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  • Presentation: 2020-06-04 10:00 Sal Harry Nyquist, Stockholm
    González, Rodrigo A.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Consistency and efficiency in continuous-time system identification2020Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Continuous-time system identification deals with the problem of building continuous-time models of dynamical systems from sampled input and output data. In this field, there are two main approaches: indirect and direct. In the indirect approach, a suitable discrete-time model is first determined, and then it is transformed into continuous-time. On the other hand, the direct approach obtains a continuous-time model directly from the sampled data. In both approaches there exists a dichotomy between discrete-time data and continuous-time models, which can induce robustness issues and complications in the theoretical analysis of identification algorithms. These difficulties are addressed in this thesis.

    First, we consider the indirect approach to continuous-time system identification. For a zero-order hold sampling mechanism, this approach usually leads to a transfer function estimate with relative degree one, independent of the relative degree of the strictly proper true system. Inspired by the indirect prediction error method, we propose an indirect-approach estimator that enforces the desired number of poles and zeros in the continuous-time transfer function estimate, and show that the estimator is consistent and asymptotically efficient. A robustification of this method is also developed, by which the estimates are also guaranteed to deliver stable models.

    In the second part of the thesis, we analyze asymptotic properties of the Simplified Refined Instrumental Variable method for Continuous-time systems (SRIVC), which is one of the most popular direct identification methods. This algorithm applies an adaptive prefiltering to the sampled input and output that requires assumptions on the intersample behavior of the signals. We present a comprehensive analysis on the consistency and asymptotic efficiency of the SRIVC estimator while taking into account the intersample behavior of the input signal. Our results show that the SRIVC estimator is generically consistent when the intersample behavior of the input is known exactly and subsequently used in the implementation of the algorithm, and we give conditions under which consistency is not achieved. In terms of statistical efficiency, we compute the asymptotic Cramér-Rao lower bound for an output error model structure with Gaussian noise, and derive the asymptotic covariance of the SRIVC estimates. We conclude that the SRIVC estimator is asymptotically efficient under mild conditions, and that this property can be lost if the intersample behavior of the input is not carefully accounted for in the SRIVC procedure.

    Moreover, we propose and analyze the statistical properties of an extension of SRIVC that is able to deal with input signals that cannot be interpolated exactly via hold reconstructions. The proposed estimator is generically consistent for any input reconstructed using zero or first-order-hold devices, and we show that it is generically consistent for continuous-time multisine inputs as well. Comparisons with the Maximum Likelihood technique and an analysis of the iterations of the method are provided, in order to reveal the influence of the intersample behavior of the output and to propose new robustifications to the SRIVC algorithm.

    Fulltekst (pdf)
  • Presentation: 2020-06-08 13:00 Via Zoom: https://kth-se.zoom.us/webinar/register/WN_8vcAAGzGR0KapHqV6MlWyQ, Stockholm, Sweden
    Ddiba, Daniel
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Hållbarhet, utvärdering och styrning. Stockholm Environment Institute (SEI).
    Exploring the circular economy of urban organic waste in sub-Saharan Africa: opportunities and challenges2020Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Globally, there is increasing awareness of the importance of applying circular economy principles to the management of organic waste streams through resource recovery. In the urban areas of sub-Saharan Africa which are going to host a significant part of population growth over the next three decades, this is especially relevant. Circular economy approaches for sanitation and waste management can provide incentives to improve infrastructure and consequently contribute resources for water, energy and food that power urban livelihoods. This thesis is situated at the intersection of the circular economy on one hand and sanitation and waste management systems on the other. It aims to contribute to knowledge about the circular economy by investigating the potential contribution of resource-oriented urban sanitation and waste management towards the implementation of a circular economy in sub-Saharan Africa and the opportunities and challenges thereof.

