| 1. |
- Abd-Elrady, Emad, 1970-
(författare)
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Nonlinear Approaches to Periodic Signal Modeling
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Periodic signal modeling plays an important role in different fields. The unifying theme of this thesis is using nonlinear techniques to model periodic signals. The suggested techniques utilize the user pre-knowledge about the signal waveform. This gives these techniques an advantage as compared to others that do not consider such priors. The technique of Part I relies on the fact that a sine wave that is passed through a static nonlinear function produces a harmonic spectrum of overtones. Consequently, the estimated signal model can be parameterized as a known periodic function (with unknown frequency) in cascade with an unknown static nonlinearity. The unknown frequency and the parameters of the static nonlinearity are estimated simultaneously using the recursive prediction error method (RPEM). A treatment of the local convergence properties of the RPEM is provided. Also, an adaptive grid point algorithm is introduced to estimate the unknown frequency and the parameters of the static nonlinearity in a number of adaptively estimated grid points. This gives the RPEM more freedom to select the grid points and hence reduces modeling errors. Limit cycle oscillations problem are encountered in many applications. Therefore, mathematical modeling of limit cycles becomes an essential topic that helps to better understand and/or to avoid limit cycle oscillations in different fields. In Part II, a second-order nonlinear ODE is used to model the periodic signal as a limit cycle oscillation. The right hand side of the ODE model is parameterized using a polynomial function in the states, and then discretized to allow for the implementation of different identification algorithms. Hence, it is possible to obtain highly accurate models by only estimating a few parameters. In Part III, different user aspects for the two nonlinear approaches of the thesis are discussed. Finally, topics for future research are presented.
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| 2. |
- Abrahamsson, Richard, 1976-
(författare)
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Estimation Problems in Array Signal Processing, System Identification, and Radar Imagery
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with parameter estimation, signal processing, and applications. In the first part, imaging using radar is considered. More specifically, two methods are presented for estimation and removal of ground-surface reflections in ground penetrating radar which otherwise hinder reliable detection of shallowly buried landmines. Further, a study of two autofocus methods for synthetic aperture radar is presented. In particular, we study their behavior in scenarios where the phase errors leading to cross-range defocusing are of a spatially variant kind. In the subsequent part, array signal processing and optimal beamforming is regarded. In particular, the phenomenon of signal cancellation in adaptive beamformers due to array perturbations, signal correlated interferences and limited data for covariance matrix estimation is considered. For the general signal cancellation problem, a class of improved adaptive beamformers is suggested based on ridge-regression. Another set of methods is suggested to mitigate signal cancellation due to correlated signal and interferences based on a novel way of finding a characterization of the interference subspace from observed array data. Further, a new minimum variance beamformer is presented for high resolution non-parametric spatial spectrum estimation in cases where the impinging signals are correlated. Lastly, a multitude of enhanced covariance matrix estimators from the statistical literature are studied as an alternative to other robust adaptive beamforming methods. The methods are also applied to space-time adaptive processing where limited data for covariance matrix estimation is a common problem. In the third and final part the estimation of the parameters of a general bilinear problem is considered. The bilinear model is motivated by the application of identifying submarines from their electromagnetic signature and by the identification of a Hamerstein-Wiener model of a non-linear dynamic system. An efficient approximate maximum-likelihood method with closed form solution is suggested for estimating the bilinear model parameters.
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| 3. |
- Airey, John, 1963-
(författare)
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Science, Language, and Literacy : Case Studies of Learning in Swedish University Physics
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents an investigation of undergraduate student learning with respect to physics lectures attended in English and Swedish. The work studies three connected areas: student learning patterns, bilingual scientific literacy and disciplinary discourse.Twenty-two physics students at two Swedish universities attended lectures in both English and Swedish as part of their regular undergraduate programme. These lectures were video-taped and used to contextualize in-depth, semi-structured interviews with students.When taught in English the students asked and answered fewer questions and reported be-ing less able to simultaneously follow the lecture and take notes. Students adapted to being taught in English by; asking questions after the lecture, no longer taking notes in class, read-ing sections of work before class or—in the worst case—by using the lecture for mechanical note taking.Analysis of student oral descriptions of the lecture content in both languages identified a small number of students who found it almost impossible to speak about disciplinary concepts in English. These students were first-years who had not been taught in English before. How-ever, the findings suggest that, above a certain threshold level of disciplinary language com-petence, it does not appear to matter which language students are taught in.Finally, the thesis makes a theoretical contribution to educational research. The initial lan-guage perspective is broadened to include a wide range of semiotic resources that are used in the teaching of undergraduate physics. Student learning is then characterized in terms of becoming fluent in a disciplinary discourse. It is posited that in order to achieve an appropri-ate, holistic experience of any given disciplinary concept, students will need to become fluent in a critical constellation of disciplinary semiotic resources.
