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  • 301.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    Ecole Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, 69622 Lyon, France.
    Walder, Rolf
    Ecole Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, 69622 Lyon, France.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Collisionless Rayleigh–Taylor-like instability of the boundary between a hot pair plasma and an electron–proton plasma: The undular mode2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 11, p. 1-14, article id 112106Article in journal (Refereed)
    Abstract [en]

    We study with a two-dimensional particle-in-cell simulation the stability of a discontinuity or piston, which separates an electron–positron cloud from a cooler electron–proton plasma. Such a piston might be present in the relativistic jets of accreting black holes separating the jet material from the surrounding ambient plasma and when pair clouds form during an x-ray flare and expand into the plasma of the accretion disk corona. We inject a pair plasma at a simulation boundary with a mildly relativistic temperature and mean speed. It flows across a spatially uniform electron–proton plasma, which is permeated by a background magnetic field. The magnetic field is aligned with one simulation direction and oriented orthogonally to the mean velocity vector of the pair cloud. The expanding pair cloud expels the magnetic field and piles it up at its front. It is amplified to a value large enough to trap ambient electrons. The current of the trapped electrons, which is carried with the expanding cloud front, drives an electric field that accelerates protons. A solitary wave grows and changes into a piston after it saturated. Our simulations show that this piston undergoes a collisionless instability similar to a Rayleigh–Taylor instability. The undular mode grows and we observe fingers in the proton density distribution. The effect of the instability is to deform the piston but it cannot destroy it.

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  • 302.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    CRAL, École Normale Supérieure, 69622 Lyon, France.
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Nordman, Aida
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Dell'Acqua, Pierangelo
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, Rolf
    CRAL, École Normale Supérieure, 69622 Lyon, France.
    Structure of a collisionless pair jet in a magnetized electron-proton plasma: Flow-aligned magnetic field2019In: High Energy Phenomena in Relativistic Outflows VII (HEPRO VII): Formation and propagation of relativistic outflows, 2019, article id 006Conference paper (Refereed)
    Abstract [en]

    We present the results from a particle-in-cell (PIC) simulation that models the interaction between a spatially localized electron-positron cloud and an electron-ion plasma. The latter is permeated by a magnetic field that is initially spatially uniform and aligned with the mean velocity vector of the pair cloud. The pair cloud expels the magnetic field and piles it up into an electromagnetic piston. Its electromagnetic field is strong enough to separate the pair cloud from the ambient plasma in the direction that is perpendicular to the cloud propagation direction. The piston propagates away from the spine of the injected pair cloud and it accelerates the protons to a high nonrelativistic speed. The accelerated protons form an outer cocoon that will eventually become separated from the unperturbed ambient plasma by a fast magnetosonic shock. No electromagnetic piston forms at the front of the cloud and a shock is mediated here by the filamentation instability. The final plasma distribution resembles that of a hydrodynamic jet. Collisionless plasma jets may form in the coronal plasma of accreting black holes and the interaction between the strong magnetic field of the piston and the hot pair cloud may contribute to radio emissions by such objects.

  • 303.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, D.
    Univ Lyon, France.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bock, Alexander
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, R.
    Univ Lyon, France.
    Three-dimensional structure and stability of discontinuities between unmagnetized pair plasma and magnetized electron-proton plasma2023In: New Journal of Physics, E-ISSN 1367-2630, Vol. 25, no 6, article id 063017Article in journal (Refereed)
    Abstract [en]

    We study with a 3D particle-in-cell simulation discontinuities between an electron-positron pair plasma and magnetized electrons and protons. A pair plasma is injected at one simulation boundary with a speed 0.6c along its normal. It expands into an electron-proton plasma and a magnetic field that points orthogonally to the injection direction. Diamagnetic currents expel the magnetic field from within the pair plasma and pile it up in front of it. It pushes electrons, which induces an electric field pulse ahead of the magnetic one. This initial electromagnetic pulse (EMP) confines the pair plasma magnetically and accelerates protons electrically. The fast flow of the injected pair plasma across the protons behind the initial EMP triggers the filamentation instability. Some electrons and positrons cross the injection boundary and build up a second EMP. Electron-cyclotron drift instabilities perturb the plasma ahead of both EMPs seeding a Rayleigh-Taylor (RT)-type instability. Despite equally strong perturbations ahead of both EMPs, the second EMP is much more stable than the initial one. We attribute the rapid collapse of the initial EMP to the filamentation instability, which perturbed the plasma behind it. The RT-type instability transforms the planar EMPs into transition layers, in which magnetic flux ropes and electrostatic forces due to uneven numbers of electrons and positrons slow down and compress the pair plasma and accelerate protons. In our simulation, the expansion speed of the pair cloud decreased by about an order of magnitude and its density increased by the same factor. Its small thickness implies that it is capable of separating a relativistic pair outflow from an electron-proton plasma, which is essential for collimating relativistic jets of pair plasma in collisionless astrophysical plasma.

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  • 304.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69622 Lyon, France.
    Bret, Antoine
    Universidad de Castilla La Mancha, ETSI Ind, E-13071 Ciudad Real, Spain.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69622 Lyon, France.
    Simulation studies of temperature anisotropy driven pair-Alfvén and aperiodic instabilities in magnetized pair plasma2019In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 8, article id 085027Article in journal (Refereed)
    Abstract [en]

    We compare with one-dimensional particle-in-cell simulations the aperiodically growing instabilities driven by a bi-Maxwellian velocity distribution in unmagnetized electron plasma (Weibel instability) and in pair plasma. The simulation box is aligned with the cool direction. The waves in both simulations evolve towards a circularly polarized non-propagating magnetic structure. Its current and magnetic field are aligned and the structure is in a force-free state. We examine how a background magnetic field B 0, which is parallel to the simulation direction, affects the waves in the pair plasma. A weak B 0 cannot inhibit the growth of the aperiodically growing instability but it prevents it from reaching the force-free stable state. The mode collapses and seeds a pair Alfvén waves. An intermediate B 0 couples the thermal anisotropy to the pair Alfvén mode and propagating magnetowaves grow. The phase speed of the pair of Alfvén waves is increased by the thermal anisotropy. Its growth is suppressed when B 0 is set to the value that stabilizes the mirror mode.

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  • 305.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, Lyon, France .
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Nordman, Aida
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Dell'Acqua, Pierangelo
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, Lyon, France .
    Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A142Article in journal (Refereed)
    Abstract [en]

    Aims. We study the effect a guiding magnetic field has on the formation and structure of a pair jet that propagates through a collisionless electron–proton plasma at rest.

    Methods. We model with a particle-in-cell (PIC) simulation a pair cloud with a temperature of 400 keV and a mean speed of 0.9c (c - light speed). Pair particles are continuously injected at the boundary. The cloud propagates through a spatially uniform, magnetized, and cool ambient electron–proton plasma at rest. The mean velocity vector of the pair cloud is aligned with the uniform background magnetic field. The pair cloud has a lateral extent of a few ion skin depths.

    Results. A jet forms in time. Its outer cocoon consists of jet-accelerated ambient plasma and is separated from the inner cocoon by an electromagnetic piston with a thickness that is comparable to the local thermal gyroradius of jet particles. The inner cocoon consists of pair plasma, which lost its directed flow energy while it swept out the background magnetic field and compressed it into the electromagnetic piston. A beam of electrons and positrons moves along the jet spine at its initial speed. Its electrons are slowed down and some positrons are accelerated as they cross the head of the jet. The latter escape upstream along the magnetic field, which yields an excess of megaelectronvolt positrons ahead of the jet. A filamentation instability between positrons and protons accelerates some of the protons, which were located behind the electromagnetic piston at the time it formed, to megaelectronvolt energies.

    Conclusions. A microscopic pair jet in collisionless plasma has a structure that is similar to that predicted by a hydrodynamic model of relativistic astrophysical pair jets. It is a source of megaelectronvolt positrons. An electromagnetic piston acts as the contact discontinuity between the inner and outer cocoons. It would form on subsecond timescales in a plasma with a density that is comparable to that of the interstellar medium in the rest frame of the latter. A supercritical fast magnetosonic shock will form between the pristine ambient plasma and the jet-accelerated plasma on a timescale that exceeds our simulation time by an order of magnitude.

