Change search
Refine search result
1234567 1 - 50 of 726
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • apa.csl
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Adamczyk, Krzysztof
    et al.
    Department of Materials Science and Engineering, Trondheim, Norway.
    Søndenå, Rune
    Department for Solar Energy, IFE, Kjeller, Norway.
    Stokkan, Gaute
    Sintef Materials and Chemistry, Trondheim, Norway.
    Looney, Erin
    Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
    Jensen, Mallory
    Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
    Lai, Barry
    Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA.
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Di Sabatino, Marisa
    Department of Materials Science and Engineering, NTNU, A. Getz vei 2B, NO-7491 Trondheim, Norway.
    Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 5, p. 1-6, article id 055705Article in journal (Refereed)
    Abstract [en]

    In this work, we applied internal quantum efficiency mapping to study the recombination activity of grain boundaries in High Performance Multicrystalline Silicon under different processing conditions. Wafers were divided into groups and underwent different thermal processing, consisting of phosphorus diffusion gettering and surface passivation with hydrogen rich layers. After these thermal treatments, wafers were processed into heterojunction with intrinsic thin layer solar cells. Light Beam Induced Current and Electron Backscatter Diffraction were applied to analyse the influence of thermal treatment during standard solar cell processing on different types of grain boundaries. The results show that after cell processing, most random-angle grain boundaries in the material are well passivated, but small-angle grain boundaries are not well passivated. Special cases of coincidence site lattice grain boundaries with high recombination activity are also found. Based on micro-X-ray fluorescence measurements, a change in the contamination level is suggested as the reason behind their increased activity.

    Download full text (pdf)
    fulltext
  • 2.
    Adamczyk, Krzysztof
    et al.
    Department of Materials Science and Engineering, Trondheim, Norway.
    Søndenå, Rune
    Department for Solar Energy, IFE, Kjeller, Norway.
    You, Chang Chuan
    Department for Solar Energy, IFE, Kjeller, Norway.
    Stokkan, Gaute
    Sintef Materials and Chemistry, Trondheim, Norway.
    Lindroos, Jeanette
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Di Sabatino, Marisa
    Department of Materials Science and Engineering, Trondheim, Norway.
    Recombination Strength of Dislocations in High-Performance Multicrystalline/Quasi-Mono Hybrid Wafers During Solar Cell Processing2018In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 215, no 2, article id 1700493Article in journal (Refereed)
    Abstract [en]

    Wafers from a hybrid silicon ingot seeded in part for High Performance Multicrystalline, in part for a quasi-mono structure, are studied in terms of the effect of gettering and hydrogenation on their final Internal Quantum Efficiency.The wafers are thermally processed in different groups – gettered and hydrogenated. Afterwards, a low temperature heterojunction with intrinsic thin layer cell process is applied to minimize the impact of temperature. Such procedure made it possible to study the effect of different processing steps on dislocation clusters in the material using the Light Beam Induced Current technique with a high spatial resolution. The dislocation densities are measuredusing automatic image recognition on polished and etched samples. The dislocation recombination strengths are obtained by a correlation of the IQE with the dislocation density according to the Donolato model. Different clusters are compared after different process steps. The results show that for the middle of the ingot, the gettering step can increase the recombination strength of dislocations by one order of magnitude. A subsequent passivation with layers containing hydrogen can lead to a decrease in the recombination strength to levels lower than in ungettered samples.

    Download full text (pdf)
    fulltext
  • 3.
    Aderne, Rian E.
    et al.
    Pontifícia Universidade Católica do Rio de Janeiro – PUC-Rio, BRA.
    Borges, Bruno Gabriel A. L.
    Universidade Federal do Rio de Janeiro-UFRJ, BRA.
    Avila, Harold C.
    University of Atlantic, COL.
    von Kieseritzky, Fredrik
    Karolinska Institutet.
    Hellberg, Jonas
    Chemtron AB, Sweden.
    Koehler, Marlus
    Universidade Federal do Paraná-UFPR, BRA.
    Cremona, Marco
    Pontifícia Universidade Católica do Rio de Janeiro – PUC-Rio, BRA.
    Roman, Lucimara S.
    Universidade Federal do Paraná-UFPR, BRA.
    Araujo, Moyses C.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University.
    Rocco, Maria Luiza M.
    Universidade Federal do Rio de Janeiro-UFRJ, BRA.
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    On the energy gap determination of organic optoelectronic materials: the case of porphyrin derivatives2022In: Materials Advances, E-ISSN 2633-5409, no 3, p. 1791-1803Article in journal (Refereed)
    Abstract [en]

    The correct determination of the ionization potential (IP) and electron affinity (EA) as well as the energy gap is essential to properly characterize a series of key phenomena related to the applications of organic semiconductors. For example, energy offsets play an essential role in charge separation in organic photovoltaics. Yet there has been a lot of confusion involving the real physical meaning behind those quantities. Experimentally the energy gap can be measured by direct techniques such as UV-Vis absorption, or indirect techniques such as cyclic voltammetry (CV). Another spectroscopic method is the Reflection Electron Energy Loss Spectroscopy (REELS). Regarding data correlation, there is little consensus on how the REELS' energy gap can be interpreted in light of the energies obtained from other methodologies such as CV, UV-Vis, or photoemission. In addition, even data acquired using those traditional techniques has been misinterpreted or applied to derive conclusions beyond the limits imposed by the physics of the measurement. A similar situation also happens when different theoretical approaches are used to assess the energy gap or employed to explain outcomes from experiments. By using a set of porphyrin derivatives as model molecules, we discuss some key aspects of those important issues. The peculiar properties of these porphyrins demonstrate that even straightforward measurements or calculations performed in a group of very similar molecules need a careful interpretation of the outcomes. Differences up to 660 meV (similar to 190 meV) are found comparing REELS (electrochemical) measurements with UV-Vis energy gaps, for instance. From the theoretical point of view, a reasonable agreement with electrochemical measurements of the IP, EA, and the gap of the porphyrins is only obtained when the calculations involve the full thermodynamics of the redox processes. The purpose of this work is to shed light on the differences and similarities of those aforementioned characterization methods and provide some insight that might help one to develop a critical analysis of the different experimental and theoretical methodologies.

