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375 results on '"Fukaya, Y."'

1. Electronic structure of a 3x3-ordered silicon layer on Al(111)

Author

Sato, Y., Fukaya, Y., Cameau, M., Kundu, A. K., Shiga, D., Yukawa, R., Horiba, K., Chen, C. -H., Huang, A., Jeng, H. -T., Ozaki, T., Kumigashira, H., Niibe, M., and Matsuda, I.

Subjects
Condensed Matter - Materials Science
Abstract

Electronic structure of the 3x3 ordered-phase of a silicon (Si) layer on Al(111) has been studied by angle resolved photoemission spectroscopy (ARPES) technique using synchrotron radiation and modeled by a trial atomic model. A closed Fermi surface originating from linearly dispersing band is identified. A band structure calculation of a trial atomic model of the honeycomb silicene on Al(111) implies that the metallic band originates from the Al-Si hybrid state that has the Dirac cone-like dispersion curves. The Si layer on Al(111) can be a model system of Xene to realize the massless electronic system through the overlayer-substrate interaction., Comment: 6 pages, 6 figures

Published
2020
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2. Structure of Superconducting Ca-intercalated Bilayer Graphene/SiC studied using Total-Reflection High-Energy Positron Diffraction

Author

Endo, Y., Fukaya, Y., Mochizuki, I., Takayama, A., Hyodo, T., and Hasegawa, S.

Subjects
Condensed Matter - Materials Science
Abstract

We have investigated the atomic structure of superconducting Ca-intercalated bilayer graphene on a SiC(0001) substrate using total-reflection high-energy positron diffraction. By comparing the experimental rocking-curves with ones calculated for various structural models using a full-dynamical theory, we have found that Ca atoms are intercalated in the graphene-buffer interlayer, rather than between the two graphene layers. From transport measurements, the superconducting transition was observed to be at Tc_onset = 4K for this structure. This study is the first to clearly identify the relation between the atomic arrangement and superconductivity in Ca-intercalated bilayer graphene.

Published
2019
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7. REACTOR PHYSICS EXPERIMENT IN A GRAPHITE-MODERATION SYSTEM FOR HTGR

Author

Fukaya Y., Goto M., Nakagawa S., Nakajima K., Takahashi K., Sakon A., Sano T., and Hashimoto K.

Subjects
graphite-moderation system, htgr, kuca, b-rack, reactor physics experiment, Physics, QC1-999
Abstract

The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs). The objectives are to introduce a generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to introduce reactor noise analysis to High Temperature Engineering Test Reactor (HTTR) experiment to observe sub-criticality. To achieve the objectives, the reactor core of graphite-moderation system named B7/4”G2/8”p8EUNU+3/8”p38EU(1) was newly composed in the B-rack of Kyoto University Critical Assembly (KUCA). The core is composed of the fuel assembly, driver fuel assembly, graphite reflector, and polyethylene reflector. The fuel assembly is composed of enriched uranium plate, natural uranium plate and graphite plates to realize the average fuel enrichment of HTTR and it’s spectrum. However, driver fuel assembly is necessary to achieve the criticality with the small-sized core. The core plays a role of the reference core of the bias factor method, and the reactor noise was measured to develop the noise analysis scheme. In this study, the overview of the criticality experiments is reported. The reactor configuration with graphite moderation system is rare case in the KUCA experiments, and this experiment is expected to contribute not only for an HTGR development but also for other types of a reactor in the graphite moderation system such as a molten salt reactor development.

Published
2021
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13. Environmental effects on layer-dependent dynamics of Dirac fermions in quasicrystalline bilayer graphene

Author

Zhao, Y., primary, Suzuki, T., additional, Iimori, T., additional, Kim, H.-W., additional, Ahn, J. R., additional, Horio, M., additional, Sato, Y., additional, Fukaya, Y., additional, Kanai, T., additional, Okazaki, K., additional, Shin, S., additional, Tanaka, S., additional, Komori, F., additional, Fukidome, H., additional, and Matsuda, I., additional

Published
2022
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31. REACTOR PHYSICS EXPERIMENT IN A GRAPHITE-MODERATION SYSTEM FOR HTGR.

Author

Margulis, M., Blaise, P., Fukaya, Y., Goto, M., Nakagawa, S., Nakajima, K., Takahashi, K., Sakon, A., Sano, T., and Hashimoto, K.

