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  • 1.
    Ahmed, Faisal Mahmood
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Estimated Droop Control for Parallel Connected Voltage Source Inverters: Stability Enhancement2013Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Renewable Energy Sources (RES) are considered as the replacement of conventionalenergy sources. These RES can use wind energy, solar light, bio waste and can alsobe in the form of small hydro power units. These RES has very poor power qualityand contains voltage uctuations and variable frequency. These factors make RES astability risk for the main utility grid. As a solution, currently inverters with dierentdesign techniques are being used as an interface between RES and main utility grid. Thecurrent study proposed a new technique "estimated droop control" for inverter design.The conventional droop control technique which was already used in inverter design, hasdiculty in synchronizing parallel connected inverters with dierent droop gains and lineimpedances. The proposed "estimated droop control" does not use any predened droopvalues for inverters and all inverters are responsible for the estimation of their own droopvalues with respect to their output power. Therefore, inverters are not bound to usesame and static droop values which are considered as a vital communication link. Theproposed design methodology has made inverters independent from this only virtual linkof communication due to which the reliability of a system has increased. The proposeddesign technique has given very good results in a simulation run. When the Simulinkmodel was run in parallel connected inverter with dierent line impedances, it was asuccess as both inverters started operating with same droop values as they were sharingan equal load. The most important test was with dierent line impedances because inconventional droop control it is dicult for inverters to keep their synchronism withdierent line impedances and an unequal load sharing make inverters to deviate fromtheir nominal values and to generate dierent tracking signals for each set. This problemhas been successfully solved with estimated droop control as in this method each inverterset its droop gains according to its output power, which helps an inverter to operate atnominal values with dierent droop gains and line impedance.

  • 2.
    Ahmed, Naeem
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Cooperative Spectrum Sensing for Cognitive Radio Networks2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The great developments in the field of wireless communications that has been accelerated by the commercial need for better services has led to the application of wireless systems in many fields of life. The effect of wireless technology is much widened, like for safety applications, home automation, smart grid control, medical wearable, embedded wireless devices, entertainment systems etc.

    Direct and indirect surveillance of spectrum treatment has acknowledged the sequential and spatial accessibility of spectrum inside allocated frequency bands. This implies that spectrum deficiency is becoming a main problem. Therefore, spectrum deficiency problem arises here in terms of that most of the licensed primary users are not using their spectrum due to any reason of either geographical variation or temporal basis, and lot of allotted spectrum is unused and under-utilized. Moreover, along with spectrum deficiency problem, other issues are also linked like interference caused by secondary unlicensed users to primary licensed users while sharing the work load among each others, and problem of vacating the spectrum band in less fewer time frames after primary users detection.

    Cognitive networks assure to tackle these spectrum deficiency and other associated problems by accommodating secondary (unlicensed) users, in the spectrum region which is under-utilized. Spectrum Sensing is the prime motivation for cognitive radio and ensures that secondary (unlicensed) users do not propose unbearable levels of interference to primary (licensed) users.

    Cooperative Spectrum Sensing methodologies are still an open window of research. This work is related to cope up the problem of spectrum deficiency and associated problems, by developing an approach for establishment of grouping/clustering between secondary users in a cooperative spectral environment. This approach ensures that members within a group are highly correlated. As a result, the workload on each sensing node within a group is reduced. The effectiveness of this approach depends upon the accuracy of fused decision related to the presence or absence of primary (licensed) user at a particular band (50MHZ to 100MHZ). This approach also depends on the factor that time taken in sensing the primary (licensed) users should be less enough so that decision in vacating the band by the Cognitive Radio secondary users could be taken in fewer time frames. This latter metric is known to be ‘agility’, which eventually comes with the outcome of minimum interference to primary users via their early recognition.

