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  • 1.
    Aaboen, Lise
    et al.
    Norwegian University of Science and Technology .
    La Rocca, Antonella
    BI Norwegian Business School.
    Lind, Frida
    Chalmers University of Technology.
    Perna, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Industrial Engineering & Management. Universita' Politecnica delle Marche.
    Shih, Tommy
    Starting up in Business Networks: Why relationships matter in entrepreneurship2016 (ed. 1st)Book (Refereed)
  • 2.
    Aakash, förnamn
    et al.
    Department of Electronics and Communication Engg., Birla Institute of Technology.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mohan, Rajendra
    Department of Physics, National Institute of Technology Patna.
    Mukherjee, Samrat
    Department of Physics, National Institute of Technology Patna.
    Structural, magnetic and hyperfine characterizations of nanocrystalline Zn-Cd doped nickel ferrites2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 441, p. 710-717Article in journal (Refereed)
    Abstract [en]

    In our present work, we have synthesized a series of Cd-Zn doped nickel ferrite ((Cd-0.5 Zn-x(x)) Ni0(.5)Fe(2)O(4); x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) through standard chemical co-precipitation method to study the influence of diamagnetic ions (Cd, Zn) on the magnetic properties of ferrites. XRD and Raman spectroscopy were employed for the structural characterizations. The refinement of the X-ray diffractogram data augmented by the Williamson-Hall plots showed the presence of Cd2+ vacancies and a strained crystal structure. The vibrational spectroscopy indicated the presence of lower space-group symmetry and a distorted crystal structure. Magnetic measurements showed the samples possessed low magnetic anisotropy along with a canted spin structure. The Mossbauer measurements confirmed the cation distribution and gave evidence of super transferred hyperfine interactions arising due to canted spin structure of the system.

  • 3. Aalhuizen, Christoffer
    Potential of V2G in a Rural Low-Voltage Grid on Gotland for Voltage and Power Capacity Control2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Swedish transportation sector needs to undergo major changes in order to achieve the established goals for climate and environment. The largest change is the replacement of fossil-fuelled vehicles to vehicles propelled by renewable energy sources, such as biofuels and electricity. To account for an increase in local electric power consumption, the electric power infrastructure of Sweden needs to adapt through expansion and reconstruction of the electric power grid. However, changes in infrastructure are usually expensive. It is therefore suitable to also examine alternative solutions, which could potentially be more cost efficient. One of these solutions are vehicle-to-grid (V2G), where electric vehicles acts as local electric power control and provides auxiliary services to the electric power grid. This thesis is a case study of a part of a low-voltage electric power grid on Gotland, with the goal of analysing the potential of V2G in the investigated area. The study focused on utilizing V2G for balancing electric power consumption and generation, and for adjusting voltage levels. Simulations of the area were executed in PSS®E for three different cases; one high-load case, low-load case and average-load case. It was found that by utilizing V2G a ramp up of electric power during mornings was delayed by approximately one hour, making the electric power grid potentially more compatible with photovoltaics (PV). However, the overall effects from V2G was fairly low. This outcome can partly be explained by the assumptions made in the report, and also due to some odd behaviour of the system model. 

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  • 4. Aarts, Fides
    et al.
    Jonsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Uijen, Johan
    Vaandrager, Frits
    Generating models of infinite-state communication protocols using regular inference with abstraction2015In: Formal methods in system design, ISSN 0925-9856, E-ISSN 1572-8102, Vol. 46, no 1, p. 1-41Article in journal (Refereed)
    Abstract [en]

    In order to facilitate model-based verification and validation, effort is underway to develop techniques for generating models of communication system components from observations of their external behavior. Most previous such work has employed regular inference techniques which generate modest-size finite-state models. They typically suppress parameters of messages, although these have a significant impact on control flow in many communication protocols. We present a framework, which adapts regular inference to include data parameters in messages and states for generating components with large or infinite message alphabets. A main idea is to adapt the framework of predicate abstraction, successfully used in formal verification. Since we are in a black-box setting, the abstraction must be supplied externally, using information about how the component manages data parameters. We have implemented our techniques by connecting the LearnLib tool for regular inference with an implementation of session initiation protocol (SIP) in ns-2 and an implementation of transmission control protocol (TCP) in Windows 8, and generated models of SIP and TCP components.

  • 5.
    Aava, Kim
    Gotland University, School of Game Design, Technology and Learning Processes.
    Game Save: Game Save Incorporation in Game Design through a MDA Analysis2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This paper is about save systems and will analyze save functions in various games. Save systems in games are usually blamed for harming the suspension of disbelief as it is an act taking place outside the game and should only be used for its intended purpose: letting the players store their game data, and progress whenever they need.

    The game save function developed as rapid leaps of technology were made, with the beginning era of home consoles and home computers allowing players to spend more time playing, creating a demand for longer play sessions in games which lead to a need of methods for storing game data.

    The analysis of save systems is carried out in this paper by using MDA Framework (Mechanics, Dynamics, Aesthetics), a tool used for documenting game design. This framework can be used to analyze a game from a designer‟s or player‟s perspective. By reversing the framework ADM (Aesthetics, Dynamics and Mechanics) one can analyze the user experience, which is how the player perceives the game‟s aesthetics to be, depending on the dynamics and mechanics.

    This analysis aims to provide knowledge of how consistency in game design and the save system can be used to create a cohesive game world that facillitates the player's experience and immersion.

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    KimAava_GameDesign
  • 6.
    Abad, Manuel David
    et al.
    Instituto de Ciencia de Materiales de Sevilla, ICMS (CSIC-US), Spanien.
    Sanjines, Rosendo
    Ecole Polytechnique Federale de Lausanne, IPMC-SB, Lausanne, Schweiz.
    Endrino, Jose Luis
    Instituto de Ciencia de Materiales de Madrid, ICMM (CSIC), Spanien.
    Gago, Raul
    Instituto de Ciencia de Materiales de Madrid, ICMM (CSIC), Spanien.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sanchez-Lopez, Juan Carlos
    Instituto de Ciencia de Materiales de Sevilla, ICMS (CSIC-US), Spanien.
    Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films: Influence on the Electrical and Optical Properties2011In: Plasma Processes and Polymers, ISSN 1612-8850, E-ISSN 1612-8869, Vol. 8, no 7, p. 579-588Article in journal (Refereed)
    Abstract [en]

    The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB(2) (60: 40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiB(x)C(y)) or mixed binary (TiB(2) and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K-and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiB(x)C(y) compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiB(x)C(y) phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.