  • 306.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69007 Lyon, France.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69007 Lyon, France.
    Romagnani, Lorenzo
    École Polytechnique, CNRS, LULI, F-91128 Palaiseau, France.
    d'Humieres, Emanuel
    Univ Bordeaux, IMB, UMR 5251, F-33405 Talence, France.
    Bret, Antoine
    ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real and Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain.
    Karlsson, Tomas
    KTH Royal Institute of Technology, School of Electrical Engineering, Space and Plasma Physics, Stockholm, Sweden.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Emergence of MHD structures in a collisionless PIC simulation plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, article id 094502Article in journal (Refereed)
    Abstract [en]

    The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell simulation over magnetohydrodynamics time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.

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  • 307.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Moreno, Quentin
    Universite de Bordeaux, CNRS, CEA, CELIA, Talence, France.
    Doria, Domenico
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Romagnani, Lorenzo
    Ecole Polytechnique, CNRS, LULI, Palaiseau, France.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Folini, Doris
    Ecole Nationale Superieure, Lyon, CRAL, Universite de Lyon, France.
    Walder, Rolf
    Ecole Nationale Superieure, Lyon, CRAL, Universite de Lyon, France.
    Bret, Antoiine
    ETSI Industriales, Universidad de Castilla-La Mancha, Spain.
    d'Humieres, Emmanuel
    Universite de Bordeaux, CNRS, CEA, CELIA, Talence, France.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Expansion of a radially symmetric blast shell into a uniformly magnetized plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 5, article id 052108Article in journal (Refereed)
    Abstract [en]

    The expansion of a thermal pressure-driven radial blast shell into a dilute ambient plasma is examined with two-dimensional PIC simulations. The purpose is to determine if laminar shocks form in a collisionless plasma which resemble their magnetohydrodynamic counterparts. The ambient plasma is composed of electrons with the temperature of 2 keV and cool fully ionized nitrogen ions. It is permeated by a spatially uniform magnetic field. A forward shock forms between the shocked ambient medium and the pristine ambient medium, which changes from an ion acoustic one through a slow magnetosonic one to a fast magnetosonic shock with increasing shock propagation angles relative to the magnetic field. The slow magnetosonic shock that propagates obliquely to the magnetic field changes into a tangential discontinuity for a perpendicular propagation direction, which is in line with the magnetohydrodynamic model. The expulsion of the magnetic field by the expanding blast shell triggers an electron-cyclotron drift instability.

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  • 308.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Palodhi, Lopamudra
    Department of Mathematics, Indian Institute of Technology Ropar, 140001, Punjab, India.
    Fegan, Conor
    Centre for Light-Matter Interactions, School of Mathematics and Physics, The Queen's University of Belfast, University Road, BT7 1NN, Belfast, United Kingdom.
    Borghesi, Marco
    Centre for Light-Matter Interactions, School of Mathematics and Physics, The Queen's University of Belfast, University Road, BT7 1NN, Belfast, United Kingdom.
    Weibel- and non-resonant Whistler wave growth in an expanding plasma in a 1D simulation geometry2024In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 99, no 4, article id 045602Article in journal (Refereed)
    Abstract [en]

    Ablating a target with an ultraintense laser pulse can create a cloud of collisionless plasma. A density ramp forms, in which the plasma density decreases and the ion's mean speed increases with distance from the plasma source. Its width increases with time. Electrons lose energy in the ion's expansion direction, which gives them a temperature anisotropy. We study with one-dimensional particle-in-cell simulations the expansion of a dense plasma into a dilute one, yielding a density ramp similar to that in laser-plasma experiments and a thermal-anisotropy-driven instability. Non-propagating Weibel-type wave modes grow in the simulation with no initial magnetic field. Their magnetic field diffuses across the shock and expands upstream. Circularly polarized propagating Whistler waves grow in a second simulation, in which a magnetic field is aligned with the ion expansion direction. Both wave modes are driven by non-resonant instabilities, they have similar exponential growth rates, and they can leave the density ramp and expand into the dilute plasma. Their large magnetic amplitude should make them detectable in experimental settings.

  • 309.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Riordan, J D
    University College Cork, Cork, Ireland.
    Pe'er, Asaf
    Bar-Ilan University, Ramat-Gan, Israel.
    Change of a Weibel-type to an Alfvénic shock in pair plasma by upstream waves2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 6, article id 062107Article in journal (Refereed)
    Abstract [en]

    We examine with particle-in-cell simulations how a parallel shock in pair plasma reacts to upstream waves, which are driven by escaping downstream particles. Initially, the shock is sustained in the two-dimensional simulation by a magnetic filamentation (beam-Weibel) instability. Escaping particles drive an electrostatic beam instability upstream. Modifications of the upstream plasma by these waves hardly affect the shock. In time, a decreasing density and an increasing temperature of the escaping particles quench the beam instability. A larger thermal energy along than perpendicular to the magnetic field destabilizes the pair-Alfvén mode. In the rest frame of the upstream plasma, the group velocity of the growing pair-Alfvén waves is below that of the shock and the latter catches up with the waves. Accumulating pair-Alfvén waves gradually change the shock in the two-dimensional simulation from a Weibel-type shock into an Alfvénic shock with a Mach number that is about 6 for our initial conditions.

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  • 310.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, G.
    Queens University of Belfast, North Ireland.
    Doria, D.
    Queens University of Belfast, North Ireland.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Borghesi, M.
    Queens University of Belfast, North Ireland.
    Particle-in-cell simulation study of a lower-hybrid shock2016In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, no 6, p. 062111-Article in journal (Refereed)
    Abstract [en]

    The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell simulations. The magnetic field points perpendicular to the plasmas expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticeable slowdown of the LH shock compared to that in an unmagnetized plasma. Published by AIP Publishing.

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  • 311.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, Belfast, United Kingdom.
    Folini, Doris
    École Normale Supérieure, Université de Lyon, Lyon, France.
    Walder, Rolf
    École Normale Supérieure, Université de Lyon, Lyon, France.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, Belfast, United Kingdom.
    Cocoon formation by a mildly relativistic pair jet in unmagnetized collisionless electron-proton plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 11, article id 112903Article in journal (Refereed)
    Abstract [en]

    By modelling the expansion of a cloud of electrons and positrons with the temperature of 400 keV which propagates at the mean speed of 0.9c (c: speed of light) through an initially unmagnetized electron-proton plasma with a particle-in-cell simulation, we find a mechanism that collimates the pair cloud into a jet. A filamentation (beam-Weibel) instability develops. Its magnetic field collimates the positrons and drives an electrostatic shock into the electron-proton plasma. The magnetic field acts as a discontinuity that separates the protons of the shocked ambient plasma, known as the outer cocoon, from the jet's interior region. The outer cocoon expands at the speed of 0.15c along the jet axis and at 0.03c perpendicularly to it. The filamentation instability converts the jet's directed flow energy into magnetic energy in the inner cocoon. The magnetic discontinuity cannot separate the ambient electrons from the jet electrons. Both species rapidly mix and become indistinguishable. The spatial distribution of the positive charge carriers is in agreement with the distributions of the ambient material and the jet material predicted by a hydrodynamic model apart from a dilute positronic outflow that is accelerated by the electromagnetic field at the jet's head.

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  • 312.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Spencer, Selina-Jane
    Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, UK.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Rowlands, George
    Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, UK.
    Preferential acceleration of positrons by a filamentation instability between an electron–proton beam and a pair plasma beam2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 12, article id 122102Article in journal (Refereed)
    Abstract [en]

    Particle-in-cell simulations of jets of electrons and positrons in an ambient electron–proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. We show that a filamentation instability, between an unmagnetized ambient electron–proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma, while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed.

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  • 313.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Ahmed, Hamad
    Center for Plasma Physics, Queen's University Belfast, UK.
    Sarri, Gianluca
    Center for Plasma Physics, Queen's University Belfast, UK.
    Doria, Domenico
    Center for Plasma Physics, Queen's University Belfast.
    Kourakis, Ioannis
    Center for Plasma Physics, Queen's University Belfast, UK.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, Université Pierre et Marie Curie, Palaiseau, France.
    Pohl, Martin
    Institute of Physics & Astronomy, University of Potsdam, Germany .
    Borghesi, Marco
    Center for Plasma Physics, Queen's University Belfast, UK.
    Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 4, p. 042111-1-042111-10Article in journal (Refereed)
    Abstract [en]

    Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.

