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  • 1.
    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. 

  • 2.
    Baks, Tim
    et al.
    Friesland Campina Research, The Netherlands.
    Boom, Remco
    Wageningen University & Research centre, The Netherlands.
    Devid, Edwin
    Leiden University, The Netherlands.
    Dresselhuis, Diane
    Friesland Campina Research, The Netherlands.
    Falco, Gianmaria
    University of Cologne, Germany .
    de Folter, Julius
    Utrecht University, The Netherlands.
    Leermakers, Frans
    Wageningen University & Research centre, The Netherlands.
    Li, Jianan
    VU University Amsterdam, The Netherlands.
    Muntean, Andrea
    Eindhoven University of Technology, The Netherlands.
    Poortinga, Albert
    Friesland Campina Research, The Netherlands.
    Robijn, Gerard
    Friesland Campina Research, The Netherlands.
    Stoyanov, Simeon
    Unilever R&D, The Netherlands.
    Teapal, Juliane
    Wageningen University & Research centre, The Netherlands.
    van der Voort Maarschalk, Kees
    University of Groningen, The Netherlands.
    Schrödinger's capsule: a (micro) capsulate that is open and closed, almost, at the same time2010In: Proceedings of the Physics with Industry 2010, 11-15 October 2010, Leiden, The Netherlands / [ed] Lorentz Center Leiden, Lorentz Center Leiden , 2010Conference paper (Refereed)
    Abstract [en]

    We exploit different routes for encapsulation of food additives, such as minerals or vitamins, in a polymeric capsule. The added active ingredients should remain inside the capsule for at least a year in an aqueous environment (e.g. a dairy product), since sensory properties or functionality of the ingredients may otherwise be affected. However, after intake the active compound should readily (within 1 h) be released due to the acidic environment in the stomach. First, we propose a phenomenological model in order to study how a polymeric matrix may limit the diffusion of incorporated active molecules. The relation between the release rate of the active compound and its molecular weight is elucidated. Second, the desired capsules may be obtained by specific binding between subunits within the capsule and the active ingredient. We show two examples that rely on this mechanism: amylose-lipid complexes and mixed metal hydroxides. Amylose is able to form inclusion complexes with various types of ligands, including iodine, monoglycerides, fatty acids and alcohols, where the hydrophobic parts of the ligands are entrapped in the hydrophobic helical cavity of amylose. Mixed metal hydroxides are a versatile class of inorganic solids that consist of sheets of metal cations that are octahedrally surrounded by hydroxide molecules. In between these layers anionic species compensate for charge neutrality. In this way, various metal cations (minerals) may be incorporated with a high loading, and negatively charged actives may be placed between the layers. Upon digestion the particles dissolve and the ingredients are digested. Finally, we show that nature has already developed many intriguing capsules.

  • 3.
    Berg, Henrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Radiation exposure to personnel during CT procedures2018Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    During X-ray examinations a large part of the radiation is scattered from the patient, contributing to larger radiation doses to medical staff operating inside the examination room. Ionizing radiation contributes to the risk of developing cancer and hereditary diseases but also to the risk of developing cataract.

     

    The aim of this thesis was to investigate the radiation environment and construct three-dimensional maps of the dose distribution, in a Computed Tomography (CT) room during examinations. 

     

    Air kerma was measured with real time dosimeters while irradiating an anthropomorphic phantom, using the X-ray tube voltages 100, 120 and 140 kV. The effective dose received by protected and unprotected medical staff inside the CT room during radiation exposure was estimated by using spectra from scattered X-ray radiation, a simulation of X-ray spectra and the dose evaluation program PCXMC. The equivalent dose to the eye lens was estimated by using spectra from scattered X-ray radiation and tabulated conversion factors from air kerma to the personal dose equivalent at 0.07 mm depth, Hp(0.07). From the estimated values of the effective dose and equivalent eye lens dose received by medical staff inside the room, three-dimensional dose distribution maps were constructed. The shielding effectiveness of a lead apron regularly used in the room was examined using tube voltages of 100, 120 and 140 kV.

     

    The radiation dose distributions have a maximum closest to the irradiated phantom for most heights except at eye level where the maximum is shifted outwards along the patient table due to strong shielding by the gantry at eye level. The strong shielding of the gantry is noticed for all energy levels and at all heights but is exceptionally noticeable at eye level. The shielding of the patient table is strongest for the lower heights but is also noticeable at eye level which may seem surprising since there were no objects between the phantom and that point. The dose distribution along directions with minimal shielding seems to follow the inverse square law well. The lead apron is effective but its efficiency decreases for higher photon energies which is expected.

     

    From information about the frequency and durations of CT-guided procedures, the estimated annual effective dose is 1.6-2.3 mSv for protected and 14.3-19.8 mSv for unprotected personnel at the operator position. The estimated annual equivalent eye lens dose is 4.7-7.8 mSv at the operator position. All annual doses at the operator position are below the annual threshold values of 20 mSv set by the ICRP.

  • 4.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Conlon, Joseph P.
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Day, Francesca
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Jennings, Nicholas
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Krippendorf, Sven
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Powell, Andrew J.
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Rummel, Markus
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Constraints on Axion-Like Particles from X-ray Observations of NGC12752017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 847, no 101, p. 1-22Article in journal (Refereed)
    Abstract [en]

    Axion-like particle s(ALPs) can induce localized oscillatory modulations in the spectra of photon sources passingthrough astrophysical magneticfields. Ultra-deep Chandraobservations of the Perseus cluster contain over 5 x 105counts from the active galactic nucleus (AGN) of the central cluster galaxy NGC1275 and represent a dataset of extraordinary quality for ALP searches. We use this data set to search for X-ray spectral irregularities fromthe AGN.

  • 5.
    Bertoni, M. I.
    et al.
    Arizona State Univ, USA.
    Sarau, G.
    Germany.
    Fenning, D. P.
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. Frauenhofer ISE, Germany.
    Rose, V.
    USA.
    Maser, J.
    USA.
    Buonassisi, T.
    USA.
    Nano-XRF and micro-Raman Studies of Metal Impurity Decoration around Dislocations in Multicrystalline Silicon2012In: 2012 38TH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC), New York, USA: IEEE, 2012, p. 1613-1616Conference paper (Refereed)
    Abstract [en]

    We push the resolution limits of synchrotron-based nano-X-ray fluorescence mapping below 100 nm to investigate the fundamental differences between benign and deleterious dislocations in multicystalline silicon solar cells. We observe that after processing recombination-active dislocations contain a high degree of nanoscale iron and copper decoration, while recombination-inactive dislocations appear clean. To study the origins of the distinct metal decorations around different dislocations we analyze as-grown samples as well as specimens at different stages of processing. We complement our X-ray studies with micro-Raman mapping to understand the relationship between metallic decoration and stress fields around dislocations.