  • 3.
    Ahmed, Umair
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Racing Driver Model in Dymola Vehicle Dynamics Library (VDL): Steering Controller Design2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Racing drivers always want to traverse path at vehicle’s maximum performance limits while keeping the vehicle at its ideal trajectory. The main objective of this report is to elaborate strategy for the path following problem in which driver has to follow the predefined 2D roads. New steering controller design for closed loop racing driver model in Dymola vehicle dynamics library is developed. The methodology proposed by Sharp et al. [2] is followed with the optimal velocity profile that tries to mimic the actions of the real drivers in real time scenarios. Vehicle handling limits i.e. longitudinal and lateral limits are defined before simulation. While travelling in the neighbourhood of optimal velocity on the straight road as well as during the curves, the performance of the steering controller is tested by conducting the test on J turn, Clothoid, Extended chicane and the closing curve path and also tested during the different environment effects e.g. when there is a side wind affecting the vehicle. Performance of existing and new steering controllers discussed and compared in result chapter. It is ensured that the drawbacks in the existing steering controller are eliminated by using the proposed methodology in new implemented steering controller.

    Key Words: Driver Model, Steering Controller, Path following, Velocity profile

  • 4. Aldaeus, Fredrik
    et al.
    Johansson, Lars-Erik
    Jönsson, Mats
    Jonsson, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Lindberg, Ulf
    Roeraade, Johan
    Hamp, Sven
    Escherichia Coli Behavior in an Open Dielectrophoretic Microsystem2004Conference paper (Other (popular science, discussion, etc.))
  • 5. Aldaeus, Fredrik
    et al.
    Yuan, Lin
    Jönsson, Mats
    Johansson, Lars-Erik
    Jonsson, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Roeraade, Johan
    Amberg, Gustav
    Dielectrophoresis of Living Cells - New Concepts and Challenges2005Conference paper (Other (popular science, discussion, etc.))
  • 6. Ali, A
    et al.
    Hoagg, J. B
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Bernstein, D. S
    Growing window recursive quadratic optimization with variable regularization2010Conference paper (Refereed)
  • 7. Andersson, Lars
    et al.
    van Elst, Henk
    Lim, Woei Chet
    Uggla, Claes
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Asymptotic silence of generic cosmological singularities2005In: Phys.Rev.Lett. 94 (2005) 051101Article in journal (Refereed)
    Abstract [en]

    In this letter we investigate the nature of generic cosmological singularities using the framework developed by Uggla et al. We do so by studying the past asymptotic dynamics of general vacuum G2 cosmologies, models that are expected to capture the singular behavior of generic cosmologies with no symmetries at all. In particular, our results indicate that asymptotic silence holds, i.e., that particle horizons along all timelines shrink to zero for generic solutions. Moreover, we provide evidence that spatial derivatives become dynamically insignificant along generic timelines, and that the evolution into the past along such timelines is governed by an asymptotic dynamical system which is associated with an invariant set -- the silent boundary. We also identify an attracting subset on the silent boundary that organizes the oscillatory dynamics of generic timelines in the singular regime. In addition, we discuss the dynamics associated with recurring spike formation

  • 8. Andersson, Lars
    et al.
    van Elst, Henk
    Uggla, Claes
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Gowdy phenomenology in scale-invariant variables2004In: Class.Quant.Grav. 21 (2004) S29-S57Article in journal (Refereed)
    Abstract [en]

    The dynamics of Gowdy vacuum spacetimes is considered in terms of Hubble-normalized scale-invariant variables, using the timelike area temporal gauge. The resulting state space formulation provides for a simple mechanism for the formation of ``false'' and ``true spikes'' in the approach to the singularity, and a geometrical formulation for the local attractor

  • 9.
    Andersson, Mattias
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Scalar fields on star graphs2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

     A star graph consists of a vertex to which a set of edges are connected. Such an object can be used to, among other things, model the electromagnetic properties of quantum wires. A scalar field theory is constructed on the star graph and its properties are investigated. It turns out that there exist Kirchoff's rules for the conserved charges in the system leading to restrictions of the possible type of boundary conditions at the vertex. Scale invariant boundary conditions are investigated in detail.

  • 10. Andersson, S.
    et al.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Dissociation of Physisorbed H_ $$2$$ through Low-Energy Electron Scattering Resonances2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, 216101-216105 p.Article in journal (Refereed)
    Abstract [en]

    Electron induced dissociation of physisorbed H2, HD, and D2 proceeds, as we observe in electron energy-loss measurements of the resulting atomic species, with a high quantum efficiency via the 2Σg+ core excited electron scattering resonances. We find that the predominant decay of the temporary H2- state to the neutral excited 3Σu+ parent state, which is intramolecularly antibonding, provides a sufficiently long-lived channel for dissociation to occur with high probability, even in the proximity of a metal surface.

