1 - 7 of 7
rss atomLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
  • Presentation: 2017-04-07 10:00 Ka-Sal C (Sal Sven-Olof Öhrvik), Stockholm
    Yaghoubi, Forough
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Agile, Resilient and Cost-efficient Mobile Backhaul Networks2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The exponentially increasing traffic demand for mobile services requires innovative solutions in both access and backhaul segments of 5th generation (5G) mobile networks. Although, heterogeneous networks (HetNets) are a promising solution for the wireless access, the backhaul segment has received considerably less attention and falls short in meeting the stringent requirements of 5G in terms of capacity and availability.

    HetNets together with mobility requirements motivate the use of microwave backhauling that supports fiber-like capacity with millimeter-wave communications. However, higher carrier frequencies are subject to weather disturbances like rain that may substantially degrade the network throughput. To mitigate this effect, we develop a fast and accurate rain detection algorithm that triggers a network-layer strategy, i.e., rerouting. The results show that with small detection error the network throughput increases while posing small overhead on the network.

    The rain impact can be alleviated by centralized rerouting under the software defined networking paradigm. However, careless reconfiguration may impose inconsistency that leads to a significant temporary congestion and limits the gain of rerouting. We propose a consistency-aware rerouting framework by considering the cost of reconfiguration. At each time, the centralized controller may either take a rerouting or no-rerouting decision in order to minimize the total data loss. We use a predictive control algorithm to provide such an online sequence of decisions. Compared to the regular rerouting, our proposed approach reduces the throughput loss and substantially decreases the number of reconfigurations.

    In the thesis we also study which backhaul option is the best from a techno-economic perspective. We develop a comprehensive framework to calculate the total cost of ownership of the backhaul segment and analyze the profitability in terms of cash flow and net present value. The results highlight the importance of selecting proper backhaul solution to increase profitability.

  • Presentation: 2017-04-07 10:00 Q2, Stockholm
    Aytekin, Arda
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asynchronous Algorithms for Large-Scale Optimization: Analysis and Implementation2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis proposes and analyzes several first-order methods for convex optimization, designed for parallel implementation in shared and distributed memory architectures. The theoretical focus is on designing algorithms that can run asynchronously, allowing computing nodes to execute their tasks with stale information without jeopardizing convergence to the optimal solution.

    The first part of the thesis focuses on shared memory architectures. We propose and analyze a family of algorithms to solve an unconstrained, smooth optimization problem consisting of a large number of component functions. Specifically, we investigate the effect of information delay, inherent in asynchronous implementations, on the convergence properties of the incremental prox-gradient descent method. Contrary to related proposals in the literature, we establish delay-insensitive convergence results: the proposed algorithms converge under any bounded information delay, and their constant step-size can be selected independently of the delay bound.

    Then, we shift focus to solving constrained, possibly non-smooth, optimization problems in a distributed memory architecture. This time, we propose and analyze two important families of gradient descent algorithms: asynchronous mini-batching and incremental aggregated gradient descent. In particular, for asynchronous mini-batching, we show that, by suitably choosing the algorithm parameters, one can recover the best-known convergence rates established for delay-free implementations, and expect a near-linear speedup with the number of computing nodes. Similarly, for incremental aggregated gradient descent, we establish global linear convergence rates for any bounded information delay.

    Extensive simulations and actual implementations of the algorithms in different platforms on representative real-world problems validate our theoretical results.

  • Presentation: 2017-04-07 10:00 D3, Stockholm
    Oakes, Benjamin Donald
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Risk Analysis of Intentional Electromagnetic Interference on Critical Infrastructures2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Our modern society depends on the functioning and interplay of a wealth of infrastructures. Practicallyall of these infrastructures are in some form or another, dependent on electrical and electronicsystems. The majority of modern infrastructure is dependent on electric power and controlled bySupervisory Control and Data Acquisition (SCADA) systems. Electronic systems are sensitive toelectromagnetic interference and at the same time, sources of electromagnetic interference are becomingmore readily available on the market.This means that certain important electronic infrastructure could be exposed to the risk of intentionalelectromagnetic interference (IEMI). Therefore, and also due to the complex nature of electronicinfrastructure, a comprehensive risk assessment methodology is needed. A game-theoretic approachfor quantitative risk assessment of the recently recognised threat of intentional electromagneticinterference on critical infrastructures is presented. The thesis bridges the gap between thefields of IEMI and risk analysis and lays a foundation for further development within this multidisciplinaryfield.In paper I, the probability distribution function of the electric field strength from a continuouswave source is estimated in complex building structures. Probability distribution functions arecombined for small and large scale fluctuations.In paper II, a structured risk assessment framework is presented for identifying and quantifyingthe risk of IEMI on a distribution network infrastructure. The dimensions and components of riskare dissected and a suitable definition of risk is formulated.In paper III, an operational model is formulated to optimise the operation of a wireless networkunder the course of a coordinated jamming attack. The model captures the time dimension andillustrates how the network operator must dynamically control the network so as to reduce the totalnetwork operational cost.

  • Presentation: 2017-04-07 13:00 FB54, Stockholm
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Effects of Dark Matter in Astrophysical Systems2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    When studying astrophysical structures with sizes ranging from dwarf galaxies to galaxy clusters, it becomes clear that there are vast amounts of unobservable gravitating mass. A compelling hypothesis is that this missing mass, which we call dark matter, consists of elementary particles that can be described in the same manner as those of the standard model of particle physics. This thesis is dedicated to the study of particle dark matter in astrophysical systems.

    The solar composition problem refers to the current mismatch between theoretical predictions and observations of the solar convection zone depth and sound speed profile. It has been shown that heat transfer by dark matter in the Sun may cool the solar core and alleviate the problem. We discuss solar capture of a self-interacting Dirac fermion dark matter candidate and show that, even though particles and antiparticles annihilate, the abundance of such a particle may be large enough to influence solar physics.