  • 7. Abadpour, Sevda
    et al.
    Pauli, Mario
    Schyr, Christian
    Klein, Florian
    Degen, René
    Siska, Jan
    Pohl, Nils
    Zwick, Thomas
    Angular Resolved RCS and Doppler Analysis of Human Body Parts in Motion2022In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670Article in journal (Refereed)
  • 8.
    Abali, B. Emek
    Technische Universität Berlin.
    Damage Formulation in Generalized Mechanics Based on a Variational Formulation2021In: Proceedings of the International scientific symposium on problems of the mechanics of deformable bodies: dedicated to the 110th anniversary from the birthday of A. A. ILYUSHIN / [ed] Brovko, G. L., Georgievskii, D. V. & Molodtsov, I. N., Moscow: Moscow State University Press, 2021, p. 350-357Conference paper (Refereed)
    Abstract [en]

    Damage mechanics is often modeled by using adhoc or phenomenological methodologies, which is useful but challenging to generalize. Especially inapplications with several length scales, a homogenization procedure leads to ametamaterial to be modeled by the generalized mechanics. We aim for a unifiedtheory of generalized damage mechanics by following a variation purelyalformulation.

  • 9.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    An Introduction to Piezoelectric and Thermoelectric Materials2022In: Handbook of Energy Materials / [ed] Ram Gupta, Singapore: Springer, 2022, p. 1-18Chapter in book (Refereed)
    Abstract [en]

    Materials may demonstrate electromagnetism and thermomechanics coupling. Although we benefit from this coupling in our modern lives, comprehending this coupling is challenging. We intuitively understand that temperature increase causes an expansion in polymers and alloys. Typical example is a plastic water bottle left in the sun, the expansion is visible by naked eyes. Yet it is more abstract to consider that an electric field may create a deformation or even a temperature change. Electromagnetic fields are more abstract since our senses fail to be sensitive to these physical quantities. There are indeed materials with so-called piezoelectric and pyroelectric properties and we use them for sensors and actuators. More confusingly, there is a thermoelectric effect relating electric current and heat flux. In order to set the ideas correctly, we explain these phenomena and introduce to the abstract world of electromagnetism and thermomechanics coupling. Furthermore, we provide an inside look to realize how different types of thermal and electric coupling phenomena work and how to model such materials adequately.

  • 10.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Asymptotic homogenization and parameter determination in metamaterials2021Conference paper (Other academic)
  • 11.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Energy based methods applied in mechanics by using the extended Noether's formalism2023In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 103, no 12Article in journal (Refereed)
    Abstract [en]

    Physical systems are modeled by field equations; these are coupled, partial differential equations in space and time. Field equations are often given by balance equations and constitutive equations, where the former are axiomatically given and the latter are thermodynamically derived. This approach is useful in thermomechanics and electromagnetism, yet challenges arise once we apply it in damage mechanics for generalized continua. For deriving governing equations, an alternative method is based on a variational framework known as the extended Noether's formalism. Its formal introduction relies on mathematical concepts limiting its use in applied mechanics as a field theory. In this work, we demonstrate the power of extended Noether's formalism by using tensor algebra and usual continuum mechanics nomenclature. We demonstrate derivation of field equations in damage mechanics for generalized continua, specifically in the case of strain gradient elasticity.

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  • 12.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Chair of Continuum Mechanics and Constitutive Theory, Institute of Mechanics, Technische Universität Berlin.
    Modeling magnetohydrodynamics and computation of metal smelting2020In: Energy-based mathematical methods for reactive multiphase flows / [ed] Liero, M.; Mehrmann, V.; Mielke, A.; Peschka, D.; Thomas, M.; Wagner, B., Berlin Mathematics Research Center MATH , 2020, p. 12-13Conference paper (Other academic)
    Abstract [en]

    Ore is a compound including minerals and is found in Earth’s crust. Ore may contain iron, aluminum, copper or even gold. Extracting these metals are called smelting. For aluminum, smelting is driven by electromagnetism, where conductive ore is a viscous melt with high temperatures and is set in motion effected by electromagnetic forces. Simulation of such an application necessitates not only a computational framework but also the consistent set of partial differential equations. Thermomechanics and electromagnetism are both well-studied independently; nevertheless, their interaction is still puzzling.

  • 13.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Aldakheel, Fadi
    Zohdi, Tarek I.
    Multiphysics Computation of Thermomechanical Fatigue in Electronics Under Electrical Loading2022In: Current Trends and Open Problems in Computational Mechanics / [ed] Fadi Aldakheel, Blaž Hudobivnik, Meisam Soleimani, Henning Wessels, Christian Weißenfels, Michele Marino, Cham: Springer Nature, 2022, p. 1-14Chapter in book (Refereed)
  • 14.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Institute of Mechanics, MS 2, Technische Universität Berlin, Einsteinufer 5, 10587, Berlin, Germany.
    Barchiesi, Emilio
    Additive manufacturing introduced substructure and computational determination of metamaterials parameters by means of the asymptotic homogenization2021In: Continuum Mechanics and Thermodynamics, ISSN 0935-1175, E-ISSN 1432-0959, Vol. 33, no 4, p. 993-1009Article in journal (Refereed)
    Abstract [en]

    Metamaterials exhibit materials response deviation from conventional elasticity. This phenomenon is captured by the generalized elasticity as a result of extending the theory at the expense of introducing additional parameters. These parameters are linked to internal length scales. Describing on a macroscopic level, a material possessing a substructure at a microscopic length scale calls for introducing additional constitutive parameters. Therefore, in principle, an asymptotic homogenization is feasible to determine these parameters given an accurate knowledge on the substructure. Especially in additive manufacturing, known under the infill ratio, topology optimization introduces a substructure leading to higher-order terms in mechanical response. Hence, weight reduction creates a metamaterial with an accurately known substructure. Herein, we develop a computational scheme using both scales for numerically identifying metamaterials parameters. As a specific example, we apply it on a honeycomb substructure and discuss the infill ratio. Such a computational approach is applicable to a wide class substructures and makes use of open-source codes; we make it publicly available for a transparent scientific exchange.

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  • 15.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Institute of Mechanics Technische Universität Berlin Einsteinufer 5 Berlin 10967 Germany.
    Klunker, Andre
    Institute of Mechanics Technische Universität Berlin Einsteinufer 5 Berlin 10967 Germany.
    Barchiesi, Emilio
    International Research Center on Mathematics and Mechanics of Complex Systems Università degli Studi dell'Aquila Via Giovanni Gronchi 18 ‐ Zona industriale di Pile L'Aquila 67100 Italy.
    Placidi, Luca
    Engineering Faculty International Telematic University Uninettuno Corso Vittorio Emanuele II Rome 39 00186 Italy.
    A novel phase‐field approach to brittle damage mechanics of gradient metamaterials combining action formalism and history variable2021In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 101, no 9, article id e202000289Article in journal (Refereed)
    Abstract [en]

    Metamaterials response is generally modeled by generalized continuum based theories. Their inherent substructure leads to a necessity for higher-order theories, and especially in damage mechanics, such a generalization is difficult to acquire. We exploit the action formalism in order to obtain the governing equations in generalized damage mechanics for metamaterials. Additionally, by using auxilliary variables, the variational formulation is endowed with the first rate of damage variable that is missing in standard approaches. The presented action formalism with auxilliary variables leads directly to the weak form. We implement a finite element method based approach by using open-source computing platform called FEniCS and solve this weak in order to obtain the deformation and damage numerically. Metamaterials simulations are demonstrated for simple geometries in mixed mode (I and II) as well as in mode III.

