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  • Public defence: 2019-10-24 13:30 Milos, Västerås
    Pozo Pérez, Francisco Manuel
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Methods for Efficient and Adaptive Scheduling of Next-Generation Time-Triggered Networks2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Real-time networks play a fundamental role in embedded systems. To meet timing requirements, provide low jitter and bounded latency in such networks the time-triggered communication paradigm is frequently applied in such networks. In this paradigm, a schedule specifying the transmission times of all the traffic is synthesized a priori. Given the steady increase in size and complexity of embedded systems, coupled with the addition of wireless communication, a new time-triggered network model of larger and mixed wired-wireless network isdeveloping. Developing such next-generation networks entails significant research challenges, especially concerning scalability, i.e., allowing generation of schedules of the very large next-generation networks in a reasonable time. A second challenge concerns a well-known limitation of the time-triggered paradigm: its lack of flexibility. Large networks exacerbate this problem, as the number of changes during network operation increases with the number of components, which renders static scheduling approaches unsuitable.

    In this thesis, we first propose a remedy to the scalability challenge that the synthesis of next-generation network schedules introduces. We propose a family of divide-and-conquer approaches that segment the entire scheduling problem into small enough subproblems that can be effectively and efficiently solved by state-of-the-art schedulers. Second, we investigate how adaptive behaviours can be introduced into the time-triggered paradigm with the implementation of a Self-Healing Protocol. This protocol addresses the flexibility challenge by only updating a small segment of the schedule in response to changes during runtime. This provides a significant advantage compared to current approaches that fully reschedule the network. In the course of our research, we found that our protocol become more effective when the slack in the original schedule is evenly distributed during the schedule synthesis. As a consequence, we also propose a new scheduling approach that maximizes the distances between frames, increasing the success rate of our protocol.

    The divide-and-conquer approaches developed in this thesis were able to synthesize schedules of two orders of magnitude more traffic and one order of magnitude more nodes in less than four hours. Moreover, when applied to current industrial size networks, they reduced the synthesis time from half an hour to less than one minute compared with state-of-the-art schedulers. The Self-Healing Protocol opened a path towards adaptive time-triggered being able to heal schedules online after link and switch failures in less than ten milliseconds.

  • Public defence: 2019-11-04 13:30 Gamma, Västerås
    Cai, Simin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Systematic Design and Analysis of Customized Data Management for Real-Time Database Systems2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Modern real-time data-intensive systems generate large amounts of data that are processed using complex data-related computations such as data aggregation. In order to maintain logical data consistency and temporal correctness of the computations, one solution is to model the latter as transactions and manage them using a Real-Time Database Management System (RTDBMS). Ideally, depending on the particular system, the transactions are customized with the desired logical and temporal correctness properties, which should be enforced by the customized RTDBMS via appropriate transaction management mechanisms. However, developing such a data management solution with high assurance is not easy, partly due to inadequate support for systematic specification and analysis during the design. Firstly, designers do not have means to identify the characteristics of the computations, especially data aggregation, and to reason about their implications. Design flaws might not be discovered early enough, and thus they may propagate to the implementation. Secondly, meeting more properties simultaneously might not be possible, so trading-off the less critical ones for the critical one, for instance, temporal correctness, is sometimes required. Nevertheless, trade-off analysis of conflicting properties, such as transaction atomicity, isolation and temporal correctness, is mainly performed ad-hoc, which increases the risk of unpredictable behavior.

    In this thesis, we address the above problems by showing how to systematically design and provide assurance of transaction-based data management with data aggregation support, customized for real-time systems. We propose a design process as our methodology for the systematic design and analysis of the trade-offs between desired properties, which is facilitated by a series of modeling and analysis techniques. Our design process consists of three major steps as follows: (i) Specifying the data-related computations, as well as the logical data consistency and temporal correctness properties, from system requirements, (ii) Selecting the appropriate transaction models to model the computations, and deciding the corresponding transaction management mechanisms that can guarantee the properties, via formal analysis, and, (iii) Generating the customized RTDBMS with the proved transaction management mechanisms, via configuration or implementation. In order to support the first step of our process, we propose a taxonomy of data aggregation processes for identifying their common and variable characteristics, based on which their inter-dependencies can be captured, and the consequent design implications can be reasoned about. Tool support is provided to check the consistency of the data aggregation design specifications. To specify transaction atomicity, isolation and temporal correctness, as well as the transaction management mechanisms, we also propose a Unified Modeling Language (UML) profile with explicit support for these elements. The second step of our process relies on the systematic analysis of trade-offs between transaction atomicity, isolation and temporal correctness. To achieve this, we propose two formal frameworks for modeling transactions with abort recovery, concurrency control, and scheduling. The first framework UPPCART utilizes timed automata as the underlying formalism, based on which the desired properties can be verified by model checking. The second framework UPPCART-SMC models the system as stochastic timed automata, which allows for probabilistic analysis of the properties for large complex RTDBMS using statistical model checking. The encoding of high-level UTRAN specifications into corresponding formal models is supported by tool automation, which we also propose in this thesis. The applicability and usefulness of our proposed techniques are validated via several industrial use cases focusing on real-time data management.

