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Kawai, Hiroyuki*; Sekikawa, Takuya; Ozaki, Taisuke*; Ono, Yoshiaki*
Journal of the Physical Society of Japan, 94(12), p.124003_1 - 124003_15, 2025/12
Times Cited Count：1 Percentile：37.78(Physics, Multidisciplinary)OpenMX, a first-principles electronic structure calculation software, is a computational code based on density functional theory primarily used to determine the stable structure and electronic states of materials. This study attempted to develop a method for accelerating calculations using OpenMX by employing a GPU, Graphics Processing Unit, typically used for image processing. Test calculations on a 512-atom diamond structure silicon system achieved approximately double the speed compared to CPU-based calculations. Furthermore, for noncollinear calculations used in magnetic structure calculations, a 384-atom silicon system achieved 2.6 times faster speed than the CPU. Especially, GPU acceleration for noncollinear calculations is unprecedented. The results obtained in this study enable the handling of larger systems than previously possible in first-principles electronic structure calculations.
Ti
)
NiSe
Tsuchida, Shun*; Hirose, Yusuke; Sekikawa, Takuya; Ono, Yoshiaki*; Hirahara, Takuya*; Sano, Sumika*; Kawaguchi, Shogo*; Kobayashi, Shintaro*; Uwatoko, Yoshiya*; Settai, Rikio*
Journal of the Physical Society of Japan, 94(11), p.114703_1 - 114703_7, 2025/10
Times Cited Count：2 Percentile：37.78(Physics, Multidisciplinary)We investigated the carrier doping effect on an excitonic insulator TaNiSe by means of the electrical resistivity 
and Hall coefficient 
using single crystals of (TaTi)NiSe, and band calculation. The excitonic transition temperature 
is continuously suppressed to 83 K at 
= 0.104 while preserving the crystal structure. With increasing substitution concentration , a semiconducting increment of and is strongly suppressed and a metallic behavior is observed at > 0.06. Ti substitution can realize an excitonic correlated metallic state. This metallization is explained by the hole doping effect based on the band calculations. Applying pressure to the carrier doped (TaTi)NiSe, we found superconductivity above 2.6 GPa, which is much smaller than that of TaNiSe around 8 GPa. The carrier doping induced by Ti substitution favors superconductivity in this compound.
Sekikawa, Takuya; Takada, Kazuki*; Kai, Takeshi; Ono, Yoshiaki*
Journal of Applied Physics, 137(20), p.203901_1 - 203901_10, 2025/05
Times Cited Count：0 Percentile：0.00(Physics, Applied)no abstracts in English
C ions based on first-principles calculationsSekikawa, Takuya; Matsuya, Yusuke; Hwang, B.*; Ishizaka, Masato*; Kawai, Hiroyuki*; Ono, Yoshiaki*; Sato, Tatsuhiko; Kai, Takeshi
Nuclear Instruments and Methods in Physics Research B, 548, p.165231_1 - 165231_6, 2024/03
Times Cited Count：1 Percentile：22.55(Instruments & Instrumentation)One of the main causes of radiation effects on the human body is thought to be damage to DNA, which carries genetic information. However, it is not fully understood what kind of molecular structural changes DNA undergoes upon radiation damage. Since it has been reported that various types of DNA damage are formed when DNA is irradiated, our group has investigated the relationship between DNA damage and various patterns of radiation-induced ionization induced by radiation. Although we have so far analyzed DNA damage in a simple system using a rigid body model of DNA, more detailed calculations are required to analyze the molecular structural changes in DNA, which are considered to be important in considering the effects on the human body. In this study, we attempted to clarify the molecular conformational changes of DNA using OpenMX, a first-principles calculation software that can discuss electronic states based on molecular structures. Specifically, we calculated the most stable structure, band dispersion, and wave function of DNA under the assumption that one and two electrons are ionized by various radiation. In the presentation, we will discuss the relationship between the energy dependence of each incident radiation type and the molecular conformational change of DNA. In addition, the radiation-induced changes in the basic physical properties of DNA (corresponding to the initial stage of DNA damage) will be discussed from the viewpoints of both radiation physics and solid state physics.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：66 Percentile：95.03(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Xe ions on proton, deuteron, and carbon targetsSun, X. H.*; Wang, H.*; Otsu, Hideaki*; Sakurai, Hiroyoshi*; Ahn, D. S.*; Aikawa, Masayuki*; Fukuda, Naoki*; Isobe, Tadaaki*; Kawakami, Shunsuke*; Koyama, Shumpei*; et al.
