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  • Public defence: 2018-04-26 10:00 B3, Stockholm
    Svidró, Péter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Jönköping University.
    On the Mechanisms of Volume Change Related Casting Defects Formation in Lamellar Graphite Iron2018Doctoral thesis, monograph (Other academic)
  • Public defence: 2018-04-27 10:00 F3, Stockholm
    van de Hoef, Sebastian
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Coordination of Heavy-Duty Vehicle Platooning2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A network-wide coordination system for heavy-duty vehicle platooning with the purpose of reducing fuel consumption is developed. Road freight is by far the dominating mode for overland transport with over 60 % modal share in the OECD countries and is thus critically important for the economy. Overcoming its strong dependency on fossil fuels and manual labor as well as handling rising congestion levels are therefore important societal challenges. Heavy-duty vehicle platooning is a promising near-term automated-driving technology. It combines vehicle-to-vehicle communication and on-board automation to slipstream in a safe manner, which can reduce fuel consumption by more than 10 %. However, in order to realize these benefits in practice, a strategy is needed to form platoons in an operational context. We propose a platoon coordination system that supports the process of automatically forming platoons over large geographic areas.

    We develop an architecture in which fleet management systems send start locations, destinations, and arrival deadlines to a platoon coordinator. By computing desirable speed profiles and by letting the vehicles' on-board systems track them, vehicles can meet en route and form platoons. Matching vehicles into platoons and deriving suitable speed profiles is treated as an optimization problem with the objective of maximizing the overall fuel savings under the constraint that vehicles arrive in time at their destinations. By updating the speed profiles and the platoon configurations based on real-time measurements of vehicle position and platoon state, the system can accommodate new vehicles joining on the fly. Using real-time measurements also makes the system resilient to disturbances and changing operating conditions. This thesis seeks to develop the theoretical foundations of such a system and evaluate its potential to improve transport efficiency.  

    We first explore the coordination of vehicle pairs. Fuel-optimal speed profiles are derived. The uncertainty arising from traffic is taken into account by modeling travel time distributions and considering the probability of two vehicles successfully merging. Building on this coordination algorithm for vehicle pairs, we derive algorithms for larger platoons and vehicle fleets. This results in an NP-hard combinatorial optimization problem. The problem is formulated as an integer program and results on the solution structure are derived. In order to handle realistic fleet sizes with thousands of vehicles and continental sized geographical areas under real-time operation, heuristic algorithms are developed. The speed profiles resulting from the combinatorial optimization are further improved using convex optimization. Moreover, we derive efficient algorithms to identify all pairs of vehicles that can platoon. Simulations demonstrate that the proposed algorithm is able to compute plans for thousands of vehicles. Coordinating approximately a tenth of Germany's heavy-duty vehicle traffic, platooning rates over 65 % can be achieved and fuel consumption can be reduced by over 5 %. The proposed system was implemented in a demonstrator system. This demonstrator system has been used in experiments on public roads that show the technical feasibility of en route platoon coordination.

  • Public defence: 2018-04-27 11:04 Gladan, Stockholm
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Railway Open System Tribology2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tribology in the railway system is of increasing interest in the new railway era due to the demand for higher speed and load capacity. Since railway vehicles operate in an open environment, their performance depends greatly on temperature, humidity and natural and artificial contaminants. Meanwhile, the “feedback” of railway vehicles to the surroundings, such as noise and airborne particles, is of great importance to the human health and the environment. Therefore, this thesis aims to investigate the strong interaction between railway tribology and the open environment. The effects of temperatures from -35 °C to 20 °C, relative humidity from 40% to 85%, natural contaminants such as ice particles on friction, wear, noise and airborne particle emissions at the wheel–rail and wheel–block brake contacts have been investigated in both lab- and full-scale contexts.

    Papers A and B investigated the effect of temperature, humidity and ice particles on the friction and wear at unoxidized and oxidized wheel–rail contacts. The results indicate that increasing humidity reduces the wear at unoxidized contacts. A decrease in temperature tends to intensify the wear until an ice layer has condensed on the wheel and rail surfaces at -25 °C. Ice particles encourage the generation of oxide flakes at the contacting path, largely inhibiting the wear process.

    Paper C, which was a lab-scale test, studied the friction, wear and noise generation from pre-oxidized wheel–rail contact with varied surface features. Major results include that the wear regime transition from mild wear to severe wear is always accompanied by an increase in noise level of 10 dB and a broader bandwidth of noise.

