High stabilization of pentavalent uranium on magnetite nanoparticles evidenced by high-energy-resolution X-ray absorption spectroscopy

Yomogida, Takumi; Scaria, J.*; Fablet, L.*; Tokunaga, Kohei; Dei, Shuntaro; Higashi, Kotaro*; Kawamura, Naomi*; Takahashi, Yoshio*; Marsac, R.*

Chemical Communications, 61(91), p.17926 - 17929, 2025/11

https://doi.org/10.1039/D5CC04540A

This paper presents insights into the influence of magnetite stoichiometry (0 R = Fe(II)/Fe(III) 0.5) on the surface reduction of U(VI) to U(V) and U(IV), as a key parameter controlling U redox speciation in natural settings. Although R can readily change due to the oxidation of structural Fe(II) or proton/ligand-promoted dissolution, prior studies have not quantified U(V) when assessing these effects. We employed U L-edge HERFD-XANES spectroscopy to investigate the electronic structure of U on magnetite with varying stoichiometries and observed a peak splitting of U(V) on magnetite. Our results demonstrate the high stability of U(V) species under a wide range of conditions, and after 10 days on magnetite by the combination of MCR-ALS analysis. A key finding is that structural Fe(II), whose abundance depends on pH and redox conditions, plays a critical role for in the stabilization of U(V) on magnetite.

Pressure-induced elongation of hydrogen-oxygen bond in sodium silicate melts

Ohashi, Tomonori*; Sakamaki, Tatsuya*; Funakoshi, Kenichi*; Steinle-Neumann, G.*; Hattori, Takanori; Yuan, L.*; Suzuki, Akio*

Journal of Mineralogical and Petrological Sciences (Internet), 120(1), p.240926a_1 - 240926a_13, 2025/06

https://doi.org/10.2465/jmps.240926a

We explore the structures of dry and hydrated (HO and DO) NaSiO melt at 0-6 GPa and 1000-1300 K and glasses recovered from high pressure and temperatures by in-situ neutron and X-ray diffraction. The structures of the melts at 0-10 GPa and 3000 K are also investigated by ab-initio molecular dynamics simulation. In-situ neutron experiments revealed that the D-O distance increases with compression due to the formation of -O-D-O- bridging species, which is reproduced by the molecular dynamics simulations. The pressure-induced -O-D-O- formation reflects a more rigid incorporation of hydrogen, which acts as a mechanism for the experimentally observed higher solubility of water in silicate melts. Together with shrinking modifier domains, this process dominates the compression behavior of hydrous NaSiO melt, whereas the compression of dry NaSiO at 0-10 GPa and 3000 K is governed largely by bending of the Si-O-Si angle. The molecular dynamics simulations on hydrous NaSiO melts further suggest that the sodium ions are scavenged from its network-modifying role via 2(Si-O + Na) Si-(O-Si-O) + 2Na and Si-O + Na + Si-OH Si-(O-H-O-Si) + Na with increasing pressure.

Density, surface tension, and viscosity of molten Ni-based superalloys using the maximum bubble pressure and oscillating crucible methods

Nishi, Tsuyoshi*; Matsumoto, Saori*; Yamano, Hidemasa; Hayashi, Kiichiro*; Endo, Rie*; Bell, M. R.*; Neubert, L.*; Volkova, O.*

Steel Research International, 96(5), p.2300766_1 - 2300766_6, 2025/05

https://doi.org/10.1002/srin.202300766

The density of Ni-based superalloys is measured using the maximum bubble pressure (MBP) method. The viscosity is evaluated using the oscillating crucible method. The surface tension is simultaneously measured using the MBP method.

Characterization of the thorium-229 defect structure in CaF crystals

Takatori, Sayuri*; Pimon, M.*; Pollitt, S.*; Bartokos, M.*; Beeks, K.*; Grneis, A.*; Hiraki, Takahiro*; Homma, Tetsuo*; Hosseini, N.*; Leitner, A.*; et al.

New Journal of Physics (Internet), 27(4), p.043024_1 - 043024_10, 2025/04

https://doi.org/10.1088/1367-2630/adce22

Recent reports on laser excitation of the low-energy thorium-229 (Th) nuclear isomeric state in calcium fluoride single crystals render this system a promising candidate for a solid-state nuclear clock. However, experimental characterization of the microscopic ion arrangement around the doped Th and its electronic charge state, crucial for the precise control of the clock transition and assessing the solid-state clock's performance, remains an unresolved task. This study uses X-ray absorption fine structure spectroscopy of Th:CaF to investigate the charge state and coordination environment of doped Th. The results indicate that Th is doped with a 4+ valence at the substitutional site of the Ca ion, with charge compensated provided by two F ions located at interstitial sites adjacent to Th.

