| 1. |
- Andersson, Jan, 1973-
(författare)
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Laborativt arbete i fysikundervisningen : Något som behöver diskuteras!
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BaksidestextI gymnasieskolans kursplaner för ämnet fysik framhålls det undersökande arbetssättet genom att betona att eleverna ska ges förutsättningar att utveckla förmågan att söka svar på frågor, planera, genomföra, tolka och redovisa experiment. Eleverna ska dessutom ges möjligheter att använda sina kunskaper i fysik för att kommunicera, argumentera och presentera slutsatser. Utgångspunkten i den här avhandlingen är att laborationsmomentet skapar en speciell diskurs där eleverna blir aktörer och läraren iträder rollen som observatör. I en sådan miljö skapas förutsättningar för att eleverna på ett naturligt sätt får möjlighet att prata och diskutera fysik, utifrån sina egna förutsättningar. Syftet med denna avhandling är att genom praktikbaserade studier tydliggöra hur fysiklaborationens utformning påverkar elevernas kommunikation och vidare hur eleverna använder språket vid laborationstillfället för att skapa förståelse. Detta bidrar till debatten om fysiklaborationens effektivitet, sett både ur ett undervisnings- och inlärningsperspektiv. Resultaten visar att olika laborationsformer är uppbyggda av liknande aktiviteter, men varierar i tid som ägnas åt de olika aktiviteterna. Aktiviteterna i sin tur skapar samtal av olika karaktär. Olika samtalsformer används för skilda syften. Ett analytiskt ramverk har skapats för att ingående kunna studera hur och vad eleverna talar om både på en lingvistisk och kognitiv nivå.
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| 2. |
- 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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| 3. |
- Coello Midence Balthasar, Zairis Aida
(författare)
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Insufficient water supply in an urban area - case study : Tegucigalpa, Honduras
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tegucigalpa, the capital of Honduras, has experienced an unsatisfied water demand during the last three decades. The state owned water utility in charge of the water supply of the country, SANAA, has faced this deficit by providing an intermittent water supply. The intermittent water supply has increased the gap between the rich and the poor, who cannot afford water storage facilities. Theories explain water scarcity either by low precipitation or by lack of investment in water structures. This thesis investigates the applicability of both explanations by quantifying the annual precipitation in the sub catchments with water supply potential for Tegucigalpa, and identifying the problems which caused the lack of investment into the water infrastructure. The analysis concluded that even if the annual precipitation is abundant, it is not evenly distributed in time and in space. Furthermore, it is argued that the financial limitations which hindered the lack of investment in water structures originated in the low tariffs imposed, and to the practices of the patronage system.
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| 4. |
- Gustafsson, Andreas
(författare)
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On the Simulation of Progressive Deformation in Nuclear Piping
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the performance of different constitutive models in ratchet simulation is investigated. Ratcheting is accumulated plastic strains which may occur when a structure is subjected to a constant load in combination with cyclic loading. In the assessment of nuclear class 1 pressure retaining component ratcheting is one of the three failure modes that are addressed and may limit the design life of nuclear pressurized components and piping systems.A steel structure subjected to a constant load in combination with cyclic loading into the plastic region undergoes a change of the material characteristics in several aspects. These cyclic material characteristics are complex and may vary for different load situations, load levels, temperatures and materials. In addition to this, the presence of a mean stress may also affect the material cyclic characteristics.In previous numerical investigations on ratcheting there has not been a sufficiently robust case of simulation. However, in most of these investigations, the simulation response is compared with ratcheting experiments which either are conducted under load levels which are not common for a nuclear pressurized component, the experimental specimen is not comparable with a pressurized component or only a few experimental tests have been conducted. Hence, it has not been settled which material characteristics need to be considered to accurately simulate ratcheting in a pressurized piping component under load levels common in a nuclear power plants. As a result of this, it is not obvious which types of constitutive material models is needed and how the model parameters should be calibrated in order to simulate ratcheting in a nuclear component accurately.As part of this thesis an extensive experimental program has been conducted on pressurized tube specimens. In total 30 test specimens made of two different materials, 316L and P235, have been manufactured and tested. In order to determine material properties, monotonic tensile load and internal pressure experiments have been performed. The remaining test specimens have been used for ratcheting experiments.The experimental results show ratcheting in the hoop direction when the tube is subjected to certain combinations of internal pressure and cyclic axial strains. The higher the pressure is and the larger the strain ranges are, the higher the ratcheting response becomes. In addition to this, also the cyclic hardening and softening behavior in the tubes axial direction and the direction of the incremental plastic strain tensor is investigated. The results show that the material cyclic hardening or softening behavior and direction of the plastic strain vector varies strongly depending on the level of primary and secondary loads.Measured ratcheting strains are compared to numerical simulations using different constitutive models. In this thesis the interrelated models of Prager, Armstrong-Frederick and Chaboche are investigated. In addition to these, the Besseling model is investigated. Among the constitutive models investigated, the Besseling multi-linear model shows by far the best agreement with the ratcheting experiments. The more advanced models are able to capture the material ratchetingbehavior, but overestimate the hoop strain in the tube tests.Investigation results also indicate that significant cyclic hardening material behavior influence the direction of the plastic stain vector and, hence, affect the accuracy of predicted results when disregarded. This effect is most apparent for the experiments subjected to high pressure and high deformation controlled loads. In the tests which experience significant cyclic hardening, the direction of the plastic strain vector starts to deviate after roughly 20 loading cycles.Simulation of ratcheting should be done with an as simple constitutive model as possible, while still capturing the essential response. Important reasons are that simple models are easier to understand and work with, and that fewer tests are needed for determining model parameters. Based on this the Besseling constitutive model is recommended for simulation of pressure equipment subjected to cyclic plastic deformation. However, if shake-down does not occur at relative early stage, effects related to cyclic softening or hardening may need to be taken into consideration.
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| 5. |
- Gustavsson, Andreas, 1982-
(författare)
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Static Timing Analysis of Parallel Systems Using Abstract Execution
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Power Wall has stopped the past trend of increasing processor throughput by increasing the clock frequency and the instruction level parallelism.Therefore, the current trend in computer hardware design is to expose explicit parallelism to the software level.This is most often done using multiple processing cores situated on a single processor chip.The cores usually share some resources on the chip, such as some level of cache memory (which means that they also share the interconnect, e.g. a bus, to that memory and also all higher levels of memory), and to fully exploit this type of parallel processor chip, programs running on it will have to be concurrent.Since multi-core processors are the new standard, even embedded real-time systems will (and some already do) incorporate this kind of processor and concurrent code.A real-time system is any system whose correctness is dependent both on its functional and temporal output. For some real-time systems, a failure to meet the temporal requirements can have catastrophic consequences. Therefore, it is of utmost importance that methods to analyze and derive safe estimations on the timing properties of parallel computer systems are developed.This thesis presents an analysis that derives safe (lower and upper) bounds on the execution time of a given parallel system.The interface to the analysis is a small concurrent programming language, based on communicating and synchronizing threads, that is formally (syntactically and semantically) defined in the thesis.The analysis is based on abstract execution, which is itself based on abstract interpretation techniques that have been commonly used within the field of timing analysis of single-core computer systems, to derive safe timing bounds in an efficient (although, over-approximative) way.Basically, abstract execution simulates the execution of several real executions of the analyzed program in one go.The thesis also proves the soundness of the presented analysis (i.e. that the estimated timing bounds are indeed safe) and includes some examples, each showing different features or characteristics of the analysis.
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| 6. |
- Palmqvist, Jan
(författare)
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On Integrity Monitoring of Integrated Navigation Systems
- 1997
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In civil aviation a new philosophy for flight safety and traffic management is under development. The goal is to enable an expected increase in air traffic density by reducing aircraft separation. The accuracy of the position estimate determined by the navigation system in each aircraft determines this separation. A necessary component to achieve this goal is a monitor that continuously supervise the navigation solution integrity, i.e., the trust that can be placed on the estimated position. Integrity monitoring is important in military applications as well.In this thesis the problem of monitoring the integrity of navigation systems is studied. Most of the proposed methods for integrity monitoring of navigation systems are formulated in a very problem oriented manner. The problem has close connections to fault detection and isolation and many connections with general methods within this area have been found and are pointed out. The thesis contains surveys on both navigation and fault detection and isolation.When using multiple navigation sensors, they could be integrated to yield better performance as well as integrity. A multi-level monitoring scheme to be used in an integrated navigation system is proposed. The scheme uses different integrity monitoring approaches at different levels to achieve improved total performance.Furthermore, one method, the Generalized Likelihood Ratio GLR test, is evaluated for integrity monitoring of an integrated inertial/satellite navigation system (INS-GNSS). In addition to prove good detection performance of the GLR test special attention is given to two problems related to the navigation application, tuning of the GLR test and fault isolation. Good fault isolation together with the GLR test statistics form the basis for compensation of the position estimate after a detected fault.The proposed methods for tuning, detection and isolation are evaluated on a simulated model of the North pointing channel of an integrated inertial-satellite navigation system.
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