  • 11.
    Andersson, S.
    et al.
    Department of Physics, Göteborg University.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Electron-Induced Desorption of Physisorbed H_ $$2$$ via Resonance Vibrational Excitation2009In: Physical review letters, ISSN 0031-9007, Vol. 102, no Issue 15, 156104- p.Article in journal (Refereed)
    Abstract [en]

    We show by electron energy-loss measurements that desorption of physisorbed H2 and D2 induced by low-energy electrons takes place with large cross sections, predominantly via resonance excitation of the molecule-surface vibrational mode. The observed H2, D2 cross-section ratio supports a picture where rotation-translation conversion of the resonance excited j=0→2 rotational transition contributes to the desorption of H2, while this channel is energetically closed for D2

  • 12.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Bernasik, Andrzej
    Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, Krakow 30–059, Poland.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Characterisation of vertical phase separation in polymer: fullerene blend films for photovoltaics by dSIMS and NEXAFS2011In: E-MRS 2011 Spring Meeting: Bilateral Energy Conference, Malden, MA: John Wiley & Sons, 2011, 62-63 p.Conference paper (Refereed)
    Abstract [en]

    Morphological control and characterization of blend films is key in the development of viable polymer solar cells. Spontaneous formation of vertical compositional gradients during solution processing has been shown for polyfluorene:PCBM blends and rationalized with thermodynamic and kinetic models of nucleation and spinodal decomposition.[1, 2] The extent of vertical stratification is affected by polymer side-chain modification aimed at controlling polymer:fullerene miscibility.[3] Here we present high-resolution film morphology results for several polymer:fullerene systems as obtained from near-edge X-ray fine structure spectroscopy (NEXAFS) in partial and in total electron yield modes. Blend films were found to be polymer- enriched at the surface. Dynamic secondary ion mass spectrometry (dSIMS) and NEXAFS give compositional information at different depths, resulting in a more complete picture of the film morphology.

     

  • 13.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Budkowski, Andrzej
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Polymer solar cells: Visualizing vertical phase separation in solution-processed films of polymer fullerene blends2012In: Proceedings of the 5th International Symposium Technologies for Polymer Electronics - TPE 12 / [ed] Hans-Klaus Roth, Klaus Heinemann, Ilmenau, Germany: Universitätsverlag Ilmenau , 2012, 125-128 p.Conference paper (Refereed)
  • 14.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Molecular Orientation and Composition at the Surface of Spin-Coated Polyfluorene:Fullerene Blend Films2013In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 51, no 3, 176-182 p.Article in journal (Refereed)
    Abstract [en]

    The surface composition in spin-coated films of polyfluorene:fullerene blends was determined quantitatively by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable-angle NEXAFS. Blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] with [6,6]-phenyl-C61-butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin-coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane-on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished

  • 15.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Photodegradation of the electronic structure of PCBM and C60 films in air2016In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 652, 220-224 p.Article in journal (Refereed)
    Abstract [en]

    Fullerenes are common electron acceptors in organic solar cells. Here the photostability in air of the electronic structures of spin-coated PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and evaporated C60 films are studied using ultraviolet photoelectron spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. After exposing these materials in air to simulated sunlight, the filled and empty molecular orbitals are strongly altered, indicating that the conjugated π-system of the C60-cage has degraded. Even a few minutes in normal lab light induces changes. These results stress the importance of protecting fullerene-based films from light and air during processing, operation, and storage.

  • 16.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wang, Ergang
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Hörmann, Ulrich
    Institute of Physics, Augsburg University.
    Opitz, Andreas
    Institute of Physics, Augsburg University.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Surface Organization in Thin-Films of Conjugated Polymers for Organic Photovoltaics2011Conference paper (Other academic)
  • 17.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wang, Ergang
    Chalmers University of Technology.
    Andersson, Mats R.
    Chalmers University of Technology.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Molecular orientation and composition at the surface of APFO3:PCBM blend films2012In: Hybrid and Organics Photovoltaics Conference: Uppsala, Sweden, 2012 / [ed] Anders Hagfeldt, SEFIN, Castelló (Spain), 2012, 278- p.Conference paper (Refereed)
  • 18.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Lindgren, Lars
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Rysz, Jakub
    Institute of Physics, Jagiellonian University, Poland.
    Bernasik, Andrzej
    Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Poland.
    Budkowski, Andrzej
    Institute of Physics, Jagiellonian University, Poland.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Tuning the Vertical Phase Separation in Polyfluorene:Fullerene Blend Films by Polymer Functionalization2011In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 23, no 9, 2295-2302 p.Article in journal (Refereed)
    Abstract [en]