  • 314.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Alejo, Aaron
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, UK.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, UK.
    Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 6, article id 062122Article in journal (Refereed)
    Abstract [en]

    The expansion of a charge-neutral cloud of electrons and positrons with the temperature 1 MeV into an unmagnetized ambient plasma is examined with a 2D particle-in-cell simulation. The pair outflow drives solitary waves in the ambient protons. Their bipolar electric fields attract electrons of the outflowing pair cloud and repel positrons. These fields can reflect some of the protons, thereby accelerating them to almost an MeV. Ion acoustic solitary waves are thus an efficient means to couple energy from the pair cloud to protons. The scattering of the electrons and positrons by the electric field slows down their expansion to a nonrelativistic speed. Only a dilute pair outflow reaches the expansion speed expected from the cloud's thermal speed. Its positrons are more energetic than its electrons. In time, an instability grows at the front of the dense slow-moving part of the pair cloud, which magnetizes the plasma. The instability is driven by the interaction of the outflowing positrons with the protons. These results shed light on how magnetic fields are created and ions are accelerated in pair-loaded astrophysical jets and winds.

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  • 315.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bock, Alexander
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ahmed, Hamad
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Doria, Domenico
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Shocks in unmagnetized plasma with a shear flow: Stability and magnetic field generation2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 7, p. 1-9, article id 072104Article in journal (Refereed)
    Abstract [en]

    A pair of curved shocks in a collisionless plasma is examined with a two-dimensional particle-in-cell simulation. The shocks are created by the collision of two electron-ion clouds at a speed that exceeds everywhere the threshold speed for shock formation. A variation of the collision speed along the initially planar collision boundary, which is comparable to the ion acoustic speed, yields a curvature of the shock that increases with time. The spatially varying Mach number of the shocks results in a variation of the downstream density in the direction along the shock boundary. This variation is eventually equilibrated by the thermal diffusion of ions. The pair of shocks is stable for tens of inverse ion plasma frequencies. The angle between the mean flow velocity vector of the inflowing upstream plasma and the shock's electrostatic field increases steadily during this time. The disalignment of both vectors gives rise to a rotational electron flow, which yields the growth of magnetic field patches that are coherent over tens of electron skin depths.

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  • 316.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bret, Antoine
    University of Castilla La Mancha, ETSI Ind, Ciudad Real, Spain.
    Simulation study of the formation of a non-relativistic pair shock2017In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 83, p. 1-19, article id 905830104Article in journal (Refereed)
    Abstract [en]

    We examine with a particle-in-cell (PIC) simulation the collision of two equally dense clouds of cold pair plasma. The clouds interpenetrate until instabilities set in, which heat up the plasma and trigger the formation of a pair of shocks. The fastest-growing waves at the collision speed $c/5$, where $c$ is the speed of light in vacuum, and low temperature are the electrostatic two-stream mode and the quasi-electrostatic oblique mode. Both waves grow and saturate via the formation of phase space vortices. The strong electric fields of these nonlinear plasma structures provide an efficient means of heating up and compressing the inflowing upstream leptons. The interaction of the hot leptons, which leak back into the upstream region, with the inflowing cool upstream leptons continuously drives electrostatic waves that mediate the shock. These waves heat up the inflowing upstream leptons primarily along the shock normal, which results in an anisotropic velocity distribution in the post-shock region. This distribution gives rise to the Weibel instability. Our simulation shows that even if the shock is mediated by quasi-electrostatic waves, strong magnetowaves will still develop in its downstream region.

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  • 317.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    Centre de Recherche Astrophysique de Lyon UMR5574, Université de Lyon 1, ENS de Lyon, CNRS, F-69007 Lyon, France.
    Walder, Rolf
    Centre de Recherche Astrophysique de Lyon UMR5574, Université de Lyon 1, ENS de Lyon, CNRS, F-69007 Lyon, France.
    The interplay of the collisionless non-linear thin-shell instability with the ion acoustic instability2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 465, no 4, p. 4240-4248Article in journal (Refereed)
    Abstract [en]

    The non-linear thin-shell instability (NTSI) may explain some of the turbulent hydrodynamic structures that are observed close to the collision boundary of energetic astrophysical outflows. It develops in non-planar shells that are bounded on either side by a hydrodynamic shock, provided that the amplitude of the seed oscillations is sufficiently large. The hydrodynamic NTSI has a microscopic counterpart in collisionless plasma. A sinusoidal displacement of a thin shell, which is formed by the collision of two clouds of unmagnetized electrons and protons, grows and saturates on time-scales of the order of the inverse proton plasma frequency. Here we increase the wavelength of the seed perturbation by a factor of 4 compared to that in a previous study. Like in the case of the hydrodynamic NTSI, the increase in the wavelength reduces the growth rate of the microscopic NTSI. The prolonged growth time of the microscopic NTSI allows the waves, which are driven by the competing ion acoustic instability, to grow to a large amplitude before the NTSI saturates and they disrupt the latter. The ion acoustic instability thus imposes a limit on the largest wavelength that can be destabilized by the NTSI in collisionless plasma. The limit can be overcome by binary collisions. We bring forward evidence for an overstability of the collisionless NTSI.

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  • 318.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    Univ Lyon, France.
    Walder, Rolf
    Univ Lyon, France.
    Charlet, Arthur
    Univ Lyon, France; Univ Montpellier, France; Open Univ Israel, Israel.
    Marcowith, Alexandre
    Univ Montpellier, France.
    Two-dimensional particle simulation of the boundary between a hot pair plasma and magnetized electrons and protons: Out-of-plane magnetic field2022In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 29, no 9, article id 092103Article in journal (Refereed)
    Abstract [en]

    By means of a particle-in-cell (PIC) simulation, we study the interaction between a uniform magnetized ambient electron-proton plasma at rest and an unmagnetized pair plasma, which we inject at one simulation boundary with a mildly relativistic mean speed and temperature. The magnetic field points out of the simulation plane. The injected pair plasma expels the magnetic field and piles it up at its front. It traps ambient electrons and drags them across the protons. An electric field grows, which accelerates protons into the pair cloud's expansion direction. This electromagnetic pulse separates the pair cloud from the ambient plasma. Electrons and positrons, which drift in the pulse's nonuniform field, trigger an instability that disrupts the current sheet ahead of the pulse. The wave vector of the growing perturbation is orthogonal to the magnetic field direction and magnetic tension cannot stabilize it. The electromagnetic pulse becomes permeable for pair plasma, which forms new electromagnetic pulses ahead of the initial one. A transition layer develops with a thickness of a few proton skin depths, in which protons and positrons are accelerated by strong electromagnetic fields. Protons form dense clumps surrounded by a strong magnetic field. The thickness of the transition layer grows less rapidly than we would expect from the typical speeds of the pair plasma particles and the latter transfer momentum to protons; hence, the transition layer acts as a discontinuity, separating the pair plasma from the ambient plasma. Such a discontinuity is an important building block for astrophysical pair plasma jets.

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  • 319.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Huete, Cesar
    Univ Carlos III Madrid, Grp Mecan Fluidos, Leganes 28911, Spain.
    Cobos Campos, Francisco
    Univ Castilla La Mancha, ETSI Ind, Ciudad Real 13071, Spain.
    Bret, Antoine Claude
    Univ Castilla La Mancha, ETSI Ind, Ciudad Real 13071, Spain.
    Folini, Doris
    Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574 F-69230, Saint-Genis-Laval, France.
    Eliasson, Bengt Erik
    Univ Strathclyde, SUPA, Glasgow G4 0NG, Scotland, United Kingdom.
    Walder, Rolf
    Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574 F-69230, Saint-Genis-Laval, France.
    PIC simulations of stable surface waves on a subcritical fast magnetosonic shock front2023In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 98, no 9, article id 095603Article in journal (Refereed)
    Abstract [en]

    We study with particle-in-cell (PIC) simulations the stability of fast magnetosonic shocks. They expand across a collisionless plasma and an orthogonal magnetic field that is aligned with one of the directions resolved by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed when it enters a layer with a reduced density of mobile ions, which decreases the shock speed by up to 15% in 1D simulations. In the 2D simulations, the density of mobile ions in the layer varies sinusoidally perpendicularly to the shock normal. We resolve one sine period. This variation only leads to small changes in the shock speed evidencing a restoring force that opposes a shock deformation. As the shock propagates through the layer, the ion density becomes increasingly spatially modulated along the shock front and the magnetic field bulges out where the mobile ion density is lowest. The perturbed shock eventually reaches a steady state. Once it leaves the layer, the perturbations of the ion density and magnetic field oscillate along its front at a frequency close to the lower-hybrid frequency; the shock is mediated by a standing wave composed of obliquely propagating lower-hybrid waves. We perform three 2D simulations with different box lengths along the shock front. The shock front oscillations are aperiodically damped in the smallest box with the fastest variation of the ion density, strongly damped in the intermediate one, and weakly damped in the largest box. The shock front oscillations perturb the magnetic field in a spatial interval that extends by several electron skin depths upstream and downstream of the shock front and could give rise to Whistler waves that propagate along the shock's magnetic field overshoot. Similar waves were observed in hybrid and PIC simulations and by the MMS satellite mission.