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  • 16.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Vazic, Bozo
    Univ Utah, Dept Mech Engn, Salt Lake City, UT USA..
    Newell, Pania
    Univ Utah, Dept Mech Engn, Salt Lake City, UT USA..
    Influence of microstructure on size effect for metamaterials applied in composite structures2022In: Mechanics research communications, ISSN 0093-6413, E-ISSN 1873-3972, Vol. 122, article id 103877Article in journal (Refereed)
    Abstract [en]

    Microstructure related deviation from elastic response is known as "size-effect."Metamaterials - for example modeled by strain gradient elasticity - capture this effect adequately by means of additional parameters to be determined. We employ a methodology based on asymptotic homogenization in order to obtain metamaterials parameters and then present the influence of these additional parameters by using simulations. By means of the finite element method, we solve metamaterials deformation modeled by the strain gradient elasticity. The implementation is established by open-source packages (FEniCS) for a realistic, composite structure with round and oval inclusions.

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  • 17.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Yardimci, Mert Yucel
    Univ Ghent, Magnel Vandepitte Lab, Dept Struct Engn & Bldg Mat, Technol Pk Zwijnaarde 60, B-9052 Ghent, Belgium.;Istanbul Okan Univ, Dept Civil Engn, TR-34959 Istanbul, Turkey..
    Zecchini, Michele
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria..
    Daisse, Gilda
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria..
    Marchesini, Flavio H.
    Univ Ghent, Dept Mat Text & Chem Engn, Technol Pk Zwijnaarde 130, B-9052 Ghent, Belgium..
    De Schutter, Geert
    Univ Ghent, Magnel Vandepitte Lab, Dept Struct Engn & Bldg Mat, Technol Pk Zwijnaarde 60, B-9052 Ghent, Belgium..
    Wan-Wendner, Roman
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria.;Univ Ghent, Magnel Vandepitte Lab, Dept Struct Engn & Bldg Mat, Technol Pk Zwijnaarde 60, B-9052 Ghent, Belgium..
    Experimental investigation for modeling the hardening of thermosetting polymers during curing2021In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 102, article id 107310Article in journal (Refereed)
    Abstract [en]

    During curing of thermosetting polymers, crosslinking results in hardening or stiffening of the material. In electronics, for example in encapsulating integrated circuits (die bonding), thermosets are fully cured in a controlled environment (under UV-light or within a thermal oven) such that the highest stiffness possible has been achieved. In building materials, specifically in thermosets used in fastening systems (adhesive anchoring), hardening occurs at environmental temperature. Daily temperature variations alter the curing process and possibly lead to a lower stiffness. We demonstrate a modeling approach for the mechanical response dependency on the degree of cure by means of rheometer measurements under a specific temperature profile. Precisely, we perform oscillatory rheometric tests and convert the storage and loss moduli to material parameters depending on the degree of cure. Moreover, the temperature dependency as well as chemical shrinkage have been determined by the same experimental protocol. The presented approach has been applied to a commercially available (epoxy) thermoset used as an adhesive. We have observed a hardening after a gelation point of 0.7 and an adequate fit for mechanical response by polynomial functions of degree four.

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  • 18.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria.
    Zecchini, Michele
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria.
    Daissè, Gilda
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria.
    Czabany, Ivana
    BOKU Univ Nat Resources & Life Sci, Dept Mat Sci & Proc Engn, Inst Wood Technol & Renewable Mat, Konrad Lorenz Str 24, A-3430 Tulln, Austria.
    Gindl-Altmutter, Wolfgang
    BOKU Univ Nat Resources & Life Sci, Dept Mat Sci & Proc Engn, Inst Wood Technol & Renewable Mat, Konrad Lorenz Str 24, A-3430 Tulln, Austria.
    Wan-Wendner, Roman
    Univ Nat Resources & Life Sci, Christian Doppler Lab LiCRoFast, Peter Jordan Str 82, A-1190 Vienna, Austria; Univ Ghent, Dept Struct Engn & Bldg Mat, Magnel Lab, Technol Pk Zwijnaarde 60, B-9052 Ghent, Belgium.
    Cure Kinetics and Inverse Analysis of Epoxy-Amine Based Adhesive Used for Fastening Systems2021In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 14, article id 3853Article in journal (Refereed)
    Abstract [en]

    Thermosetting polymers are used in building materials, for example adhesives in fastening systems. They harden in environmental conditions with a daily temperature depending on the season and location. This curing process takes hours or even days effected by the relatively low ambient temperature necessary for a fast and complete curing. As material properties depend on the degree of cure, its accurate estimation is of paramount interest and the main objective in this work. Thus, we develop an approach for modeling the curing process for epoxy based thermosetting polymers. Specifically, we perform experiments and demonstrate an inverse analysis for determining parameters in the curing model. By using calorimetry measurements and implementing an inverse analysis algorithm by using open-source packages, we obtain 10 material parameters describing the curing process. We present the methodology for two commercial, epoxy based products, where a statistical analysis provides independence of material parameters leading to the conclusion that the material equation is adequately describing the material response.

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    FULLTEXT01
  • 19.
    Abbasi, Vahid
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Phonetic Analysis and Searching with Google Glass API2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project utilizes speech recognition Application Program Interface (API) together with phonetic algorithms to search Stockholm's restaurant names via Google Glass with higher precision. This project considers the ability of phonetic algorithms and N-gram analyzer to retrieve the word and how it can be combined with automatic speech recognition to find the correct match. Significantly, the combination of these algorithms and the Google Glass limitation, e.g. its smallscreen, makes using a phonnetic filtering algorithm very helpful in getting better results.

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  • 20.
    Abdal, Zardasht
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Användbarheten i Business Intelligens-system: Utvecklingen av användbarheten och funktionaliteten i ett webbaserat BI-system2015Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this study is to evaluate an existing user interface. The company in question has a web-based user interface (available through logging in via their website), but they are interested in making the process of using the interface more convenient and the interface more accessible, so that users without a background in computing can properly manage the interface. At the same time they want to apply additional functionalities in order create and to manage increased traffic on the company’s website. For this reason it is important to take into account the issues involved in human-computer interaction (HCI) as well as aspects of cognitive psychology in order to make the tool and the web interface more usable, more motivational, and therefore more efficient and professional. When I refer to the system as “more useful”, I mean firstly that it should work better and provide better and more useful information to users. I also mean that it should become more user-friendly, which involves both being easier to use and more difficult to use incorrectly. I have had to pay attention to, and reflect over, values, structures, norms, rules, motivational factors, and routines in order to improve the usability of the web interface.