    Download full text (pdf)
    fulltext
  • 4.
    Ahlskog, Markus
    et al.
    University Jyvaskyla, FIN.
    Hokkanen, Matti J.
    University Jyvaskyla, FIN.
    Levshov, Dmitry
    Southern Federal University, RUS..
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Volodin, Alexander
    Katholieke University Leuven, BEL.
    van Haesendonck, Chris
    Katholieke University Leuven, BEL.
    Individual arc-discharge synthesized multiwalled carbon nanotubes probed with multiple measurement techniques2020In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Vol. 38, no 4, article id 042804Article in journal (Refereed)
    Abstract [en]

    Arc-discharge synthesized multiwalled carbon nanotubes (AD-MWNT), or related MWNTs, exhibit a good quality compared to the more common type of MWNT synthesized by catalytic chemical vapor deposition methods. Yet experimental measurements on these are rather few and typically have not correlated data from different measurement techniques. Here, the authors report Raman spectroscopy, scanning probe microscopy, conductivity measurements, and force microscopy on single AD-MWNTs. The results demonstrate the high quality of AD-MWNTs and are compatible with the view of them as the best approximation of MWNTs as an assembly of defect-free concentric individual single-walled carbon nanotubes. The authors also demonstrate conductance measurements over a step on the surface of an AD-MWNT, which is due to an abruptly broken outer layer(s), whereby the interlayer resistance is measured.

  • 5.
    ahmad, waqas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Development of algorithm for li-ion batteries in electric vehicles, taking into account SOC, charge control, cell balancing and SOF.2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 6.
    Aimal, Pir
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Mohsin, Main
    Analyzing Voltage control and reactive power support from full power converter wind turbine2011Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Download (pdf)
    cover
  • 7.
    Albinsson, Eric
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Nilsson, Jonathan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Från deponi till lösullsisolering: En undersökning av återbrukspotentialen för isoleringsspill i en husfabrik2022Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    Befolkningen på jorden ökar idag i en ohållbar takt. Dagens samhälle är inte förenligt med den naturresursbas som jorden besitter. Byggbranschen står för en stor del av de utsläpp som bidrar till den globala uppvärmningen. För att minska dessa krävs åtgärder där klimatet sätts i första hand. En del i att minska byggbranschens klimatpåverkan är att återbruka de produkter som redan finns. Den här studien undersöker klimatbesparingen som kan göras genom ett återbruk av isoleringsspill.

    Syftet med arbetet är att öka förståelsen för återbruk och cirkulär ekonomi inom byggprocessen. Studiens mål är att redogöra för den klimatbesparande och ekonomiska potentialen för att förädla mineralullsspill från en husfabrik. I studiens mål ingår det också att utvärdera möjligheterna till en implementering på Häggmarks husfabrik i Sunne.

    Resultatet av studien visar på att det finns flera goda möjligheter till en implementering av processen i en husfabrik. Studien har genomförts med Häggmarks AB i Sunne och Västra Ämtervik. Häggmarks har goda förutsättningar för ett återbruk av isoleringsspill. All byggnation sker inomhus skyddat från fukt. Det finns stora ytor att använda som förvaring samt lokal för en förädlingsprocess.

    Den återbrukade lösullsisoleringen visar på god isoleringsförmåga, en stor klimatbesparing samt en ekonomsik nytta för Häggmarks.

    Download full text (pdf)
    fulltext
  • 8.
    Al-Hilfi, Muna
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013), Science, Mathematics and Engineering Education Research.
    Daniels, Erika
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013), Science, Mathematics and Engineering Education Research.
    Grönområdens betydelse i en förtätad stad: Vilken påverkan har förtätning2020Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Download full text (pdf)
    fulltext
  • 9.
    Alho, Artur
    et al.
    Univ Lisbon, Ctr Math Anal Geometry & Dynam Syst, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Carloni, Sante
    Univ Lisbon, Ctr Multidisciplinar Astrofis CENTRA, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    On dynamical systems approaches and methods in f (R) cosmology2016In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 8, article id 064Article in journal (Refereed)
    Abstract [en]

    We discuss dynamical systems approaches and methods applied to flat Robertson Walker models in f(R)-gravity. We argue that a complete description of the solution space of a model requires a global state space analysis that motivates globally covering state space adapted variables. This is shown explicitly by an illustrative example, f(R) = R + alpha R-2, alpha > 0, for which we introduce new regular dynamical systems on global compactly extended state spaces for the Jordan and Einstein frames. This example also allows us to illustrate several local and global dynamical systems techniques involving, e.g., blow ups of nilpotent fixed points, center manifold analysis, averaging, and use of monotone functions. As a result of applying dynamical systems methods to globally state space adapted dynamical systems formulations, we obtain pictures of the entire solution spaces in both the Jordan and the Einstein frames. This shows, e.g., that due to the domain of the conformal transformation between the Jordan and Einstein frames, not all the solutions in the Jordan frame are completely contained in the Einstein frame. We also make comparisons with previous dynamical systems approaches to f (R) cosmology and discuss their advantages and disadvantages.

  • 10.
    Alho, Artur
    et al.
    University of Lisbon, Portugal.
    Hell, Juliette
    Free University Berlin, Germany.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and asymptotics for monomial scalar field potentials and perfect fluids2015In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 32, no 14, article id 145005Article in journal (Refereed)
    Abstract [en]

    We consider a minimally coupled scalar field with a monomial potential and a perfect fluid in flat Friedmann-Lemaitre-Robertson-Walker cosmology. We apply local and global dynamical systems techniques to a new three-dimensional dynamical systems reformulation of the field equations on a compact state space. This leads to a visual global description of the solution space and asymptotic behavior. At late times we employ averaging techniques to prove statements about how the relationship between the equation of state of the fluid and the monomial exponent of the scalar field affects asymptotic source dominance and asymptotic manifest self-similarity breaking. We also situate the ’attractor’ solution in the three-dimensional state space and show that it corresponds to the one-dimensional unstable center manifold of a de Sitter fixed point, located on an unphysical boundary associated with the dynamics at early times. By deriving a center manifold expansion we obtain approximate expressions for the attractor solution. We subsequently improve the accuracy and range of the approximation by means of Pade approximants and compare with the slow-roll approximation. 

  • 11.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Lim, Woei Chet
    University of Waikato, New Zealand.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Cosmological global dynamical systems analysis2022In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 39, no 14, p. 1-14, article id 145010Article in journal (Refereed)
    Abstract [en]

    We consider a dynamical systems formulation for models with an exponential scalar field and matter with a linear equation of state in a spatially flat and isotropic spacetime. In contrast to earlier work, which only considered linear hyperbolic fixed point analysis, we do a center manifold analysis of the non-hyperbolic fixed points associated with bifurcations. More importantly though, we construct monotonic functions and a Dulac function. Together with the complete local fixed point analysis this leads to proofs that describe the entire global dynamics of these models, thereby complementing previous local results in the literature. 

