Partial breakdown of translation symmetry at a structural quantum critical point associated with a ferroelectric soft mode

Ishii, Yui*; Yamamoto, Arisa*; Sato, Naoki*; Nambu, Yusuke*; Kawamura, Seiko; Murai, Naoki; Ohara, Koji*; Kawaguchi, Shogo*; Mori, Takao*; Mori, Shigeo*

Physical Review B, 106(13), p.134111_1 - 134111_7, 2022/10

https://doi.org/10.1103/PhysRevB.106.134111

Recent update of AMATERAS; A Cold-neutron disk-chopper spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kofu, Maiko; Murai, Naoki; Inamura, Yasuhiro; Kikuchi, Tatsuya*; Wakai, Daisuke*

JPS Conference Proceedings (Internet), 33, p.011089_1 - 011089_7, 2021/03

https://doi.org/10.7566/JPSCP.33.011089

The recent update of AMATERAS, a cold-neutron disk-chopper spectrometer at Japan Proton Accelerator Research Complex (J-PARC), is reported. AMATERAS has been operating for a decade. Since 2017, some updates have been done or are underway, which include installing new detectors, replacing the vacuum system of the scattering chamber, and other works. We are also working on the re-investigation of the resolution function. Demonstration measurements were carried out at 1MW test operations done in 2018 and 2019. Plans of upgrading the spectrometer are currently being considered.

Horizontal line nodes in SrRuO proved by spin resonance

Iida, Kazuki*; Kofu, Maiko; Suzuki, Katsuhiro*; Murai, Naoki; Kawamura, Seiko; Kajimoto, Ryoichi; Inamura, Yasuhiro; Ishikado, Motoyuki*; Hasegawa, Shunsuke*; Masuda, Takatsugu*; et al.

Journal of the Physical Society of Japan, 89(5), p.053702_1 - 053702_5, 2020/05

https://doi.org/10.7566/JPSJ.89.053702

Study on use of superconducting magnet and first inelastic neutron scattering experiment under magnetic field at 4SEASONS spectrometer

Kajimoto, Ryoichi; Ishikado, Motoyuki*; Kira, Hiroshi*; Kaneko, Koji; Nakamura, Mitsutaka; Kamazawa, Kazuya*; Inamura, Yasuhiro; Ikeuchi, Kazuhiko*; Iida, Kazuki*; Murai, Naoki; et al.

Physica B; Condensed Matter, 556, p.26 - 30, 2019/03

BB2018-0570.pdf:2.17MB

https://doi.org/10.1016/j.physb.2018.11.065

Stability of montmorillonite edge faces studied using first-principles calculations

Sakuma, Hiroshi*; Tachi, Yukio; Yotsuji, Kenji; Suehara, Shigeru*; Arima, Tatsumi*; Fujii, Naoki*; Kawamura, Katsuyuki*; Honda, Akira

Clays and Clay Minerals, 65(4), p.252 - 272, 2017/08

https://doi.org/10.1346/CCMN.2017.064062

Structure and stability of montmorillonite edge faces (110), (010), (100), and (130) of the layer charges y = 0.5 and 0.33 are investigated by the first-principles electronic calculations based on the density functional theory. Stacking and single layer models are tested for understanding the effect of stacking on the stability of montmorillonite edge faces. Most stacking layers stabilize the edge faces by making hydrogen bonds between the layers; therefore, the surface energy of stacking layers is reduced rather than the single layer model. This indicates that the surface energy of edge faces should be estimated depending on the swelling conditions. Lowest surface energies of (010) and (130) edge faces were realized by the presence of Mg ions on the edge faces. These edge faces have a strong adsorption site for cations due to local negative charge of the edges.

Colossal negative thermal expansion in BiNiO induced by intermetallic charge transfer

Azuma, Masaki*; Chen, W.*; Seki, Hayato*; Czapski, M.*; Olga, S.*; Oka, Kengo*; Mizumaki, Masaichiro*; Watanuki, Tetsu; Ishimatsu, Naoki*; Kawamura, Naomi*; et al.