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| 4. |
- Akram, Adeel
(författare)
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Towards Realistic Hyperon Reconstruction in PANDA : From Tracking with Machine Learning to Interactions with Residual Gas
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The PANDA (anti-Proton ANnihilation at DArmstadt) experiment at FAIR (Facility for Anti-proton and Ion Research) aims to study strong interactions in the confinement domain. In PANDA, a continuous beam of anti-protons will impinge on a fixed hydrogen target inside the High Energy Storage Ring (HESR), a feature intended to attain high interaction rates for various physics studies e.g. hyperon production. This thesis addresses the challenges of running PANDA under realistic conditions. The focus is two-fold: developing deep learning methods to reconstruct particle trajectories and reconstruct hyperons using realistic target profiles. Two approaches are used: (i) standard deep learning model such as dense network, and (ii) geometric deep leaning model such as interaction graph neural networks. The deep learning methods have given promising results, especially when it comes to (i) reconstruction of low-momentum particles that frequently occur in hadron physics experiments and (ii) reconstruction of tracks originating far from the interaction point. Both points are critical in many hyperon studies. However, further studies are needed to mitigate e.g. high clone rate. For the realistic target profiles, these pioneering simulations address the effect of residual gas on hyperon reconstruction. The results have shown that the signal-to-background ratio becomes worse by about a factor of 2 compared to the ideal target, however, the background level is still sufficiently low for these studies to be feasible. Further improvements can be made on the target side to achieve a better vacuum in the beam pipe and on the analysis side to improve the event selection. Finally, solutions are suggested to improve results, especially for the geometric deep learning method in handling low-momentum particles contributing to the high clone rate. In addition, a better way to build ground truth can improve the performance of our approach.
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| 5. |
- Alm Kübler, Kerstin
(författare)
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Holocene Environmental Change of Southern Öland, Sweden
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes Holocene environmental change in Ottenby, southern Öland,Sweden. Analyses of pollen sequences collected distally in the Littorina ridge and in fentroughs between lower laying beach ridges show the vegetation history during twoperiods, the first around 8000 BP and the second from 0/500 AD to about present time.Ages were obtained by radiocarbon datings.The sediments reveal the approaching Littorina transgression. A pond was formedbehind anearlier ridge, and the Littorina ridge was deposited above the organic sequence in thepond. At this time(8000 BP) the vegetation was dominated by deciduous forests of an open character.The sequences from the series of fens formed within the system of beach ridgesreveal the natureof late Holocene environmental change. During the centuries before the Viking Agecattle-breeding was important and open grasslands created by grazing prevailed.Utilization of landscape resources increased as the population increased, and a Callunaheath developed around 800 AD. This shows that under special conditions a heath candevelop in an area with low precipitation if the human impact is heavy enough.In 1546 King Gustav Vasa declared Ottenby a Royal Estate and evicted thepopulation from Ottenby village. The Ottenby area was then governed as one coherentunit. This relieved pressure on the landscape and the modern landscape came into being.The pollen sequences corresponding to the time c. 1500 AD and onwards are inaccordance with the information in the written sources.This study also shows that Fagus sylvatica most probably grew on southern Ölandduring the Middle Ages.
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| 6. |
- Andrejev, Andrej, 1980-
(författare)
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Semantic Web Queries over Scientific Data
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semantic Web and Linked Open Data provide a potential platform for interoperability of scientific data, offering a flexible model for providing machine-readable and queryable metadata. However, RDF and SPARQL gained limited adoption within the scientific community, mainly due to the lack of support for managing massive numeric data, along with certain other important features – such as extensibility with user-defined functions, query modularity, and integration with existing environments and workflows.We present the design, implementation and evaluation of Scientific SPARQL – a language for querying data and metadata combined, represented using the RDF graph model extended with numeric multidimensional arrays as node values – RDF with Arrays. The techniques used to store RDF with Arrays in a scalable way and process Scientific SPARQL queries and updates are implemented in our prototype software – Scientific SPARQL Database Manager, SSDM, and its integrations with data storage systems and computational frameworks. This includes scalable storage solutions for numeric multidimensional arrays and an efficient implementation of array operations. The arrays can be physically stored in a variety of external storage systems, including files, relational databases, and specialized array data stores, using our Array Storage Extensibility Interface. Whenever possible SSDM accumulates array operations and accesses array contents in a lazy fashion.In scientific applications numeric computations are often used for filtering or post-processing the retrieved data, which can be expressed in a functional way. Scientific SPARQL allows expressing common query sub-tasks with functions defined as parameterized queries. This becomes especially useful along with functional language abstractions such as lexical closures and second-order functions, e.g. array mappers.Existing computational libraries can be interfaced and invoked from Scientific SPARQL queries as foreign functions. Cost estimates and alternative evaluation directions may be specified, aiding the construction of better execution plans. Costly array processing, e.g. filtering and aggregation, is thus preformed on the server, saving the amount of communication. Furthermore, common supported operations are delegated to the array storage back-ends, according to their capabilities. Both expressivity and performance of Scientific SPARQL are evaluated on a real-world example, and further performance tests are run using our mini-benchmark for array queries.
