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  • Public defence: 2016-12-09 09:00 Kollegiesalen, Stockholm
    Yao, Yanmei
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Yao, Yanmei
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Study of Induction Machines with Rotating Power Electronic Converter2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates a novel induction machine topology that uses a rotating power electronic converter. Steady-state and dynamic performance of the topology is studied to understand its operational principle. Furthermore the potential of improving its efficiency and power factor is investigated. The topology is referred to as wound rotor induction machine with rotating power electronic converter (WRIM-RPEC).

        The WRIM-RPEC topology offers the possibility to magnetize the induction machine from the rotor side by introducing a reactive voltage in the rotor. Thus, the power factor of the machine can be improved. Constant speed variable load operation can be achieved by setting the frequency of the introduced voltage. Two options of rotor winding and converter configuration in the WRIM-RPEC system are investigated. The wound rotor windings can either be open-ended and fed by a three-phase back-to-back converter or Y-connected and fed by a single three-phase converter. The dc-link in both converter configurations contains only a floating capacitor. These two configurations give different dc-link voltages at the same torque and speed.

        Two analytical steady-state models of the topology are developed in this thesis. The first model can be used to analyze the operating condition of the motor at specific speed and torque. Particularly, the operating range of speed and torque of the topology is investigated. The second model is used to analyze variable power factor operation, including unity power factor operation. Analytical calculations and measurements are carried out on a 4-pole, 1.8kW induction machine and the results are compared.

         A dynamic mathematic model is then developed for the WRIM-RPEC system for the back-to-back converter configuration. The mathematic model is then applied in Matlab/Simulink to study the dynamic performance of the system including starting, loading and phase-shifting. The simulation results are compared with measurements on the 4-pole, 1.8kW induction machine. Moreover, the simulation model using the existing Simulink blocks are studied to compare with the results obtained from the mathematic model. Furthermore, the dynamic performance of the WRIM-RPEC system with the single converter configuration is investigated. In addition, harmonic spectra analysis is conducted for the stator and rotor currents.

        In the last part of the thesis, efficiency improvement is investigated on the 4-pole induction machine when it is assumed to drive a pump load. It is shown that the efficiency can be further improved by decreasing the rotor resistance. Due to space constraints it is however difficult to decrease the rotor resistance in a 4-pole induction machine. An investigation is thus carried out on a standard 12-pole, 17.5kW squirrel-cage induction machine with inherent low power factor. The cage rotor is redesigned to a wound rotor to enable the connection of converter to the rotor windings. An analytical model is developed to design the wound rotor induction machine. The machine performance from calculations is then compared with FEM simulations with good agreement. The analytical model is further used to design several WRIMs with different dimensions and rotor slot numbers. Power factor and efficiency improvement is then explored for these WRIMs. A promising efficiency increase of 6.8% is shown to be achievable.

  • Public defence: 2016-12-09 09:00 E3, Stockholm
    Caesar, Carl
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Real Estate Planning and Land Law.
    Caesar, Carl
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Real Estate Planning and Land Law.
    Municipal Landownership and Housing in Sweden: Exploring links, supply and possibilities2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis comprises a number of studies, all directed at different linkages between municipal landownership and housing in Sweden. In all, the thesis consists of four papers. Of these, initial Paper I targets the emergence of the municipal landownership that still today are of crucial importance for the Swedish housing market. The main functions of the municipal landownership from the beginning of the 20th century and up until present time are retrospectively investigated and its role within Swedish housing during different times is elaborated upon. Paper II thereafter redirects focus to present time solely, and studies the management of the municipal land from particularly a housing perspective. More concretely, the disposal procedure – or land allocation practice – of the municipal land aimed for housing is investigated empirically, based on current practice in more than 25 municipalities. Paper III builds on preceding Paper II, but with a narrowed focus to a fundamental sequence of the disposal procedure – namely the developer selection. Accordingly, four different assigning methods, all derived from municipal practice, are discerned and their individual strengths and weaknesses are systematically discussed. Lastly, Paper IV attempts to illuminate an often overlooked dimension of the municipal landownership – as a potential and powerful instrument to counter polarizations between different social-groups, within the built environment. Necessary prerequisites in order to enable this are presented and an empirical study investigates whether this, somewhat concealed, potential in the municipal landownership seems to be utilized in practice.

  • Public defence: 2016-12-09 10:00 M2, Stockholm
    Sjölin, Martin
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Sjölin, Martin
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Methods of image acquisition and calibration for x-ray computed tomography2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    X-ray computed tomography (CT) is a common medical imaging device for acquiring high-resolution 3D images of the interior of the human body. The images are formed by mathematical reconstruction from hundreds of planar x-ray images that have been acquired during less then a second.

    Photon-counting spectral detectors are seen by many as the next big step in the development of medical CT. The potential benefits include: quantitative CT, ultra-low dose imaging and optimal contrast-to-noise performance. The current aim for the research pursued by the Physics of Medical Imaging Group at KTH is to develop, and commercialize, a photon-counting spectral detector using silicon wafers in edge-on geometry. With the introduction of a new detector comes many challenges, some of which this Thesis aims to address.

    Efficient calibration schemes will be an essential part of the realization of photon-counting spectral detectors in clinical CT. In the first part of the Thesis, three calibration methods are presented: two methods for calibration of the energy thresholds on multi-bin spectral detectors and one method for geometric calibration of edge-on detectors that are mounted in a CT gantry.

    The CT image acquisition produces large amounts of data that have to be transported out of the system, preferably in real-time. Already today, fewer samples are acquired when operating at very high rotation speeds due to bandwidth limitations. For photon-counting spectral detectors, the amount of data will be even larger due to the additional energy information and the generally smaller pixels, and it is therefore desirable to minimize the number of angular samples acquired per revolution. In the second part of the Thesis, two methods for relaxing the angular sampling requirement are presented. The first method uses the built-in redundancy of multi-layer detectors to increase the angular sampling rate via a temporal offset between the detector layers. The second method uses decimation in the view (angular) direction as a means for compression of CT sinogram data. The compression can be performed on the CT gantry and thus lower the required bandwidth of the data transfer.

    Although the overall aim of this work has been to develop methods that facilitate the introduction of photon-counting spectral detectors for medical CT, the presented methods are also applicable in the broader context of calibration of x-ray detectors and CT image acquisition.

  • Public defence: 2016-12-09 10:00 D2, Stockholm
    Kadir, Ashraful
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Kadir, Ashraful
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Numerical Methods for Molecular Dynamics with Nearly Crossing Potential Surfaces2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis consists of four papers that concern error estimates for the Born-Oppenheimer molecular dynamics, and adaptive algorithms for the Car-Parrinello and Ehrenfest molecular dynamics.

    In Paper I, we study error estimates for the Born-Oppenheimer molecular dynamics with nearly crossing potential surfaces. The paper first proves an error estimate showing that the difference of the values of observables for the time-independent Schrödinger equation, with matrix valued potentials, and the values of observables for the ab initio Born-Oppenheimer molecular dynamics of the ground state depends on the probability to be in the excited states and the nuclei/electron mass ratio. Then we present a numerical method to determine the probability to be in the excited states, based on the Ehrenfest molecular dynamics, and stability analysis of a perturbed eigenvalue problem.

    In Paper II, we present an approach, motivated by the so called Landau-Zener probability estimation, to systematically choose the artificial electron mass parameters appearing in the Car-Parrinello and Ehrenfest molecular dynamics methods to approximate the Born-Oppenheimer molecular dynamics solutions.

