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  • Disputas: 2019-10-21 09:30 F3, Stockholm
    Teng, Penghua
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    CFD MODELLING AND EXPERIMENTS ON AERATOR FLOW IN CHUTE SPILLWAYS2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A chute spillway is a typical component of large dams for discharging floods. Because of the high water head, the flow velocity in the chute is often in excess of 20 m/s. Consequently, the structure is usually prone to cavitation damages. Flow aeration is evidenced to efficiently eliminate or to mitigate the damages. An aerator is a device that entrains air into the water flows and is an effective technical measure to counter the cavitation damages.

    Aerator flow includes intense air-water exchange and involves a process of air entrainment, transport, and detrainment. Because of the complex phenomena, it is still a challenge to investigate the behaviors of interaction between air and water. It is fundamental to understand the flow behaviors downstream of the aerator. This thesis investigates the aerator flow features using both the Computational Fluid Dynamics (CFD) and advanced measurement techniques.

    The CFD method presents three two-phase flow models to describe the aerator flows, namely, the Volume of Fluid Model, the Mixture Model, and the Two-Fluid Model. They are applied and evaluated via practical engineering projects and experimental data. The Volume of Fluid model leads to reasonable results regarding the water flow discharge and flow fields. For predicting the air concentration distribution and air bubble transport processes, the Two-Fluid Model is superior to others because it includes forces acting on the air bubbles. However, the model still overestimates the air content near the chute bottom. Based on the aerator flow from a chute spillway in Sweden, three two-phase flow models are applied and compared.

    Physical model tests are commonly conducted to investigate aerator flow features. Because of the scale effects, the results may lead to a discrepancy in the flow behaviors compared with the prototype. Thus, CFD modeling becomes an alternative tool when seeking the reason for the difference. Based on the aerator flow in a real spillway, CFD is applied to reproduce the flow; the discrepancy between the model tests and prototype observations is evidenced. The results show similar flow features with the prototype but differ from those of the model tests. An explanation for the discrepancy is discussed in terms of flow features, effect of surface tension in model tests, and the prerequisite for air entrainment of the free-surface flow.

    Laboratory experiments are conducted to study the aerator flow in a chute. Four image-based measurement techniques-i.e., high-speed particle image velocimetry (HSPIV), shadowgraphic image method (SIM), bubble tracking method (BTM), and bubble image velocimetry (BIV)-are employed. The study focuses on issues of exploring characteristic positions of water-air interfaces, interpreting the evaluation process of air bubbles shed from the tip of the air cavity, identifying the probabilistic means for characteristic positions near the fluctuating free surface, and obtaining the flow field both water flow and air bubbles features of the aerator flow. The application of these techniques leads to a better understanding of two-phase flow characteristics of the chute aerator.

  • Disputas: 2019-10-23 10:00 FA32, Stockholm
    De Luca, Eleonora
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Nonlinear Properties of III-V Semiconductor Nanowaveguides2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nonlinear optics (NLO) plays a major role in the modern world: nonlinear optical phenomena have been observed in a wavelength range going from the deep infrared to the extreme ultraviolet, to THz radiation. The optical nonlinearities can be found in crystals, amorphous materials, polymers, liquid crystals, liquids, organic materials, and even gases and plasmas. Nowadays, NLO is relevant for applications in quantum optics, quantum computing, ultra-cold atom physics, plasma physics, and particle accelerators. The work presented in the thesis is limited only to the semiconductors that have a second-order optical nonlinearity and includes two phenomena that use second-order nonlinearity: second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). Among the many options available, the investigation presented concerns gallium phosphide (GaP) and gallium indium phosphide (Ga0.51In0.49P), two semiconductors of the group III-V with the ¯43m crystal symmetry.

    However, some of the results found can be generalized for other materials with ¯43m crystal symmetry.

    In the thesis, the fabrication of GaP nanowaveguides with dimensions from 0.03 μm and an aspect ratio above 20 using focused ion beam (FIB) milling is discussed. The problem of the formation of gallium droplets on the surface is solved by using a pulsed laser to oxidize the excess surface gallium locally on the FIB-milled nanowaveguides. SHG is used to evaluate the optical quality of the fabricated GaP nanowaveguides. Additionally, a theoretical and experimental way to enhance SHG in nanowaveguides is introduced. This process uses the overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the SHG, which is enhanced by the longitudinal component of the nonlinear polarization density. Through this method, it was possible to obtain a maximum efficiency of 10−4, which corresponds to 50 W−1cm−2. The method can be generalized for any material with a ¯43m crystal symmetry. Furthermore, SHG is used to characterize the nonlinear properties of a nanostructure exposed for a long time to a CW laser at 405 nm to reduce the photoluminescence (PL) of Ga0.51In0.49P. The PL was reduced by -34 dB without causing any damage to the nanostructures or modifying the nonlinear properties. The fabrication process for obtaining the nanowaveguide is interesting as well, since the fabricated waveguide in Ga0.51In0.49P, whose sizes are 200 nm thick, 11 μm wide and 1.5 mm long, was transferred on silicon dioxide (SiO2). This type of nanowaveguide is interesting for SPDC, since it satisfies the long interaction length necessary for an efficient SPDC. Finally, a configuration consisting of illuminating the top surface of a nanowaveguide with a pump beam to generate signal and idler by SPDC is presented. These fabricated nanostructures open a way to the generation of counter-propagating idler and signal with orthogonal polarization. By using a different cut of the crystal, i.e. [110], it makes possible to obtain degenerate wavelength generation, and in certain conditions to obtain polarization-entangled photons or squeezed states.

