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Journal Articles

Two-step Mott transition in Ni(S,Se)$$_2$$; $$mu$$SR studies and charge-spin percolation model

Sheng, Q.*; Kaneko, Tatsuya*; Yamakawa, Kohtaro*; Guguchia, Z.*; Gong, Z.*; Zhao, G.*; Dai, G.*; Jin, C.*; Guo, S.*; Fu, L.*; et al.

Physical Review Research (Internet), 4(3), p.033172_1 - 033172_14, 2022/09

Journal Articles

Manipulation of saturation magnetization and perpendicular magnetic anisotropy in epitaxial Co$$_{x}$$Mn$$_{4-x}$$N films with ferrimagnetic compensation

Ito, Keita*; Yasutomi, Yoko*; Zhu, S.*; Nurmamat, M.*; Tahara, Masaki*; Toko, Kaoru*; Akiyama, Ryota*; Takeda, Yukiharu; Saito, Yuji; Oguchi, Tamio*; et al.

Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03

 Times Cited Count:14 Percentile:73.8(Materials Science, Multidisciplinary)

Journal Articles

Effects of diluents on the separation of minor actinides from lanthanides with tetradodecyl-1,10-phenanthroline-2,9-diamide from nitric acid medium

Tsutsui, Nao; Ban, Yasutoshi; Suzuki, Hideya*; Nakase, Masahiko*; Ito, Sayumi*; Inaba, Yusuke*; Matsumura, Tatsuro; Takeshita, Kenji*

Analytical Sciences, 36(2), p.241 - 246, 2020/02

 Times Cited Count:16 Percentile:77.16(Chemistry, Analytical)

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and ${it n}$-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform the actual extraction flow sheet. The slopes of the distribution ratio versus TDdPTDA concentration and the distribution ratio versus nitric acid concentration were similar for F-3 and nitrobenzene systems but different from ${it n}$-dodecane system. These differences were attributed to the characteristics of the diluents. This study reveals high distribution ratios of Am (${it D}$ $$_{Am}$$) and Cm (${it D}$ $$_{Cm}$$) for TDdPTDA, with the high separation factors (${it SF}$s) of Am from Lns enough for their separation.

Journal Articles

Identification of advanced spin-driven thermoelectric materials via interpretable machine learning

Iwasaki, Yuma*; Sawada, Ryoto*; Stanev, V.*; Ishida, Masahiko*; Kirihara, Akihiro*; Omori, Yasutomo*; Someya, Hiroko*; Takeuchi, Ichiro*; Saito, Eiji; Yorozu, Shinichi*

npj Computational Materials (Internet), 5, p.103_1 - 103_6, 2019/10

 Times Cited Count:38 Percentile:87.44(Chemistry, Physical)

Journal Articles

Study on evaluation method for entrained gas flow rate by free surface vortex

Ito, Kei*; Ito, Daisuke*; Saito, Yasushi*; Ezure, Toshiki; Matsushita, Kentaro; Tanaka, Masaaki; Imai, Yasutomo*

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.6632 - 6642, 2019/08

In this paper, a mechanistic model is proposed to calculate the entrained gas flow rate by a free surface vortex. The model contains the theoretical equation of transient gas core elongation and the empirical equation of critical gas core length for gas bubble detachment. Based on those two equations, the entrained gas flow rate is calculated as the portion of the gas core elongated beyond the critical gas core length per unit time. Then, the mechanistic model was applied to the calculation of the entrained gas flow rate in a simple water experiment. As a result, it is confirmed that the entrained gas flow rate grows rapidly when the liquid (water) flow rate, which determine the strength of a free surface vortex, exceeds a certain threshold value.

Journal Articles

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe$$_{2-x}$$T$$_{x}$$As$$_{2}$$ ($$T$$ = Co,Ni)

Tam, D. M.*; Song, Y.*; Man, H.*; Cheung, S. C.*; Yin, Z.*; Lu, X.*; Wang, W.*; Frandsen, B. A.*; Liu, L.*; Gong, Z.*; et al.