    In Paper III, we extend the work presented in Paper II for a set of more general problems with more than two electron states. A main conclusion of Paper III is that it is necessary to resolve the near avoided conical intersections between all electron eigenvalue gaps, including gaps between the occupied states.

    In Paper IV, we numerically compare, using simple model problems, the Ehrenfest molecular dynamics using the adaptive mass algorithm proposed in Paper II and III and the Born-Oppenheimer molecular dynamics based on the so called purification of the density matrix method concluding that the Born-Oppenheimer molecular dynamics based on purification of density matrix method performed better in terms of computational efficiency.

  • Public defence: 2016-12-09 10:00 T2, Huddinge
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Imaging and modeling the cardiovascular system2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Understanding cardiac pumping function is crucial to guiding diagnosis, predicting outcomes of interventions, and designing medical devices that interact with the cardiovascular system.  Computer simulations of hemodynamics can show how the complex cardiovascular system is influenced by changes in single or multiple parameters and can be used to test clinical hypotheses. In addition, methods for the quantification of important markers such as elevated arterial stiffness would help reduce the morbidity and mortality related to cardiovascular disease.

    The general aim of this thesis work was to improve understanding of cardiovascular physiology and develop new methods for assisting clinicians during diagnosis and follow-up of treatment in cardiovascular disease. Both computer simulations and medical imaging were used to reach this goal.

    In the first study, a cardiac model based on piston-like motions of the atrioventricular plane was developed. In the second study, the presence of the anatomical basis needed to generate hydraulic forces during diastole was assessed in heathy volunteers. In the third study, a previously validated lumped-parameter model was used to quantify the contribution of arterial and cardiac changes to blood pressure during aging. In the fourth study, in-house software that measures arterial stiffness by ultrasound shear wave elastography (SWE) was developed and validated against mechanical testing.

    The studies showed that longitudinal movements of the atrioventricular plane can well explain cardiac pumping and that the macroscopic geometry of the heart enables the generation of hydraulic forces that aid ventricular filling. Additionally, simulations showed that structural changes in both the heart and the arterial system contribute to the progression of blood pressure with age. Finally, the SWE technique was validated to accurately measure stiffness in arterial phantoms.

  • Public defence: 2016-12-09 10:00 Sal C Electrum, stockholm
    Besharat, Zahra
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Besharat, Zahra
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Adsorption of molecular thin films on metal and metal oxide surfaces2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the    Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces.  Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs.  Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth.  Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces.

     

  • Public defence: 2016-12-09 10:15 F3, Stockholm
    Shahriari, Nima
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Shahriari, Nima
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    On stability and receptivity of boundary-layer flows2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work is concerned with stability and receptivity analysis as well as studies on control of the laminar-turbulent transition in boundary-layer flows through direct numerical simulations. Various flow configurations are considered to address flow around straight and swept wings. The aim of this study is to contribute to a better understanding of stability characteristics and different means of transition control of such flows which are of great interest in aeronautical applications.

    Acoustic receptivity of flow over a finite-thickness flat plate with elliptic leading edge is considered. The objective is to compute receptivity coefficient defined as the relative amplitude of acoustic disturbances and TS wave. The existing results in the literature for this flow case plot a scattered image and are inconclusive. We have approached this problem in both compressible and incompressible frameworks and used high-order numerical methods. Our results have shown that the generally-accepted level of acoustic receptivity coefficient for this flow case is one order of magnitude too high.

    The continuous increase of computational power has enabled us to perform global stability analysis of three-dimensional boundary layers. A swept flat plate of FSC type boundary layer with surface roughness is considered. The aim is to determine the critical roughness height for which the flow becomes turbulent. Global stability characteristics of this flow have been addressed and sensitivity of such analysis to domain size and numerical parameters have been discussed.

    The last flow configuration studied here is infinite swept-wing flow. Two numerical set ups are considered which conform to wind-tunnel experiments where passive control of crossflow instabilities is investigated. Robustness of distributed roughness elements in the presence of acoustic waves have been studied. Moreover, ring-type plasma actuators are employed as virtual roughness elements to delay laminar-turbulent transition.

  • Public defence: 2016-12-09 13:00 F3, Stockholm
    Svensson, Daniel
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    Svensson, Daniel
    Philosophy and History, KTH, School of Architecture and the Built Environment (ABE), Philosophy and History of Technology, History of Science, Technology and Environment.
    Scientizing performance in endurance sports: The emergence of ‘rational training’ in cross-country skiing, 1930-19802016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Elite athletes of today use specialized, scientific training methods and the increasing role of science in sports is undeniable. Scientific methods and equipment has even found its way into the practice of everyday exercisers, a testament to the impact of sport science. From the experiential, personal training regimes of the first half of the 20th century to the scientific training theories of the 1970s, the ideas about training and the athletic body shifted.

    The rationalization process started in endurance sports in the 1940s. It was part of a struggle between two models of training; natural training and rational training. Physiologists wanted to rid training of individual and local variations and create a universal model of rational, scientific training. The rationalization of training and training landscapes is here understood as an aspect of sportification, a theory commonly used to describe similar developments in sports where increasing regimentation, specialization and rationalization are among the main criteria. This dissertation adds the concept of technologies of sportification to explain the role that micro-technologies and practices (such as training logs, training camps and scientific tests) have in the scientization of training.

    This thesis thus sets out to analyze the role that science has played in training during the 20th century. It is a history about the rationalization of training, but also about larger issues regarding the role of personal, experiential knowledge and scientific knowledge. The main conclusions are that the process of scientization never managed to rid training of components from natural, experiential training, and that the effort by Swedish physiologists to introduce rational training was part of the larger rationalization movement at the time. In the end, training knowledge was a co-production between practitioners and theoreticians, skiers and scientists.  

  • Public defence: 2016-12-09 13:00 Kollegiesalen, Stockholm
    Lekander, Jon
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Lekander, Jon
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Building and Real Estate Economics.
    Institutional Real Investments: Real Estate in a Multi-Asset Portfolio2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The purpose of this thesis is to analyze real estate investments from the vantage point of an institutional multi asset investor perspective, both in terms of the potential benefits real estate can bring as well as the challenges it can pose. The thesis consists of six papers and approaches the research question from three distinct perspectives.

    The quantitative papers consists of paper 1 and 5. Paper 1 analyses the portfolio characteristics of domestic and international real estate in a mean variance framework over seven investor domiciles. It is found that the optimal allocation to real estate is in the range of 15-25 percent depending on domicile of the investor. The fifth paper expands the analysis in paper one by expanding the data. Furthermore, the analysis is extended to investigate how the structure of the real estate portfolio can support a diversification objectives best.

    Papers 2, 3 and 4 are the market related papers. Paper 2 compares the suggested allocation weights with the allocation to real estate of institutions in four countries, and finds that the actual allocation is significantly lower and that all investor domiciles have a significant home bias. The third paper discusses changes in the institutional framework of real estate markets and the size of the investment universe. Paper 4 discusses various entry points to the real estate market, and how an investor can utilize these in order to adjust the characteristics of the real estate portfolio.

