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- Bygde, Stefan, 1980-
(författare)
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Static WCET Analysis Based on Abstract Interpretation and Counting of Elements
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a real-time system, it is crucial to ensure that all tasks of the system holdtheir deadlines. A missed deadline in a real-time system means that the systemhas not been able to function correctly. If the system is safety critical, this canlead to disaster. To ensure that all tasks keep their deadlines, the Worst-CaseExecution Time (WCET) of these tasks has to be known. This can be done bymeasuring the execution times of a task, however, this is inflexible, time consumingand in general not safe (i.e., the worst-casemight not be found). Unlessthe task is measured with all possible input combinations and configurations,which is in most cases out of the question, there is no way to guarantee that thelongest measured time actually corresponds to the real worst case.Static analysis analyses a safe model of the hardware together with thesource or object code of a program to derive an estimate of theWCET. This estimateis guaranteed to be equal to or greater than the real WCET. This is doneby making calculations which in all steps make sure that the time is exactlyor conservatively estimated. In many cases, however, the execution time of atask or a program is highly dependent on the given input. Thus, the estimatedworst case may correspond to some input or configuration which is rarely (ornever) used in practice. For such systems, where execution time is highly inputdependent, a more accurate timing analysis which take input into considerationis desired.In this thesis we present a framework based on abstract interpretation andcounting of possible semantic states of a program. This is a general methodof WCET analysis, which is language independent and platform independent.The two main applications of this framework are a loop bound analysis and aparametric analysis. The loop bound analysis can be used to quickly find upperbounds for loops in a program while the parametric framework provides aninput-dependent estimation of theWCET. The input-dependent estimation cangive much more accurate estimates if the input is known at run-time.
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| 2. |
- Fältström, Emma, 1987-
(författare)
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Towards the Control of Microplastic Pollution in Urban Waters
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water pollution has long been considered a challenge in urban areas, and new types of pollution are continuously introduced to society. Urban wastewater and stormwater act as transport pathways of pollution from urban areas to receiving waterways. Microplastics are a new type of pollution that is being highlighted as problematic, and the presence of microplastics is widespread in the environment. The knowledge about behaviour, sources and transport pathways is still limited. Still, there have been suggestions for ways to control microplastic pollution. Moreover, many other pollutants have been introduced, and to a various extent controlled, in the urban water system before, which means that there are strategies for pollution control in place.The problem of microplastic pollution is receiving attention from both research and policy. Therefore, there is a need to simultaneously explore ways to handle the pollution and learn more about the flows of microplastics. The aim of this thesis is to contribute to the understanding of flows of microplastics in urban waters and investigate strategies and measures that can control the flows. This aim has been addressed through three different studies presented in the three appended papers. The empirical material was gathered between 2017 and 2020 using both quantitative and qualitative methods. The flows of microplastics were investigated using a quantitative approach with inspiration from substance flow analysis. Strategies and measures to control pollution were investigated by means of analyses of documents, literature review and interviews.In terms of flows, the results show that laundry seems to be a large contributor to the wastewater system, while the contribution from cigarette filters was smaller than anticipated. Littering, in general, as well as paint, are potentially important sources of microplastics where the understanding is very limited. In terms of strategies and measures to control the flows, there are both preventive and treatment options for microplastics. As microplastics are a diverse pollutant group, several different solutions are needed. Some aspects that influence control efforts are related to the properties and behaviour of the specific pollutant and can therefore be more or less suitable for different pollutants. Other aspects are more general, such as what compartments are seen as valuable and prioritised in terms of protection. Further, treatment moves the pollution from the water to another medium, and this movement also needs to be considered.Challenges in terms of changing, limited or even lack of legislation, as well as unclear responsibility, and problems with collaboration among urban actors also impact the possibilities to control pollution. The case of microplastics also raises questions about when and how pollution should be controlled and by whom. Further, emerging practices in the urban water system, such as source separation, pipe-separation, and water reuse, will have implications for how pollution will be handled in the future.
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| 3. |
- Gustafsson, Stefan
(författare)
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Electromagnetic dispersion modeling and analysis for HVDC power cables
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Derivation of an electromagnetic model, regarding the wave propagation in a very long (10 km or more) High Voltage Direct Current (HVDC) power cable, is the central part of this thesis. With an existing “perfect” electromagnetic model there are potentially a wide range of applications.The electromagnetic model is focused on frequencies between 0 and 100 kHz since higher frequencies essentially will be attenuated. An exact dispersion relation is formulated and the propagation constant is computed numerically. The dominating mode is the first Transversal Magnetic (TM) mode of order zero, denoted TM01, which is also referred to as the quasi-TEM mode. A comparison is made with the second propagating TM mode of order zero denoted TM02. The electromagnetic model is verified against real time data from Time Domain Reflection (TDR) measurements on a HVDC power cable. A mismatch calibration procedure is performed due to matching difficulties between the TDR measurement equipment and the power cable regarding the single-mode transmission line model.An example of power cable length measurements is addressed, which reveals that with a “perfect” model the length of an 80 km long power cable could be estimated to an accuracy of a few centimeters. With the present model the accuracy can be estimated to approximately 100 m.In order to understand the low-frequency wave propagation characteristics, an exact asymptotic analysis is performed. It is shown that the behavior of the propagation constant is governed by a square root of the complex frequency in the lowfrequency domain. This thesis also focuses on an analysis regarding the sensitivity of the propagation constant with respect to some of the electric parameters in the model. Variables of interest when performing the parameter sensitivity study are the real relative permittivityand the conductivity.
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