Physical Review C, 101(6), p.064623_1 - 064623_12, 2020/06
Times Cited Count：8 Percentile：53.94(Physics, Nuclear)The spallation and fragmentation reactions of Xe induced by proton, deuteron and carbon at 168 MeV/nucleon were studied at RIKEN Radioactive Isotope Beam Factory via the inverse kinematics technique. The cross sections of the lighter products are larger in the carbon-induced reactions due to the higher total kinetic energy of carbon. The energy dependence was investigated by comparing the newly obtained data with previous results obtained at higher reaction energies. The experimental data were compared with the results of SPACS, EPAX, PHITS and DEURACS calculations. These data serve as benchmarks for the model calculations.
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Faenov, A. Y.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; Koga, J. K.; Mori, Michiaki; Kawase, Keigo*; et al.
RAL-TR-2015-025, P. 22, 2015/00
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; et al.
New Journal of Physics (Internet), 16(9), p.093003_1 - 093003_30, 2014/09
Times Cited Count：31 Percentile：78.97(Physics, Multidisciplinary)Esirkepov, T. Zh.; Pirozhkov, A. S.; Kando, Masaki; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A.*; Pikuz, T. A.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
AIP Conference Proceedings 1465, p.172 - 180, 2012/07
Times Cited Count：0 Percentile：0.00(Physics, Applied)The bow wave induced mechanism of high-order harmonics generation was discovered using simulations and catastrophe theory. This mechanism feasibility was successfully demonstrated in 3D and 2D PIC simulations. The mechanism and the simulations explained high-order harmonics in the XUV spectral region seen in recent experiments with terawatt lasers. Development of new XUV light and X-ray source based on the high-order harmonics generation mechanism is proposed.
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Zh.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
AIP Conference Proceedings 1465, p.167 - 171, 2012/07
Times Cited Count：1 Percentile：44.34(Physics, Applied)Norman, G.*; Starikov, S.*; Stegailov, V.*; Fortov, V.*; Skobelev, I.*; Pikuz, T. A.; Faenov, A.*; Tamotsu, Satoshi*; Kato, Yoshiaki*; Ishino, Masahiko; et al.
Journal of Applied Physics, 112(1), p.013104_1 - 013104_8, 2012/07
Times Cited Count：44 Percentile：81.50(Physics, Applied)Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Zh.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
Physical Review Letters, 108(13), p.135004_1 - 135004_5, 2012/03
Times Cited Count：74 Percentile：90.07(Physics, Multidisciplinary)We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multi-terawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving 
J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.
Ieda, Yoshiaki; Ono, Kiyoshi; Negishi, Hitoshi; Shiotani, Hiroki; Nagaoki, Yoshihiro; Namba, Takashi
Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 9 Pages, 2011/12
Since 1999, Japan Atomic Energy Agency (JAEA) has promoted R&D of the Fast Breeder Reactor Cycle in order to build the practical concepts and establish the technical systems, in cooperation with related entities. In the first 5-year of the Fast Reactor Cycle System Technology Development Project (FaCT), namely the FaCT phase1 (JFY2006-2010), the evaluation of the achievement degree to the performance target fixed by the Atomic Energy Commission and the adoption judgment of the innovative technology at present were carried out with "Sodium-cooled Fast Reactor with MOX fuel, advanced aqueous reprocessing process, and simplified MOX pellet fabrication process". FaCT phase1 moved forward almost smoothly and confirmed that the project will be able to enter the next phase to demonstrate the innovative technology by the engineering scale examination. The concrete results of the FaCT phase1 and future direction are introduced in the full paper.
Kawachi, Tetsuya; Hasegawa, Noboru; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Oba, Toshiyuki; Kaihori, Takeshi; Kishimoto, Maki; Ochi, Yoshihiro; Tanaka, Momoko; et al.
X-Ray Lasers 2010; Springer Proceedings in Physics, Vol.136, p.15 - 24, 2011/12
This paper reviews recent improvement in the source development of laser-driven X-ray lasers and the applications in the research fields of material science, laser processing, X-ray imaging, and radiation damage in biological cells. In the application for material science, we have firstly observed temporal correlation between the domain structures of ferro-electric substance under the Curie temperature. In the laser processing, new X-ray laser interferometer reveals us the nano-scale surface distortion of substance pumped by a femto-second optical pulse. In the X-ray diffraction image, we have taken several static images of micro-structure of samples: now we are trying to extend the objective to nano-scale dynamics using pump and probe method. In the radiation damage of biological cells, we observed double strand break in DNA using X-ray laser exposure; this results are compared with the case using incoherent several KeV X-ray exposure.
