1 - 17 of 17
rss atomLink til resultatlisten
Permanent link
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
  • html
  • text
  • asciidoc
  • rtf
  • Disputas: 2018-12-14 09:15 Kollegiesalen, Stockholm
    Holmstedt, Louise
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Evaluation of Sustainable Urban District Developments: The case of Stockholm Royal Seaport2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Urban sustainable development is now seen as one of the keys in the quest for a sustainable world and increased interest in developing sustainable urban districts has become an important feature of urban sustainability. However, if cities and their districts are to be part of this transition, it will be necessary to determine the state and progress of urban developments. Evaluation and follow-up activities must therefore be an integral part of modern sustainability work.

    This thesis investigated evaluation methods and strategies for determining progress towards sustainable urban district development. The Stockholm Royal Seaport district in Sweden was used as the research arena in studies based on urban metabolism theories, including a single case study approach, focus group interviews, the Framework for Strategic Sustainable Development and quantitative data analysis. The thesis main results can be summarised as follows.

    A structured frame for use in theory and practice can strengthen programme development and minimise the risk of built-in problems in environmental and sustainability plans for new urban districts. The proposed evaluation model for Stockholm Royal Seaport displayed strengths regarding core evaluation activities, such as communicating a strong vision and recognising continuity in the evaluation process. It displayed weaknesses as regards organisational structure and system boundaries.

     The proof-of-concept implementation of a Smart Urban Metabolism framework enabled real-time evaluation data on district scale to be generated and processed. The implementation process also led to identification of limitations in the framework, such as access to business sensitive data, failed integration of data streams and privacy concerns. Dynamic, high-resolution meter data can provide a higher degree of transparency in evaluation results and permit inclusion of all stakeholder groups in urban districts. The frequently used energy performance indicator kWh/m2 (Atemp) was shown to be an insufficient communication tool to mediate knowledge, due to conflation of consumption and construction parameters and the need for prior knowledge for full understanding.

  • Disputas: 2018-12-14 10:00 FD5, Stockholm
    Moosavi, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Non-equilibrium dynamics of exactly solvable quantum many-body systems2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Recent experimental advances on ultracold atomic gases and trapped ions have made it possible to simulate exactly solvable quantum systems of interacting particles. In particular, the feasibility of making rapid changes, so-called quantum quenches, to such set-ups has allowed experimentalists to probe non-equilibrium phenomena in closed interacting quantum systems. This, in turn, has spurred a considerable theoretical interest in quantum many-body systems out of equilibrium.

    In this thesis, we study non-equilibrium properties of quantum many-body systems in the framework of exactly solvable quantum field theory in one spatial dimension. Specific systems include interacting fermions described by the Luttinger model and effective descriptions of spin chains using conformal field theory (CFT). Special emphasis is placed on heat and charge transport, studied from the point of view of quench dynamics, and, in particular, the effects of breaking conformal symmetries on transport properties. Examples include the Luttinger model with non-local interactions, breaking Lorentz and scale invariance, and inhomogeneous CFT, which generalizes standard CFT in that the usual propagation velocity v is replaced by a function v(x) that depends smoothly on the position x, breaking translation invariance.

    The quench dynamics studied here is for quantum quenches between, in general, different smooth inhomogeneous systems. An example of this is the so-called smooth-profile protocol, in which the initial state is defined by, e.g., smooth inhomogeneous profiles of inverse temperature and chemical potential, and the time evolution is governed by a homogeneous Hamiltonian. Using this protocol, we compute exact analytical results for the full time evolution of the systems mentioned above. In particular, we derive finite-time results that are universal in the sense that the same relations between the non-equilibrium dynamics and the initial profiles hold for any unitary CFT. These results also make clear that heat and charge transport in standard CFT are purely ballistic.

    Finally, we propose and study an inhomogeneous CFT model with v(x) given by a random function. We argue that this model naturally emerges as an effective description of one-dimensional quantum many-body systems with certain static random impurities. Using tools from wave propagation in random media, we show that such impurities lead to normal and anomalous diffusive contributions to heat transport on top of the ballistic one known from standard CFT.

  • Disputas: 2018-12-14 10:00 F3, Stockholm
    Hariramabadran Anantha, Krishnan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    An Experimental Study to Understand the Localized Corrosion and Environment-Assisted Cracking Behavior of AISI 420-Martensitic Stainless Steel2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Motivation and aim: Currently steel molds are designed with cooling channels to reduce the solidification time of molten plastic within the mold to improve the productivity. As water is generally used as the cooling medium, corrosion and environment-assisted cracking (EAC) leading towards the dysfunction of mold, can increase the production downtime. This was observed in some cases. Hence the primary aim of this thesis is to study the corrosion and EAC behavior of a martensitic stainless steel (MSS) in Cl containing environment to further the current understanding thereby to optimize the existing alloy/s and to design and develop new steel grades.

