1 - 60 of 60
rss atomLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
  • Public defence: 2017-05-29 10:15 F3, Stockholm
    Sack, Stefan
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental and Numerical Multi-port Eduction for Duct Acoustics2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sound generation and propagation in circular ducts for frequencies beyond the cut-on frequencies of several higher order acoustic modes is investigated. To achieve this, experimental and numerical set-ups are designed and used to research aeroacoustic interactions between in-duct components and to conceive noise mitigation strategies.

    Describing in-duct sound for frequencies with a moderate number of propagating modes is important, for example, for improving the noise emission from mid-size ventilation systems. Challenges that are largely unacknowledged in the literature involve efficient test rig design, quantification of limits in the methods, numerical modelling, and development of effective noise mitigation strategies for higher order modes.

    In this thesis, in-duct sound is mapped on a set of propagating pressure eigenmodes to describe aeroacoustic components as multi-ports with sound scattering (passive properties) and a source strength (active properties). The presented analysis includes genetic algorithms and Monte Carlo Methods for test rig enhancement and evaluation, multi-port network predictions to identify model limitations, and scale resolving (IDDES) and Linearized Navier Stokes computations for numerical multi-port eduction and the silencer design.

    It is first shown that test rig optimization improves the quality of multi-port data significantly. Subsequently, measurements on orifice plates are used to test the network prediction model. The model works with high accuracy for two components that are sufficiently separated. For small separations, strong coupling effects are observed for the source strength but not for the scattering of sound. The measurements are used for numerical validation, which gives reliable results for coupled and uncoupled systems. The total acoustic power of tandem orifices is predicted with less than 2 dB deviation and the passive properties for most frequencies with less than 5 % difference from the measurement. The numerical (FEM) models are also used to design a completely integrated silencer for spinning modes that is based on micro-perforated plates and gives broadband attenuation of 3-6 dB per duct diameter silencer length.

    The multi-port method is a powerful tool when describing aerodynamically decoupled in-duct components in the low- to mid-frequency range. Due to a robust passive network prediction, multi-port methods are particular interesting for the design of silencer stages. Furthermore, the demonstrated applicability to numerical data opens novel application areas.

  • Public defence: 2017-05-29 12:00 Sal C, Stockholm
    Xhagjika, Vamis
    KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS. Polytechnic University of Catalonia.
    Resource, Data and Application Management for Cloud Federations and Multi-Clouds2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Distributed Real-Time Media Processing refers to classes of highly distributed, delay no-tolerant applications that account for the majority of the data traffic generated in the world today. Real-Time audio/video conferencing and live content streaming are of particular research interests as technology forecasts predict video traffic surpassing every other type of data traffic in the world in the near future. Live streaming refers to applications in which audio/video streams from a source need to be delivered to a set of geo-distributed destinations while maintaining low latency of stream delivery. Real-time conferencing platforms are application platforms that implement many-to-many audio/video real-time communications. Both of these categories exhibit high sensitivity to both network state (latency, jitter, packet loss, bit rate) as well as stream processing backend load profiles (latency and jitter introduced as Cloud processing of media packets). This thesis addresses enhancing real-time media processing both at the network level parameters as well as Cloud optimisations.

    We provide a novel, bandwidth management algorithm, for cloud services sharing the same network infrastructure, which provides a 2x improvement in system stability. Further examining network impact on cloud services, we provide a novel hybrid Cloud-Network distributed Cloud architecture to enable locality aware, application enhancements. This architecture led to a multi-cloud management overlay algorithm that maintains low management overhead on large scale cloud deployments. On the application level we provide a study of Media Quality parameters for a WebRTC enabled Media Cloud back-end, and provide patterns of quality metrics with respect to back-end stream load and network parameters. Additionally we empirically show that a "minimal load" algorithm for stream allocation, outperforms other Rotational, or Static Threshold based algorithms.

  • Public defence: 2017-05-30 10:00 F3, Stockholm
    Miterev, Maxim
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Organizing project-based operations: The interplay of content, context and social processes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Project-based organizations (PBOs) are becoming increasingly widespread and important for the modern economy and society. Thus, they attact significant scholarly attention to their distinctive features. The unit of analysis employed by the majority of the studies is the project-based organization as a whole. Hence, the locus of attention stays at the organizational level, whereas project-related effects are discussed in terms of aggregate properties. With very few exceptions, projects as distinct entities do not feature prominently in the discussion of project-based organizations.

    This observation creates an interesting paradox. In particular, when projects are discussed as separate units of analysis, their complex organizational dynamics, idiosyncrasies, and institutional embeddedness are among important loci of attention. However, when projects and project collections are discussed within the context of the PBO, the very same aspects tend to be downplayed. Most commonly, projects are either neglected or implicitly assumed to be homogeneous, interchangeable atomic units without internal structure or dynamics, obediently following orders of the parent organizations. Their internal organizational properties are overlooked and the individual-level variables are assumed to have little or no influence on the project outcomes. This thesis questions these assumptions and posits that understanding the dynamics at the project operations level might have important implications for explaining the effectiveness of management arrangements in the PBO.

    In particular, this thesis aims to explore the factors that shape project-based operations in the setting of the project-based organization. The thesis examines three particular factors which affect organizing of the project-based operations: (1) the content of operations; (2) the context of operations; and (3) the social processes at the operational level. Structurally, the thesis comprises a cover essay and four appended papers (three of them published in international peer-reviewed journals).

    Largely inductive in nature, the thesis builds on two research studies. The first study represents an in-depth “insider” case study of project-based operations in the Operations division of a large pharmaceutical company. It employs a combination of data collection methods, including semi-structured interviews, participant observations, and document analysis. The second study represents a structured framework-based literature review. Recognizing the organizational properties of projects, the thesis draws upon several literature streams within organization theory and design to analyze the empirical data. The results elaborate how the organizing of project-based operations in the PBO is shaped by the interplay between the content, intra-organizational and wider institutional contexts, as well as endogenous social processes.

    The thesis contributes to the literature on project-based organizations by developing an institutional, as well as extending a contingency perspective on organizing project-based operations. Further, the results call for revisiting the conceptualization of the PBO by questioning the view of projects as atomic and homogeneous units. Finally, the thesis contributes to the literature by developing an organization design perspective on the PBO.

    In terms of managerial implications, the thesis offers a few frameworks which can be used to support the decision-making process in a PBO. In particular, Paper I develops a contingency model of program management competences (the 3C model), Paper II derives a framework that can help PBO managers in evaluating the sources of isomorphic pressure on individual projects and programs, while Paper IV puts forth an organization design model for the PBO. At a more general level, Paper II discusses how the identified isomorphic processes within the PBO can limit flexibility, innovation, and efficiency. Finally, the cover essay discusses the important factors that need to be scrutinized in order to assess organizing of the project-based operations, such as the technical content, the project landscape and social landscape or the influence of institutionalised practices and models.

  • Public defence: 2017-05-30 10:00 D3, Stockhlolm
    Peerlings, Luck
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Assessing precision and accuracy in acoustic scattering matrix measurements2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Acoustic scattering matrices are used to characterize the influence of inline duct elements on the acoustic wave propagation in wave guides.When measuring the properties of these matrices, errors are always present in the results and need to be characterized to make valid statements on the correspondence between model predictions and measurements.In this study the random and systematic errors in acoustic scattering matrix measurements are investigated.Several aspects of the measurement cycle are examined, starting with the determination of the random error on the measured transfer functions between the acoustic source signal and the measured acoustic pressure.The second aspect is the determination of the random error on the scattering matrix coefficients. They are mathematically derived from the measurement data and the error has to be propagated from the data to the coefficients.This is done using uncertainty analyses and the use of linear methods to calculate the uncertainty of the coefficients is investigated.The impedance tube is an essential element of acoustic scattering matrix measurements and the third topic is a description of the systematic errors that can occur in these tubes. The effect of various systematic errors are shown, together with methods to account or reduce them.It is shown that there are still systematic errors remaining, and hypotheses to the source of these errors are discussed.In the last part, the knowledge is put to use to measure the aero-acoustic interaction present at a sudden area expansion.It is shown that the measured acoustic absorption agrees qualitatively with the models, however the deviation between the measurements and predictions are larger than the uncertainty of the measurements.The end correction agrees well with the models at high Strouhal numbers, but the scatter on the measurements at lower Strouhal numbers is too large to identify flow-acoustic interaction effects on the end correction.

    The full text will be freely available from 2017-09-01 22:33
  • Public defence: 2017-05-30 13:00 F3, Stockholm
    Mao, Huina
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Numerical and Experimental Studies of Deployment Dynamics of Space Webs and CubeSat Booms2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, experiments and simulations are performed to study the deployment dynamics of space webs and space booms, focusing on the deployment and stabilization phases of the space web and the behavior of the bi-stable tape spring booms after long-term stowage.

    The space web, Suaineadh, was launched onboard the sounding rocket REXUS-12 from the Swedish launch base Esrange in Kiruna on 19 March 2012. It served as a technology demonstrator for a space web. A reaction wheel was used to actively control the deployment and stabilization states of the 2×2 m2 space web. After ejection from the rocket, the web was deployed but entanglements occurred since the web did not start to deploy at the specified angular velocity. The deployment dynamics was reconstructed by simulations from the information recorded by inertial measurement units and cameras. Simulations show that if the web would have started to deploy at the specified angular velocity, the web would most likely have been deployed and stabilized in space by the motor, reaction wheel and controller used in the experiment. A modified control method was developed to stabilize the out-of-plane motions before or during deployment. New web arms with tape springs were proposed to avoid entanglements.

    A deployable booms assembly composed of four 1-m long bi-stable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The deployment dynamics and reliability of the SEAM boom design after long-term stowage were tested by on-ground experiments. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic strain energy relaxation, and other factors that act to decrease the deployment force. In order to mitigate the viscoelastic effects and thus ensure self-deployment, different tape springs were designed, manufactured and tested. A numerical model was used to assess the long-term stowage effects on the deployment capability of bi-stable tape springs including the friction, nonlinear-elastic and viscoelastic effects. A finite element method was used to model a meter-class fully coiled bi-stable tape spring boom and verified by analytical models.

  • Public defence: 2017-06-01 10:00 Sal F3, Stockholm
    Jonsson, Peder
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Kommunikationsmodeller inom public relations2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Once a year for over forty years public relations’ practitioners in Sweden gathers, the political week in Almedalen, in the town of Visby. There they exchange knowledge and experience on all types of subjects using different and common communication models whether they are aware of them or not. The research on communication models is sparse, with one exception: Grunig’s model. Both practitioners and researches believe them to be important, even strategic. But too little knowledge about the models as such negatively impacts the understanding of public relations’ activities. It also contributes to the view that public relations is frittered.

    The thesis studies and analyses communication models of public relations. Models have been created by theorists and practitioners to describe the phenomenon, to understand communication as such and to facilitate communication between humans. The thesis addresses basic questions such as which models there are, where they stem from, who the originators were and the characteristics of each respective model. The basis of the study is comprehensive Anglo-American literature. All in all, over twenty different models have been analyzed in three different ways, i.e. the structure of a model, its historical deposits (sediment) and the application of the model. The result is manifold, since many characteristics form ten attributes and three families of models (a reduction).

    The characteristics can be seen as the models’ building blocks, e.g. the direction of the communication, the number of contacts and synchronism. Three model families are built on three differentiating characteristics, and the families are named correspondingly. Directional model (Riktningsmodellen), the Co-orientational model (Saminriktningsmodellen) and the Connectivity model (Konnektivitetsmodellen). The classification is of course not set in stone. It should be regarded as a first step to reduce the number of models in use and concentrate on the important characteristics of the models that help public relations researchers and professionals to solve problems and theorists to explain, foresee or guide to better public relations.

    Finally, five areas of future research are presented: a multinational study of models, a study of practitioners’ model use, a deeper history study according the concept of sediment, a notational system for models and, last but not least, a development of the Connectivity model. The last subject is the one that once inspired me to write a thesis.

  • Public defence: 2017-06-02 09:00 Kollegiesalen, Stockholm
    Morfeldt, Johannes
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Tracking Emissions Reductions and Energy Efficiency in the Steel Industry2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The iron and steel industry has become increasingly globalised. Market conditions are also changing and de-carbonisation of production is challenging.

    The objective of this thesis is to assess how energy efficiency and greenhouse gas emissions reductions can be promoted and effectively monitored in the steel industry. The thesis contributes with analyses based on the Malmquist Productivity Index for a top-down analysis of the energy efficiency of EU Member States’ iron and steel production, and Partial Least Squares regression for bottom-up assessments of different monitoring tools. The thesis also contributes with a scrap availability assessment module to enhance the energy system model ETSAP-TIAM.

    The first phase of the research showed that future production needs to shift towards innovative low-CO2 technologies even when all available recycled material is fully used. Techniques using carbon capture and storage (CCS) as well as hydrogen-based technologies can be expected to become economically viable under tightened climate policies.

    The second phase of the research showed that current indicators are insufficient. System boundaries of energy use and emissions data do not align with production statistics. Indicators based on energy use or emissions in relation to production in physical terms may be useful to track specific processes. However, current indicators fail to reflect the companies’ product mix. Enhanced energy and climate indicators that adjust for the product mix provide better estimates while failing to reflect the increasing globalisation.

    Effective monitoring of industrial transformation will be increasingly important as pressure from climate policy via global CO2-pricing is unlikely in the short term. Current or enhanced indicators do not fully capture industrial transformation and are not recommended. Future research should focus on defining indicators to estimate energy use and emissions along industrial value chains in climate policy contexts.