  • 6.
    Buchberger, Igor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Strings, Gravitons, and Effective Field Theories2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns a range of aspects of theoretical physics. It is composed of two parts. In the first part we motivate our line of research, and introduce and discuss the relevant concepts. In the second part, four research papers are collected. The first paper deals with a possible extension of general relativity, namely the recently discovered classically consistent bimetric theory. In this paper we study the behavior of perturbations of the metric(s) around cosmologically viable background solutions. In the second paper, we explore possibilities for particle physics with low-scale supersymmetry. In particular we consider the addition of supersymmetric higher-dimensional operators to the minimal supersymmetric standard model, and study collider phenomenology in this class of models. The third paper deals with a possible extension of the notion of Lie algebras within category theory. Considering Lie algebras as objects in additive symmetric ribbon categories we define the proper Killing form morphism and explore its role towards a structure theory of Lie algebras in this setting. Finally, the last paper is concerned with the computation of string amplitudes in four dimensional models with reduced supersymmetry. In particular, we develop general techniques to compute amplitudes involving gauge bosons and gravitons and explicitly compute the corresponding three- and four-point functions. On the one hand, these results can be used to extract important pieces of the effective actions that string theory dictates, on the other they can be used as a tool to compute the corresponding field theory amplitudes.

  • 7.
    Enghag, Margareta
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Forsman, Jonas
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Linder, Cedric
    Department of Physics and Astronomy, Uppsala University, Sweden.
    MacKinnon, Allan
    Faculty of Education, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Using a disciplinary discourse lens to explore how representations afford meaning making in a typical wave physics course2013In: International Journal of Science and Mathematics Education, ISSN 1571-0068, E-ISSN 1573-1774, Vol. 11, no 3, p. 625-650Article in journal (Refereed)
    Abstract [en]

    We carried out a case study in a wave physics course at a Swedish university in order to investigate the relations between the representations used in the lessons and the experience of meaning making in interview–discussions. The grounding of these interview–discussions also included obtaining a rich description of the lesson environment in terms of the communicative approaches used and the students’ preferences for modes of representations that best enable meaning making. The background for this grounding was the first two lessons of a 5-week course on wave physics (70 students). The data collection for both the grounding and the principal research questions consisted of video recordings from the first two lessons: a student questionnaire of student preferences for representations (given before and after the course) and video-recorded interview–discussions with students (seven pairs and one on their own). The results characterize the use of communicative approaches, what modes of representation were used in the lectures, and the trend in what representations students’ preferred for meaning making, all in order to illustrate how students engage with these representations with respect to their experienced meaning making. Interesting aspects that emerged from the study are discussed in terms of how representations do not, in themselves, necessarily enable a range of meaning making; that meaning making from representations is critically related to how the representations get situated in the learning environment; and how constellations of modes of disciplinary discourse may be necessary but not always sufficient. Finally, pedagogical comments and further research possibilities are presented.

  • 8.
    Enghag, Margareta
    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. Karlstad University, Faculty of Technology and Science, Materials Science.
    Forsman, Jonas
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Wikman, Susanne
    Andersson, Steffan
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Linder, Cedric
    Department of Physics and Astronomy, Uppsala University, Sweden.
    Student evaluations of themselves as disciplinary practitioners2009Conference paper (Other academic)
  • 9.
    Eriksson, Nathalie
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies.
    Fenomenet fysik som innehåll i förskolans verksamhet: Förskollärarnas uppfattning2017Independent thesis Basic level (professional degree), 210 HE creditsStudent thesis
    Abstract [en]

    The purpose of this study was to ascertain how preschool teachers think the subject of physics is shown in the preschool environment. A comparison was also conducted to see if there was any difference between the preschool teachers view of working with physics depending on when they were educated.

     

    The study was conducted in the form of qualitative semi-structured interviews with active preschool teachers. The interviews were conducted in a calm environment and there was no disturbances. The interviews were used as a foundation to see if the preschool teachers thought they had sufficient knowledge in physics to be able to complete their work. A comparison was made between two newly graduated preschool teachers and two preschool teachers educated in the 1990s.

     

    The results show that the preschool teachers think physics is an interesting subject, but they don’t work with it sufficiently. They believe the reason for that this is insufficient material, lack of time, conflicting colleagues and ignorance.

  • 10.
    Eriksson, Olof
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Radiation exposure to personnel during fluoroscopic procedures: Strålningsmiljö för personal under genomlysningsarbete2018Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    There are about 17 million X-ray procedures performed in Sweden every year. Various methods are used to determine the risk for the patient, and for the staff. The objective of this project was to map X-ray scatter coming out of a patient as a result of interactions between the radiation and body tissue during certain medical procedures that involve fluoroscopy. Flouroscopy is a type of X-ray imaging method that generates a moving picture which allows an operator to view in-body procedures live. A successfully created map of the radiation field can work as a tool for risk analysis concerning the dose of radiation of which the medical staff is exposed to, this parameter will later be described as the effective dose (E). The effective dose is a tool for assessment of the risk of developing lethal cancer due to radiation exposure. This report will also investigate the radiation that reaches the eye lens of the staff, since the maximum recommended dosage for the eye lens has been lowered recently when it was discovered that the eye lens was more sensitive to radiation than previously known. In this report data was collected from radiation exposure situations, and it was concluded that distance is a good protector against radiation, which agree well with theory discussed in the report. Another theory which was discussed in the paper states that positions behind the X-ray tube will be exposed to the highest amount of radiation, this was also proven. The measured data from investigating protective equipment showed that the equipment in place was effective.