    Methods: The MSS had been austenitised at 1020°C, and subsequently quenched in nitrogen gas at fast (3°C/s), and slow quenching rates (0.6°C/s). Then tempering was done at 250°C, and 500°C, respectively, twice for two hours. Microstructure was predicted and characterized using Thermocalc simulation, dilatometry, light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, atomic force microscopy (AFM). Localized corrosion behavior was characterized using standard salt spray test, electrochemical experiments, scanning Kelvin probe force microscopy, in-situ AFM. Stress relaxation associated with 250°C, and 500°C tempering was characterized by a new method for both fast (FQ) and slow quenched (SQ) conditions. Based on the %stress relaxation, initial loading levels were altered and the corresponding environment-assisted cracking behavior was investigated at two different loading levels.

    Results: Samples tempered at 250ºC exhibited higher corrosion resistance than samples tempered at 500ºC in both FQ and SQ conditions. FQ samples exhibited higher corrosion resistance with an ability to passivate than SQ samples when tempered at 250ºC. However, when tempered at 500°C, the corrosion resistance was poor for both FQ and SQ samples. These observed differences clearly indicate the strong influence of microstructure on the corrosion behavior of the material. There are preferential active sites in the microstructure, which dictate the sequence of corrosion events. Secondary Cr-rich carbides formed during 500ºC tempering apparently deteriorate the corrosion resistance in spite of their smaller sizes as compared to undissolved Cr-rich carbides.  Stress relaxation increased with increasing tempering temperature. In the FQ condition, 250°C temper exhibited superior EAC resistance than 500°C temper in both loading scenarios, indicating the dominant role of corrosion resistance in delaying the failure. Whereas in SQ condition, 500°C temper exhibited superior EAC resistance than 250°C temper in both loading scenarios, indicating the dominant role of applied stress in delaying the failure. The pitting susceptibility increased with increasing applied stress on both FQ and SQ conditions. The fractographic features suggest that the mechanism of failure was mixed mode involving both active path dissolution and hydrogen embrittlement, which could have been operative during the failure in varying magnitude in respective scenarios. 

    Conclusions: Based on this research work, it can be concluded that, in order to have a longer service life, both the localized corrosion behavior and the residual stresses are to be considered while recommending tempering temperature to mold makers.

  • Disputas: 2018-12-14 13:00 Kollegiesalen, Stockholm
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Periodic Structures with Higher Symmetries: Analysis and Applications2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, periodic structures with higher symmetries are studied. Their wave propagation characteristics are investigated and their potential applications are discussed. 

    Higher-symmetric periodic structures are described with an additional geometrical operation beyond a translation operator. Two particular types of higher symmetry are glide and twist symmetries. Glide-symmetric periodic structures remain invariant under a translation of half a period followed by a reflection with respect to a glide plane. Twist-symmetric periodic structures remain invariant under a translation along followed by a rotation around a twist axis. 

    In a periodic structure with a higher symmetry, in which the higher order modes are excited, the frequency dispersion of the first mode is dramatically reduced. This feature overcomes the bandwidth limitations of conventional periodic structures. Therefore, higher-symmetric periodic structures can be employed for designing wideband metasurface-based antennas. For example, holey glide-symmetric metallic structures can be used to design low loss, wideband flat Luneburg lens antennas at millimeter waves, which find application in 5G communication systems. In addition, holey glide-symmetric structures can be exploited as low cost electromagnetic band gap (EBG) structures at millimeter waves, due to a wider stop-band achievable compared to non-glide-symmetric surfaces. 

    However, these attractive dispersive features can be obtained if holey surfaces are strongly coupled, so higher-order modes produce a considerable coupling between glide-symmetric holes. Hence, these structures cannot be analyzed using common homogenization methods based on the transverse resonance method. Thus, in this thesis, a mode matching formulation, taking the generalized Floquet theorem into account, is applied to analyze glide-symmetric holey periodic structures with arbitrary shape of the hole. Applying the generalized Floquet theorem, the computational domain is reduced to half of the unit cell. The method is faster and more efficient than the commercial software such as CST Microwave Studio. In addition, the proposed method provides a physical insight about the symmetry of Floquet modes propagating in these structures. 

    Moreover, in this thesis, the effect of twist symmetry and polar glide symmetry applied to a coaxial line loaded with holes is explained. A rigorous definition of polar glide symmetry, which is equivalent to glide symmetry in a cylindrical coordinate, is presented. It is demonstrated that the twist and polar glide symmetries provide an additional degree of freedom to engineer the dispersion characteristics of periodic structures. In addition, it is demonstrated that the combination of these two symmetries provides the possibility of designing reconfigurable filters. Finally, mimicking the twist symmetry effect in a flat structure possessing glide symmetry is investigated. The results demonstrate that the dispersion properties associated with twist symmetry can be mimicked in flat structures.


  • Disputas: 2018-12-14 13:00 T1, Huddinge
    Rolfö, Linda
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Ergonomi.
    Activity-based Flexible Office work environments: Design and implementation processes and outcomes2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Background: In recent years, there has been a reported increase in organizations relocating to Activity-based Flexible Offices (A-FOs) worldwide. The idea of A-FOs is to offer work conditions suitable for the workforce’s tasks and individual preferences. Benefits of the A-FO include employee autonomy, privacy and inter- and intra-team communication. However, there are reports within Swedish media on reduced performance, increased dissatisfaction, injustice, and workplace avoidance amongst employees occupying A-FOs. Added to which empirical research supporting A-FOs claimed benefits are scarce with inconsistent results.

