| 14621. |
- Lidén Eddeland, Johan, 1991
(författare)
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On Falsification of Large-Scale Cyber-Physical Systems
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the development of modern Cyber-Physical Systems, Model-Based Testing of the closed-loop system is an approach for finding potential faults and increasing quality of developed products. Testing is done on many different abstraction levels, and for large-scale industrial systems, there are several challenges. Executing tests on the systems can be time-consuming and large numbers of complex specifications need to be thoroughly tested, while many of the popular academic benchmarks do not necessarily reflect on this complexity. This thesis proposes new methods for analyzing and generating test cases as a means for being more certain that proper testing has been performed on the system under test. For analysis, the proposed approach can automatically find out how much of the physical parts of the system that the test suite has executed. For test case generation, an approach to find errors is optimization-based falsification. This thesis attempts to close the gap between academia and industry by applying falsification techniques to real-world models from Volvo Car Corporation and adapting the falsification procedure where it has shortcomings for certain classes of systems. Specifically, the main contributions of this thesis are (i) a method for automatically transforming a signal-based specification into a formal specification allowing an optimization-based falsification approach, (ii) a new collection of specifications inspired by large-scale specifications from industry, (iii) an algorithm to perform optimization-based falsification for such a large set of specifications, and (iv) a new type of coverage criterion for Cyber-Physical Systems that can help to assess when testing can be concluded. The proposed methods have been evaluated for both academic benchmark examples and real-world industrial models. One of the main conclusions is that the proposed additions and changes to the analysis and generation of tests can be useful, given that one has enough information about the system under test. The methods presented in this thesis have been applied to realworld models in a way that allows for higher-quality products by finding more faults in early phases of development.
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| 14622. |
- Lidén, Gunnar, 1961
(författare)
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On-line Monitoring Techniques for the Study of Yeast Physiology. Some Studies on the Yeasts Pichia stipitis and Saccharomyces cerevisiae
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- On-line monitoring techniques have been used with the goal of optimizing fermentation processes involving the yeasts Saccharomyces cerevisiae (Baker's yeast) and Pichia stipitis (a xylose fermenting yeast), and a highly equipped fermentor system has been developed for these studies. The fed-batch growth of S. cerevisiae on a synthetic glucose medium was controlled using a control strategy based on calorimetric measurements and an increase in cell yield by 10% compared to diauxic batch growth was obtained. Anaerobic chemostat growth of S. cerevisiae was studied under carbon limitation and nitrogen limitation. The ethanol yield was higher and the glycerol yield lower during nitrogen limited conditions. The nitrogen content of the cells was different in the two cases, with a lower level for the cells grown under nitrogen limitation. The ATP yield was also substantially lower during nitrogen limited conditions. This was probably due to either increased transport energy requirements or futile cycling. The xylose metabolism by the xylose fermenting yeast Pichia stipitis has been studied with in situ fluorescence measurements of the nucleotides NADH and NADPH. The fluorescence increase, caused by a step change from aerobic to anaerobic conditions, was much lower for P. stipitis than for C. utilis, which shows on a larger redox imbalance for the latter yeast during anaerobic conditions. A mathematical model for an open-ended fluorosensor has been developed and experimentally verified with measurements on a pure fluorophore solution. Oxygen programmed fermentation, a new method for the study of microaerobic fermentations based on a continuous ramp of oxygenation rates, is introduced and analyzed mathematically. It is shown that it may be possible to study metabolic transitions as a function of oxygenation rates at conditions which, normally, would lead to wash-out. The effect of carbon dioxide on the xylose fermentation rate by P. stipitis was also studied. In a carbon dioxide atmosphere, the specific fermentation rate was 45% lower than in a nitrogen sparged fermentor.
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| 14623. |
- Lidén, Peter, 1982
(författare)
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Development of a non-destructive field testing method for thermal assessment of district heating pipes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thermal state of a district heating (DH) network governs the heat losses. It is a parameter considered if a change is to be made in the network. Heat losses are costly and economic aspects are important when planning for the maintenance or replacement of DH pipes. In addition, knowledge of the DH network, and of the parts of the network that may contribute to high heat losses, is important for system control. Pre-insulated DH pipes have been in use for over 40 years. The thermal performance of these pipes decreases over time as a result of thermal aging, leading to higher heat losses. Present methods cannot assess these heat losses with high accuracy. This thesis proposes a developed non-destructive cooling method, the main purpose of which is to perform a temporary shutdown of a selected part of a network, and where temperature measurements are performed during the cooling phase. This thesis presents the development process and the final method to use for thermally assessing pre-insulated DH pipes with high accuracy. The main research questions of this work were linked to the accessibility and measurability of the buried pipe or its connected parts. The methodology for developing the method is based on laboratory tests, field tests with several measurement points, and mathematical models of DH pipes and connected valves. The work resulted in a method and a user guide that can be used by network owners to assess parts of a DH network. A method that by a shorter shutdown, in the range of a few hours, can be used to capture the temperature decline in a DH pipe. Results indicate that drainage valves, which are directly connected to the underlying DH network, were suitable measurement points where the temperature-decline phase of the DH pipe could be captured. The method allowed a prediction of the thermal conductivity of a buried DH pipe in operation with 2% deviation from the reference value.