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  • 21.
    Abdallah, Ali
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Det smarta hemmet – Energianvändarens framtid: En studie om smarta hem och vilka möjligheter Jämtkraft har att satsa på dessa2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Energy consumption in Sweden is relatively large in terms of population. That depends a lot on the need for heating during most of the year because of the cold climate but also on the continuous need for energy in the everyday life. The large energy consumption entails, however, large loads on both climate and environment. Thus energy efficiency is an important measure to reduce the climate and environmental impact. Smart homes are complex systems that cover various aspects of the home but are considered to be an effective resource for improving energy efficiency.

    The purpose of this master’s thesis is to investigate how to develop or combine energy-efficient products in the best way possible. Energy consumers needs and behaviors have been analyzed and a market analysis of the products available on the market today has been performed based on a survey directed to energy users and interviews with energy users and stakeholders on the smart home market.

    Energy users show a lack of knowledge about smart homes and energy-smart products, probably because the smart homes market is still new in Sweden and most stakeholders have not managed to advertise themselves and their products yet. It may also depend on other factors such as energy users’ lack of interest in energy efficiency, which may be due to the low price of electricity in Sweden.

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  • 22.
    Abdallah, Ali
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Industrial Engineering & Management.
    The perception of Nuclear powerin Sweden: How engineering students view it2017Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Nuclear power has been an important part of the electricity generatingin Sweden in almost half a century. However, the use of nuclear powerraises many complex issues such as economy, accident risks, andradioactive waste management and storage. Nuclear power has thereforebeen debated intensively in Sweden as in many other countries since the1970s. Several countries have changed their nuclear policy and starteddecommissioning programs following the nuclear accident in Fukushimaback in 2011. Citizens' support for nuclear power has declined worldwidein last few years, including in Sweden. This study aims to investigatethe perception of nuclear power among engineering students and showsthat the majority of engineering students, who generally are positivetowards technology, have been affected by their surrounding and areagainst nuclear power. Engineering students in general, both supportersand opponents of nuclear power, agree that Sweden should gradually phaseout nuclear power and replace it by renewable energy sources.

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  • 23.
    Abdallah, Lana
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Informatics and Media, Information Systems.
    Sustainability Impacts of Satellite Internet: Digital Inclusion vs Environmental Sustainability2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An estimated 450 million people globally do not have access to a fixed or mobile broadband signal. Recently satellite communication companies announced the concept of Megaconstellations which are large networks of inexpensive low Earth-orbiting satellites. These constellations aim to provide internet access across the planet. Many people believe these constellations will offer an opportunity to bridge the digital divide between developed and developing countries. However, according to the UN development agenda, it is crucial to harmonize three core elements: economic growth, social inclusion, and environmental protection, while achieving the Sustainable Development Goals (SDGs). Although many are enthusiastic about the possibility of closing the digital gap, some researchers have concerns about the environmental impacts of these mega-constellations. Some studies explored howsatellites’ mega-constellations would increase the collision rate among space objects. This by increased amount of space debris which would negatively impact the Low Earth Orbit and the planet and thereby would be inconsistent with environmental sustainability. This study aims to investigate this claim by examining the impacts of future capabilities of satellites on offering inclusive healthcare and education systems while investigating their environmental impacts. 

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  • 24.
    Abdalmoaty, Mohamed
    KTH, Reglerteknik.
    Identification of Stochastic Nonlinear Dynamical Models Using Estimating Functions2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Data-driven modeling of stochastic nonlinear systems is recognized as a very challenging problem, even when reduced to a parameter estimation problem. A main difficulty is the intractability of the likelihood function, which renders favored estimation methods, such as the maximum likelihood method, analytically intractable. During the last decade, several numerical methods have been developed to approximately solve the maximum likelihood problem. A class of algorithms that attracted considerable attention is based on sequential Monte Carlo algorithms (also known as particle filters/smoothers) and particle Markov chain Monte Carlo algorithms. These algorithms were able to obtain impressive results on several challenging benchmark problems; however, their application is so far limited to cases where fundamental limitations, such as the sample impoverishment and path degeneracy problems, can be avoided.

    This thesis introduces relatively simple alternative parameter estimation methods that may be used for fairly general stochastic nonlinear dynamical models. They are based on one-step-ahead predictors that are linear in the observed outputs and do not require the computations of the likelihood function. Therefore, the resulting estimators are relatively easy to compute and may be highly competitive in this regard: they are in fact defined by analytically tractable objective functions in several relevant cases. In cases where the predictors are analytically intractable due to the complexity of the model, it is possible to resort to {plain} Monte Carlo approximations. Under certain assumptions on the data and some conditions on the model, the convergence and consistency of the estimators can be established. Several numerical simulation examples and a recent real-data benchmark problem demonstrate a good performance of the proposed method, in several cases that are considered challenging, with a considerable reduction in computational time in comparison with state-of-the-art sequential Monte Carlo implementations of the ML estimator.

    Moreover, we provide some insight into the asymptotic properties of the proposed methods. We show that the accuracy of the estimators depends on the model parameterization and the shape of the unknown distribution of the outputs (via the third and fourth moments). In particular, it is shown that when the model is non-Gaussian, a prediction error method based on the Gaussian assumption is not necessarily more accurate than one based on an optimally weighted parameter-independent quadratic norm. Therefore, it is generally not obvious which method should be used. This result comes in contrast to a current belief in some of the literature on the subject. 

    Furthermore, we introduce the estimating functions approach, which was mainly developed in the statistics literature, as a generalization of the maximum likelihood and prediction error methods. We show how it may be used to systematically define optimal estimators, within a predefined class, using only a partial specification of the probabilistic model. Unless the model is Gaussian, this leads to estimators that are asymptotically uniformly more accurate than linear prediction error methods when quadratic criteria are used. Convergence and consistency are established under standard regularity and identifiability assumptions akin to those of prediction error methods.

    Finally, we consider the problem of closed-loop identification when the system is stochastic and nonlinear. A couple of scenarios given by the assumptions on the disturbances, the measurement noise and the knowledge of the feedback mechanism are considered. They include a challenging case where the feedback mechanism is completely unknown to the user. Our methods can be regarded as generalizations of some classical closed-loop identification approaches for the linear time-invariant case. We provide an asymptotic analysis of the methods, and demonstrate their properties in a simulation example.

  • 25.
    Abdalmoaty, Mohamed
    KTH, Reglerteknik.
    Learning Stochastic Nonlinear Dynamical Systems Using Non-stationary Linear Predictors2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The estimation problem of stochastic nonlinear parametric models is recognized to be very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the maximum likelihood estimator and the optimal mean-square error predictor using Monte Carlo methods. Albeit asymptotically optimal, these methods come with several computational challenges and fundamental limitations.