    Download full text (pdf)
    fulltext
  • 12.
    Alho, Artur
    et al.
    Technical University of Lisbon, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and inflationary center manifold and slow-roll approximants2015In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 56, no 1, article id 012502Article in journal (Refereed)
    Abstract [en]

    We consider the familiar problem of a minimally coupled scalar field with quadratic potential in flat Friedmann-Lemaître-Robertson-Walker cosmology to illustrate a number of techniques and tools, which can be applied to a wide range of scalar field potentials and problems in, e.g., modified gravity. We present a global and regular dynamical systems description that yields a global understanding of the solution space, including asymptotic features. We introduce dynamical systems techniques such as center manifold expansions and use Padé approximants to obtain improved approximations for the “attractor solution” at early times. We also show that future asymptotic behavior is associated with a limit cycle, which shows that manifest self-similarity is asymptotically broken toward the future and gives approximate expressions for this behavior. We then combine these results to obtain global approximations for the attractor solution, which, e.g., might be used in the context of global measures. In addition, we elucidate the connection between slow-roll based approximations and the attractor solution, and compare these approximations with the center manifold based approximants.

  • 13.
    Alho, Artur
    et al.
    Center for Mathematical Analysis, Geometry and Dynamical Systems, Instituto Superior Técnico, Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Inflationary alpha-attractor cosmology: A global dynamical systems perspective2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 8, article id 083517Article in journal (Refereed)
    Abstract [en]

    We study flat Friedmann-Lemaitre-Robertson-Walker alpha-attractor E- and T-models by introducing a dynamical systems framework that yields regularized unconstrained field equations on two-dimensional compact state spaces. This results in both illustrative figures and a complete description of the entire solution spaces of these models, including asymptotics. In particular, it is shown that observational viability, which requires a sufficient number of e-folds, is associated with a particular solution given by a one-dimensional center manifold of a past asymptotic de Sitter state, where the center manifold structure also explains why nearby solutions are attracted to this "inflationary attractor solution." A center manifold expansion yields a description of the inflationary regime with arbitrary analytic accuracy, where the slow-roll approximation asymptotically describes the tangency condition of the center manifold at the asymptotic de Sitter state.

    Download full text (pdf)
    fulltext
  • 14.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Quintessential α-attractor inflation: a dynamical systems analysis2023In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 11, article id 083Article in journal (Refereed)
    Abstract [en]

    The equations for quintessential alpha-attractor inflation with a single scalar field, radiation and matter in a spatially flat FLRW spacetime are recast into a regular dynamical system on a compact state space. This enables a complete description of the solution space of these models. The inflationary attractor solution is shown to correspond to the unstable center manifold of a de Sitter fixed point, and we describe connections between slow-roll and dynamical systems approximations for this solution, including Pade approximants. We also introduce a new method for systematically obtaining initial data for quintessence evolution by using dynamical systems properties; in particular, this method exploits that there exists a radiation dominated line of fixed points with an unstable quintessence attractor submanifold, which plays a role that is reminiscent of that of the inflationary attractor solution for inflation.

  • 15.
    Alho, Artur
    et al.
    Univ Lisbon, Inst Super Tecn, Ctr Math Anal Geometry & Dynam Syst, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Scalar field deformations of Lambda CDM cosmology2015In: Physical Review D, ISSN 1550-7998, Vol. 92, no 10, article id 103502Article in journal (Refereed)
    Abstract [en]

    This paper treats nonrelativistic matter and a scalar field phi with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lemaitre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose global and asymptotic bounds on lambda = -V-1 dV/d phi to obtain viable cosmological models that continuously deform Lambda CDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example.

  • 16.
    Alho, Artur
    et al.
    University Lisbon, PRT.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University Waterloo, CAN.
    Dynamical systems in perturbative scalar field cosmology2020In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 37, no 22, article id 225011Article in journal (Refereed)
    Abstract [en]

    We derive a newregulardynamical system on a three-dimensionalcompactstate space describing linear scalar perturbations of spatially flat Robertson-Walker geometries for relativistic models with a minimally coupled scalar field with an exponential potential. This enables us to construct the global solution space, illustrated with figures, where known solutions are shown to reside on special invariant sets. We also use our dynamical systems approach to obtain new results about the comoving and uniform density curvature perturbations. Finally we show how to extend our approach to more general scalar field potentials. This leads to state spaces where the state space of the models with an exponential potential appears as invariant boundary sets, thereby illustrating their role as building blocks in a hierarchy of increasingly complex cosmological models.

  • 17.
    Alho, Artur
    et al.
    Univ Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    Univ Waterloo, Canada..
    Perturbations of the Lambda-CDM model in a dynamical systems perspective2019In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 9, article id 045Article in journal (Refereed)
    Abstract [en]

    The observational success and simplicity of the ACDM model, and the explicit analytic perturbations thereof, set the standard for any alternative cosmology. It therefore serves as a comparison ground and as a test case for methods which can be extended and applied to other cosmological models. In this paper we introduce dynamical systems and methods to describe linear scalar and tensor perturbations of the ACDM model, which serve as pedagogical examples that show the global illustrative powers of dynamical systems in the context of cosmological perturbations. We also study the asymptotic properties of the shear and Weyl tensors and discuss the validity of the perturbations as approximations to the Einstein field equations. Furthermore, we give a new approximation for the linear growth 5 rate, f (z) = d ln delta/d ln a = Omega(6/11)(m) - 1/70(1-Omega(m))(5/2), where z is the cosmological redshift, Omega(m) = Omega(m)(z), while a is the background scale factor, and show that it is much more accurate than the previous ones in the literature.

  • 18.
    Alho, Artur
    et al.
    Universidade de Lisboa, PRT.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University of Waterloo, CAN.
    Quintessence from a state space perspective2023In: Physics of the Dark Universe, E-ISSN 2212-6864, Vol. 39, article id 101146Article in journal (Refereed)
    Abstract [en]

    We use dynamical systems methods to study quintessence models in a spatially flat and isotropic spacetime with matter and a scalar field with potentials for which lambda(v) = -V,v/V is bounded, thereby going beyond the exponential potential for which lambda(v) is constant. The scalar field equation of state parameter wv plays a central role when comparing quintessence models with observations, but with the dynamical systems used to date wv is an indeterminate, discontinuous, function on the state space in the asymptotically matter dominated regime. Our first main result is the introduction of new variables that lead to a regular dynamical system on a bounded three-dimensional state space on which wv is a regular function. The solution trajectories in the state space then provide a visualization of different types of quintessence evolution, and how initial conditions affect the transition between the matter and scalar field dominated epochs; this is complemented by graphs wv(N), where N is the e-fold time, which enables characterizing different types of quintessence evolution.

