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Yamanoi, Kazuto*; Sakakibara, Yuri*; Fujimoto, Junji*; Matsuo, Mamoru; Nozaki, Yukio*
Applied Physics Express, 16(6), p.063004_1 - 063004_6, 2023/06
Times Cited Count：0 Percentile：0(Physics, Applied)Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
EPJ Web of Conferences, 276, p.01015_1 - 01015_5, 2023/03
Times Cited Count：0 Percentile：0.91(Physics, Atomic, Molecular & Chemical)We investigate the QCD phase diagram in strong magnetic fields with heavy-quark impurities and determine the ground state within the mean-field analysis. The ground state is characterized by magnitudes of the pairing not only between the light quark and antiquark, i.e., chiral condensate, but also between the light quark and heavy-quark impurity, dubbed the Kondo condensate. We propose signatures of the interplay and/or competition between those two pairing phenomena reflected in the magnitude of the chiral condensate that is saturated with respect to the magnetic-field strength and anomalously increases with increasing temperature.
Suenaga, Daiki*; Araki, Yasufumi; Suzuki, Kei; Yasui, Shigehiro*
Physical Review D, 105(7), p.074028_1 - 074028_19, 2022/04
Times Cited Count：2 Percentile：36.77(Astronomy & Astrophysics)We propose a new mechanism of the heavy-quark spin polarization (HQSP) in quark matter induced by the Kondo effect under an external magnetic field. The Kondo effect is caused by a condensate between a heavy and a light quark called the Kondo condensate leading to a mixing of the heavy- and light-quark spins. Thus, the HQSP is driven through the Kondo effect from light quarks coupling with the magnetic field in quark matter. For demonstration, we employ the Nambu-Jona-Lasinio type model under a magnetic field and investigate the HQSP within the linear response theory with vertex corrections required by the 
electromagnetic gauge invariance. As a result, we find that the HQSP arises significantly with the appearance of the Kondo effect. Our findings are testable in future sign-problem-free lattice simulations.
Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki
Parallel Computing, 108, p.102851_1 - 102851_12, 2021/12
Times Cited Count：2 Percentile：32.94(Computer Science, Theory & Methods)The aerodynamics simulation code based on the lattice Boltzmann method (LBM) using forest-of-octrees-based block-structured local mesh refinement (LMR) was implemented, and its performance was evaluated on GPU-based supercomputers. We found that the conventional Space-Filling-Curve-based (SFC) domain partitioning algorithm results in costly halo communication in our aerodynamics simulations. Our new tree cutting approach improved the locality and the topology of the partitioned sub-domains and reduced the communication cost to one-third or one-fourth of the original SFC approach. In the strong scaling test, the code achieved maximum 
speedup at the performance of 2207 MLUPS (mega- lattice update per second) on 128 GPUs. In the weak scaling test, the code achieved 9620 MLUPS at 128 GPUs with 4.473 billion grid points, while the parallel efficiency was 93.4% from 8 to 128 GPUs.
Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki
Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 6 Pages, 2021/05
We introduce an improved domain partitioning method called "tree cutting approach" for the aerodynamics simulation code based on the lattice Boltzmann method (LBM) with the forest-of-octrees-based local mesh refinement (LMR). The conventional domain partitioning algorithm based on the space-filling curve (SFC), which is widely used in LMR, caused a costly halo data communication which became a bottleneck of our aerodynamics simulation on the GPU-based supercomputers. Our tree cutting approach adopts a hybrid domain partitioning with the coarse structured block decomposition and the SFC partitioning in each block. This hybrid approach improved the locality and the topology of the partitioned sub-domains and reduced the amount of the halo communication to one-third of the original SFC approach. The code achieved 
speedup on 8 GPUs, and achieved 
speedup at the performance of 2207 MLUPS (mega-lattice update per second) on 128 GPUs with strong scaling test.
Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 3(2), p.023098_1 - 023098_17, 2021/05
Spins of relativistic fermions are related to their orbital degrees of freedom. In order to quantify the effect of hybridization between relativistic and nonrelativistic degrees of freedom on spin-orbit coupling, we focus on the spin-orbital (SO) crossed susceptibility arising from spin-orbit coupling. The SO crossed susceptibility is defined as the response function of their spin polarization to the "orbital" magnetic field, namely the effect of magnetic field on the orbital motion of particles as the vector potential. Once relativistic and nonrelativistic fermions are hybridized, their SO crossed susceptibility gets modified at the Fermi energy around the band hybridization point, leading to spin polarization of nonrelativistic fermions as well. These effects are enhanced under a dynamical magnetic field that violates thermal equilibrium, arising from the interband process permitted by the band hybridization. Its experimental realization is discussed for Dirac electrons in solids with slight breaking of crystalline symmetry or doping, and also for quark matter including dilute heavy quarks strongly hybridized with light quarks, arising in a relativistic heavy-ion collision process.
Suenaga, Daiki*; Araki, Yasufumi; Suzuki, Kei; Yasui, Shigehiro*
Physical Review D, 103(5), p.054041_1 - 054041_17, 2021/03
Times Cited Count：5 Percentile：45.23(Astronomy & Astrophysics)We investigate the influence of the Kondo effect, namely, the nonperturbative effect induced by heavy impurities, on the chiral separation effect (CSE) in quark matter. We employ a simple effective model incorporating the Kondo condensate made of a light quark and a heavy quark, and compute the response function of the axial current to the magnetic field in the static and dynamical limits. As a result, we find that the Kondo effect catalyzes the CSE in both of the limits, and in particular the CSE in the dynamical limit can be enhanced by a factor of approximately 3. Our findings clearly show that the presence of heavy impurities in quark matter can play an important role in the transport phenomena of light quarks induced by a magnetic field.
Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 3(1), p.013233_1 - 013233_12, 2021/03
We investigate two different types of relativistic Kondo effects, distinguished by heavy-impurity degrees of freedom, by focusing on the energy-momentum dispersion relations of the ground state with condensates composed of a light Dirac fermion and a nonrelativistic impurity fermion. Heavy fermion degrees of freedom are introduced in terms of two types of heavy-fermion effective theories, in other words, two heavy-fermion limits for the heavy Dirac fermion, which is known as the heavy-quark effective theories (HQETs) in high-energy physics. While the first one includes only the heavy-particle component, the second one contains both the heavy-particle and heavy-antiparticle components, which are opposite in their parity. From these theories, we obtain two types of Kondo effects, in which the dispersions near the Fermi surface are very similar, but they differ in the structure at low momentum. We also classify the possible forms of condensates in the two limits. The two Kondo effects will be examined by experiments with Dirac/Weyl semimetals or quark matter, lattice simulations, and cold-atom simulations.
Collaborative Laboratories for Advanced Decommissioning Science; Keio University*
JAEA-Review 2020-047, 63 Pages, 2021/01
JAEA-Review-2020-047.pdf:3.85MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2019. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Study of corrosion and degradation of the objects in the nuclear reactor by microorganisms" conducted in FY2019. The purpose of the study is to obtain knowledge related to microorganisms that will be useful in the decommissioning process of the Fukushima Daiichi Nuclear Power Station. For this reason, the current conditions of the microbial community inhabiting the power plant and its premises will be clarified. In the first research year, we obtained environmental samples such as soils from the south of the boundary of the plant, seabed soils near the plant, and surface water 3 km offshore from the plant, and successfully prepared their microbial genomic DNAs.