    Aim: The aim of this thesis is to explore and investigate perceptions of workspace, work conditions, work environment satisfaction, and perceived performance in A-FOs (aim of Studies I-V). Additionally, the sub-aims are to explore and investigate associations with underlying factors such as design and implementation process factors including methods suggestions (aims of Studies II, IV & VI), physical workspace factors (aim of Study III), desk-sharing and speech policies (aim of Study IV), and organizational preconditions (aim of Study V).  This thesis aims at integrating the contributions of each paper and making the whole greater than the sum of its parts.

    Method: A problem centered, pragmatic approach guided the methodological choices. Two in-depth longitudinal case (n=66 & 46) and two cross-sectional (n=202 & 105) studies were conducted at five single floor A-FOs. A mixed method approach was adopted comprising of six questionnaires, 105 individual interviews, documentation of plan layouts, photographs, planning documents and observations. A third cross-sectional study with 7 additional cases was conducted on 473-715 questionnaire responses.

    Results & discussion: The results showed that work environment satisfaction and perceived performance can increase after relocation to A-FOs. Reported contributing design and implementation process factors included meaningful objectives for the employees, allocation of time and financial resources, having an organizational focus, employee empowerment, and a methodological approach. A methods framework divided into A-FO design stages is presented that can facilitate the design process of A-FOs. Reported contributing workspace design factors included ample desk-sharing ratios and workspace diversity. Desk-sharing and speech rules were identified: when to remove belongings, allowance to occupy the same workstation in open-plan and enclosed areas on consecutive days, and allocations of areas where speaking on the phone, and verbal interaction with colleagues and interruptions are allowed or forbidden. Organizational preconditions, such as innovative work tasks and an open-plan office type prior to relocation were associated with preference for the A-FO.

    Conclusion: Design and implementation factors, workspace factors, application of rules and organizational preconditions are possible predictors of work conditions, work environment satisfaction, and perceived performance. A-FOs can be perceived as noisy workplaces that create extra work, decrease interaction as well as increase uncertainty on how to act within the office. However, A-FOs can also be preferred above other office types and be perceived with high work environment satisfaction and perceived performance. This thesis has stressed the importance of a holistic sociotechnical perspective during A-FO implementations, and the importance of employee involvement and empowerment, workspace diversity and desk-sharing policies.

  • Disputas: 2018-12-14 14:00 F3, Stockholm
    Aminzadeh, Selda
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Valorization of Kraft Lignin by Fractionation and Chemical Modifications for Different Applications2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]


    Lignin is one of the most abundant biopolymers. Approximately 70 million tons of technical lignin is generated annually, but only little is used for products other than energy. The complexity of lignin hinders full utilization in high-value products and materials. In spite of the large recent progress of knowledge of lignin structure and biosynthesis, much is still not fully understood, including structural inhomogeneity. We made synthetic lignin at different pH’s and obtained structural differences that might explain the structural inhomogeneity of lignin.

    Technical lignins from the chemical pulping are available in large scale, but the processes result in alterations, such as oxidation and condensation. Therefore, to utilize technical lignin, modifications, such as fractionation and/or chemical modifications are necessary. Fractionation with ceramic membranes is one way to lower the polydispersity of lignin. The main advantage is their tolerance towards high temperature and harsh conditions. We demonstrated that low Mw lignin was extracted from industrially produced LignoBoost lignin aiming: i) to investigate the performance of the membrane over time; ii) to analyze the antioxidant properties of the low Mw lignin.

    Chemical modification can also improve the properties of lignin. By adding moieties, different properties can be obtained. Amination and methacrylation of kraft lignin were performed, as well as lignin-silica hybrid materials with potential for the adsorption were produced and investigated.

    Non-modified and methacrylated lignin were used to synthesize lignin-St-DVB porous microspheres to be utilized as a sorbent for organic pollutants. The possibility to substitute styrene with methacrylated lignin was evaluated, demonstrating that interaction between lignin and DVB, and porosity increased.

    Lignin has certain antibacterial properties. Un-modified and modified (aminated) lignin samples and sphere nanoparticles of lignin were tested for their effect against gram-positive and gram-negative bacteria’s and an injectable hydrogel was developed with encapsulated lignin for being used as an injectable gel for the open wounds. Results demonstrated promising antibacterial efficiency of lignins against gram-positive, more especially better inhibition with aminated lignins against gram-positive and negative bacterium.