    The sixth and last paper is qualitative, and investigates how institutions managing pension capital handle real estate. ​

  • Public defence: 2016-12-12 09:00 Sal 205, Kista
    Zhou, Qin
    KTH, School of Information and Communication Technology (ICT), Industrial and Medical Electronics.
    Zhou, Qin
    KTH, School of Information and Communication Technology (ICT), Industrial and Medical Electronics.
    Sub-Nyquist Sampling Impulse Radio UWB Receivers for the Internet-of-Things2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the era of Internet-of-Things, the demand for short range wireless links featured by low-power and low-cost, robust communication and high-precision positioning is growing rapidly. Impulse Radio Ultra-Wideband (IR-UWB) technology characterized by the transmission of sub-nanosecond pulses spanning up to several GHz band with extremely low power spectral density emerges as a promising candidate. Nevertheless, several challenges must be confronted in order to take the full advantage of IR-UWB technology. The most significant one lies in the reception of UWB signals. Traditional receiver requires Nyquist rate ADC which is overwhelmingly complex and power hungry. This dissertation proposes and investigates possible sub-Nyquist sampling techniques for IR-UWB receiver design.

    In the first part of this dissertation, the IR-UWB receiver based on energy detection (ED) principle is explored. A low-power ED receiver featured by flexibility and multi-mode operation is proposed. The receiver prototype for 3-5 GHz band is implemented in 90 nm CMOS. Measurement results demonstrate that 16.3 mW power consumption and -79 dBm sensitivity at 10 Mb/s data rate can be achieved. To further optimize the receiver performance, threshold optimization is suggested for the on-off-keying modulated signal, and adaptive synchronization and integration region optimization is proposed. Finally, a low complexity burst packet detection scheme is proposed, which is adaptive to the variations of noise background and link distance.

    In the second part of this dissertation, the IR-UWB receiver based on compressed sensing (CS) theory is investigated. Firstly, appropriate sparse basis, sensing matrix and reconstruction algorithms are suggested for the CS based IR-UWB receiver. And then, the architectural analysis of the CS receiver with focuses on the random noise processes in the CS measurement procedure is presented. At last, a novel two-path noise-reducing architecture for the CS receiver is proposed. Besides the improvement on the receiver performance, the proposed architecture also relaxes the hardware implementation of the CS random projection as well as the back-end signal reconstruction.

  • Public defence: 2016-12-12 10:00 Sal B, Kista
    Lin, Rui
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Lin, Rui
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    High-capacity short-reach optical communications2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The global traffic is experiencing an exponential growth posing severe challenges to the communication networks in terms of capacity. As a future-proof technology fiber communication is widely implemented in different network segments, which can be categorized by transmission distance as long-haul and short-reach. This thesis focuses on the short-reach communication networks including fiber access network connecting the end users to the metro/core networks that covering tens of kilometers and optical datacenter network handling the traffic within the datacenter with distance up to a few kilometers. For fiber access networks, wavelength division multiplexing passive optical networks (WDM-PONs) assign a dedicated wavelength channel to each user guaranteeing high data rate. Dense channels enlarges the user count but makes the signals vulnerable to the wavelength drift. In this regard we propose two schemes based on optical frequency comb technique to generate stable carriers for WDM-PONs. Meanwhile, radio-over-fiber techniques allows the transmission of radio signals between central offices and the cells. Millimeter wave (MMW) over fiber, on the other hand, offer high bandwidth for future high capacity mobile access. We propose and experimentally demonstrate a palm-shaped spectrum generation where the high-power central carrier can be used for upstream transmission while multiple MMW bands are capable of transmitting different downstream data simultaneously. Regarding optical datacenter networks, passive optical interconnects (POIs) have been proposed as an energy-efficient solution since only passive optical components are used for server interconnection. However, the high insertion loss may result in a scalability problem. We develop a methodology that considers various physical-layer aspects, e.g., receiver types, modulation formats, to quantify the scalability of POIs. Both theoretical analyses and experimental measurements have been performed to assess the scalability of various coupler-based POIs.

  • Public defence: 2016-12-12 14:00 Sal C, Kista
    Zhai, Chuanying
    KTH, School of Information and Communication Technology (ICT), Industrial and Medical Electronics.
    Zhai, Chuanying
    KTH, School of Information and Communication Technology (ICT), Industrial and Medical Electronics.
    Reliable RFID Communication and Positioning System for Industrial IoT2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The Internet of Things (IoT) has the vision to interconnect everything of the physical world and the virtual world. Advanced automated and adaptive connectivity of objects, systems, and services is expected to be achieved under the IoT context, especially in the industrial environment. Industry 4.0 with the goal of intelligent and self-adaptable manufacturing is driven by the IoT.

    The Object Layer, where real-time and reliable information acquisition from the physical objects carried out, is the basic enabler in the 3-layer industrial IoT system. Such acquisition system features deterministic access, reliable communication with failure resistance mechanism, latency-aware real-time response, deployable structure/protocol, and adaptive performance on various QoS demands.

    This thesis proposes a reliable RFID communication system for acquisition in the industrial environment. A discrete gateway structure and a contention-free communication protocol are designed to fulfill the unique system requirements. Such gateway structure offers a flexible configuration of readers and RF technologies. It enables a full duplex communication between the objects and the gateway. The designed MF-TDMA protocol can enhance the failure resistance and emergency report mechanism thanks to the separation of control link and data link in the gateway. Specifically, an optional ARQ mechanism, an independent/uniform synchronization and control method, and a slot allocation optimization algorithm are designed besides time-division and frequency-division multiplexing. Protocol implementations for different industrial situations illustrate the system ability for supporting the demands of various QoS.

    Finally, a 2.4-GHz/UWB hybrid positioning platform is explored based on the introduced RFID system. Taking advantage of the UWB technology, the positioning platform can achieve positioning accuracy from meter level to centimeter level. Hybrid tag prototype and specific communication process based on the MF-TDMA protocol are designed. An SDR UWB reader network, capable of evaluating multiple algorithms, is built to realize accurate positioning with an improved algorithm proposed.

  • Public defence: 2016-12-15 14:00 F3, Stockholm
    Greschbach, Benjamin
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Greschbach, Benjamin
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Privacy Issues in Decentralized Online Social Networks and other Decentralized Systems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Popular Online Social Networks (OSNs), such as Facebook or Twitter, are logically centralized systems. The massive information aggregation of sensitive personal data at the central providers of these services is an inherent threat to the privacy of the users. Leakages of these data collections happen regularly – both intentionally, for example by selling of user data to third parties and unintentionally, for example when outsiders successfully attack a provider.

    Motivated by this insight, the concept of Decentralized Online Social Networks (DOSNs) has emerged. In these proposed systems, no single, central provider keeps a data collection of all users. Instead, the data is spread out across multiple servers or is distributed completely among user devices that form a peer-to-peer (P2P) network. Encryption is used to enforce access rights of shared content and communication partners ideally connect directly to each other. DOSNs solve one of the biggest privacy concerns of centralized OSNs in a quite forthright way – by getting rid of the central provider. Furthermore, these decentralized systems can be designed to be more immune to censorship than centralized services. But when decentralizing OSNs, two main challenges have to be met: to provide user privacy under a significantly different threat model, and to implement equal usability and functionality without centralized components.

    In this work we analyze the general privacy-problems in DOSNs, especially those arising from the more exposed metadata in these systems. Furthermore, we suggest three privacy-preserving implementations of standard OSN features, i.e. user authentication via password-login, user search via a knowledge threshold and an event invitation system with fine-grained privacy-settings. These implementations do not rely on a trusted, central provider and are therefore applicable in a DOSN scenario but can be applied in other P2P or low-trust environments as well. Finally, we analyze a concrete attack on a specific decentralized system, the Tor anonymization network, and suggest improvements for mitigating the identified threats.

  • Public defence: 2016-12-16 10:00 Sal C, Kista, Stockholm
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Transition metal oxide surfaces: Surface structures and molecular interaction2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Metal oxides are both corrosion products and useful materials with a wide range of applications. Two of the most used metals today are iron and copper. In this thesis, surface structures and molecular interaction with surfaces of iron oxides and copper oxides are studied using spectroscopy and microscopy methods.