  • 19.
    Alho, Artur
    et al.
    Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wainwright, John
    University of Waterloo, Canada.
    Tracking Quintessence2024In: Physics of the Dark Universe, E-ISSN 2212-6864, Vol. 44, article id 101433Article in journal (Refereed)
    Abstract [en]

    Tracking quintessence, in a spatially flat and isotropic space–time with a minimally coupled canonical scalar field and an asymptotically inverse power-law potential V(φ)∝φ−p, p>0, as φ→0, is investigated. This is done by introducing a new three-dimensional regular dynamical system, which enables a rigorous explanation of the tracking feature: (1) The dynamical system has a tracker fixed point T with a two-dimensional stable manifold that pushes an open set of nearby solutions toward a single tracker solution originating from T. (2) All solutions, including the tracker solution and the solutions that track/shadow it, end at a common future attractor fixed point that depends on the potential. Thus, the open set of solutions that shadow the tracker solution share its properties during the tracking quintessence epoch. We also discuss similarities and differences of underlying mechanisms for tracking, thawing and scaling freezing quintessence, and, moreover, we illustrate with state space pictures that all of these types of quintessence exist simultaneously for certain potentials. 

    Download full text (pdf)
    fulltext
  • 20.
    Ali, Asad A.
    et al.
    Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA..
    Hoagg, Jesse B.
    Univ Kentucky, Dept Mech Engn, 151 Ralph G Anderson Bldg, Lexington, KY 40507 USA..
    Mossberg, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Bernstein, Dennis S.
    Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA..
    On the stability and convergence of a sliding-window variable-regularization recursive-least-squares algorithm2016In: International journal of adaptive control and signal processing (Print), ISSN 0890-6327, E-ISSN 1099-1115, Vol. 30, no 5, p. 715-735Article in journal (Refereed)
    Abstract [en]

    A sliding-window variable-regularization recursive-least-squares algorithm is derived, and its convergence properties, computational complexity, and numerical stability are analyzed. The algorithm operates on a finite data window and allows for time-varying regularization in the weighting and the difference between estimates. Numerical examples are provided to compare the performance of this technique with the least mean squares and affine projection algorithms. Copyright (c) 2015 John Wiley & Sons, Ltd.

  • 21.
    Al-Jaff, Mohammed
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    The ZX-Calculus: A graphical calculus for multipartite qubit systems2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis we will give a presentation of a graphical/diagrammatic calculus for quantum systems involving interacting quantum observables such as multi-partite systems of qubits, the ZX-Calculus. Unlike the Hilbert space formulation of quantum mechanics, the ZX-Calculus is based on category theory, more specically on the notion of a compact dagger symmetric monoidal category and as a consequence the graphical language associated with such a category is inherited by the calculus. This enables us to think about and deal with many calculations in quantum computation and information in a purely graphical and intuitive fashion. Although being formulated in a more general mathematical framework, huge parts of the Hilbert space formulation of quantum mechanics can be extracted from the ZX-calculus. In this thesis we will begin by giving a motivation for the need of such a calculus and then key concepts of category theory will be introduced in an intuitive manner in order to understand the ZX-calculus that will be presented afterwards. We then apply the calculus to'model' and describe certain quantum circuits and quantum teleportation.

  • 22. Almotasem, Ahmed
    et al.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holleboom, Thijs Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    A molecular dynamic study on the influence of carbide particles in ferrite on material transfer during nanoscratching of ferritic iron2016In: Proceedings of the 10th International Tool Conference: TOOL, 10th International TOOL Conference : 04th to 07th October 2016, Bratislava, Slovakia / [ed] Simancik, Frantisek, 2016Conference paper (Refereed)
  • 23.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holleboom, Thijs Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Adhesion between ferrite iron-€“iron/cementite countersurfaces: A molecular dynamics study2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, p. 113-120Article in journal (Refereed)
    Abstract [en]

    The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding. 

  • 24.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Department of Physics, Faculty of ScienceAssiut University Assiut Egyp.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013), Science, Mathematics and Engineering Education Research.
    Holleboom, Thijs Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics2017In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, no 3, p. 101-Article in journal (Refereed)
    Abstract [en]

    Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation- mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 angstrom. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.

    Download full text (pdf)
    fulltext
  • 25.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Assiut University, Egypt.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holleboom, Thijs Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching: An atomic level simulation2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 370-371, p. 39-45Article in journal (Refereed)
    Abstract [en]

    In the present work, molecular dynamics simulations were used to investigate the impact of the tool microstructure on the wear behavior of ferrite workpiece during nanoscratching. The tool microstructure was modified by varying the carbide (cementite) contents. The simulation results show that dislocations are the primary mechanism for plastic deformation of the workpiece material. It is found that total dislocation length varies significantly depending on the carbide content in the tool. Furthermore, other tribological phenomena were also observed to depend on the carbide contents. For example, the average value of frictional forces decreased while the normal force increases with increasing carbide contents, and hence the friction coefficient was decreased. Additionally, the shape and size of lateral and frontal pileups are lowered. The structural analysis of the pileup region reveals the loss of long range order and start of amorphisation. The temperature distribution of the pileup regions showed an increase of the pileup temperature when carbide is added into tool. The wear volume is considerably reduced when the carbide content increases. The average scratch hardness was found to decrease and the result was analyzed with the theoretical Taylor hardening model.

  • 26.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Influence of chemical composition on adhesion in metallic contacts2016In: International Journal of Advances in Science Engineering and Technology, ISSN 2321-9009, Vol. 4, no 3, Spl. Iss. 1, p. 229-231Article in journal (Refereed)
    Abstract [en]

    - In sheet metal forming operations, adhesive wear is the main causeof tool damage as sheet material is transferred to the tool surface during the forming operation. Means of reducing adhesive wear are of high interest for the metal forming industry.In the present work, molecular dynamics simulations were used to investigate influence of alloying iron with vanadium on adhesive properties in contact with iron. The results showed that adhesion, quantified by the work of adhesion, decreased as the vanadium content increased. Highest reduction was obtained for 10 at.% vanadium which corresponded to a decrease in adhesive work of approximately 10%.

  • 27.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Posselt, Matthias
    Helmholtz Zentrum Dresden-Rossendorf, Germany.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, p. 231-239Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.

  • 28.
    Almén, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Importance of atomic force microscopy settings for measuring the diameter of carbon nanotubes2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Carbon nanotubes (CNTs) have gathered a lot of interest because of their extraordinary mechanical, electrical and thermal properties and have potential applications in a wide variety of areas such as material-reinforcement and nano-electronics. The properties of nanotubes are dependent on their diameter and methods for determining this using atomic force microscopy (AFM) in tapping mode assume that the measured height of the tubes represent the real diameter. Based on early, faulty calculations, the forces in tapping mode were assumed to be much lower than in contact mode, however it was later shown that forces in tapping mode can at point of impact rival the forces present in contact mode. This means that there is a potential risk of tube deformation during tapping mode measurements, resulting in incorrectly determined diameters. This work studies CNTs deposited on a silicon-substrate to analyze the effect of three common AFM settings (tapping frequency, free oscillation amplitude and setpoint) to determine their effect on measured CNT diameters and recommendations for choosing settings are given.