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| 7. |
- Asimakopoulou, Eleni Myrto
(författare)
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Search for charged Higgs bosons with tau-lepton signatures at the ATLAS experiment of the Large Hadron Collider and development of novel semiconductor particle detectors
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Experimental High Energy Physics (HEP) studies are discussed in the context of exotic particle searches and data analysis techniques and the development and production of suitable detectors. The main covered topics span the aforementioned areas and are primarily related to the ATLAS experiment at the Large Hadron Collider (LHC).The Higgs boson discovery by the ATLAS and CMS experiments in 2012, solidified the Standard Model (SM), but at the same type provided a suitable probe for searches of new physics, beyond the SM (BSM). This thesis covers a study for a new particle, the charged Higgs boson, which is predicted by several BSM theories and its discovery would be a clear sign for new physics. The study was focused on the predicted τν final state using a 36.1fb−1 dataset of pp collisions collected at √s = 13TeV with the ATLAS detector. No discovery was made, but new limits on relevant parameters were set.Studies that involve hadronically decaying τ leptons, such as the aforementioned charged Higgs boson search, are affected by background processes where quark- and gluon-initiated jets as misidentified as τs. A universal method for determining the impact of this background, and the associated systematic uncertainties, is being developed in ATLAS and is introduced in this thesis.The Large Hadron Collider (LHC) is presently preparing for the High-Luminosity upgrade that is designed to meet the current physics goals. The upgrade will result in more demanding conditions for the LHC experiments, in terms of higher particle fluences and larger collected data volumes, necessitating changes in their detector systems. The ATLAS inner tracker upgrade is discussed, focusing on the workflow and the quality assurance and quality control procedures necessary for the production of the strip modules that will be part of its new end-cap system in collaboration with industry.Neutron detection is essential for a wide range of neutron science applications and research. The evaluation of a novel boron-coated semiconductor with respect to its suitability of neutron detection is discussed.
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| 8. |
- Avendaño Soto, Esteban Damián, 1975-
(författare)
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Electrochromism in Nickel-based Oxides : Coloration Mechanisms and Optimization of Sputter-deposited Thin Films
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic properties of sputter-deposited nickel-based oxide films have been studied with a two-fold goal. From a practical point of view, the optical switching performance has been improved by optimizing the deposition conditions and film stoichiometry with respect to oxygen and hydrogen, and further by adding Mg, Al, Si, Zr, Nb or Ta to the films. From a theoretical point of view, details of the coloration mechanism have been studied by means of electrochemical intercalation (CV, GITT), optical measurements (UV, VIS, NIR and MIR), RBS, XRD, XPS and EXAFS. Optimization of deposition conditions has been illustrated by the example of films made by sputtering of a non-magnetic Ni(93)V(7) % wt. target in an atmosphere of Ar/O2/H2. The optimized films exhibit transmittance modulation between 20% and 75 % at 18 mC/cm2 charge intercalation. The remaining problem with nickel oxide and nickel vanadium oxide films is their residual yellow-brown color tint in the bleached state, which disappears as the short-wavelength transmittance increases upon addition of Mg, Al, Zr or Ta. Optimization of deposition conditions by co-sputtering from two targets and the film composition for mixed oxide films has been illustrated by the example of nickel aluminium oxide. The mechanisms of coloration upon electrochemical charge insertion and ozone exposure have been investigated. In the beginning of the electrochemical cycling, first, a reconstruction and crystallization is observed with the outer most part of the grain surface being transformed from oxygen rich nickel oxide into nickel oxy-hydroxide and hydroxide by transfer of H+ and OH- groups. After the charge capacity has been stabilized, only a transfer of H+ occurs with two reversible reactions involved: the first one from Ni(OH)2 to NiOOH and the second one from NiO and Ni(OH)2 to Ni2O3. Ozone coloration is described by a similar reaction scheme. The ozone molecule is split on the surface and dehydrogenates Ni(OH)2 into NiOOH. Further dehydrogenation produces Ni2O3 as in the electrochemical coloration.
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| 9. |
- B. Forsberg, Petter, 1984-
(författare)
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Collaboration in practice : A multiple case study on collaboration between small enterprises and university researchers
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- University-industry collaborations (UICs) have been hailed as key for Sweden's innovativeness and economic growth. Similarly, building research and innovation policies for the promotion of collaboration between universities and industry have become a cornerstone for many other European countries.In academic literature there has been an emphasis on efficiency, facilitation, effects and values obtained in UICs. They have been widely studied, both in terms of the reasons why they are formed, their structure and the effects they create, but not much in terms of how they work on a daily basis. There is less attention in the literature to analyse or problematise how UIC work is carried out when a connection has already been formed or is repeatedly enacted. Additionally, there is also a lack of studies looking at small firms UICs. Through identifying a lack of perspective in the UIC literature this thesis builds on the recent developments in practice theory in addressing some of the gaps found. It thus analyses these collaborations from a perspective not present in the literature in pursuit of how UICs are carried out.Through four embedded case studies between small enterprises and university researchers the thesis questions some of the assumptions made in the UIC literature and policy documents. First of all, through the practice theory lens, the thesis shows how the creation of a node/linchpin, a boundary object or a broker, between university and industry is instrumental in enabling collaboration work to take place. Secondly, being able to work together successfully does not equal outcomes sought after by policy organisations. Nevertheless, a general conclusion is that there were valuable outcomes for both the companies and the researchers, confirming previous research on UICs. But, these benefits were often difficult to put into clear numbers or metrics and appeared only after a very long time.The thesis argues that policy (and associated organisations) should promote the connection between a research site/practices and a company site/practices rather than pushing for a joint practice. In such a way UICs can be valuable for both researchers and companies.