    Achieving control over the nanomorphology of blend films of the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester, PCBM, with light-absorbing conjugated polymers is an important challenge in the development of efficient solution-processed photovoltaics. Here, three new polyfluorene copolymers are presented, tailored for enhanced miscibility with the fullerene through the introduction of polymer segments with modified side chains, which enhance the polymer’s polar character. The composition of the spincoated polymer:PCBM films is analyzed with dynamic secondary ion mass spectrometry (dSIMS). The dSIMS depth profiles demonstrate compositional variations perpendicular to the surface plane, as a result of vertical phase separation, directed by the substrate. These variations propagate to a higher degree through the film for the polymers with a larger fraction of modified side chains. The surface composition of the films is studied by Near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Quantitative analysis of the NEXAFS spectra through a linear combination fit with the spectra of the pure components yields the surface composition. The resulting blend ratios reveal polymer-enrichment of the film surface for all three blends, which also becomes stronger as the polar character of the polymer increases. Comparison of the NEXAFS spectra collected with two different sampling depths shows that the vertical composition gradient builds up already in the first nanometers underneath the surface of the films. The results obtained with this new series of polymers shed light on the onset of formation of lamellar structures in thin polymer:PCBM films prepared from highly volatile solvents

  • 19.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Lindgren, Lars
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Hörmann, Ulrich
    Institute of Physics, University of Augsburg.
    Brütting, Wolfgang
    Institute of Physics, University of Augsburg.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Opitz, Andreas
    Institute of Physics, Humboldt University Berlin.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Polyfluorene copolymers with functionalized side chains: Opto-electronic properties and solar cell performance2012Manuscript (preprint) (Other academic)
  • 20.
    Anselmo, Ana Sofia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Morphology of Thin-Films of Polyfluorene: Fullerene Blends2008In: 1st Portuguese Young Chemists Meeting, PYCheM: Abstracts, 2008, 36-36 p.Conference paper (Refereed)
  • 21.
    Arntsson, Timmy
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Elnätet och dess anpassning för elektriska fordon: En studie av hur ett lokalnät påverkas av ett ökat antal elektriska fordon2015Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    The availability of non-renewable fuels is decreasing and therefore the prices of both petrol and diesel has increased in recent years. As a result more and more chooses to invest in cars powered by alternative fuels and the focus has long been on electric vehicles. However, this means greater weight on utility companies around the world which now have to adjust to a higher demand. The purpose of this study is to investigate how a local network are affected by electric car chargers and be able to describe the degree to which a low-voltage can be loaded with electric car chargers for commercial and private use, in order to provide recommendations for the future dimension of the local networks. Few studies have been conducted regarding electric cars from a network and supply perspective, but have instead been focused on energy storage in the actual vehicle. Therefore, this study has been processed with an electricity grid perspective.

    The intent of the study has been answered by both a measurement and several simulations. The study is based on Karlstad’s local electrical network and the commercial charging station Tesla in Våxnäs, Karlstad. The parameters of power quality for which this study has taken into account are load of the transformers, load loss, power factor, efficiency, voltage levels, voltage drop and asymmetry.

    The methodological conditions have led to a result that can be used as a basis for an expansion of electric cars, big or small. The measurement was of great support to get an overall view of how the characteristics of a charging session appeared and how the quality parameters were affected during high as well as low power charging. Limitations within the simulation program have led to the calculations to carry out in a more extreme scenario when it comes to the load. A result since the simulation time for constant power was minimum one hour.

    Based on the measurement and simulations of the charging station for commercial use is dimensioned well to cope with the current use of electric vehicle charging. More municipalities should follow Karlstad’s example for the development of commercial charging stations. In the countryside great problems occurred, especially with voltage drop at an increased use of home chargers for electric cars. The same problems emerged in the city part of the network. The study also showed serious problems with asymmetry in the city. The report concluded, therefore, several recommendations for the future dimension of local networks for private homes, for example that the local network should be divided into multiple trails.