Inogamov, N. A.*; Anisimov, S. I.*; Petrov, Y. V.*; Khokhlov, V. A.*; Zhakhovskii, V. V.*; Faenov, A. Ya.*; Pikuz, T. A.; Fortov, V. E.*; Skobelev, I. Y.*; Kato, Yoshiaki*; et al.
Journal of Optical Technology, 78(8), p.473 - 480, 2011/08
Times Cited Count：6 Percentile：31.08(Optics)Uchida, Yoshiaki*; Suzuki, Katsuaki*; Tamura, Rui*; Ikuma, Naohiko*; Shimono, Satoshi*; Noda, Yohei; Yamauchi, Jun*
Journal of the American Chemical Society, 132(28), p.9746 - 9752, 2010/06
Times Cited Count：55 Percentile：75.45(Chemistry, Multidisciplinary)An anisotropic and inhomogeneous magnetic interaction (the average spin-spin interaction constant, 
0) was observed in the various liquid crystalline (LC) phases of racemic and nonracemic all-organic radical LC compounds. We discussed how the LC superstructures induced the magnetic interaction to operate in the LC phases in terms of spin-spin dipole and exchange interactions by means of VT-EPR spectroscopy. The magnitude of the magnetic interaction depended on the type of LC phase, or the superstructure. Furthermore, these radical LC droplets floating on water were commonly attracted to a permanent magnet and moved freely under the influence of this magnet, whereas the crystallized particles of the same compounds never responded to the magnet. The response of the LC droplets to the magnet also varied depending on the type of LC phase, that is, the extent of the magnetic interaction.
Uchida, Yoshiaki*; Ikuma, Naohiko*; Tamura, Rui*; Shimono, Satoshi*; Noda, Yohei; Yamauchi, Jun*; Aoki, Yoshio*; Nohira, Hiroyuki*
Journal of Materials Chemistry, 18(25), p.2950 - 2952, 2008/07
Times Cited Count：49 Percentile：76.97(Chemistry, Physical)We found out an unusual intermolecular magnetic interaction in the liquid-crystalline (LC) state of an all-organic radical compound on surface of water (73 C); the magnetic interaction actually allows the LC droplet on water to be attracted by a weak permanent magnet, whereas the crystalline phase did not respond to the magnet.
Morihira, Masayuki; Ozawa, Takayuki; ; Suzuki, Masahiro; Shigetome, Yoshiaki; Kihara, Yoshiyuki; Kono, Shusaku
JNC TN8400 2004-014, 193 Pages, 2004/07
JNC-TN8400-2004-014.pdf:24.52MB
The collaboration project concerning sphere-pac fuel among JNC, Swiss PSI (Paul Scherrer Institut) and Dutch NRG (Nuclear Research and Consultancy Group) is in progress.Final target of the project is comparative irradiation tests of Sphere-pac fuel in the HFR (High Flux Reactor) in Petten in the Netherlands with pellet type fuel and vipack fuel. Total 16 fuel segments (8 pins) of these three types of fuel are planned to be irradiated. Two sphere-pac fuel segments contain 5%Np in addition to 20%Pu-MOX. Other segments contain no Np. Fabrication of irradiation test pins was completed till May 2003 in PSI. After transportation of the fuel pins to Petten, two times of irradiation were performed in January to March in 2004 and now post irradiation tests are in progress. Later two irradiations will be done till the autumn in 2004.This report summarized the basic plan, fuel design, and fabrication of irradiation test pins concerning this collaboration project.
; Hinai, Hiroshi; Shigetome, Yoshiaki; Kono, Shusaku;
JNC TN8410 2003-002, 29 Pages, 2003/02
Japan Nuclear Cycle Development institute (JNC) has conducted the collaboration concerning vibro-packed fuels with Paul Scherrer Institut (PSI) in Switzerland and Nuclear Research & consultancy Group (NRG) in the Netherlands. The project "Research and Development of Advanced Sphere-pac fuel" is called FUJI (FUel irradiations for JNC and PSI) Project. In this project, three types of fuels that are sphere-pac fuels, vipac fuels, and pelletized fuels will be irradiated in the High Flux Reactor (HFR) to compare the fuel performance. Based on the drawing which has been agreed among three parties, fabrication of the pin components and welding of the upper and lower connection endplugs were performed in accordance with ISO-9001 in JNC. This report describes data of fabricated pin components, results of welding qualification tests, and quality assurance of the welded components. The fabrication of pin components was successfully completed and they were delivered to PSI in October 2002.
Shigetome, Yoshiaki; Kono, Shusaku; Hellwig, C.*; Heimgartner, P.*
Proceedings of International Conference on Advanced Nuclear Energy and Fuel Cycle Systems (GLOBAL 2003) (CD-ROM), p.1342 - 1347, 2003/00
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