  • Public defence: 2017-06-02 10:00 Sal B2, Stockholm
    Delandar, Arash Hosseinzadeh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Modeling defect structure evolution in spent nuclear fuel container materials2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Materials intended for disposal of spent nuclear fuel require a particular combination of physical and chemical properties. The driving forces and mechanisms underlying the material’s behavior must be scientifically understood in order to enable modeling at the relevant time- and length-scales. The processes that determine the mechanical behavior of copper canisters and iron inserts, as well as the evolution of their mechanical properties, are strongly dependent on the properties of various defects in the bulk copper and iron alloys.

    The first part of the present thesis deals with precipitation in the cast iron insert. A nodular cast iron insert will be used as the inner container of the spent nuclear fuel. Precipitation is investigated by computing effective interaction energies for point defect pairs (solute–solute and vacancy–solute) in bcc iron using first-principles calculations. The main considered impurities in the iron matrix include 3sp (Si, P, S) and 3d (Cr, Mn, Ni, Cu) solute elements. By computing interaction energies possibility of formation of different second phase particles such as late blooming phases (LBPs) in the cast iron insert is evaluated.

    The second part is devoted to the fundamentals of dislocations and their role in plastic deformation of metals. Deformation of single-crystal copper under high strain rates is simulated by employing dislocation dynamics (DD) method to examine the effect of strain rate on mechanical properties as well as dislocation microstructure development.

    Creep deformation of copper canister at low temperatures is studied. The copper canister will be used in the long-term storage of spent nuclear fuel as the outer shell of the waste package to provide corrosion protection. A glide rate is derived based on the assumption that at low temperatures it is controlled by the climb rate of jogs on the dislocations. Using DD simulation creep deformation of copper at low temperatures is modeled by taking glide but not climb into account. Moreover, effective stresses acting on dislocations are computed using the data extracted from DD simulations.

  • Public defence: 2017-06-02 10:00 D1, Stockholm
    Kerres, Bertrand
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Competence Center for Gas Exchange (CCGEx).
    On Stability and Surge in Turbocharger Compressors2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Turbochargers are used on many automotive internal combustion engines to increase power density. The broad operating range of the engine also requires a wide range of the turbocharger compressor. At low mass flows, however, turbo compressor operation becomes unstable and eventually enters surge. Surge is characterized by large oscillations in mass flow and pressure. Due to the associated noise, control problems, and possibility of mechanical component damage, this has to be avoided.

    Different indicators exist to classify compressor operation as stable or unstable on a gas stand. They are based on pressure oscillations, speed oscillations, or inlet temperature increase. In this thesis, a new stability indicator is proposed based on the Hurst exponent of the pressure signal. The Hurst exponent is a number between zero and one that describes what kind of long-term correlations are present in a time series.

    Data from three cold gas stand experiments are analyzed using this criterion. Results show that the Hurst exponent of the compressor outlet pressure signal has good characteristics. Stable operation is being indicated by values larger than 0.5. As compressor operation moves towards the surge line, the Hurst exponent decreases towards zero. An additional distinction between the long-term correlations of small and large amplitude fluctuations by means of higher order Hurst exponents can be used as an early warning indicator.

    Further tests using compressor housing accelerometers show that the Hurst exponent is not a good choice for real-time surge detection on the engine. Reasons are the long required sampling time compared to competing methods, and the fact that other periodically repeating oscillations lead to Hurst exponents close to zero independent of compressor operation.

  • Public defence: 2017-06-02 10:00 FB52, Stockholm
    Wang, Xu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Computational Studies of Structures and Binding Properties of Protein-Ligand Complexes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Proteins are dynamic structural entities that are involved in many biophysical processes through molecular interactions with their ligands. Protein-ligand interactions are of fundamental importance for computer-aided drug discovery. Due to the fast development in computer technologies and theoretical methods, computational studies are by now able to provide atomistic-level description of structures, thermodynamic and dynamic properties of protein-ligand systems, and are becoming indispensable in understanding complicated biomolecular systems. In this dissertation, I have applied molecular dynamic (MD) simulations combined with several state of the art free-energy calculation methodologies, to understand structures and binding properties of several protein-ligand systems.

    The dissertation consists of six chapters. In the first chapter, I present a brief introduction to classical MD simulations, to recently developed methods for binding free energy calculations, and to enhanced sampling of configuration space of biological systems. The basic features, including the Hamiltonian equations, force fields, integrators, thermostats, and barostats, that contribute to a complete MD simulation are described in chapter 2. In chapter 3, two classes of commonly used algorithms for estimating binding free energies are presented. I highlight enhanced sampling approaches in chapter 4, with a special focus on replica exchange MD simulations and metadynamics, as both of them have been utilized in my work presented in the chapter thereafter. In chapter 5, I outlined the work in the 5 papers included in the thesis. In paper I and II, I applied, respectively, the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) and alchemical free energy calculation methods to identify the molecular determinant of the affibody protein ZAb3 bound to an amyloid b peptide, and to investigate the binding profile of the positive allosteric modulator NS-1738 with the α7 acetylcholine-binding protein (α7-AChBP protein); in paper III and VI, unbiased MD simulations were integrated with the well-tempered metadynamics approach, with the aim to reveal the mechanism behind the higher selectivity of an antagonist towards corticotropin-releasing factor receptor-1 (CRF1R) than towards CRF2R, and to understand how the allosteric modulation induced by a sodium ion is propagated to the intracellular side of the d-opioid receptor; in the last paper, I proved the structural heterogeneity of the intrinsically disordered AICD peptide, and then employed the bias-exchange metadynamics and kinetic Monte Carlo techniques to understand the coupled folding and binding of AICD to its receptor Fe65-PTB2. I finally proposed that the interactions between AICD and Fe65-PTB2 take place through an induced-fit mechanism. In chapter 6, I made a short conclusion of the work, with an outlook of computational simulations of biomolecular systems.

  • Public defence: 2017-06-02 10:00 M402, Borås
    Ferreira, Javier
    KTH, School of Technology and Health (STH), Medical Engineering. Högskolan i Borås.
    Modular textile-enabled bioimpedance system for personalized health monitoring applications2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A growing number of factors, including costs, technological advancements, ageing populations, and medical errors, are leading industrialized countries to invest in research on alternative solutions to improve their health-care systems and increase patients’ quality of life. Personal health systems (PHS) examplify the use of information and communication technologies that enable a paradigm shift from the traditional hospital-centered healthcare delivery model toward a preventive and person-centered approach. PHS offer the means to monitor a patient’s health using wearable, portable or implantable systems that offer ubiquitous, unobtrusive biodata

    acquisition, allowing remote monitoring of treatment and access to the patient’s status. Electrical bioimpedance (EBI) technology is non-invasive, quick and relatively affordable technique that can be used for assessing and monitoring different health conditions, e.g., body composition assessments for nutrition. When combined with state-of-the-art advances in sensors and textiles, EBI technologies are fostering the implementation of wearable bioimpedance monitors that use functional garments for personalized healthcare applications. This research work is

    focused on the development of wearable EBI-based monitoring systems for ubiquitous health monitoring applications. The monitoring systems are built upon portable monitoring instrumentation and custom-made textile electrode garments.

    Portable EBI-based monitors have been developed using the latest material technology and advances in system-on-chip technology. For instance, a portable EBI spectrometer has been validated against a commercial spectrometer for total body composition assessment using functional textile electrode garments. The development of wearable EBI-based monitoring units using functional garments and dry textile electrodes for body composition assessment and respiratory monitoring has been shown to be a feasible approach. The availability of these measurement systems indicates progress toward the real implementation of personalized healthcare systems.

  • Public defence: 2017-06-02 13:00 FD5, Stockholm
    Fogelqvist, Emelie
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Laboratory Soft X-Ray Cryo Microscopy: Source, System and Bio Applications2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Soft x-ray microscopes routinely perform high-resolution 3D imaging of biological cells in their near-native environment with short exposure times at synchrotron radiation facilities. Some laboratory-sized microscopes are aiming to make this imaging technique more accessible to a wider scientific community. However, these systems have been hampered by source instabilities hindering routine imaging of biological samples with short exposure times.

    This Thesis presents work performed on the Stockholm laboratory x-ray microscope. A novel heat control system has been implemented, improving the stability of the laser-produced plasma source. In combination with recent upgrades to the imaging system and an improved cryofixation method, the microscope now has the capability to routinely produce images with 10-second exposure time of cryofixed biological samples. This has allowed for tomographic imaging of cell autophagy and cell-cell interactions. Furthermore, a numerical 3D image formation model is presented as well as a novel reconstruction approach dealing with the limited depth of focus in x-ray microscopes.

  • Public defence: 2017-06-02 13:00 F3, Stockholm
    Perez-Ramos, María Isabel
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    A QUEST FOR ENVIRONMENTAL SOVEREIGNTY: Chicana/o Literary Experiences of Water (Mis)Management and Environmental Degradation in the US Southwest2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The U.S. Southwest is a semi-arid region affected by numerous environmental problems. Chicana/o communities have been directly affected by such problems, especially ever since the region was annexed from Mexico by the United States in the mid-nineteenth century. From this moment onwards they lost their environmental sovereignty, mostly through their dispossession of the natural resources.

     

    This environmental humanities dissertation focuses on the ethics, politics, and practices around water (management), for water is a key natural resource and a central element of Chicana/o cultural identity. It explores the ways in which Chicana/o culture is interconnected with environmental practices and sites in subaltern literary works about the Chicana/o experience. It investigates how the hegemonic Anglo-American environmental, political, and economic practices have challenged and undermined Chicana/o culture, identity, and wellbeing, and how this has been addressed in fiction; and it questions whether establishing such a connection adds any useful insights to the larger discussion on the global socio-environmental crisis. This dissertation also analyzes the writer activist character of the subaltern narratives of the corpus, with attention to the relevance of rhetoric in subverting and constructing environmental discourses and ethics.

     

    By examining regional and border narratives, as well as fiction and non-fiction narratives about the socio-environmental struggles of other ethnic minorities in the Southwest and in other parts of the world, this dissertation puts literature about the Chicana/o experience in a regional, national, and transnational context. It moreover explores the pivotal role of literature in reclaiming environmental sovereignty, in asserting cultural identities, and in countering the environmental crisis by imagining alternative managerial practices and socio-environmental relations, as much as in challenging cultural hegemonies.

  • Public defence: 2017-06-02 13:00 T2, Huddinge
    Giordano, Chiara
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Development of an Anisotropic Finite Element Head Model for Traumatic Brain Injury Prediction2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Traumatic brain injury (TBI) is a worldwide health care problem with very high associatedmorbidity and mortality rates. In particular, the diagnosis of TBI is challenging: symptomsoverlap with other pathologies and the injury is typically not visible with conventionalneuroimaging techniques.Finite element (FE) head models can provide valuable insight into uncovering themechanism underlying brain damage. These models enable the calculation of tissue loadsand deformation patterns, which are thought to be associated with the injury. Measuresbased on tissue strain or invariants of the strain tensor are used as injury predictors and riskinjury curves can be inferred to establish the tolerance of the human head to external loads.However, while in-vitro research shows that the vulnerability to injury is due to highlyorganized structure in white matter tracts, the majority of the current FE models model thebrain as isotropic and homogenous. The deformation of white matter tracts is not calculated.The aim of this doctoral thesis was to incorporate the effects of inhomogeneity andanisotropy of brain tissue into injury analysis. Based on in-vitro experimental evidence, thestrain in the direction of the axons (axonal strain) was proposed as a new, more anatomicallyrelevant, injury predictor. The initial hypothesis to investigate was that an FE anisotropichead model is a better tool to represent TBI because it is more biofidelic in describing thelocal mechanism of axonal impairment.The studies reported in this thesis describe a method for implementing the orientation of thewhite matter tracts in an anisotropic constitutive law for FE modeling. Results from thestudies suggested that the anisotropy of the brain significantly affected the injury predictionsof an FE head model. For an injury dataset from the American National Football League, thepeak of axonal strain - MAS - was found to be a better predictor of injury than isotropic localor global predictors. Finally, based on 27 cases of intracranial pressure, relative skull-brainmotion and brain deformation, the introduction of the brain anisotropy in the FE modelpartially enhanced the biofidelity of the simulations. However, given that the enhancementin biofidelity was not major, it was concluded that further research is necessary forunderstanding the relationship between tissue-level loading and axonal injury.

  • Public defence: 2017-06-02 14:00 Q2, Stockholm
    Yuan, Yunxia
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Royal Institute of Technology KTH.
    Attitude and Trajectory Estimation for Small Suborbital Payloads2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sounding rockets and small suborbital payloads provide a means for research in situ of the atmosphere and ionosphere. The trajectory and the attitude of the payload are critical for the evaluation of the scientific measurements and experiments. The trajectory refers the location of the measurement, while the attitude determines the orientation of the sensors.

    This thesis covers methods of trajectory and attitude reconstruction implemented in several experiments with small suborbital payloads carried out by the Department of Space and Plasma Physics in 2012--2016.

    The problem of trajectory reconstruction based on raw GPS data was studied for small suborbital payloads. It was formulated as a global least squares optimization problem. The method was applied to flight data of two suborbital payloads of the RAIN REXUS experiment. Positions and velocities were obtained with high accuracy.