     

    The surface structures of iron oxides grown on the low-index iron (Fe) surfaces (100) and (110) have been studied during the initial oxidation phase. The oxidation condition for both iron surfaces was 400 °C and 1×10−6 mbar of oxygen gas. For the Fe(100)-surface, a Fe3O4(100)-film is formed beyond the oxygen adsorbate structures. For the Fe(110)-surface, a FeO(111)-film is first formed. When the FeO(111)-film grows thicker, it transforms into a Fe3O4(111)-film.

     

    The surface structures of Cu2O(100) was studied and the main finding is that the most common surface structure that previously in literature has been described to have a periodicity of (3√2×√2)R45° actually has a periodicity described by the matrix (3,0;1,1). Furthermore, the low-binding energy component in the photoelectron spectroscopy O 1s-spectrum is determined to origin from surface oxygen atoms.

     

    Sulfur dioxide, a corrosive molecule that in the environment to large share comes from human activities such as burning of fossil fuels, was studied using photoelectron spectroscopy when interacting with surfaces of iron oxide thin films and bulk Cu2O-surfaces. On the iron oxide thin film surfaces under ultra-high vacuum conditions, sulfur dioxide adsorbs partly as SO4-species and partly dissociates and forms FeS2. On the Cu2O-surfaces under ultra-high vacuum conditions, the adsorption of sulfur dioxide is non-dissociative and forms SO3-species. When interacting with near-ambient pressures of water, it is observed in the photoelectron spectroscopy S 2p-region that the sulfur from SO3-species shifts to Cu2S.

  • Public defence: 2016-12-16 10:00 M311, Stockholm
    Bai, Haitong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Bai, Haitong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.

  • Public defence: 2016-12-16 10:00 FD5, Stockholm
    Hendil-Forssell, Peter
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Hendil-Forssell, Peter
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Rational engineering of esterases for improved amidase specificity in amide synthesis and hydrolysis2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biocatalysis is an ever evolving field that uses enzymes or microorganisms for chemical synthesis. By utilizing enzymes that generally have evolved for specific reactions under mild conditions and temperatures, biocatalysis can be a more environmentally friendly option compared to traditional chemistry.

    Amide-type chemistries are important and bond formation avoiding poor atom economy is of high priority in organic chemistry. Biocatalysis could potentially be a solution but restricted substrate scope is a limitation. Esterases/lipases usually display broad substrate scope and catalytic promiscuity but are poor at hydrolyzing amides compared to amidases/proteases. The difference between the two enzyme classes is hypothesized to reside in one key hydrogen bond present in amidases, which facilitates the transition state for nitrogen inversion during catalysis.

    In this thesis the work has been focused on introducing a stabilizing hydrogen bond acceptor in esterases, mimicking that found in amidases, to develop better enzymatic catalysts for amide-based chemistries.

    By two strategies, side-chain or water interaction, variants were created in three esterases that displayed up to 210-times increased relative amidase specificity compared to the wild type. The best variant displayed reduced activation enthalpy corresponding to a weak hydrogen bond. The results show an estimated lower limit on how much the hydrogen bond can be worth to catalysis.

    MsAcT catalyze kinetically controlled N-acylations in water. An enzymatic one-pot one-step cascade was developed for the formation of amides from aldehydes in water that gave 97% conversion. In addition, engineered variants of MsAcT with increased substrate scope could synthesize an amide in water with 81% conversion, where the wild type gave no conversion. Moreover, variants of MsAcT displayed up to 32-fold change in specificity towards amide synthesis and a switch in reaction preference favoring amide over ester synthesis.

  • Public defence: 2016-12-16 10:15 D3, Stockholm
    Imani Jajarmi, Ramin
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Imani Jajarmi, Ramin
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Acoustic separation and electrostatic sampling of submicron particles suspended in air2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    We investigate experimentally the effects of acoustic forces on submicron aerosol in a channel flow. This technique can potentially overcome some of the limitations of conventional separation systems and provide advanced manipulation capabilities such as sorting according to size or density. The theoretical framework for acoustophoresis at such small length scales where molecular effects are expected to be significant is still incomplete and in need of experimental validation. The main objectives of this thesis are to identify the physical limitations and capabilities of acoustophoretic manipulation for submicron aerosol particles.

    Two sets of experiments were carried out: first, qualitative results revealed that acoustic manipulation is possible for submicron particles in air and that the acoustic force follows the trend expected by theoretical models developed for particles in inviscid fluids. The acoustic force on submicron particles was estimated in a second set of measurements performed with quantitative diagnostic tools. Comparison of these results with available theoretical models for the acoustic radiation forces demonstrates that for such small particles additional forces have to be considered. At submicron length scales, the magnitude of the forces observed is orders of magnitude higher than the predictions from the inviscid theory.

    One potential application for acoustophoresis is specifically investigated in this thesis: assist electrostatic precipitation (ESP) samplers to target very small aerosols, such as those carrying airborne viruses. To identify the shortcomings of ESP samplers that acoustophoresis should overcome, two ESP designs have been investigated to quantify capture efficiency as a function of the particle size and of the air velocity in a wind tunnel. The results reveal that both designs have limitations when it comes to sampling submicron aerosol particles. When exposed to polydispersed suspensions they behave as low-pass filters.

  • Public defence: 2016-12-16 10:30 K1, Stockholm
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Mechanics-based Design Framework for Flexible Pavements2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Load induced top-down fatigue cracking has been recognized recently as a major distress phenomenon in asphalt pavements. This paper presents a mechanics-based design framework in load and resistance factor design (LRFD) format for the top-down fatigue cracking performance evaluation of flexible pavements. This was achieved by enhancing further the hot mix asphalt fracture mechanics (HMA-FM) model through the incorporation of mixture morphology influence on key fracture properties, and incorporating partial safety factors to account for variabilities and uncertainties. The analysis framework was calibrated and validated using pavement sections that have high quality laboratory data and well documented field performance histories. Moreover, as traffic volume was identified in having a dominant influence on predicted performance, a further investigation was performed to establish and evaluate truck traffic characterization parameters effect on predicted results.

    A two-component reliability analysis methodology, which uses central composite design (CCD) based response surface approach for surrogate model generation and the first order reliability method (FORM) for reliability estimation was used for the development of the LRFD mechanics-based design framework. The effectiveness of the design framework was investigated through design examples, and the results have shown that the formulated partial safety factors have accounted effectively the variabilities involved in the design process. Further investigation was performed to establish the influence design inputs variabilities have on target reliabilities through case studies that combine input variabilities in a systematic way. It was observed from the results that the coefficient of variation (COV) level of the variability irrespective of the distribution type used have a significant influence on estimated target reliability.

  • Public defence: 2016-12-16 10:30 Kollegiesalen, Stockholm
    Maleki, Laleh
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Maleki, Laleh
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Synthesis of AcGGM Polysaccharide Hydrogels2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lignocellulosic biomass is believed to serve a prominent role in tomorrow’s sustainable energy and material development. Among the polysaccharide fractions of lignocellulosic biomass, the potential of hemicelluloses as a valuable material resource is increasingly recognized. Thanks to their hydrophilic structure, hemicelluloses are suitable substrates for hydrogel design. The work summarized in this thesis aims to develop feasible strategies for the conversion of O-acetyl galactoglucomannan (AcGGM), an ample hemicellulose in softwood, into hydrogels. Within this framework, four synthetic pathways targeting the formation of crosslinked hydrogel networks from pure or unrefined AcGGM fractions were developed.