  • Disputas: 2019-10-24 10:00 sal F3, Stockholm
    Josefsson, Leila
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Bioanalysis using capillary electrophoresis and mass spectrometry: Applied on proteins, protein nanofibrils and polyvinyl alcohol microbubbles2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The sequencing of the genome of various species, including the human species, have led to increased understanding about how a protein structure is generated, and how specific structures are related to the proteins’ functionality. In paper I and II of this thesis, the folding of proteins in vitro to form hierarchical nanostructures, which in vivo often have a pathological effect, have been studied. Protein isolates from soybean and potato, that are byproducts from oil and starch production, respectively, were used as a starting material for protein nanofibril (PNF) formation, and mass spectrometry was used to identify the building blocks that are included in the formed PNF. The five peptides identified in soybean PNF and the six peptides identified in potato PNF originated from the major seed storage proteins for the respective crop.

    The use of ionic liquids has increased for improvement of the performance of different separation techniques due to their adjustable properties, and good solvating ability. In paper III, an ionic liquid and water mixture was used as background electrolyte in capillary electrophoresis for protein separation. The system showed high reproducibility at basic conditions, and could potentially be used for routine control analysis.

    Many diseases and injuries require clinical diagnosis techniques e.g. ultrasound imaging, to be detected, and for the physician to be able to decide the correct therapy. To increase the resolution of such imaging techniques, contrast agents can be used. In paper IV-VI, a newly developed contrast agent consisting of air-filled microbubbles stabilized with a shell of polyvinyl alcohol (PVA-MBs) was studied. Development of a capillary electrophoretic method for analysis of the PVA-MBs with the intentions to be used for clinical diagnosis is performed, where different detectors such as a UV detector, a UV area imaging detector and an in-house constructed microscope are used to increase the sensitivity of detection for the PVA-MBs. The developed method could be used for quantification of the contrast agent, since individual PVA-MBs were visible using the imaging detectors. Findings regarding the mobility of the PVA-MBs in human blood plasma and in water implies that a protein corona was formed around the MBs.

  • Disputas: 2019-10-24 10:00 Kollegiesalen, Stockholm
    Ruggieri, Federica
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Industriell bioteknologi.
    Transaminase Biocatalysis: Applications and Fundamental Studies2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Biocatalysis is the branch of science at the intersection between chemistry and biology and specifcally dedicated to the application of natural evolvable catalysts, i.e. enzymes, in human-designed chemical processes. Among the array of promising biocatalysts, transaminases (EC 2.6.1.x) are possibly one of the enzyme classes with the largest unrealized potential. Fast inactivation, poor acceptance towards unnatural substrates and limited tolerance to cosolvents are some of the main factors hampering their implementation in chemical synthesis. In the present thesis work advances in both transaminase application and molecular understanding are presented. Indeed, these two topics are deeply interconnected, as a better molecular understanding is expected to ease the generation of novel enzyme variants suitable for new desired applications.

    From the application perspective, the design of an effective one-pot transaminase-based racemization system offers new possibilities for the design of fully biocatalytic dynamic kinetic resolutions of valuable chiral amines. Similarly, the successful structure-guided redesign of the small substrate binding pocket of the Chromobacterium violaceum (S)-selective transaminase (Cv-TA) granted access to a new enzyme variant active on semi-preparative scale towards the unnatural substrate 1,2-diphenylethylamine.

    From the molecular understanding perspective, the combination of crystallographic and computational techniques led to the formulation of a dimer dissociation model valid for Cv-TA and possibly for other enzymes belonging to the same fold type. This model, which aided the improvement of the Cv-TA stability by structure-based engineering, will hopefully enable similar results in other structurally related enzymes.

  • Disputas: 2019-10-25 09:00 Atrium, solna
    Mahdessian, Diana
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Proteinvetenskap, Cellulär och klinisk proteomik.
    Spatiotemporal characterization of the human proteome2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Characterizing the molecular components of the basic unit of life; the cell, is crucial for a complete understanding of human biology. The cell is divided into compartments to create a suitable environment for the resident proteins to fulfill their functions. Therefore, spatial mapping of the human proteome is essential to understand protein function in health and disease.

     

    Spatial proteomics is most commonly investigated using mass spectrometry or imaging, combined with machine learning for the data analysis. Until now, studies have been limited to high abundant proteins and relied on the purification of organelle fractions from a bulk of cells. Within the scope of this thesis, we were able to systematically localize proteins in their native cellular environment using antibody-based imaging techniques, and to investigate protein subcellular localization and dynamics on a single cell level, introducing a major advance within the field of spatial proteomics.

     

    Paper I of this thesis presents a subcellular map of the human proteome, where the spatial distribution of 12,003 human proteins was mapped into 30 subcellular structures, half of which were not previously localized. Besides providing a valuable dataset for cell biology, this study is the first to reveal the spatial complexity of human cells with proteins localizing to multiple compartments and pronounced single cell variations. Paper II reports on the systematic temporal dissection of these single cell variations and the identification of cell cycle correlated variations. We identified 258 novel cell cycle regulated proteins and showed that several of these proteins may be connected to proliferative diseases. A key finding of Paper II is that proteins showing non-cell cycle dependent variations are significantly enriched in mitochondria, whereas cell cycle dependent proteins are enriched in nucleoli. In Paper III and IV, we spatiotemporally characterized the proteomes of these two organelles, mitochondria and nucleoli, in greater detail.