    Based on the trajectory reconstruction technique, atmospheric densities, temperatures, and horizontal wind speeds below 80 km were obtained using rigid free falling spheres of the LEEWAVES experiment. Comparison with independent data indicates that the results are reliable for densities below 70 km, temperatures below 50 km, and wind speeds below 45 km.

    Attitude reconstruction of suborbital payloads from yaw-pitch-roll Euler angles was studied. The Euler angles were established by two methods: a global optimization method and an Unscented Kalman Filter (UKF) technique. The comparison of the results shows that the global optimization method provides a more accurate fit to the observations than the UKF.

    Improving the results of the falling sphere experiments requires understanding of the attitude motion of the sphere. An analytical consideration was developed for a free falling and axisymmetric sphere under aerodynamic torques. The motion can generally be defined as a superposition of precession and nutation. These motion phenomena were modeled numerically and compared to flight data.

    The full text will be freely available from 2017-06-02 14:00
  • Public defence: 2017-06-07 13:00 Sal F3, Stockholm
    Liljenberg, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Quantum Chemical Studies of Aromatic Substitution Reactions2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, density functional theory (DFT) is used to investigate the mechanisms and reactivities of electrophilic and nucleophilic aromatic substitution reactions (SEAr and SNAr respectively). For SEAr, the σ-complex intermediate is preceded by one (halogenation) or two (nitration) π-complex intermediates. Whereas the rate-determining transition state (TS) for nitration resembles the second π-complex, the corresponding chlorination TS is much closer to the σ-complex. The last step, the expulsion of the proton, is modeled with an explicit solvent molecule in combination with PCM and confirmed to be a nearly barrierless process for nitration/chlorination and involves a substantial energy barrier for iodination. It is also shown for nitration that the gas phase structures and energetics are very different from those in polar solvent. The potential energy surface for SNAr reactions differs greatly depending on leaving group; the σ-complex intermediate exist for F-/HF, but for Cl-/HCl or Br-/HBr the calculations indicate a concerted mechanism. These mechanistic results form a basis for the investigations of predictive reactivity models for aromatic substitution reactions. For SEAr reactions, the free energy of the rate-determining TS reproduces both local (regioselectivity) and global reactivity (substrate selectivity) with good to excellent accuracy. For SNAr reactions good accuracies are obtained for Cl-/HCl or Br-/HBr as leaving group, using TS structures representing a one-step concerted mechanism. The σ-complex intermediate can be used as a reactivity indicator for the TS energy, and for SEAr the accuracy of this method varies in a way that can be rationalized with the Hammond postulate. It is more accurate the later the rate-determining TS, that is the more deactivated the reaction. For SNAr reactions with F-/HF as leaving group, the same method gives excellent accuracy for both local and global reactivity irrespective of the degree of activation.

  • Public defence: 2017-06-07 13:00 Room T1 (Emmy Rappesalen), Stockholm
    Lind, Carl
    KTH, School of Technology and Health (STH), Health Systems Engineering, Ergonomics.
    Assessment and design of industrial manual handling to reduce physical ergonomics hazards: – use and development of assessment tools2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Despite efforts of reducing harmful physical ergonomics exposures related to manual handling, the occurrence of heavy or repetitive manual handling, and non-neutral postures is high in many occupational sectors. To reduce these exposures, interventions and job design strategies can utilize risk assessment. A need was identified of an observation-based tool which supported occupational health and safety practitioners for assessments of risk factors related to manual handling.

    The aim of this thesis was to explore the use and important usability-related aspects of observation-based assessment tools among professional ergonomists, and to develop new research based assessment and screening tools, to present their scientific basis and to evaluate their reliability and usability. A web-based questionnaire was employed to gain knowledge on the use and usability aspects of risk assessment tools among ergonomists in Sweden. The assessment tools RAMP I and RAMP II were developed in an iterative process, including literature searches, expert group judgments, and with input from more than 80 practitioners. The reliability and usability evaluations included assessments and ratings by practitioners.

    The thesis points to a low use of several internationally spread assessment tools among Swedish ergonomists, and a relatively higher use of tools promoted by the Swedish Work Environment Authority. Several usability-related aspects were identified as important, such as being easy and quick to use, its ability to communicate and visualize the results, and its ability to facilitate improvement measures. The developed tools support assessment of a broad range of risk factors related to manual handling. The thesis supports that assessments with acceptable reliability can be achieved for the majority of items of the two developed tools. The thesis supports that the tools are usable in supporting risk assessments targeting risk factors related to industrial manual handling.

  • Public defence: 2017-06-08 10:00 Sal F3, Stockholm
    Levi, Lea
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. Department of Physical Geography and the Bolin Center for Climate Research, Stockholm University, Stockholm, Sweden; Department of Applied Hydraulics, Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia.
    Data-driven analysis of water and nutrient flows: Case of the Sava River Catchment and comparison with other regions2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A growing human population and demands for food, freshwater and energy are causing extensive changes in the water and biogeochemical cycles of river catchments around the world. Addressing and investigating such changes is particularly important for transboundary river catchments, where they impose additional risk to a region’s stability. This thesis investigates and develops data-driven methodologies for detecting hydro-climatic and nutrient load changes and their drivers with limited available data and on different catchment scales. As a specific case study, we analyze the Sava River Catchment (SRC) and compare its results with other world regions. A past–present to future evaluation of hydro-climatic data is done on the basis of a water balance approach including analysis of historic developments of land use and hydropower development data and projections of the Coupled Model Intercomparison Project, Phase 5 (CMIP5) output. Using observed water discharge and nutrient concentration data, we propose a novel conceptual model for estimating and spatially resolving total nitrogen (TN) and total phosphorus (TP) input and delivery-retention properties for a river catchment and its nested subcatchments, as well as detection of nutrient hotspots. The thesis identifies hydroclimatic change signals of hydropower-related drivers and finds consistency with other world regions. The proposed nutrient screening methodology provides a good distinction between human-related nutrient inputs and landscape-related transport influences on nutrient loading at subcatchment to catchment scale. A cross-regional comparison of the SRC data with the Baltic region shows similarity between nutrient-relevant indicators and driving socio-economic and hydro-climatic conditions. The study highlights a number of complexities with regard to CMIP5 model representation of water fluxes. The large intermodel range of CMIP5 future projections of fluxes calls for caution when using individual model results for assessing ongoing and future water and nutrient changes.

  • Public defence: 2017-06-08 10:00 Brinellsalen M311, Stockholm
    A Asif, Farazee M
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Circular Manufacturing Systems: A development framework with analysis methods and tools for implementation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The society today lives on the philosophy of ‘take-make-use-dispose.’ In the long run, this is not sustainable as the natural resources and the waste carrying capacity of the earth are limited. Therefore, it is essential to reduce dependency on the natural resources by decoupling the growth from the consumption. In this venture, both the society and the manufacturing industry have a vital role to play. The society needs to shift towards Circular Economy that rests upon the philosophy of ‘take-make-use-reuse’ and the manufacturing industry has to be a major stakeholder in this shift. Despite being proven to be both economically and environmentally beneficial, successful examples of circular systems are few today. This is primarily due to two reasons; firstly, there is a lack of systemic and systematic approach to guide industries and secondly, there is a lack of analysis methods and tools that are capable of assessing different aspects of circular manufacturing systems. Taking on to these challenges, the objective of this research is to bring forward a framework with methods and decision support tools that are essential to implement circular manufacturing systems. The initial conceptual framework with the systemic approach is developed based on extensive review and analysis of research, which is further adapted for industrial implementation. Systematic analysis methods, decision support and implementation tools are developed to facilitate this adaptation. This development has been supported by four cases from diverse manufacturing sectors. Behind each decision support tool, there are analysis methods built upon mainly system dynamics principles. These tools are based on simulation platforms called Stella and Anylogic. Among other things, these tools are capable of assessing the performance of closed-loop supply chains, consequences of resource scarcity, potential gains from resource conservation and overall economic and environmental performance of circular manufacturing systems.

  • Public defence: 2017-06-08 10:00 M3, Stockholm
    Mentis, Dimitris
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Spatially explicit electrification modelling insights: Applications, benefits, limitations and an open tool for geospatial electrification modelling2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Developing countries confront the challenge of generating more electricity to meet demands in a sustainable manner. According to the World Bank’s 2015 Global Tracking Framework, roughly 15% of world population (or 1.1 billion people) lack access to electricity, and many more rely on poor quality electricity supplies. In September 2015, the United Nations General Assembly adopted Agenda 2030 comprised of a set of 17 Sustainable Development Goals (SDGs) and defined by 169 targets. “Ensuring access to affordable, reliable, sustainable and modern energy for all by 2030” is the seventh goal (SDG7). While energy access refers to more than electricity, it is the central focus of this work.

    Models addressing electrification and access typically need large volumes of reliable energy-related data and information, which in most developing countries have been limited or not available. This paucity of information has decelerated energy planning in the developing World. That situation has fundamentally changed with increasing availability and application of Geographic Information Systems (GIS). GIS layers can provide location specific energy-related information that has not been previously accessible. The focus of this thesis lies on integrating a simple electricity supply model into GIS. In so doing a novel open source spatial electrification tool is developed. It estimates power capacity needs and associated investment (and other) costs for achieving universal access to electricity in developing countries.

    The dissertation includes a cover essay and six appended papers presenting quantitative methods on coupling selected aspects of GIS and energy systems. It strives to answer three key research questions. 

    The first research question is: What is the spatially explicit renewable energy potential that can be technically and economically exploited? This information is currently either missing or scattered in developing countries. The provision of low cost, locally available energy can provide a significant opportunity to empower a better standard of living. The first paper presents a GIS based approach to assess the onshore technical wind energy potential on the African continent by applying socioeconomic and geographic restrictions regarding the localization of wind farms and state of the art wind data analysis. The second paper builds on this knowledge and moves one step further by assessing the economic potential and providing cost indicators to assess the viability of wind power (this time in India). The third paper maps the economic wind power potential in Africa based on the methodologies developed in the two preceding papers. Not only wind power but most energy resources have a spatial nature and their availability is linked to geography. Evaluating these other energy sources (solar, hydro etc.) are included and analysed in Papers IV-VI.

    The second research question is: what is the least-cost set of technologies needed to meet different levels of electricity use accounting for different geographies? Increasing access to electricity effectively requires, inter alia, strategies and programmes that address and account for the geographical, infrastructural and socioeconomic characteristics of a country or region. Paper IV introduces a GIS based methodology to inform electrification planning. It builds on the previous work by taking into account the techno-economic wind, and other resource mapping. This methodology is applied in Nigeria in order to determine the least cost technology mix considering the country’s infrastructure and resource availability on a spatial basis. Paper V utilizes this method and in so doing demonstrates the importance of geospatial calculations in energy access planning. It highlights differences in investment estimates between alternate scenarios with regards to energy demand and technology deployment. Paper VI enhances this methodology and applies it to every square kilometre of Sub-Saharan Africa. The method is subsequently implemented in an Open Source Spatial Electrification Tool (OnSSET) to facilitate education, repeatability and further research.

    Finally, the third question is: Are there gains to be had by linking geographically explicit analysis with typical (non-spatially explicit) long term energy systems models? The work shows that not only do long-term systems models influence geospatially optimal technology deployment. But vice versa, their output influences long term systems models’ investment profile.  That is because the geospatial disaggregation allows for a better determination of grid versus off-grid connections, and in turn power demand on the national grid. This thesis demonstrates that energy system models should take into consideration the geographic dimension of energy-related parameters, as these play a fundamental role in determining the optimal energy system of a region.

  • Public defence: 2017-06-09 10:00 F3, Stockholm
    Linse, Charlotta
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Ambiguity at the heart of design work: Sensing and negotiating ambiguity in knowledge-creation work2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Ambiguities have long intrigued design and new product development (NPD) researchers: The fascination seems rooted in an endeavor to understand how design outcomes may be created despite the ambiguous nature of such work. There are several classic contributions on how to categorize, avoid and approach ambiguities. Some of the newer theories have also pointed to benefits arising from temporarily sustaining ambiguity.

    Little research has considered how ambiguities emerge, how ambiguities are sensed by practitioners, and the actions the practitioners take, either to harness or to reduce the generative and transformative power of ambiguity, however.

    This is unfortunate, since ambiguities are at the heart of such knowing-work. If one does not know how to sense the emergence of ambiguities and act to reduce or harness their generative and transformative power, i.e. negotiate ambiguity, the work might become unproductive, confused, uncreative, and might require more energy and attention.

    The purpose of this research is to portray how ambiguities emerge and are negotiated in knowing-work. This is achieved by drawing on two cases of design and NPD work, from practice epistemology.

    The results indicated that the emerging ambiguities changed in the ongoing work, some being reduced, others becoming obsolete or persisting. The results also included five generalized actions to negotiate ambiguity: (1) constructing points of references, (2) mediating between perspectives, (3) anchoring in expertise, (4) disarming future resistance, and (5) creating shared visions.

    This research has concluded that the very essence of design work concerns the emergence and fading away of ambiguity. The actions taken to negotiate ambiguity mediates the emergence of the design outcome. This research makes two contributions: first, it illustrates how ambiguities open up design work by creating a space for action; second, it illustrates how actions to negotiate ambiguity maneuver in this space for action.

