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  • 1.
    Herper, H. C.
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Ahmed, T.
    Institute for Materials Science, Los Alamos National Laboratory, Los Alamos New Mexico, USA.
    Wills, J. M.
    Theoretical Division, Los Alamos National Laboratory, Los Alamos New Mexico, USA.
    Di Marco, I.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Björkman, T.
    Department of Natural Sciences, Åbo Akademi, Turku, Finland.
    Iusan, D.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Balatsky, A. V.
    Institute for Materials Science, Los Alamos National Laboratory, Los Alamos New Mexico, USA; AlbaNova University Center Nordita, Stockholm, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Combining electronic structure and many-body theory with large databases: A method for predicting the nature of 4 f states in Ce compounds2017In: Physical Review Materials, ISSN 2475-9953, Vol. 1, no 3, 033802Article in journal (Refereed)
    Abstract [en]

    Recent progress in materials informatics has opened up the possibility of a new approach to accessing properties of materials in which one assays the aggregate properties of a large set of materials within the same class in addition to a detailed investigation of each compound in that class. Here we present a large scale investigation of electronic properties and correlated magnetism in Ce-based compounds accompanied by a systematic study of the electronic structure and 4f-hybridization function of a large body of Ce compounds. We systematically study the electronic structure and 4f-hybridization function of a large body of Ce compounds with the goal of elucidating the nature of the 4f states and their interrelation with the measured Kondo energy in these compounds. The hybridization function has been analyzed for more than 350 data sets (being part of the IMS database) of cubic Ce compounds using electronic structure theory that relies on a full-potential approach. We demonstrate that the strength of the hybridization function, evaluated in this way, allows us to draw precise conclusions about the degree of localization of the 4f states in these compounds. The theoretical results are entirely consistent with all experimental information, relevant to the degree of 4f localization for all investigated materials. Furthermore, a more detailed analysis of the electronic structure and the hybridization function allows us to make precise statements about Kondo correlations in these systems. The calculated hybridization functions, together with the corresponding density of states, reproduce the expected exponential behavior of the observed Kondo temperatures and prove a consistent trend in real materials. This trend allows us to predict which systems may be correctly identified as Kondo systems. A strong anticorrelation between the size of the hybridization function and the volume of the systems has been observed. The information entropy for this set of systems is about 0.42. Our approach demonstrates the predictive power of materials informatics when a large number of materials is used to establish significant trends. This predictive power can be used to design new materials with desired properties. The applicability of this approach for other correlated electron systems is discussed.

  • 2.
    Morfeldt, Johannes
    Örebro University, School of Science and Technology.
    Optically Selective Surfaces in low concentrating PV/T systems2009Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the traditional approaches to reduce costs of solar energy is to use inexpensive reflectors to focus the light onto highly efficient solar cells. Several research projects have resulted in designs, where the excess heat is used as solar thermal energy.

    Unlike a solar thermal system, which has a selective surface to reduce the radiant heat loss, a CPV/T (Concentrating PhotoVoltaic/Thermal) system uses a receiver covered with solar cells with high thermal emittance.

    This project analyzes whether the heat loss from the receiver can be reduced by covering parts of the receiver surface, not already covered with solar cells, with an optically selective coating. Comparing different methods of applying such a coating and the long-term stability of low cost alternatives are also part of the objectives of this project.

    To calculate the heat loss reductions of the optically selective surface coating a mathematical model was developed, which takes the thermal emittances and the solar absorptances of the different surfaces into account. Furthermore, a full-size experiment was constructed to verify the theoretical predictions.

    The coating results in a heat loss reduction of approximately 20 % in such a CPV/T system and one of the companies involved in the study is already changing their design to make use of the results.

  • 3.
    Møller-Andersen, Jakob
    et al.
    Department of Applied Mathematics and Computer Science, Technical University of Denmark, Lyngby, Denmark.
    Ögren, Magnus
    Örebro University, School of Science and Technology. Department of Applied Mathematics and Computer Science, Technical University of Denmark, Lyngby, Denmark; Nano Science Center, Department of Chemistry, University of Copenhagen, København, Denmark.
    Perturbative semiclassical trace formulae for harmonic oscillators2015In: Reports on mathematical physics, ISSN 0034-4877, E-ISSN 1879-0674, Vol. 75, no 3, 359-382 p.Article in journal (Refereed)
    Abstract [en]

    In this article we extend previous semiclassical studies by including more general perturbative potentials of the harmonic oscillator in arbitrary spatial dimensions. Our starting point is a radial harmonic potential with an arbitrary even monomial perturbation, which we use to study the resulting U(D) to O(D) symmetry breaking. We derive the gross structure of the semiclassical spectrum from periodic orbit theory, in the form of a perturbative (ħ → 0) trace formula. We then show how to apply the results to even-order polynomial potentials, possibly including mean-field terms. We have drawn the conclusion that the gross structure of the quantum spectrum is determined from only classical circular and diameter orbits for this class of systems.

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