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| 14624. |
- Lidén, Peter, 1982
(författare)
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Development of a non-destructive testing method for thermal assessment of a district heating network
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the development of a non-destructive testing (NDT)method for thermal assessment of pre-insulated district heating (DH) pipes with high accuracy, in which the development process from literature review to its present stage is presented and discussed. Pre-insulated DH pipes have been in use for more than 40 years. The thermal performance of these pipes decreases over time as a result of thermal aging, which leads to higher heat losses. Present methods are unable to assess these heat losses with a high accuracy. The main idea with the method is to perform a temporary shutdown of a selected part of a network for less than two hours, which enables temperature measurements during the cooling phase. Measured temperatures are then used for analyzing the thermal performance of the pipes. The accessibility for temperature measurements on the pipes depend on the conditions in field. Thus, the methodology for the development of this cooling method involves different measuring points during different conditions in field. This thesis covers three conducted field tests during maintenance, which allowed for temperature measurements on the service pipe, the casing pipe, and connected valves. Furthermore, the method utilizes the copper wire, which is already embedded in the polyurethane insulation for detection of water leakage, as a sensor for measuring the mean temperature at copper wire position along the pipe under assessment. This thesis presents the possibilities and uncertainties with the cooling method at its present stage. The method shows good potential to meet the aim as an NDT method with high accuracy, and to be a future tool for the network owners.
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| 14625. |
- Lidén, Peter, 1964
(författare)
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Fault Simulation and Physical Fault Injection Applied to MOS Transistor Networks
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Detailed information on a system's behavior in the presence of faults is often vital. It may be used to grade or construct tests for the efficient detection of faults or to increase confidence in high-reliable systems. Fault injection, which is the process of artificially inserting faults into circuits, is in many cases the only feasible technique to obtain knowledge of the circuit in the presence of faults. When realistic faults are introduced in switch-level descriptions of CMOS networks, steady-state undetermined node values (X) frequently occur in the networks, which reduces confidence in the simulation results. Two new algorithms to reduce the number of nodes assigned the undermined logic state are presented in this thesis. It is verified that the proposed algorithms increase the fault modeling capability of a switch-level simulator. A switch-level fault simulation algorithm for the simulation of voltage transients in CMOS networks is also presented in the thesis. Electrical-level fault simulation can provide detailed information of the behavior of vital parts of a complex circuit in the presence of realistic faults. The thesis investigates the effects of node stuck-at and gate stuck-at faults in CMOS checkers. Furthermore, an investigation of a variety of transistor terminal short and open faults injected into CMOS checkers shows that the fault models can be reduced to four sets, for which the fault models included in each set show identical behavior. It is possible to inject transients into a circuit by irradiating the circuit with heavy ions emitted from a Californium-252 source. The thesis presents a new experimental method based on heavy-ion radiation to determine to what extent particle-induced transients in combinational parts of a circuit propagate into memory elements. The thesis also presents a comparison between a Cf-252 fault injection experiment with the MC6809E microprocessor and an error injection experiment using a high level software simulation model of the processor.
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| 14626. |
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| 14627. |
- Lidman, Jacob, 1985
(författare)
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Compiler optimizations in the presence of uncertain semantics
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As transistors sizes shrink and architects put more and more cores on chip, computer systems become more susceptible to outside interference. This interference can cause faults that manifest as unexpected and uncontrolled state transitions, possibly leading to costly or harmful consequences. Coping with faults requires introducing some form of redundancy. On the other hand, redundancy is often removed in improving the performance of an application. Compiler optimizations are used to exploit computational capabilities to their full extent. Previously, compiler optimizations often targeted performance, but recently optimizations are being introduced to trade performance for reliability. This thesis presents optimizations that try to improve both performance and reliability, prioritizing one of the other based on need.First, I introduce a framework for semi-automatically adding software fault-tolerance to an application. Using this framework I show that together with an appropriate voting mechanism, redundant executions can increase reliability while keeping performance overhead as low as 18%.Second, I present an algorithm based on geometric programming for minimizing the number of redundant executions in an application while maintaining a reliability threshold. Often a static number of redundant executions per statement is employed throughout the whole application. To minimize performance overhead I exploit that some operations are naturally more reliable, and more costly, than others.Third, I introduce a voting system that adds redundant executions as needed, up to a number decided by our optimization method. Using this scheme, I show improvement in performance and reliability over a scheme where a fixed number of redundant executions is used.Finally, I present an analysis based on abstract interpretation to determine the impact of a finite number of faults. An analysis based on abstract interpretation guarantees logical soundness by construction, and we evaluate its applicability on kernels and corner cases. This analysis could be used to decide where redundant executions are not needed.