  • Public defence: 2017-06-09 10:00 Electrum, Sal C, Kista
    Rodrigo Navarro, Jaime
    KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO. ACREO Swedish ICT.
    Phase Noise Tolerant Modulation Formats and DSP Algorithms for Coherent Optical Systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coherent detection together with multilevel modulation formats has the potential to significantly increase the capacity of existing optical communication systems at no extra cost in signal bandwidth. However, these modulation formats are more susceptible to the impact of different noise sources and distortions as the distance between its constellation points in the complex plane reduces with the modulation index. In this context, digital signal processing (DSP) plays a key role as it allows compensating for the impairments occurring during signal generation, transmission and/or detection relaxing the complexity of the overall system. The transition towards pluggable optical transceivers, offers flexibility for network design/upgrade but sets strict requirements on the power consumption of the DSP thus limiting its complexity. The DSP module complexity however, scales with the modulation order and, in this scenario, low complex yet high performance DSP algorithms are highly desired.

    In this thesis, we mainly focus on the impact of laser phase noise arising from the transmitter and local oscillator (LO) lasers in coherent optical communication systems employing high order modulation formats. In these systems, the phase noise of the transmitting and LO lasers translate into phase noise in the received constellation impeding the proper recovery of the transmitted data. In order to increase the system phase noise tolerance, we firstly explore the possibility of re-arranging the constellation points in a circularly shaped mQAM (C-mQAM) constellation shape to exploit its inherent phase noise tolerance. Different low-complex carrier phase recovery (CPR) schemes applicable to these constellations are proposed along with a discussion on its performance and implementation complexity. Secondly, the design guidelines of high performance and low complex CPR schemes for conventional square mQAM constellations are presented. We identify the inherent limitation of the state-of-the-art blind phase search (BPS) carrier phase recovery algorithm which hinders its achievable performance and implementation complexity and present a low complex solution to overcome it. The design guidelines of multi-stage CPR schemes for high order modulation formats, where the BPS algorithm is employed at any of the stages, are also provided and discussed. Finally, the interplay between the received dispersed signal and the LO phase noise is analytically investigated to characterize the origin of the equalization enhanced phase noise phenomena.

  • Public defence: 2017-06-09 10:00 Kollegiesalen, Stockholm
    Peñaloza, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. RISE - Research Institutes of Sweden.
    The role of biobased building materials in the climate impacts of construction: Effects of increased use of biobased materials in the Swedish building sector2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A significant share of the global climate change impacts can be attributed to the construction sector. One mitigation strategy is increasing the use of biobased materials. Life cycle assessment (LCA) has been used to demonstrate the benefits of this, but forest complexities create uncertainty due to omission of key aspects. This aim of this thesis is to enhance understanding of the effects of increasing use of biobased materials in climate change mitigation of construction works with a life cycle perspective. Non-traditional LCA methodology aspects were identified and the climate impact effects of increasing the use of biobased materials while accounting for these was studied. The method applied was dynamic LCA combined with forest carbon data under multi-approach scenarios. Diverse case studies (a building, a small road bridge and the Swedish building stock) were used. Most scenarios result in impact reductions from increasing the use of biobased materials in construction. The inclusion of non-traditional aspects affected the results, but not this outcome. Results show that the climate mitigation potential is maximized by simultaneously implementing other strategies (such as increased use of low-impact concrete). Biobased building materials should not be generalised as climate neutral because it depends on case-sensitive factors. Some of these factors depend on the modelling of the forest system (timing of tree growth, spatial level approach, forest land use baseline) or LCA modelling parameters (choice of the time horizon, end-of-life assumptions, service life). To decrease uncertainty, it is recommended to use at least one metric that allows assessment of emissions based on their timing and to use long-term time horizons. Practitioners should clearly state if and how non-traditional aspects are handled, and study several methodological settings. Technological changes should be accounted for when studying long-term climate impacts of building stocks.

  • Public defence: 2017-06-09 10:00 Hörsal E2, Stockholm
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Studies on Current Commutation in Hybrid DC-breakers2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Compared to conventional AC-circuit breakers, a DC-breaker has to act fast and force the current down to zero. Many different DC-breaker topologies are available, and this thesis is focused on the hybrid DC-breaker comprising a mechanical switch and high power semiconductors.

    The main part of this thesis is focused on the current commutations in the hybrid DC-breaker. The two current commutations: from the mechanical switch to the semiconductor branch, and from the semiconductor to the metal oxide varistor, have completely different characteristics. When the mechanical switch opens, the metallic contacts separate and an electric arc is formed. As the voltage across the arc is higher than the voltage across the semiconductors, the current is pushed over to the semiconductor branch. The undesired stray inductance in the loop limits the current derivative and slows down the commutation. As the contacts keep separating, the arc voltage increases and eventually all current is conducted by the semiconductor and the arc ceases.

    For a hybrid DC-breaker, the worst case is a solid ground fault, as the fast rising current results in high current levels and makes the commutation from the mechanical switch to the semiconductor both difficult and slow. However, the fast rise of the current can be used to enhance the commutation by using coupled inductors in the two parallel branches. When the fault current rises in the semiconductor branch, the mutual coupling of the inductors causes the current in the mechanical switch to decrease and helps the commutation. The result is that the commutation time decreases with decreasing fault impedance, and makes the solid ground fault easier to handle.

    The commutation from the semiconductor to the metal oxide varistor is controlled by the turn-off of the semiconductor. When the semiconductor is turned off, it pulls the current down to zero with a rather constant current derivative regardless of the surrounding circuit and the system current is taken over by the metal oxide varistor. Hence, any inductance in the commutation loop will result in an over-voltage proportional to this inductance on top of the varistor voltage. By connecting a smaller metal oxide varistor, as a snubber, close to the semiconductor, the over-voltage can be controlled and the commutation from the snubber to the metal oxide varistor will be driven by the voltage difference between the two varistors.

    It is shown that for a 12 kV DC-system, a possible design of the mechanical switch in the hybrid DC-breaker comprises two contact gaps in series and opens with a velocity of 11 m/s. It has been experimentally verified that when starting the commutation at 4 kA, the commutation takes less than 700 us and is over before the switch has opened 1 mm.

    The thesis also contains proposed designs for an 80 kV DC-breaker that can be used as a modular solution for higher system voltages. For this higher voltage, the design will be a choice of the combination between the number of contact gaps in series and the opening velocity of the mechanical switch.

  • Public defence: 2017-06-09 10:00 M311, Stockholm
    Ratanathavorn, Wallop
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Welding Technology.
    Dissimilar joining of aluminium to ultra-high strength steels by friction stir welding2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multi-material structures are increasingly used in vehicle bodies to reduce weight of cars. The use of these lightweight structures is driven by requirements to improve fuel economy and reduce CO2 emissions. The automotive industry has replaced conventional steel components by lighter metals such as aluminium alloy. This is done together with cutting weight of structures using more advanced strength steels. However, sound joining is still difficult to achieve due to differences in chemical and thermal properties.

     

    This research aims to develop a new innovative welding technique for joining aluminium alloy to ultra-high strength steels. The technique is based on friction stir welding process while the non-consumable tool is made of an ordinary tool steel. Welding was done by penetrating the rotating tool from the aluminium side without penetrating into the steel surface. One grade of Al-Mg aluminium alloy was welded to ultra-high strength steels under lap joint configuration. Different types of steel surface coatings including uncoated, hot-dipped galvanised and electrogalvanised coating have been studied in order to investigate the influence of zinc on the joint properties. The correlation among welding parameters, microstructures, intermetallic formation and mechanical properties are demonstrated in this thesis.  Results have shown that friction stir welding can deliver fully strong joints between aluminium alloy and ultra-high strength steels. Two intermetallic phases, Al5Fe2 and Al13Fe4, were formed at the interface of Al to Fe regardless of surface coating conditions. The presence of zinc can improve joint strength especially at low heat input welding due to an increased atomic bonding at Al-Fe interface. The formation of intermetallic phases as well as their characteristics has been demonstrated in this thesis. The proposed welding mechanisms are given based on metallography investigations and related literature.

  • Public defence: 2017-06-09 10:15 sal E3, Stockholm
    Kabral, Raimo
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Turbocharger Aeroacoustics and Optimal Damping of Sound2017Doctoral thesis, comprehensive summary (Other academic)
  • Public defence: 2017-06-09 10:15 D3, Stockholm
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Millimeter-wave Networking: Fundamental Limits, Scalable Algorithms, and Design Insights2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The current demands for extremely high data rate wireless services and the spectrum scarcity at the sub-6 GHz bands are forcefully motivating the use of the millimeter-wave (mmWave) frequencies. The main characteristics of mmWave communications are severe attenuation, sparse-scattering environment, huge bandwidth, vulnerability to obstacles and antenna misalignment, massive beamforming, and possible noise-limited operation. These characteristics constitute a major difference with respect to legacy communication technologies, primarily designed for the sub-6 GHz bands, and are posing major theoretical design challenges that have not been sufficiently addressed so far. Motivated by these challenges, this doctoral thesis considers mmWave communications and investigates medium access control (MAC) layer design principles and performance analysis. Specifically, we focus on fundamental performance metrics, including coverage, fairness, robustness, throughput, and delay, which we address by three main research threads of increasing complexity.

    The first thread of the thesis analyzes the interference behavior in mmWave networks.We first propose a new index for assessing the accuracy of any interference model under any network scenario, which helps us develop a simple interference model of adequate accuracy. We then derive closed-form expressions for the throughput of mmWave ad hoc networks. The new analysis reveals that mmWave networks may exhibit a non-negligible transitional behavior from a noise-limited to an interference-limited behavior, depending on the system parameters such as density of transmitters, transmission power, and operating beamwidth. The second thread of this thesis builds on the previous one and addresses resource allocation in mmWave networks. For the short-term resource allocation, we establish a mathematical framework to investigate the impact of beam training (alignment) overhead on the network throughput. For the long-term resource allocation, we formulate a series of optimization problems that address relaying capability, frequent handovers, small multiuser interference, and load balancing. The third thread of this thesis extends the second one toward spectrum sharing in mmWave networks and characterizes the gains of beamforming and coordination in spectrum sharing via several optimization problems. We analyze these problems in the asymptotic regimes when the number of antennas becomes large and conclude that spectrum sharing with light on-demand coordination is feasible, especially at higher mmWave frequencies (for example, 73 GHz).

    The original analysis proposed in this thesis gives novel insights into many MAC layer issues such as resource allocation, interference management, random access, mobility management, and synchronization in future mmWave networks. The thesis also highlights that the design of mmWave networks poses open problems at the intersection of optimization and learning theories. Given the recent interest in the standardization of mmWave cellular networks and the highly sub-optimal nature of the existing standards for mmWave short-range networks, the results of this thesis may have the potential to substantially steer future standardizations.

  • Public defence: 2017-06-09 13:00 F3, Stockholm
    Lönnqvist, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Biogas in Swedish transport – a policy-driven systemic transition2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis analyzes the conditions for biogas in the Swedish transport sector. Biogas can contribute to the achievement of Sweden’s ambitious targets of decreased emissions of greenhouse gases and an increased share of renewables in the transport sector, a sector that encompasses the major challenges in the phase-out of fossil fuels.

    Biogas development has stagnated during recent years and there are several factors that have contributed to this. The use of biogas in transport has developed in niches strongly affected by policy instruments and in this thesis, the progress is understood as a policy-driven systemic transition. Biogas has (started to) become established at the regime level and has begun to replace fossil fuels. The major obstacles for continued biogas development are found to be the stagnated vehicle gas demand, the low predictability of Swedish policy instruments, and electric car development. Moreover, the current prolonged period of low oil prices has also contributed to a lack of top-down pressure.

    A large share of the cheap and easily accessible feedstock for conventional biogas production is already utilized and an increased use of vehicle gas could enable a commercial introduction of forest-derived methane. However, the technologies to produce forest-derived methane are still not commercial, although there are industrial actors with technological know-how.

    Future biogas development depends on how the policy framework develops. Policy makers should consider the dynamics of biogas as a young sociotechnical system where different system fronts develop at a varying pace. Currently the demand side is lagging behind. However, it is necessary to maintain predictable policy support throughout the entire biogas value chain, since the system fronts that lag can vary over time. The low predictability of Swedish policy instruments indicates that policy makers should exercise care in their design to create a more robust policy framework moving forward.

  • Public defence: 2017-06-09 13:00 Ka-Sal B (Sal Peter Weissglas), Stockholm
    Katic, Janko
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Highly-Efficient Energy Harvesting Interfaces for Implantable Biosensors2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Energy harvesting is identified as an alternative solution for powering implantable biosensors. It can potentially enable the development of self-powered implants if the harvested energy is properly handled. This development implies that batteries, which impose many limitations, are replaced by miniature harvesting devices. Customized interface circuits are necessary to correct for differences in the voltage and power levels provided by harvesting devices from one side, and required by biosensor circuits from another. This thesis investigates the available harvesting sources within the human body, proposes various methods and techniques for designing power-efficient interfaces, and presents two CMOS implementations of such interfaces.

    Based on the investigation of suitable sources, this thesis focuses on glucose biofuel cells and thermoelectric harvesters, which provide appropriate performance in terms of power density and lifetime. In order to maximize the efficiency of the power transfer, this thesis undertakes the following steps. First, it performs a detailed analysis of all potential losses within the converter. Second, in relation to the performed analysis, it proposes a design methodology that aims to minimize the sum of losses and the power consumption of the control circuit. Finally, it presents multiple design techniques to further improve the overall efficiency.