Physical Review B, 95(6), p.060505_1 - 060505_6, 2017/02

 Times Cited Count:23 Percentile:71.84(Materials Science, Multidisciplinary)

Journal Articles

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

Frandsen, B. A.*; Liu, L.*; Cheung, S. C.*; Guguchia, Z.*; Khasanov, R.*; Morenzoni, E.*; Munsie, T. J. S.*; Hallas, A. M.*; Wilson, M. N.*; Cai, Y.*; et al.

Nature Communications (Internet), 7, p.12519_1 - 12519_8, 2016/08

 Times Cited Count:31 Percentile:77.41(Multidisciplinary Sciences)

Journal Articles

Development of numerical simulation system for thermal-hydraulic analysis in fuel assembly of sodium-cooled fast reactor

Ohshima, Hiroyuki; Uwaba, Tomoyuki; Hashimoto, Akihiko*; Imai, Yasutomo*; Ito, Masahiro*

AIP Conference Proceedings 1702, p.040011_1 - 040011_4, 2015/12

A numerical simulation system, which consists of a deformation analysis program and three kinds of thermal-hydraulics analysis programs, is being developed in Japan Atomic Energy Agency in order to offer methodologies to clarify thermal-hydraulic phenomena in fuel assemblies of sodium-cooled fast reactors under various operating conditions including fuel deformation. This paper gives a summary of numerical methods of component programs of the system and their validation studies.

Journal Articles

Formative mechanism of inhomogeneous distribution of fractures, an example of the Toki Granite, Central Japan

Sasao, Eiji; Yuguchi, Takashi*; Ito, Yasuto*; Inoue, Takashi*; Ishibashi, Masayuki

Proceedings of 10th Asian Regional Conference of International Association for Engineering Geology and the Environment (IAEG ARS 2015) (USB Flash Drive), 6 Pages, 2015/09

Understanding of the fracture network is important for disposal of high-level radioactive waste. We present our hypothesis on the formative mechanism of inhomogeneous distribution of fracture in the Toki Granite. In the Toki Granite, low- and high-angle fractures are abundant at the shallower part, while less at the deeper part where high-angle fracture is dominant. Distribution of the high-angle fracture is inhomogeneous. Thermochronological study revealed that the rapid cooling occurred at the early stage of granite formation. Paleomagnetic directions of the intact granite were dispersed. This suggests granite was plastically deformed during rapid cooling period. The rapid cooling might cause inhomogeneous distribution of cooling strain. When the granite reached to brittle deformation field, inhomogeneous fracture distribution was formed by the inhomogeneous strain. If so, recognition of the cooling history is essential to understand the distribution of the fracture network.

Journal Articles

X-ray magnetic circular dichroism for Co$$_{x}$$Fe$$_{4-x}$$N (x = 0, 3, 4) films grown by molecular beam epitaxy

Ito, Keita*; Sanai, Tatsunori*; Yasutomi, Yoko*; Zhu, S.-Y.*; Toko, Kaoru*; Takeda, Yukiharu; Saito, Yuji; Kimura, Akio*; Suemasu, Takashi*

Journal of Applied Physics, 115(17), p.17C712_1 - 17C712_3, 2014/05

 Times Cited Count:18 Percentile:60.54(Physics, Applied)

Journal Articles

Study on simulation code for dilute bubbly flow

Ito, Kei; Takata, Takashi*; Ohno, Shuji; Kogawa, Hiroyuki; Kamide, Hideki; Imai, Yasutomo*; Kawamura, Takumi*

Nihon Kikai Gakkai Rombunshu, B, 79(808), p.2630 - 2634, 2013/12

In a sodium-cooled fast reactor, inert gas exists in the primary coolant system as bubbles or dissolved gas. Similarly, small bubbles exist also in the mercury target loop in J-PARC to suppress cavitation erosion. To simulate these inert gas behaviors in liquid metal flows, the Japan Atomic Energy Agency (JAEA) has developed a plant dynamics code VIBUL. In this study, new models, i.e. the bubble release and bubble carry under models, are introduced to simulate the bubble behaviors in the fast reactor and mercury target system. Then, the small bubble behavior in the mercury target system is simulated to check the validity of the new models.