    Paper D was a validation of the major findings of paper C in a full-scale test, which also saw an increase in noise level as well as a broader bandwidth when the wheel–rail contact transformed from mild to severe wear.

    Paper E studied the effect of humidity on the friction, wear and airborne particle emissions of three railway brake-block materials. The results show that cast iron generated the highest friction coefficient, wear and particle emission, and organic composite the lowest levels.

    Paper F conducted a thorough literature review on the open system tribology at the wheel–rail contact. Commonly seen parameters such as temperature, humidity and natural and artificial contaminants on friction, wear, noise and particle emissions were investigated.

  • Public defence: 2018-04-27 13:00 Kollegiesalen, Stockholm
    Heil, Katharina F.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST). University of Edinburgh.
    A Systems Biological Approach to Parkinson's Disease2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Parkinson’s Disease (PD) is the second most common neurodegenerative disease in the Western world. Itshows a high degree of genetic and phenotypic complexity with many implicated factors, various diseasemanifestations but few clear causal links. Ongoing research has identified a growing number of molecularalterations linked to the disease.Dopaminergic neurons in the substantia nigra, specifically their synapses, are the key-affected region in PD.Therefore, this work focuses on understanding the disease effects on the synapse, aiming to identify potentialgenetic triggers and synaptic PD associated mechanisms. Currently, one of the main challenges in this area isdata quality and accessibility.In order to study PD, publicly available data were systematically retrieved and analysed. 418 PD associatedgenes could be identified, based on mutations and curated annotations. I curated an up-to-date and completesynaptic proteome map containing a total of 6,706 proteins. Region specific datasets describing thepresynapse, postsynapse and synaptosome were also delimited. These datasets were analysed, investigatingsimilarities and differences, including reproducibility and functional interpretations.The use of Protein-Protein-Interaction Network (PPIN) analysis was chosen to gain deeper knowledgeregarding specific effects of PD on the synapse. Thus I generated a customised, filtered, human specificProtein-Protein Interaction (PPI) dataset, containing 211,824 direct interactions, from four public databases.Proteomics data and PPI information allowed the construction of PPINs. These were analysed and a set oflow level statistics, including modularity, clustering coefficient and node degree, explaining the network’stopology from a mathematical point of view were obtained.Apart from low-level network statistics, high-level topology of the PPINs was studied. To identify functionalnetwork subgroups, different clustering algorithms were investigated. In the context of biological networks, theunderlying hypothesis is that proteins in a structural community are more likely to share common functions.Therefore I attempted to identify PD enriched communities of synaptic proteins. Once identified, they werecompared amongst each other. Three community clusters could be identified as containing largely overlappinggene sets. These contain 24 PD associated genes. Apart from the known disease associated genes in thesecommunities, a total of 322 genes was identified. Each of the three clusters is specifically enriched for specificbiological processes and cellular components, which include neurotransmitter secretion, positive regulation ofsynapse assembly, pre- and post-synaptic membrane, scaffolding proteins, neuromuscular junctiondevelopment and complement activation (classical pathway) amongst others.The presented approach combined a curated set of PD associated genes, filtered PPI information andsynaptic proteomes. Various small- and large-scale analytical approaches, including PPIN topology analysis,clustering algorithms and enrichment studies identified highly PD affected synaptic proteins and subregions.Specific disease associated functions confirmed known research insights and allowed me to propose a newlist of so far unknown potential disease associated genes. Due to the open design, this approach can be usedto answer similar research questions regarding other complex diseases amongst others.

  • Public defence: 2018-04-27 13:00 F3, Stockholm
    Tongur, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Preparing for takeoff: Analyzing the development of electric road systems from a business model perspective2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electric road systems (ERS) are road transportation systems based on technologies that support electric power transfer from roads to vehicles in motion. Transition toward alternative technologies, such as ERS, is necessary in order to achieve the sustainability goals in road transportation. While several studies have emphasized that new business models are necessary in order to commercialize such technologies, they tend to neglect the fact thatmany of these technologies require socio-technical change, such as investments in alternative infrastructure.Hence, this thesis examines the relationship between business models and socio-technical change.

    The research was explorative and based on two case studies investigating the development of ERS: a longitudinal case study in Sweden and an in-depth case study in Los Angeles, USA. The findings suggest different roles that business models can have in different types of projects when preparing ERS for commercial takeoff: first, new business models were not part of the pilot projects which focused on radical innovation; second, business models were developed in demonstration projects with user interactions; and, third, business models were evaluated, and in this case rejected, in a deployment project aiming to transform the existing socio-technical system.