    The combination of the proposed methods and techniques are validated by two highly efficient energy harvesting interfaces. The first implementation, a thermoelectric energy harvesting interface, is based on a single-inductor dual-output boost converter. The measurement results show that it achieves a peak efficiency of 86.6% at 30 μW. The second implementation combines the energy from two sources, glucose biofuel cell and thermoelectric harvester, to accomplish reliable multi-source harvesting. The measurements show that it achieves a peak efficiency of 89.5% when the combined input power is 66 μW. 

  • Public defence: 2017-06-09 13:00 L1, Stockholm
    Katzler, Sigrid
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Improving strategic decisions for real estate investors: Perspectives on allocation and management2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Real estate is an attractive asset class in the mixed-asset portfolio due to favorable risk return characteristics and low correlations with other asset classes like stock and bonds. Unlike financial assets, real estate is a physical asset where large lot sizes/indivisibility, heterogeneity, low liquidity and high transaction costs make applying financial models like modern portfolio theory (MPT) challenging. Optimal allocations to real estate found in literature are generally lower than actual allocations by investors and portfolio managers indicating there are aspects of the application of MPT to real estate that are not fully understood. Since management of real estate is costly and requires expert skills, the question on whether to outsource property management functions is of paramount interest for the real estate industry.

    The aim of the thesis is to contribute to the literature on strategic decisions for real estate investors on allocation and management, Apart from reviewing literature relevant for strategic decisions at different levels and using a top-down approach to illustrate how selected allocation and management decisions are connected, four separate empirical studies are made to investigate the nature of selected strategic decisions for real estate investors.

  • Public defence: 2017-06-09 13:00 M3, Stockholm
    Taliotis, Constantinos
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Large scale renewable energy deployment - Insights offered by long-term energy models from selected case studies2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The United Nations’ Sustainable Development Goal 7 (SDG7) of Agenda 2030 calls for an increase in the use of renewable energy sources, among other targets. The percentage of fossil fuel-fired thermal generation for electricity is increasingly being reduced as renewable energy technologies (RET) advance in cost-competitiveness, and as greenhouse gas and industrial air pollutant emission limits become more stringent. In certain cases, renewable energy contributes to energy security by improving a nation’s trade balance, since local resources are harnessed and imports are reduced. RET investments are becoming more frequent gaining a sizeable share in the electric power mix of numerous countries.

    However, RET is affected by existing fossil fuel-fired electricity generation, especially in countries that have domestic reserves. While coal may be dirty, others such as natural gas provide multiple benefits, presenting a challenge to renewables. Additionally, RET endowment varies for each geographical location. This often does not correspond to the location of major electricity demand centers.  Therefore, large scale RET adoption and integration becomes logistically more cumbersome, as it necessitates existence of a developed grid network.

    Utilizing a series of analyses in two different settings – Africa and Cyprus – this thesis draws insights on RET growth policy and the level of technology representation in long term energy models. In order to capture specific challenges of RET integration, enhancements in traditional long-term energy system models are called for and carried out.

     The case of Africa is used to assess adoption of RET under various trade scenarios. It is home to some of the world’s greatest RET resource potential and the single largest potential RET project, Grand Inga.  While, the island of Cyprus has goals of introducing large percentages of RET into its electric power mix. Each have important idiosyncrasies which are reflected in the analysis. On the one hand, natural gas competes with RET in Cyprus and forms a key transition fuel away from oil. On the other hand, lack of cross-border interconnectors limit RET project development across Africa.

  • Public defence: 2017-06-09 13:30 F2, Stockholm
    Bodin, Anders
    KTH, School of Architecture and the Built Environment (ABE), Architecture, History and Theory of Architecture.
    Helgo Zettervalls arkitektur2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Helgo Zettervall (1831–1907) was one of Sweden’s principal architects and design talents. He was professionally active for 40 years, from the late 1850s to the mid-1890s – a period of intensive building activity in Sweden. For the first twenty years of his career, he had his practice in Lund, and in the subsequent twenty years he lived in Stockholm as head of Sweden’s state authority for public buildings. Zettervall was very productive. His portfolio contains 281 projects, of which 160 were executed, ranging from large cathedral restorations with thousands of detailed drawings and large public buildings to porch extensions and smaller residences.

    This dissertation highlights Zettervall’s works by putting them in a context and by analysing their qualitative aspects. Carried out as a historiographical case study, the framework for the dissertation is the architectural monograph. The individual architectural projects are the core of the presentation, assembling and making archive material readily accessible, and the method is leaning towards that of an oeuvre complète raisonné. The method includes three distinct approaches: a factual accounting of documents and drawings, a context-setting frame story that provides the conditions, and an architectural analysis.

    Zettervall belonged to the first generation of architects who could receive a well-planned and broad training in Sweden. All of this training took place against a backdrop of what a specific assignment demanded in terms of responsiveness and understanding. Zettervall developed a special talent for utilizing new construction methods and materials. Each assignment was a challenge to investigate new design principles and new spatial ideas. The investigation shows that every project was unique for Zettervall, and that his various solutions depended on the specific situation, regarding site and program. Zettervall was a distinct pragmatic. Every assignment had its unique conditions, and thus had a unique solution.

  • Public defence: 2017-06-09 14:00 E2, Stockholm
    Vinyals, Marc
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Space in Proof Complexity2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    ropositional proof complexity is the study of the resources that are needed to prove formulas in propositional logic. In this thesis we are concerned with the size and space of proofs, and in particular with the latter.

    Different approaches to reasoning are captured by corresponding proof systems. The simplest and most well studied proof system is resolution, and we try to get our understanding of other proof systems closer to that of resolution.

    In resolution we can prove a space lower bound just by showing that any proof must have a large clause. We prove a similar relation between resolution width and polynomial calculus space that lets us derive space lower bounds, and we use it to separate degree and space.

    For cutting planes we show length-space trade-offs. This is, there are formulas that have a proof in small space and a proof in small length, but there is no proof that can optimize both measures at the same time.

    We introduce a new measure of space, cumulative space, that accounts for the space used throughout a proof rather than only its maximum. This is exploratory work, but we can also prove new results for the usual space measure.

    We define a new proof system that aims to capture the power of current SAT solvers, and we show a landscape of length-space trade-offs comparable to those in resolution.

    To prove these results we build and use tools from other areas of computational complexity. One area is pebble games, very simple computational models that are useful for modelling space. In addition to results with applications to proof complexity, we show that pebble game cost is PSPACE-hard to approximate.

    Another area is communication complexity, the study of the amount of communication that is needed to solve a problem when its description is shared by multiple parties. We prove a simulation theorem that relates the query complexity of a function with the communication complexity of a composed function.

  • Public defence: 2017-06-09 14:00 Sal. C, Stockholm
    Kakkar, Aditya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
    Frequency Noise in Coherent Optical Systems: Impact and Mitigation Methods2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increase in capacity demand along with the advancement in digital signal processing (DSP) have recently revived the interest in coherent optical communications and led to its commercialization. However, design and development of robust DSP algorithms for example for carrier phase recovery (CPR) becomes complex as we opt for high order modulation formats such as 16QAM and beyond. Further, electrical-domain dispersion compensation (EDC), while providing many advantages, makes the system more susceptible to laser frequency noise (FN). For instance, in coherent optical links with post-reception EDC, while the transmitter frequency noise causes only phase impairment, the local oscillator (LO) FN in these systems results in a noise enhancement in both amplitude and phase. This noise is commonly known as equalization enhanced phase noise (EEPN). It results in asymmetric requirements for transmitter laser and LO laser. Further, the system design in the presence of lasers with non-white frequency noise becomes increasingly challenging for increased capacity-distance product.

    The main contributions of this thesis are, firstly, an experimentally validated theory of coherent optical links with lasers having general non-white frequency noise spectrum and corresponding system/laser design criteria and mitigation technique. Secondly, low complexity and high phase noise tolerant CPR for high order modulation formats.

    The general theory propounded in this thesis elucidates the origin of the laser frequency noise induced noise enhancement in coherent optical links with different DSP configurations. The thesis establishes the existence of multiple frequency noise regimes and shows that each regime results in different set of impairments. The influence of the impairments due to some regimes can ideally be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Experimentally validated theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided. Further, an EEPN mitigation method and its two possible implementations are proposed and discussed.

    The thesis also demonstrates an intrinsic limitation of the conventional Blind Phase Search (BPS) algorithm due to angular quantization and provides methods to overcome it. Finally, this thesis proposes and demonstrates single stage and multi-stage carrier phase recovery algorithms for compensation of phase impairments due to the two lasers for higher order circular and square modulations. The proposed methods outperform the state of art algorithms both in performance and in complexity.

  • Public defence: 2017-06-09 14:00 Kollegiesalen, Stockholm
    Najari Moghadam, Nima
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    On Multiantenna Cellular Communications: From Theory to Practice2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today, wireless communications are an essential part of our everyday life. Both the number of users and their demands for wireless data have increasedtremendously during the last decade. Multiantenna communicationsis a promising solution to meet this ever-growing traffic demands. However, impairments that exist in most practical communication networks may substantially limit the performance of a multiantenna system. The characterizationof such a performance loss and how to minimize that are still largelyopen problems. The present thesis addresses this important research gap. Inparticular, we focus on three major impairments of a multiantenna cellularnetwork: impairment in the channel state information (CSI), interference andimpairment in the transceiver hardware components.To fully realize the benefits of multiantenna communications, the users need to acquire a certain level of information about their propagation environment; that is, their corresponding CSI. In practice, the CSI is not known bythe users and should be acquired by allocating part of the network resourcesfor pilot transmission. This problem is mainly important in the systems with a large number of antennas, as in general the required network resources for CSI acquisition scales with the number of transmitting antennas. Theproblem of CSI acquisition in a single-cell multiuser multiple-input multipleoutput(MIMO) system is addressed in this thesis. A linear spatial precodingand combining scheme for pilot transmission is proposed. This scheme requiresless number of network resources for channel estimation compared tothe conventional schemes. The gains of the proposed scheme are characterized by finding an upper-bound and a lower-bound on the channel estimation error.Moreover, as an ultimate performance metric, an achievable sum-rate ofthe network is formulated and analyzed numerically.Due to the broadcast nature of the wireless channels, the performanceof the users in a network is intertwined; the desired signal of one user mayinterfere other users. Hence, the interference is another major impairment inwireless communication systems. In this thesis, the practical challenges of aninterference management technique, namely MIMO interference alignment isinvestigated by implementation on a multiuser MIMO testbed. Then, in thecontext of interference alignment, the problem of optimal power allocation forpilot and data transmission is studied and verified by the measurements.The impairment in the hardware components of the transceivers, that is, any deviation of the components from their ideal behavior, degrades the performance of a communication system. In particular, the impact of nonlineartransmitter power amplifiers (PA)s is investigated in this thesis. First, consideringa memoryless third-order polynomial model for the PAs, a model forthe transmitted nonlinear distortion signal from a multiantenna transmitter isproposed and validated by measurements. This model implies that the spatialdirection of the transmitted distortion is dependent on the spatial directionof the desired signal. Then, this model is extended for a general arbitrary order polynomial model. Exploiting the developed distortion model, the energyefficiency of a multiantenna system operating at millimeter wave frequenciesis studied.

  • Public defence: 2017-06-12 09:00 F3, Stockholm
    Stiehler, Beate
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Identification and assessment of luxury brand segments in the emerging markets: Case of South Africa2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Africa has been identified as an upcoming market in which luxury brands should secure future growth opportunities. A review of related academic literature, however, reveals that limited research has been conducted which focuses specifically on the continent’s luxury consumers. This gap in the literature highlights the need to further the body of knowledge on luxury consumer behaviour in this context. However, as the continent comprises a vast number of countries with diverse consumer profiles, it was decided that this study would focus on the assessment of the behaviour of the members of luxury consumer segments in the South African market.

    The specific areas that require research in order to establish an understanding of luxury consumer segments’ behaviour commenced from a review of different trends and developments in the South African market. The core trends, along with calls for further research on luxury brands in the international academic literature were combined to identify numerous avenues for further research. This eclectic approach aimed to not only contribute to an enhanced understanding of the behaviour of luxury consumer segments in the South African market, but to develop and extend the existing body of academic knowledge and literature on luxury brands.

    Four research questions were developed from both the identified avenues from the review of the trends in the market, and the calls for further research in the academic literature. Each of these questions was then addressed by four individual papers.  This thesis makes a number of contributions to the related body of knowledge as it details the behaviour of different luxury brand consumer segments in the South African market, thereby serving as a step towards addressing the gap in the literature on luxury consumers on the African continent. 

  • Public defence: 2017-06-12 09:00 Kollegiesalen, Stockholm
    Odhage, John
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Otraditionella lösningar med traditionella medel: Åtgärdsvalstudien som planeringsfenomen2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis aims to understand the method of strategic choice (MSC, Sw. metodik för åtgärdsvalsstudier) in Swedish transport planning as a planning phenomenon. Based on a normative interpretative approach and critical theory, underlying ideas and thinking that surround the context of MSC and how they are expressed in practice, in the guidelines and in concrete planning situations were investigated. The starting point was that changing conditions in society have necessitated reform of the transport sector and a new method has been introduced. It aims to enable a broader grip on transport issues by opening them up together with other actors, thus increasing scope and spreading responsibility for more sectors and activities, enabling new and unconventional solutions to transport problems for a sustainable future. MSC is described and interpreted here as a manifold phenomenon that reveals a tension between different perspectives and mindsets, but also leads to certain aspects being more often expressed which complicates wider and deeper perspectives on complex societal problems. More concretely, it was found that the collaboration in MSC is limited prematurely and is often limited at an early stage of the process, and that this leads to a more narrow understanding of the problem to be solved than would otherwise be the case. Furthermore, one specific perspective, namely the transport system perspective, is proposed explicitly as the basis for assessments. The study has also identified challenges related to the consideration of conflicting and contradictory knowledge claims in the process. Assessments of the effects of actions are assumed to be based upon logical premises, and not on judgments in dialogue and argumentation. However, the analysis suggested that the functional instrumental reasoning of success-oriented action does not seem to take normative and political issues into consideration in order to better address sustainable development issues in the complex, democratic and pluralist society. In conclusion, the analysis identifies the need for these processes in addressing a sustainable future to be kept open in a more inclusive and diverse way, drawing on more and different possible futures.