    The contributions of this thesis can be divided into two main parts. In the first part, approximate solutions to the maximum likelihood problem are explored. Both analytical and numerical approaches, based on the expectation-maximization algorithm and the quasi-Newton algorithm, are considered. While analytic approximations are difficult to analyze, asymptotic guarantees can be established for methods based on Monte Carlo approximations. Yet, Monte Carlo methods come with their own computational difficulties; sampling in high-dimensional spaces requires an efficient proposal distribution to reduce the number of required samples to a reasonable value.

    In the second part, relatively simple prediction error method estimators are proposed. They are based on non-stationary one-step ahead predictors which are linear in the observed outputs, but are nonlinear in the (assumed known) input. These predictors rely only on the first two moments of the model and the computation of the likelihood function is not required. Consequently, the resulting estimators are defined via analytically tractable objective functions in several relevant cases. It is shown that, under mild assumptions, the estimators are consistent and asymptotically normal. In cases where the first two moments are analytically intractable due to the complexity of the model, it is possible to resort to vanilla Monte Carlo approximations. Several numerical examples demonstrate a good performance of the suggested estimators in several cases that are usually considered challenging.

  • 26.
    Abdalmoaty, Mohamed
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Coimbatore Anand, Sribalaji
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Signals and Systems.
    Teixeira, André
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Signals and Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Privacy and Security in Network Controlled Systems via Dynamic Masking2023In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 56, no 2, p. 991-996Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose a new architecture to enhance the privacy and security of networked control systems against malicious adversaries. We consider an adversary which first learns the system using system identification techniques (privacy), and then performs a data injection attack (security). In particular, we consider an adversary conducting zero-dynamics attacks (ZDA) which maximizes the performance cost of the system whilst staying undetected. Using the proposed architecture, we show that it is possible to (i) introduce significant bias in the system estimates obtained by the adversary: thus providing privacy, and (ii) efficiently detect attacks when the adversary performs a ZDA using the identified system: thus providing security. Through numerical simulations, we illustrate the efficacy of the proposed architecture

  • 27.
    Abdalmoaty, Mohamed
    et al.
    KTH, Reglerteknik.
    Henrion, D.
    Rodrigues, L.
    Measures and LMIs for optimal control of piecewise-affine systems2013In: 2013 European Control Conference, ECC 2013, IEEE , 2013, p. 3173-3178, article id 6669627Conference paper (Refereed)
    Abstract [en]

    This paper considers the class of deterministic continuous-time optimal control problems (OCPs) with piecewise-affine (PWA) vector field, polynomial Lagrangian and semialgebraic input and state constraints. The OCP is first relaxed as an infinite-dimensional linear program (LP) over a space of occupation measures. This LP is then approached by an asymptotically converging hierarchy of linear matrix inequality (LMI) relaxations. The relaxed dual of the original LP returns a polynomial approximation of the value function that solves the Hamilton-Jacobi-Bellman (HJB) equation of the OCP. Based on this polynomial approximation, a suboptimal policy is developed to construct a state feedback in a sample-and-hold manner. The results show that the suboptimal policy succeeds in providing a suboptimal state feedback law that drives the system relatively close to the optimal trajectories and respects the given constraints.

  • 28.
    Abdalmoaty, Mohamed
    et al.
    Division of Decision and Control Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Hjalmarsson, Håkan
    Division of Decision and Control Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Identification of Stochastic Nonlinear Models Using Optimal Estimating Functions2020In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 119, article id 109055Article in journal (Refereed)
    Abstract [en]

    The first part of the paper examines the asymptotic properties of linear prediction error method estimators, which were recently suggested for the identification of nonlinear stochastic dynamical models. It is shown that their accuracy depends not only on the shape of the unknown distribution of the data, but also on how the model is parameterized. Therefore, it is not obvious in general which linear prediction error method should be preferred. In the second part, the estimating functions approach is introduced and used to construct estimators that are asymptotically optimal with respect to a specific class of estimators. These estimators rely on a partial probabilistic parametric models, and therefore neither require the computations of the likelihood function nor any marginalization integrals. The convergence and consistency of the proposed estimators are established under standard regularity and identifiability assumptions akin to those of prediction error methods. The paper is concluded by several numerical simulation examples.

  • 29.
    Abdalmoaty, Mohamed
    et al.
    Division of Decision and Control Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Hjalmarsson, Håkan
    Division of Decision and Control Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Linear Prediction Error Methods for Stochastic Nonlinear Models2019In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 105, p. 49-63Article in journal (Refereed)
    Abstract [en]

    The estimation problem for stochastic parametric nonlinear dynamical models is recognized to be challenging. The main difficulty is the intractability of the likelihood function and the optimal one-step ahead predictor. In this paper, we present relatively simple prediction error methods based on non-stationary predictors that are linear in the outputs. They can be seen as extensions of the linear identification methods for the case where the hypothesized model is stochastic and nonlinear. The resulting estimators are defined by analytically tractable objective functions in several common cases. It is shown that, under certain identifiability and standard regularity conditions, the estimators are consistent and asymptotically normal. We discuss the relationship between the suggested estimators and those based on second-order equivalent models as well as the maximum likelihood method. The paper is concluded with a numerical simulation example as well as a real-data benchmark problem.

  • 30.
    Abdalmoaty, Mohamed
    et al.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    On Re-Weighting, Regularization Selection, and Transient in Nuclear Norm Based Identification2015In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 48, no 28, p. 92-97Article in journal (Refereed)
    Abstract [en]

    In this contribution, we consider the classical problem of estimating an Output Error model given a set of input-output measurements. First, we develop a regularization method based on the re-weighted nuclear norm heuristic. We show that the re-weighting improves the estimate in terms of better fit. Second, we suggest an implementation method that helps in eliminating the regularization parameters from the problem by introducing a constant based on a validation criterion. Finally, we develop a method for considering the effect of the transient when the initial conditions are unknown. A simple numerical example is used to demonstrate the proposed method in comparison to classical and another recent method based on the nuclear norm heuristic.

  • 31.
    Abdalmoaty, Mohamed
    et al.
    Division of Decision and Control Systems in the School of Electrical Engineering and Computer Science at KTH Royal Institute of Technology, Stockholm, Sweden.
    Hjalmarsson, Håkan
    Division of Decision and Control Systems in the School of Electrical Engineering and Computer Science at KTH Royal Institute of Technology, Stockholm, Sweden.
    Wahlberg, Bo
    Division of Decision and Control Systems in the School of Electrical Engineering and Computer Science at KTH Royal Institute of Technology, Stockholm, Sweden.
    The Gaussian MLE versus the Optimally weighted LSE2020In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 37, no 6, p. 195-199Article in journal (Refereed)
    Abstract [en]

    In this note, we derive and compare the asymptotic covariance matrices of two parametric estimators: the Gaussian Maximum Likelihood Estimator (MLE), and the optimally weighted Least-Squares Estimator (LSE). We assume a general model parameterization where the model's mean and variance are jointly parameterized, and consider Gaussian and non-Gaussian data distributions.

