indicated a positive and statistically significant spatialautocorrelation (SA) for all cases and TEs are not randomly distributed at 99%confidence level.

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  • Public defence: 2020-06-12 09:00 https://kth-se.zoom.us/j/62560073937
    Remnestål, Julia
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Affinity Proteomics.
    Dementia Proteomics2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The term dementia encompass a number of conditions arising as a consequence of tissue degeneration in the brain. This degeneration is caused by molecular events occurring on a cellular level including inflammation, defective waste disposal and accumulation of insoluble proteins and peptides. Many of these molecular events are in turn also reflected in the composition of the cerebrospinal fluid (CSF) which circulates within and around the brain. This thesis summarise five studies conducted with the aim to explore and profile CSF proteins in the context of dementia and other neurodegenerative disorders. Protein profiles were obtained by so-called suspension bead arrays (SBAs), created by coupling antibodies to color-coded microspheres, allowing detection of more than 350 CSF proteins simultaneously. The majority of the explored proteins are referred to as brain-enriched, entailing that the corresponding genes are highly expressed in brain tissue in comparison to other tissues.

     

    In Paper I, the SBA technology was utilised to profile about 280 proteins in CSF from several neurodegenerative disorders, i.e. Alzheimer’s disease (AD), dementia with Lewy Bodies and Parkinson’s disease. Distinct differences in the CSF proteome were identified depending on site of collection (ventricular or lumbar) and time point (post mortem or ante mortem). Disease-associated profiles for the two synaptic proteins neuromodulin (GAP43) and neurogranin (NRGN) could be confirmed, in which both proteins displayed higher levels in AD compared to controls. High levels of the two proteins were furthermore observed in patients at preclinical stages of AD in two independent cohorts. To verify the identified protein profiles, parallel reaction monitoring (PRM) assays were developed for 17 proteins in Paper II, including GAP43. Eight proteins displayed concordance to data generated with SBAs and among these were GAP43, cholecystokinin, neurofilament medium chain (NF-M), leucine-rich alpha-2-glycoprotein and vascular cell adhesion protein 1. 

     

    In Paper III, the SBA technology was again applied to characterise early dementia-related changes in the CSF proteome by comparing samples from individuals with mild cognitive impairment (MCI), controls and AD patients in two independent cohorts. The MCI individuals were moreover stratified based on CSF concentration of the core AD biomarkers Aβ42 and tau. The six proteins amphiphysin, aquaporin 4, cAMP regulated phosphoprotein 21, β-synuclein, GAP43 and NF-M did all show significant differences between sample groups in both cohorts. Further exploration of how the pathological processes preceding dementia affect the CSF proteome, was done by analysis of 104 brain-enriched proteins in CSF from asymptomatic 70 year-olds in Paper IV. Protein profiles were correlated to Aβ42, t-tau and p-tau CSF concentration, revealing a large number of proteins displaying significant correlations to tau levels. Upon dividing the asymptomatic individuals based on Aβ42 CSF pathology, some proteins showed significantly different associations in the two groups. Most of these proteins yielding interesting profiles, were plasma membrane proteins or proteins connected to synaptic vesicle transport.

     

    While AD is the most common form of dementia, accounting for more than 60 % of all cases worldwide, frontotemporal dementia (FTD) is the most frequently occurring form of young-onset dementia. In Paper V, CSF protein profiles were explored in the context of FTD. Patients with behavioural variant FTD and primary progressive aphasia, were compared to unaffected individuals with a high risk of developing FTD. Proteomic differences between patients with FTD and the unaffected individuals were observed already at a global level, and particularly for the six proteins NF-M, neurosecretory protein VGF, neuronal pentraxin receptor, prodynorphin, transmembrane protein 132D and tenascin-R.

     

    The disease-associated profiles identified in the presented studies provide a basis for future research within dementia proteomics. Whether the proteins identified will have the possibility to aid in clinical diagnosis, prognosis or characterisation of dementia, remains to be evaluated. Given the fortunate situation, especially in Sweden, with access to large and well characterised CSF collections, there are ample opportunities for future proteomic studies to elucidate the true potential of these proteins.

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    Dementia Proteomics Kappa Remnestaal
  • Public defence: 2020-06-12 09:30 D5, Stockholm
    Yu, Peng
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Modelling and Simulation of Reactor Pressure Vessel Failure during Severe Accidents2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis aims at the development of new coupling approaches and new models for the thermo-fluid-structure coupling problem of reactor pressure vessel (RPV) failure during severe accidents and related physical phenomena. The thesis work consists of five parts: (i) development of a three-stage creep model for RPV steel 16MND5, (ii) development of a thermo-fluid-structure coupling approach for RPV failure analysis, (iii) performance comparison of the new approach that uses volume loads mapping (VLM) for data transfer with the previous approach that uses surface loads mapping (SLM), (iv) development of a lumped-parameter code for quick estimate of transient melt pool heat transfer, and (v) development of a hybrid coupling approach for efficient analysis of RPV failure.