  • 22. Avizzano, C.A.
    et al.
    Raspolli, M.
    Solis, Jorge
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Marcheshi, S.
    Bergamasco, M.
    Haptic Desktop for Office Automation and Assisted Design2005In: Proceedings of the 2005 IEEE International Conference on Robotics and Automation, IEEE conference proceedings, 2005, 4086-4091 p.Conference paper (Refereed)
    Abstract [en]

    The present paper describes the conceptual and technical design of a new multimodal device named Haptic Desktop System (HDS). Haptic Desktop System is an integrated system, which merges haptic functionalities, and VDT systems into one. Specific care has been given to HDS design for enhancing and improving human-computer interaction from the following points of view: esthetical, ergonomic and functional. In order to improve the quality of the interaction, the HDS fully integrates proprioceptive, visual, audio and haptic functionalities, into a desk while minimizing the visual interference of the physical components. In the proposed approach classic input devices (i.e. keyboard and mouse) have been replaced by new features integrated within audio and haptic. Such features allow commanding and rendering natural force stimuli in such a way that they are completely coherent and co-located with respect to the visual information. The new features of the HDS are designed for reducing considerably the mental load required to the users during interaction operations. In the present paper the design guidelines and the achieved results are reported

  • 23. Avizzano, C.A.
    et al.
    Solis, Jorge
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Frisoli, A.
    Bergamasco, M.
    Motor Learning Skill Experiments Using Haptic Interface Capabilities2002In: 11th IEEE International Workshop on Robot and Human Interactive Communication. Proceedings., IEEE , 2002, 198-203 p.Conference paper (Refereed)
    Abstract [en]

    This paper investigated the influence that proportional feedback programmed into haptic interface (HI) can have in the development of motor skills. The haptic interface design, adapted to the task to be performed, plays a key role inside motor learning processes as the kinesthetic and proprioceptive are the information pathway in the perception of incoming stimuli. Subjects learned to draw a shape using two kinds of training methods: visual, visual and haptic. The error position distance was measured and a statistical analysis was done in order to identify user's motion improvement when training trials were alternated with practice trials. In order to constraint the user to draw a predefined path, a control law is presented.

  • 24.
    Baladi, Jibran
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Khan, Naeem ullah
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Analysis and Reporting of the control tests conducted in connection withcommissioning for control systemupgrade at Ringhals 2.2013Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    This master thesis project was carried out at Ringhals AB Unit 2. It is focused on modeling and introducing a new control strategy for control loop 21414V141/131 which is a condensate water system. Existing control strategy of the selected control loop is simple feedback control system with one PID controller. Results of current control strategy were taken into account for improvements in terms o f system stability, valve movements and unwanted transients. Problems found in selected loop were; large variations in process variable, extra movement in valve positions and inefficient opening of valves.Simulation model with similar control strategy and results as of real power plant was createdand validated, as new control strategy can be applied and results can be compared. The main recommendation to improve the control system performance was found through cascade control strategy that could assist the current controller. The recommendation was evaluated by designing and implementing the cascade control strategy on the Dymola simulation model. Simulation results pointed out considerable increase in system performanceaccording to the requirements of Vattenfall AB.