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| 10. |
- Backeman, Peter
(författare)
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Quantifiers and Theories : A Lazy Approach
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we study Automated Theorem Proving (ATP) as well as Satisfiability Modulo Theories (SMT) and present lazy strategies for improving reasoning within these areas. A lazy strategy works by simplifying a problem, and gradually refines the abstraction only when necessary. Often, a solution can be found without solving the full problem, saving valuable resources. We formulate our contributions within two key challenges in ATP and SMT: theory and quantifier reasoning.Many problems need first-order reasoning modulo a theory, i.e., reasoning where symbols in formulas are interpreted according to some background theory. In software verification, which often involves conditions over machine arithmetic, bit-vectors as well as floating-point numbers play an important role. Finding methods for how to reason with these theories in an efficient manner is therefore an important task. In this thesis we present a lazy method for handling bit-vector constraints as well as bit-vector interpolation, which improves performance and produces simpler interpolants. Moreover, a modular approximation framework is described, which allows for high-level description of lazy strategies applicable to a multitude of theories. Such a strategy is combined with a back-end, creating an approximating SMT solver. We use floating-point arithmetic as an illustrating use case, showing how the lazy strategy can improve the overall efficiency.The quantifier is a language construct which allows for making statements about one or all objects of some universe. However, with great power comes great cost - reasoning with quantifiers is very hard. Many decision problems involving quantifiers are not decidable, e.g., validity of first-order logic. Intricate strategies are needed to handle formulas with quantifiers, especially in combination with theory reasoning. We present a new restricted form of unification, by lazy expansion of the domain of substitution, as well as efficient procedures to solve it. This is incorporated into a complete and sound sequent calculus for the combination of the theory of equality and quantifiers.
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| 11. |
- Bahne, Adrian, 1983-
(författare)
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Multichannel Audio Signal Processing : Room Correction and Sound Perception
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns and combines multichannel sound reproduction, digital room correction, audio signal processing, and human sound perception. It investigates perceived sound quality and new methods to improve timbral and spatial fidelity of loudspeaker-based multichannel sound reproduction in reverberant environments.In the first part of the thesis, the perceived sound quality of regular optimized stereo sound systems is investigated by means of a listening experiment based on subjective comparison judgments. It is shown that average listeners' preferences are in favor of the optimized version of the systems.The second part of the thesis takes on with three novel equalization schemes, which are based on insights from human perception. First, a general filter design framework based on multiple-input multiple-output (MIMO) feedforward control is introduced. The main objective is to provide means to jointly equalize a single loudspeaker by utilizing all available loudspeakers in a multichannel sound system.Well-known drawbacks of standard multichannel sound reproduction are (a) that symmetrical system setups are generally assumed, and (b) that high fidelity sound reproduction is limited to a tight region in space, the so-called sweet spot. In order to ease drawback (a), the MIMO similarity framework incorporating a pairwise channel similarity requirement is introduced, which is based on a mathematical description of the perception of virtual sound sources created in multichannel sound reproduction. The aim is to obtain similar (symmetrical) room transfer functions in the listening area of a given listening environment. In order to ease drawbacks (a) and (b), the personal audio framework is introduced. It aims at producing filters which improve spatial and timbral sound reproduction in multiple listening positions simultaneously.Evaluations based on simulations and measurements acquired in representative listening environments strongly indicate that the proposed methods successfully treat several causes which are known to impair sound quality and thus yield improved sound reproduction.
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| 12. |
- Bastani, Mehrdad
(författare)
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EnviroMT : A new controlled source/radio magnetotoelluric system
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the frame of an EU project, a new electromagnetic prospecting instrument was designed and constructed for environmental and engineering applications. The instrument works in the frequency domain in the band 1-250 kHz, whereby the collected data can be used to study the variation of ground resistivity from the surface to a maximum depth of few hundred meters. The system is operational in two modes, the Radio Magnetotelluric (RMT) and the Controlled Source Tensor Magnetotelluric (CSTMT). The RMT method makes use of the signals generated by powerful distant radio transmitters operating in the frequency range 14-250 kHz. The CSTMT technique, with a remotely controllable double magnetic dipole source covering the band 1-100 kHz, is utilized when deeper targets are aimed at or low resistivity terrains are studied. With the aid of user-friendly database software the collected data can be visualized and modeled in1D, directly in the field. In November 1998, the first test survey at the Collendoorn dumpsite in the Netherlands was conducted to map the vertical boundaries and lateral extensions of the pollution plume along four RMT profiles located east of the dumpsite. The results of 1D inversion of the data correlated well with the bore-hole logs, revealing that the estimated resistivities and depths to the top of the pollution plume were realistic. The pollution plume appears to be extending more in the northern part. Another test was carried out north of Uppsala, at Skediga in Sweden, using both RMT and CSTMT techniques, to study the morphology of a clay-sandy aquifer. The depth of the resistive crystalline bedrock as estimated by 1D and 2D inversion of the EnviroMT data is in good agreement with bore-hole data. To the east, towards River Fyris the conductive clay lenses become thicker.