    Currently, direct and indirect methods are employed in searches for dark matter. In this context, we study inelastic dark matter, where a small mass splitting separates two dark matter particles and scattering takes one into the other. This affects the scattering kinematics, which in turn affects direct detection and solar capture rates. We also discuss the information contained in a direct detection signal and how it can be used to infer a minimal solar capture rate of dark matter.

    When comparing simulated dark matter halos with collisionless dark matter with dark matter halos inferred from observations, problems appear in the smallest structures. A proposed solution is self-interacting dark matter with long range forces. As the simplest models are under severe constraints, we study self-interactions in a model of inelastic dark matter.

  • Presentation: 2017-04-20 14:00 E51, Stockholm
    Niazi Ardekani, Mehdi
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Numerical study of non-spherical/spherical particles in laminar and turbulent flows2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The presence of solid rigid particles alters the global transport and rheological properties of the mixture in complex (and often unpredictable) ways. In recent years a few studies have been devoted to investigating the behavior of dense suspensions in the turbulent/inertial regime with the majority of theses analyses limited to mono-disperse rigid neutrally-buoyant spheres. However, one interesting parameter that is rarely studied for particles with high inertia is the particle shape. Spheroidal particles introduce an anisotropy, e.g. a tendency to orient in a certain direction, which can affect the bulk behavior of a suspension in an unexpected ways. The main focus of this study is therefore to investigate the behavior of spheroidal particles and their effect on turbulent/inertial flows.

    We perform fully resolved simulations of particulate flows with spherical/spheroidal particles, using an efficient/accurate numerical approach that enables us to simulate thousands of particles with high resolutions in order to capture all the fluid-solid interactions.

    Several conclusions are drawn from this study that reveal the importance of particle's shape effect on the behaviour of a suspension e.g. spheroidal particles tend to cluster while sedimenting. This phenomenon is observed in this work for both particles with high inertia, sedimenting in a quiescent fluid and inertialess particles (point-like tracer prolates) settling in homogenous isotropic turbulence. The mechanisms for clustering is indeed different between these two situations, however, it is the shape of particles that governs these mechanisms, as clustering is not observed for spherical particles. Another striking finding of this work is drag reduction in particulate turbulent channel flow with rigid oblate particles. Again this drag reduction is absent for spherical particles, which instead increase the drag with respect to single-phase turbulence. 

  • Presentation: 2017-04-28 10:00 K1, Stockholm
    Ottenhall, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Water purification using polyelectrolyte modified cellulose fibers and filters to adsorb bacteria2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Clean water is necessary for human survival and there is a need for development of cheap and easy water purification techniques to use in emergency situations when there is no access to safe drinking water. Bacteria contaminated water can cause lethal diarrheal diseases and is globally the second most common cause of death among children less than five years of age.

    Bacteria adsorbing filter paper made from cellulose could be an environmentally and economically sustainable alternative for disposable water purification filters. This thesis investigates the possibility to use polyelectrolyte multilayer modified cellulose pulp fibers and filter papers to adsorb and remove bacteria from water. The bacterial removal efficiency of the modified materials has been tested both in suspension and through filtration.

    The surface modification provides the cellulose fibers with a positively charged surface that can attract and bind the negatively charged bacteria. The bacterial adsorption through electrostatic interactions makes it possible to remove bacteria, even when the pore size of the cellulose filters is larger than bacteria. Bacterial reduction tests shows that it is possible to remove over 99.9 % of the bacteria when filtering water through the modified materials. An increased amount of adsorbed cationic polyelectrolyte, polyvinylamine, resulted in an increased bacterial removal capacity. It has also been shown that the bacterial removal efficiency increases with an increased the amount of bacteria adsorbing materials in the filter.

    The modified materials have been compared with a commercial product and the filtration efficiency has shown to be greater for the polyelectrolyte-modified materials, under the test conditions used in this thesis. Tests with natural water samples shows that it is important to use a filtration mode to remove particles from the water in combination with the bacterial adsorption, as the particles interfere with the bacterial adsorption.

    The full text will be freely available from 2017-12-31 17:09
  • Presentation: 2017-05-23 15:30 M108, Stockholm
    Solat Yavari, Majid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Slab Frame Bridges: Structural Optimization Considering Investment Cost and Environmental Impacts2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This research encompasses the automated design and structural optimization of reinforced concrete slab frame bridges, considering investment costs and environmental impacts. The most important feature of this work is that it focusses on realistic and complete models of slab frame bridges rather than on optimization of only individual members or sections of a bridge. The thesis consists of an extended summary of publications and three appended papers. In the first paper, using simple assumptions, the possibility of applying cost-optimization to the structural design of slab frame bridges was investigated. The results of the optimization of an existing constructed bridge showed the potential to reduce the investment cost of slab frame bridges. The procedure was further developed in the second paper. In this paper, automated design was integrated to a more refined cost-optimization methodology based on more detailed assumptions and including extra constructability factors. This procedure was then applied to a bridge under design, before its construction. From the point of view of sustainability, bridge design should not only consider criteria such as cost but also environmental performance. The third paper thus integrated life cycle assessment (LCA) with the design optimization procedure to perform environmental impact optimization of the same case study bridge as in the second paper. The results of investment cost and environmental impact optimization were then compared. The obtained results presented in the appended papers highlight the successful application of optimization techniques to the structural design of reinforced concrete slab frame bridges. Moreover, the results indicate that a multi-objective optimization that simultaneously considers both environmental impacts and investment cost is necessary in order to generate more sustainable designs. The presented methodology has been applied to the design process for a time-effective, sustainable, and optimal design of concrete slab frame bridges.