    Download full text (pdf)
    fulltext
    Download full text (pdf)
    Arkivfil
  • 29.
    Almén, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Photophysics of the polymer acceptor PF5-Y5 in organic photovoltaics: A first principles theory based study2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Non-fullerene Acceptors (NFAs) have gathered a great deal of interest for use inorganic photovoltaics (OPVs) due to recent breakthroughs in their power conversion efficiency and other advantages they offer over their Fullerene-based counterparts.

    In this work, a new promising non-fullerene polymer acceptor, PF5-Y5, have been studied using density functional theory and time-dependent density functional theory; and the effects that oligomer length, geometry relaxation and exchange-correlation interaction has on the exciton binding energies (the difference between optical and fundamental energy gaps) have been investigated.

    Both the fundamental and optical gaps are significantly affected by the choice of functional (i.e., the description of the exchange-correlation interaction). However, it does not appear to significantly impact obtained exciton binding energies as the effects of the fundamental and optical gaps cancel each other out.

    Both the fundamental and optical energy gap are shown to slightly reduce as a function of the oligomer length (~0.1 - 0.3 𝑒𝑉 reduction for each repeated monomer). As both gaps are reduced by a similar amount per repeated monomer, they counteract each other and the total effect that oligomer length has on the exciton binding energy is very low.

    Geometry relaxation and thermal effects showed the largest impact on the fundamental gap and exciton binding energy, with their combined effect resulting in a ~0.5 𝑒𝑉 reduction in binding energy. 

    Download full text (pdf)
    fulltext
    Download full text (pdf)
    Arkivfil
  • 30.
    Alpmarken, Ia
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Studie av tekniska och ekonomiska fördelar av olika lösningar vid instrumentinstallation2015Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    Inom industrin är tendensen att allt mer arbete automatiseras för snabbare, mer kostnadseffektiv samt exaktare tillverkning eller bearbetning. Vid automatisering av en processindustri möts konstruktören av ett flertal utmaningar, i minst att välja vilken installationsmetod som skall användas i det aktuella fallet.Vid en ombyggnation eller tillbyggnad av en existerande processindustri finns ofta begränsningar som styr vilken installationsmetod som kan användas, kunden kan exempelvis önska att den nya installationen utförs på liknande sätt som den tidigare.En nyinstallation kan däremot ge att konstruktören har möjlighet att själv påverka installationsmetod.

    I samarbete med Sweco Industry, ett konsultbolag som bland annat ägnar sig åt att konstruera system för processtyrning åt kunder, samt Valmet, ett företag som konstruerar anläggningar för tillverkning av mjukpapper, har därför en studie utförts för att studera vilken typ av installation som är mest kostnadseffektiv för ett uppbyggt typfall.

    Detta har utförts genom att planera fem installationer för det uppbyggda fallet och jämföra dess delkostnader samt totalkostnader.

    Den installationsmetod som påvisat lägst totalkostnad är en installation med distribuerade I/O-moduler anslutna till styrsystemet via PROFIBUS DP fältbuss.

    Trots en något högre totalkostnad rekommenderas dock en installation medelst fältinstrument anslutna till en fältbuss av lägre nivå då detta medför en störningssäker kommunikation och ger en tidseffektiv installation.

    Download full text (pdf)
    fulltext
  • 31.
    Amiri, Karim
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Konceptutveckling av en lastcykel: Ett projekt med syfte att utveckla en lastcykel för rullstolsburna2022Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    The report deals with a project carried out in connection with the course Examensarbete för höskoleingenjörsexamen i innovationsteknik och design, MSGC36, at Karlstad University. The project was carried out by the student Karim Amiri during the spring semester 2022 and comprises 22.5 credits.

    The aim of the project is to explore and develop a bicycle concept that enables the ability to transport gods, with a focus on people who use assistive devices in everyday life to get around. By getting more people to cycle and accompany the journey, the contact and creation of air pollution can be reduced in the community, leading to increased well-being. The results of the project are limited to work statically environment and not dynamically in practice, where calculations on wheels and how the bicycle behaves in motion are excluded.

    The project builds from the product development process using Double Diamond's phases: Discover, Define, Develop and Deliver. Where the aim is to find the problems and then to find solutions to weave it together into a concept proposal.

    The result of the project is based on a long john cargo bicycle, with a load capacity for one passenger and their wheelchair. With the lack of feasibility study on which manual wheelchairs are popular, it was decided to make a limitation to models Etac Cross 5/6 and Panther U3 with a seat width of 450 mm. The Taxi concept that was selected was justified to be chosen as it is considered that there are no similar ones on the market, that would offer something new and reminiscent of the way of sitting in a car.

    Download full text (pdf)
    fulltext
  • 32.
    Andersson, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Different Styles of Laboratory Work - Different Types of Communication: Students’ talk during laboratory work in upper secondary school physicsManuscript (preprint) (Other academic)
  • 33.
    Andersson, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Laborativt arbete i fysikundervisningen: Något som behöver diskuteras!2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [sv]

    Baksidestext

    I gymnasieskolans kursplaner för ämnet fysik framhålls det undersökande arbetssättet genom att betona att eleverna ska ges förutsättningar att utveckla förmågan att söka svar på frågor, planera, genomföra, tolka och redovisa experiment. Eleverna ska dessutom ges möjligheter att använda sina kunskaper i fysik för att kommunicera, argumentera och presentera slutsatser. Utgångspunkten i den här avhandlingen är att laborationsmomentet skapar en speciell diskurs där eleverna blir aktörer och läraren iträder rollen som observatör. I en sådan miljö skapas förutsättningar för att eleverna på ett naturligt sätt får möjlighet att prata och diskutera fysik, utifrån sina egna förutsättningar. Syftet med denna avhandling är att genom praktikbaserade studier tydliggöra hur fysiklaborationens utformning påverkar elevernas kommunikation och vidare hur eleverna använder språket vid laborationstillfället för att skapa förståelse. Detta bidrar till debatten om fysiklaborationens effektivitet, sett både ur ett undervisnings- och inlärningsperspektiv. Resultaten visar att olika laborationsformer är uppbyggda av liknande aktiviteter, men varierar i tid som ägnas åt de olika aktiviteterna. Aktiviteterna i sin tur skapar samtal av olika karaktär. Olika samtalsformer används för skilda syften. Ett analytiskt ramverk har skapats för att ingående kunna studera hur och vad eleverna talar om både på en lingvistisk och kognitiv nivå.