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  • 320.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Quinn, Kevin
    Queen's University Belfast, UK.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Murphy, Gareth Charles
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Kourakis, Ioannis
    Queen's University Belfast, UK.
    Macchi, Andrea
    CNR, Istituto Nazionale di Ottica, Pisa, Italy.
    Fuchs, Julien
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Willi, Oswald
    Univ. Düsseldorf, Inst. Laser & Plasmaphys., Düsseldorf, Germany.
    Borghesi, Marco
    Queen's University Belfast.
    The Weibel instability in a circular rarefaction wave2012In: Proceedings of the 39th European Physical Society Conference & 16th Int. Congress on Plasma Physics, 2012, p. P1.176-1-P1.176-4Conference paper (Refereed)
    Abstract [en]

    Instabilities behind the front of a cylindrically expanding plasma have been investigated experimentally and with a particle-in-cell simulation. Tubelike filamentary structures form behind the front of a plasma created by irradiating wire targets with a ps-duration and intense ( 1019 W cm-2) laser pulse. These filaments exhibit coherent magnetic fields with a remarkable stability ( 103 / wp: plasma frequency). PIC simulations indicate that an instability driven by a thermal anisotropy of the electron population is the cause. This instability requires a plasma density gradient and hot electrons. It can thus contribute to the generation of strongsustained magnetic fields in astrophysical jets.

  • 321.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Queen's University of Belfast, UK.
    Borghesi, Marco
    Queen's University of Belfast, UK.
    Magnetic instability in a dilute circular rarefaction wave2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 12, p. 122102-1-122102-7Article in journal (Refereed)
    Abstract [en]

    The growth of magnetic fields in the density gradient of a rarefaction wave has been observed in simulations and in laboratory experiments. The thermal anisotropy of the electrons, which gives rise to the magnetic instability, is maintained by the ambipolar electric field. This simple mechanism could be important for the magnetic field amplification in astrophysical jets or in the interstellar medium ahead of supernova remnant shocks. The acceleration of protons and the generation of a magnetic field by the rarefaction wave, which is fed by an expanding circular plasma cloud, is examined here in form of a 2D particle-in-cell simulation. The core of the plasma cloud is modeled by immobile charges, and the mobile protons form a small ring close to the cloud's surface. The number density of mobile protons is thus less than that of the electrons. The protons of the rarefaction wave are accelerated to 1/10 of the electron thermal speed, and the acceleration results in a thermal anisotropy of the electron distribution in the entire plasma cloud. The instability in the rarefaction wave is outrun by a TM wave, which grows in the dense core distribution, and its magnetic field expands into the rarefaction wave. This expansion drives a secondary TE wave.

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  • 322.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Doria, Domenico
    Queen's University Belfast, UK.
    Ahmed, Hamad
    Queen's University Belfast, UK.
    Borghesi, Marco
    Queen's University Belfast, UK.
    Evolution of slow electrostatic shock into a plasma shock mediated by electrostatic turbulence2014In: New Journal of Physics, E-ISSN 1367-2630, Vol. 16, p. 073001-1-073001-25Article in journal (Refereed)
    Abstract [en]

    The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios, such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D particle-in-cell simulation. The ion temperatures of both clouds differ by a factor of ten. Both clouds collide at a speed that is realistic for laboratory studies and for SNR shocks in their late evolution phase, like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that of SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with hotter ions. It does not steepen into a reverse shock because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock, widens its transition layer, and thermalizes the ions, but the forward shock remains intact.

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  • 323.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Doria, Domenico
    Queen's University Belfast, UK.
    Pohl, Martin
    University of Potsdam, Germany .
    Borghesi, Marco
    Queen's University Belfast, UK.
    Modification of the formation of high-Mach number electrostatic shock-like structures by the ion acoustic instability2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 10, p. 102112-1-102112-12Article in journal (Refereed)
    Abstract [en]

    The formation of unmagnetized electrostatic shock-like structures with a high Mach number is examined with one-and two-dimensional particle-in-cell (PIC) simulations. The structures are generated through the collision of two identical plasma clouds, which consist of equally hot electrons and ions with a mass ratio of 250. The Mach number of the collision speed with respect to the initial ion acoustic speed of the plasma is set to 4.6. This high Mach number delays the formation of such structures by tens of inverse ion plasma frequencies. A pair of stable shock-like structures is observed after this time in the 1D simulation, which gradually evolves into electrostatic shocks. The ion acoustic instability, which can develop in the 2D simulation but not in the 1D one, competes with the nonlinear process that gives rise to these structures. The oblique ion acoustic waves fragment their electric field. The transition layer, across which the bulk of the ions change their speed, widens and their speed change is reduced. Double layer-shock hybrid structures develop.

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  • 324.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, Gianluca
    Queen's University Belfast. BT7 1NN, Belfast, United Kingdom.
    Markoff, Sera
    University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
    Borghesi, Marco
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Zepf, Matt
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    PIC simulation study of the interaction between a relativisticallymoving leptonic micro-cloud and ambient electrons.2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, no A137, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Context. The jets of compact accreting objects are composed of electrons and a mixture of positrons and ions. These outflows impinge on the interstellar or intergalactic medium and both plasmas interact via collisionless processes. Filamentation (beam-Weibel) instabilities give rise to the growth of strong electromagnetic fields. These fields thermalize the interpenetrating plasmas.

    Aims. Hitherto, the effects imposed by a spatial non-uniformity on filamentation instabilities have remained unexplored. We examine the interaction between spatially uniform background electrons and a minuscule cloud of electrons and positrons. The cloud size is comparable to that created in recent laboratory experiments and such clouds may exist close to internal and external shocks of leptonic jets. The purpose of our study is to determine the prevalent instabilities, their ability to generate electromagnetic fields and the mechanism, by which the lepton micro-cloud transfers energy to the background plasma.

    Methods. A square micro-cloud of equally dense electrons and positrons impinges in our particle-in-cell (PIC) simulation on a spatially uniform plasma at rest. The latter consists of electrons with a temperature of 1 keV and immobile ions. The initially charge- and current neutral micro-cloud has a temperature of 100 keV and a side length of 2.5 plasma skin depths of the micro-cloud. The side length is given in the reference frame of the background plasma. The mean speed of the micro-cloud corresponds to a relativistic factor of 15, which is relevant for laboratory experiments and for relativistic astrophysical outflows. The spatial distributions of the leptons and of the electromagnetic fields are examined at several times.

    Results. A filamentation instability develops between the magnetic field carried by the micro-cloud and the background electrons. The electromagnetic fields, which grow from noise levels, redistribute the electrons and positrons within the cloud, which boosts the peak magnetic field amplitude. The current density and the moduli of the electromagnetic fields grow aperiodically in time and steadily along the direction that is anti-parallel to the cloud’s velocity vector. The micro-cloud remains conjoined during the simulation. The instability induces an electrostatic wakefield in the background plasma.

    Conclusions. Relativistic clouds of leptons can generate and amplify magnetic fields even if they have a microscopic size, which implies that the underlying processes can be studied in the laboratory. The interaction of the localized magnetic field and high-energy leptons will give rise to synchrotron jitter radiation. The wakefield in the background plasma dissipates the kinetic energy of the lepton cloud. Even the fastest lepton micro-clouds can be slowed down by this collisionless mechanism. Moderately fast charge- and current neutralized lepton micro–clouds will deposit their energy close to relativistic shocks and hence they do not constitute an energy loss mechanism for the shock.