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| 13. |
- Ben Henda, Noomene, 1978-
(författare)
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Infinite-state Stochastic and Parameterized Systems
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major current challenge consists in extending formal methods in order to handle infinite-state systems. Infiniteness stems from the fact that the system operates on unbounded data structure such as stacks, queues, clocks, integers; as well as parameterization. Systems with unbounded data structure are natural models for reasoning about communication protocols, concurrent programs, real-time systems, etc. While parameterized systems are more suitable if the system consists of an arbitrary number of identical processes which is the case for cache coherence protocols, distributed algorithms and so forth. In this thesis, we consider model checking problems for certain fundamental classes of probabilistic infinite-state systems, as well as the verification of safety properties in parameterized systems. First, we consider probabilistic systems with unbounded data structures. In particular, we study probabilistic extensions of Lossy Channel Systems (PLCS), Vector addition Systems with States (PVASS) and Noisy Turing Machine (PNTM). We show how we can describe the semantics of such models by infinite-state Markov chains; and then define certain abstract properties, which allow model checking several qualitative and quantitative problems. Then, we consider parameterized systems and provide a method which allows checking safety for several classes that differ in the topologies (linear or tree) and the semantics (atomic or non-atomic). The method is based on deriving an over-approximation which allows the use of a symbolic backward reachability scheme. For each class, the over-approximation we define guarantees monotonicity of the induced approximate transition system with respect to an appropriate order. This property is convenient in the sense that it preserves upward closedness when computing sets of predecessors.
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| 14. |
- Bendjamin, John
(författare)
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Characteristics of electrostatic discharges (ESD) based on current,optical and magnetic radiation fields
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis parameters characterising electrostatic discharges such as the current, the magnetic fieldand the optical radiation are investigated. Optical radiation and magnetic fields generated by ESD aremeasured together with their current signatures in the time domain. Observations show that during theinitial growth, the temporal variation of the optical pulse is similar to that of the current. The peakcurrent is linearly correlated to the peak optical radiation, with a correlation coefficient of about 0.9.The results show that both the optical radiation and the magnetic fields can be used to remote sense thecurrents in electrostatic discharges, which is difficult to measure directly.It is shown that magnetic fields very close to an ESD can be predicted by modelling theradiating discharge current path as a sequence of electric dipoles. Time domain measurements of thecurrent and the magnetic fields generated by human-metal electrostatic discharges produced by an ESDgenerator are used for verification. An ESD current with a peak of 28 A and a risetime of 10 ns cancreate magnetic flux density derivative of about 105 T/s at a distance of 10 mm from the discharge. Current generated by ESD events between metal electrodes and a finitely conducting mediumwere measured simultaneously with their magnetic fields and optical radiation in the time domain.Finitely conducting water was used as the medium. The conductivity of water was changed by addingsalt (NaCl) and an ESD was applied through a point plane electrode configuration with a fixed gapdistance. For a given voltage, the peak current and the peak magnetic field derivative increases withincreasing conductivity. The duration of the ESD current also varies with the conductivity of water. Itincreases with decreasing conductivity initially but reaches a maximum and then starts to decreaseagain. It is shown that an RLC model canpredict the general features of the experimental results. Magnetic fields and optical radiation generated by ESD from metal objects held by peopletogether with their current signatures are also measured in the time domain. The peak measured currentwaveforms are between 25-50 A and the risetime is about 10 ns for a 10 kV discharge, which wassimilar to the current measured from the human body model ESD generator (IEC 801-2). The resultscan be used to estimate the RLC circuit components of the human body model ESD generator.
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| 15. |
- Bengtsson, Johan, 1971-
(författare)
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Clocks, DBMs and States in Timed Systems
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today, computers are used to control various technical systems in our society. In many cases, time plays a crucial role in the operation of computers embedded in such systems. This thesis is about techniques and tools for the analysis of timing behaviours of computer systems. Its main contributions are in the development and implementation of UPPAAL, a tool designed to automate the analysis process of systems modelled as timed automata. As the first contribution, we present a software package for timing constraints represented as Difference Bound Matrices. We describe in details, all data-structures and operations for DBMs needed in state-space exploration of timed automata, as well as techniques for efficient implementation. In particular, we have developed two normalisation algorithms to guarantee termination of reachability analysis for timed automata containing constraints on clock differences, that transform DBMs according to not only maximal constants of clocks as in algorithms published in the literature, but also difference constraints appearing in the automata. The second contribution of this thesis is a collection of low level optimisations on the internal data-structures and algorithms of UPPAAL to minimise memory and time consumption. We present compression techniques to allow the state-space of a system to be efficiently stored and manipulated in main memory. We also study super-trace and hash-compaction methods for timed automata to deal with system-models for which the size of available memory is too small to store the explored state-space. Our experiments show that these techniques have greatly improved the performance of UPPAAL. The third contribution is in partial-order reduction techniques for timed-systems. A major problem in automatic verification is the large number of redundant states and transitions introduced by modelling concurrent events as interleaved transitions. We propose a notion of committed locations for timed automata. Committed locations are annotations that can be used for not only modelling of intermediate states within atomic transitions, but also guiding the model checker to ignore unnecessary interleavings in state-space exploration. The notion of committed locations has been generalised to give a local-time semantics for networks of timed automata, which allows for the application of existing partial order reduction techniques to timed systems.