    Download full text (pdf)
    2015:14
    Download (jpg)
    presentationsbild
  • 34.
    Andersson, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Learning Physics Through Communication During Laboratory Work: An empirical study at upper secondary school2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Laboratory work as a teaching and learning method is given prominence in the Swedish physics curriculum for upper secondary school. It is emphasised that students should be given opportunities to develop the ability to search for answers to questions, plan, conduct, interpret and present results. Moreover, students should also be encouraged to use their physics knowledge to communicate, argument and present conclusions. This thesis is based on the belief that physics laboratory work creates a special discourse, where the student becomes the actor and the teacher becomes the organiser and observer. Such an environment enables students to naturally engage in physics discussions using their own terms. The aim is to explore students’ laboratory work at upper secondary school in-depth, with respect to its design and influence on students’ communication. Through analysis of students’ communication, the purpose is to better understand the physics laboratory work’s possibilities as a teaching and learning method. This will contribute to ongoing debate about the effectiveness of laboratory work. The results show that laboratory work consists of similar activities but differs in amount of time allocated to the different activities. Different types of talk are used for different purposes. An analytical framework has been created to enable deeper investigations of how and what students are talking about at both a linguistic and cognitive level. Moreover, the analysis shows the importance of students acquiring knowledge about physics and understanding the value of using an investigative approach as well as acquiring core content physics knowledge.

    Download full text (pdf)
    fulltext
    Download (jpg)
    preview image
  • 35.
    Andersson, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Open Inquiry-Based Learning in Physics: Students' Communicative Moves Under ScrutinyManuscript (preprint) (Other academic)
  • 36.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Enghag, Margareta
    Stockholms universitet.
    Different Types of Laboratory Work - Different Types of Communication: Students’ talk during laboratory work in upper secondary school physicsManuscript (preprint) (Other academic)
  • 37.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Enghag, Margareta
    Stockholms universitet.
    Student talk during the process of laboratory work of linear motion in school physicsManuscript (preprint) (Other academic)
  • 38.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Enghag, Margareta
    Stockholms universitet.
    The Effectiveness of Laboratory Work in Physics: A Case Study at Upper Secondary School in Sweden2012In: Proceedings of The World Conference on Physics Education 2012: WCPE 2012 / [ed] Mehmet Fatih Taşar, 2012, p. 729-740Conference paper (Refereed)
    Abstract [en]

    The present paper reports on a case study that examined the effectiveness of a practical activity in physics, at a Swedish upper secondary school. A teacher and 19 students participated in the study. The students were observed while working with the topic motion, in a computer based laboratory environment (CBL). This case study is part of an ongoing longitudinal study, about the role of laboratory work with different degrees of freedom. The analysis of interviews, written reports and posttest, shows that the practical work was effective based on Millar’s model. Even so, the students had difficulties expressing what they learned from the activity. This study emphasizes the complexity of planning and conducting laboratory work that is effective, from several different aspects. 

  • 39.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Enghag, Margareta
    Stockholm Univ, Dept Math & Sci Educ, Sci Educ, Stockholm, Sweden.
    The laboratory work style's influence on students' communication2017In: Journal of Baltic Science Education, ISSN 1648-3898, E-ISSN 2538-7138, Vol. 16, no 6, p. 958-979Article in journal (Refereed)
    Abstract [en]

    More knowledge of how the actual design of the laboratory work influence students' communication, is needed to design and implement physics laboratory work lessons. The aim with this quantitative research, conducted at a Swedish upper secondary school, was to explore how the design of the laboratory work affects students' communication. Twenty students divided into five groups participated in this natural case study and were video recorded while performing four practical tasks with the theme uniformly accelerated motion, designed by their teacher. The four workstations were categorised based on three predefined descriptors: outcome, approach and procedure. Students' work at each workstation was coded according to five defined activities: planning, preparing equipment, collecting data, processing data and analysis of results. The activities were thereafter divided into shorter episodes that were coded for three different types of communication: disputational talk, cumulative talk and exploratory talk. The result shows that the amount of exploratory talk students engaged in are influenced by the style of the laboratory work and the character of the activity. Based on these research results, teachers can better accustom the laboratory work to facilitate fruitful physics discussions which endorse students' learning.

    Download full text (pdf)
    fulltext
  • 40.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Enghag, Margareta
    Stockholms universitet.
    The relation between students’ communicative moves during laboratory work in physics and outcomes of their actions2017In: International Journal of Science Education, ISSN 0950-0693, E-ISSN 1464-5289, Vol. 39, no 2, p. 158-180Article in journal (Refereed)
    Abstract [en]

    In this case study, we explore students’ communication during practical work in physics at an upper secondary school in Sweden from a sociocultural perspective. We investigate the relation between the interaction and content of students’ communication and outcomes of their actions, with the purpose of finding new knowledge for informing teachers in their choice of instruction. We make discourse analysis of how students interact but also of what students are discussing in terms of underlying content at a linguistic and cognitive level. Twenty students divided into five groups were video recorded while performing four practical tasks at different stations during laboratory work about motion. An analytical framework was developed and applied for one group to three parts of the transcripts in which three different talk-types occurred. Discursive, content, action and purposive moves in the process were identified for each talk-type at both linguistic and cognitive levels. These moves represent information concerning what the teacher actually assigns students to do, and how students make meaning of the activities. Through these different communicative moves, students experience how laboratory work can enhance their competence to collaborate in a scientific environment with complex practical and theoretical questions to solve quickly. Implications of the findings are discussed. 

  • 41.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). SMEER.
    Haglund, Jesper
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). SMEER.
    Lärarstudenter konkretiserar energi genom energiteater2019In: Forum för forskningsbaserad NT-undervisning: Bidrag från konferensen FobasNT18 13 – 14 mars 2018 i Norrköping / [ed] Karin Stolpe, Gunnar Höst och Andreas Larsson, Linköping: Linköping University Electronic Press, 2019, p. 23-38Conference paper (Other academic)
    Abstract [sv]

    Vid Karlstads universitet har vi sedan hösten 2017 infört energiteater som en aktivitet i fysikkurser på samtliga grund- och ämneslärarutbildningar. Energiteater kan betraktas som en kompletterande undervisnings- och inlärningsform, där studenter förväntas att i mindre grupper tillsammans diskutera och sedan gestalta förekommande energiformer och energiomvandlingar i olika vardagsscenarier. I den här studien har videoinspelningar av en grupps gestaltningar kring två skilda scenarier analyserats i syfte att klargöra på vilket sätt energiteater stimulerar studenternas kommunikation och interaktion. Scenarierna involverarde energiomvandlingar som sker då en studsboll studsar mot marken, respektive de energiomvandlingar som sker i ett snurrande änglaspel. Resultatet visar att energiteater i stor utsträckning stimulerar utforskande samtal mellan studenterna, vilket kan betraktas somen meningsskapande dialog. Aktivitetens karaktär bidrar till att alla deltagare blir aktiva och förtrogna med förekommande energiformer och energiomvandlingar. Planerandet och genomförandet av gestaltningen skapar spontana kvalitativa diskussioner kring flödet av energi mellan olika system, som på ett naturligt sätt motiverar studenterna att vidareutveckla själva gestaltningen. Vi menar att energiteater kan stärka lärarstudenternas egen förståelse av energi, men att den även kan erbjuda en möjlig alternativ undervisningsansats för lärarstudenterna i sin blivande roll som lärare i skolan.