Suenaga, Daiki*; Suzuki, Kei; Araki, Yasufumi; Yasui, Shigehiro*
Physical Review Research (Internet), 2(2), p.023312_1 - 023312_13, 2020/06
The Kondo effect is induced by the interaction between light fermions near the Fermi surface and heavy impurities, and it affects electric/thermal/transport properties of matter. The chirality (right-handed or left-handed) is one of the unique properties of relativistic (Dirac or Weyl) fermions. In normal matter, the numbers of right- and left-handed particles are equivalent to each other, but environments with a chirality imbalance can also be realized. In this paper, we theoretically propose the Kondo effect driven by a chirality imbalance (or chiral chemical potential) of relativistic light fermions. This effect is caused by the mixing between a right-handed (or left-handed) fermion and a heavy impurity in the chirality imbalanced matter. This is different from the usual Kondo effect induced by finite density (or chemical potential) for light fermions. We construct an effective model with an interaction between a relativistic fermion and a heavy impurity, and we derive the realization of the Kondo effect from both a perturbative calculation and a nonperturbative mean-field approach. We also discuss the temperature dependence, the coupling constant dependence, the susceptibilities, and the order of the phase transition for the Kondo effect. Such a Kondo effect will be tested by future lattice simulations.
Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 2(2), p.023066_1 - 023066_11, 2020/04
The QCD Kondo effect is a quantum phenomenon in which heavy (charm or bottom) quarks exist as impurity particles in quark matter composed of light quarks at extremely high density. In this paper, we theoretically predict the existence of the exciton modes above the ground state of the quark matter governed by the QCD Kondo effect. We construct an effective model based on the mean field approximation and investigate possible quantum numbers (such as spin and parity) of excitons and their dispersion relations. These excitons can be electrically (color) neutral, so that they are observed as the neutral currents in transport phenomena. As a result, they contribute to violation of the Wiedemann-Franz law for the electric (color) and heat conductivities. Such Kondo excitons are an universal phenomenon for relativistic (Dirac or Weyl) fermions, and the same concept will also be applied to Dirac or Weyl electron systems.
Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi
AIP Conference Proceedings 1515, p.22 - 30, 2013/02
Times Cited Count：10 Percentile：94.9(Physics, Applied)We have developed the integrated 2D PIC code for the analysis of the negative ion beam optics, in which an overall region from the source plasma to the accelerator is modeled. Thus, the negative ion trajectory can be solved self-consistently without any assumption of the plasma meniscus form initially. This code can reproduce the negative ion beam halo observed in an actual negative ion beam. It is confirmed that the surface produced negative ions which are extracted near the edge of the meniscus can be one of the reasons for the beam halo: these negative ions are over-focused due to the curvature of the meniscus. The negative ions are not focused by the electrostatic lens, and consequently become the beam halo.
Okuda, Shin*; Miyamoto, Kenji*; Fukuyama, Toshishige*; Nishioka, Shu*; Hatayama, Akiyoshi*; Fukano, Azusa*; Hanada, Masaya; Kojima, Atsushi
AIP Conference Proceedings 1515, p.107 - 113, 2013/02
Times Cited Count：9 Percentile：94(Physics, Applied)A meniscus of plasma-beam boundary in H
ion sources largely affects the extracted H ion beam optics. Recently it is shown that the beam halo is mainly caused by the meniscus, i.e. ion emissive surface, close to the plasma grid (PG) where its curvature is large. The purpose of this study is to clarify the effect of H surface production rate on plasma meniscus and beam halo formation with PIC (particle-in-cell) modeling. It is shown that the plasma meniscus and beam halo formation is strongly dependent on the amount of surface produced H ions.
Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi
Applied Physics Letters, 102(2), p.023512_1 - 023512_4, 2013/01
Times Cited Count：25 Percentile：68.99(Physics, Applied)To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.
ions by using two-dimensional particle-in-cell methodMiyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya
Review of Scientific Instruments, 83(2), p.02A723_1 - 02A723_4, 2012/02
Times Cited Count：8 Percentile：37.67(Instruments & Instrumentation)The modeling and analysis of a negative ion source is proceeding by using a 2D particle-in-cell simulation. The effect of the H ion production on the plasma grid (PG) surface is investigated. It is shown that with the increase of H ions per time step, the H ion current density is enhanced, while the electron current density decreases with increasing the H production rate on the PG surface. Theseresults agree well with the experimental results observed in typical negative ion sources. Moreover, it is found that plasma quasi-neutrality is held mainly by both H
and H ions in the bulk plasma.