    A creep model called ‘modified theta projection model’ was developed for the 16MND5 steel so that it covers three-stage creep process. Creep curves are expressed as a function of time with five parameters  (i=1~4 and m) in the new creep model. A dataset for the model parameters was constructed based on the available experimental creep curves, given the monotonicity assumption of creep strain vs temperature and stress. New creep curves can be predicted by interpolating model parameters from this dataset, in contrast to the previous method that employs an extra fitting process. The new treatment better accommodates all the experimental curves over the wide ranges of temperature and stress loads. The model was implemented into the ANSYS Mechanical code, and its predictions successfully captured all three creep stages and a good agreement was achieved between the experimental and predicted creep curves. For dynamic loads that change with time, the widely used time hardening and strain hardening models were implemented with a reasonable performance. These properties fulfil the requirements of a creep model for structural analysis.

    A thermo-fluid-structure coupling approach was developed by coupling the ANSYS Fluent for the fluid dynamics of melt pool heat transfer and ANSYS Structural for structural mechanics of RPV. An extension tool was introduced to realize transient load transfer from ANSYS Fluent to Structural and minimize the user effort. Both CFD with turbulence models and the effective model PECM can be employed for predicting melt pool heat transfer. The modified theta projection model was used for creep analysis of the RPV. The coupling approach does not only capture the transient thermo-fluid-structure interaction feature, but also support the advanced models in both melt pool convection and structural mechanics to improve fidelity and facilitate implementation. The coupling approach performs well in the validation against the FOREVER-EC2 experiment, and can be applied complex geometries, such as a BWR lower head with forest of penetrations (control rod guide tubes and instrument guide tubes).

    In the comparative analysis, the VLM and SLM coupling approaches generally have the similar performance, in terms of their predictability of the FOREVER-EC2 experiment and applicability to the reactor case. Though the SLM approach predicted slightly earlier failure times than VLM in both cases, the difference was negligible compared to the large scale of vessel failure time (~  s). The VLM approach showed higher computational efficiency than the SLM.

    The idea of the hybrid coupling is to employ a lumped-parameter code for quick estimate of thermal load which can be employed in detailed structural analysis. Such a coupling approach can significantly increase the calculation efficiency which is important to the case of a prototypical RPV where mechanistic simulation of melt pool convection is computationally expensive and unnecessary. The transIVR code was developed for this purpose, which is not only capable of quick estimate of transient heat transfer of one- and two- layer melt pool, but also solving heat conduction problem in the RPV wall with 2D finite difference method to provide spatial thermal details for RPV structural analysis. The capabilities of transIVR in modelling two-layer pool heat transfer and transient pool heat transfer were demonstrated by calculations against the UCSB FIBS benchmark case and the LIVE-7V experiment, respectively. The transIVR code was then coupled to the mechanical solver ANSYS Mechanical for detailed RPV failure analysis. Validation against the FOREVER-EC2 experiment indicates the coupling framework successfully captured the vessel creep failure characteristics.

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  • Public defence: 2020-06-12 10:00 Zoom
    Berggren, Tomas
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    On determinantal point processes and random tilings with doubly periodic weights2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is dedicated to asymptotic analysis of determinantal point processes originating from random matrix theory and random tiling models. Our main interest lies in random tilings of planar domains with doubly periodic weights.

    Uniformly distributed random tiling models are known to be a very rich class of models where many interesting phenomena can be observed. These models have therefore been under investigation for many years and many aspects of the models are by now well understood. Random tiling models with doubly periodic weights are in fact an even richer class of models. However, these models are much more difficult to analyze and for a thorough study of their behavior new ideas are needed. This thesis increases the understanding of random tiling models with doubly periodic weights.

    The thesis consists of three papers and two chapters; one introductory and background chapter and one chapter giving an overview of the papers.

    Paper A deals with linear statistics of the thinned Circular Unitary Ensemble and the thinned sine process. The thinning creates a transition from the Circular Unitary Ensemble respectively sine process to the Poisson process. We study a part of these transitions in detail.

    In Papers B and C we study random tiling models with doubly periodic weights. These two papers constitute the main contribution of this thesis.

    In Paper B we give a general method how to analyze a large family of random tiling models. In particular, we provide a double integral formula for the correlation kernel in terms of a Wiener-Hopf factorization of an associated matrix-valued function. We also present a recursive method on how to construct the Wiener-Hopf factorization.

    The method developed in Paper B is used in Paper C to analyze the 2×k-periodic Aztec diamond. More precisely, we derive the correlation kernel for the Aztec diamond of finite size and give a detailed description of the model as the size tends to infinity.