Subjects
NUCLEAR reactions, NUCLEAR reactor reactivity, NUCLEAR physics, URANIUM, NUCLEAR fuels
Abstract

The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs). The objectives are to introduce a generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to introduce reactor noise analysis to High Temperature Engineering Test Reactor (HTTR) experiment to observe sub-criticality. To achieve the objectives, the reactor core of graphite-moderation system named B7/4"G2/8"p8EUNU+3/8"p38EU(1) was newly composed in the B-rack of Kyoto University Critical Assembly (KUCA). The core is composed of the fuel assembly, driver fuel assembly, graphite reflector, and polyethylene reflector. The fuel assembly is composed of enriched uranium plate, natural uranium plate and graphite plates to realize the average fuel enrichment of HTTR and it's spectrum. However, driver fuel assembly is necessary to achieve the criticality with the small-sized core. The core plays a role of the reference core of the bias factor method, and the reactor noise was measured to develop the noise analysis scheme. In this study, the overview of the criticality experiments is reported. The reactor configuration with graphite moderation system is rare case in the KUCA experiments, and this experiment is expected to contribute not only for an HTGR development but also for other types of a reactor in the graphite moderation system such as a molten salt reactor development. [ABSTRACT FROM AUTHOR]

Published
2021
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37. Structure determination of the rutile-TiO2(110)-(1 × 2) surface using total-reflection high-energy positron diffraction (TRHEPD)

Author

Mochizuki, I., 1000090570911, Ariga, H., Fukaya, Y., Wada, K., Maekawa, M., Kawasuso, A., Shidara, T., Asakura, K., Hyodo, T., Mochizuki, I., 1000090570911, Ariga, H., Fukaya, Y., Wada, K., Maekawa, M., Kawasuso, A., Shidara, T., Asakura, K., and Hyodo, T.

Abstract

The exact structure of the rutile-TiO2(110)-(1×2) surface, which had been under debate over the past 30 years, was investigated using the newly developed technique of total-reflection high-energy positron diffraction (TRHEPD), which is a positron counterpart of reflection high-energy electron diffraction (RHEED). The rocking-curves for the 00-spot obtained from the experimental diffraction patterns were compared to the curves for various models calculated with a full-dynamical theory. It was found that the rocking-curves matched those for a surface consisting of a Ti2O3 configuration, originally suggested by Onishi and Iwasawa [H. Onishi and Y. Iwasawa, Surf. Sci., 1994, 313, L783], but with a further modification of atomic positions close to the ones proposed by Wang et al. [Q. Wang, A. R. Oganov, Q. Zhu and X. F. Zhou, Phys. Rev. Lett., 2014, 113, 266101]. This result demonstrates that TRHEPD can distinguish between the existence and absence of the oxygen atoms on the topmost surface, and between the Ti atoms residing in positions at the interstitial-vertical sites and those at interstitialhorizontal sites.

Published
2016

47. The study on degradation of engineered barrier in radioactive waste repositories, III

Author

Iriya, Keishiro, Kubo, Hiroshi, Fukaya, Y., and Fujita, Hideki

Abstract

TRU廃棄物の処分システムの構成材料としてコンクリートや圧縮成型したベントナイトが有力な候補として考えられている。圧縮成型ベントナイトは、止水性やコロイド等のフィルトレーションに優れるが、施工性や機械的強度は劣る。一方セメント系材料は、ひび割れや施工継ぎ目等により止水性やコロイドのフィルトレーションは劣るが、施工性や処分場操業期間内の機械的強度に優れているといったように両者は長所・短所を持つ。ベントナイトとセメントがお互いの短所をお互いの長所により補完することを考慮しながら処分場の設計を進めていくことが、処分場の性能確保や経済性の観点から必要である。また、TRU廃棄物には多量の硝酸塩を含んでいることからセメントの硝酸塩に対する変質挙動を調査しておく必要がある。以上の観点から、これら材料の長期的な安定性を実験的に調査することにより、TRU廃棄物の処分システムの概念構築に反映させることを目的として本研究を実施する。

Published
1999

49. New experiment stations at KEK Slow Positron Facility

Author

Wada, K, primary, Hyodo, T, additional, Kosuge, T, additional, Saito, Y, additional, Ikeda, M, additional, Ohsawa, S, additional, Shidara, T, additional, Michishio, K, additional, Tachibana, T, additional, Terabe, H, additional, Suzuki, R H, additional, Nagashima, Y, additional, Fukaya, Y, additional, Maekawa, M, additional, Mochizuki, I, additional, and Kawasuso, A, additional

Published
2013
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