    In pursuit of the above aim, the thesis employs a mixed methods approach and is operationalized in two case study locations: Kampala (Uganda) and Naivasha (Kenya). The findings reveal the quantities of resource recovery products like biogas, compost and black soldier fly larvae that can be obtained from the organic waste streams collected in a large city, demonstrate the viability of valorizing dried faecal sludge as a solid fuel for industrial applications, and identify the factors that facilitate or impede the governance capacity to implement circular economy approaches to the management of organic waste streams in urban areas in sub-Saharan Africa. The methods used for quantifying the potential for valorizing organic waste streams and for assessing governance capacity demonstrate approaches that could be applied in other urban contexts with interest in implementing circular economy principles. The discussion highlights some key implications of these findings for sanitation and waste management practices, arguing that it is time for a shift in sub-Saharan Africa from designing sanitation and waste management systems for disposal to designing them for resource recovery.

    Fulltekst (pdf)
  • Presentation: 2020-06-10 13:00 https://kth-se.zoom.us/j/66045421296, Stockholm
    Candel, Melissa
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande, Ledning och organisering i byggande och förvaltning. KTH Royal Institute of Technology.
    Co-Developing Sustainability Requirements: Exploring client and municipal perspectives in housing development2020Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Construction has major environmental, social and economic impacts. Improving sustainability both during and after the construction process is widely discussed among a slew of practitioners, governments and researchers. Construction clients, such as housing developers, are considered key actors for change and innovation because of their position to set requirements when procuring construction projects. The process of developing project requirements has therefore mainly been studied during the construction clients’ procurement process. At the same time, municipalities use their position as land owners to drive sustainable development. Land allocation agreements allow municipalities to set project-specific sustainability requirements for construction projects on municipal land. The purpose of this thesis is to explore how municipal sustainability requirements affect housing developers when planning and designing their projects.

    The research is based on a single empirical case study of an urban development programme comprising multiple parallel and sequential housing construction projects. In this study, the municipality’s and housing developers’ perspectives are explored. The results demonstrate that the housing developers perceive several barriers to implementing municipal sustainability requirements. The three main barriers that were identified are reduced flexibility coupled with uncertainty, conflicting interests coupled with reduced autonomy and interdependencies, and a lack of trust and transparency coupled with interdependencies. The municipal sustainability requirements are initially developed by the municipality for the land allocation agreement. They are then co-developed further by the municipality and the housing developers together through negotiations before being finalised in conjunction with the developers’ procurement process.

    The study is focused on the period following the housing developers’ signing of land allocation agreements with the municipality and before starting their procurement process. During this period, the housing developers attempt to negotiate municipal sustainability requirements that they anticipate will increase costs, risk and uncertainty and decrease the value of their final product. Negotiations between the housing developers and the municipality can be viewed as value co-creation processes stimulated by functional conflict. These findings build on three papers that are included in the thesis.

    Contributions are made to literature on the role of construction clients and their perceived barriers to implementing and developing sustainable construction solutions and practices and barriers to change in general. Theoretical contributions are also made to literature on value co-creation in construction by illustrating how clients engage in the co-creation of value with municipalities and other clients. Finally, the theoretical link between value co-creation and functional conflict is studied and developed. 

    Fulltekst (pdf)
  • Presentation: 2020-06-10 15:15 A5:1003, Stockholm
    Samuelsson, Filip
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..
    Multi-messenger emission from gamma-ray bursts2020Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Multi-messenger astronomy is a very hot topic in the astrophysical community. A messenger is something that carries information. Different astrophysical messenger types are photons, cosmic rays, neutrinos, and gravitational waves. They all carry unique and complementary information to one another. The idea with multi-messenger astronomy is that the more different types of messengers one can obtain from the same event, the more complete the physical picture becomes.

    In this thesis I study the multi-messenger emission from gamma-ray bursts (GRBs), the most luminous events known in the Universe. Specifically, I study the connection of GRBs to extremely energetic particles called ultra-high-energy cosmic rays (UHECRs). UHECRs have unknown origin despite extensive research. GRBs have long been one of the best candidates for the acceleration of these particles but a firm connection is yet to be made. In Paper I and Paper II, we study the possible GRB-UHECR connection by looking at the electromagnetic radiation from electrons that would also be accelerated together with the UHECR. My conclusion is that the signal from these electrons does not match current GRB observation, disfavoring that a majority of UHECRs comes from GRBs.

    Fulltekst (pdf)