Aoyagi, Yoshiteru; Shimokawa, Tomotsugu*; Shizawa, Kazuyuki*; Kaji, Yoshiyuki
Materials Science Forum, 706-709, p.1751 - 1756, 2012/01
Times Cited Count：2 Percentile：73.92(Materials Science, Multidisciplinary)In this study, we develop a crystal plasticity model considering an effect of grain boundary. In order to predict increase of local critical resolved shear stress due to existence of grain boundaries, information of grain boundary as a role of dislocation sources is introduced into a hardening law of crystal plasticity. In addition, carrying out FE simulation for plastic deformation of FCC polycrystal, the stress-strain responses such as increase of yield stress due to existence of grain boundary are discussed. We investigate comprehensively the effect of dislocation behavior on the material property of nanostructured metal. The increase of yield stress and the decrease of hardening ratio with the reduction of grain size are caused by local differences on CRSS and dislocation behavior, respectively.
Aoyagi, Yoshiteru; Kobayashi, Ryotaro*; Shizawa, Kazuyuki*
Nihon Kikai Gakkai Rombunshu, A, 77(775), p.448 - 461, 2011/03
Ultrafine-grained metals whose grain size is less than one micron have attracted interest as high strength materials. However, a mechanism of ultrafine-graining based on evolution of dislocation structures has not been clarified. In this study, we derive reaction-diffusion equations for dislocation patterning of dislocation cell structures and subgrains. In order to express the generation of dislocation pattern responding to deformation progress, information of slip rate and stress and effect of interactions between slip systems on formation of cell structures are introduced into the reaction rate coefficients of reaction-diffusion equations. Moreover, we propose a multiscale crystal plasticity model based on dislocation patterning. Then we carry out two-dimensional FE-FD simulation for severe compression of FCC polycrystal using the present model. Some processes of ultrafine-graining, i.e., generation of dislocation cell structures, subgrains, dense dislocation walls and lamella subdivisions with high angle boundary is numerically reproduced, and we investigate the effect of dislocation behaviors on the processes of ultrafine-graining.
Kurosawa, Eisuke*; Aoyagi, Yoshiteru; Shizawa, Kazuyuki*
Nihon Kikai Gakkai Rombunshu, A, 76(772), p.1547 - 1556, 2010/12
In order to express the increase of critical resolved shear stress, the conventional Bailey-Hirsh's relationship is extended on the basis of physical consideration for grain boundary that plays a role of dislocation source. A triple-scale dislocation-crystal plasticity FE simulation based on the above model, geometrically necessary crystal defects and the homogenization method is carried out for annealed FCC polycrystals with different initial grain size and initial dislocation density. Yield point drop and propagation of L
ders bands observed in macroscopic specimen with annealed FCC fine-grains are numerically reproduced. Moreover, macroscopic yielding of specimen and microscopic grain yielding are investigated in detail so as to clarify the initial yield behavior of annealed ultrafine-grained metals. It is also shown that plastic deformation is easy to be localized and the tensile ductility decreases as the grain size reduces.
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Nakao, Hironori*; Owada, Kenji; Shimomura, Susumu*; Ochiai, Akira*; Namikawa, Kazumichi*; Mizuki, Junichiro; Mimura, Hidekazu*; Yamauchi, Kazuto*; Murakami, Yoichi*
AIP Conference Proceedings 1234, p.935 - 938, 2010/06
Times Cited Count：2 Percentile：66.93(Physics, Applied)Owada, Kenji; Namikawa, Kazumichi*; Shimomura, Susumu*; Nakao, Hironori*; Mimura, Hidekazu*; Yamauchi, Kazuto*; Matsushita, Mitsuyoshi*; Mizuki, Junichiro
Japanese Journal of Applied Physics, 49(2), p.020216_1 - 020216_3, 2010/02
Times Cited Count：3 Percentile：14.99(Physics, Applied)