  • 32.
    Abdalmoaty, Mohamed
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Noise reduction in Laguerre-domain discrete delay estimation2022In: 2022 IEEE 61st Conference on Decision and Control (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2022, p. 6254-6259Conference paper (Refereed)
    Abstract [en]

    This paper introduces a stochastic framework for a recently proposed discrete-time delay estimation method in Laguerre-domain, i.e. with the delay block input and output signals being represented by the corresponding Laguerre series. A novel Laguerre-domain disturbance model allowing the involved signals to be square-summable sequences is devised. The relation to two commonly used time-domain disturbance models is clarified. Furthermore, by forming the input signal in a certain way, the signal shape of an additive output disturbance can be estimated and utilized for noise reduction. It is demonstrated that a significant improvement in the delay estimation error is achieved when the noise sequence is correlated. The noise reduction approach is applicable to other Laguerre-domain problems than pure delay estimation.

  • 33.
    Abdalmoaty, Mohamed R. H.
    et al.
    KTH, Reglerteknik.
    Eriksson, Oscar
    KTH, Programvaruteknik och datorsystem, SCS.
    Bereza, Robert
    KTH, Reglerteknik.
    Broman, David
    KTH, Programvaruteknik och datorsystem, SCS.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    Identification of Non-Linear Differential-Algebraic Equation Models with Process Disturbances2021In: 2021 60th IEEE Conference on Decision and Control (CDC), IEEE, 2021, p. 2300-2305Conference paper (Refereed)
    Abstract [en]

    Differential-algebraic equations (DAEs) arise naturally as a result of equation-based object-oriented modeling. In many cases, these models contain unknown parameters that have to be estimated using experimental data. However, often the system is subject to unknown disturbances which, if not taken into account in the estimation, can severely affect the model's accuracy. For non-linear state-space models, particle filter methods have been developed to tackle this issue. Unfortunately, applying such methods to non-linear DAEs requires a transformation into a state-space form, which is particularly difficult to obtain for models with process disturbances. In this paper, we propose a simulation-based prediction error method that can be used for non-linear DAEs where disturbances are modeled as continuous-time stochastic processes. To the authors' best knowledge, there are no general methods successfully dealing with parameter estimation for this type of model. One of the challenges in particle filtering  methods are random variations in the minimized cost function due to the nature of the algorithm. In our approach, a similar phenomenon occurs and we explicitly consider how to sample the underlying continuous process to mitigate this problem. The method is illustrated numerically on a pendulum example. The results suggest that the method is able to deliver consistent estimates.

  • 34.
    Abdalmoaty, Mohamed R. H.
    et al.
    KTH, Reglerteknik.
    Rojas, Cristian R.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    Identification of a Class of Nonlinear Dynamical Networks2018In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, no 15, p. 868-873Article in journal (Refereed)
    Abstract [en]

    Identifcation of dynamic networks has attracted considerable interest recently. So far the main focus has been on linear time-invariant networks. Meanwhile, most real-life systems exhibit nonlinear behaviors; consider, for example, two stochastic linear time-invariant systems connected in series, each of which has a nonlinearity at its output. The estimation problem in this case is recognized to be challenging, due to the analytical intractability of both the likelihood function and the optimal one-step ahead predictors of the measured nodes. In this contribution, we introduce a relatively simple prediction error method that may be used for the estimation of nonlinear dynamical networks. The estimator is defined using a deterministic predictor that is nonlinear in the known signals. The estimation problem can be defined using closed-form analytical expressions in several non-trivial cases, and Monte Carlo approximations are not necessarily required. We show, that this is the case for some block-oriented networks with no feedback loops and where all the nonlinear modules are polynomials. Consequently, the proposed method can be applied in situations considered challenging by current approaches. The performance of the estimation method is illustrated on a numerical simulation example.

  • 35.
    Abdalmoaty, Mohamed Rasheed
    et al.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    A Simulated Maximum Likelihood Method for Estimation of Stochastic Wiener Systems2016In: 2016 IEEE 55th Conference on Decision and Control (CDC), IEEE, 2016, p. 3060-3065Conference paper (Refereed)
    Abstract [en]

    This paper introduces a simulation-based method for maximum likelihood estimation of stochastic Wienersystems. It is well known that the likelihood function ofthe observed outputs for the general class of stochasticWiener systems is analytically intractable. However, when the distributions of the process disturbance and the measurement noise are available, the likelihood can be approximated byrunning a Monte-Carlo simulation on the model. We suggest the use of Laplace importance sampling techniques for the likelihood approximation. The algorithm is tested on a simple first order linear example which is excited only by the process disturbance. Further, we demonstrate the algorithm on an FIR system with cubic nonlinearity. The performance of the algorithm is compared to the maximum likelihood method and other recent techniques.

  • 36.
    Abdalmoaty, Mohamed Rasheed
    et al.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    Application of a Linear PEM Estimator to a Stochastic Wiener-Hammerstein Benchmark Problem2018In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, no 15, p. 784-789Article in journal (Refereed)
    Abstract [en]

    The estimation problem of stochastic Wiener-Hammerstein models is recognized to be challenging, mainly due to the analytical intractability of the likelihood function. In this contribution, we apply a computationally attractive prediction error method estimator to a real-data stochastic Wiener-Hammerstein benchmark problem. The estimator is defined using a deterministic predictor that is nonlinear in the input. The prediction error method results in tractable expressions, and Monte Carlo approximations are not necessary. This allows us to tackle several issues considered challenging from the perspective of the current mainstream approach. Under mild conditions, the estimator can be shown to be consistent and asymptotically normal. The results of the method applied to the benchmark data are presented and discussed.

  • 37.
    Abdalmoaty, Mohamed Rasheed
    et al.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    Consistent Estimators of Stochastic MIMO Wiener Models based on Suboptimal Predictors2018In: 2018 IEEE Conference on Decision and Control (CDC), IEEE, 2018, p. 3842-3847Conference paper (Refereed)
    Abstract [en]

    We consider a parameter estimation problem in a general class of stochastic multiple-inputs multiple-outputs Wiener models, where the likelihood function is, in general, analytically intractable. When the output signal is a scalar independent stochastic process, the likelihood function of the parameters is given by a product of scalar integrals. In this case, numerical integration may be efficiently used to approximately solve the maximum likelihood problem. Otherwise, the likelihood function is given by a challenging multidimensional integral. In this contribution, we argue that by ignoring the temporal and spatial dependence of the stochastic disturbances, a computationally attractive estimator based on a suboptimal predictor can be constructed by evaluating scalar integrals regardless of the number of outputs. Under some conditions, the convergence of the resulting estimators can be established and consistency is achieved under certain identifiability hypothesis. We highlight the relationship between the resulting estimators and a recently proposed prediction error method estimator. We also remark that the method can be used for a wider class of stochastic nonlinear models. The performance of the method is demonstrated by a numerical simulation example using a 2-inputs 2-outputs model with 9 parameters.