    Given these findings, this thesis argues that the business model concept could be used as a perspective from which to understand the evolutionary processes that take place during the early phases of transition, and that the challenges of commercializing and deploying systemic innovations, such as ERS, are more complex than often accounted for in the business model and sustainability transition literature.

    This thesis also discusses whether or not ERS is likely to take off. Thereby, this research nuances our view of predevelopment processes of a niche innovation before it has actually taken off and improves our understanding of what hinders and enables sustainable transitions.

  • Public defence: 2018-05-03 09:30 Kollegiesalen, Stockholm
    Yang, Guang
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Throughput and Latency of Millimeter-Wave Networks: Performance Analyses and Design Principles2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nowadays, the ever-increasing demands on higher data rates and better serviceperformance have posed extremely huge challenges to the existing wireless communicationswithin sub-6 GHz bands, mainly due to the spectrum scarcity in lowerfrequency bands. In recent years, the millimeter-wave (mm-wave) technology, as apromising candidate to meet the aforementioned demands, have attracted extensiveresearch attention, and has been regarded as one of the key enablers for theforthcoming the 5th generation (5G) mobile communications. The main featuresof mm-wave communications include: abundant spectral resources, high penetrationloss, severe path loss, weak multi-path effects, and narrow antenna beams, andthese particular features make the potential challenges and solutions with mm-wavediffer a lot from those in the conventional 6-GHz systems.

    It is known that the high throughput and the low latency are two critical qualityof-service (QoS) aspects in future mobile networks, while the related research withmm-wave are fairly recent and insufficient in the past few years. Motived by theurgent needs for further development and the blanks remained in previous works,in this doctoral thesis, we investigate the throughput and the latency in mm-wavenetworks through conducting performance analyses and identifying design principles,with the objective of seeking clues for improving the QoS of mm-wave wirelesscommunications in practice.

    Our main research regarding throughput and latency in mm-wave networksthat are included in this doctoral thesis can be categorized from the following threeaspects:

    (i) Throughput of mm-wave relay networks: For indoor scenarios, we study thehalf-duplex (HD) relaying with mm-wave in the presence of random linkblockages, where a distance-based routing algorithm is proposed to maximizethe throughput. For outdoor scenarios, focusing on a two-hop amplifyand-forward (AF) relay network in the HD or the full-duplex (FD) mode, weinvestigate the impacts of beamwidth, ground reflections, and self-interferencecoefficient on the throughput, where Gaussian-type directional antenna modeland two-ray channel model are jointly adopted.

    (ii) Latency analysis via stochastic network calculus: With the aid of stochasticnetwork calculus, we derive upper bounds for the probabilistic delay tokeep track of the latency performance of buffer-aided mm-wave networks. We mainly study mm-wave systems designed in tandem or parallel manners,and also consider a hybrid design that combines the tandem and parallelschemes in a flexible manner. Moreover, the capability of achieving low-latencymm-wave communications is characterized and investigated in terms of effectivecapacity, and the comparison among different transmission schemes isconducted to identify the respective strengths and proper conditions for theirapplications.

    (iii) Traffic allocation for low-latency mm-wave systems: Traffic allocation schemesfor low latency in buffer-aided mm-wave networks are investigated. Due tothe use of buffers, the delay optimization problem hereby differs from thosewithout buffers, where the conventional graph-based network optimizationtechniques become intractable. We demonstrate the impacts of different trafficallocation schemes on the latency. For multi-hop networks with multipleparallel channels in each hop, we consider both local and global traffic allocationschemes, quantify their resulting end-to-end (E2E) latencies, and analyzethe respective strengths and weaknesses.