  • 25. Bellman, J.
    et al.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Andersson, S.
    Molecular Hydrogen Adsorption at surface adatoms2006In: Journal of Chemical PhysicsArticle in journal (Refereed)
  • 26. Benckert, Sylvia
    et al.
    Enghag, Margareta
    Gustafsson, Peter
    Johansson, Ove
    Jonsson, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Norman, Robert
    Petersson, Sune
    Diskutera fysik i grupp! Utgå från kontextrika problem2007Book (Refereed)
  • 27. Bengtsson, L.
    et al.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Hassel, M.
    Bellman, J.
    Persson, M.
    Andersson, S.
    H_{2} adsorbed in a two-dimensional quantum rotor state on a stepped copper surface2000In: Physical Review BArticle in journal (Refereed)
  • 28.
    Bengtsson, P.
    et al.
    Nanofactory Instruments AB.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Olin, H.
    Applied scicence and design, Mid Sweden University.
    Von Dorrien, M.
    Nanofactory Instruments AB.
    Control Signal for Inertial Slider2008Patent (Other (popular science, discussion, etc.))
  • 29. Bengtsson, P.
    et al.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Olin, H.
    von Dorrien, M.
    Control signal for inertial slider2007Patent (Other (popular science, discussion, etc.))
  • 30.
    Bergström, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Carling, Karin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Andersson, J
    Secondary hardening carbides in hot work tool steels analyzed by TEM2009In: / [ed] P beiss, C Brockmann, S Franke, B Keysselitz, Aachen: Verlag mainz, Wissenschaftsverlag , 2009Conference paper (Refereed)
  • 31.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    An example of what one teacher focuses when teaching the technology subject in Swedish compulsory school2005Conference paper (Refereed)
  • 32.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    En levande tradition: Teknik i år 7, 8 och 92005In: KAPET, 1(1), 43-58Article in journal (Other academic)
  • 33.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Holistic learning in the dual education system: A study of technical vocational education in upper secondary school2010Conference paper (Refereed)
  • 34.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Holistiskt lärande i dubbelt utbildningssystem: En studie av teknisk gymnasial yrkesutbildning2010Conference paper (Other (popular science, discussion, etc.))
  • 35.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Reasons for choosing a technically oriented education: An interview study within the fields of pipefitting and industry2012In: International journal of technology and design education, ISSN 0957-7572, E-ISSN 1573-1804, Vol. 22, no 3, 377-397 p.Article in journal (Refereed)
    Abstract [en]

    The article examines how professionals within technical businesses describe their ways into their trade and why they have remained. Semi-structured interviews, analyzed by analysis of narratives, have been conducted with six informants within pipefitting and industrial work aiming to understand how technically oriented professions can attract young potentials into the field. The results from the study are thus a contribution within the field of vocational education, in order to understand why youths should consider to study the Energy Programme or the Industry Programme at upper secondary school. The results show that factors that influence people to start working within technically oriented trades are:

    1. to use your hands to screw things together,
    2. to get an income and
    3. if relatives work in the branch.

    Based on the study it is not obvious to young people what they want to do when they have graduated. But the study also shows that even though the choice of careers is not obvious from the beginning people who chose the field of pipefitting or industry remain for many years.This implies that programmes for recruitment could use the advantages shown in this study for arguments to increase the amount of students who chose the technically oriented educations. The reasons for staying in the professions are:

    1. variation and freedom,
    2. creativity and influence and
    3. you get to work with your hands.

    This significant content within the technically oriented trades contribute with specific arguments for promotion of the plumbing and industrial work in particular and also for the technical trades and technical education in general.

  • 36.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Same syllabus - different kinds of subject2007Conference paper (Refereed)
  • 37.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Teknikdidaktik2011Book (Refereed)
  • 38.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Teknikundervisning i den svenska grundskolan: elever, lärare och styrdokumenten2004Conference paper (Other (popular science, discussion, etc.))
  • 39.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Teknikundervisning i den svenska skolan2004In: Utbilder, 1, 10-11 p.Article in journal (Other (popular science, discussion, etc.))
  • 40.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Teknikämnets gestaltningar: En studie av lärares arbete i skolämnet teknik2008Doctoral thesis, monograph (Other academic)
    Abstract [sv]

    Teknikämnets gestaltningar handlar om lärares arbete med skolämnet teknik i den svenska grundskolans senare år (7-9). Studien bygger på intervjuer med fem lärare och på observationer av deras undervisningspraktik. Studien undersöker hur lärare förstår begreppet teknik och skolämnet teknik. Den undersöker också vad lärare väljer för ämnesinnehåll i teknik och hur de arbetar med detta samt vilka förmågor elever erbjuds att utveckla i ämnet teknik. Avhandlingens forskningsansats är empiriskt grundad i teknikämnets undervisningspraktik och studiens empiriska analyser grundas i narrativ analys och variationsteori.