  • 38.
    Abdalmoaty, Mohamed Rasheed
    et al.
    KTH, Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Reglerteknik.
    Simulated Pseudo Maximum Likelihood Identification of Nonlinear Models2017In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 50, no 1, p. 14058-14063Article in journal (Refereed)
    Abstract [en]

    Nonlinear stochastic parametric models are widely used in various fields. However, for these models, the problem of maximum likelihood identification is very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the analytically intractable likelihood function and compute either the maximum likelihood or a Bayesian estimator. These methods, albeit asymptotically optimal, are computationally expensive. In this contribution, we present a simulation-based pseudo likelihood estimator for nonlinear stochastic models. It relies only on the first two moments of the model, which are easy to approximate using Monte-Carlo simulations on the model. The resulting estimator is consistent and asymptotically normal. We show that the pseudo maximum likelihood estimator, based on a multivariate normal family, solves a prediction error minimization problem using a parameterized norm and an implicit linear predictor. In the light of this interpretation, we compare with the predictor defined by an ensemble Kalman filter. Although not identical, simulations indicate a close relationship. The performance of the simulated pseudo maximum likelihood method is illustrated in three examples. They include a challenging state-space model of dimension 100 with one output and 2 unknown parameters, as well as an application-motivated model with 5 states, 2 outputs and 5 unknown parameters.

  • 39.
    Abdellah, Mohamed
    et al.
    Lund Univ, Div Chem Phys, Box 124, S-22100 Lund, Sweden.;Lund Univ, NanoLund, Box 124, S-22100 Lund, Sweden.;South Valley Univ, Qena Fac Sci, Dept Chem, Qena 83523, Egypt..
    Poulsen, Felipe
    Univ Copenhagen, Dept Chem, DK-2100 Copenhagen, Denmark..
    Zhu, Qiushi
    Lund Univ, Div Chem Phys, Box 124, S-22100 Lund, Sweden.;Lund Univ, NanoLund, Box 124, S-22100 Lund, Sweden..
    Zhu, Nan
    Tech Univ Denmark, Dept Chem, Kemitorvet Bldg 207, DK-2800 Lyngby, Denmark.;Dalian Univ Technol, Zhang Dayu Sch Chem, Dalian 116024, Peoples R China..
    Zidek, Karel
    Acad Sci Czech Republ, Inst Plasma Phys, Reg Ctr Special Opt & Optoelect Syst TOPTEC, Za Slovankou 1782-3, Prague 18200 8, Czech Republic..
    Chabera, Pavel
    Lund Univ, Div Chem Phys, Box 124, S-22100 Lund, Sweden.;Lund Univ, NanoLund, Box 124, S-22100 Lund, Sweden..
    Corti, Annamaria
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hansen, Thorsten
    Univ Copenhagen, Dept Chem, DK-2100 Copenhagen, Denmark..
    Chi, Qijin
    Tech Univ Denmark, Dept Chem, Kemitorvet Bldg 207, DK-2800 Lyngby, Denmark..
    Canton, Sophie E.
    DESY, Attosecond Sci Grp, Notkestr 85, D-22607 Hamburg, Germany.;ELI HU Nonprofit Ltd, ELI ALPS, Dugonics Ter 13, H-6720 Szeged, Hungary..
    Zheng, Kaibo
    Lund Univ, Div Chem Phys, Box 124, S-22100 Lund, Sweden.;Lund Univ, NanoLund, Box 124, S-22100 Lund, Sweden.;Qatar Univ, Coll Engn, Gas Proc Ctr, POB 2713, Doha, Qatar..
    Pullerits, Tonu
    Lund Univ, Div Chem Phys, Box 124, S-22100 Lund, Sweden.;Lund Univ, NanoLund, Box 124, S-22100 Lund, Sweden..
    Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1−xS1−y quantum dots2017In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 34, p. 12503-12508Article in journal (Refereed)
    Abstract [en]

    Ultrafast fluorescence spectroscopy was used to investigate the hole injection in CdxSeyZn1-xS1-y gradient core-shell quantum dot (CSQD) sensitized p-type NiO photocathodes. A series of CSQDs with a wide range of shell thicknesses was studied. Complementary photoelectrochemical cell measurements were carried out to confirm that the hole injection from the active core through the gradient shell to NiO takes place. The hole injection from the valence band of the QDs to NiO depends much less on the shell thickness when compared to the corresponding electron injection to n-type semiconductor (ZnO). We simulate the charge carrier tunneling through the potential barrier due to the gradient shell by numerically solving the Schrodinger equation. The details of the band alignment determining the potential barrier are obtained from X-ray spectroscopy measurements. The observed drastic differences between the hole and electron injection are consistent with a model where the hole effective mass decreases, while the gradient shell thickness increases.

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  • 40.
    Abd-Elrady, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Convergence of the RPEM as applied to harmonic signal modeling2000Report (Other academic)
    Abstract [en]

    Arbitrary periodic signals can be estimated recursively by exploiting the fact that a sine wave passing through a static nonlinear function generates a spectrum of overtones. The estimated signal model is hence parameterized as a real wave with unknown period in cascade with a piecewise linear function. The driving periodic wave can be chosen depending on any prior knowledge. The performance of a recursive Gauss-Newton prediction error identification algorithm for joint estimation of the driving frequency and the parameters of the nonlinear output function is therefore studied. A theoretical analysis of local convergence to the true parameter vector as well as numerical examples are given. Furthermore, the Cramer-Rao bound (CRB) is calculated in this report.

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  • 41.
    Abd-Elrady, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Harmonic signal modeling based on the Wiener model structure2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The estimation of frequencies and corresponding harmonic overtones is a problem of great importance in many situations. Applications can, for example, be found in supervision of electrical power transmission lines, in seismology and in acoustics. Generally, a periodic function with an unknown fundamental frequency in cascade with a parameterized and unknown nonlinear function can be used as a signal model for an arbitrary periodic signal. The main objective of the proposed modeling technique is to estimate the fundamental frequency of the periodic function in addition to the parameters of the nonlinear function.

    The thesis is divided into four parts. In the first part, a general introduction to the harmonic signal modeling problem and different approaches to solve the problem are given. Also, an outline of the thesis and future research topics are introduced.

    In the second part, a previously suggested recursive prediction error method (RPEM) for harmonic signal modeling is studied by numerical examples to explore the ability of the algorithm to converge to the true parameter vector. Also, the algorithm is modified to increase its ability to track the fundamental frequency variations.