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  • Public defence: 2020-06-12 10:00 Stockholm
    Bergendal, Erik
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Fatty Acid Self-Assembly at the Air–Water Interface: Curvature, Patterning, and Biomimetics: A Study by Neutron Reflectometry and Atomic Force Microscopy2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    For more than a hundred years of interfacial science, long chain fatty acids have been the primary system for the study of floating monolayers at the air–water interface due to their amphiphilic nature and system simplicity: an insoluble hydrocarbon chain and a soluble carboxyl group at a flat air–water interface. Despite―or perhaps rather due to―the assumed simplicity of such systems and the maturity of the research field, the seemingly fundamentally rooted notion of a two-dimensional water surface has yet to be challenged.

    The naturally occurring methyl-branched long chain fatty acid 18-methyleicosanoic acid and one of its isomers form monolayers consisting of monodisperse domains of tens of nanometres, varying in size with the placement of the methyl branch. The ability of domain-forming monolayers to three-dimensionally texture the air–water interface is investigated as a result of hydrocarbon packing constraints owing to the methyl branch.

    In this work, neutron reflectometry has been used to study monolayers of branched long chain fatty acids directly at the air–water interface, which allowed precise probing of how a deformable water surface is affected by monolayer structure. Such films were also transferred by Langmuir–Blodgett deposition to the air–solid interface, and subsequently imaged by atomic force microscopy. Combined, the results unanimously―and all but unambiguously―show that the self-assembly of branched long chain fatty acids texture the air–water interface, inducing domain formation by a local curvature of the water surface, and thus controverting the preconceived notion of a planar air–water interface. The size and shape of the observed domains are shown to be tuneable using three different parameters: in mixed systems of branched and unbranched fatty acids, with varying hydrocarbon length of the straight chain, and altering subphase electrolyte properties. Each of these factors effectively allows changing the local curvature of the monolayer, much like analogous three-dimensional systems in bulk lyotropic crystals. This precise tuneability opens up for sustainable nanopatterning. Finally, the results lead to a plausible hypothesis of self-healing properties as to why the surface of hair and wool have a significant proportion of branched fatty acid.

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  • Public defence: 2020-06-12 10:00 U1, Stockholm
    Tang, Jiexiong
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Deep Learning Assisted Visual Odometry2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The capabilities to autonomously explore and interact with the environmenthas always been a greatly demanded capability for robots. Varioussensor based SLAM methods were investigated and served for this purposein the past decades. Vision intuitively provides 3D understanding of the surroundingand contains a vast amount of information that require high levelintelligence to interpret. Sensors like LIDAR, returns the range measurementdirectly. The motion estimation and scene reconstruction using camera is aharder problem. In this thesis, we are in particular interested in the trackingfrond-end of vision based SLAM, i.e. Visual Odometry (VO), with afocus on deep learning approaches. Recently, learning based methods havedominated most of the vision applications and gradually appears in our dailylife and real-world applications. Different to classical methods, deep learningbased methods can potentially tackle some of the intrinsic problems inmulti-view geometry and straightforwardly improve the performance of crucialprocedures of VO. For example, the correspondences estimation, densereconstruction and semantic representation.

    In this work, we propose novel learning schemes for assisting both directand in-direct visual odometry methods. For the direct approaches, weinvestigate mainly the monocular setup. The lack of the baseline that providesscale as in stereo has been one of the well-known intrinsic problems inthis case. We propose a coupled single view depth and normal estimationmethod to reduce the scale drift and address the issue of lacking observationsof the absolute scale. It is achieved by providing priors for the depthoptimization. Moreover, we utilize higher-order geometrical information toguide the dense reconstruction in a sparse-to-dense manner. For the in-directmethods, we propose novel feature learning based methods which noticeablyimprove the feature matching performance in comparison with common classicalfeature detectors and descriptors. Finally, we discuss potential ways tomake the training self-supervised. This is accomplished by incorporating thedifferential motion estimation into the training while performing multi-viewadaptation to maximize the repeatability and matching performance. We alsoinvestigate using a different type of supervisory signal for the training. Weadd a higher-level proxy task and show that it is possible to train a featureextraction network even without the explicit loss for it.

    In summary, this thesis presents successful examples of incorporating deeplearning techniques to assist a classical visual odometry system. The resultsare promising and have been extensively evaluated on challenging benchmarks,real robot and handheld cameras. The problem we investigate is stillin an early stage, but is attracting more and more interest from researcher inrelated fields.

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  • Public defence: 2020-06-12 13:00 FB42, Stockholm
    Capel, Francesca
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Cosmic clues from astrophysical particles2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ultra-high-energy cosmic rays (UHECRs) are charged particles that have been accelerated to extreme energies, such that they are effectively travelling at the speed of light. Interactions of these particles with the Earth’s atmosphere lead to the development of extensive showers of particles and radiation that can be measured with existing technology. Despite decades of research, the origins of UHECRs remain mysterious. However, they are thought to be accelerated within powerful astrophysical sources that lie beyond the borders of our Galaxy. This thesis explores different ideas towards the common goal of reaching a deeper understanding of UHECR phenomenology. Part I concerns the development of a novel space-based observatory that has the potential to detect unprecedented numbers of these enigmatic particles. The feasibility of such a project is demonstrated by the results from the Mini-EUSO instrument, a small ultraviolet telescope that is currently on-board the International Space Station. In Part II, the focus is on fully exploiting the available information with advanced analysis techniques to close the gap between theory and data. UHECRs are closely connected to the production of neutrinos and gamma rays, so frameworks for the joint analysis of these complementary cosmic messengers are also developed. The results presented herein demonstrate that to progress, it is crucial to invest in the development of both detection and analysis techniques. By taking a closer look at the existing data, new clues can be revealed to reach a more comprehensive understanding and better inform the design of future experiments. 

