Butsuri
Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Volume 75 , Issue 6
Showing 1-18 articles out of 18 articles from the selected issue
Preface
Contents
Researches
  • Yuki Izumida
    Type: Researches
    2020 Volume 75 Issue 6 Pages 324-328
    Published: June 05, 2020
    Released: October 14, 2020
    JOURNAL FREE ACCESS

    I introduce a nonlinear dynamics model of a low-temperature-differential Stirling engine. The model describes the engine as a driven nonlinear pendulum powered by temperature difference. The rotational motion of the engine is expressed as a limit cycle of simple dynamical equations. It is found that the limit cycle disappears via a homoclinic bifurcation with the temperature difference being a bifurcation parameter. Detailed analysis of the engine model would contribute to the development of the physics of autonomous nonequilibrium heat engines.

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  • Kohei Kamada
    Type: Researches
    2020 Volume 75 Issue 6 Pages 329-334
    Published: June 05, 2020
    Released: October 14, 2020
    JOURNAL FREE ACCESS

    Recent observations of TeV blazars by Fermi identified deficits of secondary GeV cascade photons. These observations can be explained by intergalactic void magnetic fields, which may have a primordial origin. If the magnetic fields are helical and generated in the early Universe such as before the electroweak symmetry breaking, nontrivial interaction between (hyper) magnetic fields and other particles can cause some interesting and non negligible phenomena. In this article, it is shown that the baryon asymmetry can be generated by the chiral anomaly, and baryon asymmetry is not completely washed out by the electroweak sphalerons. Thus, this mechanism can be responsible for the present baryon asymmetry of the Universe. If this mechanism is responsible for the present Universe, the physics beyond the Standard Model of particle physics is needed for the generation of (hyper) magnetic fields but not for the baryogenesis. As mechanisms of magnetogenesis suitable for this baryogenesis, pseudoscalar inflation and chiral plasma instability are discussed.

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  • Kotaro Tamaoka, Koji Umemoto
    Type: Researches
    2020 Volume 75 Issue 6 Pages 335-339
    Published: June 05, 2020
    Released: October 14, 2020
    JOURNAL FREE ACCESS

    We propose dualities between quantum information measures for mixed states and geometrical objects in the light of holography, especially the AdS/CFT correspondence in the string theory. First, we review the Ryu–Takayanagi formula which relates the entanglement entropy in CFT and the area of minimal surfaces in AdS. This formula suggests that the structure of entanglement should be directly related to one of spacetime via holography. We also stress that this formula should be generalized when we consider mixed states on the CFT side. Next, we define entanglement wedge cross-sections as a generalization of minimal surfaces that appeared in the Ryu–Takayanagi formula. Finally, we introduce entanglement of purification and odd entropy, which are measures of quantum correlations for mixed states. In particular, we argue that these quantities are dual to the entanglement wedge cross-sections. We discuss the validity of our proposals from both qualitative and quantitative viewpoints.

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  • Hirokazu Tahara, Yoshihiko Kanemitsu
    Type: Researches
    2020 Volume 75 Issue 6 Pages 340-345
    Published: June 05, 2020
    Released: October 14, 2020
    JOURNAL FREE ACCESS

    Quantum dot solar cells are intensively investigated to realize highly efficient solar cells. It is desired to deeply understand the ultrafast dynamics of multiple excitons in quantum dots. We describe our recent findings for ultrafast exciton dynamics in colloidal quantum dots. We developed an interference detection method for transient absorption spectroscopy and observed ultrafast coherent dynamics during optical pulse irradiation. We found that multiple excitons generate harmonic quantum coherence. Furthermore, we clarified that excitonic coherence assists multiphoton absorption processes.

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