    Download full text (pdf)
    fulltext
  • 42.
    Andersson, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Jonsson, Gunnar
    Mälardalens Högskola Eskilstuna Västerås.
    Primary teacher students' understanding of electromagnetic induction2019Conference paper (Refereed)
    Abstract [en]

    In the present study, a teaching sequence concerning electromagnetic induction was introduced to 24 primary teacher students divided into six groups, in order to provide the students with deeper knowledge about how kinetic energy can be transformed into electricity. The aim of this study was to investigate to what extent these teacher students, developed an understanding of electromagnetic induction, without using a mathematical language. The teaching sequence consisted of a group discussion, a practical exercise, computer simulations and a final didactical group reflection. We used a context rich problem, where students were asked to describe how a wind power plant works. During these discussions, the students realised that some kind of generator was needed, but they did not understand its function and concluded that they as teachers only needed to know that it gives rise to an energy transformation. The practical exercise contributed to a deeper understanding of the observed phenomenon, even though students’ ability to structure their inquiry varied a lot. The computer simulations turned out to be a valuable complement to the practical exercise. The practical experiment, together with the simulation, helped the students to understand how electrical current is produced. Based on our analysis, we can see how the different parts of the teaching activity, together but in different ways, help the students to develop their understanding and view of electromagnetic induction. The students’ final group reflections show how important it is to have good physics content knowledge to be able to value and take advantage of the children’s curiosity.

  • 43.
    Andersson, Johan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Jansson, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Analys av solcellsanläggningar påverkan på elnätet2015Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    Sammanfattning

    Examensarbetet handlar om vilka effekter mikroproduktion i form av solcellsenheter har och kommer att ha på Karlstads elnät. Via flera mätserier har här sammanställts vad som händer med elkvaliteten i nätet och vilka krav som ställs på elnätsbolag och framtida mikroproducenter. Genom bred teoretisk kunskap och praktiskt arbete med ett antal dataprogram har denna rapport arbetats fram och sammanställts. Vid ett flertal tillfällen har upphovsmännen bakom denna rapport gett sig ut i fält för att på plats ta del utav dagens former av solkraft samt också iakttagit arbetet bakom och inför elkvalitetsundersökningar.Syftet har i grunden varit att ge kunskap inför ökande volymer av mikroproduktion och att förbereda för framtida förändringar och ombyggnationer i det lokala elnätet. Arbetet har resulterat i en tydlig bild av att dagens elnät har goda möjligheter att möta en ökning av producenter med låga produktionsnivåer. Det har konstaterats att försiktighet bör tas vid inkoppling av anläggningar vad gäller enfas och trefas. Eftersträvansvärt är att använda trefasinkoppling för att undvika snedbelastningar i nätet.

    Download full text (pdf)
    fulltext
  • 44.
    Andersson, Johannes
    et al.
    Swedish Armed Forces, Stockholm, Sweden.
    Olsson, Henrik
    Elsäkerhetsverket, Kristinehamn, Sweden.
    Theocharis, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Analysis of electromagnetic compatibility in photovoltaic installations validated by site measurements2021In: 2021 IEEE Madrid PowerTech, PowerTech 2021 - Conference Proceedings, IEEE, 2021, article id 9494791Conference paper (Refereed)
    Abstract [en]

    The paper presents an analysis on electromagnetic compatibility issues in photovoltaic installations. The main purpose is a qualitative investigation of the effect of a solar power optimizer in combination to inverter's operation from an electromagnetic compatibility and interference perspective. Extended measurements have been conducted in a real photovoltaic installation in the range of 3-500 MHz. The first series of the measured frequency spectrums are presented in this paper and indicate interference in the lower frequencies due to the optimizer operation that also depend on the operational ON/OFF state of the inverter. In particular, the measured data rise questions regarding the conformity with the regulations of the installations from a systems' perspective while on components level, the individual units might successfully meet the requirements. Finally, the findings are evaluated from a technical point of view by taking into account the European and Swedish regulations about electromagnetic compatibility and interference issues.

  • 45.
    Andersson, Jonatan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    A lattice model for topological phases2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Matter exists in many different phases, for example in solid state or in liquid phase. There are also phases in which the ordering of atoms is the same, but which differ in some other respect, for example ferromagnetic and paramagnetic states. According to Landau's symmetry breaking theory every phase transition is connected to a symmetry breaking process. A solid material has discrete translational symmetry, while liquid phase has continuous translational symmetry. But it has turned out that there also exist phase transitions that can occur without a symmetry breaking. This phenomenon is called topological order. In this thesis we consider one example of a theoretical model constructed on a two dimensional lattice in which one obtains topological order.

    Download full text (pdf)
    fulltext
  • 46.
    Andersson, Jonatan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    AFM study of Micro Fibrllated Cellulose, (MFC) in controlled atmosphere2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, Atomic Force Microscopy (AFM) is used to characterize Micro Fibrillated Cellulose (MFC) produced by two different methods according to their size and shape. For one of these MFC-types, their interaction with the humidity in the atmosphere is investigated and their swelling is calculated. MFC is a relatively new material based on cellulose fibres extracted from wood. This study is performed in co-operation with Stora Enso research centre. Stora Enso is a renewable material company which uses mostly wood based raw materials in their production. The measured swelling is ~ 5 % and depends on the number of elementary fibrils included in the fibre.