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  • Public defence: 2020-06-12 14:00 Publikt via ZOOM
    Szipka, Károly
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Uncertainty Management for Automated Diagnostics of Production Machinery2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Neither production machinery, nor production systems will ever become completely describable or predictable. This results in the continuous need for monitoring and diagnostics of such systems in order to manage related uncertainties. In advanced production systems uncertainty has to be the subject to a systematic management process to maintain machine health and improve performance. Automation of diagnostics can fundamentally improve this management process by providing an affordable and scalable information source. In this thesis, the important aspects of uncertainty management in production systems are established and serve as a basis for the composition of an uncertainty-based machine diagnostics framework. The proposed framework requires flexible, fast, integrated and automated diagnostics methods. An inertial measurement-based test method is presented in order to satisfy these requirements and enable automated measurements for diagnostics of production machinery. The gained insights and knowledge about production machine health and capability improve transparency, predictability and dependability of production machinery and production systems. These improvements lead to increased overall equipment effectiveness and higher level of sustainability in operation.

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  • Public defence: 2020-06-12 14:00 Zoom-webinar: https://kth-se.zoom.us/webinar/register/WN_Atk97qAwS9OiEW8dTC0Fyg
    Held, Manne
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Fuel-Efficient Look-Ahead Control for Heavy-Duty Vehicles with Varying Velocity Demands2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The fuel consumption of heavy-duty vehicles can be reduced by using information about the upcoming road section when controlling the vehicles. Most manufacturers of heavy-duty vehicles today offer such look-ahead controllers for highway driving, where the information consists of the road grade and the velocity only has small variations. This thesis considers look-ahead control for applications where the velocity of the vehicle has large variations, such as distribution vehicles or vehicles in mining applications. In such conditions, other look-ahead information is important, for instance legal speed limits and curvature. Fuel-efficient control is found by formulating and solving the driving missions as optimal control problems.

    First, it is shown how look-ahead information can be used to set constraints in the optimal control problems. A velocity reference from a driving cycle is modified to create an upper and a lower bound for the allowed velocity, denoted the velocity corridor. In order to prevent the solution of the optimal control problem from deviating too much from a normal way of the driving, statistics derived from data collected during live truck operation are used when formulating the constraints. It is also shown how curvature and speed limits can be used together with actuator limitations and driveability considerations to create the velocity corridor.

    Second, a vehicle model based on forces is used to find energy-efficient velocity control. The problem is first solved using Pontryagin's maximum principle to find the energy savings for different settings of the velocity corridor. The problem is then solved in a receding horizon fashion using a model predictive controller to investigate the influence of the control horizon on the energy consumption. The phasing and timing of traffic lights are then added to the available information to derive optimal control when driving in the presence of traffic lights.

    Third, the vehicle model is extended to include powertrain components in two different approaches. In a first approach, a Boolean variable is added to represent open or closed powertrain. This enables the vehicle to freewheel, in order to save fuel by reducing the losses due to engine drag. The problem is formulated as a mixed integer quadratic program. In a second approach, the full powertrain is modeled including a fuel map and a model of the gearbox losses, both based on measurements on real components. The problem is solved using dynamic programming, with transitions between states including gear shifts, freewheeling, and coasting in gear.

    Forth, the optimal control framework is used to implement an optimal control-based powertrain controller in a real Scania truck. The problem is first solved offline resulting in trajectories for velocity and freewheeling. These are used online in the vehicle as references to the existing controllers for torque and gear demands. Experiments are performed with fuel measurements, resulting in 16% fuel savings, compared to 18% savings by solving the optimal control problem.

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  • Public defence: 2020-06-12 16:00 Seminar Room, Floor 5, Stockholm
    Gomez-Torrent, Adrian
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Micro and Nanosystems.
    Submillimeter-Wave Waveguide Frontends by Silicon-on-Insulator Micromachining2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents novel radiofrequency (RF) frontend components in the submillimeter-wave (sub-mmW) range implemented by silicon micromachining, or deep reactive ion etching (DRIE). DRIE is rapidly becoming a driving technology for the fabrication of waveguide components and systems when approaching the terahertz (THz) frequency range. The conventional method to manufacture microwave waveguide components, CNC-milling, shows important limitations when used at sub-mmW frequencies or above, due to the reduced size of the waveguides. At the same time, the classic electromagnetic designs, oriented to CNC-milling, are often not suitable for their fabrication using alternative technologies. The work in this thesis aims to develop fabrication-oriented electromagnetic structures, making use of the full flexibility of silicon on insulator (SOI) micromachining, and enabling the implementation of complex RF frontends at a low fabrication complexity.