  • Public defence: 2018-05-04 10:00 F3, Stockholm
    Koklukaya, Oruc
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Flame-Retardant Cellulose Fibre/Fibril Based Materials via Layer-by-Layer Technique2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    According to an analysis conducted by the Swedish Chemicals Inspectorate in 2006, the approximate numbers of fire injuries per year in Sweden are 100 deaths, 700 major and 700 minor injuries.1 Observations also show that there has been an increase in the number of house fires during recent years. One possible explanation can be the increased use of plastics in the building industry and in furniture. The advantages of easy processing, light weight and low cost make plastic materials most prevalent in the market.  However, plastics behave significantly differently from natural materials in the case of fire. Polymeric materials, including rigid polyurethane foams (PU) which are widely used in the building industry due to their insulating properties, are highly flammable and they release heat at a very high rate. In addition, polymeric materials release more harmful smoke, toxic gases and combustion products than natural materials. A house fire typically starts with the ignition of a combustible material. Flames then spread to nearby materials and shortly thereafter the heat radiation generated reaches a point where the contents of the room suddenly and simultaneously ignite. This stage is called a flash over. After this stage, the fire is fully developed and it continues until everything is consumed. The higher rate of heat and smoke production from plastic materials reduces the time to flash over and hence the time to escape from a fire. The traditional flame-retardant treatments are based mainly on halogenated compounds which are classified as gas phase flame-retardants. The halogenated flame-retardants are under severe investigation due to their adverse effect on health and on the environment since they release toxic gases during combustion and they may leach out and accumulate in the food chain.2-3 The restrictions due to growing environmental concerns have been a driving force to develop alternative flame-retardants by using natural and renewable resources. In recent years, the layer-by-layer (LbL) technique has been used as a simple and versatile surface engineering technique to construct functional nanocoatings through the sequential adsorption of polyelectrolytes and charged nanoparticles in an effort to impart flame-retardant characteristics by inhibiting the combustion cycle.4-5 This thesis presents the physical modification of cellulose fibre/fibril based materials as a means of improving flame-retardant properties.

    In the first part of work described in this thesis, the adsorption of polyelectrolyte multilayers onto pulp fibres was investigated as a way to impart flame-retardant characteristics to paper-based materials. It was found that intumescent nanocoatings consisting of nitrogen and phosphorus containing polyelectrolytes such as chitosan (CH) and poly(vinylphosphonic acid) (PVPA) were able to significantly improve the thermal stability and flame-retardant properties of sheets made of LbL-treated fibres, and were able to self-extinguish the flame in the horizontal flame test (HFT). High magnification images revealed that this improvement in flame-retardancy was due to the formation of a coherent char layer on the fibres (Paper I).6 In addition to imparting flame-retardancy by the LbL-coating of polyethylenimine (PEI) and sodium hexametaphosphate (SHMP), it was also possible to improve the mechanical properties of the paper material with this treatment (Paper III).7

    In the second part of the work, wet-stable porous cellulose fibril-based aerogels were developed by freeze-drying and used as a template for the build-up of intumescent nano-brick wall assemblies. The formation of multilayers of CH, PVPA and montmorillonite clay (MMT) was investigated as a function of solution concentration, and it was found that five quadlayers (QL) of CH/PVPA/CH/MMT treated aerogels using 5 g/L solutions of the respective components were able to self-extinguish the flame in HFT and that they showed no ignition under the heat flux of 35 kW/m2 used in cone calorimetry (Paper II).8 In a different application, a novel low density, porous, wet-stable cellulose fibre network was developed using chemically modified cellulose fibres by solvent exchange from water to acetone followed by drying at room temperature. The fibre networks (FN) were modified using the LbL technique to construct a flame-retardant nanocoating consisting of CH, SHMP, and inorganic particles (i.e., MMT, sepiolite (SEP), and colloidal silica (SNP)). The influence of the shape of the nanoparticles on flame-retardancy was investigated and it was found that plate-like and rod-like clays with a high aspect ratio showed self-extinguishing behaviour in HFT. A 5 QL of CH/SHMP/CH/SEP reduced the peak heat release rate and total smoke release by 47% and 43%, respectively, with an addition of only ~8 wt% to FN (Paper IV).

    Finally, non-crystalline cellulose gel beads were used as a substrate for the LbL assembly of CH and SHMP in model studies aimed at identifying the molecular mechanisms responsible for the fire-retardant properties of the LbL structures. The beads were formed by precipitating the dissolved cellulose-rich fibres according to an earlier described procedure,9 and it was shown that these smooth cellulose beads can be utilized as a model substrate to study the influence of LbL chemistry and nanostructure on flame-retardancy. These new types of model systems thus constitute a new important tool for clarifying the mechanism behind flame-retardant nanocoating systems (Paper V).  