    In Paper III, we expanded the mitochondrial proteome with 560 novel proteins. As many as 20% of the mitochondrial proteome showed variations in their expression pattern at the single cell level, most often independent of the cell cycle. Paper IV provides a complete characterization of the nucleolar proteome. Nucleoli are not only important for ribosome synthesis and assembly, but are also crucial for cell cycle regulation through the recruitment of its proteins to the chromosomal periphery during cell division. Here, we presented the first proteome-wide spatiotemporal analysis of the nucleolus with its sub-compartments, and identified 69 nucleolar proteins that relocated to the chromosomes periphery during mitosis.

     

    In conclusion, this thesis unravels the spatiotemporal proteome organization of the human cell over the course of a cell cycle and offers a valuable starting point for a better understanding of human cell biology in health and disease.

  • Disputas: 2019-10-25 10:00 F3, Stockholm
    Wei, Xin-Feng
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Ageing behavior of plastics used in automotive fuel systems2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The increase in service temperature and the use of biobased fuels, such as biodiesel, have raised concerns on the short/long-term performance of plastic components used in automotive fuel systems.

    In this work the ageing behavior of unreinforced and glass-fibre reinforced polyamide 12 (PA12), exposed to three different fuels (petroleum diesel, biodiesel, and a mixture of these (80/20)) at high temperature, was investigated. The interactions between the polymer and the fuel, and the associated polymer ageing mechanisms (fuel uptake, extraction of monomer and oligomers, annealing and oxidation), were found to be “generic” in the sense that they occurred, although to various extent, for all fuels. In the glass-fibre reinforced polyamides, the ageing occurred mainly in the polyamide matrix and not in the matrix-fibre interface. The semi-aromatic polyamide showed better performance when exposed to fuels than the aliphatic PA12.  

    At a component level, multilayer polyamide-based pipes, with polyamide or fluoropolymer as inner layer, were aged under “in-vehicle” conditions where the pipes were exposed to fuel on the inside and to the air on the outside. All pipes stiffened during ageing but embrittlement occurred only for the pipes with polyamide being the inner layer. Compared to polyamide, the fluoropolymer inner layer showed significantly better barrier properties towards the fuel and no material was extracted into the fuel. The plasticizer loss from the PA12 outer layers into air was diffusion controlled and its diffusivity followed a linear Arrhenius behavior in the high temperature region. Relationships between plasticizer loss and the changes in mechanical properties were established.

    The polyamides experienced diffusion-limited oxidation when exposed to air and/or fuel, involving the formation of a thin oxidized surface layer which was responsible for a significant decrease in strain-at-break. 

    The fracture behavior of PA 6 in air at high temperature, found to involve three distinct stages, were systematically studied and linked to underlying mechanisms responsible for the reduction in strain-at-break.

  • Disputas: 2019-10-25 10:00 Ångdomen, Stockholm
    Ottonello Briano, Floria
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Mid-infrared photonic devices for on-chip optical gas sensing2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Gas detection is crucial in a wide range of fields and applications, such as safety and process control in the industry, atmospheric sciences, and breath diagnostics. Optical gas sensing offers some key advantages, compared to other sensing methods such as electrochemical and semiconductor sensing: high specificity, fast response, and minimal drift.

    Wavelengths between 3 and 10 μm are of particular interest for gas sensing. This spectral range, called the mid-infrared (mid-IR), is also known as the fingerprint region, because several gas species can be identified by their sharp absorption lines in this region. The most relevant mid-IR-active gases are the trace gases carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), ammonia (NH3), and nitrous oxide (N2O). They are greenhouse gases, contributing to global warming. They are waste products of human activities and widely used in agriculture and industry. Therefore, it is crucial to accurately and extensively monitor them. However, traditional optical gas sensors with a free-space optical path configuration, are too bulky, power-hungry, and expensive to be widely adopted.

    This thesis presents mid-IR integrated photonic devices that enable the on-chip integration of optical gas sensors, with a focus on CO2 sensing. The reported technologies address the fundamental sensor functionalities: light-gas interaction, infrared light generation, and infrared light detection. The thesis introduces a novel mid-IR silicon photonic waveguide that allows a light path as long as tens of centimeters to fit in a volume smaller than a few cubic millimeters. Mid-IR CO2 spectroscopy demonstrates the high sensing performance of the waveguide. The thesis also explores the refractive index sensing of CO2 with a mid-IR silicon photonic micro-ring resonator.

    Furthermore, the thesis proposes platinum nanowires as low-cost infrared light sources and detectors that can be easily integrated on photonic waveguides. Finally, the thesis presents a large-area infrared emitter fabricated by highs-peed wire bonding and integrated in a non-dispersive infrared sensor for the detection of alcohol in breath.

    The technologies presented in this thesis are suited for cost-effective mass production and large-scale adoption. Miniaturized integrated optical gas sensors have the potential to become the main choice for an increasingly broad range of existing and new applications, such as portable, distributed, and networked environmental monitoring, and high-volume medical and consumer applications.