     

    Aqueous AcGGM-rich and lignin-containing side-stream process liquors of forest industry, known as softwood hydrolysates (SWHs) were formulated into highly swellable hydrogels by: i) allyl-functionalization of AcGGM chains of crude SWH to obtain a viable precursor for hydrogel synthesis via free-radical crosslinking, ii) directly incorporating unmodified SWH fractions into semi-interpenetrating polymer networks (semi-IPNs). SWH hydrogels and semi-IPNs were characterized with appreciable maximum swelling ratios of Qeq = 170 and Qeq = 225, respectively.

     

    Rapid crosslinking of AcGGM through thiol-click chemistry was addressed by first imparting thiol functionality onto pure AcGGM chains in a one-pot procedure. The thiolated AcGGM proved to be a suitable substrate for the synthesis of hemicellulose hydrogels via thiol-ene and thiol Michael addition reactions. Finally, sequential full IPNs were developed by subjecting single network hydrogels of pure AcGGM to a second network formation. IPNs obtained through either free radical crosslinking or thiol-ene crosslinking exhibited higher shear storage moduli than their single network counterparts. 

  • Public defence: 2016-12-16 13:00 Rockefeller, Solna
    Danielsson, Frida
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. Human Protein Atlas.
    Danielsson, Frida
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. Human Protein Atlas.
    Integration of RNA and protein expression profiles to study human cells2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cellular life is highly complex. In order to expand our understanding of the workings of human cells, in particular in the context of health and disease, detailed knowledge about the underlying molecular systems is needed. The unifying theme of this thesis concerns the use of data derived from sequencing of RNA, both within the field of transcriptomics itself and as a guide for further studies at the level of protein expression. In paper I, we showed that publicly available RNA-seq datasets are consistent across different studies, requiring only light processing for the data to cluster according to biological, rather than technical characteristics. This suggests that RNA-seq has developed into a reliable and highly reproducible technology, and that the increasing amount of publicly available RNA-seq data constitutes a valuable resource for meta-analyses. In paper II, we explored the ability to extrapolate protein concentrations by the use of RNA expression levels. We showed that mRNA and corresponding steady-state protein concentrations correlate well by introducing a gene-specific RNA-to-protein conversion factor that is stable across various cell types and tissues. The results from this study indicate the utility of RNA-seq also within the field of proteomics.

    The second part of the thesis starts with a paper in which we used transcriptomics to guide subsequent protein studies of the molecular mechanisms underlying malignant transformation. In paper III, we applied a transcriptomics approach to a cell model for defined steps of malignant transformation, and identified several genes with interesting expression patterns whose corresponding proteins were further analyzed with subcellular spatial resolution. Several of these proteins were further studied in clinical tumor samples, confirming that this cell model provides a relevant system for studying cancer mechanisms. In paper IV, we continued to explore the transcriptional landscape in the same cell model under moderate hypoxic conditions.

    To conclude, this thesis demonstrates the usefulness of RNA-seq data, from a transcriptomics perspective and beyond; to guide in analyses of protein expression, with the ultimate goal to unravel the complexity of the human cell, from a holistic point of view.

  • Public defence: 2016-12-16 13:00 F3, Stockholm
    Kis, Filip
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Kis, Filip
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Prototyping with Data: Opportunistic Development of Data-Driven Interactive Applications2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There is a growing amount of digital information available from Open-Data initiatives, Internet-of-Things technologies, and web APIs in general. At the same time, an increasing amount of technology in our lives is creating a desire to take advantage of the generated data for personal or professional interests. Building interactive applications that would address this desire is challenging since it requires advanced engineering skills that are normally reserved for professional software developers. However, more and more interactive applications are prototyped outside of enterprise environments, in more opportunistic settings. For example, knowledge workers apply end-user development techniques to solve their tasks, or groups of friends get together for a weekend hackathon in the hope of becoming the next big startup. This thesis focuses on how to design prototyping tools that support opportunistic development of interactive applications that take advantage of the growing amount of available data.

    In particular, the goal of this thesis is to understand what are the current challenges of prototyping with data and to identify important qualities of tools addressing these challenges. To accomplish this, declarative development tools were explored, while keeping focus on what data and interaction the application should afford rather than on how they should be implemented (programmed). The work presented in this thesis was carried out as an iterative process which started with a design exploration of Model-based UI Development, followed by observations of prototyping practices through a series of hackathon events and an iterative design of Endev – a prototyping tool for data-driven web applications. Formative evaluations of Endev were conducted with programmers and interaction designers. 

    The main results of this thesis are the identified challenges for prototyping with data and the key qualities required of prototyping tools that aim to address these challenges. The identified key qualities that lower the threshold for prototyping with data are: declarative prototyping, familiar and setup-free environment, and support tools. Qualities that raise the ceiling for what can be prototyped are: support for heterogeneous data and for advanced look and feel.

  • Public defence: 2016-12-16 13:15 Hörsal Q2, Stockholm
    Magnusson, Klas E. G.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Magnusson, Klas E. G.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Segmentation and tracking of cells and particles in time-lapse microscopy2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In biology, many different kinds of microscopy are used to study cells. There are many different kinds of transmission microscopy, where light is passed through the cells, that can be used without staining or other treatments that can harm the cells. There is also fluorescence microscopy, where fluorescent proteins or dyes are placed in the cells or in parts of the cells, so that they emit light of a specific wavelength when they are illuminated with light of a different wavelength. Many fluorescence microscopes can take images on many different depths in a sample and thereby build a three-dimensional image of the sample. Fluorescence microscopy can also be used to study particles, for example viruses, inside cells. Modern microscopes often have digital cameras or other equipment to take images or record time-lapse video.

    When biologists perform experiments on cells, they often record image sequences or sequences of three-dimensional volumes to see how the cells behave when they are subjected to different drugs, culture substrates, or other external factors. Previously, the analysis of recorded data has often been done manually, but that is very time-consuming and the results often become subjective and hard to reproduce. Therefore there is a great need for technology for automated analysis of image sequences with cells and particles inside cells. Such technology is needed especially in biological research and drug development. But the technology could also be used clinically, for example to tailor a cancer treatment to an individual patient by evaluating different treatments on cells from a biopsy.

    This thesis presents algorithms to find cells and particles in images, and to calculate tracks that show how they have moved during an experiment. We have developed a complete system that can find and track cells in all commonly used imaging modalities. We selected and extended a number of existing segmentation algorithms, and thereby created a complete tool to find cell outlines. To link the segmented objects into tracks, we developed a new track linking algorithm. The algorithm adds tracks one by one using dynamic programming, and has many advantages over prior algorithms. Among other things, it is fast, it calculates tracks which are optimal for the entire image sequence, and it can handle situations where multiple cells have been segmented incorrectly as one object. To make it possible to use information about the velocities of the objects in the linking, we developed a method where the positions of the objects are preprocessed using a filter before the linking is performed. This is important for tracking of some particles inside cells and for tracking of cell nuclei in some embryos.

     

     

     

    We have developed an open source software which contains all tools that are necessary to analyze image sequences with cells or particles. It has tools for segmentation and tracking of objects, optimization of settings, manual correction, and analysis of outlines and tracks. We developed the software together with biologists who used it in their research. The software has already been used for data analysis in a number of biology publications. Our system has also achieved outstanding performance in three international objective comparisons of systems for tracking of cells.