    The full text will be freely available from 2020-12-31 10:00
  • Public defence: 2018-05-04 13:00 L1, Stockholm
    Donner, Herman
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Essays on Foreclosures and Housing Debt2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis consists of four self-contained essays in the field of real estate economics, and specifically, the market for single-family homes. The first three essays examine sales of foreclosed properties, while essay four is on the conversion process of rental apartments to owner-occupied units in the co-operative form. These topics have a common denominator in the analysis of real estate markets and a link to debt financing. The effect of a foreclosure on price is examined through several methods. In the first essay, a spatial hedonic model is applied on transaction data. In the second essay, the impact on holding-period returns and the rate-of-turnover is estimated through propensity-score matching. Hedonic regressions and appraisal data is used in the third essay, which analyzes the determinants of the price impact caused by a forced sale. The impact of local market conditions is tested and a discount on price is related to the search process among market participants.

    The second topic of conversions is addressed in essay four, which focuses on an informational asymmetry between tenants involved in the conversion process and other market participants. An incentive to mismanage housing co-operatives financially is examined through hedonic models applied to apartment transaction data. 

  • Public defence: 2018-05-04 13:00 Kollegiesalen, Stockholm
    Arvidsson, Therese
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Train–Track–Bridge Interaction for the Analysis of Railway Bridges and Train Running Safety2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, train–track–bridge interaction (TTBI) models are used to study the dynamic response of railway bridges. A TTBI model considers the dynamics of the train in addition to that of the track–bridge system. The TTBI model enables the assessment of train running safety and passenger comfort. In the bridge design stage, a moving force model is instead typically used for the train load. The main aim of this thesis is to use results from TTBI models to assess the validity of some of the Eurocode design criteria for dynamic analysis of bridges.

    A 2D rigid contact TTBI model was implemented in ABAQUS (Paper II) and in MATLAB (Paper III). In Paper V, the model was further developed to account for wheel–rail contact loss. The models were applied to study various aspects of the TTBI system, including track irregularities. The 2D analysis is motivated by the assumption that the vertical bridge vibration, which is of main interest, is primarily dependent on the vertical vehicle response and vertical wheel–rail force.

    The reduction in bridge response from train–bridge interaction was studied in Papers I–II with additional results in Part A of the thesis. Eurocode EN 1991-2 accounts for this reduction by an additional damping Δζ. The results show that Δζ is non-conservative for many train–bridge systems since the effect of train–bridge interaction varies with various train–bridge relations. Hence, the use of Δζ is not appropriate in the bridge design stage.

    Eurocode EN 1990-A2 specifies a deck acceleration criterion for the running safety at bridges. The limit for non-ballasted bridges (5 m/s2) is related to the assumed loss of contact between the wheel and the rail at the gravitational acceleration 1 g. This assumption is studied in Paper V based on running safety indices from the wheel–rail force for bridges at the design limit for acceleration and deflection. The conclusion is that the EN 1990-A2 deck acceleration limit for non-ballasted bridges is overly conservative and that there is a potential in improving the design criterion.

  • Public defence: 2018-05-04 13:00 E3, Stockholm
    Kubyshkina, Elena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Ab initio modelling of interfaces in nanocomposites for high voltage insulation2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dielectric nanocomposite materials have been experimentally proven to have properties that are beneficial in applications for efficient energy transport. However, today there are still no empirical models or rules that can predict the performance of a certain combination of materials in the nanocomposite, and there are also no definitive explanations of their dielectric behavior. A deeper understanding of the phenomena behind these materials' response to an applied electric field can open new possibilities for improvement of the insulating properties of nanocomposites.

    The goal of this work is to locate the key processes that are responsible for dielectric performance. The methodology of the study is based on ab initio technology, that relies solely on the knowledge of chemical and structural composition of the material. In this work, the charge-related properties of nanocomposite interfaces are studied. The primary material of the study is chosen to be polyethylene-based composite with magnesium oxide nanoparticles.

    The impact of the nanoparticle crystal surface termination and its silane treatment on the electronic structure of the interface between MgO and polyethylene are investigated here. Moreover, the effects of presence of carboxyl defect and water molecule near the interface are considered in this work as well.

    Based on the calculated electronic structure data, a model for charge dynamics is proposed. The model explains mechanisms for conductivity and space charge reduction in nanocomposites, but also predicts an increase in thermal stress and susceptibility for chemical defects. It is suggested here that the suppression mechanisms for space charge and conductivity in nanocomposites are inherently unstable and can also accelerate material aging.