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| 16. |
- Berg, Marcus
(författare)
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Estimation of hydrophobicity of insulating surfaces by studying sessile water drops
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today, the traditional insulator materials for high voltage powerlines, i.e. glass and porcelain, are gradually being replaced with new materials, most notably silicone rubber. One of the properties that make composite insulators based on silicone rubber attractive is their hydrophobicity, which in the laboratory can be estimated by measuring contact angles of sessile water drops. The hydrophobic surface gives composite insulators better electrical flashover characteristics than hydrophilic insulators when being wet or polluted. However, the hydrophobicity of insulators in service is degraded by many factors such as pollution deposits, surface arcing and ageing, and should therefore be checked regularly. In this thesis, image analysis of water drop patterns on an inclined flat polymeric insulator surface has been performed in order to find a simple mathematical function that indicates the level of hydrophobicity of the insulator surface. The result, given the name of "Average of Normalised Entropies", ANE, seems to correlate well with hydrophobicity as defined by the classification of the Swedish Transmission Research Institute. This function is a composition of three other functions, viz. the standard deviation, the Shannon entropy and the "fraction of small differences". All these are in turn based on the histogram of horizontal nearest-neighbour pixel differences for a given digital greyscale image of a water drop pattern. ANE is fairly independent of illumination intensity (exposure), electronic gain and offset, and also of limited changes in the surface inclination. It is known that the shape of water drops can enhance the local electric field and influence the initiation of electrical discharges on the insulator surface. In this thesis, a particularly simple form of the Young-Laplace equation governing the shape of a sessile drop is derived and augmented with measures that facilitate efficient numerical computation. This mathematical representation will be useful for simulating axisymmetric drops in a vertical electric field as well as for contact angle measurement methods based on fitting theoretical drop shapes to sessile drops in digital images.
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| 17. |
- Berglund, Anders, 1956-
(författare)
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Learning computer systems in a distributed project course : The what, why, how and where
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Senior university students taking an internationally distributed project course in computer systems find themselves in a complex learning situation. To understand how they experience computer systems and act in their learning situation, the what, the why, the how and the where of their learning have been studied from the students’ perspective. The what aspect concerns the students’ understanding of concepts within computer systems: network protocols. The why aspect concerns the students’ objectives to learn computer systems. The how aspect concerns how the students go about learning. The where aspect concerns the students’ experience of their learning environment. These metaphorical entities are then synthesised to form a whole. The emphasis on the students’ experience of their learning motivates a phenomenographic research approach as the core of a study that is extended with elements of activity theory. The methodological framework that is developed from these research approaches enables the researcher to retain focus on learning, and specifically the learning of computer systems, throughout. By applying the framework, the complexity in the learning is unpacked and conclusions are drawn on the students’ learning of computer systems. The results are structural, qualitative, and empirically derived from interview data. They depict the students’ experience of their learning of computer systems in their experienced learning situation and highlight factors that facilitate learning. The results comprise sets of qualitatively different categories that describe how the students relate to their learning in their experienced learning environment. The sets of categories, grouped after the four components (what, why, how and where), are synthesised to describe the whole of the students’ experience of learning computer systems. This study advances the discussion about learning computer systems and demonstrates how theoretically anchored research contributes to teaching and learning in the field. Its multi-faceted, multi-disciplinary character invites further debate, and thus, advances the field.
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| 18. |
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| 19. |
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| 20. |
- Blom, Johan, 1966-
(författare)
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Model-Based Protocol Testing in an Erlang Environment
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Testing is the dominant technique for quality assurance of software systems. It typically consumes considerable resources in development projects, and is often performed in an ad hoc manner. This thesis is concerned with model-based testing, which is an approach to make testing more systematic and more automated. The general idea in model-based testing is to start from a formal model, which captures the intended behavior of the software system to be tested. On the basis of this model, test cases can be generated in a systematic way. Since the model is formal, the generation of test suites can be automated and with adequate tool support one can automatically quantify to which degree they exercise the tested software.Despite the significant improvements on model-based testing in the last 20 years, acceptance by industry has so far been limited. A number of commercially available tools exist, but still most testing in industry relies on manually constructed test cases.This thesis address this problem by presenting a methodology and associated tool support, which is intended to be used for model-based testing of communication protocol implementations in industry. A major goal was to make the developed tool suitable for industrial usage, implying that we had to consider several problems that typically are not addressed by the literature on model-based testing. The thesis presents several technical contributions to the area of model-based testing, including- a new specification language based on the functional programming language Erlang,- a novel technique for specifying coverage criteria for test suite generation, and- a technique for automatically generating test suites.Based on these developments, we have implemented a complete tool chain that generates and executes complete test suites, given a model in our specification language. The thesis also presents a substantial industrial case study, where our technical contributions and the implemented tool chain are evaluated. Findings from the case study include that test suites generated using (model) coverage criteria have at least as good fault-detection capability as equally large random test suites, and that model-based testing could discover faults in previously well-tested software where previous testing had employed a relaxed validation of requirements.