  • Public defence: 2017-06-12 13:15 Sal D3, Stockholm
    Chen, Rongzhen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively.

    The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient.

    CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm.

  • Public defence: 2017-06-12 14:00 Ka-Sal C Electrum, Kista
    Wang, Kun
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab). RISE Acreo.
    Migration Towards Next Generation Optical Access and Transport Networks2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    By 2020 there will be 50 billion connected devices over the Internet. With the fast-increasing data traffic demand in both fixed and mobile networks, network operators need to migrate networks towards next generation solutions. The network migration requires the enormous investment in equipment and infrastructure, while the revenues are not expected to grow significantly. Therefore, one of the main challenges for network operators is to find out a proper cost-effective optical network solution that can match future high capacity demand and flexibly support multiple network services on a common network infrastructure.

    The first part of the thesis addresses the Active Optical Network (AON) and its migration strategies towards Next Generation Optical Access (NGOA) solutions. Several migration strategies are proposed from the perspective of network topology, data plane and control plane. A general methodology for Techno-Economic analysis has been developed and applied to the Total Cost of Ownership (TCO) calculation of different NGOA solutions. The thesis provides a complete cost evaluation of AON migration paths, which can be used by network operators to assess the economic feasibility of network migration.

    A converged Optical Transport Network (OTN) that can serve both fixed and mobile network services is beneficial from the cost-saving perspective. However, the different types of services, require different network performance. The second part of the thesis focuses on the investigation of the converged OTN that can be flexibly and timely adjusted to satisfy varying service conditions. A programmable OTN featured with Wavelength Division Multiplexing (WDM) in the data plane and Software Defined Networking (SDN) in control plane has been proposed. To demonstrate the benefits of the converged OTN, the thesis also provides a multi-domain orchestration architecture for the multiple network services.  The resource orchestration, across three network domains: OTN, mobile network and cloud, enables agile service creation and optimized resource allocation among the multiple domains.

  • Public defence: 2017-06-13 09:00 F3, Stockholm
    Güler, Püren
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Learning Object Properties From Manipulation for Manipulation2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The world contains objects with various properties - rigid, granular, liquid, elastic or plastic. As humans, while interacting with the objects, we plan our manipulation by considering their properties. For instance, while holding a rigid object such as a brick, we adapt our grasp based on its centre of mass not to drop it. On the other hand while manipulating a deformable object, we may consider additional properties to the centre of mass such elasticity, brittleness etc. for grasp stability. Therefore, knowing object properties is an integral part of skilled manipulation of objects. 

    For manipulating objects skillfully, robots should be able to predict the object properties as humans do. To predict the properties, interactions with objects are essential. These interactions give rise distinct sensory signals that contains information about the object properties. The signals coming from a single sensory modality may give ambiguous information or noisy measurements. Hence, by integrating multi-sensory modalities (vision, touch, audio or proprioceptive), a manipulated object can be observed from different aspects and this can decrease the uncertainty in the observed properties. By analyzing the perceived sensory signals, a robot reasons about the object properties and adjusts its manipulation based on this information. During this adjustment, the robot can make use of a simulation model to predict the object behavior to plan the next action. For instance, if an object is assumed to be rigid before interaction and exhibit deformable behavior after interaction, an internal simulation model can be used to predict the load force exerted on the object, so that appropriate manipulation can be planned in the next action. Thus, learning about object properties can be defined as an active procedure. The robot explores the object properties actively and purposefully by interacting with the object, and adjusting its manipulation based on the sensory information and predicted object behavior through an internal simulation model.

    This thesis investigates the necessary mechanisms that we mentioned above to learn object properties: (i) multi-sensory information, (ii) simulation and (iii) active exploration. In particular, we investigate these three mechanisms that represent different and complementary ways of extracting a certain object property, the deformability of objects. Firstly, we investigate the feasibility of using visual and/or tactile data to classify the content of a container based on the deformation observed when a robotic hand squeezes and deforms the container. According to our result, both visual and tactile sensory data individually give high accuracy rates while classifying the content type based on the deformation. Next, we investigate the usage of a simulation model to estimate the object deformability that is revealed through a manipulation. The proposed method identify accurately the deformability of the test objects in synthetic and real-world data. Finally, we investigate the integration of the deformation simulation in a robotic active perception framework to extract the heterogenous deformability properties of an environment through physical interactions. In the experiments that we apply on real-world objects, we illustrate that the active perception framework can map the heterogeneous deformability properties of a surface.

  • Public defence: 2017-06-13 09:00 Sal M235, Stockholm
    Woldemariam, Daniel Minilu
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    District Heating-driven Membrane Distillation for Water Purification in Industrial Applications2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Domestic and industrial water demands are growing globally due to population growth and rapid economic development, placing increasing strains on water resources. Wastewater effluents generated from these and other activities impact the environment and are thus subject to tightening regulation. The focus of research and development in water treatment processes aims at both pollutant removal efficiency and cost of purification.

    Membrane distillation (MD) is a developing thermally driven technology capable of achieving extremely high environmental performance utilizing renewable energy sources to a high degree. District heating networks, and in particular those driven by biomass, represent an ideal heat supply for MD systems.

    This thesis presents a technoeconomic assessment of district heating driven MD for water purification in selected industrial applications. The study covers analysis of MD separation performance and the related costs from different district heating integration scenarios. The analyses are based on three types of semi-commercial MD modules, with experiments conducted at laboratory and pilot scales. The case studies include pharmaceutical residue removal from effluents of municipal wastewater treatment plant, wastewater purification in pharmaceutical industry, and ethanol concentration in bioethanol production plant. Full-scale simulation studies were carried out for the identified case studies based on the experimental data obtained from MD module along with process information gathered from the industries. Results from the pharmaceutical residue removal pilot trials showed very good to excellent separation efficiency for 37 compounds at feed concentrations ranging from ng/L to mg/L. From alcohol-water feeds, ethanol concentrations were increased from 5% to nearly 90%. Simulation studies revealed that district heating integration of MD systems is feasible. Costs per unit volume of purified water are higher than competing technologies, however the configurations enable enhanced environmental performance that would be difficult to achieve otherwise.

  • Public defence: 2017-06-13 10:00 Kollegiesalen, Stockholm
    Moiseeva, Ekaterina
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Impact of High levels of Wind Penetration on the Exercise of Market Power in the Multi-Area Systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    New European energy policies have set a goal of a high share of renewable energy in electricity markets. In the presence of high levels of renewable generation, and especially wind, there is more uncertainty in the supply. It is natural, that volatility in energy production induces the volatility in energy prices. This can create incentives for the generators to exercise market power by traditional means: withholding the output by conventional generators, bidding not the true marginal costs, or using locational market power. In addition, a new type of market power has been recently observed: exercise of market power on ramp rate. This dissertation focuses on modeling the exercise of market power in power systems with high penetration of wind power. The models consider a single, or multiple profit-maximizing generators. Flexibility is identified as one of the major issues in wind-integrated power systems. Therefore, part of the research studies the behavior of strategic hydropower producers as main providers of flexibility in systems, where hydropower is available.Developed models are formulated as mathematical and equilibrium problems with equilibrium constraints (MPECs and EPECs). The models are recast as mixed-integer linear programs (MILPs) using discretization. Resulting MILPs can be solved directly by commercially-available MILP solvers, or by applying decomposition. Proposed Modified Benders Decomposition Algorithm (MBDA) significantly improves the computational efficiency.

    The full text will be freely available from 2017-06-13 16:00
  • Public defence: 2017-06-13 10:00 D3, Stockholm
    Davari, Mohammad Mehdi
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Exploiting over-actuation to reduce tyre energy losses in vehicle manoeuvres2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to environmental and economic challenges road vehicles need bettersolutions to reduce energy consumption. Improvement in tyre rolling e-ciency is one of the key enablers for lower energy consumption. The shifttowards electrication and intelligent driving creates new opportunities todevelop energy-ecient vehicles. For instant over-actuated vehicles whichenables dierent objectives such as safety, performance and energy e-ciency to be fullled during a manoeuvre. The objective of this thesis is todevelop a simulation environment to simulate the energy dissipated fromthe tyre in order to investigate the potential to controlling dierent chassisparameters to reduce rolling losses during driving.The rst part of the thesis is dedicated to develop a high-delity semi-physical non-linear tyre model called the Extended Brush Tyre Model(EBM) to be used for energy studies in vehicle dynamics simulations andlater answer whether it is reasonable to believe that there is any potentialto reduce the rolling loss, and thereby energy consumption, using over-actuation.In the second part of the thesis the benets of over-actuation are invest-igated to enable rolling loss reduction. A control strategy using camber-sideslip control (CSC) is proposed. The allocation problem is solved in the formof an optimisation problem using Dynamics Programming (DP) and ModelPredictive Control (MPC). Exploiting the function for a chosen vehicle ina simulation environment shows a signicant improvement of about 60% inrolling loss reduction while maintaining path tracking. Also by using thisfunction the tyre forces can be distributed more evenly while maintainingthe global force, which results in an increase in the available tyre forcesthat is especially benecial when driving at the limit. It is revealed thatoptimising the vehicle manoeuvre from an energy perspective is sometimesin con ict with the safety demand, thus the energy and safety criteria needto be considered simultaneously during optimisation.Finally, experimental studies using an over-actuated concept vehicleconrmed that the CSC function can reduce overall energy consumptionduring low velocity manoeuvres up to about 13%. By increasing the speed,the saving potential decreases but the contribution is nonetheless of signi-cance. The developed simulation environment, including the EBM, willenable future studies of dierent solutions using over-actuation to reducerolling losses in dierent types of vehicles and driving tasks.

    The full text will be freely available from 2017-06-30 00:29
  • Public defence: 2017-06-13 11:15 F3, Stockholm
    Bamzar, Roya
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Ensuring elderly mobility: environmental and safety issues2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis is to provide a better understanding of the issues of safe mobility ‎for the elderly population in Sweden. ‎This is achieved first by assessing the geography and patterns of ‎elderly falls at the county level and then by conducting a detailed survey with residents in senior ‎housing to investigate the relationship between indoor and/or outdoor environmental ‎characteristics and elderly safety. Safety is regarded as a multidimensional concept that ‎involves risk of falls, crime victimization and elderly people’s perception of their ‎overall safety. Using a case study approach, the study also assesses the types of outdoor places where most crimes ‎against the elderly take place and the types of places most feared by them. The study ‎adapts a set of qualitative and quantitative methods ‎to capture the nature of the phenomena; trends, patterns and frameworks that support ‎the analysis and implications of the results for both research and practice. The findings show ‎that elderly falls in Sweden vary geographically and exhibit gender, age, environmental, and socio-‎economic differences. The mobility of the older population is influenced by their ‎perceived safety in indoor and outdoor environments. Certain features of apartment layout and furniture arrangement are identified as potential causes of falls. Older adults’ ‎perception of safety exhibits a distance-decay effect from their senior housing building. Distance decay indicates that safety is deemed highest closest to their homes and decreases as the distance increases. There are indications that older adults take longer routes and increase their mobility because they are fearful at certain spots in their neighbourhood. The thesis ‎concludes with a discussion of the results and implications for both research and policy making at the local and ‎county levels. ‎

  • Public defence: 2017-06-13 12:00 Aula Perez Pulgar, Madrid, Spain
    Izadkhast, Seyedmahdi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Aggregation of Plug-in Electric Vehicles in Power Systems for Primary Frequency Control2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The number of plug-in electric vehicles (PEVs) is likely to increase in the near future and these vehicles will probably be connected to the electric grid most of the day time. PEVs are interesting options to provide a wide variety of services such as primary frequency control (PFC), because they are able to quickly control their active power using electronic power converters. However, to evaluate the impact of PEVs on PFC, one should either carry out complex and time consuming simulation involving a large number of PEVs or formulate and develop aggregate models which could efficiently reduce simulation complexity and time while maintaining accuracy.

    This thesis proposes aggregate models of PEVs for PFC. The final aggregate model has been developed gradually through the following steps. First of all, an aggregate model of PEVs for the PFC has been developed where various technical characteristics of PEVs such as operating modes (i.e., idle, disconnected, and charging) and PEV’s state of charge have been formulated and incorporated. Secondly, some technical characteristics of distribution networks have been added to the previous aggregate model of PEVs for the PFC. For this purpose, the power consumed in the network during PFC as well as the maximum allowed current of the lines and transformers have been taken into account. Thirdly, the frequency stability margins of power systems including PEVs have been evaluated and a strategy to design the frequency-droop controller of PEVs for PFC has been described. The controller designed guaranties similar stability margins, in the worst case scenario, to those of the system without PEVs. Finally, a method to evaluate the positive economic impact of PEVs participation in PFC has been proposed.