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| 14628. |
- Lidman, Jacob, 1985
(författare)
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Program Analysis for Performance and Reliability
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased demand for computing power has lead designers to put an ever increasing number of cores on processor dies. This advance has been made possible through miniaturization and effectivization of the underlying semi-conductor technology. As a by-product, however, the resulting computer systems are more vulnerable to interference. This has made reliability a first-order concern and is treated both in software and hardware through some form of redundancy. Redundancy is however detrimental to performance leading to more resources spent re-computing. Efficient use of hardware requires software that can take advantage of the computer system. Compilers are responsible for translating high-level source-code into efficient machine-code. Transformations in the compiler can improve performance and/or reliability of the software. Prior to applying such transformation the compiler needs to verify the legality and benefit of this optimization through program analysis.This thesis develops program analyses for reasoning about performance and reliability properties and show how these synthesize information that could not be made available from previous approaches.First, I present an analysis based on abstract interpretation to determine the impactof a finite number of faults. An analysis based on abstract interpretation guaranteeslogical soundness by construction, and I evaluate its applicability by deducing the fault susceptibility of kernels and how a program optimization affect reliability.Second, I present the fuzzy program analysis framework and show that it admits a sound approximation in the abstract interpretation framework. Fuzzy sets allow non-binary membership and, in extension, a qualitative static program analysis that can perform common-case analyses. Furthermore this frameworkadmits a dynamic analysis based on fuzzy control theory that refines the result from the static analysis online.Using the framework I show improvement on a code motion algorithm and several classical program analyses that target performance properties.Third, I present an analysis based on geometric programming for deciding the minimalnumber of redundant executions of an program statement while maintaining a reliabilitythreshold. Often a fixed number of redundant executions per statement is employedthroughout the whole program. To minimize performance overhead I exploit thatsome statements are naturally more reliable, and more costly, than others. Using the analysis I show improvement in reliability and performance overhead due to use of a redundancy level that is tailored for each statement individually.
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| 14629. |
- Lie, Anders, 1959, et al.
(författare)
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Automated vehicles: How do they relate to vision zero
- 2022
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Ingår i: The Vision Zero Handbook: Theory, Technology and Management for a Zero Casualty Policy. - Cham : Springer International Publishing. ; , s. 1057-1071
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish Transport Administration (STA) work to reduce the number of suicides in the transport system. Fatalities, i.e., on roads, railways, and bridges, originate from either accidents or suicides, natural death excluded. Knowing the correct manner of death is needed to work with optimal prevention strategies. The aims are to separate fatalities due to suicides, follow the development, and implement measures for suicide prevention. Methods are developed for suicide classification and criteria for the selection in which suicides were suspected. Fatalities in level one and two of five were classified as suicides. Data from the STA's databases are used and so are data from the psychosocial investigations done by a trained investigator in the topic and with clinical experience from counselling at hospitals. 2129 persons died on the roads in Sweden, 10% (206 persons) were classified as suicides. 336 persons died after being hit by trains, 85% (284 persons) were suicides. 130 persons died by jumping from bridges. The number of suicides increases with population density. Suicide in the transport system is a major problem; firstly personal tragedies, it is also a work environment problem for truck and train drivers and for the emergency staff. It generates delays and costs for passenger and cargo transport. By analyzing the results of countermeasures in the form of obstructive barriers, the physical environment can be improved and high-risk areas can be accentuated. Restricting access to the means of suicide is important in suicide prevention. Strategies for the STA include suicide prevention in the design of new roads, railways, and bridges, as well as by identifying and reducing existing high-risk locations. Sharing the results with other authorities and organizations and cooperation within suicide prevention missions are vital for the enhancement of the overall suicide prevention work in society.
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| 14630. |
- Lie, Anders, 1959, et al.
(författare)
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ISO 39001 road traffic safety management system, performance recording, and reporting
- 2022
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Ingår i: The Vision Zero Handbook: Theory, Technology and Management for a Zero Casualty Policy. - Cham : Springer International Publishing. ; , s. 675-686
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Traffic safety has shifted from being a solely individual issue to also include responsibilities from those organizations that influences the use and quality of the road transport system. This chapter explores the background of this and presents how ISO 39001 has been introduced as a tool to manage traffic safety in organisations. Further it is setting organizational road traffic safety into context of the 3rd Global Ministerial Conference on Road Safety, the Stockholm declaration and the decision of the United Nations general Assembly. The chapter also discusses how a value chain analysis can help organisations in understanding and tackling their road safety footprint and part of their sustainability reporting.
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