  • Public defence: 2016-12-16 14:00 Kollegiesalen, Stockholm
    Pezo Silvano, Ary
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Pezo Silvano, Ary
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Advancing Traffic Safety: An evaluation of speed limits, vehicle-bicycle interactions, and I2V systems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the introduction of motor vehicles, the number of fatalities and accidents has been a concern for society.The number of fatalities on roads is amongst the most common causes of mortality worldwide (WHO, 2015).Even in industrialized countries the number of fatalities remains unacceptable. Therefore, in the last decades, anumber of approaches have emerged to support and boost traffic safety towards a system free from fatalities andserious impairment outcomes. ‘Sustainable Safety’ and ‘Vision Zero’ are well-known examples aiming to avoidfatalities within the traffic system and reduce injury severity when a traffic accident is inevitable. However, thenumber of fatalities and seriously injured accidents are still relatively high. More specifically, vulnerable roadusers remain involved in fatal and serious accidents even in industrialized countries. Therefore, further advancesin traffic safety studies are needed. This thesis aims at evaluating the impact of road characteristics, traffic rulesand information provision towards a safer traffic system. The thesis is composed of five scientific papers whichsummarizes the main contributions of this work.

  • Public defence: 2016-12-19 10:00 F3, Stockholm
    Jin, Lebing
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Jin, Lebing
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Integrated Compact Drives for Electric and Hybrid Electric Vehicles2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    To develop more competitive solutions, one of the trends in the development of drive systems for electric and hybrid electric vehicles (EVs/HEVs) is to integrate the power electronic converter and the electric motor. This thesis aims to investigate the performance and the operation of modular converters in integrated motor drive systems for EVs/HEVs.

    In the first part, the concept of integrated modular motor drive systems for EVs/HEVs is introduced. Three suitable modular converter topologies, namely, the stacked polyphase bridges (SPB) converter, the parallel-connected polyphase bridges (PPB) converter and the modular high frequency (MHF) converter, are evaluated and compared with conventional electric drives in terms of power losses, energy storage requirements, and semiconductor costs.

    In the second part of the thesis, the harmonic content of the dc-link current of the SPB converter is analyzed. By adopting an interleaving modulation the size of the dc-link capacitor can be reduced without increasing the switching frequency, which is beneficial for achieving a compact integrated system. This method allows for around 80% reduction of the dc-link capacitance for vehicle drives, resulting in a significant size reduction of the power converter and improved integration.

    Finally, a communication-based distributed control system for the SPB converter is presented. The communication delay arising from the serial communication is inevitable, thus a timing analysis is also presented. It has been found that stability is maintained even when the baud rate of the SPI communication is lower than 1 Mbps, indicating that other communication protocols with lower bandwidths can also be adopted for this topology.

    The analytical investigations provided in this thesis are validated by experiments on a four-submodule laboratory prototype. Experimental results verify the correctness of the theoretical analysis, as well as the dynamic performance of the distributed control system.

  • Public defence: 2016-12-19 10:00 Kollegiesalen, Stockholm
    Long, Mengni
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Long, Mengni
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Attachment of Lightning Flashes to Wind Turbines2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis aims at investigating the attachment of lightning flashes to wind turbines. Modern wind turbines are highly exposed to lightning strikes, due to the increase of their height and the rotation of the blades. Upward lightning is the dominant mechanism of lightning strikes to them. Therefore, this study evaluates the initiation of the initial upward leader discharge and the process of lightning attachment of dart leaders taking place prior to the first return stroke in upward flashes.

    This work extends the self-consistent leader inception and propagation model (SLIM) to evaluate the lightning attachment of dart and dart-stepped leaders to grounded objects. SLIM was originally proposed to evaluate the lightning attachment of stepped leaders. Unlike the well-studied lightning attachment of stepped leaders, upward connecting leaders initiated in response to dart and dart-stepped leaders develop under a significantly faster change of the ambient electric field. Additionally, these connecting leaders could develop in warm air pre-conditioned by the previous strokes in the same flash. An analytical expression to evaluate the charge required to thermalize the connecting leader per unit length is also developed in the extended model. This model is validated through the analysis of three attachment events recorded in rocket-triggered lightning experiments. Good agreement between the predicted properties of the upward leaders and the measurements has been found. The model is utilized to evaluate the different conditions where connecting leaders can develop prior to the return strokes in upward lightning.

    The extended model of SLIM is also applied to study the interception of lightning dart leaders by upward connecting leaders initiated from wind turbines. The evaluation considers the influence of the return stroke peak current, the blade rotation and wind on the attachment of lightning dart leaders to wind turbines. The probability of lightning strikes to the receptors along the blade and on the nacelle is calculated for upward lightning flashes. It is shown that the lightning attachment of dart leaders is a mechanism that can explain the lightning damages to the inboard region of the blades (more than 10 meters from the tip) and the nacelle of wind turbines.

    Furthermore, the critical stabilization electric field required to initiate upward lightning from wind turbines is evaluated for both ‘self-initiated’ and ‘other-triggered’ upward flashes. The calculation shows that the stabilization electric field of an operating wind turbine periodically changes due to the rotation of its blades.  The initiation of upward lightning is greatly facilitated by the electric field change produced by nearby lightning events. However, the rate of rise of the electric field only has a weak impact on the stabilization electric field. The evaluation of the stabilization electric field provides essential information needed for the estimation of the incidence of upward lightning to wind turbines.

  • Public defence: 2016-12-20 10:00 B2, Stockhoolm
    Nabeel, Muhammad
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nabeel, Muhammad
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A study of micro-particles in the dust and melt at different stages of iron and steelmaking2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The dust particles generated due to mechanical wear of iron ore pellets and clusters formed in molten stainless steel alloyed with rare earth metals (REM) are considered in this study. Firstly, the influence of the characteristics of iron ore pellets, applied load on a pellet bed and partial reduction of the pellets on the size distribution of the generated dust was investigated. Secondly, REM clusters are investigated to evaluate the size distribution of the clusters. Also, an extreme value distribution (EVD) analysis has been applied for the observed REM clusters.

    The large sized pellets showed 10-20% higher wear rate than small sized pellets during wear in a planetary mill. Moreover, an increase of ~67% was observed in the friction and dust generation in the pellet bed as the applied load increased from 1 to 3 kg. Also, it was observed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. The mechanical wear experiments of pellets reduced at 500 °C (P500) and 850 °C (P850) showed that P500 pellets exhibit ~16-35% higher wear rate than unreduced pellets. For the P850 pellets, the wear is inhibited by formation of a metallic layer at the outer surface of the pellets. The mechanism of dust generation has been explained using the obtained results.

    A reliable cluster size distribution of REM clusters was obtained by improving the observation method and it was used to explicate the formation and growth mechanism of REM clusters. The results show that the growth of clusters is governed by different types of collisions depending on the size of the clusters. For EVD analysis three different size parameters were considered. Moreover, using the maximum length of clusters results in a better correlation of EVD regression lines compared to other size parameters. Moreover, a comparison of predicted and observed maximum lengths of clusters showed that further work is required for the application of EVD analyses for REM clusters.

  • Public defence: 2016-12-20 10:00 F3, Stockholm
    Grytsan, Andrii
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
    Grytsan, Andrii
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
    Abdominal aortic aneurysm inception and evolution - A computational model2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Abdominal aortic aneurysm (AAA) is characterized by a bulge in the abdominal aorta. AAA development is mostly asymptomatic, but such a bulge may suddenly rupture, which is associated with a high mortality rate. Unfortunately, there is no medication that can prevent AAA from expanding or rupturing. Therefore, patients with detected AAA are monitored until treatment indication, such as maximum AAA diameter of 55 mm or expansion rate of 1 cm/year. Models of AAA development may help to understand the disease progression and to inform decision-making on a patient-specific basis. AAA growth and remodeling (G&R) models are rather complex, and before the challenge is undertaken, sound clinical validation is required.