    The first part of the thesis reports on a turnstile orthomode transducer (OMT) in the WM-864 band (220 – 330 GHz). OMTs are key components in the feed-chain for radio astronomy, communications, or radiometry applications. However, their complex geometry has often limited their use when approaching the THz range, where polarization diversity is commonly avoided, or optical systems are preferred.

    The second part reports on a high-gain and broadband waveguide corporatefed array antenna in the WM-570 band (330 – 500 GHz). High gain and broadband antennas are required for the future generation of THz wireless communications. Reflector and lens antennas can meet these specifications, but their fabrication for the THz range requires precision machining, resultingin a high cost, low yield, and small scale production. The use of silicon micromachined antenna arrays overcomes these issues while providing a more compact frontend.

    In the third part of the thesis, a parallel plate waveguide (PPW) leaky wave antenna (LWA) fed by a quasi-optical beamforming network (BFN) in the WM-864 band is presented. The antenna frontend generates a pencil shaped beam scanning in elevation. The compact design, large bandwidth, and beam steering capabilities make this antenna a suitable frontend for THz radar applications.

    The final part of this thesis reports on a novel waveguide single pole double throw (SPDT) switch in the WM-570 band. The switch is demonstrated in a two-port network configuration with two switching states (ON/LOAD), used for receiver calibration, or for avoiding backward waves in transmitter switching. A more complex 1×4 switching matrix is also designed for the implementation of an active radar antenna operating at 340 GHz.

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  • Public defence: 2020-06-15 09:30 https://kth-se.zoom.us/webinar/register/WN_WLb9GyXjRD2hY9sCg9I_nQ
    Jin, Hongyu
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    Cooperative Privacy and Security for Mobile Systems2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The growing popularity of powerful mobile devices, along with increased computation and storage of computing infrastructure, opened possibilities for versatile mobile system applications. Users, leveraging sensing capabilities of the devices, can collect rich data and exchange the data with diverse Service Providers (SPs) or their close neighboring devices. Provision of such user status awareness to the involved system entities, can facilitate customized user experience for system participants.

    Nonetheless, the open and decentralized nature of mobile systems raise concerns on both security and privacy of users and the system infrastructure. Sensitive user data could be exposed to honest-but-curious entities, which can further process data to profile users. At the same time, compromised system entities can feed faulty data to disrupt system functionalities or mislead users. Such issues necessitate secure and privacy-enhancing mobile systems, while not compromising the quality of service the systems provide to their users. More specifically, the solutions should be efficient and scale as the system grows, and resilient to both external and internal adversaries. This thesis considers two mobile system instances: Location-based Services (LBSs) and Vehicle-to-Vehicle (V2V) safety applications. We address security and privacy in a cooperative manner, relying on cooperation among the users to protect themselves against the adversaries. Due to the reliance on peers, input from the peers should be examined, in order to ensure the reli- ability of the applications. We adapt pseudonymous authentication, designed for Vehicular Communication (VC) systems, and integrate it with LBSs. This protects user privacy and holds users accountable for their actions, which are non-repudiable. At the same time, our scheme prevents malicious nodes from aggressively passing on bogus data. We leverage redundancy of shared data from multiple cooperating nodes to detect potential conflicts. Any conflict triggers proactive checking on the data with the authoritative entity that reveals the actual misbehaving users. For V2V safety applications, we extend safety beacons, i.e., Cooperative Awareness Messages (CAMs), to share signature verification effort, for more efficient message verification. Similarly to the LBSs, redundancy of such piggybacked claims is also key for remedying malicious nodes that abuse this cooperative verification. In addition, the extended beacon format facilitates verification of event-driven messages, including Decentralized Environmental Notification Messages (DENMs), leveraging proactive authenticator distribution.

    We qualitatively and quantitatively evaluate achieved security and privacy protection. The latter is based on extensive simulation results. We propose a location privacy metric to capture the achieved protection for LBSs, taking into consideration the pseudonymous authentication. The performance of the privacy-enhancing LBS is experimentally evaluated with the help of an implementation on a small scale automotive computer testbed. We embed processing delays and queue management for message processing in simulations of V2V communication, to show scalability and efficiency of the resilient V2V communication scheme. The results confirm the resilience to both internal and external adversaries for the both systems.

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  • Public defence: 2020-06-15 10:00 Publikt via Zoom, Stockholm
    Rahatulain, Afifa
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Sustainable evolution of SMEs in response to socio-technical emergence2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Technological advancements such as digitalization, cloud computing, and cyber-physical systems are transforming the present-day manufacturing industry. However, striving solely on the technological shift alone is insufficient to attain a sustainable competitive advantage. Therefore, an organization has to be treated as a socio-technical system where technological development has to go hand in hand with constant evolution of organizational aspects such as human development, knowledge management, organizational capability, etc.