    Det fanns ett gemensamt element i lärarnas sätt att förstå begreppet teknik: Teknik är saker som människan utvecklat för att uppfylla praktiska behov. När det gäller lärarnas sätt att förstå skolämnet teknik skiljde de sig åt mellan att förstå syftet med teknikämnet som att: (1) träna hantverksskicklighet, (2) förbereda eleverna för framtida karriärer som ingenjörer, (3) tillämpa naturvetenskap, (4) stärka flickors självförtroende och (5) intressera framtida tekniker och uppfinnare.

    Vidare tyder studien på att teknikundervisningen specifikt bidrar till att utveckla tre förmågor hos eleverna: (1) att värdera och testa funktionalitet, (2) precision och noggrannhet och (3) att bygga, konstruera och montera. De tre förmågorna tränades enbart med undervisningsinnehåll av praktisk karaktär. Den variationsteoretiska analysen visar att variationsmönstret kontrastering lämpar sig bra i ett produktionsperspektiv där det kostar att göra fel.

    Studiens övergripande resultat visar att lärares tolkningar av de officiella styrdokumenten, i kombination med deras val av undervisningsinnehåll och undervisningsmetoder, påverkar vad elever erbjuds att lära i skolämnet teknik.

    Den här studien visar att det saknas verklighetsanknytning i grundskolans teknikundervisning. För att elever ska få möjlighet att utveckla en medvetenhet om vikten av utbildning i teknikämnet, som en nyckelfaktor för framtida utveckling vad gäller natur, människa och samhälle, är det uppenbart att betydelsen av den svenska grundskolans teknikämne behöver mer uppmärksamhet från de nationella utbildningsmyndigheterna.

  • 41.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Vad, varför och hur?: En studie av handledning av examensarbeten inom naturvetenskap och teknik2010Conference paper (Other (popular science, discussion, etc.))
  • 42.
    Bjurulf, Veronica
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    What kinds of variation are made available in technology education?2006Conference paper (Refereed)
    Abstract [en]

    Five teachers from the Swedish compulsory school were interviewed about technology

    and technology as a subject in school. One field of work for each of the teachers was

    observed. The analysis is under work based on the variation theory. The aim of this

    paper is to present what kinds of variation that are made available in two teachers

    classrooms. Examples from the data show that there are different kinds of variation in

    Johns1 and Gustavs teaching, but one kind more frequent than others. In Gustavs case

    the principle-apply variation is most common, which means that there is a

    fundamental idea needed to be understood by the students, for them to be capable to

    make suitable choices and/or acts. In Johns case the most frequent kind of variation is

    the example variation. It means that the examples of a specific aspect vary. Interesting

    to discuss is how these results affect the shape of the technology subject in the two

    teachers classrooms

  • 43.
    Bjurulf, Veronica
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Kilbrink, Nina
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Different kinds of transfer in Technical Vocational Education2011In: PATT25: Cript 8: Perspectives on Learning in Design & Technology Education / [ed] Kay, Stables; Clare Benson; Marc de Vries, London: Goldsmiths University of London , 2011, 231-235 p.Conference paper (Other academic)
  • 44.
    Bjurulf, Veronica
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Kilbrink, Nina
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Technology in Education: Ongoing research2006Conference paper (Refereed)
  • 45.
    Bjurulf, Veronica
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Kilbrink, Nina
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    The Importance of Interweaving Theoretical and Practical Tasks in Technology education2008In: Exploring technology education: solutions to issues in a globalised world : proceedings of the 5th Biennial International Conference on Technology Education Research held at the Crowne Plaza Surfers Paradise, Australia, 27-29 November 2008, Griffith University , 2008, 27-34 p.Conference paper (Refereed)
  • 46.
    Bjurulf, Veronica
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Kilbrink, Nina
    Karlstad University, Faculty of Arts and Education, Department of Education.
    Segolsson, Mikael
    Ämnet teknik i grundskolan - med empiriska exempel2009In: Ämnesdidaktiska brobyggen: didaktiska perspektiv inom lärande och forskning, Karlstad: Karlstad University Press , 2009, 100-109 p.Chapter in book (Other academic)
  • 47.
    Bjurulf, Veronica
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Rovio-Johansson, Airi
    External and internal Perspectives on Learning Object: Emergent Knowledge for Teachers Professionalization2009Conference paper (Other (popular science, discussion, etc.))
    Abstract