  • Public defence: 2018-05-04 14:00 F3, Stockholm
    Turri, Valerio
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Look-ahead control for fuel-efficient and safe heavy-duty vehicle platooning2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The operation of heavy-duty vehicles at small inter-vehicular distances, known as platoons, lowers the aerodynamic drag and, therefore, reduces fuel consumption and greenhouse gas emissions. Tests conducted on flat roads have shown the potential of platooning to reduce the fuel consumption of about 10%. However, platoons are expected to operate on public highways with varying topography alongside other vehicles. Due to the large mass and limited engine power of heavy-duty vehicles, road slopes have a significant impact on feasible and optimal speed profiles. For single vehicles, experiments have shown that optimizing the speed according to the road profile resulted in fuel saving of up to 3.5%. The use of such a look-ahead control framework is expected to lead to large benefits also for platooning.

    This thesis presents the design of safe and fuel-efficient control of heavy-duty vehicle platoons driving on realistic road profiles. The scenario where the platooning vehicles cooperate to optimize their overall fuel-efficiency is studied together with the scenario where the vehicles do not explicitly cooperate.

    First, we propose a control architecture that splits the cooperative platooning control problem into two layers. The top layer computes a reference speed profile that ensures fuel-efficient operation of the entire platoon based on dynamic programming. The bottom layer relies on model predictive control to safely track the reference speed. Simulations show the ability of the proposed controller to save up to 12% of fuel for following vehicles compared to existing platoon controllers and to safely react to emergency braking of the leading vehicle.

    Second, we propose a gear management layer that fits in the cooperative platooning control architecture and explicitly takes the gear selection into account. The underlying optimal control problem aims at minimizing the vehicle fuel consumption and the reference tracking deviations. Simulations indicate how this formulation outperforms existing alternatives, both in terms of fuel-efficiency and tracking error.

    Third, we address non-cooperative platooning by proposing a vehicle-following controller suitable for fuel-efficient control of heavy-duty vehicles. The proposed controller explores both the benefits given by the short inter-vehicular distance and those given by pulse-and-glide, i.e., alternating traction and coasting phases. A simulation study suggests fuel saving of up to 18% compared to the single vehicle case, and up to 7% compared to when a constant-distance vehicle-following controller is used.

    Last, we propose a vehicle-following controller aimed at exploiting long preview of the preceding vehicle trajectory by directly manipulating the inputs of low-level vehicle controllers. This is achieved through a model predictive controller that uses a short prediction horizon and includes a terminal state set that incorporates preview information about the preceding vehicle. Experiments indicate the ability of the controller to avoid unnecessary braking, while simulations show behavior similar to the optimal control behavior.

  • Public defence: 2018-05-07 09:00 Sal B, Stockholm
    Nasir, Muhammad Anis Uddin
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Mining Big and Fast Data: Algorithms and Optimizations for Real-Time Data Processing2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last decade, real-time data processing has attracted much attention from both academic community and industry, as the meaning of big data has evolved to incorporate as well the speed of data. The massive and rapid production of data comes via numerous services, i.e., Web, social networks, Internet of Things (IoT) and mobile devices. For instance, global positioning systems are producing continuous data points using various location-based services. IoT devices are continuously monitoring variety of parameters, like temperature, heart beats, and others, and sending the data over the network. Moreover, part of the data produced by these real-time services is linked-data that requires tools for streaming graph analytics. Real-time graphs are ubiquitous in many fields, from the web advertising to bio-analytics. Developing analytical tools to process this amount of information at a real-time is challenging, yet extremely essential, for developing new services in areas such as web analytics, e-health and marketing.

    Distributed stream processing engines (dspes) are often employed for real-time data processing, as they distribute work to many machines to achieve the required performance guarantees, i.e., low latency and high throughput. However, the scalability of dspes is often questioned when the input streams are skewed or the underlying resources are heterogeneous. In this thesis, we perform a scalability study for dspes. In particular, we study the load- balancing problem for dspes, which is caused by the skewness in the workload and heterogeneity in the cluster. In doing so, we develop several efficient and accurate algorithms to reduce the load imbalance in a distributed system. Moreover, our algorithms are integrated into Apache Storm, which is an open source stream processing framework.

