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Journal Articles

Machine learning molecular dynamics reveals the structural origin of the first sharp diffraction peak in high-density silica glasses

Kobayashi, Keita; Okumura, Masahiko; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Urata, Shingo*; Suzuya, Kentaro

Scientific Reports (Internet), 13, p.18721_1 - 18721_12, 2023/11

https://doi.org/10.1038/s41598-023-44732-0

The first sharp peak diffraction peak (FSDP) in the structure factor of amorphous materials is thought to reflect the medium-range order structure in amorphous materials, and the structural origin of the FSDP has been a subject of ongoing debate. In this study, we employed machine learning molecular dynamics (MLMD) with nearly first-principles calculation accuracy to investigate the structural origin of the FSDP in high-density silica glass. First, we successfully reproduced various experimental data of high-density silica glass using MLMD. Furthermore, we revealed that the development (or reduction) of the FSDP in high-density silica glass is characterized by the deformation behavior of ring structures in Si-O covalent bond networks under compression.

Journal Articles

First observation of $^{28}$ O

Kondo, Yosuke*; Achouri, N. L.*; Al Falou, H.*; Atar, L.*; Aumann, T.*; Baba, Hidetada*; Boretzky, K.*; Caesar, C.*; Calvet, D.*; Chae, H.*; et al.

Nature, 620(7976), p.965 - 970, 2023/08

https://doi.org/10.1038/s41586-023-06352-6

no abstracts in English

Journal Articles

Intruder configurations in $^{29}$ Ne at the transition into the island of inversion; Detailed structure study of $^{28}$ Ne

Wang, H.*; Yasuda, Masahiro*; Kondo, Yosuke*; Nakamura, Takashi*; Tostevin, J. A.*; Ogata, Kazuyuki*; Otsuka, Takaharu*; Poves, A.*; Shimizu, Noritaka*; Yoshida, Kazuki; et al.

Physics Letters B, 843, p.138038_1 - 138038_9, 2023/08

https://doi.org/10.1016/j.physletb.2023.138038

Detailed -ray spectroscopy of the exotic neon isotope $^{28}$ Ne has been performed using the one-neutron removal reaction from $^{29}$ Ne. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for $^{28}$ Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N = 20 and N = 28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.

Journal Articles

Machine learning molecular dynamics simulations for evaluation of high-temperature properties of nuclear fuel materials

Kobayashi, Keita; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Materia, 62(3), p.175 - 181, 2023/03

https://doi.org/10.2320/materia.62.175

no abstracts in English

Journal Articles

Machine learning potentials of kaolinite based on the potential energy surfaces of GGA and meta-GGA density functional theory

Kobayashi, Keita; Yamaguchi, Akiko; Okumura, Masahiko

Applied Clay Science, 228, p.106596_1 - 106596_11, 2022/10

https://doi.org/10.1016/j.clay.2022.106596

Times Cited Count：4 Percentile：79.38(Chemistry, Physical)

no abstracts in English

Journal Articles

Materials science and fuel technologies of uranium and plutonium mixed oxide

Kato, Masato; Machida, Masahiko; Hirooka, Shun; Nakamichi, Shinya; Ikusawa, Yoshihisa; Nakamura, Hiroki; Kobayashi, Keita; Ozawa, Takayuki; Maeda, Koji; Sasaki, Shinji; et al.

Materials Science and Fuel Technologies of Uranium and Plutonium mixed Oxide, 171 Pages, 2022/10

https://doi.org/10.1201/9781003298205

Innovative and advanced nuclear reactors using plutonium fuel has been developed in each country. In order to develop a new nuclear fuel, irradiation tests are indispensable, and it is necessary to demonstrate the performance and safety of nuclear fuels. If we can develop a technology that accurately simulates irradiation behavior as a technology that complements the irradiation test, the cost, time, and labor involved in nuclear fuel research and development will be greatly reduced. And safety and reliability can be significantly improved through simulation of nuclear fuel irradiation behavior. In order to evaluate the performance of nuclear fuel, it is necessary to know the physical and chemical properties of the fuel at high temperatures. And it is indispensable to develop a behavior model that describes various phenomena that occur during irradiation. In previous research and development, empirical methods with fitting parameters have been used in many parts of model development. However, empirical techniques can give very different results in areas where there is no data. Therefore, the purpose of this study is to construct a scientific descriptive model that can extrapolate the basic characteristics of fuel to the composition and temperature, and to develop an irradiation behavior analysis code to which the model is applied.

Journal Articles

Extended X-ray absorption fine structure spectroscopy measurements and molecular dynamics simulations reveal the hydration structure of the radium(II) ion

Yamaguchi, Akiko; Nagata, Kojiro*; Kobayashi, Keita; Tanaka, Kazuya; Kobayashi, Toru; Tanida, Hajime; Shimojo, Kojiro; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.

iScience (Internet), 25(8), p.104763_1 - 104763_12, 2022/08

https://doi.org/10.1016/j.isci.2022.104763

Times Cited Count：3 Percentile：45.22(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

Machine learning molecular dynamics simulations toward exploration of high-temperature properties of nuclear fuel materials; Case study of thorium dioxide

Kobayashi, Keita; Okumura, Masahiko; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Cooper, M. W. D.*

Scientific Reports (Internet), 12(1), p.9808_1 - 9808_11, 2022/06

https://doi.org/10.1038/s41598-022-13869-9

Times Cited Count：1 Percentile：70.83(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

Investigation of hydration and adsorption structures on clay minerals of radium by EXAFS

Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.

