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  • Public defence: 2017-11-29 10:00 Gladan, Stockholm
    Sun, Xuan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A methodology for situated and effective design of haptic devices2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The realism of virtual surgery through a surgical simulator depends largely on the precision and reliability of the haptic device. The quality of perception depends on the design of the haptic device, which presents a complex design task due to the multi-criteria and conflicting character of the functional and performance requirements. In the model-based evaluation of the performance criteria of a haptic device, the required computational resources increase with the complexity of the device structure as well as with the increased level of detail that is created in the detail design phases. Due to uncertain requirements and a significant knowledge gap, the design task is fuzzy and more complex in the early design phases.

    The goal of this thesis is to propose a situated, i.e., flexible, scalable and efficient, methodology for multi-objective and multi-disciplinary design optimization of high-performing 6-DOF haptic devices.

    The main contributions of this thesis are:

    1. A model-based and simulation-driven engineering design methodology and a flexible pilot framework are proposed for design optimization of high-performing haptic devices. The multi-disciplinary design optimization method was utilized to balance the conflicting criteria/requirements of a multi-domain design case and to solve the design optimization problems concurrently.

    2. A multi-tool framework is proposed. The framework integrates metamodel-based design optimization with complementary engineering tools from different software vendors, which was shown to significantly reduce the total computationally effort.

    3. The metamodeling methods and sampling sizes for specific performance indices found from case studies were shown to be applicable and usable for several kinds of 6-degrees-of-freedom haptic devices.

    4. The multi-tool framework and the assisting methodology were further developed to enable computationally efficient and situated design multi-objective optimization of high-performing haptic devices. The design-of-experiment (DOE) and metamodeling techniques are integrated with the optimization process in the framework as an option to solve the design optimization case with a process that depends on the present system complexity.

  • Public defence: 2017-12-01 10:00 T1 Emmy Rappesalen, Huddinge
    Schmidt, Lisa
    KTH, School of Technology and Health (STH), Health Systems Engineering, Ergonomics. IVL Svenska Miljöinstitutet.
    Samarbete mellan kund och företagshälsovård: Mekanismer av betydelse för förebyggande arbetsmiljöarbete2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    According to the Work Environment Act, employers should, when there is lack of knowledge and competence regarding the occupational health and safety management (OHSM, employ an occupational health service (OHS) provider or comparable resource. Research on how this collaboration works is however limited. The purpose of the thesis is to investigate whether the OHS provider serves as support in the custom-er's preventive OHSM and to identify which mechanisms are important for the collaboration between the OHS provider and customer.The data collection in the four qualitative case studies was conducted using semi-structured and the-matic interviews, telephone interviews and group interviews in small and large companies as well as the public sector. The interviews were analyzed with qualitative content analysis and the overall result has been analyzed using realistic evaluation.The results show that collaboration and support from OHS providers in preventative OHSM is lacking. Contextual conditions affected collaboration, such as New Public Management and HR transformation. In the realistic evaluation, mechanisms were identified that positively or negatively affect collaboration between OHS provider and client customer. Mechanisms that affect the collaboration positively are for example; a cooperative relationship between the employers and safety representatives in OHSM at the client customer, OHS providers also need access to the client customer's internal processes. Identified mechanisms that affect the collaboration negatively are; that cooperation in the workplace between employers and employees is lacking, the OHSM does not work. Other mechanisms that negatively affect are when top management not is involved in the collaboration with the OHS provider and when the OHS provider does not get information of the client customer's OHSM.  The conclusion from the thesis is that OHS providers do not largely support the client customer's pre-ventive OHSM.

  • Public defence: 2017-12-01 13:00 F3, Stockholm
    Erixon Aalto, Hanna
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Critical Studies in Architecture.
    Projecting Urban Natures: Investigating integrative approaches to urban development and nature conservation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Projecting Urban Natures is a compilation thesis in critical studies in architecture. It comprises three journal articles and four design proposals in which I have taken an active part. The point of departure for this thesis is the renewed emphasis on social-ecological interaction and resilience that is currently taking place within ecological systems science, and the opportunities that these paradigmatic insights in turn have opened up within urbanism and design. The thesis argues that although they are promising, these emerging integrative frameworks are seldom brought into mainstream planning and urban design practice. Instead, the structuring of “nature” and “city” into a dualistic balance relationship still permeates not only the general planning discourse, but also makes its way into planning documents, notably influencing distinctions between professions. In response, this thesis sets out to rethink and explore more integrated approaches to human/nature relationships, through the utilization of design-based and transdisciplinary research methods. While this core aim of the thesis remains the same throughout the work, the task is approached from different perspectives: through different constellations of collaborative work as well as through parallel case-based explorations that emphasize the relational, anti-essentialist and situated articulation of values of urban natures and how these forces come into play. The work has been propelled through workshop-based, site-specific, and experimental design processes with professionals and researchers from the fields of e.g. systems ecology, natural resource management, political ecology, urban design, architecture, and landscape design, as well as planners, developers, local interest groups, and NGOs. Specifically, projects performed within this thesis include: Nature as an Infrastructural Potential – An Urban Strategy for Järvafältet; Kymlinge UrbanNatur together with NOD, Wingårdhs, MUST and Storylab; Årsta Urban Natures with James Corner Field Operations and Buro Happold; and Albano Resilient Campus — a collaboration between Stockholm Resilience Centre, KTH and KIT.

  • Public defence: 2017-12-05 14:00 F3, Stockholm
    Iqbal, Asifa
    KTH, School of Architecture and the Built Environment (ABE). KTH.
    Park Matters:: Studies on Safety and Property Values2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This study develops a better understanding of the nature of urban parks from a safety perspective in two international contexts. To achieve this aim, the study is divided into two geographical scales (a macro scale and a micro scale) that test a set of quantitative and qualitative research methods. The macro-scale analysis provides an overall view of the effects of parks in the neighbourhood and at the city level. A particular focus is given to the impact of parks on housing prices. Overall, the findings show that parks function as an amenity that contributes to urban quality, which in turn influences property prices in Stockholm. However, this effect depends on a number of factors such as park type, location, and the level of safety and security of the parks. Safety also matters: Parks embedded in area with high-crime rates are less valued than in areas with low-crime rates. The micro-scale of study focuses on parks as a unit of analysis and looks at the environment of parks and how it triggers crime and affects people’s safety. The first analysis is based on whether—and, if so, how—park environments affect safety (crime occurrence) using the principles of crime prevention through environmental design (CPTED) as an inventory tool in a park in an area with a high-crime rate in Stockholm, Sweden. Building on the methodology from the first study, the second study investigates the nature of women-only parks (WOPs) in Karachi, Pakistan, by looking at both the environment of the parks and the users’ and non-users’ perceptions of safety. Regardless of context, the findings show that the safety conditions of a park are highly associated with the park’s environment (design and management features). Of importance to park safety are park size in relation to the number of access routes (entrance and exit points), the opportunities for surveillance in relation to the maintenance and the lighting conditions in parks. A clear lesson is that a CPTED-informed park design promotes guardianship and therefore should be encouraged, regardless of whether it is located in Stockholm or Karachi. However, the urban context does matter to park safety conditions and is highly dependent on the local, city-wide, and national contexts in which the park is embedded.