JAEA Reports

Study on numerical simulation of bubble and dissolved gas behavior in liquid metal flow

Ito, Kei; Ohno, Shuji; Kamide, Hideki; Kogawa, Hiroyuki; Futakawa, Masatoshi; Kawamura, Takumi*; Imai, Yasutomo*

JAEA-Research 2013-008, 117 Pages, 2013/10

JAEA-Research-2013-008.pdf:6.55MB

The Japan Atomic Energy Agency has been developed a plant dynamics code VIBUL to simulate the concentration distributions of the dissolved gas and the bubbles in a fast reactor. In this study, the VIBUL code is improved to achieve accurate simulations, e.g. rigorous mole conservation of inert gas. Moreover, new modles are introduced to simulate the small bubble behaviors in the J-PARC mercury target system. To validate the improved models and the newly developed models, the inert gas behaviors in the large-scale sodium-cooled reactor and the small bubble behaviors are simulated. As a result, it is confirmed that the complicated bubble dynamics in each component, e.g. core, IHX or surge tank, can be simulated appropriately by the VIBUL code.

JAEA Reports

Study on evaluation method for gas entrainment and vortex cavitation phenomena; Evaluation of gas entrainment behavior in large-scale test and development of proto-type evaluation method for vortex cavitation

Ito, Kei; Ezure, Toshiki; Ohno, Shuji; Kamide, Hideki; Nakamine, Yoshiaki*; Imai, Yasutomo*

JAEA-Research 2013-007, 75 Pages, 2013/10

JAEA-Research-2013-007.pdf:5.21MB

In Japan Atomic Energy Agency (JAEA), various thermal hydraulics phenomena in an upper plenum region are evaluated in the study on the safety design criteria of the sodium-cooled fast reactor in Japan (JSFR). The gas entrainment (GE) from a free surface of coolant and the vortex cavitation (VC) at the H/L intake are important phenomena to be evaluated. Since these phenomena occur by the significant pressure drop in the vicinity of a vortex center, a technique to evaluate a vortex behavior is indispensable. The authors are developing a GE evaluation method using a numerical analysis and a vortex model. In this study, the evaluations are performed on the GE behavior in the 1/1.8 scaled water model test. In addition, a VC evaluation method is proposed on the basis of the GE evaluation method. As a basic validation of the VC evaluation method, the basic sub-surface vortex test in JAEA is evaluated.

Journal Articles

Study on turbulent modeling in gas entrainment evaluation method

Ito, Kei; Ohshima, Hiroyuki; Nakamine, Yoshiaki*; Imai, Yasutomo*

Journal of Power and Energy Systems (Internet), 6(2), p.151 - 164, 2012/06

Suppression of gas entrainment (GE) phenomena caused by free surface vortices are very important to establish an economically superior design of the sodium-cooled fast reactor in Japan (JSFR). Therefore, the authors are developing a CFD-based evaluation method in which the non-linearity and locality of the GE phenomena can be considered. In this study, the authors develop a turbulent vortex model to evaluate the GE phenomena more accurately. Then, the improved GE evaluation method with the turbulent viscosity model is validated by analyzing the GC lengths observed in a simple experiment. The evaluation results show that the GC lengths analyzed by the improved method are shorter in comparison to the original method, and give better agreement with the experimental data.