    The purpose is to investigate how teachers are using the subject content in order to develop students understanding of the learning object and their capabilities according to the curricula. The theoretical and the conceptual frame of the studies is the phenomenographic research approach and the variation theory, a learning theory. The variation theory is a general theory about the specific content. On the one hand the analytical tools of the variation theory are possible to use in the analysis of the teachers way of working with the learning object. On the other hand, the theory sets out to uncover the different ways in which students experiences the learning object (Marton and Booth, 1997; Marton and Tsui, 2004; Lo et al., 2005, Rovio-Johansson, A. and Lumsden, M., 2007). Two examples from different studies are used to illustrate (1) the teachers way of moulding a learning object in teaching technology in compulsory school and (2) students understanding of the learning object identified in a problem solving process in an examination in Management accounting during their second semester at higher education.

    In the first example empirical data are collected from five teachers teaching technology at Swedish junior high schools, pupils aged 13-15 (Bjurulf, 2008). Variation theory was applied as a tool in the analysis of the data from the classroom observations, i.e. the teachers ways of working with the subject matter. The analysis indicated that the most frequently used pattern of variation was contrast. Through the contrast-pattern the teachers managed to contrast better or worse alternatives of construction and the use artefacts. It can be argued that this contrast-pattern of variation is the proper pattern when pupils are working with limited or expensive material. Results also indicated that technology as a school subject was taught in different ways depending on the teachers educational background, the physical learning environment and the size of the school class.

    In the second example, empirical data are collected from a sample of students taking part in a Swedish three year undergraduate programme in Business, during their second semester (Rovio-Johansson and Johansson, 2006). The study uses the theoretical framework of variation theory and focuses on the students understandings of a basic concept in Management accounting during students second semester. Drawing on extensive interview material of semi-structured interviews and students´ solutions of a specific examination problem, the analysis revealed three qualitatively different categories illustrating in which ways the students understood the concept return on investment. The learning object and its critical aspects were identified as qualitative categories of descriptions, hierarchically organised.

    The empirically grounded didactic knowledge indicates that educationally critical aspects of the learning object, observed by the researcher or experienced by the students, may aid educators and teachers how to reorganize curricula, courses and teaching in order to enhance the quality of learning and teaching opportunities offered the students. Implications of the findings are promoted as means to accomplish further investigations of teachers ways of using the subject matter and students understanding of the learning object in subject matter areas.

  • 48.
    Björnsson, Jonas
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Strings, Branes and Non-trivial Space-times2008Doctoral thesis, monograph (Other academic)
  • 49.
    Björnsson, Jonas
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Strings, Branes and Non-trivial Space-times2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with different aspects of string and /p/-brane theories. One of the motivations for string theory is to unify the forces in nature and produce a quantum theory of gravity. /p/-branes and related objects arise in string theory and are related to a non-perturbative definition of the theory. The results of this thesis might help in understanding string theory better. The first part of the thesis introduces and discusses relevant topics for the second part of the thesis which consists of five papers.

    In the three first papers we develop and treat a perturbative approach to relativistic /p/-branes around stretched geometries. The unperturbed theory is described by a string- or particle-like theory. The theory is solved, within perturbation theory, by constructing successive canonical transformations which map the theory to the unperturbed one order by order. The result is used to define a quantum theory which requires for consistency d = 25 + p dimensions for the bosonic /p/-branes and d = 11 for the supermembrane. This is one of the first quantum results for extended objects beyond string theory and is a confirmation of the expectation of an eleven-dimensional quantum membrane.

    The two last papers deal with a gauged WZNW-approach to strings moving on non-trivial space-times. The groups used in the formulation of these models are connected to Hermitian symmetric spaces of non-compact type. We have found that the GKO-construction does not yield a unitary spectrum. We will show that there exists, however, a different approach, the BRST approach, which gives unitarity under certain conditions. This is the first example of a difference between the GKO- and BRST construction. This is one of the first proofs of unitarity of a string theory in a non-trivial non-compact space-time. Furthermore, new critical string theories in dimensions less then 26 or 10 is found for the bosonic and supersymmetric string, respectively.

  • 50. Björnsson, Jonas
    et al.
    Hwang, Stephen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    On small tension p-branes2008In: Physics Letters B 662 (2008) 270-274Article in journal (Refereed)
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