    In Paper A, an existing thick-walled model of growth and remodeling of one layer of an AAA slice has been extended to a two-layered model, which better reflects the layered structure of the vessel wall. A parameter study was performed to investigate the influence of mechanical properties and G&R parameters of such a model on the aneurysm growth.

    In Paper B, the model from Paper A was extended to an organ level model of AAA growth. Furthermore, the model was incorporated into a Fluid-Solid-Growth (FSG) framework. A patient-specific geometry of the abdominal aorta is used to illustrate the model capabilities.

    In Paper C, the evolution of the patient-specific biomechanical characteristics of the AAA was investigated. Four patients with five to eight Computed Tomography-Angiography (CT-A) scans at different time points were analyzed. Several non-trivial statistical correlations were found between the analyzed parameters.

    In Paper D, the effect of different growth kinematics on AAA growth was investigated. The transverse isotropic in-thickness growth was the most suitable AAA growth assumption, while fully isotropic growth and transverse isotropic in-plane growth produced unrealistic results. In addition, modeling of the tissue volume change improved the wall thickness prediction, but still overestimated thinning of the wall during aneurysm expansion.

  • Public defence: 2017-01-09 10:00 F3, Stockholm
    Beheshti, Reza
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Beheshti, Reza
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Sustainable Aluminum and Iron Production2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Aluminium recycling requires 95% less energy than primary production with no loss of quality. The Black Dross (BD) produced during secondary aluminium production contains high amounts of water-soluble compounds, therefore it is considered as a toxic waste. In the present work, salt removal from BD by thermal treatment has been investigated in laboratory scale. The optimum conditions for treatment were established, i.e., temperature, gas flow rate, holding time, rotation rate, and sample size. The overall degree of chloride removal was established to increase as a function of time and temperature. Even Pretreated Black Dross (PBD) was evaluated as a possible raw material for the production of a calcium aluminate-based ladle-fluxing agent to be used in the steel industry. The effects of different process parameters on the properties of the produced flux were experimentally investigated, i.e. CaO/Al2O3 ratio, temperature, holding time, and cooling media. The utilization of PBD as the alumina source during the production of a calcium aluminate fluxing agent shows promising results. The iron/steel industry is responsible for 9% of anthropogenic energy and process CO2 emissions. It is believed that the only way to a long-term reduction of the CO2 emissions from the iron/steel industry is commercialization of alternative processes such as Direct Reduction (DR) of iron oxide. Detailed knowledge of the kinetics of the reduction reactions is, however, a prerequisite for the design and optimization of the DR process. To obtain a better understanding of the reduction kinetics, a model was developed step-by-step, from a single pellet to a fixed bed with many pellets. The equations were solved using the commercial software COMSOL Multiphysics®. The final model considers the reaction rate and mass transfer inside the pellet, as well as the mass transfers and heat transfer in the fixed bed. All the models were verified against experimental results, and where found to describe the results in a satisfying way.

  • Public defence: 2017-01-13 13:00 Air & Fire, Solna
    Jemt, Anders
    KTH, School of Biotechnology (BIO), Gene Technology.
    Jemt, Anders
    KTH, School of Biotechnology (BIO), Gene Technology.
    Library Preparation for High Throughput DNA Sequencing2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Order 3 billion base pairs of DNA in the correct order and you get the blueprint of a human, the genome. Before the introduction of massively parallel sequencing a little more than a decade ago it would cost around $10 million to get this blueprint. Since then, sequencing throughput and cost have plummeted and now that figure is around $1000, and large sequencing centres such as the National Genomics Infrastructure in Stockholm is sequencing the equivalent of 25 human genomes per hour. The papers that form the basis of this thesis cover different aspects of the rapidly expanding DNA sequencing field.

     

    Paper I describes a model system that employ massively parallel sequencing to characterize the behaviour of type IIS restriction enzymes. Enzymes are biological macromolecules that catalyse chemical reactions in the cell. All commercially available sequencing systems use enzymes to prepare the nucleic acids before they are loaded on the machine. Thus, intimate knowledge of enzymes is vital not only when designing new sequencing protocols, but also for understanding the limitations of current protocols. Paper II covers the automation of a library preparation protocol for spatially resolved transcriptome sequencing. Automation increases the sample throughput and also minimises the risk of human errors that can introduce technical noise in the data. In paper III, the power of massively parallel sequencing is employed to describe the RNA content of the endometrium at two different time points during the menstrual cycle. Finally, paper IV covers the sequencing of highly degraded nucleic acids from formalin fixed, paraffin embedded samples. These samples often have a rich clinical background, making them extremely valuable for researchers. However, it is challenging to sequence these samples and this study looks at the impact that different preparation kits have on the quality of the sequencing data. 

  • Public defence: 2017-01-20 14:00 D2, Stockholm
    Mikša, Mladen
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Mikša, Mladen
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On Complexity Measures in Polynomial Calculus2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Proof complexity is the study of different resources that a proof needs in different proof systems for propositional logic. This line of inquiry relates to the fundamental questions in theoretical computer science, as lower bounds on proof size for an arbitrary proof system would separate P from NP.

    We study two simple proof systems: resolution and polynomial calculus. In resolution we reason using clauses, while in polynomial calculus we use polynomials. We study three measures of complexity of proofs: size, space, and width/degree. Size is the number of clauses or monomials that appear in a resolution or polynomial calculus proof, respectively. Space is the maximum number of clauses/monomials we need to keep at each time step of the proof. Width/degree is the size of the largest clause/monomial in a proof.

    Width is a lower bound for space in resolution. The original proof of this claim used finite model theory. In this thesis we give a different, more direct proof of the space-width relation. We can ask whether a similar relation holds between space and degree in polynomial calculus. We make some progress on this front by showing that when a formula F requires resolution width w then the XORified version of F requires polynomial calculus space Ω(w). We also show that space lower bounds do not imply degree lower bounds in polynomial calculus.

    Width/degree and size are also related, as strong lower bounds for width/degree imply strong lower bounds for size. Currently, proving width lower bounds has a well-developed machinery behind it. However, the degree measure is much less well-understood. We provide a unified framework for almost all previous degree lower bounds. We also prove some new degree and size lower bounds. In addition, we explore the relation between theory and practice by running experiments on some current state-of-the-art SAT solvers.

    The full text will be freely available from 2016-12-26 12:00
  • Public defence: 2017-01-27 10:00 Q2, Stockholm
    Lopez Nina, Luis Gagarin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA-Universidad Mayor de San Andrés, Bolivia.
    Lopez Nina, Luis Gagarin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA-Universidad Mayor de San Andrés, Bolivia.
    Catalytic conversion of syngas to ethanol and higher alcohols over Rh and Cu based catalysts2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thermochemical process converts almost any kind of biomass to a desired final product, i.e. gaseous or liquid transportation fuels and chemicals. The transportation fuels obtained in this way are renewable biofuels, which are alternatives to fossil fuels. During the last few years, thermochemical plants for the production of bioethanol have been launched and another is under construction. A total of about 290 million liters of ethanol are expected to be processed per year, mostly using municipal solid waste. Considerable efforts have been made in order to find a more selective catalyst for the conversion of biomass-derived syngas to ethanol.