    Fulltekst tilgjengelig fra 2019-11-22 11:08
  • Disputas: 2018-12-18 09:30 Q2, Stockholm
    Siyal, Shahid Hussain
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Energisystemanalys. NA.
    Techno-economic assessment of wind energy for renewable hydrogen production in Sweden2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Wind energy deployment has been growing globally. The resource is expected to play an important role in achieving economic and environmental sustainability - depending on its level of availability, economics, and policy.  Sweden has committed to have 20 TWh/year production of onshore wind energy in the national electricity sector by the year 2020. Further, Sweden has a target for a fossil fuel free transport sector by 2030. Local wind energy coupled to electrolysis-derived hydrogen fuel production offers a pathway for achieving both targets. The analysis of wind energy’s potential in this context necessitates a new type of approach, one that captures the complexities of wind turbine siting in relation to the build-up of hydrogen infrastructure, including refueling stations. In this thesis, high-resolution spatial assessments were performed to evaluate wind energy and wind-to-hydrogen energy potentials, including land use restrictions and techno-economic evaluations. The methodology combines Geographic Information System (GIS) data with the Hybrid Optimization Model for Multiple Energy Resources (HOMER) tool and includes key constraints with the purpose of improving the fidelity of the assessments.

    Overall, significant potentials for wind and hydrogen energy can be harnessed in Sweden. Wind-generated hydrogen can be produced economically at selected sites along existing roads. After applying all possible land use restrictions, results show that around 31% of the total land area is viable for wind energy applications in the country. In total, 190 TWh/year wind electricity could be generated in areas within 30 km from the national electricity grid. Moreover, approximately 26000 kton/year of hydrogen fuel could be supplied by installing wind turbines on the viable land area. While considering standalone wind-powered hydrogen refueling stations, the cost of hydrogen lies in the range of 6-10 USD∕kg, depending on wind speed models employed and other factors.

  • Disputas: 2018-12-19 13:00 Kollegiesalen, Stockholm
    Fauré, Eléonore
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Strategiska hållbarhetsstudier.
    Sharing the doughnut: Exploring sustainable and just futures2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Despite decades of international discussions or summits on the need to radically reduce e.g. increasing concentrations of greenhouse gases (GHGs) or biodiversity loss, these are still rising. While these negative environmental trends continue, it is important to discuss alternative futures in an attempt to redirect society on a more sustainable and just path.

    The overall aim of the thesis is to develop images of the future and explore what sustainable and just futures might look like. The current environmental impact of Swedish consumption, both in Sweden and abroad, is shown using eight indicators of environmental pressures and resource use – illustrating where in the world the pressures or resource use occur and for which product groups. This gives us a starting point as to where we are today regarding some of the environmental challenges facing Sweden.

    Alternative futures that can challenge existing unsustainable trends are explored using four images of the future – so-called backcasting or long-term transformative scenarios. All of these need to fulfil two environmental and two social sustainability goals and do not rely on continued GDP growth.

    These images represent different strategies to reach the four selected goals.

    Such strategies may however have different consequences not just for these four specific goals but also for other sustainability issues and may have different implications for various groups in society. Therefore, they need to be evaluated accordingly. Existing methods to evaluate future scenarios regarding sustainability aspects are discussed in this thesis as well as the need to develop new methods to encompass all issues.

    A combination of methods and data is used to evaluate what it would actually mean if the scenarios were to fulfil a climate target for Swedish consumption in line with the 1.5°C. trajectory suggested as the target to strive for in the Paris Climate Agreement and in the latest IPCC report (IPCC, 2018) as regards reduction of goods consumption and altered consumption patterns in Sweden.

    This thesis stresses the need to clarify the assumptions made when formulating goals such as whether a perspective on intergenerational (between different generations) and intragenerational justice (within the current generation) is considered. It also underlines the need to identify and discuss potential goal conflicts that necessarily occur when considering several sustainability goals, whether they can be avoided or require potential trade-offs. It highlights the importance of making the underlying values embedded in assessment methods more visible. The intention in revealing goal conflicts, contradictions or hidden values is not to reach consensus but to ensure that the decisions are informed and made in a transparent manner.

    Indeed, these considerations imply moving from a first and rather vague level of meaning of the concept of sustainability where everyone can agree on a definition but no concrete and practical guidance can be gained to a second level where conflicts arise and values differ.

  • Disputas: 2018-12-20 10:00 F3, Stockholm
    Björlenius, Berndt
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Industriell bioteknologi.
    Pharmaceuticals – improved removal from municipal wastewater and their occurrence in the Baltic Sea2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Pharmaceutical residues are found in the environment due to extensive use in human and veterinary medicine. The active pharmaceutical ingredients (APIs) have a potential impact in non-target organisms. Municipal wastewater treatment plants (WWTPs) are not designed to remove APIs.

    In this thesis, two related matters are addressed 1) evaluation of advanced treatment to remove APIs from municipal wastewater and 2) the prevalence and degradation of APIs in the Baltic Sea.

    A stationary pilot plant with nanofiltration (NF) and a mobile pilot plant with activated carbon and ozonation were designed to study the removal of APIs at four WWTPs. By NF, removal reached 90%, but the retentate needed further treatment. A predictive model of the rejection of APIs by NF was developed based on the variables: polarizability, globularity, ratio hydrophobic to polar water accessible surface and charge. The pilot plants with granular and powdered activated carbon (GAC) and (PAC) removed more than 95% of the APIs. Screening of activated carbon products was essential, because of a broad variation in adsorption capacity. Recirculation of PAC or longer contact time, increased the removal of APIs. Ozonation with 5-7 g/m3 ozone resulted in 87-95% removal of APIs. Elevated activity and transcription of biomarkers indicated presence of xenobiotics in regular effluent. Chemical analysis of APIs, together with analysis of biomarkers, were valuable and showed that GAC-filtration and ozonation can be implemented to remove APIs in WWTPs, with decreased biomarker responses.