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| 21. |
- Bokan, Petar
(författare)
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Pair production of Higgs bosons in the final state with bottom quarks and τ leptons in the ATLAS experiment : Search results using LHC Run 2 data and prospect studies at the HL-LHC
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After the discovery of the Higgs boson, the ultimate test of the electroweak symmetry breaking and the Standard Model (SM) of particle physics is to establish evidence of Higgs boson self-coupling, which can be achieved by searching for pair production of Higgs bosons. In addition, many theories beyond the SM predict heavy resonances that could decay into pairs of Higgs bosons. A search for non-resonant and resonant pair production of Higgs bosons in the final state with two bottom quarks and two τ leptons (bb̄τ+ τ−) is presented for 36.1 fb-1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider (LHC). The observed (expected) 95% confidence level (CL) upper limit on the non-resonant Higgs boson pair production cross-section times the bb̄τ+τ- branching ratio corresponds to 12.7 (14.8) times the SM prediction. The ratio of the Higgs boson self-coupling to its SM expectation, κλ, is observed (expected) to be constrained to κλ ∈ [-7.4, 15.7] ([-8.9, 16.8]) at 95% CL. The sensitivity is extrapolated to a 14 TeV centre-of-mass energy and 3000 fb-1, which is the target integrated luminosity of the High-Luminosity LHC (HL-LHC). Various extrapolation assumptions are taken into account. The estimated expected signal significance for the SM Higgs boson pair production in the bb̄τ+τ- final state at the HL-LHC reaches 2.1 standard deviations, while the expected allowed κλ interval is κλ ∈ [-0.8, 8.8] at 95% CL, assuming the SM Higgs boson couplings. Furthermore, potential improvements of the analysis techniques are discussed in the context of searches for pair production of Higgs bosons with the full Run 2 ATLAS data.
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| 22. |
- Brus, Linda, 1977-
(författare)
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Nonlinear Identification and Control with Solar Energy Applications
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nonlinear systems occur in industrial processes, economical systems, biotechnology and in many other areas. The thesis treats methods for system identification and control of such nonlinear systems, and applies the proposed methods to a solar heating/cooling plant. Two applications, an anaerobic digestion process and a domestic solar heating system are first used to illustrate properties of an existing nonlinear recursive prediction error identification algorithm. In both cases, the accuracy of the obtained nonlinear black-box models are comparable to the results of application specific grey-box models. Next a convergence analysis is performed, where conditions for convergence are formulated. The results, together with the examples, indicate the need of a method for providing initial parameters for the nonlinear prediction error algorithm. Such a method is then suggested and shown to increase the usefulness of the prediction error algorithm, significantly decreasing the risk for convergence to suboptimal minimum points. Next, the thesis treats model based control of systems with input signal dependent time delays. The approach taken is to develop a controller for systems with constant time delays, and embed it by input signal dependent resampling; the resampling acting as an interface between the system and the controller. Finally a solar collector field for combined cooling and heating of office buildings is used to illustrate the system identification and control strategies discussed earlier in the thesis, the control objective being to control the solar collector output temperature. The system has nonlinear dynamic behavior and large flow dependent time delays. The simulated evaluation using measured disturbances confirm that the controller works as intended. A significant reduction of the impact of variations in solar radiation on the collector outlet temperature is achieved, though the limited control range of the system itself prevents full exploitation of the proposed feedforward control. The methods and results contribute to a better utilization of solar power.
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| 23. |
- Burgman, Alexander, 1991-
(författare)
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Bright Needles in a Haystack : A Search for Magnetic Monopoles Using the IceCube Neutrino Observatory
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The IceCube Neutrino Observatory at the geographic South Pole is designed to detect the light produced by the daughter-particles of in-ice neutrino-nucleon interactions, using one cubic kilometer of ice instrumented with more than 5000 optical sensors.Magnetic monopoles are hypothetical particles with non-zero magnetic charge, predicted to exist in many extensions of the Standard Model of particle physics. The monopole mass is allowed within a wide range, depending on the production mechanism. A cosmic flux of magnetic monopoles would be accelerated by extraterrestrial magnetic fields to a broad final velocity distribution that depends on the monopole mass.The analysis presented in this thesis constitutes a search for magnetic monopoles with a speed in the range [0.750;0.995] in units of the speed of light. A monopole within this speed range would produce Cherenkov light when traversing the IceCube detector, with a smooth and elongated light signature, and a high brightness.This analysis is divided into two main steps. Step I is based on a previous IceCube analysis, developed for a cosmogenic neutrino search, with similar signal event characteristics as in this analysis. The Step I event selection reduces the acceptance of atmospheric events to lower than 0.1 events per analysis livetime. Step II is developed to reject the neutrino events that Step I inherently accepts, and employs a boosted decision tree for event classification. The (astrophysical) neutrino rate is reduced to 0.265 events per analysis livetime, corresponding to a 97.4 % rejection efficiency for events with a primary energy above 1E+5 GeV.No events were observed at final analysis level over eight years of experimental data. The resulting upper limit on the magnetic monopole flux was determined to 2.54E–19 per square centimeter per second per steradian, averaged over the covered speed region. This constitutes an improvement of around one order of magnitude over previous results.