    The thesis is the summary of five publications. The first two publications (Papers I and II) review the state of the art of ethanol and higher alcohols production from biomass, as well as the current status of synthetic fuels production by other processes such as the Fischer-Tropsch synthesis. Paper III analyses the catalytic performance of a mesoporous Rh/MCM-41 (MCM-41 is a hexagonal mesoporous silica) in the synthesis of ethanol which is compared to a typical Rh/SiO2 catalyst. Exhaustive catalytic testing including the addition of water vapor and modifying the hydrogen partial pressure in the syngas feed-stream which, in addition to the catalyst characterization (XRD, BET, XPS, chemisorption, TEM and TPR) before and after the catalytic testing, have allowed concluding that some water vapor can be concentrated in the pores of the Rh/MCM-41 catalyst. The concentration of water-vapor promotes the occurrence of the water gas shift reaction, which in turn induces some secondary reactions that change the product distribution, as compared to results obtained from the typical Rh/SiO2 catalyst. These results have been verified in a wide range of syngas conversion levels (1-68 %) and for different catalyst activation procedures (catalyst reduction at 200 °C, 500 °C and no-reduction) as shown in Paper IV. Finally, similar insights about the use of mesoporous catalyst have been found over a Cu/MCM-41 catalyst, shown in Paper V. Also in Paper V, the effect of metal promoters (Fe and K) has been studied; a noticeable increase of ethanol reaction rate was found over Cu-Fe-K/MCM-41 catalyst as compared to Cu/MCM-41. 

    The full text will be freely available from 2017-02-03 17:05
  • Public defence: 2017-01-31 10:00 FA32, Stockholm
    Pegonen, Reijo
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Pegonen, Reijo
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Development of an Improved Thermal-Hydraulic Modeling of the Jules Horowitz Reactor2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The newest European high performance material testing reactor, the Jules Horowitz Reactor, is under construction at CEA Cadarache research center in France. The reactor will support existing and future nuclear reactor technologies, with the first criticality expected at the end of this decade.

    The current/reference CEA methodology for simulating the thermalhydraulic behavior of the reactor gives reliable results. The CATHARE2 code simulates the full reactor circuit with a simplified approach for the core. The results of this model are used as boundary conditions in a three-dimensional FLICA4 core simulation. However this procedure needs further improvement and simplification to shorten the computational requirements and give more accurate core level data. The reactor’s high performance (e.g. high neutron fluxes, high power densities) and its design (e.g. narrow flow channels in the core) render the reactor modeling challenging compared to more conventional designs. It is possible via thermal-hydraulic or solely hydraulic Computational Fluid Dynamics (CFD) simulations to achieve a better insight of the flow and thermal aspects of the reactor’s performance. This approach is utilized to assess the initial modeling assumptions and to detect if more accurate modeling is necessary. There were no CFD thermal-hydraulic publications available on the JHR prior to the current PhD thesis project.

    The improvement process is split into five steps. In the first step, the state-of-the-art CEA methodology for thermal-hydraulic modeling of the reactor using the system code CATHARE2 and the core analysis code FLICA4 is described. In the second and third steps, a CFD thermal-hydraulic simulations of the reactor’s hot fuel element are undertaken with the code STAR-CCM+. Moreover, a conjugate heat transfer analysis is performed for the hot channel. The knowledge of the flow and temperature fields between different channels is important for performing safety analyses and for accurate modeling. In the fourth step, the flow field of the full reactor vessel is investigated by conducting CFD hydraulic simulations in order to identify the mass flow split between the 36 fuel elements and to describe the flow field in the upper and lower plenums. As a side study a thermal-hydraulic calculation, similar to those performed in previous steps is undertaken utilizing the outcome of the hydraulic calculation as an input. The final step culminates by producing an improved, more realistic, purely CATHARE2 based, JHR model, incorporating all the new knowledge acquired from the previous steps.

    The primary outcome of this four year PhD research project is the improved, more realistic, CATHARE2 model of the JHR with two approaches for the hot fuel element. Furthermore, the project has led to improved thermal-hydraulic knowledge of the complex reactor (including the hot fuel element), with the most prominent findings presented.

  • Public defence: 2017-02-17 13:00 Q2, Stockholm
    Yajnanarayana, Vijaya Parampalli
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Yajnanarayana, Vijaya Parampalli
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ultra Wideband: Communication and Localization2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The first part of this thesis develops methods for UWB communication. To meet the stringent regulatory body constraints, the physical layer signaling technique of the UWB transceiver should be optimally designed. We propose two signaling schemes which are variants of pulse position modulation (PPM) signaling for impulse radio (IR) UWB communication. We also discuss the detectors for the signaling schemes and evaluate the performance of these detectors.  IR-UWB can be used for precise range measurements as it provides a very high time resolution. This enables accurate time of arrival (TOA) estimations from which precise range values can be derived. We propose methods which use range information to arrive at optimal schedules for an all-to-all broadcast problem. Results indicate that throughput can be increased on average by three to ten times for typical network configurations compared to the traditional methods. Next, we discuss hypothesis testing in the context of UWB transceivers. We show that, when multiple detector outputs from a hardware platform are available, fusing the results from them can yield better performance in hypothesis testing than relying on a single detector output. In the second part of this thesis, the emphasis is placed on localization and joint estimation of location and communication parameters. Here, we focus on estimating the TOA of the signal. The wide bandwidth of the UWB signal requires high speed analog to digital converts (ADC) which makes the cost of the digital transceivers prohibitively high. To address this problem, we take two different strategies. In the first approach, we propose a multichannel receiver with each channel having a low-cost energy detector operating at a sub-Nyquist rate. In the second approach, we consider a compressive sampling based technique. Here, we propose a new acquisition front end, using which the sampling rate of the ADC can be significantly reduced. We extended the idea of compressive sampling based TOA estimation towards joint estimation of TOA and PPM symbols. Here, two signaling methods along with the algorithms are proposed based on the dynamicity of the target. They provide similar performance to the ML based estimation, however with a significant savings in the ADC resources.

  • Public defence: 2017-02-24 10:15 99133, Gävle
    Amin, Shoaib
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Amin, Shoaib
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Characterization and Linearization of Multi-band Multi-channel RF Power Amplifiers2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The World today is deeply transformed by the advancement in wireless technology. The envision of a smart society where interactions between physical and virtual dimensions of life are intertwined and where human interaction is mediated by machines, e.g., smart phones, demands increasingly more data traffic. This continual increase in data traffic requires re-designing of the wireless technologies for increased system capacity and flexibility. In this thesis, aspects related to behavioral modeling, characterization, and linearization of multi-channel/band power amplifiers (PAs) are discussed.

    When building a model of any system, it is advantageous to take into account the knowledge of the physics of the system and include into the model. This approach could help to improve the model performance. In this context, three novel behavioral models and DPD schemes for nonlinear MIMO transmitters are proposed.

    To model and compensate distortions in GaN based RF PAs in presence of long-term memory effects, novel models for SISO and concurrent dual-band PAs are proposed. These models are based on a fixed pole expansion technique and have infinite impulse response. They show substantial performance improvement. A behavioral model based on the physical knowledge of the concurrent dual-band PA is derived, and its performance is investigated both for behavioral modeling and compensation of nonlinear distortions.

    Two-tone characterization is a fingerprint method for the characterization of memory effects in dynamic nonlinear systems. In this context, two novel techniques are proposed. The first technique is a dual two-tone characterization technique to characterize the memory effects of self- and cross-modulation products in concurrent dual-band transmitter. The second technique is for the characterization and analysis of self- and cross-Volterra kernels of nonlinear 3x3 MIMO systems using three-tone signals.