    Another dimension of real-time data processing involves developing novel algorithms for graph-related problems. The later part of the thesis presents several algorithms for evolving graphs. One of the most interesting features of real-world networks is the presence of community structure, which divides a network into groups of nodes with dense connections internally and sparse connections between groups. We study the community detection problem in the fully dynamic settings by formulating it as a top-k densest subgraph problem. In doing so, we achieve an extremely efficient approximation algorithm that scales to graphs with billions of edges. Further, we study the top-k graph pattern-mining problem in fully dynamic settings and develop a probabilistic algorithm using reservoir sampling. We provide the theoretical analysis for the proposed algorithms and show via empirical evaluation that our algorithms achieve up to several orders of magnitude improvement compared to the state-of-the-art algorithm.

  • Public defence: 2018-05-09 10:00 F3, Stockholm
    Mussa, Abdilbari Shifa
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering. KTH The Royal Institute of Technology.
    Durability Aspects of Fast Charging, Mechanical Constraint, and Inhomogeneity in Lithium-Ion Batteries2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of lithium-ion batteries with higher energy and power density, better safety, and lower cost has significantly contributed to the increased market share of electric vehicles (EVs) in the last decade. However, the expectations of end-users of EVs still require a continuous quest for better performance. One important end-user expectation is the ability of the battery to be charged rapidly, but the durability of lithium-ion batteries could be affected by the fast charging. Hence, detailed investigations are required to understand the extent and mechanism of the degradation for an optimized battery usage and material development.   

    In order to meet the high energy and power required in EVs, multiple large-format cells are connected in series and in parallel. Such a condition leads to an uneven distribution of temperature, pressure, and current in a cell or among cells that may cause locally inhomogeneous ageing and accelerate the global battery ageing. This thesis investigates the effects of charging rate, charging protocol, and external compression on battery durability. The impacts of inhomogeneities induced by cell design constraint, and uneven compression and temperature distributions are also addressed. The studies are based LiNi1/3Mn1/3Co1/3O2/graphite cells. Cell housing for a controlled pressure and temperature application was developed. Electrochemical and material characterization techniques were used in the investigation.

    The results show that fast charging at a rate equivalent to full charging in 20 minutes (3C rate) or less accelerates battery ageing. The ageing rate is less sensitive to charging rate in a longer charging time, i.e. at 2C and below, where it is determined more by factors such as the extent of full charging. In all cases, the capacity loss is limited by the cyclable lithium loss. External compression of a battery in an optimum range reduces ageing, but compression above or below the optimum range accelerates ageing. Lithium-ion batteries age non-uniformly. Cycling induces an increase in the impedance at the outer radius of curvature of a prismatic cell jellyroll, associated with a loss of contact between the current collector and the electrode coating. An unfavorable current distribution induced by uneven temperature distribution can accelerate battery ageing. 

  • Public defence: 2018-05-15 13:00 Kollegiesalen, Stockholm
    Aichmayer, Lukas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Solar receiver development for gas-turbine based solar dish systems2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Small-scale concentrating solar power plants such as micro gas-turbine based solar dish systems have the potential to harness solar energy in an effective way and supply electricity to customers in remote areas. In such systems, the solar receiver transfers the power of concentrated solar radiation to the working fluid of the power conversion cycle. It is one of the key components as it needs to operate at high temperatures to ensure a high power cycle efficiency and under high flux densities to ensure a high receiver efficiency. In order to address these challenges and to ensure efficient and reliable operation innovative designs are needed.

    This research work focuses on the complete development of a novel solar receiver applying a new systematic design and analysis methodology. Therefore, a comprehensive receiver design and experimental evaluation process were developed and implemented. The design process includes the identification of technical specifications and requirements, the development of receiver design tools of different investigation levels coupled with multi-objective optimization tools, the evaluation of scaling effects between tests in the KTH high-flux solar simulator and the full-scale solar dish system. As a result of the design process a representative final receiver was established with material temperatures and stresses below critical limits while respecting the design specification.

    The experimental evaluation includes the enhancement of the KTH high-flux solar simulator to provide stable and reliable operating conditions, the precise characterization of the radiative boundary conditions, the design of a receiver test bed recreating the operating behavior of a gas-turbine, and the final receiver testing for multiple operating points. It was shown that the prototype reaches an efficiency of 69.3% for an air outlet temperature of 800°C and a mass flow of 29.5 g/s. For a larger mass flow of 38.4 g/s a receiver efficiency of 84.8% was achieved with an air outlet temperature of 749°C.

    The measurement results obtained were then used for a multi-point validation of the receiver design tools, resulting in a high level of confidence in the accuracy of the tools. The validated models were then harnessed to calculate the performance of a full-scale solar receiver integrated into the OMSoP solar dish system. It was shown that a solar receiver can be designed, which delivers air at 800°C with a receiver efficiency of 82.2%.