Hosha Kagaku, (45), p.28 - 30, 2022/03

no abstracts in English

Journal Articles

Construction of machine-learning Zr interatomic potentials for identifying the formation process of c-type dislocation loops

Okita, Taira*; Terayama, Satoshi*; Tsugawa, Kiyoto*; Kobayashi, Keita; Okumura, Masahiko; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 202, p.110865_1 - 110865_9, 2022/02

https://doi.org/10.1016/j.commatsci.2021.110865

Times Cited Count：5 Percentile：48.63(Materials Science, Multidisciplinary)

Journal Articles

Autoradiography system with phosphor powder (ZnS:Ag) for imaging radioisotope dynamics in a living plant

Kurita, Keisuke; Sakai, Takuro; Suzui, Nobuo*; Yin, Y.-G.*; Sugita, Ryohei*; Kobayashi, Natsuko*; Tanoi, Keitaro*; Kawachi, Naoki*

Japanese Journal of Applied Physics, 60(11), p.116501_1 - 116501_4, 2021/11

https://doi.org/10.35848/1347-4065/ac2b50

Times Cited Count：1 Percentile：9.56(Physics, Applied)

Radioisotope tracer imaging is useful for studying plant physiological phenomena. In this study, we developed an autoradiography system with phosphor powder (ZnS:Ag), "Live-autoradiography", for imaging radioisotope dynamics in a living plant. This system visualizes the element migration and accumulation in intact plants continuously under a light environment. An imaging test was performed on point sources of $^{137}$ Cs, with a radioactivity of 10-100 kBq of being observed; this indicates satisfactory system linearity between the image intensity and the radioactivity of $^{137}$ Cs. Moreover, dynamics imaging of $^{137}$ Cs was performed on an intact soybean plant for four days. The serial images indicated $^{137}$ Cs accumulation in the node, vein, and growing point of the plant. The developed system can be used for studying plant physiological phenomena and can be employed for quantitative measurement of radionuclides.

Journal Articles

Hydration structures of barium ions; molecular dynamics simulations using the SCAN meta-GGA density functional and EXAFS spectroscopy studies

Yamaguchi, Akiko; Kobayashi, Keita; Takahashi, Yoshio*; Machida, Masahiko; Okumura, Masahiko

Chemical Physics Letters, 780, p.138945_1 - 138945_5, 2021/10

https://doi.org/10.1016/j.cplett.2021.138945

Times Cited Count：4 Percentile：42.08(Chemistry, Physical)

no abstracts in English

Journal Articles

Self-learning hybrid Monte Carlo method for isothermal-isobaric ensemble; Application to liquid silica

Kobayashi, Keita; Nagai, Yuki; Itakura, Mitsuhiro; Shiga, Motoyuki

Journal of Chemical Physics, 155(3), p.034106_1 - 034106_9, 2021/07

https://doi.org/10.1063/5.0055341

Times Cited Count：4 Percentile：42.08(Chemistry, Physical)

no abstracts in English

Journal Articles

Machine learning potentials for tobermorite minerals

Kobayashi, Keita; Nakamura, Hiroki; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Computational Materials Science, 188, p.110173_1 - 110173_14, 2021/02

https://doi.org/10.1016/j.commatsci.2020.110173

Times Cited Count：12 Percentile：75.78(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Self-learning hybrid Monte Carlo; A First-principles approach

Nagai, Yuki; Okumura, Masahiko; Kobayashi, Keita*; Shiga, Motoyuki

Physical Review B, 102(4), p.041124_1 - 041124_6, 2020/07

https://doi.org/10.1103/PhysRevB.102.041124

Times Cited Count：11 Percentile：66.96(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Superconductivity in repulsively interacting fermions on a diamond chain; Flat-band-induced pairing

Kobayashi, Keita*; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko; Aoki, Hideo*

Physical Review B, 94(21), p.214501_1 - 214501_7, 2016/12

https://doi.org/10.1103/PhysRevB.94.214501

Times Cited Count：52 Percentile：89.03(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Development of a high power wideband polarizer for electron cyclotron current drive system in JT-60SA

Saigusa, Mikio*; Oyama, Gaku*; Matsubara, Fumiaki*; Takii, Keita*; Sai, Takuma*; Kobayashi, Takayuki; Moriyama, Shinichi

Fusion Engineering and Design, 96-97, p.577 - 582, 2015/10

https://doi.org/10.1016/j.fusengdes.2015.04.013

Times Cited Count：6 Percentile：46.9(Nuclear Science & Technology)

A wideband polarizer has been developed for an ECCD system in JT-60SA. The groove depth of the mirrors installed in miter bends were optimized for two frequencies (110 GHz and 138 GHz) by numerical simulations. All surfaces of Poincare spheres were covered at both of the frequencies in low power test. The thermal stress of polarizer were estimated by the numerical simulations. The twister polarizer has been tested up to 0.24 MW during 3 s at 110 GHz.

Journal Articles