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| 24. |
- Caldeira Balkeståhl, Li
(författare)
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Measurement of the Dalitz Plot Distribution for η→π+π−π0 with KLOE
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mechanism of the isospin violating η→π+π−π0 decay is studied in a high precision experiment using a Dalitz plot analysis. The process is sensitive to the difference between up and down quark masses. The measurement provides an important input for the determination of the light quark masses and for the theoretical description of the low energy strong interactions.The measurement was carried out between 2004 and 2005 using the KLOE detector at the DAΦNE e+e− collider located in Frascati, Italy. The data was collected at a center of mass energy corresponding to the φ-meson peak (1019.5 MeV) with an integrated luminosity of 1.6 fb−1. The source of the η-mesons is the radiative decay of the φ-meson: e+e−→φ→ηγ, resulting in the world’s largest data sample of about 4.7·106 η→π+π−π0 decay events.In this thesis, the KLOE Monte Carlo simulation and reconstruction programs are used to optimize the background rejection cuts and to evaluate the signal efficiency. The background contamination in the final data sample is below 1%. The data sample is used to construct the Dalitz plot distribution in the normalized dimensionless variables X and Y. The distribution is parametrized by determining the coefficients of the third order polynomial in the X and Y variables (so called Dalitz plot parameters). The statistical accuracy of the extracted parameters is two times better than any of the previous measurements. In particular the contribution of the X2Y term is found to be different from zero with a significance of approximately 3σ. The systematic effects are studied and found to be of the same size as the statistical uncertainty. The contribution of the terms related to charge conjugation violation (odd powers of the X variable) and the measured charge asymmetries are consistent with zero.The background subtracted and acceptance corrected bin contents of the Dalitz plot distribution are provided to facilitate direct comparison with other experiments and with theoretical calculations.
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| 25. |
- Costa, Marcio, 1982-
(författare)
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First-principles Studies of Local Structure Effects in Magnetic Materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focus on the magnetic behavior, from single atoms to bulk materials. The materials considered in this thesis have been studied by computational methods based on ab initio theory, density functional theory (DFT), including treatment of the spin-orbit coupling, non-collinear magnetism, and methods capable of treating discorded systems. Furthermore strongly correlated materials have been investigated using the dynamical mean field theory (DMFT). The uniaxial magnetic anisotropy energy (MAE) of the Fe2P was investigated using the full-potential linear muffin tin orbital (FP-LMTO) method. Based on a band structure analysis, the microscopical origin of the large magnetic anisotropy found for this system is explained. It is also shown that by straining the crystal structure, the MAE can be enhanced further. This opens up for the possibility of obtaining a room temperature permanent magnet based on the Fe2P. The spectral properties of Fe impurities in a Cs host have been investigated, for both surface and bulk systems, by means of combination of density-functional theory in the local density approximation and the dynamical mean-field theory (LDA+DMFT), using two different impurity solvers, the Hubbard I approximation (HIA) and the Exact Diagonalization (ED) method were used. It is shown that noticeable differences can be seen in the unoccupied part of the spectrum for different positions of Fe atoms inside the host. The calculations show good agreement with the experimental photoemission spectra. The stability of the 12-fold metal-phosphorous coordination, existing in the meteorite mineral melliniite has been investigated trough total energy calculations using the coherent potential approximation (CPA) combined with an analysis of the chemical bonds, performed by balanced crystal overlap population (BCOOP). It was shown that its uniquely high metal–phosphorous coordination is due to a balance between covalent Fe–P binding, configurational entropy and a weaker nickel–phosphorus binding. Supported clusters have drawn a lot of attention as possible building blocks for future data storage applications. This topic was investigated using a real space noncollinear formalism where the exchange interactions between Co atoms were shown to be tuned by varying the substrate surface composition. Furthermore the spin dynamics of small Co clusters an a Cu(111) surface have been investigated and a new kind of dynamics, where magnetization switching can be accelerated by decreasing the switching field, has been found. A method for calculating the electronic structure for both ordered and disordered alloys, the augmented space recursion (ASR) method, have been extended to treat non-collinear magnetic order. The method has been used to investigate the energy stability of non-collinear arrangements of MnPt and Mn3Rh alloys.
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