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  • 325.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Murphy, Gareth
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Bret, Antoine
    Harvard-Smithsonian Center for Astrophysics.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France .
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Drury, Luke o'c
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave2012In: New Journal of Physics, E-ISSN 1367-2630, Vol. 14, no 023007Article in journal (Refereed)
    Abstract [en]

    The expansion of an initially unmagnetized planar rarefaction wave has recently been shown to trigger a thermal anisotropy-driven Weibel instability (TAWI), which can generate magnetic fields from noise levels. It is examined here whether the TAWI can also grow in a curved rarefaction wave. The expansion of an initially unmagnetized circular plasma cloud, which consists of protons and hot electrons, into a vacuum is modelled for this purpose with a two-dimensional particle-in-cell (PIC) simulation. It is shown that the momentum transfer from the electrons to the radially accelerating protons can indeed trigger a TAWI. Radial current channels form and the aperiodic growth of a magnetowave is observed, which has a magnetic field that is oriented orthogonal to the simulation plane. The induced electric field implies that the electron density gradient is no longer parallel to the electric field. Evidence is presented here that this electric field modification triggers a second magnetic instability, which results in a rotational low-frequency magnetowave. The relevance of the TAWI is discussed for the growth of small-scale magnetic fields in astrophysical environments, which are needed to explain the electromagnetic emissions by astrophysical jets. It is outlined how this instability could be examined experimentally.

  • 326.
    Diepenbrock, Stefan
    et al.
    University of Münster, Germany.
    Ropinski, Timo
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    From Imprecise User Input to Precise Vessel Segmentations2012In: Eurographics Workshop on Visual Computing for Biology and Medicine, VCBM 2012, The Eurographics Association , 2012, p. 65-72Conference paper (Refereed)
    Abstract [en]

    Vessel segmentation is an important prerequisite for many medical applications. While automatic vessel segmentation is an active field of research, interaction and visualization techniques for semi-automatic solutions have gotten far less attention. Nevertheless, since automatic techniques do not generally achieve perfect results, interaction is necessary. Especially for tasks that require an in-detail inspection or analysis of the shape of vascular structures precise segmentations are essential. However, in many cases these can only be generated by incorporating expert knowledge. In this paper we propose a visual vessel segmentation system that allows the user to interactively generate vessel segmentations. Therefore, we employ multiple linked views which allow to assess different aspects of the segmentation and depict its different quality metrics. Based on these quality metrics, the user is guided, can assess the segmentation quality in detail and modify the segmentation accordingly. One common modification is the editing of branches, for which we propose a semi-automatic sketch-based interaction metaphor. Additionally, the user can also influence the shape of the vessel wall or the centerline through sketching. To assess the value of our system we discuss feedback from medical experts and have performed a thorough evaluation.

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  • 327.
    Djurberg, Elin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    An Analysis of an internal Workflow2023Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In todays complex society many companies have large and complex workflows which may involve several different tools. This report will look into the workflow of a big programming company, from when a mistake is found in the code until it has been corrected and see how the workflow can be improved.

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  • 328.
    Dofsand, Felicia
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Lundegård, Lina
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Var nionde kvinna2021Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    SammanfattningBröstcancer drabbar var nionde kvinna i Sverige och är den näst vanligaste dödsorsaken förkvinnor under 40 år. Självundersökning är en relativt enkel metod för att upptäcka tidigatecken på bröstcancer. Trots detta gör inte 63.8% av kvinnor mellan 20-40 årsjälvundersökning. Denna studie undersökte hur motivationen hos målgruppen påverkadesutifrån olika kommunikationsstilar, en narrativ och en didaktisk. Undersökningengenomfördes i form av framtagandet av två olika animerade informationsfilmer omsjälvundersökning. Resultatet visar att bägge filmerna ökar motivationen hos respondenternamen att den narrativa filmen ger störst effekt. Motivationen påverkar även hur lätt eller svårtrespondenterna tycker att det känns att genomföra självundersökning, varpå vid högremotivation visar resultatet att det upplevs lättare att genomföra. Slutsatsen som dras för dennastudie är att en narrativ kommunikationsstil är att föredra för att öka motivation hos kvinnormellan 20-40 år, samt att filmen bör återfinnas i sociala medier och kan då fungera som entrigger för ökad motivation. 

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  • 329.
    Dolo, Gilbert
    et al.
    University of Cape Town, South Africa.
    Haglund, Jesper
    Karlstad University, Sweden.
    Schönborn, Konrad
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Thermal Cameras as a Semiotic Resource for Inquiry in a South African Township School Context2018In: Designs for Learning, ISSN 1654-7608, Vol. 10, no 1, p. 123-134Article in journal (Refereed)
    Abstract [en]

    Inquiry-based approaches to science education are central to recent South African primary and secondary school curricula, but have been found challenging to adopt in disadvantaged township contexts. It is therefore important to find ways of introducing inquiry-based approaches, where pupils are encouraged to investigate phenomena they are interested in and to engage in true dialogue, as opposed to teacher-led triadic dialogue. We typically experience thermal phenomena through the sense of touch, but infrared (IR) cameras provide an additional opportunity to experience heat-related phenomena through the visual sense. Previously, in a Swedish context, we have found that hand-held IR cameras allow for strong pedagogical affordances and inspire pupils to engage in inquiry in the area of thermal science. In the present case study, grade 7 and 8 pupils (13–14 years old) in two South African township schools were introduced to IR cameras during predict-observe-explain (POE) exercises on heat conduction. The results revealed that if pupils had a sufficient conceptual understanding of heat conduction beforehand, they were capable of engaging in true dialogue in relation to the exercises and interpreting the thermal camera visual imagery. However, if pupils did not show such understanding, it was tempting for them and the facilitator to resort to triadic dialogue.

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  • 330.
    Dolo, Gilbert
    et al.
    University of Cape Town, South Africa.
    Haglund, Jesper
    Karlstad University, Sweden.
    Schönborn, Konrad
    Linköping University, Department of Science and Technology, Media and Information Technology.
    Thermal Cameras as a Semiotic Resource for Teaching in South African Township Schools2019In: Book of Long Paper Abstracts, Symposia, Short Papers, Snapshots of the 27th Annual Meeting of the Southern African Association for Research in Mathematics, Science and Technology Education (SAARMSTE) / [ed] Good, M. & Stevenson-Milln, C., Durban, 2019, p. 460-463Conference paper (Refereed)
    Abstract [en]

    This study investigates how thermal cameras can be used in meaning-making around thermal phenomena. Predict-observe-explain (POE) tasks were conducted with Grade 7 and 8 learners in two township schools. Results showed that learners coordinated multiple semiotic resources including dynamic thermal images, spoken language and touch in reasoning about heat and temperature. Although results support the literature in that inquiry-based approaches are challenging to implement in this context, the Grade 8 learners indicated that true dialogue was possible to achieve by demonstrating different lines of collaborative inquiry.

  • 331.
    Domova, Veronika
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. ABB Corporate Research, Västerås.
    Designing visualization and interaction for industrial control rooms of the future2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the last decades, the industry has been undergoing extensive digitization leading to complex ensembles of humans, machines, autonomous agents, and sensors. With this new setup comes the challenge of how to appropriately support work-practices of industrial operators who now need to monitor and control complex industrial processes through remote interfaces. Information overflow and restrictive interfaces are two significant problems that operators face in their daily routines. In this PhD, I explore approaches to visualization and interaction that would reduce industrial operators' information load and enable them to perform their duties in an efficient, reliable, and safe manner. Industrial users and industrial settings are the starting points of my research.

    In this thesis, I describe multiple examples of custom-tailored data visualizations that reduce the operator's visual load by consolidating large amounts of data into compact overview displays with often nontrivial data presentation. With respect to interaction, I propose several tangible and tactile interfaces, as well as concepts for natural interaction, that let the user freely interact with the control station and the information it depicts. Finally, I propose several concepts of adaptive systems that adjust to the operator's context to ensure their high situational awareness and convenience of interaction.

    Even though this thesis is primarily intended for the community of interaction designers, I expect it to be of interest to a broader audience due to its relation to the user experience field. To a certain extent, everyone can resonate with the user's problems because, in our everyday life, we all are users of some technology and services. Furthermore, for a lay reader, this work can be seen as a comprehensive introduction to how the industry works and what role the human plays there.

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  • 332.
    Domova, Veronika
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Guiding the Operators Attention Among a Plurality of Operator Workstation Screens2020In: 2020 25TH IEEE INTERNATIONAL CONFERENCE ON EMERGING TECHNOLOGIES AND FACTORY AUTOMATION (ETFA), IEEE , 2020, p. 541-548Conference paper (Refereed)
    Abstract [en]

    In the age of extensive industrial digitalization, industrial operators are facing increasing pressure from the growing amount of data being delivered to industrial control rooms. Humans limited perceptual system is the bottleneck when it comes to processing large volumes of information. Too many screens crammed with textual and numerical data make the user disoriented in information potentially leading to fatal mistakes and insufficient situation awareness. This paper explores possibilities of guiding operators attention to the most urgent information by means of visual aid systems. In this work, two concepts of such systems were developed and evaluated in a lab environment. The evaluation results indicate a clear benefit of using the developed concepts.

  • 333.
    Domova, Veronika
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Untethered Workspaces: A Zones Concept Towards Supporting Operator Movements In Control Rooms2016Conference paper (Refereed)
    Abstract [en]

    Within industrial domains there is a need for control room operators to be in constant contact with the different processes they are responsible for controlling. With this responsibility comes the need to constantly be near their workstations in order to monitor, diagnose and quickly troubleshoot issues presented. These workstations, however, restrict operators in control rooms from moving freely within the control room itself, such as between their own and their colleague’s workstations since they cannot interact with the system from a distance. These systems also restrict those operators who need to continuously enter the control room from the plant/factory floor since interacting with process graphics requires them to remove all of their specialized equipment every time (e.g. large bulky safety gloves). We therefore present a concept for control room operators that supports their untethering from dedicated workstations, providing them with the ability to interact in a more flexible way.

  • 334.
    Domova, Veronika
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Gärtner, Erik
    Lund University, Lund, Sweden.
    Präntare, Fredrik
    Linköping University, Department of Computer and Information Science, Artificial Intelligence and Integrated Computer Systems. Linköping University, Faculty of Science & Engineering.
    Pallin, Martin
    Royal Institute of Technology, Stockholm, Sweden.
    Källström, Johan
    Linköping University, Department of Computer and Information Science, Artificial Intelligence and Integrated Computer Systems. Linköping University, Faculty of Science & Engineering.
    Korzhitskii, Nikita
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Improving Usability of Search and Rescue Decision Support Systems: WARA-PS Case Study2020In: In proceedings of the 2020 25th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA), Vienna, Austria: IEEE conference proceedings, 2020, p. 1251-1254Conference paper (Refereed)
    Abstract [en]

    Novel autonomous search and rescue systems, although powerful, still require a human decision-maker involvement. In this project, we focus on the human aspect of one such novel autonomous SAR system. Relying on the knowledge gained in a field study, as well as through the literature, we introduced several extensions to the system that allowed us to achieve a more user-centered interface. In the evaluation session with a rescue service specialist, we received positive feedback and defined potential directions for future work.

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  • 335.
    Domova, Veronika
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. ABB Corp Res, Sweden.
    Munoz, Alvaro Aranda
    RISE, Sweden.
    Vaara, Elsa
    RISE, Sweden.
    Edoff, Petra
    RISE, Sweden.
    Feel the Water: Expressing Physicality of District Heating Processes in Functional Overview Displays2019In: PROCEEDINGS OF THE 2019 ACM INTERNATIONAL CONFERENCE ON INTERACTIVE SURFACES AND SPACES (ISS 19), ASSOC COMPUTING MACHINERY , 2019, p. 229-240Conference paper (Refereed)
    Abstract [en]

    This paper describes an explorative design study conducted in the scope of a collaborative research project in the district heating domain. In the scope of the project, we have arranged extensive field studies at two power plants to understand the workflows, problems, and needs of industrial operators. We relied on the gained knowledge to design and develop novel visual interfaces that would communicate the overall status of the district heating system at-a-glance. We aimed at exploring potential directions and alternatives beyond conventional industrial interfaces. One particular aspect of our research was related to how the physicality of the underlying industrial processes can be expressed by purely visual means. The paper introduces three high-fidelity prototypes demonstrating the novel visualizations developed. The paper explains the design choices made, namely the relation between the selected visual encodings to the requirements of the industrial operators tasks. Preliminary evaluation indicates industrial operators interest in the designed solutions. Future work will incorporate an extensive qualitative evaluation on site.

  • 336.
    Domova, Veronika
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. ABB Corporate Research, Västerås, Sweden.
    Sander-Tavallaey, Shiva
    ABB Corporate Research, Västerås, Sweden.
    Visualization for Quality Healthcare: Patient Flow Exploration2019In: 2019 IEEE International Conference on Big Data (Big Data), IEEE, 2019, p. 1072-1079Conference paper (Refereed)
    Abstract [en]

    The health and medical institutes and hospitalsare facing several challenges in the short and long term, i.e.demographic changes, demands on improving quality, limitedresources and cost requirements. To cope with these challenges,the health care sector needs to become more efficient, whilemaintaining and improving the quality of care. Efficient andtransparent information flow across the whole system plays a keyrole even in this context. Being able to analyze the patient flowsas the first step will provide the possibility to more efficientlymanage medical resources and better serve incoming patients. Inthis work, we have developed a web-based portal for interactiveanalysis of patient flow data to assist hospital authorities toimprove and optimize the time and quality of the providedservices. The developed tool facilitates short and long termoptimization of resource allocation by analyzing the past, as wellas current, patient flows, identifying bottlenecks and exploringthe reasons for the occurred waiting times.

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  • 337.
    Domova, Veronika
    et al.
    Stanford Univ, CA 94305 USA.
    Vrotsou, Katerina
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    A Model for Types and Levels of Automation in Visual Analytics: A Survey, a Taxonomy, and Examples2023In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 29, no 8, p. 3550-3568Article in journal (Refereed)
    Abstract [en]

    The continuous growth in availability and access to data presents a major challenge to the human analyst. As the manual analysis of large and complex datasets is nowadays practically impossible, the need for assisting tools that can automate the analysis process while keeping the human analyst in the loop is imperative. A large and growing body of literature recognizes the crucial role of automation in Visual Analytics and suggests that automation is among the most important constituents for effective Visual Analytics systems. Today, however, there is no appropriate taxonomy nor terminology for assessing the extent of automation in a Visual Analytics system. In this article, we aim to address this gap by introducing a model of levels of automation tailored for the Visual Analytics domain. The consistent terminology of the proposed taxonomy could provide a ground for users/readers/reviewers to describe and compare automation in Visual Analytics systems. Our taxonomy is grounded on a combination of several existing and well-established taxonomies of levels of automation in the human-machine interaction domain and relevant models within the visual analytics field. To exemplify the proposed taxonomy, we selected a set of existing systems from the event-sequence analytics domain and mapped the automation of their visual analytics process stages against the automation levels in our taxonomy.

  • 338.
    Doyle, Scott
    et al.
    Rutgers University, Dept. of Biomedical Engineering Piscataway, NJ, USA.
    Monaco, James
    Rutgers University, Dept. of Biomedical Engineering Piscataway, NJ, USA.
    Madabhushi, Anant
    Rutgers University, Dept. of Biomedical Engineering Piscataway, NJ, USA.
    Lindholm, Stefan
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. Siemens Corporate Research,Princeton, NJ, USA.
    Ljung, Patric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. Siemens Corporate Research,Princeton, NJ, USA.
    Ladic, Lance
    Siemens Corporate Research,Princeton, NJ, USA.
    Tomaszewski, John
    University of Pennsylvania,Dept. of Surgical Pathology Philadelphia, PA, USA.
    Feldman, Michael
    University of Pennsylvania,Dept. of Surgical Pathology Philadelphia, PA, USA.
    Evaluation of effects of JPEG2000 compression on a computer-aided detection system for prostate cancer on digitized histopathology2010In: Biomedical Imaging: From Nano to Macro, 2010 IEEE International Symposium on, 2010, p. 1313-1316Conference paper (Refereed)
    Abstract [en]

    A single digital pathology image can occupy over 10 gigabytes of hard disk space, rendering it difficult to store, analyze, and transmit. Though image compression provides a means of reducing the storage requirement, its effects on computer-aided diagnosis (CAD) and pathologist performance are not yet clear. In this work we assess the impact of compression on the ability of a CAD system to detect carcinoma of the prostate (CaP) on histological sections. The CAD algorithm proceeds as follows: Glands in the tissue are segmented using a region-growing algorithm, and the size of each gland is extracted. A Markov prior (specifically, a probabilistic pairwise Markov model) is employed to encourage nearby glands to share the same class (i.e. cancerous or non-cancerous). Finally, cancerous glands are aggregated into continuous regions using a distancehull algorithm. We trained the CAD system on 28 images of wholemount histology (WMH) and evaluated performance on 12 images compressed at 14 different compression ratios (a total of 168 experiments) using JPEG2000. Algorithm performance (measured using the under the receiver operating characteristic curves) remains relatively constant for compression ratios up to1 :256, beyond which performance degrades precipitously. For completeness we also have an expert pathologist view a randomly-selected set of compressed images from one of the whole mount studies and assign a confidence measure as to their diagnostic fidelity. Pathologist confidence declined with increasing compression ratio as the information necessary to diagnose the sample was lost, dropping from 100% confidence at ratio 1:64 to 0% at ratio 1:8192.

  • 339.
    Dromberg, Peder
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Maric, Ivanna
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Escape the Decision Arena: Designing and evaluating an immersive collaborative gaming experience in a cylindrical environment2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Decision Arena in Linköping University contains a 360° cylindrical display with a complementary 360° sound system consisting of eight evenly spaced speakers along the bottom edge of the screen. This paper explores if an immersive game can be developed for such a non-typical gaming environment. The result was a two-player cooperative puzzle-solving game inspired by Escape Rooms where the final product was evaluated through playtesting, questionnaires and interviews by participants. The game was developed using Unreal Engine for the graphics and game logic, SuperCollider for sound implementation, and a custom website was used to control the game, which uses WebSockets to communicate with Unreal Engine. The evaluation results show that most participants found the game immersive and engaging, which points to that it is possible to develop immersive games for the Decision Arena. According to feedback, the most challenging, and sometimes immersionbreaking, aspect of the game was localizing the sound. The evaluation results also suggests that certain sounds are easier to localize in the Decision Arena than others, which led to the conclusion that further research in sound localization is beneficial if more sound-based games were to be developed for this environment.

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  • 340.
    Durmén Blunt, Tina
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Personalized visualization of blog statistics2013Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report documents the research, implementation and result for a master thesis in Media Technology and Engineering at Linkoping University. The aim of the project was to develop a personalized visualization application of blog statistics to be implemented on a web based community for blog authors. The purpose of the application is to provide the users with a tool to explore statistics connected to their own blog. Based on a literature study in usability and information visualization the application design was developed and implemented. The implementation resulted in a JavaScript based application, BlogVis, that allows the users to compare their own blog statistics with others, as well as compare periods of time in the statistic history of the blog.

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  • 341.
    Dwyer, Tim
    et al.
    Monash University, Australia.
    Elmqvist, Niklas
    University of Maryland, MD 20742 USA.
    Fisher, Brian
    Simon Fraser University, Canada.
    Franconeri, Steve
    Northwestern University, IL 60208 USA.
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Mike Kirby, Robert M.
    University of Utah, UT 84112 USA.
    Liu, Shixia
    Tsinghua University, Peoples R China.
    Schreck, Tobias
    Graz University of Technology, Austria.
    Yuan, Xiaoru
    Peking University, Peoples R China.
    Message from the VIS Paper Chairs and Guest Editors Preface2018In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 24, no 1, p. XI-XVArticle in journal (Other academic)
  • 342.
    Dynewall, Tove
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Johansson, Ida
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Att interagera med 3D-objekt i en förstärkt verklighet2018Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Augmented reality (AR), eller förstärkt verklighet, är variation av virtuell verklighet. AR är ett relativt nytt medium och har på senare tiden blivit allt vanligare i applikationer för mobilen. Då AR är så starkt kopplat till den verkliga världen har det blivit allt vanligare att integrera 3D objekt som man kan manipulera. I och med att AR är ett så pass ungt medium har man inte satt alla riktlinjer än för hur utformningen av en AR-applikation ska se ut vilket, kan komma att resultera i vissa hinder. Ett sådant hinder som vi har sett är hur man fysiskt utför gester och interagerar med 3D objekt. Vi har därför valt att arbeta med hur man på ett så effektivt sätt som möjligt ska kunna utföra dessa interaktioner, då det idag inte finns någon riktigt standard och olika applikationer använder sig av olika gester för olika interaktioner, vilket inte är användarvänligt utan förvirrande. Med hjälp av teoretiska ramverk har vi fått förståelse för mediet och har även lagt en grund för den övriga studien. Vi har även utfört en kartläggning av interaktioner i redan existerande applikationer, vi har gjort en workshop med yrkesverksamma och ett användartest där vi har undersökt hur användaren själv vill utföra interaktionerna. Med hjälp av dessa har vi kommit fram till ett antal rekommendationer på gester som intuitivt kopplas till en särskild interaktion och särskilda interaktioner. Vi har även definierat problem kopplade till dessa.

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    Att interagera med 3D-objekt i en förstärkt verklighet
  • 343.
    Edhag, Hanna
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Fälth, Ebba
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Välkommen till Norrköping: Att designa en användbar applikation för att hjälpa människor upptäcka Norrköping2020Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This study examines how a useable application to help people explore the city of Norrköping  could be designed. The design process has proceeded with the users’ needs in mind through  user tests, observations and interviews with potential users. The process has also included a  pre-study, a processing phase and a detailing phase where the concept and the design for  the application have been developed and evaluated which resulted in an interactive digital  prototype.   The study intended to answer the question "How can an application that aims to help people  explore points of interest (places, tourist attractions, events and activities) in Norrköping be  designed to give the user a positive user experience?". The result shows that the produced  prototype for the application Welcome to Norrköping gives the user a positive user experience and that the application would be helpful for exploring the city. 

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  • 344.
    Edström, Emil
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Cardell, Tim
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Lundin Palmerius, Karljohan
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Improved Offset Handling in Hand-centered Object Manipulation Extending Ray-casting2022In: 2022 IEEE CONFERENCE ON VIRTUAL REALITY AND 3D USER INTERFACES ABSTRACTS AND WORKSHOPS (VRW 2022), IEEE COMPUTER SOC , 2022, p. 655-656Conference paper (Refereed)
    Abstract [en]

    As Virtual Reality (VR) is becoming a readily available tool in an increasing number of fields, we see also an increasing number of non-technical users entering virtual environments (VEs). One pose manipulation technique that has the potential to be both fast and intuitive to use, is the Hand-centered Object Manipulation Extending Ray-casting (HOMER), presented first by Bowman and Hodges [1]. In this paper we take a look at how a naive implementation of HO-MER can lead to unintuitive interaction and present mathematics for avoiding this problem, by using a rotational offset of the grab vector instead of a static offset vector. Subsequently we compare the naive and rotation-based versions with respect to task completion time and number of re-grabs, and measure their respective System Usability Scale (SUS) score and Raw NASA Task Load Index (RTLX)

  • 345.
    Edström, Jonas
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Friedner, Sol
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Målfokuserad webbdesign2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    HTH är ett danskt bolag som främst säljer exklusiva och kvalitativa kök. HTH har tre mätbara mål för sin webbplats, att besökarna når avdelningarna för e-shop, för boka möte samt använder den digitala designtjänsten. Få besökare når webbplatsens avdelningar för målen, därför är studiens syfte att undersöka hur en webbdesign kan påverka i vilken grad besökarna når fastställda mål för en webbplats. De frågor som har undersökts är vad som är viktigt i utvecklingen av en målanpassad webbdesign, samt hur en redesign kan påverka i vilken grad besökarna når fastställda mål och samtidigt får en positiv upplevelse. Teorikapitlet redogör för litteratur inom design och beteendevetenskap för att förstå olika aspekter av design samt hur en design påverkar användarens upplevelse. Studien har genomförts med en kombination av kvantitativ och kvalitativ metod där samtliga användartester har använt metoderna Tänka-högt och Semantic differential. För att fullfölja studiens syfte delades studien in i tre steg. Första steget var att utifrån HTH:s mål för webbplatsen, analysera den befintliga webbdesignen, där analysen kopplades till litteratur. Utifrån resultatet från steg ett utvecklade studiens författare ett förslag på en korrigerad webbdesign i form av en digital prototyp. Avslutningsvis utfördes användartester för att jämföra och utvärdera den befintliga webbdesignen med författarnas designförslag. Användartesterna utvärderades med fem kriterier för en användbar design, samtidigt som data kopplades till litteratur och analyserades. Det framgick av utvärderingen att webbdesignens struktur och visuella uttryck påverkar hur effektivt besökaren noterar de primära målen för webbplatsen. En mer avskalad webbdesign utför en mindre risk att användaren blir distraherad påväg mot webbplatsens fastställda mål och därmed en ökad chans att de fastställda målen enklare och effektivare nås.

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  • 346.
    Edström, Sofie
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Interior visualization of an office in Braxen 32013Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Den här rapporten beskriver ett antal olika visualiseringstekniker som testats med hjälp av 3ds Max Design 2012, Revit Architecture 2012 samt Photoshop CS5. Syftet var att ta reda på om de kunde användas vid interiör visualisering och hur de används. Projektet grundar sig i att White Arkitekter AB arbetar med utvecklingen av sitt blivande kontor i Braxen 3 och de ville testa de olika teknikerna i utvecklingssyfte i samband med designutveckling av kontoret. Visualiseringsteknikerna beskrivs utifrån vad de kan användas till och vad de har används till i de tre olika scener som byggts upp med hjälp av programmen, men även hur arbetsgången fungerade. Viss jämförelse mellan olika tekniker och olika sätt att utföra samma tekniker har gjorts. Till en början beskrivs hur modelleringen av scenerna har gått till. Efter det beskrivs de tekniker som används för att utveckla de tre olika scenerna och för att nå ett resultat i form av ett antal slutrenderingar som sedan redovisas i resultatdelen. Slutsatsen som drogs var att alla de tekniker som beskrivits är tillämpbara för interiör visualisering rent praktiskt, men de kanske inte är tillämpbara av tids- och kostnadsaspekter. Sedan diskuterar författaren kring teknikernas användbarhet och åsikter som utvecklats kring teknikerna och arbetsgången under arbetets genomförande.

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  • 347.
    Eilertsen, Gabriel
    Linköping University, Department of Science and Technology, Media and Information Technology.
    High-resolution simulation and rendering of gaseous phenomena from low-resolution data2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Numerical simulations are often used in computer graphics to capture the effects of natural phenomena such as fire, water and smoke. However, simulating large-scale events in this way, with the details needed for feature film, poses serious problems. Grid-based simulations at resolutions sufficient to incorporate small-scale details would be costly and use large amounts of memory, and likewise for particle based techniques.

    To overcome these problems, a new framework for simulation and rendering of gaseous phenomena is presented in this thesis. It makes use of a combination of different existing concepts for such phenomena to resolve many of the issues in using them separately, and the result is a potent method for high-detailed simulation and rendering at low cost.

    The developed method utilizes a slice refinement technique, where a coarse particle input is transformed into a set of two-dimensional view-aligned slices, which are simulated at high resolution. These slices are subsequently used in a rendering framework accounting for light scattering behaviors in participating media to achieve a final highly detailed volume rendering outcome. However,the transformations from three to two dimensions and back easily introduces visible artifacts, so a number of techniques have been considered to overcome these problems, where e.g. a turbulence function is used in the final volume density function to break up possible interpolation artifacts.

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  • 348.
    Eilertsen, Gabriel
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    The high dynamic range imaging pipeline: Tone-mapping, distribution, and single-exposure reconstruction2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Techniques for high dynamic range (HDR) imaging make it possible to capture and store an increased range of luminances and colors as compared to what can be achieved with a conventional camera. This high amount of image information can be used in a wide range of applications, such as HDR displays, image-based lighting, tone-mapping, computer vision, and post-processing operations. HDR imaging has been an important concept in research and development for many years. Within the last couple of years it has also reached the consumer market, e.g. with TV displays that are capable of reproducing an increased dynamic range and peak luminance.

    This thesis presents a set of technical contributions within the field of HDR imaging. First, the area of HDR video tone-mapping is thoroughly reviewed, evaluated and developed upon. A subjective comparison experiment of existing methods is performed, followed by the development of novel techniques that overcome many of the problems evidenced by the evaluation. Second, a largescale objective comparison is presented, which evaluates existing techniques that are involved in HDR video distribution. From the results, a first open-source HDR video codec solution, Luma HDRv, is built using the best performing techniques. Third, a machine learning method is proposed for the purpose of reconstructing an HDR image from one single-exposure low dynamic range (LDR) image. The method is trained on a large set of HDR images, using recent advances in deep learning, and the results increase the quality and performance significantly as compared to existing algorithms.

    The areas for which contributions are presented can be closely inter-linked in the HDR imaging pipeline. Here, the thesis work helps in promoting efficient and high-quality HDR video distribution and display, as well as robust HDR image reconstruction from a single conventional LDR image.

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    The high dynamic range imaging pipeline: Tone-mapping, distribution, and single-exposure reconstruction
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  • 349.
    Eilertsen, Gabriel
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Forssén, Per-Erik
    Linköping University, Department of Electrical Engineering, Computer Vision. Linköping University, Faculty of Science & Engineering.
    Unger, Jonas
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    BriefMatch: Dense binary feature matching for real-time optical flow estimation2017In: Proceedings of the Scandinavian Conference on Image Analysis (SCIA17) / [ed] Puneet Sharma, Filippo Maria Bianchi, Springer, 2017, Vol. 10269, p. 221-233Conference paper (Refereed)
    Abstract [en]

    Research in optical flow estimation has to a large extent focused on achieving the best possible quality with no regards to running time. Nevertheless, in a number of important applications the speed is crucial. To address this problem we present BriefMatch, a real-time optical flow method that is suitable for live applications. The method combines binary features with the search strategy from PatchMatch in order to efficiently find a dense correspondence field between images. We show that the BRIEF descriptor provides better candidates (less outlier-prone) in shorter time, when compared to direct pixel comparisons and the Census transform. This allows us to achieve high quality results from a simple filtering of the initially matched candidates. Currently, BriefMatch has the fastest running time on the Middlebury benchmark, while placing highest of all the methods that run in shorter than 0.5 seconds.

  • 350.
    Eilertsen, Gabriel
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Hajisharif, Saghi
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hanji, Param
    Univ Cambridge, England.
    Tsirikoglou, Apostolia
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Mantiuk, Rafal K.
    Univ Cambridge, England.
    Unger, Jonas
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    How to cheat with metrics in single-image HDR reconstruction2021In: 2021 IEEE/CVF INTERNATIONAL CONFERENCE ON COMPUTER VISION WORKSHOPS (ICCVW 2021), IEEE COMPUTER SOC , 2021, p. 3981-3990Conference paper (Refereed)
    Abstract [en]

    Single-image high dynamic range (SI-HDR) reconstruction has recently emerged as a problem well-suited for deep learning methods. Each successive technique demonstrates an improvement over existing methods by reporting higher image quality scores. This paper, however, highlights that such improvements in objective metrics do not necessarily translate to visually superior images. The first problem is the use of disparate evaluation conditions in terms of data and metric parameters, calling for a standardized protocol to make it possible to compare between papers. The second problem, which forms the main focus of this paper, is the inherent difficulty in evaluating SI-HDR reconstructions since certain aspects of the reconstruction problem dominate objective differences, thereby introducing a bias. Here, we reproduce a typical evaluation using existing as well as simulated SI-HDR methods to demonstrate how different aspects of the problem affect objective quality metrics. Surprisingly, we found that methods that do not even reconstruct HDR information can compete with state-of-the-art deep learning methods. We show how such results are not representative of the perceived quality and that SI-HDR reconstruction needs better evaluation protocols.

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