  • Disputas: 2019-10-25 14:00 F3, STOCKHOLM
    Bakyayita, Grace Kizito
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Vatten- och miljöteknik. Makerere University, Kyambogo University.
    Batch Sorption Studies of Aqueous Cadmium and Lead from Contaminated Water onto Selected Biosorbents2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Groundwater, wastewater, surface runoff and surface water samples from Lake Victoria basin, Uganda was assessed for trace metals contamination. Untreated, base-treated and peroxide-treated biosorbents from Albizia coriaria, Coffea canephora, Cyperus papyrus, Erythrina abyssinica and Musa spp were investigated for removal of selected trace metals from contaminated water in batch studies. The assessed shallow groundwater and surface water was contaminated with iron and manganese. Selected speciation studies using Visual MINTEQ showed that in leachates from Municipal dumpsites 74% of the metal ions were bound to DOM, 13% were free ions and 13% were in inorganic forms moreover for urban streams 37% of the metal ions were bound to DOM, 44% were free ions and 19% were in inorganic forms. The metal levels in surface water, landfill leachate and surface runoff showed elevated levels and revealed increased risks to environmental health. Risk analysis based on the Swedish EPA showed that varied risks of negative effects in 30% – 76% of the sample sites ranging from high to increased risk in surface water whereas the results from Bio-met tool showed potential risk to toxicity effects of Cu2+, Ni2+, Zn2+ and Pb2+ in 15.3% - 30.8% surface water samples and 8.3% - 62.5% groundwater samples. Batch sorption studies revealed that the optimal conditions for Cd2+ and Pb2+ ions uptake were; pH 3.5 – 5.0 for contact time 3.0 – 3.5 hours and biosorbent dosage 10 – 12.5 g/L. Base-treated biosorbents showed 10 – 17 % sorption enhancement for Cd2+ ions and 1.6 – 2.3 % uptake reduction for Pb2+ ions. The biomass negative potential for binding base cations was in the order; Musa spp. > A. coriaria > E. abyssinica and base treatment reduced DOC leaching from biosorbents in the order; E. abyssinica > A. coriaria > Musa spp. Speciation studies showed that more ions were complexed to DOC in solutions at various pH levels. The maximum sorption intensities for both Cd2+ and Pb2+ ions uptake onto biomass occurred for low initial metal concentration; 5 mg/L. Freundlich model best fitted data for Pb2+ ions ions uptake whereas Temkin model fitted the sorption data for Cd2+ ions onto both treated and untreated biomass. For peroxide treated biomass, the maximum sorption efficiencies for both Cd2+ and Pb2+ ions were between 95.2 – 98.7% for C.canephora, 79.9 – 92.2% for Musa spp. and 42.0 – 91.3% for C.papyrus in non-competitive media and 90.8 – 98.0% for C.canephora, 56.4 – 89.3% for Musa spp. and 19.5 – 90.4% for C.papyrus in competitive media. The Langmiur model fitted non-competitive sorption data with 0.769 ≤ R2 ≥ 0.999 and the Freundlich model fitted competitive sorption data with 0.867 ≤ R2 ≥ 0.989. The pseudo second order kinetic model fitted the sorption data for Cd2+ and Pb2+ ions for untreated, peroxide treated and base treated biomass with 0.917 ≤ R2 ≥ 1.000. The sorption of trace metals was a complex potentially monolayer chemisorption with heterogeneous surface properties exhibited. In competitive sorption, sorption suppression effects observed were greater for Cd2+ than Pb2+ ions. The comparative studies on sorption performance presented agreement and no significant difference between the untreated and base treated biosorbents. 

  • Disputas: 2019-10-28 14:00 F3, Stockholm
    Pechsiri, Joseph
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Nutrient Recovery as an Added Benefit to Harvests of Photosynthetic Marine Biomass: A Holistic Systems Perspective on Harvesting Marine Microalgae, Cyanobacteria, and Macroalgae2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    As a result of increasing environmental burdens from anthropogenic activities andresource scarcity, interest for the development of solutions utilizing photosyntheticmarine biomass has also been increasing in both academia and industries. Medium tolarge scale production and harvest of photosynthetic marine biomass have beenpracticed to achieve numerous services, including improving tourism industries,production of biofuels, and production of food/feed. However, few studies haveevaluated the potential for nutrient recovery as an added benefit to the aforementionedservices and the potential environmental burdens of such solutions from a holisticsystems perspective. This thesis, therefore, sought to determine the nutrient recoverypotential of harvesting photosynthetic marine biomass at industrial scales whileassessing the environmental burdens from a holistic systems perspective. Techniquesinvolving life cycle inventory and analysis, input-output analysis, growth modellingand experimentation, energy analysis, and assessment of greenhouse gas emissionsfrom a life cycle perspective were used to assess the potential environmental burdensof large scale harvest of photosynthetic marine biomass.This study employed five real world case studies of five different photosynthetic marinebiomass species at various geographical locations across the globe. Each case wasassessed to determine the potential to recover nutrients while evaluating the potentialenvironmental burdens from an energy and greenhouse gas perspective. Each casecontains unique specific details and therefore methods applied were case specific.Results showed that nutrient recovery potential existed in most cases with the exceptionof one case. Cases evaluated for their potential environmental burdens showed thatlarge scale harvest of photosynthetic marine biomass is resource intensive regardless ofspecies but showed mixed results from an energy perspective. The key findings of thisthesis were that a) the potential for nutrient recovery was estimated in both large scalecultivation and large scale wild harvest of photosynthetic marine biomass, b) from anenergy and biomass harvesting perspective, the viability of industrial harvests ofphotosynthetic marine biomass were found for both large scale cultivations and wildharvesting of biomass blooms, and c) scale of operations is an important factor towardsevaluating the environmental performance of photosynthetic marine biomassproduction systems.

  • Disputas: 2019-11-04 10:00 F3, Stockholm
    Paulraj, Thomas
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material.
    Plant cell-inspiredmicrocontainers: Fabrication, Characterization and Applications2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Biomimetic materials have been inspiring mankind since a longtime for applications in a variety of fields. In particular, the production of lipidbasedvesicles have aided in our understanding of a variety of functions in animalcells, and also served as e.g. drug delivery systems and bioreactors. On thecontrary, the preparation of synthetic plant cells is limited, which is mainly due tothe challenges of building the complex plant primary cell wall fencing the lipidplasma membrane in real plant cells.The present thesis focuses on the bottom-up fabrication ofbiomimetic microcontainers that can serve as simple model systems for plant cells.In the first part, the interactions of plant cell wall polysaccharides, cellulosenanofibers (CNFs), pectin and xyloglucan, are examined. The knowledge is used inthe fabrication of microcapsules and the permeability properties were assessed.The results show that the polysaccharides must be assembled in a specific order inthe capsule wall to incorporate all the three polysaccharides. Additionally, thestructural stability and permeability highly depend on the capsule wallcomposition. The permeability also depends on the composition of thesurrounding media.The second part deals with the fabrication of more advancedbiomimetic microcapsules, with a lipid layer beneath the polysaccharide capsulewall. These capsules are semi-permeable and the phase behavior of the lipids isexploited to grow tubular structures (long filamentous structures) through thecapsule wall, as well as create a vesicle-crowded interior. Real plant cells usetubular structure (Plasmodesmata) for intercellular communications.In the third part, application-oriented aspects of the fabricatedmicrocapsules are discussed. The LbL-derived microcapsules (from the first part)were loaded with active glucose oxidase enzyme, thereby allowing their use as aglucose sensor. The capsule wall acts like a sieve, only allowing small molecules toeffectively pass through. Finally, cell culture experiments demonstrate theirbiocompatibility, paving way for tissue culture applications.

    Fulltekst tilgjengelig fra 2020-10-01 11:00
  • Disputas: 2019-11-05 10:00 F3, Stockholm
    Eriksson, Björn
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Electrochemical evaluation of new materials in polymer electrolyte fuel cells2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Polymer electrolyte fuel cells (PEFC) convert the chemical energy in hydrogen to electrical energy and heat, with the only exhaust being water. Fuel cells are considered key in achieving a sustainable energy sector. The main obstacles to wide scale commercialization are cost and durability. The aim of this thesis is to evaluate new materials for PEFC to potentially lower cost and increase durability. To lower the amount of expensive platinum catalyst in the fuel cell, the activities of Pt-rare earth metal (REM) alloy catalysts have been tested. To improve the lifetime of the carbon support, the carbon corrosion properties of multi walled carbon nanotubes have been evaluated. To reduce the overall cost of fuel cell stacks, carbon coated and metal coated bipolar plates have been tested. To increase the performance and lifetime of anion exchange membranes, the water transport has been studied.

    The results show that the Pt-REM catalysts had at least two times higher specific activity than pure platinum, and even higher activities should be obtainable if the surface structures are further refined.

    Multi-walled carbon nanotubes had lower carbon corrosion than conventional carbon Vulcan XC-72. However, once severely corroded their porous structure collapsed, causing major performance losses.

    The carbon coated metallic bipolar plates showed no significant increase of internal contact resistance (ICR) by cycling, suggesting that these coatings are stable in fuel cells. The NiMo- and NiMoP coated bipolar plates showed low ICR, however, presence of the coated bipolar plates caused secondary harmful effects on the polymer membrane and ionomer.

    Considering the water transport through anion exchange membranes it was found that most membranes showed very similar water transport properties, with more water detected at both the anode and cathode when a current was applied. The most significant factor governing the water transport properties was the membrane thickness, with thicker membranes reducing the backflow of water from anode to cathode.

    The results indicate that all of the new tested materials have the capability to improve the lifetime and reduce cost and thereby improve the overall performance of PEFC.

  • Disputas: 2019-11-05 12:00
    Jovanovic, Nenad
    KTH, Skolan för elektroteknik och datavetenskap (EECS). Research Technology Institute, Comillas Pontifical University, Spain; Delft University of Technology, the Netherlands..
    Electricity markets operation planning with risk-averse agents: stochastic decomposition and equilibium2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The growing penetration of renewable energy sources in electricity systems requires adapting operation models to face the inherent variability and uncertainty of wind or solar generation. In addition, the volatility of fuel prices (such as natural gas) or the uncertainty of the hydraulic natural inflows requires to take into account all these sources of uncertainty within the operation planning of the generation system. Thus, stochastic optimization techniques have been widely used in this context. From the point of view of the system operation, the introduction of wind and solar generation in the mix has forced conventional generators to be subject to more demanding schedules from the technical point of view, increasing for example the number of start-up and shutdown decisions during the week, or having to face more pronounced ramps. From the point of view of the market, all these technical issues are transferred to the market prices that are subject to greater volatility. This thesis focuses on the problem of risk management using the Conditional Value at Risk (CVaR) as a coherent risk measure. The thesis presents a novel iterative method that can be used by a market agent to optimize its operating decisions in the short term when the uncertainty is characterized by a set of random variable scenarios. The thesis analyses how it is possible to decompose the problem of risk management by means of Lagrangian Relaxation techniques and Benders decomposition, and shows that the proposed iterative algorithm (Iterative-CVaR) converges to the same solution as under the direct optimization setting. The algorithm is applied to two typical problems faced by agents: 1) optimization of the operation of a combined cycle power plant (CCGT) that has to cope with the volatility in the spot market price to build the supply curve for the futures market, and 2) strategic unit-commitment model. In a second part of the thesis the problem of market equilibrium is studied to model the interaction between several generating companies with mixed generation portfolios (thermal, hydraulic and renewable). The thesis analyses how the Nash equilibrium solution is modified at different risk-aversion level of the risk of the agents. In particular, the thesis studies how the management of hydroelectric reservoirs ismodified along the annual horizon when agents are risk-averse, and it is compared with the risk-neutral solution that coincides with a centralized planning when the objective is the minimization expected operational cost.

  • Disputas: 2019-11-06 10:00 Kollegiesalen, Stockholm
    Song, Meng
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Planning and Operation of Demand-Side Flexibility2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Power systems are changing with growing penetration of non-dispatchable renewable generation and increased demand of electric energy. More generation, transmission or distribution capacities are needed to balance the varying production and higher consumption. Demand-side flexibility is a potential solutionto tackle those challenges. By shifting the consumption time and temporarily increase or decrease the power demand, the demand-side flexibility can help to integrate more wind and solar energy in the system, alleviate network congestion and postpone the investment for grid reinforcement. Therefore, technical and regulatory measures are undergoing in many countries to encourage demand response and engage customers.

    On the other hand, unlocking the flexibility will introduce more complexityand uncertainty on demand side. This would result in difficulties for different actors in power systems and power markets to make optimal decisionsin their planning and operation. The thesis addresses the problem by proposing methods to support the decision making of actors on demand side. Firstly, it develops models to facilitate residential customers and commercial electric vehicle fleet operators scheduling their shiftable appliances for reducing electricity cost. The willingness of households for responding to time-varying price is taken into account. Results from Stockholm Royal Seaport project are analysed to demonstrate such willingness. Secondly, the thesis develops models for the short-term planning of retailers and balance responsible players. Different approaches are deployed under price-taker and price-maker assumptions respectively. The planning concerns the price sensitivityof end customers and the risk related with certain bidding strategies.Thirdly, the thesis proposes models to coordinate and aggregate the flexible charging power of electric vehicles to provide regulation service on the balancing market. The models encompass the decision process from day-aheadplanning to real-time operation management. The proposed models in the thesis are based on the rules of Nordic electricity market and could be further developed for adapting to other market frameworks. Stochastic programmingis applied to address the uncertainties about consumption and market behaviours.In addition, the thesis discusses the impacts of demand response interms of generation cost, system reliability and market price. It shows that a widely implemented demand response can reduce the total generation cost, improve the reliability of supply and decrease the market price.

  • Disputas: 2019-11-07 10:00 Kollegiesalen, Stockholm
    Stigsson, Martin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Structural Uncertainties of Rock Fractures and their Effect on Flow and Tracer Transport2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [sv]

    Att förstå flöde och transport av lösta ämnen genom sprickorna i berggrunden är viktigt för den långsiktiga säkerheten av ett geologiskt slutförvar av farligt avfall. I en diskret spricknätverksmodell byggs flödesvägarna upp av kedjor av flödesvägar genom de enskilda sprickorna i bergmassan. Varje sådan flödesväg genom varje spricka bidrar således till bergmassans totala flödes- och transportegenskaper. Därmed är kunskap om flödes- och transportegenskaper för de enskilda sprickorna viktiga för att kunna utföra en säkerhetsanalys av ett geologiskt slutförvar av farligt avfall.Hålrummet som utgör en spricka beror av de begränsande ytornas råhet tillsammans med den normalspänning som verkar på sprickan. Därmed är uppskattningen av hålrummet beroende av noggranna mätningar av sprickans orientering i förhållande till omgivande spänningsfält samt råheten på begränsningsytorna. Eftersom alla mätningar är behäftade med osäkerheter, såsom osäkerheter i verktyg, yttre störningar och mänskliga faktorer, kommer de tolkade egenskaperna inte att beskrivas av enskilda deterministiska värden utan av sannolikhetsfördelningar. Beroende på kombinationen av använda värden från dessa fördelningar kommer flödes- och transportegenskaperna för sprickorna att variera.Syftet med denna avhandling är därför att presentera en metod att beskriva det geometriska ramverket för sprickor i kristallint berg, inklusive osäkerheter, samt att undersöka hur dessa kan påverka tolkningen av flödes- och transportegenskaper för grundvatten och lösta ämnen. Genom att beräkna sprickornas orientering och osäkerhet från sprickornas skärning med borrhål, kan ett utfallsrum för orienteringsosäkerheten beräknas. Denna osäkerhet i orientering kommer således, under antagande av ett fixt spänningstillstånd, att resultera i en fördelning av normalspänningar som kan verka på sprickan och därmed hur hoptryckt sprickan är. Råheten på sprickytorna och dess osäkerheter kan beräknas från den sprickyta som uppstår då sprickan korsar borrkärnan, givet tillräcklig upplösning på ytan samt att ytan är representativ för hela sprickan. Denna beräknade råhet påverkar korrelationsstrukturen av hålrummet mellan de två ytorna som definierar sprickan. Således kommer median och varians för tjockleken samt dess korrelationsstruktur påverkas av vilken parameterkombination som dras från utfallsrummen för normalspänning och råhet. Detta medför att flödes- och transportegenskaperna är beroende av osäkerheterna i det geometriska ramverket, dvs osäkerheterna påverkar flödesvägar, flödestider, transportmotstånd och flödesvätt yta. Typiskt kommer en högre normalspänning som verkar på sprickan att resultera i längre flödestider, längre flödesvägar, högre flödesmotstånd och större flödesvätt yta medan en råare sprickyta typiskt kommer att resultera i kortare flödestider, längre flödesvägar, lägre flödesmotstånd och mindre flödesvätt yta. Slutsatsen av arbetet är således att osäkerheterna i att bestämma det geometriska ramverket påverkar resultatet för sprickornas tolkade flödes- och transportegenskaper.

  • Disputas: 2019-11-07 13:00 F3, Stockholm
    Åsberg, Per
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Brand Architecture from Above: Understanding the Customer Disconnect2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Global business is transforming. Information technology in general, and the Internet specifically, has globalized business and empowered the consumer with more information and choice than ever before. Consequently, academic research into brand portfolios and brand architecture is faced with new challenges to reflect this changing reality.

    Traditional research into brand portfolio management and its structural embodiment using brand architecture has approached these concepts from the perceptive of the brand owner/company. For instance, the portfolio has been mapped based on legal ownership of brands, which has been criticized as being a too narrow approach that exclude key contributors of the portfolio’s collective brand equity. Even in the cases where partner brands are acknowledged as part of the portfolio, their inclusion is often based on the revenue stream they represent or their link in the distribution chain instead of association. Brand architecture research has therefor focused on structural representations based on hierarchical trees created within the walls of the company itself, without necessarily investigating if the intended structure works as expected.

    The missing ingredient in this halting logic is the perceptions of the market in which the portfolio and its architecture operates. Associations and transfer of brand equity is dependent on a concept’s mental perception in the minds of consumers. An endorsement that does not get noticed by the target market is a mirage in the minds of marketing managers, and an historical collaboration that was cancelled years ago may still influence the brand portfolio today by means of association in consumer memory.

    The research presented in this thesis extends current theory in brand portfolio management and brand architecture to directly include the consumer perspective. This thesis re-classifies the portfolio and architecture concept as perceptual constructs whose efficiency is determined by the mental alignment between company representatives as the creators of the intended meaning and customers as the interpreters, or even co-creators, of the same. Study results presented indicate significant misalignment not only between stakeholder groups as a collective, but also between individuals within each group – even for brand managers working together on the same portfolio day after day. Current hierarchical models for representing brand architecture are extended using the perceptual dimension as well as a layer accounting for the openness of the portfolio, and a new brand portfolio model segregating brands based on the degree of perceptual inclusion in the portfolio is presented.

    This introduction of the perceptual dimension into both brand portfolio management and brand architecture represents a new way to view these abstract concepts, a conceptual idea that has ripple effects into areas such as brand equity transfer, brand alliances, and portfolio risk management.

  • Disputas: 2019-11-20 10:00 Kollegiesalen, Stockholm
    Bakas, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid Converters for HVDC Transmission2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The line-commutated converter (LCC) and the voltage-source converter (VSC) are the two main converter technologies utilized in high-voltage direct current (HVDC) transmission applications. Depending on the application requirements, one technology might be more advantageous than the other. On the one hand, the LCC features technological maturity, high efficiency, and high power-transfer capability, but it lacks the ability to independently control active and reactive power and to ride through ac faults. On the other hand, the VSC overcomes the shortcomings of the LCC and offers more functionality, as it features the ability to independently control active and reactive power, ac-fault ride through capability, black-start capability, and superior harmonic performance. Yet, it is less mature, less efficient, and has lower power-transfer capability than the LCC. Thus, the combination of the LCC and the VSC topologies could yield hybrid converters that leverage the complementary characteristics of both technologies and thus are optimized for HVDC applications. Therefore, the main objective of this thesis is to investigate existing and derive new hybrid converters that combine the complementary characteristics of the LCC and VSC technologies.

    The hybrid converters investigated in this thesis are divided in two main categories, namely: (a) current-source; and (b) voltage-source hybrid converters. The former category includes hybrid converters that are based on the LCC structure and utilize a VSC part either for compensating the reactive power consumed by the LCC, or for active filtering of the LCC current harmonics, or for independently controlling active and reactive power, or for achieving a combination of these functionalities. Four different current-source hybrid converters have been investigated and compared in terms of functionality, conduction losses, and semiconductor requirements.

    The second category includes more complex circuits that combine thyristors and modular VSC elements in ways that enable these hybrid converters to operate as VSCs and to achieve high active-power capability. Two new voltage-source hybrid converters are analyzed and compared in terms of active-power capability, semiconductor requirements, and controllability. This study reveals that the hybrid alternate-common-arm converter (HACC) is the most interesting circuit; thus, an in-depth analysis is performed for this converter. The theoretical analysis shows that, under certain operating conditions, the HACC can transfer twice the active power of the full-bridge modular multilevel converter (FB-MMC) with lower semiconductor rating per unit of active power. Yet, if the total commutation time of the thyristors and/or the power angle are increased beyond certain values, the active-power capability of the HACC is reduced. Finally, simulation and experimental results are provided in order to verify the theoretical analysis and prove the feasibility of the HACC.

  • Disputas: 2019-11-22 10:00 M3, Stockholm
    He, Yunjuan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Corrosion protection and nanomechanical properties of waterborne acrylate-based coating with and without nanocellulose on carbon steel2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Corrosion protection is commonly achieved by applying a thin polymer coating on metal surfaces. In this doctoral thesis, a waterborne hydroxyacrylate-melamine copolymer coating was used for this purpose. The first step was to find the optimal curing conditions. To this end the effect of curing time at 180 °C on the conversion of the cross-linking reaction, surface topography, nanomechanical and nanowear properties were investigated using atomic force microscopy, AFM. The results demonstrated that optimal performance required 10 min curing at 180 °C. This resulted in 80% conversion of the cross-linking reaction, as well as good barrier performance with polarization resistance of the order of 109Ω·cm2during 35 days in 0.1 M NaCl solution as determined by Electrochemical Impedance Spectroscopy (EIS). It also resulted in minor surface roughness and high surface elastic modulus in the order of GPa. 