    Finally, the economic potential of micro gas-turbine based solar systems was investigated and it was shown that they are ideally suited for small-scale stand-alone and off-grid applications.

    The results of the receiver development highlight the feasibility of using volumetric solar receivers to provide heat input to micro gas-turbine based solar dish systems and no major hurdles were found.

  • Public defence: 2018-05-16 13:00 E2
    Xylia, Maria
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Towards electrified public bus transport: The case of Stockholm2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis addresses the challenge of road transport electrification using a systems approach for the particular context of Stockholm’s public transport system. The objective is to identify the benefits of large-scale bus electrification on energy efficiency and greenhouse gas emissions, as well as the cost and planning considerations required for achieving such a shift. Quantitative and qualitative methods are deployed for answering the research questions, including the development and use of an optimisation model, survey research, and interviews. 

    The results of the optimisation model developed for this thesis show that an optimal system configuration is obtained with a combination of electricity and biodiesel. The high energy efficiency of electric buses would lead to a significant reduction of energy consumption in Stockholm, even if not all bus routes in the network are electrified. Although larger battery capacities could support the electrification of more bus routes, this does not necessarily lead to lower environmental impact. In any case, electricity from renewable sources should be used to maximise emission reductions. 

    The results also show that the annual costs necessary to invest in electric buses can be balanced by lower fuel costs. An effective utilisation of the charging infrastructure is of high priority in order to justify the costs of the required investments. The model results confirm the benefits of creating a dense initial network of charging stations in the inner city’s public transport hubs, which would facilitate the electrification of multiple routes and high infrastructure utilisation at lower costs. 

    The survey and interviews with stakeholders indicate that multiple issues affect the choice of charging technology, not just costs. Compatibility, reliability, bus dwell time, as well as weather conditions and visual impact are some of the additional aspects taken into account. The introduction of electricity tax exemption for electric buses, the expansion of the electric bus premium to include private stakeholders, as well as the expansion of infrastructure investment subsidy programmes are among the policy instruments suggested for assisting a faster introduction of electric buses into Stockholm’s public transport system. 

    Although the focus is on Stockholm, the conclusions of this work can be applicable to other cities in Sweden and around the world, which also face the challenge of making public transport a more sustainable option.

  • Public defence: 2018-05-30 13:00 Ka-Sal C (Sal Sven-Olof Öhrvik), Kista
    Apanasevic, Tatjana
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS.
    Opportunities and challenges of mobile payment services: The perspective of service providers2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     Mobile payments are transforming the payments industry. These services open up the opportunity for non-banking actors to enter the market. In order to embrace this challenge, banks, traditional payments market players, are forced to launch mobile payments. However, in Europe and most developed economies, a big number of launched services get terminated soon after their introduction in the market. Hence, the ability of different actors to act locally calls for additional research.

    The main objective of this thesis is to broaden knowledge and understanding about the ways mobile payment service providers address the opportunities and challenges of mobile payment services. In order to investigate this problem, this research (i) explores factors stimulating and hindering the introduction of mobile payments using perspectives of different types of service providers (i.e., banks, independent providers, direct operator billing providers, retailers, and public transport companies) and (ii) seeks to explain the importance of these factors for each type of provider.

    The primary data collected using interview method. More than 40 industry representatives in six countries were contacted. The Service, Technology, Organisation, and Finance (STOF) model was used as a theoretical research framework. This is a business modelling framework that specifies a set of critical design issues that have to  be considered within each model’s domain.

    Research findings highlight that the organisation domain is the key domain, which  affects all other domains and has an impact on the general viability of the business model. A comparison of the approaches used by different service providers to address each of the critical design issues helped to identify the factors that are most important within each domain. These factors stimulate or hinder development of a viable business model within each category of service providers.

    This research contributes to a better understanding of challenges and success factors associated with the design of business models for new mobile services and uses the lens of the STOF model. The contributions to the academic research on mobile payments are: (i) collection and analysis of a rich empirical data set on mobile payment services implemented in six Northern European countries, (ii) discussion of a bigger picture by connecting research findings to the context of the existing payment system, (iii) extension  of knowledge on business models for mobile ticketing, and (iv) extension of knowledge on the value of mobile ticketing services in the business-to-business (B2B) context.