  • Public defence: 2017-12-07 13:00 F3, Stockholm
    Viveca, Lindahl
    KTH, School of Engineering Sciences (SCI), Physics.
    Optimizing sampling of important events in complex biomolecular systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Proteins and DNA are large, complex molecules that carry out biological functions essential to all life. Their successful operation relies on adopting specific structures, stabilized by intra-molecular interactions between atoms. The spatial and temporal resolution required to study the mechanics of these molecules in full detail can only be obtained using computer simulations of molecular models. In a molecular dynamics simulation, a trajectory of the system is generated, which allows mapping out the states and dynamics of the molecule. However, the time and length scales characteristic of biological events are many orders of magnitude larger than the resolution needed to accurately describe the microscopic processes of the atoms. To overcome this problem, sampling methods have been developed that enhance the occurrence of rare but important events, which improves the statistics of simulation data.

    This thesis summarizes my work on developing the AWH method, an algorithm that adaptively optimizes sampling toward a target function and simultaneously finds and assigns probabilities to states of the simulated system. I have adapted AWH for use in molecular dynamics simulations. In doing so, I investigated the convergence of the method as a function of its input parameters and improved the robustness of the method. I have also worked on a generally applicable approach for calculating the target function in an automatic and non-arbitrary way. Traditionally, the target is set in an ad hoc way, while now sampling can be improved by 50% or more without extra effort. I have also used AWH to improve sampling in two biologically relevant applications. In one paper, we study the opening of a DNA base pair, which due to the stability of the DNA double helix only very rarely occurs spontaneously. We show that the probability of opening depends on both nearest-neighbor and longer-range sequence effect and furthermore structurally characterize the open states. In the second application the permeability and ammonia selectivity of the membrane protein aquaporin is investigated and we show that these functions are sensitive to specific mutations.

  • Public defence: 2017-12-08 10:00 FA31, Stockholm
    Lindgren, Gustav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Studies on Domain Wall Properties andDynamics in KTiOPO4 and Rb-doped KTiOPO42017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    KTiOPO4 (KTP) and Rb-doped KTP (RKTP) are two of the most attractive nonlinear opticalmaterials for engineering of periodically poled domain structures, commonly used as frequencyconversiondevices for laser radiation via the quasi-phase matching (QPM) technique. Thesematerials have excellent non-linearity, wide transparency windows and high resistance to opticaldamage. Furthermore their large domain-velocity anisotropy allows the fabrication of highaspect-ratio domain structures, needed for many QPM applications. To create highly efficientdevices, precise control over the structure uniformity and duty-cycle is required. Constantimprovement of the domain engineering techniques has allowed pushing the limits of theachievable domain aspect-ratio. For this development to continue, a deeper understanding of theformation dynamics and stability of the domain gratings is of utmost importance. As the domainsizein nanostructured devices decreases, the density of the domains walls (DWs) increases andtheir properties are ever more important for device performance. Indeed, more knowledge on thedomain wall properties, and the means to engineer them, could enable new applicationsexploiting these properties.This thesis presents studies on domain wall properties and dynamics in KTP and RKTP. Thesub-millisecond dynamics of grating formation in RKTP under an applied electric field has beenstudied in the high-field regime using online second harmonic generation. The effects ofdifferent pulse shapes were compared and single triangular pulses were found to be superior interms of the resulting grating quality.The high-temperature stability of domain gratings was investigated. The domain wall motioninduced by annealing was shown to be highly anisotropic along the a- and b-crystal axes, anddependent on the period of the grating period.The local charge transportation at the domains and domain walls in KTP was characterized usingatomic force microscopy, demonstrating a fourfold increase of conductivity at the walls.Voltage-cycling measurements revealed memristive-like characteristics, attributed to the effectof ionic motion and local charge accumulation. The enhanced conductivity of charged domainwalls was used as an imaging tool, to study domain wall dynamics while inducing motionthrough the application of an external field.Finally, the interplay between ionic motion, spontaneous polarization and polarization reversalwas investigated, showing direct evidence of elastic modulus modification during localpolarization switching.

  • Public defence: 2017-12-08 10:00 Kollegiesalen, Stockholm
    Heng, Piseth
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.

    In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.

    The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.

  • Public defence: 2017-12-08 10:00 B2, Stockholm
    Xu, Xin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. KTH.
    Phase Separation in Stainless Steels Studied by Small-angle Neutron Scattering2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fe-Cr based steels, i.e. stainless steels, possessing a combination of excellent corrosion resistance and good mechanical properties, have indispensable applications ranging from low-end cooking utensils, to sophisticated components for nuclear power plants. However, the bcc/bct phase containing stainless steels which have a miscibility gap (MG) suffer from the so-called “475 oC embrittlement” leading to hardness increase and toughness deterioration. It occurs due to demixing of Fe and Cr leading to the formation of Fe-rich (α) and Cr-rich (α′) regions in bcc/bct phases. The demixing is referred to as phase separation (PS).

    The goal of this work was to study PS in ferrite containing stainless steels mainly by small-angle neutron scattering (SANS). Firstly, the application of different experimental techniques for the study of phase separation in Fe-Cr based steels was reviewed and supplemented by new measurements. SANS was shown to be very sensitive to the nanostructure change caused by PS and capable of characterizing the early stages of PS in Fe-Cr alloys. However, atom probe tomography and transmission electron microscopy are complementary to SANS. Therefore, in order to have a more complete view of the microstructure, the combination of these techniques should be pursued. Secondly, the factors affecting the initial microstructure prior to aging treatment and the effect of the resulted initial microstructure on PS were systematically investigated using binary Fe-Cr model alloys. The critical temperature of the MG was determined to be located between 560 and 580 oC in binary Fe-Cr. The results indicate that the solution treatment temperature above the MG and the cooling rate after solution treatment have significant effects on the initial microstructure and thus on PS during subsequent aging. The mechanisms responsible for the changed aging behavior are Cr clustering, quenched-in vacancy and decomposition during cooling. Therefore, computational simulations should take into account these factors and the initial microstructure to make predictions that are more accurate. Thirdly, the study was extended to PS in commercial duplex stainless steels (DSSs) which are of practical importance in various industries, e.g., nuclear power. It is found that alloying elements have an important effect on PS in DSSs. The grade 2507 (25 %Cr, 7 %Ni) experiences stronger PS than grade 2205 (22 %Cr, 5 % Ni) for the same heat treatment. Moreover, the fracture mechanisms as well as the mechanical properties depend on the extent of PS.  Finally, the fundamental aspects regarding the neutron scattering behavior for Fe-Cr alloys were examined. The results show that the nuclear and magnetic scattering of neutrons depend on the evolution of the nanoscale compositional fluctuation in Fe-Cr alloys. The ratio of the magnitude of nuclear scattering versus magnetic scattering varies with the extent of PS.