  • Public defence: 2019-11-05 13:00 Sal 320, Borlänge
    Swing Gustafsson, Moa
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. Mälardalens Högskola.
    Heating of buildings from a system perspective2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Energy efficiency measures in buildings are considered to have great potential for reducing total energy use, and contribute to a reduced climate and environmental impact. In Sweden, however, there is a focus on bought energy, which does not always reflect the environmental and climate impact. Focusing on bought energy means that a house owner may choose an electricity based heat pump instead of district heating (DH), since heat pumps result in less bought energy compared to DH.

    The energy system surrounding the buildings is affected by the choice of energy carriers used for heating. This thesis uses three different methods to study how the energy system is affected. In the first part, primary energy use has been calculated for a simulated building with different heating systems, resulting in different electricity and DH demands. The second part studies the impact on peak demand and annual consumption in the power grid and DH system due to different market shares of electricity based heating and DH. In the third part, the life cycle cost is calculated for different heating solutions from both a building and a socio-economic perspective, for 100 % renewable energy system scenarios.

    The results show that the choice of energy carrier has a great influence on primary energy use. However, this depends even more on the calculation method used. Which heating solution, and thus which energy carrier, gives the lowest primary energy use varies with the different methods.

    The power grid and DH system are affected by the choice of energy carrier. There is a potential to lower peak demand in the power grid by more efficient heat pumps. But an even greater potential is shown by using DH instead of electricity based heating. A larger share of DH also allows the production of more electricity with the use of combined heat and power.

    The life cycle cost for different heating solutions also depends on the method used. From a building owner’s perspective, with current electricity and DH prices, electricity based heating is more economical. However, from a socio-economic perspective, with increasing electricity system costs due to a larger share of variable electricity production in a 100 % renewable system, DH becomes more economically profitable in several scenarios.

    The choice of energy carrier for heating in buildings affects the energy system to a high degree. A system perspective is therefore important in local, national and global energy efficiency policies and projects.

    The full text will be freely available from 2019-10-15 08:00
  • Public defence: 2019-11-13 13:15 Kappa, Västerås
    Brehmer, Daniel
    Mälardalen University, School of Education, Culture and Communication.
    Support for mathematics teachers’ change: Examining catalysts for teacher learning and role of the teacher in professional development programmes2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When the perception changes regarding what mathematics students should be able to manage, this is typically addressed through a new national curriculum. To establish and implement this new curriculum in practice, teachers must be given the opportunity to change according to it. For such change, they need support in interpreting and implementing the new curriculum. Typically, there are two common ways to support teacher change: (1) developing and launching curriculum materials that correspond to the national curriculum; and (2) implementing professional development programmes (PDPs) that correspond to the new national curriculum. This thesis includes both aspects and aims to contribute to research on support for mathematics teachers’ change. This aim is operationalized by: (1) studying mathematics textbooks in which tasks and plausible teaching intentions are analysed; (2) studying teacher agency in collegial discussions in relation to the design of a PDP; and (3) mapping and describing catalysts for teacher learning from PDPs in research literature. These studies resulted in five papers, which are included in this thesis. The main results of the papers cover: the distribution of types of tasks in Swedish mathematics textbooks; the type of learning approach advocated in these textbooks; how different types of texts in PDPs relate to teacher agency in collegial discussions; and an identification and description of catalysts for teacher learning from PDPs for mathematics teachers. In the kappa1 of this thesis, these results are merged and discussed in relation to different models of teacher change. The focus in the kappa is on examining catalysts for teacher learning from such initiatives and the role of the teacher in PDPs. This examination suggests elaborations on parts of a conceptual framework for effective PDPs (Desimone, 2009). More precisely, the elaborations concern core critical features for effective PDPs, presented in this framework: Content Focus, Active Learning, Collective Participation, Duration, and Coherence. The main contributions of this thesis concern: a tool for analysing tasks in textbooks with respect to problem-solving tasks; an organizing frame for mapping learning catalysts from articles describing PDPs; a description of catalysts for teacher learning from PDPs as specifications of core critical features for effective PDPs; and the role of the teacher in PDPs as a catalyst for learning. Implications and suggestions for future research are discussed.

    ___________________________

    1The Swedish term kappa will be used in this thesis in the absence of an equivalent English term for the introductory chapters of an aggregation dissertation