  • Public defence: 2017-06-14 09:00 F3, Stockholm
    Okwir, Simon
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Collaborative Measures: Challenges in Airport Operations2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Over the last 20 years, internal use of Performance Management(PM) within organizations has become much more complex in terms measurement techniques and approaches as well as their deployment within different organizational structures. In contrast to the traditional use of PM as an intra-organizational system, the emergence of networked operations, has extended organizational boundaries of Performance Management System (PMS) to new operational settings where actors often deal with a challenge of Collaborative Measures. Consequently, there is a significant lack of feedback and feedforward reporting mechanisms. This raises an important question for Performance Measurement & Management (PMM) literature. How do actors manage operations through inter- organizational performance measures? Hence, the purpose of this thesis is to investigate the management of collaborative measures in a quest to attain better operational performance for inter- organizational PM.

    The thesis builds on four studies investigating a collaborative PMS for capacity enhancements in airport operations. Due to their operational complexity and highly networked subsystems, airport operations provided a fitting empirical scene for studying PM that transcends organizational boundaries. Within the context of this thesis, airports are viewed as a System of System (SoS), and inter- organizational PM is investigated with the dimensions Organizational Complexity, Continuous Improvement and Social system. The studies use a multimethod approach, including longitudinal action research, multiple-case study, Systematic Literature Review (SLR), Classification and Regression Tree method (CART) and Artificial Neural Network (ANN) Method.

    The findings show that that (1) inter- organizational performance is affected by intrinsic Performance Measurement Complexity (PMC) which aggregates as interactive complexity with many actors. (2) The challenge of feedback and feedforward mechanisms as a dual control for collaborative performance is analysed with four cybernetic functions: sensor, commander, actuator and process. (3) The concept of Reflective Performance Measurement System (RPMS) is introduced with general conditions to facilitate collaborative decision-making within such platforms.

  • Public defence: 2017-06-14 10:00 B2, Stockholm
    Yin, Jiaqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Formation of Bainite in Steels2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A systematic survey of morphology of bainite and proeutectoid ferrite was carried out in order to validate some old thoughts of bainite transformation mechanism. It is confirmed that there is no morphological evidence supporting a sharp change neither between Widmanstätten ferrite and the ferritic component of upper bainite, nor between upper and lower bainite. Both Widmanstätten ferrite and upper bainite start with precipitation of ferrite plates at a grain boundary while lower bainite starts with intragranular nucleation. In case of grain boundary nucleation, a group of parallel plates with same crystallographic orientation to the parent austenite grain forms. This process is followed by a second stage of decomposition of the austenitic interspace, which remained in between the primary ferrite plates. At high temperature, the austenitic interspace would either retain as thin slabs or transform into pearlite through a nodule originated from a grain boundary. At lower temperature, cementite precipitation starts to be possible and initiates simultaneous growth of ferrite. Generally, there are two modes of such eutectoid reactions operating in the second stage, i.e. a degenerate and a cooperative mode, which would lead to typical upper and lower bainite, respectively, in definition of carbides morphology. Both upper and lower bainite according to this definition are observed in a wide temperature range. A sharp temperature between the upper and lower bainite structures thus exists only when the definition is based on their nucleation sites, i.e. grain boundary nucleation for upper bainite and intragranular nucleation for lower bainite. Supposing that the first stage is a diffusionless process it should have a high growth rate to prevent carbon diffusion. This is not supported by lengthening rate obtained in current study as well as data from literature for Fe-C alloys. Finally, it is shown that the “subunits” play no role in the lengthening process of bainite.

  • Public defence: 2017-06-14 13:00 Sal C, Kista
    Rathore, Muhammad Siraj
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Performance, Isolation and Service Guarantees in Virtualized Network Functions2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A network is generally a collection of different hardware-based network devices carrying out various network functions, (NF). These NF implementations are special purpose and expensive. Network function virtualization (NFV) is an alternative which uses software-based implementation of NFs in inexpensive commodity servers. However, it is challenging to achieve high networking performance due to bottlenecks in software, particularly in a virtualized environment where NFs are implemented inside the virtual machines (VM). The performance isolation is yet another challenge, which means that the load on one VM should not affect the performance of other VMs. However, it is difficult to provide performance isolation due to resource contention in a commodity server. Furthermore, different NFs may require different service guarantees which are difficult to ensure due to the non-deterministic performance behavior of a commodity server.

    In this thesis we investigate how the challenges of performance, isolation and service guarantees can be addressed for virtual routers (VR), as an example of a virtualized NF. It is argued that the forwarding path of a VR can be modified in an efficient manner in order to improve the forwarding performance. When it comes to performance isolation, poor isolation is observed due to shared network queues and CPU sharing among VRs. We propose a design with SR-IOV, which allows reserving a network queue and CPU core for each VR. As a result, the resource contention is reduced and strong performance isolation is achieved. Finally, it is investigated how average throughput and bounded packet delay can be guaranteed to VRs. We argue that a classic rate-controlled service discipline can be adapted in a virtual environment to achieve service guarantees. We demonstrate that firm service guarantees can be achieved with little overhead of adding token bucket regulator in the forwarding path of a VR.

  • Public defence: 2017-06-14 14:00 FB54, Stockholm
    Zhang, Ye
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    High cell density perfusion process development for antibody producing Chinese Hamster Ovary cells2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Perfusion operation mode is currently under fast expansion in mammalian cell based manufacturing of biopharmaceuticals, not only for labile drug protein but also for stable proteins such as monoclonal antibodies (mAbs). Perfusion mode can advantageously offer a stable cell environment, long-term production with high productivity and consistent product quality. Intensified high cell density culture (HCDC) is certainly one of the most attractive features of a perfusion process due to the high volumetric productivity in a small footprint that it can provide. Advancements in single-use technology have alleviated the intrinsic complexity of perfusion processes while the maturing in cell retention devices has improved process robustness. The knowledge for perfusion process has been gradually built and the “continuous” concept is getting more and more acceptance in the field.

    This thesis presents the development of robust perfusion process at very high cell densities in various culture systems. Four HCDC perfusion systems were developed with industrial collaborators with three different mAb producing Chinese Hamster Ovary (CHO) cell lines: 1-2) WAVE Bioreactor™ Cellbag prototype equipped with cell separation by hollow fiber filter utilizing Alternating Tangential Flow (ATF) and Tangential Flow Filtration (TFF) techniques; 3) Fiber matrix based CellTank™ prototype; 4) Glass stirred tank bioreactor equipped with ATF. In all the systems, extremely high viable cell densities above 130 million viable cells per milliliter (MVC/mL) up to 214 MVC/mL were achieved. Steady states were maintained and studied at 20-30 MVC/mL and 100-130 MVC/mL for process development. Perfusion rate selection based on cell specific perfusion rate (CSPR) was systematically investigated and exometabolome study was performed to explore the metabolic footprint of HCDC perfusion process.

    The full text will be freely available from 2017-05-29 14:03
  • Public defence: 2017-06-15 09:00 Kollegiesalen, Stockholm
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    On Reliability of SiC Power Devices in Power Electronics2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Silicon Carbide (SiC) is a wide-bandgap (WBG) semiconductor materialwhich has several advantages such as higher maximum electric field, lowerON-state resistance, higher switching speeds, and higher maximum allowablejunction operation temperature compared to Silicon (Si). In the 1.2 kV - 1.7kV voltage range, power devices in SiC are foreseen to replace Si Insulatedgatebipolar transistors (IGBTs) for applications targeting high efficiency,high operation temperatures and/or volume reductions. In particular, theSiC Metal-oxide semiconductor field-effect transistor (MOSFET) – which isvoltage controlled and normally-OFF – is the device of choice due to the easeof its implementation in designs using Si IGBTs.In this work the reliability of SiC devices, in particular that of the SiCMOSFET, has been investigated. First, the possibility of paralleling two discreteSiC MOSFETs is investigated and validated through static and dynamictests. Parallel-connection was found to be unproblematic. Secondly, drifts ofthe threshold voltage and forward voltage of the body diode of the SiC MOSFETare investigated through long-term tests. Also these reliability aspectswere found to be unproblematic. Thirdly, the impact of the package on thechip reliability is discussed through a modeling of the parasitic inductancesof a standard module and the impact of those inductances on the gate oxide.The model shows imbalances in stray inductances and parasitic elementsthat are problematic for high-speed switching. A long-term test on the impactof humidity on junction terminations of SiC MOSFETs dies and SiCSchottky dies encapsulated in the same standard package reveals early degradationfor some modules situated outdoors. Then, the short-circuit behaviorof three different types (bipolar junction transistor, junction field-effect transistor,and MOSFET) of 1.2 kV SiC switching devices is investigated throughexperiments and simulations. The necessity to turn OFF the device quicklyduring a fault is supported with a detailed electro-thermal analysis for eachdevice. Design guidelines towards a rugged and fast short-circuit protectionare derived. For each device, a short-circuit protection driver was designed,built and validated experimentally. The possibility of designing diode-lessconverters with SiC MOSFETs is investigated with focus on surge currenttests through the body diode. The discovered fault mechanism is the triggeringof the npn parasitic bipolar transistor. Finally, a life-cycle cost analysis(LCCA) has been performed revealing that the introduction of SiC MOSFETsin already existing IGBT designs is economically interesting. In fact,the initial investment is saved later on due to a higher efficiency. Moreover,the reliability is improved, which is beneficial from a risk-management pointof-view. The total investment over 20 years is approximately 30 % lower fora converter with SiC MOSFETs although the initial converter cost is 30 %higher.

  • Public defence: 2017-06-15 09:15 FA32, Stockholm
    Liljestrand, Charlotte
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Advanced nano- and microdomain engineering of Rb-doped KTiOPO4 for nonlinear optical applications2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fine-pitch ferroelectric domain gratings are extensively used for generation of light in the visible and near-infrared spectral regions through quasi-phase matched (QPM) frequency conversion. Sub-μm QPM devices enables demonstration of nonlinear optics with counterpropagating waves, a field of nonlinear optics which remains sparsely explored due to the difficulty of fabricatinghigh quality gratings.

    In recent years, bulk Rb-doped KTiOPO4 (RKTP) has emerged as a highly promising nonlinear materials for fabrication of fine-pitch QPM devices through periodic electric-field poling. RKTP possesses large optical nonlinearity and high resistance to optical damage, while demonstrating improved material homogeneity and lower ionic conductivity than its isomorphs, which are important features for poling. Although fine-pitch QPM gratings, as well as large aperture QPM devices, have been demonstrated, fabrication of sub-μm high quality QPM devices remains a challenge.

    The primary aim of this research was to develop a reliable method to fabricate high-quality sub-μm periodically poled RKTP crystals (PPRKTP) and exploit them in novel optical applications. For this purpose, a novel poling method was developed. It was based on periodic modulation of the coercive field through ion exchange, where K+ ions are exchanged with Rb+ in the crystal, to modulate the coercive field and the ionic conductivity. This enables periodic poling of higher quality and with shorter period than ever before.

    High quality PPRKTP with a period of 755 nm were fabricated and used to demonstrate the first cascaded mirrorless optical parametric oscillator (MOPO), as well as the first MOPO pumped by a Q-switched laser. PPRKTP samples for blue light generation were fabricated, and second harmonic generation (SHG) was investigated with a high power 946 nm fiber laser. Up to 2 W of blue power was demonstrated for bulk samples, where the output power was limited by absorption of the SHG, leading to thermal dephasing of the devices. Laser-written waveguides were fabricated in PPRKTP for the first time, and a record high SHG power of 76 mW was obtained.

    Finally, the high-temperature stability of ferroelectric domain gratings was investigated. This is of utmost importance when a PPRKTP crystal is used as a seed for crystal growth. It was found that for charged domains walls, the domain-wall motion was highly anisotropic with rapid movement in y-direction while only small movements were observed in the x-direction of the crystal.

  • Public defence: 2017-06-15 10:00 SAL F3, Stockholm
    Gummesson, Karl
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Training measures and technologies for air contaminant risks2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Abstract

    As air contaminants continue to pose a problem in organizations, more studies are needed to identify and reduce employees’ exposure to air contaminants. Limited research proposes methods for managing air contaminants, especially with focus on reducing exposure by improving safety behavior, safety knowledge, safety attitudes and safety motivation among employees in the workplace, by, for instance, using safety training.The aim of this thesis is to develop existing safety measures and analyze new measures for reducing air contaminants in typical industrial work situations by focusing on human aspects, such as safety attitudes and safety motivation. This is carried out by studying safety attitudes, safety motivation, and safety training in relation to air contaminant safety in current Swedish organizations by means of questionnaires, interviews, reviews of research, as well as the exposure monitoring method, PIMEX. This thesis comprises four papers.