    Download full text (pdf)
    fulltext
    Download full text (pdf)
    Arkivfil
  • 47.
    Andersson, Markus
    et al.
    KAU.
    Berg, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Vertikal förskjutning i höga byggnader med träregelstomme: Vertikal förskjutning i lägenhetsskiljande vägg orsakad av momentan belastning och krypning i hammarband samt uttorkning i träregelstomme.2021Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    I Europa har det under de senaste 20 åren skett en snabb utveckling av byggkonstruktioner i trä. Detta till följd av implementeringen av den Europeiska unionens byggproduktdirektiv in i medlemsländernas egen bygglagstiftning. Byggproduktdirektivet har på senare tid ersatts med byggproduktförordningen, Construction Products Regulation, CPR. Övergången till det som idag heter CPR innebar att med mer funktionsbaserade bestämmelser möjliggöra uppförande av högre och större byggnader samtidigt som det främjar den tekniska utvecklingen inom träbyggnation. En limiterande faktor som uppstår vid uppförandet av höga byggnader med träregelstomme är det lokala tryck som uppstår vinkelrätt fiberriktningen i hammarband/syll vilket leder till att en vertikal förskjutning uppstår i byggnaden, något som dels kan äventyra fasadmaterialens väderskyddande egenskaper dels byggnadens funktion i stort.

    Syftet med detta examensarbete är att undersöka hur den teoretiska tryckkraft hammarbanden i ett typhus utsätts för ökar med en ökad belastning från byggnaden samt hur denna tryckkraft påverkar den vertikala förskjutning som uppstår, även effekter av långtidslaster tas med i beräkning av vertikal förskjutning. I examensarbetet jämförs 6 olika varianter av konstruktionslösningar samt en kontroll för att avgöra om avväxlingsregeln har någon inverkan på hammarbandets tryckkraftskapacitet samt den vertikala förskjutningen som uppstår. Arbetet görs för att förbättra möjligheterna till att bygga högre hus med traditionell träregelstomme.

    Resultaten visar att användningen av en avväxlingsregel för öppningar i väggar leder till större deformationer i form av vertikal förskjutning och bör undvikas i höga byggnader med träregelstomme. Användningen av KL-trä som hammarband tillsammans med en avväxlingsregel i konstruktionsvirke visar på lägre vertikal förskjutning samt högre tryckhållfasthet än i de fall där både hammarband samt avväxlingsregel består av konstruktionsvirke, användningen av KL-trä som hammarband ger därför goda förutsättningar för högre byggnader med träregelstomme. Resultaten visar även att fuktkvotsförändringen i trämaterialet spelar en stor roll i den vertikala förskjutning som uppstår i byggnaden, där mellanbjälklagen står för den största vertikala förskjutningen. Resultatet visar att konstruktioner där mellanbjälklaget placeras på väggen bör undvikas och bör i stället fästas in i väggens sida.

    Download full text (pdf)
    fulltext
  • 48.
    Andersson, Oscar
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Influence of primary precipitate shape, size volume fraction and distribution in PM tool steels on galling resistance2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In sheet metal forming (SMF), the major failure reason is galling. Galling is a process of different wear stages that leads to destruction of both the forming tool and the sheet metal working piece and is, because of that, of big economic importance for the SMF industries. Therefore, investigations and researches about how tool steels microstructure affect the tool steels galling resistance is of high priority. In the present work, different carbide properties were studied to find out how their properties affected the tool materials galling resistance. The investigated carbide properties were:

    • Shape and size of the carbides  
    • Carbide volume fraction
    • Carbide distribution in the microstructure

    The investigation included three tools, all made of the PM tool steel S390, that were heattreated differently in order to achieve different carbide properties but still maintain the same hardness. The tools were galling tested in a slider-on-flat-surface (SOFS) tribometer to determine their galling resistances. In a scanning surface electron microscope (SEM) the tools galling marks were analyzed to find explanations for the SOFS tribometer results and the connection to the tools different carbide properties. 

    The investigations most galling resistant tool was the tool that had the microstructure with largest carbides which were distributed at grain boundaries and the second highest carbide volume fraction among the investigated tools.

    Download full text (pdf)
    fulltext
  • 49.
    Andersson, Stig
    et al.
    Göteborgs Universitet.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Excitation and desorption of physisorbed H2 via the 2Σu electron scattering resonance.2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, p. 114703-1-114703-11, article id 114703Article in journal (Refereed)
    Abstract [en]

    Our high-resolution electron energy-loss measurements concern physisorbed H2 and comprise dif- ferential cross sections for the excitation of the internal H2 modes and the H2-surface bonding mode and their combinations and extend over the electron impact energy range of the classical low-energy H2 2Σu resonance. Comparison with corresponding data for the excitation of the internal modes of gas phase H2 reveals that strong elastic electron reflectivity from the Cu(100) substrate profoundly distorts the inelastic scattering pattern for physisorbed H2. We find that this influence can be corrected for and that the resulting peak cross sections agree with the H2 gas phase data, in accordance with theoretical predictions for the excitation of the internal H2 vibration. We have used corrected cross sections for the rotational mode spectra of physisorbed H2, HD, and D2 in a model concerning elec- tron induced desorption via rotation-translation energy conversion. These spectra include transitions from the ground state as well as excited levels of the physisorption potential well. H2 and HD can desorb from all levels while D2, for energetic reason, can only desorb from the excited levels. This model gives a satisfactory account of the observed desorption cross sections and predicts character- istic velocity distributions of the desorbing molecules. The cross section data for H2 and HD reveals that direct bound-free transitions also contribute to the electron induced desorption. 

    Download full text (pdf)
    fulltext
  • 50.
    Andronic, L.
    et al.
    Transilvania University of Braso, Romania.
    Moldarev, D.
    Institute for Energy Technology, Norway.
    Deribew, Dargie
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Karazhanov, S. Z.
    Institute for Energy Technology, Norway.
    Photocatalytic self-cleaning properties of thin films of photochromic yttrium oxyhydride2022In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 316, article id 123599Article in journal (Refereed)
    Abstract [en]

    Oxyhydride of yttrium (YHO) belongs to an emerging class of materials, with oxide and hydride anions sharingthe same sites in the lattice. Under sunlight irradiation, the material is transparent to visible light with trans-parency exceeding 85% and can absorb about 10% of sunlight. Furthermore, increasing light transmittance in thevisible light enhanced the self-cleaning properties of the coated materials, making these materials promisingcandidates for smart windows applications. However, the light-absorbing properties of the materials wereincreased with exposure time, and in the photodarkening state, they can absorb about 40% of sunlight. Kelvinprobe measurements show work function values between 2.9 and 4.2 eV for YHO, depending on the H2/Arpressure in the deposition chamber. Using the Kelvin probe, we demonstrate that the work function decreaseswith decreasing deposition pressure and hydrogen flow. Measurements under solar light reveal a decrease of workfunction by 0.2 eV followed by a slow relaxation with the light off. Moreover, the self-cleaning test shows that theoxyhydroxide thin films have excellent photocatalytic activity and total self-cleaning in 40 h.

1234567 1 - 50 of 726
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • apa.csl
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf