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  • 1.
    Castleton, C W M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Mirbt, S
    Condensed Matter Theory, Department of Physics, Uppsala University, Uppsala, Sweden.
    Ab initio study of neutral vacancies in InP using supercells and finite size scaling2003In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, p. 407-411Article in journal (Refereed)
    Abstract [en]

    The formation energies and relaxed structures of the neutral vacancies in InP are calculated by planewave density functional theory, using supercells of 8, 64, 216 and 512 atoms together with finite size scaling. The effects of electrostatic defect-defect interactions and the truncation of elastic relaxations by the finite supercell are examined. The unrelaxed formation energies are 4.95+/-0.10 and 3.00+/-0.10eV for V-In(+0) and V-P(+0) respectively, and the relaxed formation energies are 4.20+/-0.05 and 2.35+/-0.15 eV. When relaxed, V-In(+0) remains very nearly symmetric with a 40% volume reduction, V-P(+0) on the other hand develops a double dimerized structure, with an similar to12% Jahn-Teller distortion and a 45% volume reduction. It is shown that finite size scaling sometimes reveals that energies are not converged even in the 512 atom supercell, and can thus be important tool in theoretical studies of defects in semiconductors, if sufficient care is taken with strongly Jahn Teller active defects.

  • 2. Davidsson, P
    et al.
    Olin, Håkan
    Department of Physics, Chalmers University of Technology and University of Göteborg.
    Vortex mapping on gold covered conventional type II superconductors using the very low temperature tunnelling microscope1994In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 194-196, no Part 1, p. 375-376Article in journal (Refereed)
    Abstract [en]

    We have used a dilution refrigerator cooled STM for investigating the vortex state in lead-bismuth alloy 4000Aofilms. The vortices were recognized by the decreasing dynamic conductance near the gap voltage when the instrument was operated in its normal feed back mode. A clean surface suitable for tunneling was maintained by a 75Aolayer of gold deposited on top of the sample film. The temperature was kept at 80 mK and magnetic fields between 0 and 0.2 T were used.

     

  • 3.
    Kanaki, Kalliopi
    et al.
    European Spallation Source ERIC, Lund.
    Kittelmann, Thomas
    European Spallation Source ERIC, Lund.
    Cai, Xiao Xiao
    European Spallation Source ERIC, Lund; Technical University of Denmark, DTU, Kgs. Lyngby, Denmark.
    Klinkby, Esben
    European Spallation Source ERIC, Lund; Technical University of Denmark, DTU, Kgs. Lyngby, Denmark.
    Knudsen, Erik B.
    Technical University of Denmark, DTU, Kgs. Lyngby, Denmark.
    Willendrup, Peter
    European Spallation Source ERIC, Lund; Technical University of Denmark, DTU, Kgs. Lyngby, Denmark.
    Hall-Wilton, Richard
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. European Spallation Source ERIC, Lund.
    Simulation tools for detector and instrument design2018In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 551, p. 386-389Article in journal (Refereed)
    Abstract [en]

    The high performance requirements at the European Spallation Source have been driving the technological advances on the neutron detector front. Now more than ever is it important to optimize the design of detectors and instruments, to fully exploit the ESS source brilliance. Most of the simulation tools the neutron scattering community has at their disposal target the instrument optimization until the sample position, with little focus on detectors. The ESS Detector Group has extended the capabilities of existing detector simulation tools to bridge this gap. An extensive software framework has been developed, enabling efficient and collaborative developments of required simulations and analyses – based on the use of the Geant4 Monte Carlo toolkit, but with extended physics capabilities where relevant (like for Bragg diffraction of thermal neutrons in crystals). Furthermore, the MCPL (Monte Carlo Particle Lists) particle data exchange file format, currently supported for the primary Monte Carlo tools of the community (McStas, Geant4 and MCNP), facilitates the integration of detector simulations with existing simulations of instruments using these software packages. These means offer a powerful set of tools to tailor the detector and instrument design to the instrument application. 

  • 4.
    Koptioug, Andrei
    et al.
    aInstitute of Chemical Kinetics and Combustion, USSR Academy of Sciences, Novosibirsk 630090, USSR.
    Saik, Vladimir
    Anisimov, Oleg
    Molin, Yurij
    Antzutkin, Oleg
    Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions1990In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 164, no 1-2, p. 200-204Article in journal (Refereed)
    Abstract [en]

    It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.

  • 5. Kubatkin, S E
    et al.
    Olin, Håkan
    Physics Department, Chalmers University of Technology.
    Davidsson, P
    Danilov, A V
    Claeson, T
    Movement of scattering centers in a point contact induced by a scanning tunneling microscope1994In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 194-196, no Part 1, p. 991-992Article in journal (Refereed)
    Abstract [en]

    A new method is introduced to study transport in a mesoscopic sample. The electric field from an STM-tip is used to locally influence a mesoscopic object. We detect abrupt changes in the mesoscopic signal both as a function of the tip position and tip-sample voltage. They could be interpreted as due to spatial shifts or changes in the activity of scattering centers in the sample.

     

  • 6.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martinez, A.
    Sannemo, Ulf
    Hjelm, Mats
    Bellotti, E.
    Brennan, K.
    Monte Carlo simulation of high field hole transport in 4H-SiC including band to band tunneling and optical interband transisitons2002In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 314, no 1-4, p. 68-71Article in journal (Refereed)
    Abstract [en]

    The high field hole transport in 4H-SiC has been studied using a full band Monte Carlo (MC) simulation model that includes band to band tunneling and allows mixing of the band states during carrier drift. Impact ionization coefficients along the c-axis direction have been extracted and compared with experimental data. It is shown that the band to band tunneling mechanism is crucial in order to explain experimental results. The carrier distribution function obtained from the MC simulations has been used to determine the breakdown luminescence spectra coming from interband transitions. Our results are in good agreement with the available experimental luminescence spectra for SiC polytypes, and the importance of including interband tunneling is clearly demonstrated.

  • 7.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Differentiation and power loss computation of classical Preisach model2004In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 343, no 1-4, p. 96-100Article in journal (Refereed)
    Abstract [en]

    In certain applications of hysteresis, the differentiated output is of interest rather than the output described by a model of hysteresis. Instead of numerical backward differentiation, a direct differentiation of the classical Preisach model is presented here. This gives rise to five cases depending on the hysteresis history. An energy state for the hysteresis model is defined in the paper. The power loss can then be computed by differentiating the energy state, whereby the same five cases occur. Moreover, the computation time of the energy loss is considerably reduced when applying numerical integration of this power loss, compared to methods in the literature. The derived expressions have been employed in simulations of an equivalent circuit for superconductors using standard simulation tools.

  • 8.
    Sjöström, Mårten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Grilli, F.
    Spreafico, S.
    Modelling of a three-phase concentric HTS-cable2008In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 403, no 2-3, p. 405-409Article in journal (Refereed)
    Abstract [en]

    We have considered a three-phase concentric HTS-cable with a copper shield neutral wire in a three-phase system. An equivalent circuit model describing the cable by the global quantities current and voltage has been developed, by which the effects of design parameters such as material, layer radii and pitch length can be investigated. The equivalent circuit consists of a nonlinear resistance and a hysteretic inductance (to model HTS), and an inductance (to model mutual inductances). The equivalent circuit is here extended with a by-pass resistance that models the silver matrix of the HTS tape. This enables to consider over-critical currents (i.e. beyond hysteresis saturation), whereby extra care must be taken for the numerical simulations. We have considered a design of fixed radii and have optimized the pitch length of each layer in order to have equal reactances for all phases.

  • 9.
    Sjöström, Mårten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Gulliksson, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Identifiability Analysis of Prandtl-Ishilinskii Hysteresis Model with Saturation2008In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 403, no 2-3, p. 266-270Article in journal (Refereed)
    Abstract [en]

    A new class of Preisach operators based on play operators with an inverse in a closed form and allowing for saturation has recently been proposed. Its existence criteria and identification procedure were considered in earlier articles. The present paper analyses the identification procedure with respect to the sensitivity to underlying functions (i.e. intrinsic behaviour of the hysteretic system), to spline approximation, and to the least square error estimation procedure. The analysis shows that model errors are significantly influenced by large derivatives of the underlying functions. Spline approximations have generally little effect on model errors. In particular, an upper bound of for the relative parameter error due to measurement discrepancies has been derived for the least square error problem. The bound increases, the closer to saturation data are measured.

  • 10.
    Sjöström, Mårten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Visone, C.
    "Moving" Prandtl-Ishilinskii operators with compensator in a closed form2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 372, no 1-2, p. 97-100Article in journal (Refereed)
    Abstract [en]

    The present paper proposes a class of Preisach-like hysteresis models with saturation having the compensator operator in a closed form, where a mean field contribution (moving model or feedback model) is also considered. The paper pays attention to the conditions for which such a "moving" model is well-defined. Moreover, attention is given to the identification procedures requiring a limited amount of data, where some constraints enhance the correspondence of the model to the underlying hysteresis. Examples showing performances of the model in cases of physical interest are provided.

  • 11. Visone, C.
    et al.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Exact invertible hysteresis models based on play operators2004In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 343, no 1-4, p. 148-152Article in journal (Refereed)
    Abstract [en]

    The present paper considers the definition of a class of hysteresis models, based on the superposition of play operators, which can be used to describe magnetic materials and superconductors. As a first step, the paper defines a class of non-local hysteresis models having an inverse operator in a closed form. That class specifies a Preisach model for which the exact inverse is defined. In this frame such a result is a generalization of the well-known result by Krejci. Moreover, a self-contained identification procedure is further addressed by using data measured either on magnetic materials and on superconductors.

  • 12.
    Zhang, Renyun
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Single layer porous gold films grown at different temperatures2010In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 405, no 21, p. 4517-4522Article in journal (Refereed)
    Abstract [en]

    Large area porous gold films can be used in several areas including electrochemical electrodes, as an essential component in sensors, or as a conducting material in electronics. Here, we report on evaporation induced crystal growth of large area porous gold films at 20, 40 and 60 °C. The gold films were grown on liquid surface at 20 °C, while the films were grown on the wall of beakers when temperature increased to 40 and 60 °C. The porous gold films consisted of a dense network of gold nanowires as characterized by TEM and SEM. TEM diffraction results indicated that higher temperature formed larger crystallites of gold wires. An in situ TEM imaging of the coalescence of gold nanoparticles mimicked the process of the growth of these porous films, and a plotting of the coalescence time and the neck radius showed a diffusion process. The densities of these gold films were also characterized by transmittance, and the results showed film grown at 20 °C had the highest density, while the film grown at 60 °C had the lowest consistent with SEM and TEM characterization. Electrical measurements of these gold films showed that the most conductive films were the ones grown at 40 °C. The conductivities of the gold films were related to the amount of contamination, density and the diameter of the gold nanowires in the films. In addition, a gold film/gold nanoparticle hybrid was made, which showed a 10% decrease in transmittance during hybridization, pointing to applications as chemical and biological sensors. © 2010 Elsevier B.V. All rights reserved.

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