    A manufacturing organization can also be considered as a socio-technical system of systems (SoS). It is vulnerable to the stochastic and emergent nature of the external environment, such as varying market conditions, diverse customer demands, etc. To achieve a deterministic and effective output in response to emergence, it is necessary to have an utmost awareness of the system behaviour itself. This research proposes that understanding the organizational behaviour and the interfaces that exists within the system could help the organizations in responding effectively to emergence. This in turn helps in transformation from a response mechanism based on presumptions to a fact-based approach by considering both the environmental emergence and internal organizational knowledge. The main focus of this work is on organizational capability and knowledge management within manufacturing SMEs.

    The first major contribution of this work is the utilization of Viable Systems Model (VSM) for understanding the behaviour of a manufacturing organization from a holistic perspective and identification of the knowledge interfaces (KIs) within the system. The type of knowledge required at each interface is determined and a KI mapping approach has been proposed to facilitate organizations in performing system analysis. The results are analysed using the empirical data for product development process from an industrial case study.

    Identification of organizational challenges for SMEs going through strategic transformations and their impact on the knowledge interfaces is the second main contribution of this work. The VSM-based KI mapping approach is used in identifying the knowledge gaps through visualization of respective KIs.

    Lastly, the work addresses common pitfalls and obstacles faced by the current manufacturing companies in terms of organizational capability and provides some guidelines and improvement suggestions for achieving an effective organization.

    Improved organizational capabilities of SMEs also result in enhancing regional growth through retaining competence and provision of jobs. Therefore this work can also be considered as a step towards strengthening social sustainability.

  • Public defence: 2020-06-15 10:00 https://kth-se.zoom.us/webinar/register/WN_UXIld9K6RkO3KR7fU9FQig
    Korkovelos, Alexandros
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Advancing the state of geospatial electrification modelling: New data, methods, applications, insight and electrification investment outlooks2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Globally, it is estimated that there are approximately 860 million people without access to electricity. Achieving universal electricity access over the next decade – as part of Sustainable Development Goal 7 – indicates that many countries will soon need to set in place roadmaps, action plans and policy for ramping-up electrification. The challenge is significant. It requires the motivation of considerable financial resources so that electricity can reach poor, rural populations in least developed areas. 

     

    A look back at history however, reveals that such a ramp-up of electrification activity is not unprecedented. Many countries in the “Global North” have faced similar challenges about a century ago. Past examples indicate that electrification planning – and ensuing policy – can take different shapes based on underlying social, technological, economic and political conditions. This brings forward the importance of considering inputs that reflect these conditions. It also highlights the need for reliable data and information that best describe the local context (e.g. resource availability, distribution of population, economic activities or infrastructure). While advancements in geo-spatial information technology have greatly improved the availability of such information in the past years, their use in electrification planning is not fully exploited. 

     

    This dissertation aims to advance the state of geospatial electrification modelling by demonstrating new data, methods, applications and insights over the course of four academic papers covering three research questions. 

    The first question searches for common – across different times and geographies – patterns, policy dilemmas and constraints related to electrification, the reading of which can shed light on current and future electrification planning activities. In response, paper I takes a retrospective look into the electrification challenge in the United States of America, the United Kingdom, Sweden and China and examines strategies, success stories and failures in each case. Results unveil key lessons regarding the development phases of electrification - with a focus on the role of isolated, small mini-grids. 

     

    The second question asks whether the use of geospatial information technology can introduce new data and methods into an existing modelling framework (e.g. OnSSET) and help tackle electrification planning dilemmas. In response, paper II leverages new open access datasets to provide spatially explicit estimates of small-scale hydropower potential in Sub-Saharan Africa. Paper III demonstrates twenty-six new, updated or missing datasets, the processing of which allows new angles of analysis over electrification planning.

     

    The third research question focuses on how the OnSSET modelling framework can be improved, open sourced and scaled so as to allow a broader audience develop fast, informative, country and context specific electrification investment strategies. Here, papers III and IV, leverage OnSSET’s modular structure, calibrate its functions and develop customized electrification investment outlooks for Malawi and Afghanistan respectively. These, explore different scenarios tuned according to the policy challenges in each country (e.g. gradual electrification in Malawi or planning under conflict risk in Afghanistan). Moreover, this dissertation has expanded OnSSET’s application range as part of the Global Electrification Platform (GEP). The GEP is an open access, collaborative environment that now hosts 216 electrification investment scenarios (together with underlying input data and models) for 59 countries worldwide, thus improving the transparency surrounding their review, reproduction or replication by a broader audience.​

     

     