Nature Communications (Internet), 2, p.347_1 - 347_5, 2011/06

https://doi.org/10.1038/ncomms1361

no abstracts in English

Simulation of concentrations of anthropogenic radionuclides in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*; Togawa, Orihiko

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 4 Pages, 2010/10

This study aims to demonstrate many findings in the Japan Sea expeditions by Japan Atomic Energy Agency between 1997 and 2002 making use of an ocean general circulation model. A numerical experiment is performed between 1945 and 2000 with deposition at the sea surface by global fallout as main source of anthropogenic radionuclides. The concentrations of Sr and Cs in the surface layer are approximately in the range of 1.0-1.5 Bq/m and 2.0-2.5 Bq/m and they exponentially decrease with depth from the sea surface to the sea bottom. Total amounts of Sr and Cs in the seawater of the Japan Sea are estimated to be about 1.34 PBq (1 PBq = 10 Bq) and 2.02 PBq in the numerical experiment, which demonstrates observational estimations in the Japan Sea expeditions. Time series of the total amounts show that they attain the maximums of 4.86 PBq for Sr and 7.33 PBq for Cs in 1964.

Modeling of the branches of the Tsushima Warm Current in the eastern Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Hirose, Naoki*; Takikawa, Tetsutaro*; Yoon, J.-H.*

Journal of Oceanography, 65(4), p.439 - 454, 2009/08

https://doi.org/10.1007/s10872-009-0039-3

This study aims at reproducing branches of the Tsushima Warm Current making use of an ocean general circulation model, which is important for movement of pollutants in the Japan Sea. The model was laterally exerted by volume transports measured by ADCP through the Tsushima Straits and the Tsugaru Strait. Sea level variation measured by coastal tide-stations as well as satellite altimeters is assimilated into the numerical model. It was demonstrated that an assimilation of sea level variation at the coastal tide-stations is useful to simulate oceanic condition in the nearshore region.

Sequential forecasting of the surface and subsurface conditions in the Japan Sea

Hirose, Naoki*; Kawamura, Hideyuki; Lee, H. J.*; Yoon, J.-H.*

Journal of Oceanography, 63(3), p.467 - 481, 2007/06

https://doi.org/10.1007/s10872-007-0042-5

This study estimates and forecasts a realistic change of the Japan Sea by assimilating satellite measurements into an eddy-resolving circulation model. Suboptimal but feasible assimilation schemes of approximate filtering and nudging play essential roles in a system. The sequential updates of error covariance significantly outperforms the asymptotic covariance due to irregular sampling patterns from multiple altimeter satellites. The best estimate shows an average rms difference of 1.2 C only to the radiometer data, and also explain about half of sea level variances measured by the microwave observation. It is demonstrated that a forecast persistency strongly depends on variable, depth, and location.

Oil spill simulation in the Japan Sea

Kawamura, Hideyuki; Kobayashi, Takuya; Hirose, Naoki*; Ito, Toshimichi; Togawa, Orihiko

WIT Transactions on Ecology and the Environment, Vol.88, p.273 - 278, 2006/00

An assessment system of marine environment in the Japan Sea is being constructed in the Japan Atomic Energy Agency. It is composed of an ocean general circulation model (RIAMOM), a particle random-walk model (SEA-GEARN) and a radiation dose assessment model (COLDOS). This study aims to confirm a validity of the assessment system by reproducing a movement of spilled oil at an incident of Russian tanker Nakhodka, in January 1997. Realistic reproduction of ocean conditions is a significant factor for accurate simulations of the movement of spilled oil. In this study, one of data assimilation techniques, an approximate Kalman filter, was introduced by combining RIAMOM with sea level measurements of satellite data. The assimilated results were in good agreement with observed oceanic phenomena both qualitatively and quantitatively. Using the calculated ocean currents, simulations of behaviour of spilled oil was performed with SEA-GEARN. The tanker was ruptured in a storm about 100 km north of the Oki Islands in Shimane Prefecture, Japan, on January 2, 1997. Most of oil spread over off Hyogo, Kyoto, Fukui and Ishikawa Prefecture, meanwhile a part of it reached a coast of Niigata Prefecture detouring around Noto Peninsula by January 21, 1997. The most important feature in these regions is considered to be a branch of the Tsushima Warm Current (TWC). Owing to a variability of TWC, ocean eddy activities and a sea surface wind, the spilled oil dispersed widely in space. On the other hand, the strong northeastward component of TWC was likely to drive the spilled oil to Niigata Prefecture. A number of experiments with different parameters and situations showed that the assimilated daily ocean currents with wind drift gave the best effect on simulation for the movement of spilled oil.