    Sampling of the Baltic Sea showed presence of APIs in 41 out of 43 locations. A developed grey box model predicted concentration and half-life of carbamazepine in the Baltic Sea to be 1.8 ng/L and 1300 d respectively.

    In conclusion, APIs were removed to 95% by GAC or PAC treatment. The additional treatment resulted in lower biomarker responses than today and some APIs were shown to be widespread in the aquatic environment.

  • Disputas: 2018-12-20 14:00 FA31, Stockholm
    Manickam, Louis
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnkraftssäkerhet.
    An Experimental Study on Melt Fragmentation, Oxidation and Steam Explosion during Fuel Coolant Interactions2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nordic type boiling water reactors (BWRs) adopt reactor cavity flooding as a severe accident mitigation strategy (SAMS) to achieve core melt fragmentation and long-term cooling of decay heat generating core debris. The qualification of this SAMS needs to address two main severe accident issues: debris bed coolability and steam explosion. 


    Since the coolability of a debris bed is determined by the bed’s  properties including debris particle’s size distribution and morphology as well as the bed’s configuration and inhomogeneity, it is important to investigate the mechanisms of melt jet breakup and resulting fragmentation in water which affect debris bed’s properties. Hence, the first part of this thesis is concerned with characterization of melt jet breakup and resulting debris particles.  A series of jet breakup experiments have been conducted in small scale with simulant binary oxide melt mixtures of WO3-Bi2O3, WO3-ZrO2 and Wood's metal. The experiments reveal significant influence of melt superheat, water subcooling, melt jet diameter and material properties on debris size and morphology. Specifically, transition in debris size and morphology is found to occur at a specific water subcooling range. The difference in debris properties at varied melt release conditions is attributed to the competition between liquid melt hydrodynamic fragmentation and thermomechanical fracture of quenched particles.


    The second part of this thesis work is dedicated to provide a new understanding of steam explosion (SE) with the support of small-scale experiments at the level of droplets. Self- and externally-triggered SE experiments are conducted with simulant binary oxide melt mixtures in the temperature range of 1100 to 1500°C. The dynamics of steam explosion process is recorded using a sophisticated simultaneous visualization system of videography and X-ray radiography. Further, the influence of melt composition on steam explosion is summoned.  The results reveal that a droplet of eutectic composition is more explosive than a droplet of non-eutectic composition since latter may form a mushy zone which thereby limits the amount of melt actively participating in a steam explosion. To reduce the temperature difference between simulant melt and corium, investigation was extended to perform high temperature (˃2000°C) melt experiments. For this purpose, steam explosion of a molten Al2O3 droplet was investigated, and the experimental results confirmed that Al2O3 melt can undergo spontaneously triggered steam explosion at a high melt superheat and high subcooling. Within the context the effects of melt superheat and water subcooling were obtained.


    The third part of this thesis is concerned with the oxidation of metallic melt representing unmixable metallic liquid of molten corium, which interactions with water can be spatially and chronologically separated from the oxidic corium FCI. The objective of the study  is to provide new insights into the characteristics of oxidation of Zr droplet falling in a water pool through a series of small-scale experiments. The dynamics of droplet and bubbles were recorded by high-speed cameras, and the spatial distributions of the elements in the quenched droplet (debris) were acquired by Energy- Dispersive X-Ray Spectroscopy (EDS). The results have shown noticeable influence of generated hydrogen and oxidation heat on droplet behavior and cooling rate. Water subcooling had significant influence on oxidation kinetics, and the oxygen content of the solidified particle increased with decreasing subcooling. Incomplete oxidation of Zr happened before melt crystallization and cooling down in all experiments.  

  • Disputas: 2019-01-07 13:00 F3, Stockholm
    Joyce, Peter James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Hållbarhet, utvärdering och styrning.
    Environmental Considerations in the Zero-waste Valorisation of Bauxite Residue: A Life Cycle Perspective2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Bauxite residue, also known as red mud, is produced in large quantities as a result of alumina refining (the first stage in aluminium production), and is one of the world’s most abundant and important industrial wastes. As demand for aluminium continues to increase and space to store this residue diminishes, the potential to utilise bauxite residue as a secondary resource is increasingly being considered by the alumina industry. Bauxite residue can be used as a source of iron, aluminium, titanium oxide, scandium and rare earth oxides, or utilised for its bulk properties to create cement clinkers or inorganic polymers. Achieving any of these uses however requires a series of complex valorisation processes, which in turn require inputs of energy and materials. Some bauxite residues also contain trace amounts of naturally occurring radionuclides.