  • Public defence: 2017-12-08 13:00 F3, Stockhom
    Svensson, Anna
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    A Utopian Quest for Universal Knowledge: Diachronic Histories of Botanical Collections between the Sixteenth Century and the Present2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores the history of botany as a global collection-based science by tracing parallels between utopian traditions and botanical collecting, from their sixteenth-century beginnings to the present. A range of botanical collections, such as gardens, herbaria and classification systems, have played a central role in the struggle to discover a global or universal scientific order for the chaotic, diverse and locally shaped kingdom of plants. These collections and utopia intersect historically, and are characterised by the same epistemology of collecting: the creation of order through confined collecting spaces or “no-place.” They are manipulations of space and time. Between chaos and order, both seek to make a whole from – often unruly – parts.

     

    The long history of botanical collecting is characterised by a degree of continuity of practice that is unusual in the sciences.  For instance, the basic technology of the herbarium – preserving plants by mounting and labelling dried specimens on paper – has been in use for almost five centuries, from sixteenth-century Italy to ongoing digitisation projects. The format of the compilation thesis is well-suited to handling the historiographical challenge of tracing continuity and discontinuity with such a long chronological scope.

     

    The thesis is structured as a walled quadripartite garden, with the Kappa enclosing four research papers and an epilogue. The papers take a diachronic approach to explore different perspectives on botanical collections: botanical collecting in seventeenth-century Oxford, pressed plants in books that are not formally collections; and the digitisation of botanical collections. These accounts are all shaped by the world of books, text and publication, historically a male-dominated sphere. In order to acknowledge marginalisation of other groups and other ways of knowing plants, the epilogue is an explanation of an embroidered patchwork of plant-dyed fabric, which forms the cover of the thesis.

  • Public defence: 2017-12-08 14:00 Kollegiesalen, Stockholm
    Vigren, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Statens väg- och transportforskningsinstitut.
    Competition in Public Transport: Essays on competitive tendering and open-access competition in Sweden2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The results of this work show that the cost efficiency of tendered bus services is similar across all Swedish counties, except for the more high-density counties where efficiency is lower. Considerably lower efficiency is also found for contracts with services run in-house by the Public Transport Authority (PTA), compared to when the same service is run by a private actor. With respect to the competitive environment, it was found that many contract design factors have little or no effect on the number of bids that the PTA sees in their tenders. No measure that could be imposed by a single PTA was found to increase the total number of bidders by more than 0.5 bidders. However, the results suggest that PTAs as a collective could try to avoid tendering too many contracts at the same time because this was shown to reduce participation by up to about two bidders. In addition, these studies show that the local competitive environment is important for the PTAs to consider. The way in which contract areas are defined will also affect the participation rate as operators were found to participate in tenders to a lower extent the farther their workplaces are from the contract area. While larger operators appear to be less sensitive with respect to such distances, the fact that smaller operators are, and that they often bid as one unit as members of cooperation companies, makes the competitive environment important. The results suggest that depots could be included in the contract to stimulate participation, but this is by no means the only nor an easy solution.

    This thesis has also analyzed the entry made in 2015 by MTR Express (MTR) on the Stockholm-Gothenburg railway line. The overall conclusion is that customers are indeed facing lower prices one and a half years after the entry. MTR's prices are on average 100 SEK lower than the incumbent SJ's prices. Furthermore, the analysis shows that the incumbent’s prices have also gone down, by almost 13 percent, following the entry.

  • Public defence: 2017-12-11 10:00 F3, Stockholm
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Synchrophasor Applications and their Vulnerability to Time Synchronization Impairment2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Recent years have seen the significance of utilizing time-synchronized, high resolution measurements from phasor measurement units (PMUs) to develop and implement wide-area monitoring, protection and control (WAMPAC) systems. WAMPAC systems aim to provide holistic view of the power system and enable detection and control of certain power system phenomena to enhance reliability and integrity of the grid.

    This thesis focuses on the design, development and experimental validation of WAMPAC applications, and investigates their vulnerability to time synchronization impairment. To this purpose, a state-of-the-art real-time hardware-in-the-loop (RT-HIL) test-bench was established for prototyping of synchrophasor-based applications. This platform was extensively used throughout the thesis for end-to-end testing of the proposed WAMPAC applications. To facilitate the development of WAMPAC applications, an open-source real-time data mediator is presented that parses the incoming synchrophasor stream and provides access to raw data in LabVIEW environment.

    Within the domain of wide-area protection applications, the thesis proposes hybrid synchrophasor and IEC 61850-8-1 GOOSE-based islanding detection and automatic synchronization schemes. These applications utilize synchrophasor measurements to assess the state of the power system and initiate protection / corrective action using GOOSE messages. The associated communication latencies incurred due to the utilization of synchrophasors and GOOSE messages are also determined. It is shown that such applications can have a seamless and cost-effective deployment in the field.

      Within the context of wide-area control applications, this thesis explores the possibility of utilizing synchrophasor-based damping signals in a commercial excitation control system (ECS). For this purpose, a hardware prototype of wide-area damping controller (WADC) is presented together with its interface with ECS. The WADC allows real-time monitoring and remote parameter tuning that could potentially facilitate system operators’ to exploit existing damping assets (e.g. conventional generators) when changes in operating conditions or network topology emerges.

    Finally the thesis experimentally investigates the impact of time synchronization impairment on WAMPAC applications by designing RT-HIL experiments for time synchronization signal loss and time synchronization spoofing. It is experimentally demonstrated that GPS-based time synchronization impairment results in corrupt phase angle computations by PMUs, and the impact this has on associated WAMPAC application. 

  • Public defence: 2017-12-11 13:00 Kollegiesalen, Stockholm
    Kolitsidas, Christos
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Electromagnetic Engineering.
    Next Generation Wideband Antenna Arrays for Communications and Radio Astrophysics2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wideband, wide-scan antenna arrays are a promising candidate for the future wireless networks and as well as an essential part of experimental radio astrophysics. Understanding the underline physics of the element performance in the array environment is paramount to develop and improve the performance of array systems. The focus of this thesis is to develop novel wideband antenna array technologies and develop new theoretical insights of the fundamental limits of antenna arrays. The developed methodologies have also been extended to include a radio astrophysics application for the global 21cm experiment.  

    Investigating the fundamental antenna array limits and extracting general performance measures can provide a priori estimates for any application of arrays. In this thesis, a general measure for antenna arrays, the array figure of merit is proposed. This measure couples bandwidth, height from the ground plane and reflection coefficient in a bounded quantity. An extension of the array figure of merit that is able to provide matching, bandwidth and directivity/gain limits is also introduced.

    The soft Vivaldi array is introduced as a novel wideband, wide-scan angle array technology. Periodic structure loading has been utilized to improve the array's performance and mold the electromagnetic wave behavior to our benefit. The soft condition has been utilized in the same manner as the conventional soft-horn antenna at the Vivaldi element. An integrated matching layer in the form of periodic strip loading is introduced. A single polarized soft Vivaldi array prototype has been developed fabricated and measured. The developed finite array has been loaded with a soft condition in the periphery to mitigate edge effects. The results indicated improved cross-polarization and side-lobe levels.

    A new class of wideband antenna arrays, the Strongly Coupled Asymmetric Dipole Array (SCADA) was also proposed in this thesis. Exploiting asymmetry in the array element introduces an additional degree of freedom that improves bandwidth and scanning performance. A novel methodology for terminating finite arrays is also proposed. The theory and an experimental antenna array is presented with good agreement between measured and simulated results. An effort to integrate a vertical wide angle matching layer was also addressed and a prototype array with this concept is presented.