Federated learning of creep rupture time and high temperature tensile strength prediction models

Sakurai, Junya*; Torigata, Keisuke*; Matsunaga, Manabu*; Takanashi, Naoto*; Hibino, Shinya*; Kizu, Kenichi*; Morita, Akira*; Inomoto, Masahiro*; Shimohata, Nobuaki*; Toyota, Kodai; et al.

Tetsu To Hagane, 111(5), p.246 - 262, 2025/04

https://doi.org/10.2355/tetsutohagane.TETSU-2024-124

Characteristics of temporal variability of long-duration bursts of high-energy radiation associated with thunderclouds on the Tibetan plateau

Tsuchiya, Harufumi; Hibino, Kinya*; Kawata, Kazumasa*; Onishi, Munehiro*; Takita, Masato*; Munakata, Kazuoki*; Kato, Chihiro*; Shimoda, Susumu*; Shi, Q.*; Wang, S.*; et al.

Progress of Earth and Planetary Science (Internet), 11, p.26_1 - 26_14, 2024/05

https://doi.org/10.1186/s40645-024-00625-y

Influence of the strain effect on magnetocrystalline anisotropy in CoFeMnSi Heusler alloys

Nabialek, A.*; Chumak, O. M.*; Aleshkevych, P.*; Domagala, J. Z.*; Pacewicz, A.*; Salski, B.*; Krupka, J.*; Seki, Takeshi*; Takanashi, Koki; Baczewski, L. T.*; et al.

Scientific Reports (Internet), 13, p.17016_1 - 17016_9, 2023/10

https://doi.org/10.1038/s41598-023-43979-x

Some considerations on the dependence to numerical schemes of Lagrangian radionuclide transport models for the aquatic environment

Periez, R.*; Brovchenko, I.*; Jung, K. T.*; Kim, K. O.*; Liptak, L.*; Little, A.*; Kobayashi, Takuya; Maderich, V.*; Min, B. I.*; Suh, K. S.*

Journal of Environmental Radioactivity, 261, p.107138_1 - 107138_8, 2023/05

https://doi.org/10.1016/j.jenvrad.2023.107138

Lagrangian models present several advantages over Eulerian models to simulate the transport of radionuclides in the aquatic environment in emergency situations. A radionuclide release is simulated as a number of particles whose trajectories are calculated along time and thus these models do not require a spatial discretization. In this paper we investigate the dependence of a Lagrangian model output with the grid spacing which is used to calculate concentrations from the final distribution of particles, with the number of particles in the simulation and with the interpolation schemes which are required because of the discrete nature of the water circulation data used to feed the model.

Oxidation of anatase TiO(001) surface using supersonic seeded oxygen molecular beam

Katsube, Daiki*; Ono, Shinya*; Takayanagi, Shuhei*; Ojima, Shoki*; Maeda, Motoyasu*; Origuchi, Naoki*; Ogawa, Arata*; Ikeda, Natsuki*; Aoyagi, Yoshihide*; Kabutoya, Yuito*; et al.

Langmuir, 37(42), p.12313 - 12317, 2021/10

https://doi.org/10.1021/acs.langmuir.1c01752

We investigated the oxidation of oxygen vacancies at the surface of anatase TiO(001) using supersonic seeded molecular beam (SSMB) of oxygen. The oxygen vacancies at the top-surface and sub-surface could be eliminated by the supply of oxygen using an SSMB. These results indicate that the interstitial vacancies can be mostly assigned to oxygen vacancies, which can be effectively eliminated by using an oxygen SSMB. Oxygen vacancies are present on the surface of anatase TiO(001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the as-grown condition, could also be effectively eliminated using the oxygen SSMB.

Data-driven derivation of partial differential equations using neural network model

Koyamada, Koji*; Yu, L.*; Kawamura, Takuma; Konishi, Katsumi*

International Journal of Modeling, Simulation, and Scientific Computing, 12(2), p.2140001_1 - 2140001_19, 2021/04

https://doi.org/10.1142/S1793962321400018

With the improvement of sensors technologies in various fields such as fluid dynamics, meteorology, and space observation, it is an important issue to derive explanatory models using partial differential equations (PDEs) for the big data obtained from them. In this paper, we propose a technique for estimating linear PDEs with higher-order derivatives for spatiotemporally discrete point cloud data. The technique calculates the time and space derivatives from a neural network (NN) trained on the point cloud data, and estimates the derivative term of the PDE using regression analysis techniques. In the experiment, we computed the error of the estimated PDEs for various meta-parameters for the PDEs with exact solutions. As a result, we found that increasing the hierarchy of NNs to match the order of the derivative terms in the exact solution PDEs and adopting L1 regularization with LASSO as the method of regression analysis increased the accuracy of the model.