     

    This waterborne coating and its nanocomposite containing 0.5 wt.% cellulose nanocrystals (CNC) were systematically studied, focusing on their corrosion protection performance and the effect of environment and localized wear on the properties of the top surface. The results show that both coatings have high polarization resistance, Rp. For the matrix coating the polarization resistance displays a slightly decreasing trend with time, as expected for a barrier coating. In contrast, the CNC nanocomposite coating exhibits an unusual and unexpected increase in polarization resistance with time. The difference in the time dependence of Rp can be attributed to the reinforcement effect of CNC, which form strong hydrogen bonding interactions with the matrix coating. Further, the appearance of a second time constant in the corresponding EIS spectra implies formation of a more protective second layer at the metal-coating interface. The presence of this compact layer also contributes to the corrosion protection offered by the CNC nanocomposite coating. In addition, both coatings show only limited water-uptake during long term exposure to 0.1 M NaCl. The water up-take is too small to measurably change the coating capacitance, as studied by EIS. However, AFM studies of surface nanomechanical properties show that for the CNC nanocomposite some water penetration occurs, which irreversibly renders the surface softer.

     

    Inspired by the CNC nanocomposite coating and its favorable corrosion protective properties, 0.5 wt.% cellulose nanofibrils, CNF, nanocomposite coatings were also studied using the same methodologies. The results revealed that the CNF nanocomposite coating cannot provide efficient corrosion protection performance even over a period of 24 h. The measured polarization resistance decreases rapidly over time, and consistently water uptake is readily observed by analyzing coating capacitance using EIS technique. The substantial difference in corrosion protective properties of the CNC nanocomposite and the CNF nanocomposite are explained mainly from the perspective of microstructure, matrix-CNC or matrix-CNF interactions by using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show the presence of defects on the surface and in the bulk and absence of strong hydrogen bonding interactions between matrix and CNF. These are two reasons for why the CNC nanocomposite performs well in terms of corrosion protection, whereas the CNF nanocomposite does not. 

     

    In real applications good barrier coatings may also fail due to external forces such as erosion by wind and water, impact of solid particles or sliding motions against other objects, which may destroy the coating integrity. This motivated further studies of the matrix and the CNC nanocomposite, by focusing on their nanomechanical and nano-wear properties using local measurements by means of AFM. The effect of applied normal load, ranging from 50 – 400 nN, scanning speed, ranging from 1 – 20 µm/s, operating environment including air and water, as well as exposure to corrosive 0.1 M NaCl solution, were systematically studied and discussed.

  • Disputas: 2019-12-03 10:00 Kollegiesalen, Stockholm
    Ahmed, Laeeq
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Beräkningsvetenskap och beräkningsteknik (CST).
    Scalable Analysis of Large Datasets in Life Sciences2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    We are experiencing a deluge of data in all fields of scientific and business research, particularly in the life sciences, due to the development of better instrumentation and the rapid advancements that have occurred in information technology in recent times. There are major challenges when it comes to handling such large amounts of data. These range from the practicalities of managing these large volumes of data, to understanding the meaning and practical implications of the data.

    In this thesis, I present parallel methods to efficiently manage, process, analyse and visualize large sets of data from several life sciences fields at a rapid rate, while building and utilizing various machine learning techniques in a novel way. Most of the work is centred on applying the latest Big Data Analytics frameworks for creating efficient virtual screening strategies while working with large datasets. Virtual screening is a method in cheminformatics used for Drug discovery by searching large libraries of molecule structures. I also present a method for the analysis of large Electroencephalography data in real time. Electroencephalography is one of the main techniques used to measure the brain electrical activity.

    First, I evaluate the suitability of Spark, a parallel framework for large datasets, for performing parallel ligand-based virtual screening. As a case study, I classify molecular library using prebuilt classification models to filter out the active molecules. I also demonstrate a strategy to create cloud-ready pipelines for structure-based virtual screening. The major advantages of this strategy are increased productivity and high throughput. In this work, I show that Spark can be applied to virtual screening, and that it is, in general, an appropriate solution for large-scale parallel pipelining. Moreover, I illustrate how Big Data analytics are valuable in working with life sciences datasets.

    Secondly, I present a method to further reduce the overall time of the structured-based virtual screening strategy using machine learning and a conformal-prediction-based iterative modelling strategy. The idea is to only dock those molecules that have a better than average chance of being an inhibitor when searching for molecules that could potentially be used as drugs. Using machine learning models from this work, I built a web service to predict the target profile of multiple compounds against ready-made models for a list of targets where 3D structures are available. These target predictions can be used to understand off-target effects, for example in the early stages of drug discovery projects.

    Thirdly, I present a method to detect seizures in long term Electroencephalography readings - this method works in real time taking the ongoing readings in as live data streams. The method involves tackling the challenges of real-time decision-making, storing large datasets in memory and updating the prediction model with newly produced data at a rapid rate. The resulting algorithm not only classifies seizures in real time, it also learns the threshold in real time. I also present a new feature "top-k amplitude measure" for classifying which parts of the data correspond to seizures. Furthermore, this feature helps to reduce the amount of data that needs to be processed in the subsequent steps.