     

  • Public defence: 2017-06-15 10:00 Q2, Stockholm
    Bleiker, Simon J.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Heterogeneous 3D Integration and Packaging Technologies for Nano-Electromechanical Systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Three-dimensional (3D) integration of micro- and nano-electromechanical systems (MEMS/NEMS) with integrated circuits (ICs) is an emerging technology that offers great advantages over conventional state-of-the-art microelectronics. MEMS and NEMS are most commonly employed as sensor and actuator components that enable a vast array of functionalities typically not attainable by conventional ICs. 3D integration of NEMS and ICs also contributes to more compact device footprints, improves device performance, and lowers the power consumption. Therefore, 3D integration of NEMS and ICs has been proposed as a promising solution to the end of Moore’s law, i.e. the slowing advancement of complementary metal-oxide-semiconductor (CMOS) technology.In this Ph.D. thesis, I propose a comprehensive fabrication methodology for heterogeneous 3D integration of NEM devices directly on top of CMOS circuits. In heterogeneous integration, the NEMS and CMOS components are fully or partially fabricated on separate substrates and subsequently merged into one. This enables process flexibility for the NEMS components while maintaining full compatibility with standard CMOS fabrication. The first part of this thesis presents an adhesive wafer bonding method using ultra-thin intermediate bonding layers which is utilized for merging the NEMS components with the CMOS substrate. In the second part, a novel NEM switch concept is introduced and the performance of CMOS-integrated NEM switch circuits for logic and computation applications is discussed. The third part examines two different packaging approaches for integrated MEMS and NEMS devices with either hermetic vacuum cavities or low-cost glass lids for optical applications. Finally, a novel fabrication approach for through silicon vias (TSVs) by magnetic assembly is presented, which is used to establish an electrical connection from the packaged devices to the outside world.

  • Public defence: 2017-06-15 10:00 FD5, D5:3008,, Stockholm
    Marino, Raffaele
    KTH, School of Computer Science and Communication (CSC). Nordita.
    Dynamics and Thermodynamics of Translational and Rotational Diffusion Processes Driven out of Equilibrium2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Diffusion processes play an important role in describing systems in many fields of science, as in physics, biology, finance and social science. One of the most famous examples of the diffusion process is the Brownian motion. 

     

    At mesoscopic scale, the Brownian theory describes the very irregular and animated motion of a particle suspended in a fluid. In this thesis, the dynamics and thermodynamics of diffusion processes driven out of equilibrium, at mesoscopic scale, are investigated. 

     

    For dynamics, the theory of Brownian motion for a particle which is able to rotate and translate in three dimensions is presented. 

    Moreover, it is presented how to treat diffusion process on n-dimensional Riemann manifolds defining the Kolmogorov forward equation on such manifold.

     

    For thermodynamics, this thesis describes how to define thermodynamics quantities at mesoscopic scale using the tools of Brownian theory. The theory

    of stochastic energetics and how to compute entropy production along a trajectory are presented introducing the new field of stochastic thermodynamics.

    Moreover, the "anomalous entropy production" is introduced. This anomaly in the entropy production arises when diffusion processes are driven out of equilibrium by space dependent temperature field. The presence of this term expresses the fallacy of the overdamped approximation in computing thermodynamic quantities. 

     

    In the first part of the thesis the translational and rotational motion of an ellipsoidal particle in a heterogeneous thermal environment, with a space-dependent temperature field, is analyzed from the point of view of stochastic thermodynamics. 

     

    In the final part of the thesis, the motion of a Brownian rigid body three-dimensional space in a homogeneous thermal environment under the presence of an external force field is analyzed, using multiscale method and homogenization. 

  • Public defence: 2017-06-15 10:00 M311, Stockholm
    Daemi, Bita
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Enhanced image analysis, a tool for precision metrology in the micro and macro world2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The need for high speed and cost efficient inspection in manufacturing lineshas led to a vast usage of camera-based vision systems. The performance ofthese systems is sufficient to determine shape and size, but hardly to an accuracylevel comparable with traditional metrology tools. To achieve highprecision shape/position/defect measurements, the camera techniques haveto be combined with high performance image metrology techniques whichare developed and adapted to the manufactured components. The focus ofthis thesis is the application of enhanced image analysis as a tool for highprecision metrology. Dedicated algorithms have been developed, tested andevaluated in three practical cases ranging from micro manufacturing at submicronprecision to meter sized aerospace components with precision requirementsin the 10 μm range.The latter measurement challenge was solved by low cost standard consumerproducts, i.e. digital cameras in a stereo configuration and structured lightfrom a gobo-projector. Combined with high-precision image analysis and anew approach in camera calibration and 3D reconstruction for precise 3Dshape measurement of meter sized surfaces, the achievement was fulfilledand verified by two conventional measurement systems; a high precisioncoordinate measurement machine and a laser scanner.The sub-micron challenge was the implementation of image metrology forverification of micro manufacturing installations within a joint Europeaninfrastructure network, EUMINAfab. The results were an unpleasant surprisefor some of the participating laboratories, but became a big step forwardto improve the dimensional accuracy of the investigated laser micromachining, micro milling and micro-printing systems, since the accuracy ofthese techniques are very difficult to assess.The third high precision metrology challenge was the measurement of longrange,low-amplitude topographic structures on specular (shiny) aerodynamicsurfaces. In this case Fringe Reflection Technique (FRT) was appliedand image analysis algorithms were used to evaluate the fringe deformationas a measure of the surface slopes to obtain high resolution data. The resultwas compared with an interferometric analysis showing height deviation inthe range of tens of micrometers over a lateral extension of several cm.

  • Public defence: 2017-06-15 10:00 Sal V1, Stockholm
    Kholoma, Ezekiel
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. KTH Royal Institute of Technology.
    Fortification of soil-based wastewater treatment systems with versatile ubiquitous reactive media for enhanced removal of phosphorus and other pollutants2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Concerns about potential risks posed by discharge from small-scale wastewater treatment (SWT) systems to receiving water bodies have prompted robust enforcement of national discharge quality standards in rural areas of most developed countries. Consequently, communities in such places are in need of effective technologies with which to achieve compliance. Currently, reactive filter (RF) media are increasingly preferred over advanced alternatives, due mainly to their simplicity, affordability and proven potential. However, many of the field-tested filters are commercial products which are costly and scarce but also only capable of removing few contaminants they are engineered to target hence often requiring to be coupled with other treatment units to achieve full treatment. In the preliminary findings of this study, biochar (BC) was identified and thus suggested basing on existing literature, as a versatile ubiquitous low-cost material for treating wastewater. Its effectiveness in fortifying sand (Sa) and gas concrete (GC)-based SWT facilities was later demonstrated in long-term experiments using laboratory packed bed reactors and field constructed filter beds. The efficacy of SaBC and GCBC systems in reducing turbidity (>95%), DOC (60%; p<0.05) and PO43- (40-90%; p<0.05) was significantly higher than for their reference counterparts. Further, sorbed P was more leachable from Sa (11.2 mgkg-1) and SaBC (20.5 mgkg-1) filters but more extractable and hence plant-available in GC (65-91 mgkg-1). Therefore, the study concluded that fortification of soil-based systems with biochar filters may be a promising solution in enhancing performances of soil-based wastewater treatment systems, while P-rich RF media can act as a nutrient source for plants if recycled to agriculture.

  • Public defence: 2017-06-15 13:00 Kollegiesalen, Stockholm
    Liljeblad, Elisabet
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Structures and processes in the Mercury magnetosphere2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The mechanisms involved in the transfer of mass and energy from the solar wind to any planetary magnetosphere is considered an important topic in space physics. With the use of the Mercury spacecraft MESSENGER's data, it has been possible to study these processes in an environment different, yet similar, to Earth's. These data have resulted in new knowledge advancing not only the extraterrestrial space plasma research, but also the general space physics field.

     

    This thesis aims to investigate mechanisms for the transfer of mass and energy into Mercury’s magnetosphere, and magnetospheric regions affected by, and processes directly driven by, these. The work includes the Kelvin-Helmholtz instability (KHI) at the magnetopause, which is one of the main drivers for mass and energy transfer on Earth, the low-latitude boundary layer (LLBL), which is in direct connection to the magnetopause and proposed to be affected by the KHI, magnetospheric ultra-low frequency (ULF) waves driven by the KHI, and isolated magnetic field structures in the magnetosheath as possible analogues to the Earth magnetosheath plasmoids and jets.

     

    Kelvin-Helmholtz waves (KHW) and the LLBL are identified and characterized. The KHWs are observed almost exclusively on the duskside magnetopause, something that has not been observed on Earth. In contrast, the LLBL shows an opposite asymmetry. Results suggest that the KHI and LLBL are connected, possibly by the LLBL creating the asymmetry observed for the KHWs.

     

    Isolated changes of the total magnetic field strength in the magnetosheath are identified. The similar properties of the solar wind and magnetosheath negative magnetic field structures suggest that they are analogues to diamagnetic plasmoids found on Earth. No clear analogues to paramagnetic plasmoids are found.  

     

    Distinct magnetospheric ULF wave signatures are detected frequently in close connection to KHWs. Results from the polarization analysis on the dayside ULF waves indicate that the majority of these are most probably driven by the KHI. In general, likely KHI driven ULF waves are observed frequently in the Hermean magnetosphere. 

    Although similar in many aspects, Mercury and Earth show fundamental differences in processes and structures, making Mercury a highly interesting planet to study to increase our knowledge of Earth-like planets.

  • Public defence: 2017-06-15 13:15 B1, Stockholm
    Gustafsson, Marcus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Högskolan Dalarna.
    Energy Efficient Renovation Strategies for Swedish and Other European Residential and Office Buildings2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The high energy use in the European building stock is attributable to the large share of old buildings with poor energy performance. Energy renovation of buildings is therefore vital in the work towards energy efficiency and reduced environmental impact in the EU. Yet, the strategies and energy system implications of this work have not been made clear, and the rate of building renovation is currently very low.

    The aim of this thesis is to investigate the economic and environmental aspects of energy renovation strategies, with two main objectives:

    • Renovation of Swedish district heated multi-family houses, including life-cycle cost and environmental analysis and impact on the local energy system;

    • Renovation of European residential and office buildings, including life-cycle cost and environmental analysis and influence of climatic conditions.

    Buildings typical for the respective regions and the period of construction 1945-1970 were simulated, in order to determine the feasibility and energy saving potential of energy renovation measures in European climates. A variety of systems for heating, cooling and ventilation were studied, as well as solar energy systems, with focus on heat pumps, district heating, low-temperature heating systems and air heat recovery.

    Compared to normal building renovation, energy renovation can often reduce the life-cycle costs and environmental impact. In renovation of typical European office buildings, as well as Southern European multi-family houses, more ambitious renovation levels can also be more profitable.

    Exhaust air heat pumps can be cost-effective complements in district heated multi-family houses, while ventilation with heat recovery is more expensive but also more likely to reduce the primary energy use. From a system perspective, simple exhaust ventilation can reduce the primary energy use in the district-heating plant as much as an exhaust air heat pump, due to the lower electricity use.

  • Public defence: 2017-06-15 14:00 M311, Stockholm
    Li, Yujiang
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Computer Systems for Design and Manufacturing.
    Architecting model driven system integration in production engineering2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    System integration is a key enabler to maximize information value in an engineering context. The valuable information is normally represented by information models which play a decisive role in the implementation of system integration. The information models are designed to efficiently and effectively capture, process and communicate information among different functional and business units. However, use of the information models in implementing system integration is challenged by insufficient support from current settings of modeling architectures. This situation calls for new strategies to ease the use of information models.

    To address this challenge, this study presents a new twofold solution: Model driven system integration. It includes 1) a modeling architecture to guide the development of information models and 2) an integrated implementation process to guide the use of information models. Thus, this work improves practical applicability of an information model in its entire modeling lifecycle.

    The results contribute not only to the performance of modeling practices but also to improved understanding of information modeling in system integration. Implementation contexts and implementation models are introduced to develop an implementation-oriented modeling architecture. Further, the potential of information models as a knowledge base to sup-port implementation practices is identified.

    To concretely discuss behaviors and structures of information models, this study adopts ISO 10303 and the related standards as major references of existing information models.

    Case studies on model driven system integration validate this research in scenarios concerning kinematic modeling, kinematic error modeling, cutting tools classification and product catalogue modeling. Model driven system integration exhibits high efficiency in implementation, enhanced interoperability and increased value of information models.

  • Public defence: 2017-06-15 15:00 F3, Stockholm
    Velander, Erik
    KTH, School of Electrical Engineering (EES). Bombardier Transportation Sweden AB.
    On Gate Drivers for MOS-Controlled Power Devices and dv-dt Filters for Train Traction Converters2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, low-loss gate-drive solutions and a proposed dv/dt-filter have been investigated with focus on train traction converters with dv/dt constraints.By using the silicon carbide (SiC) junction field-effect transistor (JFET), the switching losses can be significantly reduced compared to the commonly used insulated-gate bipolar transistor (IGBT), but complex gate-driver solutions are required for high utilization in terms of loss reduction.For the IGBT and the p-i-n diode, the dv/dt across the diode at the turn-ON process of the IGBT was found to be as highest with low phase current and low temperature while the losses are as highest at high phase currents and temperatures. Therefore, a proposal meeting this tradeoff has been addressed in this thesis tailored at minimal cost for the new half-bridge package resulting in a switching loss reduction of up to 30 %.For the SiC metal oxide semiconductor field effect transistor (MOSFET), an investigation has been performed in order to use the train operation point in order to minimize the switching losses given a certain dv/dt requirement. In addition, separate control of the di/dt and dv/dt were implemented. In total, a loss reduction of 20 % is achieved. In addition, phase short-circuit investigations have been performed using the SiC MOSFET with a gate-driver proposal meeting the application requirements. The results show that short circuits with fast current rise can be terminated.Finally, a new dv/dt filter which uses the stray inductance present in the inter-connections between the power devices and the convert output terminals as a filter component is proposed. By doing so, the SiC MOSFETs can be fully utilized with high dv/dt and low switching losses even though the converter output dv/dt levels are in the range of the levels for which an IGBT equipped converter exhibits with ultra-low additional filter losses. As a consequence, the switching frequency can be four times higher for the same switching losses.