Journal Articles

Study on turbulent modeling in gas entrainment evaluation method

Ito, Kei; Ohshima, Hiroyuki; Imai, Yasutomo*

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 8 Pages, 2011/10

In the design study on a large-scale sodium-cooled fast reactor in Japan (JSFR), the suppression of gas entrainment (GE) phenomena caused by free surface vortices are very important. However, due to the non-linearity and/or locality of the GE phenomena, it is not easy to evaluate the occurrences of the GE phenomena accurately. Therefore, the authors are developing a CFD-based evaluation method in which the non-linearity and locality of the GE phenomena can be considered. In this study, the authors develop a turbulent vortex model to evaluate the GE phenomena more accurately. Then, the improved GE evaluation method with the turbulent viscosity model is validated by analyzing the GC lengths observed in a simple experiment. The evaluation results show that the GC lengths analyzed by the improved method are shorter in comparison to the original method, and give better agreement with the experimental data.

Journal Articles

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; Goko, Tatsuo*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 Times Cited Count:150 Percentile:93.71(Multidisciplinary Sciences)

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)As in bulk materials. We reported that ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess compounds, which have p-type carriers.

JAEA Reports

Study on improvement of gas entrainment evaluation method

Ito, Kei; Ohshima, Hiroyuki; Xu, Y.*; Imai, Yasutomo*

JAEA-Research 2010-063, 58 Pages, 2011/03

JAEA-Research-2010-063.pdf:2.09MB

Japan Atomic Energy Agency has conducted the FaCT project to study a conceptional design of a large-scale sodium-cooled fast reactor in which the coolant in the vessel has relatively higher velocity than conventional designs and may causes cover gas entrainment (GE) in an upper plenum region. The authors has been studied a evaluation method of GE in fast reactors and the 1st proposal (prototype) of "Design Guideline for Gas Entrainment Prevention Using CFD Method" was published in 2006. In this study, the prototype evaluation method was improved by introducing the surface tension and turbulent effects. The improved GE evaluation method was validated by analyzing the gas core lengths observed in simple experiments. Results showed that the analytical gas core lengths calculated by the improved GE evaluation method were shorter in comparison to the prototype GE evaluation method, and gave better agreement with the experimental data.

Journal Articles

$$mu$$SR study of CeRhIn$$_5$$ under applied pressure

Heffner, R.*; Goko, Tatsuo*; Andreica, D.*; Oishi, Kazuki*; Higemoto, Wataru; Ito, Takashi; Amato, A.*; Spehling, J.*; Klauss, H. H.*; Bauer, E. D.*; et al.

Journal of Physics; Conference Series, 225, p.012011_1 - 012011_6, 2010/06

 Times Cited Count:1 Percentile:50.39

Journal Articles

Muon spin rotation measurements of heterogeneous field response in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

MacDougall, G. J.*; Savici, A. T.*; Aczel, A. A.*; Birgeneau, R. J.*; Kim, H.*; Kim, S.-J.*; Ito, Toshimitsu*; Rodriguez, J. A.*; Russo, P. L.*; Uemura, Yasutomo*; et al.

Physical Review B, 81(1), p.014508_1 - 014508_7, 2010/01

 Times Cited Count:10 Percentile:46.2(Materials Science, Multidisciplinary)

Journal Articles

Absence of broken time-reversal symmetry in the pseudogap state of the high temperature La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ superconductor from muon-spin-relaxation measurements

MacDougall, G. J.*; Aczel, A. A.*; Carlo, J. P.*; Ito, Toshimitsu*; Rodriguez, J.*; Russo, P. L.*; Uemura, Yasutomo*; Wakimoto, Shuichi; Luke, G. M.*

Physical Review Letters, 101(1), p.017001_1 - 017001_4, 2008/07

 Times Cited Count:60 Percentile:88.15(Physics, Multidisciplinary)

We have performed zero-field muon spin rotation measurements on single crystals of La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ to search for spontaneous currents in the pseudo-gap state. By comparing measurements on materials across the phase diagram, we put strict upper limits on any possible time-reversal symmetry breaking fields that could be associated with the pseudo-gap. Comparison between experimental limits and proposed circulating current states effectively eliminates the possibility that such states exist in this family of materials.

38 (Records 1-20 displayed on this page)