    The EU Horizon 2020 MSCA-ETN REDMUD project was set up to investigate the valorisation of bauxite residue in an integrated manner. The ultimate aim of the REDMUD project is to develop environmentally-friendly, zero-waste, integrated processes for extracting valuable materials from bauxite residue and/or utilising it at high volume. This thesis presents the environmental perspective on this aim, taking a life cycle view; that is, taking into account the upstream and downstream impacts, in addition to the direct impacts, which may result from diverting bauxite residue from landfill to the proposed valorisation processes. This involves using Life Cycle Assessment (LCA) approaches to understand the environmental balance between the impact avoided through landfill diversion and the substitution of conventional materials, and the impacts incurred by the use of materials and energy in the valorisation processes themselves. Importantly, the potential ionising radiation impact from naturally occurring radionuclides is also considered from a life cycle perspective for the first time.

    A new life cycle impact assessment method for assessing the impacts of naturally occurring radionuclides was developed. In addition, two pieces of research software, designed to overcome the current shortcomings in LCA software with respect to streamlined and prospective LCA studies of emerging technologies are presented as part of this thesis.

    The potential hotspots of environmental impact in a single step valorisation process, the production of high bauxite residue content inorganic polymers, were identified. The results identify the high temperature processing of bauxite residue, in order to transform it into a reactive precursor capable of forming solid inorganic polymers, as a hotspot of environmental impact across a range of environmental impact measures. The production of alkaline activating solutions (the other reagent in the polymerisation reaction) also represented a hotspot of environmental impact. These hotspots were used to identify possible future research directions for this process, which have the potential to reduce the environmental impact of this valorisation process.

    Finally it was shown that even in the absence of a detailed and quantified system description, qualitative approaches based on life cycle thinking can be usefully applied to identify important aspects on both sides of the environmental balance between the impacts avoided and the impacts incurred in waste valorisation. Chemical reaction products, chemical synthesis, thermal and mechanical energy are highlighted as potential sources of environmental impact. A case study, looking at the combined extraction of iron and production of inorganic polymers from bauxite residue was used to demonstrate the validity of these qualitative approaches. This study also demonstrated that combining the extraction of iron and inorganic polymers is vital in order to yield a net environmental benefit in terms of climate change.

    This thesis provides an initial step on the road towards the environmentally sustainable valorisation of bauxite residue, as well as the analytical tools and additional impact assessment measures required to ensure that this journey can be continued, both within the REDMUD project and beyond.

  • Disputas: 2019-01-17 13:00 F3, Stockholm
    Ringh, Axel
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Multidimensional inverse problems in imaging and identification using low-complexity models, optimal mass transport, and machine learning2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis, which mainly consists of six appended papers, primarily considers a number of inverse problems in imaging and system identification.

    In particular, the first two papers generalize results for the rational covariance extension problem from one to higher dimensions. The rational covariance extension problem stems from system identification and can be formulated as a trigonometric moment problem, but with a complexity constraint on the sought measure. The papers investigate a solution method based on varia tional regularization and convex optimization. We prove the existence and uniqueness of a solution to the variational problem, both when enforcing exact moment matching and when considering two different versions of approximate moment matching. A number of related questions are also considered, such as well-posedness, and the theory is illustrated with a number of examples.

    The third paper considers the maximum delay margin problem in robust control: To find the largest time delay in a feedback loop for a linear dynamical system so that there still exists a single controller that stabilizes the system for all delays smaller than or equal to this time delay. A sufficient condition for robust stabilization is recast as an analytic interpolation problem, which leads to an algorithm for computing a lower bound on the maximum delay margin. The algorithm is based on bisection, where positive semi-definiteness of a Pick matrix is used as selection criteria.

    Paper four investigate the use of optimal transport as a regularizing functional to incorporate prior information in variational formulations for image reconstruction. This is done by observing that the so-called Sinkhorn iterations, which are used to solve large scale optimal transport problems, can be seen as coordinate ascent in a dual optimization problem. Using this, we extend the idea of Sinkhorn iterations and derive a iterative algorithm for computing the proximal operator. This allows us to solve large-scale convex optimization problems that include an optimal transport term.

    In paper five, optimal transport is used as a loss function in machine learning for inverse problems in imaging. This is motivated by noise in the training data which has a geometrical characteristic. We derive theoretical results that indicate that optimal transport is better at compensating for this type of noise, compared to the standard 2-norm, and the effect is demonstrated in a numerical experiment.

    The sixth paper considers using machine learning techniques for solving large-scale convex optimization problems. We first parametrizes a family of algorithms, from which a new optimization algorithm is derived. Then we apply machine learning techniques to learn optimal parameters for given families of optimization problems, while imposing a fixed number of iterations in the scheme. By constraining the parameters appropriately, this gives learned optimization algorithms with provable convergence.

  • Disputas: 2019-01-18 13:00 Kollegiesalen, Stockholm
    Wadi, Amer
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Soil-Steel Composite Bridges: Research advances and application2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Soil-steel composite bridges are considered competitive structures being an economical alternative to similar span concrete bridges. This frequently stimulates practitioners to push their design limits and expand the different areas of application including their performance in sloping terrain. This also implies that most design methods are continuously being developed to address new market challenges and at the same time to seek for better design and construction.

    This thesis compiles the recent research efforts to advance the knowledge on the structural performance of soil-steel composite bridges (SSCB). The first part of the thesis investigates the performance of SSCB in sloping terrain, where numerical simulations are used to predict the behaviour of three case studies. This includes structural response under sloped soils and also avalanche loads (Paper I and Paper II). The research enabled to realize the importance of soil configuration around the wall conduit and its influence on the structural response. While the presence of surface slopes emphasizes the susceptibility of SSCB with low depths of soil cover, higher covers may help in reducing the influence of steep slopes and avalanche loads. It was also found that the downhill soil configuration has substantial effects on the flexural response. The findings of the study were also used to provide methods for preliminary estimates of normal forces under sloped soils and avalanches.

    To better understand the load bearing capacity of SSCB, the second part of this thesis deals with the behaviour of large-span structures. It includes the use of finite element method simulations (FEM) for the analysis and the prediction of a previous full-scale loading-to-failure test (Paper III). The study also presents response predictions on the ultimate capacity of a large-span structure pertaining to its ongoing preparation for a full-scale field test (Paper IV). The thesis also includes discussions and possible refinements on current design equations concerning buckling calculations and live load effects. The results of the study have allowed to realize the major role of the soil load effects on the subsequent formation of yield areas and failure loads. It is found that the load position has a direct influence on the ultimate capacity especially for large-span structures. The study also highlighted the variations in the distribution of the live load sectional forces in both the circumferential and the transverse directions of the corrugations. Furthermore, possible refinements are proposed on current design equations of which are believed closely relevant on the path for the design development of large-span structures.

  • Disputas: 2019-01-18 14:00 F3, Stockholm
    Tegling, Emma
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Fundamental Limitations of Distributed Feedback Control in Large-Scale Networks2018Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Networked systems accomplish global behaviors through local feedback interactions. The purpose of a distributed control design is to select interaction rules and control protocols that achieve desired global control objectives. In this thesis, we address the question of fundamental limitations to such control designs, in terms of the global performance that is achievable in large-scale networks. 

    We consider networked dynamical systems with single- and double- integrator dynamics controlled with linear consensus-like protocols. Such systems can be used to model, for example, vehicular formation dynamics and synchronization in electric power networks. We assume that the systems are subject to distributed disturbances and study performance in terms of H2 norm metrics that capture the notion of network coherence. In the context of power networks, we also show how such metrics can be used to quantify resistive losses caused by non-equilibrium, or transient, power flows due to a lack of synchrony. 

    Distributed static feedback control based on localized, relative state measurements is subject to known limitations that, for example, cause coherence metrics to scale unfavorably with network size in lattices of low spatial dimensions. This causes an inevitable lack of rigidity in one-dimensional formations, such as strings of vehicles. We show here that the same limitations in general apply also to dynamic feedback controllers that are locally of first order. The proof relies partly on a fundamental limitation of localized relative feedback in networks of integrators of order three or higher, which we show to cause instability if the network grows beyond a certain finite size. 

    This result holds unless the controller can access measurements of its local state with respect to an absolute reference frame, in which case dynamic feedback in the form of distributed derivative or integral control can fundamentally improve performance. This case applies, for example, to frequency control in power networks. However, if the absolute state measurements are subject to noise, the advantage of the distributed integral controller in terms of its performance scaling is lost. We show that scalable integral control of networks in principle requires centralization or all-to-all communication. 

    For electric power networks, we show that performance in terms of transient power losses scales with the number of generator nodes in a network. However, in sharp contrast to the previous results, an increased connectivity does not in general improve performance. We discuss possible implications of these results in terms of the design of future power grids with increasingly distributed electricity generation. 

  • Disputas: 2019-01-25 10:30 H1, Stockholm
    Niazi Ardekani, Mehdi
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Numerical study of transport phenomena in particle suspensions2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Suspensions of solid particles in a viscous liquid are of scientific and technological interest in a wide range of applications. Sediment transport in estuaries, blood flow in the human body, pyroclastic flows from volcanos and pulp fibers in papermaking are among the examples. Often, these particulate flows also include heat transfer among the two phases or the fluid might exhibit a viscoelastic behavior. Predicting these flows and the heat transfer within requires a vast knowledge of how particles are distributed across the domain, how particles affect the flow field and finally how they affect the global behavior of the suspension. The aim of this work is therefore to improve the physical understanding of these flows, including the effect of physical and mechanical properties of the particles and the domain that bounds them.To this purpose, particle-resolved direct numerical simulations (PR-DNS) of spherical/non-spherical particles in different flow regimes and geometries are performed, using an efficient/accurate numerical tool that is developed within this work. The code is based on the Immersed Boundary Method (IBM) for the fluid-solid interactions with lubrication, friction and collision models for the close range particle-particle (particle-wall) interactions, also able to resolve for heat transfer equation in both Newtonian and non-Newtonian fluids.