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  • Public defence: 2020-06-15 14:00 Stockholm
    Khodaei, Mohammad
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    The Key to Intelligent Transportation Systems: Identity and Credential Management for Secure and Privacy-Preserving Vehicular Communication Systems2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Vehicular Communication (VC) systems can greatly enhance road safety and transportation efficiency and enable a variety of applications providing traffic efficiency, environmental hazards, road conditions and infotainment. Vehicles are equipped with sensors and radars to sense their surroundings and external environment, as well as with an internal Controller Area Network (CAN) bus. Hence, vehicles are becoming part of a large-scale network, the so-called Internet of Vehicles (IoV). Deploying such a large-scale VC system cannot materialize unless the VC systems are secure and do not expose their users’ privacy. On the one hand, vehicles could be compromised or their sensors become faulty, thus disseminating erroneous information across the network. Therefore, participating vehicles should be held accountable for their actions and credentials (their Long Term Certificates (LTCs) and their pseudonyms) can be efficiently revoked and disseminated in a timely manner throughout a large-scale (multi-domain) VC system. On the other hand, user privacy is at stake: according to standards, vehicles should disseminate spatio-temporal information frequently, e.g., location and velocity. Due to the openness of the wireless communication, an observer can eavesdrop the vehicular communication to infer users’ sensitive information, and possibly profile users based on different attributes, e.g., trace their commutes and identify home/work locations. The objective is to secure the communication, i.e., prevent malicious or compromised entities from affecting the system operation, and ensure user privacy, i.e., keep users anonymous to any external observer but also for security infrastructure entities and service providers. This is not very straightforward because accountability and privacy, at the same time, appear contradictory. 

    In this thesis, we first focus on the identity and credential management infrastructure for VC systems, taking security, privacy, and efficiency into account. We begin with a detailed investigation and critical survey of the standardization and harmonization efforts, along with industrial projects and proposals. We point out the remaining challenges to be addressed in order to build a central building block of secure and privacy-preserving VC systems, a Vehicular Public-Key Infrastructure (VPKI). Towards that, we provide a secure and privacy-preserving VPKI design that improves upon existing proposals in terms of security and privacy protection and efficiency. More precisely, our scheme facilitates multi-domain operations in VC systems and enhances user privacy, notably preventing linking of pseudonyms based on timing information and offering increased protection in the presence of honest-but-curious VPKI entities. We further extensively evaluate the performance, i.e., scalability, efficiency, and robustness, of the full-blown implementation of our VPKI for a large-scale VC deployment. We provide tangible evidence that it is possible to support a large area of vehicles by investing in modest computing resources for the VPKI entities. Our results confirm the efficiency, scalability and robustness of our VPKI.

    As a second main contribution of this thesis, we focus on the distribution of Certificate Revocation Lists (CRLs) in VC systems. The main challenges here lie exactly in (i) crafting an efficient and timely distribution of CRLs for numerous anonymous credentials, pseudonyms, (ii) maintaining strong privacy for vehicles prior to revocation events, even with honest-but-curious system entities, (iii) and catering to computation and communication constraints of on-board units with intermittent connectivity to the infrastructure. Relying on peers to distribute the CRLs is a double-edged sword: abusive peers could "pollute" the process, thus degrading the timely CRLs distribution. We propose a vehicle-centric solution that addresses all these challenges and thus closes a gap in the literature. Our scheme radically reduces CRL distribution overhead: each vehicle receives CRLs corresponding only to its region of operation and its actual trip duration. Moreover, a "fingerprint" of CRL ‘pieces’ is attached to a subset of (verifiable) pseudonyms for fast CRL ‘piece’ validation (while mitigating resource depletion attacks abusing the CRL distribution). Our experimental evaluation shows that our scheme is efficient, scalable, dependable, and practical: with no more than 25 KB/s of traffic load, the latest CRL can be delivered to 95% of the vehicles in a region (15x15 KM) within 15s, i.e., more than 40 times faster than the state-of-the-art. Overall, our scheme is a comprehensive solution that complements standards and can catalyze the deployment of secure and privacy-protecting VC systems. 

    As the third main contribution of the thesis, we focus on enhancing location privacy protection: vehicular communications disclose rich information about the vehicles and their whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones were proposed to facilitate vehicles covertly transition to new ephemeral credentials. The resilience to (syntactic and semantic) pseudonym linking (attacks) highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. Our experimental results show that an eavesdropper could successfully link 73% of pseudonyms (during non-rush hours) and 62% of pseudonyms (during rush hours) after vehicles change their pseudonyms in a mix-zone. To mitigate such inference attacks, we present a novel cooperative mix-zone scheme that enhances user privacy regardless of the vehicle mobility patterns, vehicle density, and arrival rate to the mix-zone. A subset of vehicles, termed relaying vehicles, are selected to be responsible for emulating non-existing vehicles. Such vehicles cooperatively disseminate decoy traffic without affecting safety-critical operations: with 50% of vehicles as relaying vehicles, the probability of linking pseudonyms (for the entire interval) drops from 68% to 18%. On average, this imposes 28 ms extra computation overhead, per second, on the Roadside Units (RSUs) and 4.67 ms extra computation overhead, per second, on the (relaying) vehicle side; it also introduces 1.46 KB/sec extra communication overhead by (relaying) vehicles and 45 KB/sec by RSUs for the dissemination of decoy traffic. Thus, user privacy is enhanced at the cost of low computation and communication overhead.

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  • Public defence: 2020-08-18 13:00 Videolänk kommer / Video link is forthcoming, Stockholm
    de Frias Lopez, Ricardo
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    DEM Modelling of Unbound Granular Materials for Transport Infrastructures: On soil fabric and rockfill embankments2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Unbound granular materials (UGM) are widely used as load-bearing layers and for embankment construction within transport infrastructures. These play a significant role on operation and maintenance of transportation systems. However, pavement and railway engineering still today rely heavily on empirical models based on macroscopic observations. This approach results in limited knowledge on the fundamentals at particle scale dictating the macroscopic response of the material. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of processes at particulate level. Additionally, it allows obtaining information at particulate level in a way that cannot be matched by traditional laboratory testing. All of this, in turn, can result in greater micromechanical insight.This thesis aims at contributing to the body of knowledge of the fundamentals of granular matter. UGM for transport infrastructures are studied by means of DEM in order to gain insight on their response under cyclic loading. Two main issues are considered: (1) soil fabric and its effect on the performance of coarse-fine mixtures and (2) modelling of high rockfill railway embankments. Among the main contributions of this research there is the establishing of a unified soil fabric classification system based exclusively on force transmission considerations that furthermore correlates with performance. In particular, fabrics characterized by a strong interaction between the coarse and fine fractions resulted in improved performance. A soil fabric type with a potential for instability was also identified. Regarding embankments, DEM modelling shows that traffic induced settlements accumulate on the top layers and therefore seem to be unaffected by embankment height above a certain value. A marked influence of degradation, even considering its nearly negligible magnitude, was observed, largely resulting in increased settlements.

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  • Public defence: 2020-08-21 12:00 FD5, Stockholm
    Kördel, Mikael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Biological Laboratory X-Ray Microscopy2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Soft x-ray microscopy in the water window (𝜆 ≈ 2.3 − 4.3 nm) is a powerful technique for high-resolution biological imaging. The strong natural contrast between carbon-based structures and water allows visualization of hydrated and unstained samples, while providing enough transmission through up to ∼ 10 μm of organic matter. Furthermore, the full potential of this technique can be exploited by performing computed tomography, thus obtaining a complete 3D image of the object.

    Routine short-exposure water-window microscopy of whole cells and tissue is currently performed at synchrotron-radiation facilities around the world, but with a limited accessibility to the wider research community. For this reason, laboratory-based systems have been developed, which are now reaching maturity. The benefits compared to the synchrotron-based instruments include easier integration with complementary methods in the home laboratory, in addition to the increased access that allows for the often time-consuming optimization of experimental parameters as well as longitudinal studies.

    This Thesis presents recent developments of the Stockholm laboratory x-ray microscope as well as several biological applications. Work has been done on improving the mechanical and thermal stability of the microscope, resulting in a resolution of 25 nm (half period) in images of test targets. The biological applications were enabled by a significantly increased x-ray flux through the system as well as an improved operational stability. This work demonstrates 10-second exposure imaging of whole cryofixed cells, imaging of viral infections in cells, and 20 minutes total exposure cryotomography.

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  • Public defence: 2020-08-26 10:00 Stockholm
    Karlsson, Mattias E.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
    Fundamentals of Polyethylene Composites for HVDC Cable Insulation – Interfaces and Charge Carriers2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Power transmission over long distances by using high voltage direct current (HVDC) cables is important for the transition from fossil energy to using renewable energy sources, e.g. wind, solar and water. Higher operating voltages enable longer transmission lines but better insulation materials with a much lower conductivity than today´s crosslinked polyethylene (PE) are required to reach the goal of 1 MV by 2030. Nanocomposites consisting of small fractions of metal oxide nanoparticles in PE are promising insulation materials, showing ca. 100 times lower conductivity. The reasons for the better insulating properties are however not fully understood.

    The properties of PE and inorganic nanoparticles were studied in this project to evaluate the influence of different material parameters on the conductivity of the cable insulation material. For pristine PE, the polymer morphology and oxidation were found to have a significant impact on the conductivity. For PE nanocomposites, the particle/polymer interface was shown to adsorb polar molecules, which are present in PE cable insulation. A suggested hypothesis is that the adsorption on particle surfaces results in cleaning of the bulk polymer from impurities, which in turn contributes to decreased nanocomposite conductivity. Since the particle interface is believed to be decisive for the nanocomposite properties, the role of particle terminations was investigated in detail. Oxygen dominated particle terminations resulted in 2 times higher composite conductivity than with zinc dominated surfaces, while fully oxygen covered surfaces showed 10 times higher conductivity. Composite systems with micro-sized particles allowed for evaluating parameters independently, which is not possible for nanocomposites. Terminations of ‘PE-like’ hydrocarbon chains lowered the conductivity and these trends could also be transferred to similar zinc oxide nanocomposite systems.

    The full text will be freely available from 2021-05-20 08:55