  • 11.
    Fuchs, Jürgen
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Schweigert, Christoph
    Hamburg University, Germany.
    Stigner, Carl
    Camatec industriteknik AB Karlstad.
    From non-semisimple Hopf algebras to correlation functions for logarithmic CFT2013In: Journal of Physics A: Mathematical and General, ISSN 0305-4470, E-ISSN 1361-6447, Vol. 46, no 49Article in journal (Refereed)
    Abstract [en]

    We use factorizable finite tensor categories, and specifically the representation categories of factorizable ribbon Hopf algebras H, as a laboratory for exploring bulk correlation functions in local logarithmic conformal field theories. For any ribbon Hopf algebra automorphism ω of H, we present a candidate for the space of bulk fields and endow it with a natural structure of a commutative symmetric Frobenius algebra. We derive an expression for the corresponding bulk partition functions as bilinear combinations of irreducible characters; as a crucial ingredient this involves the Cartan matrix of the category. We also show how for any candidate bulk state space of the type we consider, correlation functions of bulk fields for closed oriented world sheets of any genus can be constructed that are invariant under the natural action of the relevant mapping class group

  • 12.
    Fuchs, Jürgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Schweigert, Christoph
    Hamburg University.
    Valentino, Allessandro
    Hamburg University.
    Bicategories for boundary conditions and for surface defects in 3-d TFT2013In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 321, no 2, p. 543-575Article in journal (Refereed)
    Abstract [en]

    We analyze topological boundary conditions and topological surface defects in three-dimensional topological field theories of Reshetikhin-Turaev type based on arbitrary modular tensor categories. Boundary conditions are described by central functors that lift to trivializations in the Witt group of modular tensor categories. The bicategory of boundary conditions can be described through the bicategory of module categories over any such trivialization. A similar description is obtained for topological surface defects. Using string diagrams for bicategories we also establish a precise relation between special symmetric Frobenius algebras and Wilson lines involving special defects. We compare our results with previous work of Kapustin-Saulina and of Kitaev-Kong on boundary conditions and surface defects in abelian Chern-Simons theories and in Turaev-Viro type TFTs, respectively

  • 13.
    Gustafsson, Marcus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Thermal Contributions and Balances in Flatness Measuring Roll: Modelling of Thermal Balances and Convective Heat Transfer Using CFD2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Devices for measurement of flatness in rolling mills is important to ensure high quality products and fewer strip breaks. One of these devices take the form of a measuring roll, which the strip is guided over after it has exited the reduction stage in the mill. The roll is traditionally used in cold rolling applications, and a desire to move to hot rolling introduces demands for research into the thermal balances that develops under operation. This report aims to create an overview into some of the contributions that make up the thermal balance, namely external convection and friction losses in bearings. Other contributions have been investigated by C. Karlsson (Master of Science thesis, Karlstad University, 2018). The heat transfer coefficients obtained for external convection proved to be too small to sustain reasonable temperatures under operation, if no type of cooling apparatus is utilized. Even with external cooling using pressurized air, the convective heat dissipation is too low, due to efficient strip-to-roll conduction. From the modelling performed in this report, friction losses from bearings can be considered as negligible. A model for describing the thermal balances using Newton’s law of cooling was developed, and related to steady state operating conditions by the use of a correction factor. The factor was obtained by comparing the cooling law with the results of a more precise numerical model. The studies in this project elucidate the critical aspects of the thermal balances and provides a basis for further, more detailed modelling.

  • 14.
    Gustafsson, Oscar
    et al.
    KT.
    Karim, Amir
    Acreo AB, Sweden.
    Berggren, Jesper
    KTH.
    Wang, Qin
    Acreo AB, Sweden.
    Reuterskiöld-Hedlund, Carl
    KTH.
    Ernerheim-Jokumsen, Christopher
    KTH.
    Soldemo, Markus
    KTH.
    Weissenrieder, Jonas
    KTH.
    Persson, Sirpa
    Acreo AB, Sweden.
    Almqvist, Susanne
    Acreo AB, Sweden.
    Ekenberg, Ulf
    KTH.
    Noharet, Bertrand
    Asplund, Carl
    IRnova AB, Sweden.
    Göthelid, Mats
    KTH.
    Andersson, Jan Y.
    Acreo AB, Sweden.
    Hammar, Mattias
    KTH.
    Photoluminescence and photoresponse from InSb/InAs-based quantum dot structures2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 19, p. 21264-21271Article in journal (Refereed)
    Abstract [en]

    InSb-based quantum dots grown by metal-organic vapor-phase epitaxy (MOVPE) on InAs substrates are studied for use as the active material in interband photon detectors. Long-wavelength infrared (LWIR) photoluminescence is demonstrated with peak emission at 8.5 mu m and photoresponse, interpreted to originate from type-II interband transitions in a p-i-n photodiode, was measured up to 6 mu m, both at 80 K. The possibilities and benefits of operation in the LWIR range (8-12 mu m) are discussed and the results suggest that InSb-based quantum dot structures can be suitable candidates for photon detection in the LWIR regime.

  • 15.
    Gustavsson, Anders
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Klimatsimulering av ett kontorsrum: Hur de termiska stigkrafterna påverkar ventilationseffektiviteten2006Independent thesis Basic level (professional degree), 10 points / 15 hpStudent thesis
    Abstract [en]

    Abstract

    In urban societies people spend more and more time indoors, which put great demands on the indoor environment. If the ventilation is to manage the removal of unwanted substances in the indoor air, a good mixing of the air is required. The question arises that, whether the buoyancy forces will counteract a good mixing of the indoor air or not?

    This report aims to clear up the difficulties whether you need to consider the buoyancy forces or not, when adjusting a ventilation unit. For studying the indoor mixing of the air a two dimensional model is constructed in COMSOL Multiphysics. In this model several supply air temperatures is simulated to see how much the temperature affects the mixing of the air.

    The physical relations that are being used in this model is the Navier-Stoke’s equation for Non-Isothermal flow, the relations for General Heat transfer and the relation for Convection and Diffusion. These relations exist as tools in COMSOL Multiphysics.

    It wasn’t possible to get the model to converge at low air velocities, because the model is dependent of accuracy in the field of cm or mm.

    The lowest velocity, in the zone of occupancy, which the model was able to simulate was 0.5 m/s but it takes velocities below 0.2 m/s to fulfill the indoor climate requirements due to the problems concerning draft.

    It was possible to see that the buoyancy forces affect the mixing of the air to a certain degree, despite high air velocities.

    Unfortunately it wasn’t possible to see to what degree you have to consider the buoyancy forces when adjusting a ventilation unit. To see the affects of the buoyancy forces or not, is highly dependent on the velocity of the air. Because the force generated by the supply air increases by the square of the velocity change.

    When constructing a more detailed model, which is a requirement for convergence when having low velocities, the memory of the computer isn’t enough.

    The results of the simulations show that a computer with more calculation capacity, than the Karlstad University can offer, is needed to make a successful simulation.

  • 16.
    Hertz, Hans
    et al.
    KTH.
    von Hofsten, Olov
    KTH.
    Bertilson, Mikael
    KTH.
    Vogt, Ulrich
    KTH.
    Holmberg, Anders
    KTH.
    Reinspach, Julia Antonia
    KTH.
    Martz, Dale
    KTH.
    Selin, Mårten
    KTH.
    Christakou, Athanasia
    KTH.
    Jerlström-Hultqvist, J
    Uppsala University.
    Svärd, S
    Uppsala University.
    Laboratory cryo soft X-ray microscopy2012In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 177, no 2, p. 267-272Article in journal (Refereed)
    Abstract [en]

    Lens-based water-window X-ray microscopy allows two- and three-dimensional (2D and 3D) imaging of intact unstained cells in their near-native state with unprecedented contrast and resolution. Cryofixation is essential to avoid radiation damage to the sample. Present cryo X-ray microscopes rely on synchrotron radiation sources, thereby limiting the accessibility for a wider community of biologists. In the present paper we demonstrate water-window cryo X-ray microscopy with a laboratory-source-based arrangement. The microscope relies on a lambda = 2.48-nm liquid-jet high-brightness laser-plasma source, normal-incidence multilayer condenser optics, 30-nm zone-plate optics, and a cryo sample chamber. We demonstrate 2D imaging of test patterns, and intact unstained yeast, protozoan parasites and mammalian cells. Overview 3D information is obtained by stereo imaging while complete 3D microscopy is provided by full tomographic reconstruction. The laboratory microscope image quality approaches that of the synchrotron microscopes, but with longer exposure times. The experimental image quality is analyzed from a numerical wave-propagation model of the imaging system and a path to reach synchrotron-like exposure times in laboratory microscopy is outlined.

  • 17.
    Jakobsson, Liza
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    ”För att de måste sitta ihop, för att kunna åka in överallt”: En studie om att undersöka förskolebarns uppfattningar om elektricitet2018Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of the study is to determine how pre-school children between the ages of four and six perceive electricity. The study used observation as a method and a field study equipped with a video camera. A semi-structured interview was also conducted to capture the pre-school teacher’s experiences and perceptions of the study. The observation took place on three different occasions: a gathering, a lesson and a reading session. The material used was a fact-based children’s book with associated experimental material and tutorials. The result of the study showed that the children related their knowledge of what electricity is to their daily lives. They could distinguish whether things required electricity,and there was some knowledge that electricity has a source and of electricity's dangers. During the study, pre-school teachers raised both opportunities and challenges to design activities with electricity. The children showed great dedication and general knowledge of electricity and thought that the subject was interesting. There is a need for further education within physics and natural sciences for pre-school teachers. The goal for the pre-school teachers is to create a balance so that each and every child is offered meaningful education.

  • 18.
    Johansson, Adam
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Phased Array System toolbox: An implementation of Radar System: A qualitative study of plane geometry and bearing estimation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 19.
    Kadhim, Yasser
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Metalization of Micro Fibrillated Cellulose (MFC) films2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, two MFC based films Carboxymethylated-Microfibrillated Cellulose (MFC) and Enzymatic-MFC were characterized and metalized in order to improve the barrier properties at high relative humidity. Several methods were used for the characterization process, which were Atomic Force Microscopy (AFM), Contact Angle (CA), Energy Dispersive Spectra (EDS), Light Microscopy (LM), Scanning Electron Microscopy (SEM), and Oxygen Transmission Rate (OTR). Physical Vapor Deposition (PVD) system was used for the metalization of film, a thin layer of aluminium with a thickness of 200 nm was deposited on the films. The results revealed that ENZ-MFC exhibit a higher roughness and lower OTR values, compared to CM-MFC. The contact angle values proved that both non-metalized MFC films exhibited a hydrophilic surface with values around 50 degrees. SEM and EDS images showed that both films exhibited surface defects with dimensions in the order of a micrometer.

    The best barrier improvement by metalization was achieved for the metalized CM-MFC, where the OTR values were decreased by one order of magnitude after metalization. However, for ENZ-MFC metalization did not improve OTR at high RH. The protective layer was successfully protecting the MFC film as long as the surface roughness of the film was not too high. The limit is between 40 and 140nm (in root mean square roughness values).

  • 20.
    Karlsson, Christian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Regression Models of 3D Wakes for Propellers2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this work, regression models for the wake field entering a propeller at certain axial andnominal position have been proposed. Wakes are non-uniform flows following a body immersedin a viscous fluid. We have proposed models for the axial and tangential velocity distribution asfunctions of ship hull and propeller measures. The regression models were modelled using Fourierseries and parameter estimations based on skewed-Gaussian and sine functions. The wake fieldis an important parameter in propeller design. The regression models are based on experimentaldata provided by the Rolls-Royce Hydrodynamic Research Center in Kristinehamn. Also we havestudied the flow in the axial velocity distribution in the propeller plane using the coherent structurecoloring method. The coherent structure coloring is used to study coherent patterns by looking atfluid particle kinematics. Using this type of analysis, we observed that the velocity distributionbehaves kinematically similar in the different regions of the wake distribution, which according tothe coherent structure coloring indicate coherence.

  • 21.
    Karlsson, Christopher
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Thermal Analysis of Flatness Measuring System for Rolling Applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In rolling applications it is critical to be able to control the flatness of the metal strip. An uneven strip may in the most extreme cases lead to strip breaks. One of the systems used to measure the flatness consists of a measuring roll, which the strip is deflected over. During the contact time, heat is transferred from the hot strip to the roll. The roll is not allowed to get too hot due to risks of overheating the electronics. Previously the measuring roll have only been used in cold rolling applications, where this is usually not a problem. There is now an increased interested in using the roll in more extreme applications with higher strip temperatures. This requires knowledge about all the potential heat sources present in the system. The subject of this thesis work has been to investigate some of the contributions to the thermal balances of the measuring roll. A numerical model has been developed to describe conductive heat transfer between the metal strip and the measuring roll. Using the numerical model, the heat transfer was obtained as a function of the temperature, contact time and thickness of the strip. From these simulations a heat transfer coefficient associated with an external cooling demand was derived. The flatness measuring roll is equipped with pressure sensitive sensors used to measure the flatness of the strip. These sensors are located in internal channels and generate heat through resistive heating. The impact of this on the overall temperature of the roll was determined to be small. In the internal channels there is also a flow of air. In normal operation scenarios the flow is very low, leading to a small cooling capacity. From the thermal balance of the system it was concluded that the dominant heat source was the heat transfer between the strip and roll. This heat transfer is however heavily dependent on material properties and surface characteristics. The model used to describe the conductive heat transfer assumes no contact resistance between the strip and roll. This provides an upper-bound estimate of the heat transfer. If the contact resistance is included within the model the impact of the individual heat sources increases. Both the material properties and contact resistance requires further investigation. Combining the results of M. Gustafsson (Master of Science thesis, Karlstad University, 2018), a thermal balance for the measuring roll has successfully been developed. This balance clarifies the critical parameters which should be considered when designing the external cooling of the roll.

  • 22.
    Klippmark, Ellinor
    Karlstad University.
    Ytinitierat utmattningsbrott vid mycket höga cykler: Utmattningsprovning med ultraljudsutrustning följt av karaktärisering av brottytor i ett svepelektronmikroskop av ett höghållfast stål2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    I detta projekt analyseras utmattningsbrott orsakade av ytdefekter i höghållfast stål som utsätts för fler än tio miljoner cykliska belastningar. Vanligen orsakas utmattningsbrott i denna region av interna materialdefekter där brottytan ofta innehåller ett område med grövre morfologi - fine granular area (FGA). FGA är en ackumulerad skada som bildas under sprickinitieringsstadiet och utgör cirka 99 % av den totala utmattningslivslängden. Resterande 1 % utgörs av spricktillväxt. På grund av detta är mekanismen som initierar sprickor i detta skede essentiell. Om FGA kan observeras vid ytinitierade utmattningsbrott för material som utsätts för fler än tio miljoner cykliska belastningar, är ännu inte fastställt. . Det här projektet syftar till att undersöka om FGA kan observeras i ytinitierat utmattningsbrott gällande material med väldigt långa livslängder, samt till att utreda hur ytinitieringar påverkar utmattningslivslängden. För att söka svar på dessa frågor utförs utmattningsprovning med ultraljudsutrustning, följt av karaktärisering av brottytorna i svepelektronmikroskop för att studera de morfologiska förändringarna. Vidare utförs finita element analyser med mjukvaran ABAQUS för att jämföra den maximala huvudspänningen mellan prov med, respektive utan ytdefekter. Resultatet från ABAQUS visar att proven med hårdhetsintryck utsätts för en större maximal huvudspänning än proven utan hårdhetsintryck, därigenom kan skillnaden i livslängder förklaras. . Testresultaten från utmattningsprovningen presenteras i ett S-N diagram som visar spänningsamplituden i förhållande till materialets livslängd. De analyserade bilderna från svepelektronmikroskopet av ytinitierat utmattningsbrott visar en antydan till FGA i två av 20 prov. Däremot tycks sprickorna, i samtliga fall, initiera på grund av ackumulering av plastisk deformation i ytan. Interna materialdefekter orsakade inte utmattningsbrott i något av de 20 testade proverna med ytdefekter. Två prover utan ytdefekter genomgick samma process och för båda dessa introducerades en spricka på grund av interna materialdefekter, båda innehöll ett tydligt FGA. Sammanfattningsvis indikerar resultaten från denna studie att FGA inte är lika uppenbara och eventuellt lika vanligt förekommande vid ytinitierat utmattningsbrott av höghållfasta stål med mycket långa livslängder. Även att ytdefekter introducerar en högre maximal huvudspänning i provets centrum, vilket resulterar i en kortare utmattningslivslängd. 

  • 23.
    Kolyada, Viktor
    Karlstad University, Faculty of Technology and Science, Department of Mathematics.
    Iterated rearrangements and Gagliardo-Sobolev type inequalities2012In: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, Vol. 387, no 1, p. 335-348Article in journal (Refereed)
    Abstract [en]

    In this paper we consider Lorentz type spaces defined in terms of iterated rearrangements of functions of several variables (σ is a permutation of {1,…,n}). Further, we study Fournier–Gagliardo mixed norm spaces V(Rn) closely related to Sobolev spaces . We prove estimate of via ‖fV with the sharp constant. In particular, this gives a refinement of the known Sobolev type inequalities for the space .

  • 24.
    Kronberg, Simon
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Morphology Formation from Ternary Mixtures upon Evaporation: a Square Cell Model Approach2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    We present a novel modelling approach for the morphology formation from ternary mixtures upon evaporation, which takes into consideration two different length scales of the interaction, and further allows for these length scales to be altered. A quantitative study of the interfacial energy hints towards the existence of a mesoscopic regime - further research is needed to verify the validity of this claim however. We also demonstrate that the solvent initially follows a Fickian law of diffusion, then deviates from this behaviour, presumably due to the phase separated regions produced by the two remaining (active) components. We also attempt to bridge the gap between this work and a hypothetical three-dimensional model by considering a top-down view of the system. Here, we observe domain growth dominated by Ostwald ripening, with some coalescence. The domain growth was further characterised using Fourier image analysis.

  • 25.
    Linder, Tom
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Optimizing fuel cell channel geometry to favour water transport2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 26.
    Lundin, Lukas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Tip vortex cavitation and diffused vorticity of propeller profiles: a modelling approach: Investigation of an implemented TVI model, and  implementation and investigation of a DVH model2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To predict fluid properties and interactions is an important task for the industry. It is plagued, however, by being close to impossible to predict analytically. Hence, it is customary to turn to numerical solutions. This in itself comes with many different methods and approaches suitable for different needs. This work focuses on two methods: Tip Vortex Index (TVI) and Diffused Vortex Hydrodynamics (DVH). TVI is a method to predict when a marine propeller will experience cavitation of tip vortices and is based on calculations from a Boundary Element Method (BEM). DVH is a particle method for simulating the circulation of a fluid in two dimensions and three dimensions. The aim is to investigate an implemented TVI model based on MPUF-3A for different marine propeller series, with different sub-designs for a total of 28 unique propellers, and implement the DVH method and test it for 3 different bodies. The results of this thesis show that the implemented TVI model is non-functional for the 28 different propellers, but the DVH method is successfully implemented and able to handle 2 different bodies.

  • 27.
    Lundström, Robin
    Karlstad University.
    Machine Learning for Air Flow Characterization: An application of Theory-Guided Data Science for Air Fow characterization in an Industrial Foundry2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In industrial environments, operators are exposed to polluted air which after constant exposure can cause irreversible lethal diseases such as lung cancer. The current air monitoring techniques are carried out sparely in either a single day annually or at few measurement positions for a few days.In this thesis a theory-guided data science (TGDS) model is presented. This hybrid model combines a steady state Computational Fluid Dynamics (CFD) model with a machine learning model. Both the CFD model and the machine learning algorithm was developed in Matlab. The CFD model serves as a basis for the airflow whereas the machine learning model addresses dynamical features in the foundry. Measurements have previously been made at a foundry where five stationary sensors and one mobile robot were used for data acquisition. An Echo State Network was used as a supervised learning technique for airflow predictions at each robot measurement position and Gaussian Processes (GP) were used as a regression technique to form an Echo State Map (ESM). The stationary sensor data were used as input for the echo state network and the difference between the CFD and robot measurements were used as teacher signal which formed a dynamic correction map that was added to the steady state CFD. The proposed model utilizes the high spatio-temporal resolution of the echo state map whilst making use of the physical consistency of the CFD. The initial applications of the novel hybrid model proves that the best qualities of these two models could come together in symbiosis to give enhanced characterizations.The proposed model could have an important role for future characterization of airflow and more research on this and similar topics are encouraged to make sure we properly understand the potential of this novel model.

  • 28.
    Martz, Dale H.
    et al.
    KTH.
    Selin, Mårten
    KTH.
    von Hofsten, Olov
    KTH.
    Fogelqvist, Emelie
    KTH.
    Holmberg, Anders
    KTH.
    Vogt, Ulrich
    KTH.
    Legall, H.
    Max-Born-Institute, Germany .
    Blobel, G.
    Max-Born-Institute, Germany .
    Seim, C.
    nstitute of Optics and Atomic Physics—Analytical X-ray physics, Germany .
    Stiel, H.
    Max-Born-Institute, Germany .
    Hertz, Hans M.
    KTH.
    High average brightness water window source for short-exposure cryomicroscopy2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 21, p. 4425-4427Article in journal (Refereed)
    Abstract [en]

    Laboratory water window cryomicroscopy has recently demonstrated similar image quality as synchrotron-based microscopy but still with much longer exposure times, prohibiting the spread to a wider scientific community. Here we demonstrate high-resolution laboratory water window imaging of cryofrozen cells with 10 s range exposure times. The major improvement is the operation of a lambda = 2.48 nm, 2 kHz liquid nitrogen jet laser plasma source with high spatial and temporal stability at high average brightness >1.5 x 10(12) ph/(s x sr x mu m(2) x line), i.e., close to that of early synchrotrons. Thus, this source enables not only biological x-ray microscopy in the home laboratory but potentially other applications previously only accessible at synchrotron facilities.

  • 29.
    Nilsson, Daniel
    et al.
    KTH.
    Uhlén, Fredrik
    KTH.
    Holmberg, Anders
    KTH.
    Hertz, Hans M.
    KTH.
    Schropp, Andreas
    SLAC National Accelerator Laboratory, Menlo Park, CA, USA & Institute of Structural Physics, Technische Universität Dresden, Germany.
    Patommel, Jens
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Hoppe, Robert
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Seiboth, Frank
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Meier, Vivienne
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Schroer, Christian G.
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Galtier, Eric
    Institute of Structural Physics, Technische Universität Dresden, Germany.
    Nagler, Bob
    SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
    Lee, Hae Ja
    SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
    Vogt, Ulrich
    KTH.
    Ronchi test for characterization of nanofocusing optics at a hard x-ray free-electron laser2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 24, p. 5046-5048Article in journal (Refereed)
    Abstract [en]

    We demonstrate the use of the classical Ronchi test to characterize aberrations in focusing optics at a hard x-ray free-electron laser. A grating is placed close to the focus and the interference between the different orders after the grating is observed in the far field. Any aberrations in the beam or the optics will distort the interference fringes. The methodis simple to implement and can provide single-shot information about the focusing quality. We used the Ronchi test to measure the aberrations in a nanofocusing Fresnel zone plate at the Linac Coherent Light Source at 8.194 keV.

  • 30.
    Nilsson, Frida
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013), Science, Mathematics and Engineering Education Research.
    Hole transport layers in organic solar cells: A study of work functions in nanofilms2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Organic solar cells have been showing promise as a way of producing renewableenergy with the help of light, flexible, and production effective materials.The efficiencies and lifetimes reached in organic solar cells have steadily beenincreasing over the years as more research in the field is being conducted.One way of increasing the efficiency in organic solar cell devices is introducingan interlayer between the photoactive material and the anode, referred toas the ’hole transport layer’. Most commonly used as a hole transport layer isthe material PEDOT:PSS, which offers desired properties such as transparency,simple processing and good ohmic contact between anode and photoactive material.PEDOT:PSS is also known to be a degradation site in organic solar cells,as it will corrode the electrode in the presence of water.This project has consisted of investigating PEDOT:PSS along with two othercandidates that may one day come to replace PEDOT:PSS as the most commonlyused material, molybdenum trioxide (MoO3) and phosphomolybdic acid(PMA). The aim was to investigate how the different materials energy bandstructure would be affected upon exposure to sunlight, air and annealing, byobserving the work function under different conditions.

  • 31.
    Stigner, Carl
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    A classifying algebra for CFT boundary conditions2009Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Conformal field theories (CFT) constitute an interesting class of twodimensionalquantum field theories, with applications in string theoryas well as condensed matter physics. The symmetries of a CFT can beencoded in the mathematical structure of a conformal vertex algebra.The rational CFT’s are distinguished by the property that the categoryof representations of the vertex algebra is a modular tensor category.The solution of a rational CFT can be split off into two separate tasks, apurely complex analytic and a purely algebraic part.

    The TFT-construction gives a solution to the second part of the problem.This construction gets its name from one of the crucial ingredients,a three-dimensional topological field theory (TFT). The correlators obtainedby the TFT-construction satisfy all consistency conditions of thetheory. Among them are the factorization constraints, whose implicationsfor boundary conditions are the main topic of this thesis.

    The main result reviewed in this thesis is that the factorization constraintsgive rise to a semisimple commutative associative complex algebrawhose irreducible representations are the so-called reflection coefficients.The reflection coefficients capture essential information aboutboundary conditions, such as ground-state degeneracies and Ramond-Ramond charges of string compactifications. We also show that the annuluspartition function can be derived fromthis classifying algebra andits representation theory.

  • 32.
    Stigner, Carl
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Hopf and Frobenius algebras in conformal field theory2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    There are several reasons to be interested in conformal field theories in two dimensions. Apart from arising in various physical applications, ranging from statistical mechanics to string theory, conformal field theory is a class of quantum field theories that is interesting on its own. First of all there is a large amount of symmetries. In addition, many of the interesting theories satisfy a finiteness condition, that together with the symmetries allows for a fully non-perturbative treatment, and even for a complete solution in a mathematically rigorous manner. One of the crucial tools which make such a treatment possible is provided by category theory.

    This thesis contains results relevant for two different classes of conformal field theory. We partly treat rational conformal field theory, but also derive results that aim at a better understanding of logarithmic conformal field theory. For rational conformal field theory, we generalize the proof that the construction of correlators, via three-dimensional topological field theory, satisfies the consistency conditions to oriented world sheets with defect lines. We also derive a classifying algebra for defects. This is a semisimple commutative associative algebra over the complex numbers whose one-dimensional representations are in bijection with the topological defect lines of the theory.

    Then we relax the semisimplicity condition of rational conformal field theory and consider a larger class of categories, containing non-semisimple ones, that is relevant for logarithmic conformal field theory. We obtain, for any finite-dimensional factorizable ribbon Hopf algebra H, a family of symmetric commutative Frobenius algebras in the category of bimodules over H. For any such Frobenius algebra, which can be constructed as a coend, we associate to any Riemann surface a morphism in the bimodule category. We prove that this morphism is invariant under a projective action of the mapping class group ofthe Riemann surface. This suggests to regard these morphisms as candidates for correlators of bulk fields of a full conformal field theories whose chiral data are described by the category of left-modules over H.

  • 33.
    Strømnes, Sofia
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    Sniglar har mycket friktion fröken!: En studie av samspelets betydelse för lärandet i förskolan2018Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of this study was to observe in which way educator´s interactions with children stimulate the learning process, in this case of the study about friction. How does the interaction between preeschool teachers and children affect and stimulate their curiosity to learn? The study was conducted with a preschool teacher and 6 children between the ages 4-6 years. The preschool teacher planned an activity that involved separate ways to learn about friction and performed this with the children. The chosen method of the study was a qualitative non-participation observation and an open interview with the preschool teacher. The result shows that interaction play an important part in children's learning processes, that by confirming and sharing knowledge with others in a social context, it is also easier to ask questions and explore the phenomenon of friction. The study shows that when an educator is active and present, cooperation between children-children but also children-educator increases, and it gives the children an increased understanding of the learning object

  • 34.
    Tang, Wai Ho
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Quantum Entanglement and Superconducting Qubits2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Conventional computing based on classical technologies is approaching its limits. Therefore scientists are starting to consider the applications of quantum mechanics as a means for constructing more powerful computers. After proposing theoretical methods, many experimental setups have been designed to achieve quantum computing in reality. This thesis gives some background information on the subject of quantum computing. We first review the concept of quantum entanglement, which plays a key role in quantum computing, and then we discuss the physics of the SQUIDs-cavity method proposed by Yang et al., and give the definitions of quantum gates which are the elements that are needed to construct quantum circuits. Finally we give an overview of recent developments of SQUIDs-cavity systems and quantum circuits after Yang et al.'s proposal in 2003. These new developments help to take a step towards the constructions of higher levels of quantum technologies, e.g. quantum algorithms and quantum circuits.

  • 35.
    Uhlén, Fredrik
    et al.
    KTH.
    Nilsson, Daniel
    KTH.
    Holmberg, Anders
    KTH.
    Hertz, Hans M.
    KTH.
    Schroer, C. G.
    Seiboth, F.
    Patommel, J.
    Meier, V.
    Hoppe, R.
    Schropp, A.
    Lee, H. J.
    Nagler, B.
    Galtier, E.
    Krzywinski, J.
    Sinn, H.
    Vogt, Ulrich
    KTH.
    Damage investigation on tungsten and diamond diffractive optics at a hard x-ray free-electron laser2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 7, p. 8051-8061Article in journal (Refereed)
    Abstract [en]

    Focusing hard x-ray free-electron laser radiation with extremely high fluence sets stringent demands on the x-ray optics. Any material placed in an intense x-ray beam is at risk of being damaged. Therefore, it is crucial to find the damage thresholds for focusing optics. In this paper we report experimental results of exposing tungsten and diamond diffractive optics to a prefocused 8.2 keV free-electron laser beam in order to find damage threshold fluence levels. Tungsten nanostructures were damaged at fluence levels above 500 mJ/cm(2). The damage was of mechanical character, caused by thermal stress variations. Diamond nanostructures were affected at a fluence of 59 000 mJ/cm(2). For fluence levels above this, a significant graphitization process was initiated. Scanning Electron Microscopy (SEM) and mu-Raman analysis were used to analyze exposed nanostructures.

  • 36.
    Uhlén, Fredrik
    et al.
    KTH.
    Nilsson, Daniel
    KTH.
    Rahomäki, Jussi
    KTH.
    Belova, Liubov
    KTH.
    Schroer, Christian G.
    Seiboth, Frank
    Holmberg, Anders
    KTH.
    Hertz, Hans M.
    KTH.
    Vogt, Ulrich
    KTH.
    Nanofabrication of tungsten zone plates with integrated platinum central stop for hard X-ray applications2014In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 116, p. 40-43Article in journal (Refereed)
    Abstract [en]

    We present a nanofabrication process for producing tungsten zone plates used in hard X-ray applications including a method of integrating a high-energy absorbing central stop with the optic. Tungsten zone plates are structured with electron-beam lithography and subsequent reactive ion etching. The central stop originates from a platinum wire. It is cut to dimension by focused ion beam etching, and afterwards attached to the zone plate center using ion beam induced deposition of platinum. A zone plate with integrated central stop will simplify alignment in hard X-ray scanning microscope arrangements where the 0th order light must be eliminated. The focusing performance of the zone plate device was investigated by scanning coherent diffraction imaging (ptychography) at 8 keV photon energy. We could demonstrate a diffraction-limited focus size of 53 nm diameter full-width-at-half-maximum. Tungsten zone plates with integrated central stops show promising results for use in hard X-ray microscopes at high-brightness facilities.

  • 37.
    Wang, Yuming
    et al.
    Nanjing Tech University, China; Linkoping University .
    Jafari, Mohammad Javad
    Linköping University .
    Wang, Nana
    Nanjing Tech University, China.
    Qian, Deping
    Linkoping University.
    Zhang, Fengling
    Linkoping University.
    Ederth, Thomas
    Linkoping University.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Wang, Jianpu
    Nanjing Technical University, China.
    Inganas, Olle
    Linköping University.
    Huang, Wei
    Nanjing Technical University, China.
    Gao, Feng
    Linkoping University.
    Light-induced degradation of fullerenes in organic solar cells: a case study on TQ1:PC71BM2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 25, p. 11884-11889Article in journal (Refereed)
    Abstract [en]

    The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.

  • 38.
    Yngman, Sofie
    Karlstad University, Faculty of Technology and Science.
    Mechanical properties of carbon nanotubes grown by pyrolysis of ferrocene2012Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Carbon nanotubes (CNTs) have drawn a lot of attention during the last decades due to its promising mechanical and electrical properties. Extensive research regarding the mechanical properties of CNTs has been carried out during the last decades. A lot of effort has been put into developing methods to properly characterize features such as Young’s modulus and the deformation processes of carbon nanotubes. A detailed knowledge of these properties is important for many of the suggested applications of carbon nanotubes.Here we have examined multiwalled carbon nanotubes (MWCNTs) grown by pyrolysis of ferrocene. In some cases the carbon nanotube contained an iron core or traces of iron in the core. The carbon nanotubes ranged from 20 nm to 65 nm in radius and 1000 nm to 4000 nm in length.An atomic force microscope (AFM) was used inside a scanning electron microscope (SEM) for in situ force measurements. The AFM cantilever was used to displace individual carbon nanotubes from their equilibrium positions. The forces used to displace the carbon nanotubes have been plotted against the displacements of the tubes to obtain the characteristic force-displacement curves. From the slope of these curves the spring constants of the carbon nanotubes have been found. Young’s modulus for each tube was derived from the spring constant and the tube dimensions.We found that Young’s modulus ranged from 7 GPa to 340 GPa with no observed dependence on the radius or the length. Previous works suggest that deformation processes such as rippling and buckling will drastically change the spring constant of the tubes when displaced. The maximum values of the applied forces in our measurements were smaller than those needed to push the tubes into the deformation stages. The relatively low values of Young’s modulus indicate that these tubes are rich in defects which dominate their mechanical behaviour.

  • 39.
    Yngman, Sofie
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Probing mechanical properties of carbon nanotubes2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose with this c-level thesis is to investigate Young’s modulus of carbon nanotubes (CNTs). The force measurements as well as the imaging are done by an atomic force microscope (AFM). This has been done before by Eric W. Wong et al in 19971. These earlier experiments report techniques using clean-room facilities not available at Karlstad University. Our task is to investigate probabilities in which to perform the experiment by using the available instruments at Karlstad University.The force measurements are done by using the AFM tip to push the CNTs. A force curve is obtained from where it is possible to determine the spring constant of the CNT. By knowing some essential characteristics of the cantilever and the tip, Young’s modulus can be calculated. The CNT needs to be fixed in one end and able to push to the sides in the other end. Our main focuses in this thesis is how to fix the CNTs and what surface to use. Essentially two methods of fixing the tubes have been tried out. Partly we have been looking for large particles on the surface lying on top of a CNT fixing one end, partly we have evaporated gold to achieve an edge under which the CNTs can be attached.In conclusion we can say that it is hard and time-consuming looking for CNTs randomly fixed by particles on the surface. Further we can say that the choice of surface is important. A surface with a low friction was desired but the low friction causes trouble during imaging. The force between the tip and the cantilever during imaging seems to be enough to disturb the CNT and the surface, making measurements hard.

  • 40.
    Zabel, Thomas
    et al.
    KTH.
    Reuterskiöld Hedlund, Carl
    KTH.
    Gustafsson, Oscar
    KTH.
    Karim, A.
    Acreo AB, Sweden.
    Berggren, Jesper
    KTH.
    Wang, Q.
    Acreo AB.
    Ernerheim Jokumsen, Christopher
    KTH.
    Soldemo, Markus
    KTH.
    Weissenrieder, Jonas
    KTH.
    Gotelid, Mats
    KTH.
    Hammar, Mattias
    KTH.
    Auger recombination in In(Ga)Sb/InAs quantum dots2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 1, article id 013103Article in journal (Refereed)
    Abstract [en]

    We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170-200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 x 10(-28) cm(6)/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 x 10(-27) cm(6)/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.

  • 41.
    Zhang, Xiaojing
    et al.
    ABB Corporate Research.
    Lindberg, Therese
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Vyatkin, Valeriy
    Department of Computer Science, Electrical and Space Engineering at LuleåUniversity of Technology, Sweden and the Department of Electrical Engineering and Automation, Aalto University, Finland.
    Mousavi, Arash
    Department of Computer Science, Electrical and Space Engineering at LuleåUniversity of Technology, Sweden.
    Power Consumption Modeling of Data Center IT Room with Distributed Air Flow2016In: International Journal of Modeling and Optimization, ISSN 2010-3697, Vol. 6, no 1, p. 33-38Article in journal (Refereed)
    Abstract [en]

    Modern data centers are characterized by large sizes, high energy consumption and complexity involving IT, power supply, ventilation and cooling. Data center energy efficiency is a major concern for data center design and operation. To improve data center energy efficiency through efficient cooling and ventilation, advanced process control and optimization, process models to describe the process power consumption are required. In this work, data center power consumption models are investigated. A concept of distributed air flow control is presented. The objective is to develop a comprehensive data center power consumption model to describe IT room, computer room air handling (CRAH), data center ventilation and cooling characteristics as well as distributed air flow control. Data center operation scenarios with uneven IT load are simulated. Results show that the distributed air flow control can save the cooling energy significantly.

  • 42.
    Österdahl, Emma
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    Barns utforskande av fysikaliska fenomen på kullar: En design-baserad studie om barns utforskande av friktion.2019Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the study is to provide knowledge about how children explore, understand and reason about the physical phenomenon of friction. This study have been based on the younger children’s exploring. The method of the study has been observation in order to get as close to the environment that’s being investigated and to bring attention to the younger children’s actions. A nonparticipating observation was also used for the observer to influence the children as little as possible. The observations that have been made have taken place over two days and have been video recorded to ensure documentation of children's reasoning, body language and actions. The result shows how the children focused on overcoming the friction to get an object to slide instead of getting stuck. The participants’ interaction also emerged in the result as central to driving the exploration further. The conclusions drawn after the study is that the result can be linked to the preschool’s curriculum, which addresses the fact that the children should be given the opportunity to explore, discuss and develop understanding of physical phenomena. The study has also highlighted that hills can be used as a tool for teaching and exploring the phenomenon of friction.

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