    In the last part of this thesis, a methodology for the detection of the global cosmological 21cm signal from the Epoch of Reionization (EoR) is developed. The main sources of errors in this experiment, the foregrounds and the antenna chromaticity are evaluated. A new algorithmic methodology for extracting the global EoR signal is proposed. The method is based on piecewise polynomial fitting and has successfully been applied and evaluated. An antenna array that is based on the methodologies described in this thesis has been developed and evaluated with the proposed algorithm.

  • Public defence: 2017-12-12 09:30 Kollegiesalen, Stockholm
    Wang, Wei
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics. National University of Defense Technology, China.
    Spatially Adaptive Analysis and Segmentation of Polarimetric SAR Data2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, Polarimetric Synthetic Aperture Radar (PolSAR) has been one of the most important instruments for earth observation, and is increasingly used in various remote sensing applications. Statistical modelling and scattering analysis are two main ways for PolSAR data interpretation, and have been intensively investigated in the past two decades. Moreover, spatial analysis was applied in the analysis of PolSAR data and found to be beneficial to achieve more accurate interpretation results. This thesis focuses on extracting typical spatial information, i.e., edges and regions by exploring the statistical characteristics of PolSAR data. The existing spatial analysing methods are mainly based on the complex Wishart distribution, which well characterizes the inherent statistical features in homogeneous areas. However, the non-Gaussian models can give better representation of the PolSAR statistics, and therefore have the potential to improve the performance of spatial analysis, especially in heterogeneous areas. In addition, the traditional fixed-shape windows cannot accurately estimate the distribution parameter in some complicated areas, leading to the loss of the refined spatial details. Furthermore, many of the existing methods are not spatially adaptive so that the obtained results are promising in some areas whereas unsatisfactory in other areas. Therefore, this thesis is dedicated to extracting spatial information by applying the non-Gaussian statistical models and spatially adaptive strategies. The specific objectives of the thesis include: (1) to develop reliable edge detection method, (2) to develop spatially adaptive superpixel generation method, and (3) to investigate a new framework of region-based segmentation. Automatic edge detection plays a fundamental role in spatial analysis, whereas the performance of classical PolSAR edge detection methods is limited by the fixed-shape windows. Paper 1 investigates an enhanced edge detection method using the proposed directional span-driven adaptive (DSDA) window. The DSDA window has variable sizes and flexible shapes, and can overcome the limitation of fixed-shape windows by adaptively selecting homogeneous samples. The spherically invariant random vector (SIRV) product model is adopted to characterize the PolSAR data, and a span ratio is combined with the SIRV distance to highlight the dissimilarity measure. The experimental results demonstrated that the proposed method can detect not only the obvious edges, but also the tiny and inconspicuous edges in heterogeneous areas. Edge detection and region segmentation are two important aspects of spatial analysis. As to the region segmentation, paper 2 presents an adaptive PolSAR superpixel generation method based on the simple linear iterative clustering (SLIC) framework. In the k-means clustering procedure, multiple cues including polarimetric, spatial, and texture information are considered to measure the distance. Since the constant weighting factor which balances the spectral similarity and spatial proximity may cause over- or under-superpixel segmentation in different areas, the proposed method sets the factor adaptively based on the homogeneity analysis. Then, in heterogeneous areas, the spectral similarity is more significant than the spatial constraint, generating superpixels which better preserved local details and refined structures. Paper 3 investigates another PolSAR superpixel generation method, which is achieved from the global optimization aspect, using the entropy rate method. The distance between neighbouring pixels is calculated based on their corresponding DSDA regions. In addition, the SIRV distance and the Wishart distance are combined together. Therefore, the proposed method makes good use of the entropy rate framework, and also incorporates the merits of the SIRV distance and the Wishart distance. The superpixels are generated in a homogeneity-adaptive manner, resulting in smooth representation of the land covers in homogeneous areas, and well preserved details in heterogeneous areas.

  • Public defence: 2017-12-12 10:00 F3, Stockholm
    Bogodorova, Tetiana
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Modeling, Model Validation and Uncertainty Identification for Power System Analysis2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    It is widely accepted that correct system modeling and identification are among the most important issues power system operators face when managing instability and post-contingency scenarios. The latter is usually performed involving special computational tools that allow the operator to forecast, prevent system failure and take appropriate actions according to protocols for different contingency cases in the system. To ensure that operators make the correct simulation-based decisions, the power system models have to be validated continuously. This thesis investigates power system modeling, identification and validation problems that are formulated and based on data provided by operators, and offers new methods and deeper insight into stages of an identification cycle considering the specifics of power systems.

    One of the problems this thesis tackled is the selection of a modeling and simulation environment that provides transparency and possibility for unambiguous model exchange between system operators. Modelica as equation-based language fulfills these requirements. In this thesis Modelica phasor time domain models were developed and software-to-software validated against conventional simulation environments, i.e. SPS/Simulink and PSAT in MATLAB.

    Parameter estimation tasks for Modelica models require a modular and extensible toolbox. Thus, RaPiD Toolbox, a framework that provides system identification algorithms for Modelica models, was developed in MATLAB. Contributions of this thesis are an implementation of the Particle Filter algorithm and validation metrics for parameter identification. The performance of the proposed algorithm has been compared with Particle Swarm Optimization (PSO) algorithm when combined with simplex search and parallelized to get computational speed up. The Particle Filter outperformed PSO when estimating turbine-governor model parameters in the Greek power plant model relying on real measurements.

    This thesis also analyses different model structures (Nonlinear AutoRegressive eXogenous (NARX) model, Hammerstein-Wiener model, and high order transfer function) that are selected to reproduce nonlinear dynamics of a Static VAR Compensator (SVC) under incomplete information available for National Grid system operator. The study has shown that standard SVC model poorly reproduces the measured dynamics of the real system. Therefore, black-box mathematical modeling and identification approach has been proposed to solve the problem. Also, the introduced combination of first-principle and black-box approach has shown the best output fit. The methodology following identification cycle together with model order selection and model validation issues was presented in detail.

    Finally, one of the major contributions is a new method to formulate the uncertainty of parameters estimated in the form of a multimodal Gaussian mixture distribution that is estimated from the Particle Filter output by applying statistical methods to select the standard deviations. The proposed methodology gives additional insight into power system properties when estimating the parameters of the model. This allows power system analysts to decide on the design of validation tests for the chosen model.

  • Public defence: 2017-12-12 10:00 B1, Stockholm
    Kellner, Hans
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Study of Non-metallic Inclusion in Alloy 8252017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt.

    The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting.

    Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes <20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor.

    Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes.

  • Public defence: 2017-12-13 09:00 F3, Stockholm
    Fridström, Richard
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Resonant magnetic perturbation effect on the tearing mode dynamics: Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode.

    In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity.

    In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.

  • Public defence: 2017-12-13 09:30 E36, Stockholm
    Lin, Jingyi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Spatial analysis and modeling of urban transportation networks2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Transport systems in general, and urban transportation systems in particular, are the backbone of a country or a city, therefore play an intrinsic role in the socio-economic development. There have been numerous studies on real transportation systems from multiple fileds, including geography, urban planning, and engineering. Geographers have extensively investigated transportation systems, and transport geography has developed as an important branch of geography with various studies on system structure, efficiency optimization, and flow distribution. However, the emergence of complex network theory provided a brand-new perspective for geographers and other researchers; therefore, it invoked more widespread interest in exploring transportation systems that present a typical node-link network structure. This trend inspires the author and, to a large extent, constitutes the motivation of this thesis.

     

    The overall objective of this thesis is to study and simulate the structure and dynamics of urban transportation systems, including aviation systems and ground transportation systems. More specificically, topological features, geometric properties, and dynamic evolution processes are explored and discussed in this thesis. To illustrate different construction mechanisms, as well as distinct evolving backgrounds of aviation systems and ground systems, China’s aviation network, U.S. airline network, Stockholm’s street network, Toronto’s street network, and Nanjing’s street network are respectively studied and compared.

     

    Considering the existence of numerous studies, a clear and comprehensive literature review in this field is presented as the first step. Most studies on transport systems from the complex network perspective published within the last decade are reviewed and summarized. It is found that a majority of the studies focused on topological features of transportation systems, however geometric properties have not earned sufficient attention. On the other hand, since there is a long history of transportation systems and limited availability of related data, it is difficult for researchers to develop empirical evolution analyses on real transportation systems; instead, computer simulations based on mathematical reasoning are considered as the most widely used way to depict evolution features of transport systems. These findings lay the foundation of the author’s thesis research.

     

    In this thesis, most network features, including both local and global measures, such as centrality, clustering, and efficiency, are respectively discussed in terms of aviation systems and urban street networks. Although transportation systems are affected by various factors, they do present a small-world structure and a double Pareto distribution regardless of sizes and socio-economic states. A hierarchical structure is also detected for aviation systems of China and the US.

    To study the geometric properties, the famous gravity model is introduced to detect the distance effect in aviation systems. It is found that a logarithmic hyperbolic model can better depict the distance decay effect than a power law model. In addition, the distribution patterns of the spatial distance of aviation systems and ground systems are explained. Spatial patterns of street networks in different urban development schemes are discussed and compared as well. Self-organized cities show more heterogeneity in both measures. In comparison, Toronto presents a single peak distribution for the cell area. The distribution of closeness centrality, which is regarded as a measure of accessibility, clearly depicts that the strictly planned city is better accessed from the overall perspective.

     

    A static perspective is far from enough to understand and model transportation systems. The evolution process is an essential supplement to depict underlying features of complex systems. To further study network growth modeling, a model for the evolution of aviation systems is proposed. Both topological and geometric features are examined in the evolution process. The model suggests that the bigger the weight coefficient is, the slower the network efficiency decreases. The empirical analysis about the U.S. airline network during 1990–2010 is also developed to validate this model.

     

    The main contributions of this thesis can be summarized as follows. First, it provides a comprehensive review of complex network topology of transportation systems for researchers from different backgrounds. It not only lists the research results from various subjects, but it also bridges and compares the results from different viewpoints and angles, which is necessary to explore this interdisciplinary topic. Moreover, a spatial perspective constitutes the main focus of this thesis, trying to bridge the traditional geographic analysis and complex network theory. Lastly, empirical analyses are developed to explore the evolving process of transportation systems, providing a valuable baseline for theoretical simulations in this field. However, as mentioned above, the spatial structures are preliminarily explored in this work, and more efforts are expected in the near future. On the other hand, this work is generally driven by data analysis and computer simulation. Although these approaches are effective to analyze and model transportation systems, more real-world factors, such as urban development variables and spatial constraints, should be considered in further studies from a geographic perspective.

  • Public defence: 2017-12-13 10:15 D3, Stockholm
    Sundström, Elias
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Flow instabilities in centrifugal compressors at low mass flow rate2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A centrifugal compressor is a mechanical machine with purpose to convert kineticenergy from a rotating impeller wheel into the fluid medium by compressingit. One application involves supplying boost air pressure to downsized internalcombustion engines (ICE). This allows, for a given combustion chamber volume,more oxygen to the combustion process, which is key for an elevated energeticefficiency and reducing emissions. However, the centrifugal compressor is limitedat off-design operating conditions by the inception of flow instabilities causingrotating stall and/or surge. These instabilities appear at low flow rates andtypically leads to large vibrations and stress levels. Such instabilities affectthe operating life-time of the machine and are associated with significant noiselevels.The flow in centrifugal compressors is complex due to the presence of a widerange of temporal- and spatial-scales and flow instabilities. The success fromconverting basic technology into a working design depends on understandingthe flow instabilities at off-design operating conditions, which limit significantlythe performance of the compressor. Therefore, the thesis aims to elucidate theunderlying flow mechanisms leading to rotating stall and/or surge by means ofnumerical analysis. Such knowledge may allow improved centrifugal compressordesigns enabling them to operate more silent over a broader operating range.Centrifugal compressors may have complex shapes with a rotating partthat generate turbulent flow separation, shear-layers and wakes. These flowfeatures must be assessed if one wants to understand the interactions among theflow structures at different locations within the compressor. For high fidelityprediction of the complex flow field, the Large Eddy Simulation (LES) approachis employed, which enables capturing relevant flow-driven instabilities underoff-design conditions. The LES solution sensitivity to the grid resolution usedand to the time-step employed has been assessed. Available experimentaldata in terms of compressor performance parameters, time-averaged velocity,pressure data (time-averaged and spectra) were used for validation purposes.LES produces a substantial amount of temporal and spatial flow data. Thisnecessitates efficient post-processing and introduction of statistical averagingin order to extract useful information from the instantaneous chaotic data. Inthe thesis, flow mode decomposition techniques and statistical methods, suchas Fourier spectra analysis, Dynamic Mode Decomposition (DMD), ProperOrthogonal Decomposition (POD) and two-point correlations, respectively, areemployed. These methods allow quantifying large coherent flow structures atvfrequencies of interest. Among the main findings a dominant mode was foundassociated with surge, which is categorized as a filling and emptying processof the system as a whole. The computed LES data suggest that it is causedby substantial periodic oscillation of the impeller blade incidence flow angleleading to complete system flow reversal. The rotating stall flow mode occurringprior to surge and co-existing with it, was also captured. It shows rotating flowfeatures upstream of the impeller as well as in the diffuser.

  • Public defence: 2017-12-13 14:00 Salongen, Stockholm
    Edström, Kristina
    KTH, School of Education and Communication in Engineering Science (ECE), Learning.
    Exploring the dual nature of engineering education: Opportunities and challenges in integrating the academic and professional aspects in the curriculum2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Engineering education is both academic, emphasising theory in a range of subjects, and professional, preparing students for engineering practice. Ideally, these aspects are also in a meaningful relationship in the curriculum, but the dual nature ideal is simultaneously a source of tensions. This theme is explored in the context of engineering education development, represented by the CDIO (Conceive, Design, Implement, Operate) approach. Cases on programme and course level illustrate how the dual nature ideal is pursued in the integrated curriculum. CDIO is also compared with PBL (problem/project-based learning), and opportunities to further emphasise research in the CDIO community are explored.

    Two critical accounts suggest widening the perspective from curriculum development per se, to the organisational conditions. First, the views of Carl Richard Söderberg (1895-1979) are compared with CDIO, showing considerable similarities in ideals, arguments, and strategies. This leads to a critique of the swinging pendulum metaphor. Then, experiences of unsustainable change leads to a model called organisational gravity, explaining the stability of programmes and implying two change strategies, with different availability, risks, resource demands, and sustainability of results.

    Refuting a rationalist view on organisation, an institutional logics perspective is used to analyse the tensions within engineering education. It is suggested that the logics of the academic profession dominates over the logics of the engineering profession, hence favouring “teaching theory” over “teaching professionals”. The integrated curriculum strategy is contingent on educators’ ability to unite theoretical and professional aspects in courses, and on the collegial capacity for coordination. Finally, the CDIO initiative is conceptualised as a field-level driver of institutional innovation, identifying some strategies for legitimacy.

  • Public defence: 2017-12-14 10:00 D3, Stockholm
    Brynjell-Rahkola, Mattias
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Studies on instability and optimal forcing of incompressible flows2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis considers the hydrodynamic instability and optimal forcing of a number of incompressible flow cases. In the first part, the instabilities of three problems that are of great interest in energy and aerospace applications are studied, namely a Blasius boundary layer subject to localized wall-suction, a Falkner–Skan–Cooke boundary layer with a localized surface roughness, and a pair of helical vortices. The two boundary layer flows are studied through spectral element simulations and eigenvalue computations, which enable their long-term behavior as well as the mechanisms causing transition to be determined. The emergence of transition in these cases is found to originate from a linear flow instability, but whereas the onset of this instability in the Blasius flow can be associated with a localized region in the vicinity of the suction orifice, the instability in the Falkner–Skan–Cooke flow involves the entire flow field. Due to this difference, the results of the eigenvalue analysis in the former case are found to be robust with respect to numerical parameters and domain size, whereas the results in the latter case exhibit an extreme sensitivity that prevents domain independent critical parameters from being determined. The instability of the two helices is primarily addressed through experiments and analytic theory. It is shown that the well known pairing instability of neighboring vortex filaments is responsible for transition, and careful measurements enable growth rates of the instabilities to be obtained that are in close agreement with theoretical predictions. Using the experimental baseflow data, a successful attempt is subsequently also made to reproduce this experiment numerically.

    In the second part of the thesis, a novel method for computing the optimal forcing of a dynamical system is developed. The method is based on an application of the inverse power method preconditioned by the Laplace preconditioner to the direct and adjoint resolvent operators. The method is analyzed for the Ginzburg–Landau equation and afterwards the Navier–Stokes equations, where it is implemented in the spectral element method and validated on the two-dimensional lid-driven cavity flow and the flow around a cylinder.

  • Public defence: 2017-12-15 09:00 Sal-C, Kista.
    Awan, Ahsan Javed
    KTH, School of Information and Communication Technology (ICT), Software and Computer systems, SCS.
    Performance Characterization and Optimization of In-Memory Data Analytics on a Scale-up Server2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The sheer increase in the volume of data over the last decade has triggered research in cluster computing frameworks that enable web enterprises to extract big insights from big data. While Apache Spark defines the state of the art in big data analytics platforms for (i) exploiting data-flow and in-memory computing and (ii) for exhibiting superior scale-out performance on the commodity machines, little effort has been devoted to understanding the performance of in-memory data analytics with Spark on modern scale-up servers. This thesis characterizes the performance of in-memory data analytics with Spark on scale-up servers.Through empirical evaluation of representative benchmark workloads on a dual socket server, we have found that in-memory data analytics with Spark exhibit poor multi-core scalability beyond 12 cores due to thread level load imbalance and work-time inflation (the additional CPU time spent by threads in a multi-threaded computation beyond the CPU time required to perform the same work in a sequential computation). We have also found that workloads are bound by the latency of frequent data accesses to the memory. By enlarging input data size, application performance degrades significantly due to the substantial increase in wait time during I/O operations and garbage collection, despite 10% better instruction retirement rate (due to lower L1cache misses and higher core utilization).For data accesses, we have found that simultaneous multi-threading is effective in hiding the data latencies. We have also observed that (i) data locality on NUMA nodes can improve the performance by 10% on average,(ii) disabling next-line L1-D prefetchers can reduce the execution time by upto14%. For garbage collection impact, we match memory behavior with the garbage collector to improve the performance of applications between 1.6xto 3x and recommend using multiple small Spark executors that can provide up to 36% reduction in execution time over single large executor. Based on the characteristics of workloads, the thesis envisions near-memory and near storage hardware acceleration to improve the single-node performance of scale-out frameworks like Apache Spark. Using modeling techniques, it estimates the speed-up of 4x for Apache Spark on scale-up servers augmented with near-data accelerators.

  • Public defence: 2017-12-15 09:00 M2, Stockholm
    Zhou, Xiamo
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    OSTE Microfluidic Technologies for Cell Encapsulation and Biomolecular Analysis2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In novel drug delivery system, the encapsulation of therapeutic cells in microparticles has great promises for the treatment of a range of health con- ditions. Therefore, the encapsulation material and technology are of great importance to the validity and efficiency of the advanced medical therapy. Several unsolved challenges in regards to versatile microparticle synthesis ma- terials and methods form the main obstacle for a translation of novel cell therapy concepts from research to clinical practice.

    Thiol-ene based polymer systems have emerged and gained great popular- ity in material development in general and in biomedical applications specif- ically. The thiol-ene platform is broad and therefore of interest for a variety of applications. At the same time, many aspects of this material platform are largely unexplored, for example material and manufacturing technology developments for microfluidic applications .

    In this Ph.D. thesis, thiol-ene materials are explored for use in cell encap- sulation. The marriage of these two technology fields breeds the possibility for a novel microfluidic cell encapsulation approach using a novel encapsulation material. To this end, several new manufacturing technologies for thiol-ene and thiol-ene-epoxy droplet microfluidic devices were developed. Moreover, core-shell microparticle synthesis for cell encapsulation based on a novel co- synthesis concept using a thiol-ene based material was developed and inves- tigated. Finally, a thiol-ene-epoxy system was also used for the formation of microwells and microchannels that improve protein analysis on microarrays.

    The first part of the thesis presents the background and state-of-the-art technologies in regards to cell therapy, microfluidics, and thiol-ene based ma- terials. In the second part of the thesis, a novel manufacturing approach of thiol-ene-epoxy material as well as core-shell particle co-synthesis in micro- fluidics using thiol-ene based material are presented and characterized. The third part of the thesis presents the cell viability studies of encapsulated cells using the novel encapsulation material and method. In the final part of the thesis, two applications of thiol-ene-epoxy gaskets for protein detection mi- croarrays are presented. 

  • Public defence: 2017-12-15 09:15 Kollegiesalen, Stockholm
    Zea, Elias
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Sound field separation with microphone arrays2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sound field analysis is a fundamental tool in the design, manufacturing, testing and diagnosis of machines and transportation means, as well as the legislations that regulate noise levels in order to minimize environmental pollution. Customary solutions to the problem of sound field analysis are microphone array technologies such as near-field acoustic holography (NAH) and beamforming. One of the challenges of using these technologies often lies in the difficulty for separating disturbing sounds from the target source, specially when these are correlated. For example, NAH requires that no reflecting surfaces are found in the vicinity of the array, which is in theory only possible in an echo-free chamber. On the other hand, beamforming is most suitably used to separate uncorrelated sound sources, which is not the case of, for instance, the noise generated by the contact between the wheel of a train and a railway track. The present thesis examines the research problems of separating a sound source from its reflections, and separating the rail noise from the total noise radiated by a passing train. The overall goal of the thesis is to push the limits of microphone array technologies in the context of sound field separation, to the end of minimizing the cost and complexity of measurements and analyses. The proposed separation methods are formulated in the wavenumber domain, and the measurements are done with uniform single layer microphone arrays. The problem of separating reflections is addressed in three different papers: (i) compact sources and a parallel reflector, (ii) planar source and a parallel reflector, and (iii) a perpendicular reflector with respect to the microphone array, and the common requirement is the knowledge of the reflector impedance. The problem of separating rail noise is studied in a fourth paper, and the proposed method is formulated such that it does not require prior knowledge of the rail properties. Upon the findings obtained in the papers, a comprehensive description of areas for future work, as well as strategies to approach them, is given at the end of the thesis. 

    The full text will be freely available from 2017-12-15 09:15
  • Public defence: 2017-12-15 10:00 F3, Stockholm
    Andrén, Oliver
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Exploring bis-MPA Based Dendritic Structures in Biomedicine2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last decades there has been significant advances in polymer chemistry. New coupling chemistries, polymerization techniques and accelerated approaches enable researches to push the limits of structural control. One outcome of such development is the field of linear dendritic (LD) and dendritic linear dendritic (DLD) hybrid materials, drawing benefit from both linear and dendritic material properties. LD-hybrids with their high density of functional groups and customizability offer much promise for use in biological applications. This thesis deals with the potential use of sophisticated LD-hybrid materials focusing on the field of biomedicine and biomedical applications. The linear component is manly poly(ethylene glycol) (PEG) while the dendritic part consists of 2,2-Bis(hydroxymethyl)propionic (bis-MPA) building blocks.

    Initially a family of unsymmetrical LD amphiphiles was constructed and evaluated as carriers for drug delivery of chemotherapeutics. Through self-assembly driven by their amphiphilic nature nanocarriers (NC) were constructed with a hydrophobic core and hydrophilic corona. NC were found to enhance the effect of conventional therapeutics by relocating the drug from just the nucleus to the mitochondria among other organelles. Their versatile nature allowed for dual loading of a combination of chemotherapeutics and circumvented the resistance mechanism of resistant cancer cells.

    Dendrimers containing a disulfide in the backbone were also constructed, these enabled the selective fragmentation of the dendrimer by reduction to small molecular thiols. The fragments were also envisioned to disrupt the delicate thiol-disulfide balance intracellularly causing reactive oxygen species (ROS). Dendrimers were elaborated by conjugation to linear PEG creating LD-hybrids and evaluated in vitro and where found to cause high degree of ROS in cancerous cells.

    Thiol functional polymers were created, including linear polymers, dendrimers and DLD-hybrids. The DLD-hybrids were utilized as hydrogels through two efficient chemistries relying on the versatility of the thiol. By varying the generation of the LD-hybrid and the cross-linking chemistry the modulus could be tuned.

    Amine functional LD-hybrids were constructed utilizing the amino acid alanine. Scaffolds were utilized as antimicrobial hydrogels for prophylaxis during surgical intervention. LD-hybrids were initially evaluated in planktonic mode, and were found to have broad spectrum effect and were highly effective against resistant bacteria. Gelation was studied relying on N-hydroxysuccinimide (NHS) esters as cross-linkers, enabling instantaneous gelation under biological conditions. The gels moduli could be varied to match various tissues including stromal and muscle. The effect of the antimicrobial coatings was investigated with promising results both in vitro and in vivo.

    Finally, more industrially applicable hyperbranched LD-hybrids were constructed. The synthetic strategy relied on a convenient pseudo one-pot approach using Fisher esterification along with sequential monomer addition. Materials were found to have properties and characteristics similar to those of perfect dendritic LD-hybrids. And the scaffolds were evaluated in a range of applications such as hydrogels and isopourous films with promising results.

    The full text will be freely available from 2018-11-24 00:00
  • Public defence: 2017-12-15 16:57 D3, Stockholm
    Fornari, Walter
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Suspensions of finite-size rigid particles in laminar and turbulent flows2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dispersed multiphase flows occur in many biological, engineering and geophysical applications such as fluidized beds, soot particle dispersion and pyroclastic flows. Understanding the behavior of suspensions is a very difficult task. Indeed particles may differ in size, shape, density and stiffness, their concentration varies from one case to another, and the carrier fluid may be quiescent or turbulent. When turbulent flows are considered, the problem is further complicated by the interactions between particles and eddies of different size, ranging from the smallest dissipative scales up to the largest integral scales. Most of theinvestigations on this topic have dealt with heavy small particles (typically smaller than the dissipative scale) and in the dilute regime. Less is known regarding the behavior of suspensions of finite-size particles (particles that are larger than the smallest length scales of the fluid phase).

    In the present work, we numerically study the behavior of suspensions of finite-size rigid particles in different flows. In particular, we perform direct numerical simulations using an immersed boundary method to account for the solid phase. Firstly, the sedimentation of spherical particles slightly smaller than the Taylor microscale in sustained homogeneous isotropic turbulence and quiescent fluid is investigated. The results show that the mean settling velocity is lower in an already turbulent flow than in a quiescent fluid. By estimating the mean drag acting on the particles, we find that non stationary effects explain the increased reduction in mean settling velocity in turbulent environments. Moreover, when the turbulence root-mean-square velocity is larger than the terminal speed of a particle, the overall drag is further enhanced due to the large particles cross-flow velocities.

    We also investigate the settling in quiescent fluid of oblate particles. We find that at low volume fractions the mean settling speed of the suspension is substantially larger than the terminal speed of an isolated oblate. This is due to the formation of clusters that appear as columnar-like structures.

    Suspensions of finite-size spheres are also studied in turbulent channel flow. We change the solid volume and mass fractions, and the solid-to-fluid density ratio in an idealized scenario where gravity is neglected. The aim is to independently understand the effects of these parameters on both fluid and solid phases statistics. It is found that the statistics are substantially altered by changes in volume fraction, while the main effect of increasing the density ratio is a shear-induced migration toward the centerline. However, at very high density ratios (∼ 1000) the solid phase decouples from the fluid, and the particles behave as a dense gas.

    In this flow case, we also study the effects of polydispersity by considering Gaussian distributions of particle radii (with increasing standard deviation), at constant volume fraction. We find that fluid and particle statistics are almost unaltered with respect to the reference monodisperse suspension. These results confirm the importance of the solid volume fraction in determing the behavior of a suspension of spheres.

    We then consider suspensions of solid spheres in turbulent duct flows. We see that particles accumulate mostly at the corners. However, at large volume fractions the particles concentrate mostly at the duct core. Secondary motions are enhanced by increasing the volume fraction, until excluded volume effects are so strong that the turbulence activity is reduced. The same is found for the mean friction Reynolds number.

    The inertial migration of spheres in laminar square duct flows is also investigated. We consider dilute and semi-dilute suspensions at different bulk Reynolds numbers and duct-to-particle size ratios. The highest particle concentration is found in regions around the focusing points, except at very large volume fractions since particles distribute uniformly in the cross-section. Particles also induce secondary fluid motions that become more intense with the volume fraction, until a critical value of the latter quantity is reached.

    Finally we study the rheology of confined dense suspensions of spheres in simple shear flow. We focus on the weakly inertial regime and show that the suspension effective viscosity varies non-monotonically with increasing confinement. The minima of the effective viscosity occur when the channel width is approximately an integer number of particle diameters. At these confinements, the particles self-organize into two-dimensional frozen layers that slide onto each other.

  • Public defence: 2017-12-18 10:00 Kollegiesal, Stockholm
    Armendáriz, Mikel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Cost-effective Communication and Control Architectures for Active Low Voltage Grids2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional flow of power. However, nowadays the massive integration of distributed energy resources into distribution grids, such as solar photovoltaics, distributed storage, electric vehicles and demand response programs, presents some challenges. For instance, the unidirectional top-down power flow is being replaced by power flows in any direction: top-down and bottom-up. This paradigm shift adds extra regulatory, economic, and technical complexity for the Distribution System Operators (DSO). Thus to overcome the possible operational constraints, thermal limits, or voltage problems in the grid, an update of the existing electricity infrastructures is required. In response to this new situation, this thesis investigates the cost-effective communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a DSO’s perspective. The solutions include: i) optimal sensor placement configuration to perform low voltage state estimation, ii) optimal metering infrastructure designs for active low voltage monitoring applications, iii) coordinated control strategies to allow the integration of microgrid-like structures into the distribution grids, iv) optimal placement of actuators for operating the control strategies, v) a multiagent-based control solution for self-healing and feeder reconfiguration applications, and vi) a framework model and simulations to assess the reliability of the ICT infrastructure that enables the monitoring and control applications. As concluding remark, since the deployment of technology at low voltage grids is restricted to assets owned by the DSO, the operability of the grid is limited. This condition makes it so that the required communication and control enhancement solutions shall prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analyses of the potential improvement solutions for each grid, because this will allow deploying the right technology only at the necessary locations.

  • Public defence: 2017-12-18 10:00 K1, Stockholm
    Lindberg, Jonas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Electrochemical Investigation of the Reaction Mechanism in Lithium-Oxygen Batteries2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges.

    Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased.

    Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one.

    Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface.

    During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed.

    The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium.

    During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence.

  • Public defence: 2017-12-19 12:00 Madrid
    Khan, Zarrar
    KTH, School of Electrical Engineering (EES). Universidad Pontificia Comillas.
    Integrating Water and Energy Systems for Long-Term Resource Management2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Availability of and access to water and energy are key ingredients for economic and social development. Predictions show that pressure on already limited water and energy resources is expected to increase in many parts of the world as a result of growing populations, rapid urbanization, increasing pollution and climate change impacts. The water and energy systems are highly interdependent and these interlinks provide important opportunities to improve resource security and prevent inefficient decisions which could exacerbate problems even further.

    This thesis explores the benefits to be gained from and the drawbacks of ignoring the various interlinks. A review of several existing water-energy integration modeling methodologies shows that the different physical, temporal and spatial characteristics of the water and energy systems present several hurdles in analyzing the two resources simultaneously. This thesis overcomes many of these issues by developing a fully integrated hard-linked water-energy linear optimization model. A case study from Spain is used to demonstrate the applications of the model for simultaneous analysis of water, energy and climate change adaptation strategies. An integrated approach is shown to have several benefits including lower total costs, better resource efficiency and improved robustness for a wide range of variations in several uncertain parameters.

  • Public defence: 2017-12-20 13:15 Kollegiesalen, Stockholm
    Wahlström, Johan
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Sensor Fusion for Smartphone-based Vehicle Telematics2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The fields of navigation and motion inference have rapidly been transformed by advances in computing, connectivity, and sensor design. As a result, unprecedented amounts of data are today being collected by cheap and small navigation sensors residing in our surroundings. Often, these sensors will be embedded into personal mobile devices such as smartphones and tablets. To transform the collected data into valuable information, one must typically formulate and solve a statistical inference problem.

    This thesis is concerned with inference problems that arise when trying to use smartphone sensors to extract information on driving behavior and traffic conditions. One of the fundamental differences between smartphone-based driver behavior profiling and traditional analysis based on vehicle-fixed sensors is that the former is based on measurements from sensors that are mobile with respect to the vehicle. Thus, the utility of data from smartphone-embedded sensors is diminished by not knowing the relative orientation and position of the smartphone and the vehicle.

    The problem of estimating the relative smartphone-to-vehicle orientation is solved by extending the state-space model of a global navigation satellite system-aided inertial navigation system. Specifically, the state vector is augmented to include the relative orientation, and the measurement vector is augmented with pseudo observations describing well-known characteristics of car dynamics. To estimate the relative positions of multiple smartphones, we exploit the kinematic relation between the accelerometer measurements from different smartphones. The characteristics of the estimation problem are examined using the Cramér-Rao bound, and the positioning method is evaluated in a field study using concurrent measurements from seven smartphones.

    The characteristics of smartphone data vary with the smartphone's placement in the vehicle. To investigate this, a large set of vehicle trip segments are clustered based on measurements from smartphone-embedded sensors and vehicle-fixed accelerometers. The clusters are interpreted as representing the smartphone being rigidly mounted on a cradle, placed on the passenger seat, held by hand, etc. Finally, the problem of fusing speed measurements from the on-board diagnostics system and a global navigation satellite system receiver is considered. Estimators of the vehicle’s speed and the scale factor of the wheel speed sensors are derived under the assumptions of synchronous and asynchronous samples.

  • Public defence: 2018-01-09 10:00 Kollegiesalen, Stockholm
    Nejad Ghafar, Ali
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    An Experimental Study to Measure Grout Penetrability, Improve the Grout Spread, and Evaluate the Real Time Grouting Control Theory2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to the significant influence of the grout penetrability properties on spread of grout in rock fractures, this study aimed to investigate the grout penetrability from four different aspects. In Part (a), after review of all the existing methodologies developed to measure the grout penetrability, Filter-pump and Penetrability-meter were examined against Short-slot to figure out which one is more reliable. The study decisively considered Short-slot more reliable. In part (b), the so-called varying aperture long slot (VALS), an artificial fracture with apertures of 230-10 μm, was developed to study the gout penetrability more realistically. In part (c), a low-frequency rectangular pressure impulse was introduced to improve the grout spread by successive erosion of the produced filter cakes in consecutive cycles. The results showed considerable improvement in experiments using Short-slot. The dissipation of the pressure impulses was then investigated using VALS with noticeable remaining amplitudes after 2.0-2.7 m. In part (d), VALS was once more introduced to examine RTGC theory in a fracture with variable aperture. The study showed a relatively satisfactory agreement between the experimental results and the predictions of the grout propagation using the hydraulic aperture, whereas the predictions using the mean physical aperture showed considerably faster spread.