    Several conclusions are drawn from this study, revealing the importance of the particle's shape and inertia on the global behavior of a suspension, e.g. spheroidal particles tend to cluster while sedimenting. This phenomenon is observed here for both particles with high inertia, sedimenting in a quiescent fluid and inertialess particles (point-like tracer prolates) settling in homogeneous isotropic turbulence. The mechanisms for clustering is indeed different between these two situations, however, it is the shape of the particles that governs these mechanisms, as clustering is not observed for spherical particles. Another striking finding of this work is drag reduction in particulate turbulent channel flow with disk-like spheroidal particles. Again this drag reduction is absent for spherical particles, which instead increase the drag with respect to single-phase turbulence. In particular, we show that inertia at the particle scale induces a non-linear increase of the heat transfer as a function of the volume fraction, unlike the case at vanishing inertia where heat transfer increases linearly within the suspension.

  • Disputas: 2019-01-25 13:00 Kollegiesalen, Stockholm
    Gürdür, Didem
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Mekatronik.
    Data and Visual Analytics for Cyber-physical Systems: Current Situation and Strategies for Action2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Today, cyber-physical systems (CPS) exist everywhere in different sizes, with different functionalities and capabilities. CPS often support critical missions that have significant economic and societal importance. They require software systems, communications technologies, sensors/actuators, embedded technologies, and physical systems to work together seamlessly, and they are seen as a driving force behind digital transformation. This dissertation describes the research work carried out to investigate applicability of data and visual analytics for CPS to overcome three main challenges: interoperability, complexity, and sustainability.

    To this end, several case studies are used to effectively implement and test different data and visual analytics solutions to aid stakeholders when they make decisions on interoperability, complexity, and sustainability for CPS. These studies raised questions about issues found to be of importance for the success of data and visual analytics approaches, including accessibility, availability, quality, volume, and variety of data—issues. Moreover, additional studies are used to show the benefits of blending different approaches, such as systems thinking and design thinking, and the current data analytics readiness of the Swedish industry is assessed through a questionnaire completed by more than a hundred respondents. 

    The data and visual analytics are positioned between digitalization and machine intelligence as a research focus. Data and visual analytics is the next step after digitalizing the information by adding analytical capabilities to the data. It is also an important phase before developing machine intelligence applications. Earlier studies clearly show that only a fraction of companies have machine intelligence applications across the enterprise. One important reason behind this is the lack of strong digital capabilities that big data and advanced data analytics technologies could bring. The findings of the work carried out as part of this thesis show the importance of this middle phase—data and visual analytics—for the success of not only the CPS but also these two concepts—digitalization and machine intelligence.

    This thesis concludes by highlighting that currentdata and visual analytics approaches in CPS are closely dependent onthe availability, accessibility, quality, volume, and variety of the data. Notably, the huge amount of industrial data that exists in CPS manufacturers data repositories does not always mean that this data is useful, especially for analytical purposes. To this end, firstly, the CPS industry should concentrate its efforts to collect useful data that will benefit the industry by providing analytical insight intothe environments where CPS is produced and operated. Secondly, the industry should make necessary organizational changes such as considering to employ data scientists, analysts, and business intelligence developers and make data accessible tothese people for further usage. Thirdly, the data management procedures and data analytics roadmaps of companies should be created and shared with other employees, and necessary mechanisms needto be considered to improve and guarantee the quality of the data. Lastly, the variety of data needs to be addressed by the industry. 

    Data and visual analytics provides an opportunity to extract patterns; to evaluate the interoperability, complexity, and sustainability; to create an overview of the current challenge by providing different viewpoints adapted to different stakeholders, focusing on key concerns for the respective stakeholder; to optimize performance, automation, and cooperation of distributed CPS, development environment, and teams; and overall, to improve any of the challenges that are mentioned above by, basically, providing a better understanding.

    To this end, I suggest that the industry discuss the next step after digitalization and address the challenges related to the availability, accessibility, quality, volume, and variety of data by considering user-centric approaches and organizational needs of the future development and manufacturing environments. The CPS industry should plan and act on these challenges as part of its data analytics strategies to expedite the machine intelligence applications of the future.

  • Disputas: 2019-02-01 10:00 Kollegiesalen, Stockholm
    Choutri, Salah Eddine
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Topics in Mean-Field Control and Games for Pure Jump Processes2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is the collection of four papers addressing topics in stochastic optimal control, zero-sum games, backward stochastic differential equations, Pontryagin stochastic maximum principle and relaxed stochastic optimal control.

    In the first two papers, we establish existence of Markov chains of mean-field type, with countable state space and unbounded jump intensities. We further show existence of nearly-optimal controls and, using a Markov chain backward SDE approach, we derive conditions for existence of an optimal control and a saddle-point for a zero-sum differential game associated with risk-neutral and risk-sensitive payoff functionals of mean-field type, under dynamics driven by Markov chains of mean-field type. Our formulation of the control problems is of weak-type, where the dynamics are given in terms of a family of probability measures, under which the coordinate process is a pure jump process with controlled jump intensities.

    In the third paper, we characterize the optimal controls obtained in the first pa-per by deriving sufficient and necessary optimality conditions in terms of a stochastic maximum principle (SMP). Finally, within a completely different setup, in the fourth paper we establish existence of an optimal stochastic relaxed control for stochastic differential equations driven by a G-Brownian motion.