    A modified algorithm is introduced in the third part to give the algorithm of the second part a more stable performance. The modifications in the RPEM are obtained by introducing an interval in the nonlinear block with fixed static gain. The modifications that result in the convergence analysis are, however, substantial and allows a complete treatment of the local convergence properties of the algorithm. Moreover, the Cramér–Rao bound (CRB) is derived for the modified algorithm and numerical simulations indicate that the method gives good results especially for moderate signal to noise ratios (SNR).

    In the fourth part, the idea is to give the algorithm of the third part the ability to estimate the driving frequency and the parameters of the nonlinear output function parameterized also in a number of adaptively estimated grid points. Allowing the algorithm to automatically adapt the grid points as well as the parameters of the nonlinear block, reduces the modeling errors and gives the algorithm more freedom to choose the suitable grid points. Numerical simulations indicate that the algorithm converges to the true parameter vector and gives better performance than the fixed grid point technique. Also, the CRB is derived for the adaptive grid point technique.

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  • 42.
    Abd-Elrady, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Nonlinear Approaches to Periodic Signal Modeling2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    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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  • 43.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal analysis using orbits of nonlinear ODEs based on the Markov estimate2004Conference paper (Refereed)
  • 44.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal modeling based on Liénard's equation2004In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 49, no 10, p. 1773-1778Article in journal (Refereed)
  • 45.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal modeling based on Liénard's equation2003Report (Other academic)
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  • 46.
    Abdi-Jalebi, Mojtaba
    et al.
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Pazoki, Meysam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dar, M. Ibrahim
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, Lausanne, Switzerland.
    Alsari, Mejd
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Sadhanala, Aditya
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Diyitini, Giorgio
    Univ Cambridge, Dept Mat Sci & Met, Charles Babbage Rd, Cambridge, England.
    Imani, Roghayeh
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lilliu, Samuele
    Univ Sheffield, Dept Phys & Astron, Sheffield, S Yorkshire, England; UAE Ctr Crystallog, Dubai, U Arab Emirates.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Gratzel, Michael
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, Lausanne, Switzerland.
    Friend, Richard H.
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 7, p. 7301-7311Article in journal (Refereed)
    Abstract [en]

    We report significant improvements in the optoelectronic properties of lead halide perovskites with the addition of monovalent ions with ionic radii close to Pb2+. We investigate the chemical distribution and electronic structure of solution processed CH3NH3PbI3 perovskite structures containing Na+, Cu+, and Ag+, which are lower valence metal ions than Pb2+ but have similar ionic radii. Synchrotron X-ray diffraction reveals a pronounced shift in the main perovskite peaks for the monovalent cation-based films, suggesting incorporation of these cations into the perovskite lattice as well as a preferential crystal growth in Ag+ containing perovskite structures. Furthermore, the synchrotron X-ray photoelectron measurements show a significant change in the valence band position for Cu- and Ag-doped films, although the perovskite bandgap remains the same, indicating a shift in the Fermi level position toward the middle of the bandgap. Such a shift infers that incorporation of these monovalent cations dedope the n-type perovskite films when formed without added cations. This dedoping effect leads to cleaner bandgaps as reflected by the lower energetic disorder in the monovalent cation-doped perovskite thin films as compared to pristine films. We also find that in contrast to Ag+ and Cu+, Na+ locates mainly at the grain boundaries and surfaces. Our theoretical calculations confirm the observed shifts in X-ray diffraction peaks and Fermi level as well as absence of intrabandgap states upon energetically favorable doping of perovskite lattice by the monovalent cations. We also model a significant change in the local structure, chemical bonding of metal-halide, and the electronic structure in the doped perovskites. In summary, our work highlights the local chemistry and influence of monovalent cation dopants on crystallization and the electronic structure in the doped perovskite thin films.

  • 47. Abdin, Amir
    et al.
    Feyzabi, Kaveh
    Hellman, Oskar
    Nordström, Henrietta
    Rasa, Dilman
    Thaung Tolförs, Gustav
    Öqvist, Per-Olof
    Methods to create compressive stress in high strength steel components2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Residual compressive stresses can be used to increase the lifetime of parts under cyclic stress as they negate the applied tensile stresses that cause crack initiation and propagation in the material. The goal of this project was to investigate methods to induce stresses, their advantages and disadvantages as well as depth and magnitude of induced stresses, and also to find methods of analyzing the induced residual stresses. This was done on behalf of Epiroc Drilling Tools AB in order for them to induce stresses on the insides of their long, narrow and hollow rods, where stress induction is difficult. Shot peening was used as a reference as that is the method currently in use by the company. The results show that the two most promising methods are cavitation peening and laser shock peening; two relatively new methods with large magnitudes and depth of induced stress as well as a great capability of inducing stresses on the hard-to-reach insides of the rods. Ultrasonic needle peening, ultrasonic shot peening as well as induction hardening, cryogenic treatment and friction stir processing were also investigated. Methods of analyzing the stresses include X-ray diffraction and slitting, hole drilling and ultrasonic methods.

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  • 48.
    Abdlbari, Abdulbari
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Informatics and Media.
    Product registration in e-commerce for small and medium companies (SMEs): Usability aspects2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    People these days are able to buy almost anything online. With a continuously increased E-commerce, small and medium sized companies (SMEs) feel obligated to enter the competitive E-commerce market. Moreover, for small companies with little or no experience in e-commerce it could become overwhelming to get a web-shop up and running. One important tasks in managing a web-shop is to register products into the system. This must be easy and efficient. The focus of this thesis is to answer the question "How can user-centered design principles improve productregistration, particularly in the SME context?". At the start of this study, surveys and interviews were conducted, which showed that product registration is very time consuming at the moment. User tests were conducted to measure the efficiency and the general usability of a system maintaining over 100 active web-shops. Based on the results of the first iteration of the user test conducted, design changes were proposed and implemented. A second iteration of the user test showed improved efficiency and substantially less errors. The most important new design elements were related to navigation, workflow and adjustment of input fields to the data sources. Thus it has been shown that the threshold for SME web-shops to go online can be lowered by a systematic application of user-centered design of the user interface.

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  • 49.
    Abdou, Elhassan M
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Visual Planning and Verification of Deep Brain Stimulation Interventions2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
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  • 50.
    Abdul Kader, Leyla
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Anomaly Detection in Financial Transaction Time Series Data2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis investigates two methods of anomaly detection on financial time series data. It aims to determine an optimal method for anomaly detection with the purpose of flagging anomalous transactions within foreign exchange trading data. It also aims to determine whether the data points flagged as anomalies have any commonalities. This was achieved by first looking into a statistical technique that predicts future transactions based on historical records and subsequently using that to create a threshold for anomaly detection and later with the use of unsupervised machine learning in the form of an autoencoder. The results show that the autoencoder outperformed the statistical technique and was successful at pointing out possible anomalous data points showing a number of common features.    

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