Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
and machine learning potentials for modeling nuclear quantum effects in waterThomsen, B.; Nagai, Yuki*; Kobayashi, Keita; Hamada, Ikutaro*; Shiga, Motoyuki
Journal of Chemical Physics, 161(20), p.204109_1 - 204109_18, 2024/11
Times Cited Count：1 Percentile：42.16(Chemistry, Physical)We introduce the self-learning path integral hybrid Monte Carlo with mixed and machine learning potentials (SL-PIHMC-MIX) method which allows the application of hybrid Monte Carlo for both path integrals and for larger system sizes. The method shows savings of an order of magnitude with respect to the number of DFT calculations needed to calculate and converge the structure of room temperature water when using SL-PIHMC-MIX over ab initio path integral molecular dynamics (PIMD).
Tanaka, Takuro*; Fukuoka, Masafumi*; Toda, Kanako*; Nakanishi, Takahiro; Terashima, Motoki; Fujiwara, Kenso; Niwano, Yuma*; Kato, Hiroaki*; Kobayashi, Natsuko*; Tanoi, Keitaro*; et al.
ACS ES&T Water (Internet), 4(8), p.3579 - 3586, 2024/08
Kobayashi, Keita
New Glass, 39(2), p.13 - 17, 2024/07
The atomic arrangement in glass structures lacks periodicity, and the information obtained experimentally reflects an average structure. Therefore, to estimate the three-dimensional structure of glass materials, molecular dynamics simulations are effective. The results of molecular dynamics calculations strongly depend on the interatomic potential. We have created a machine learning potential (MLP) trained on first-principles calculation results for silica materials. This paper outlines our research of structural analysis of high-density silica glass using machine learning molecular dynamics (MLMD) with the MLP. The MLMD successfully reproduced the experimental data of silica glass. Furthermore, it was revealed that changes in the medium-range order structure in high-density silica glass are characterized by the deformation behavior of ring structures within the Si-O covalent bond network due to the compression.
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
Times Cited Count：11 Percentile：74.59(Multidisciplinary Sciences)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.
OKondo, 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
Times Cited Count：27 Percentile：94.86(Multidisciplinary Sciences)no abstracts in English
Ne at the transition into the island of inversion; Detailed structure study of NeWang, 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
Times Cited Count：4 Percentile：69.46(Astronomy & Astrophysics)Detailed 
-ray spectroscopy of the exotic neon isotope Ne has been performed using the one-neutron removal reaction from Ne. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 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.
Kobayashi, Keita; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko
Materia, 62(3), p.175 - 181, 2023/03
no abstracts in English
Kobayashi, Keita; Yamaguchi, Akiko; Okumura, Masahiko
Applied Clay Science, 228, p.106596_1 - 106596_11, 2022/10
Times Cited Count：9 Percentile：73.45(Chemistry, Physical)no abstracts in English
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
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.
molecular dynamics simulations reveal the hydration structure of the radium(II) ionYamaguchi, 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
Times Cited Count：17 Percentile：68.06(Multidisciplinary Sciences)no abstracts in English
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
Times Cited Count：15 Percentile：68.20(Multidisciplinary Sciences)no abstracts in English
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
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
Times Cited Count：7 Percentile：34.09(Materials Science, Multidisciplinary)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
Times Cited Count：2 Percentile：10.80(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 
Cs, with a radioactivity of 10-100 kBq of being observed; this indicates satisfactory system linearity between the image intensity and the radioactivity of Cs. Moreover, dynamics imaging of Cs was performed on an intact soybean plant for four days. The serial images indicated 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.
molecular dynamics simulations using the SCAN meta-GGA density functional and EXAFS spectroscopy studiesYamaguchi, Akiko; Kobayashi, Keita; Takahashi, Yoshio*; Machida, Masahiko; Okumura, Masahiko
Chemical Physics Letters, 780, p.138945_1 - 138945_5, 2021/10
Times Cited Count：12 Percentile：65.52(Chemistry, Physical)no abstracts in English
Kobayashi, Keita; Nagai, Yuki; Itakura, Mitsuhiro; Shiga, Motoyuki
Journal of Chemical Physics, 155(3), p.034106_1 - 034106_9, 2021/07
Times Cited Count：13 Percentile：68.59(Chemistry, Physical)no abstracts in English
Kobayashi, Keita; Nakamura, Hiroki; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko
Computational Materials Science, 188, p.110173_1 - 110173_14, 2021/02
Times Cited Count：24 Percentile：76.41(Materials Science, Multidisciplinary)no abstracts in English
Nagai, Yuki; Okumura, Masahiko; Kobayashi, Keita*; Shiga, Motoyuki
Physical Review B, 102(4), p.041124_1 - 041124_6, 2020/07
Times Cited Count：27 Percentile：79.33(Materials Science, Multidisciplinary)no abstracts in English
Kobayashi, Keita*; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko; Aoki, Hideo*
Physical Review B, 94(21), p.214501_1 - 214501_7, 2016/12
Times Cited Count：65 Percentile：89.73(Materials Science, Multidisciplinary)no abstracts in English
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
Times Cited Count：6 Percentile：42.50(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.
