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Journal Articles

$$mu$$SR studies on copper minerals

Fujihara, Masayoshi; Okabe, Hirotaka*; Koda, Akihiro*

Interactions (Internet), 245(1), p.13_1 - 13_6, 2024/12

Quantum states are difficult to observe experimentally. In addition, ideal model materials have not been found for some of the lattice systems in which exotic quantum states are predicted to be realized. Numerous candidates for low-dimensional quantum magnets are hidden in copper minerals, and the number of candidates is increasing every year. We succeeded to synthesize seven copper minerals by imitating the environment where they are discovered and reported their quantum states. The properties of pulsed muons are very suitable for investigating the spin state of artificial copper minerals.

Journal Articles

Spin gap in the weakly interacting quantum spin chain antiferromagnet KCuPO$$_{4}$$$$cdot$$H$$_{2}$$O

Fujihara, Masayoshi; Hagihara, Masato; Morita, Katsuhiro*; Murai, Naoki; Koda, Akihiro*; Okabe, Hirotaka*; Mitsuda, Setsuo*

Physical Review B, 107(5), p.054435_1 - 054435_8, 2023/02

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The $$S$$ = 1/2 Heisenberg linear chain antiferromagnet is the simplest spin model; nevertheless it serves as a platform for various quantum many-body phenomena. Here, we report the magnetic behavior of a quasi-one-dimensional antiferromagnet KCuPO$$_{4}$$$$cdot$$H$$_{2}$$O. A long-range commensurate antiferromagnetic order with ordered moment 0.31(1) $$mu_{rm{B}}$$ per spin occurs at $$T_{rm{N}}$$ = 11.7(1) K. Above $$T_{rm{N}}$$, the inelastic neutron excitation is characterized by a two spinon continuum. The intrachain interaction $$J$$ and interchain interaction $$|J'|$$ are estimated to be 172 K and 4.25(4) K, respectively; thus the ratio of the $$|J'|$$/$$J$$ = 0.0247(3). At lower energies, below $$T_{rm{N}}$$, a spin gap is observed in the dispersive excitations. These results are consistent with characteristics observed in weakly interacting $$S$$ = 1/2 Heisenberg chain system.

Journal Articles

Birchite Cd$$_{2}$$Cu$$_{2}$$(PO$$_{4}$$)$$_{2}$$SO$$_{4}$$ $$cdot$$ 5H$$_{2}$$O as a model antiferromagnetic spin-1/2 Heisenberg $${it J}$$$$_{1}$$-$${it J}$$$$_{2}$$ chain

Fujihara, Masayoshi; Jeschke, H. O.*; Morita, Katsuhiro*; Kuwai, Tomohiko*; Koda, Akihiro*; Okabe, Hirotaka*; Matsuo, Akira*; Kindo, Koichi*; Mitsuda, Setsuo*

Physical Review Materials (Internet), 6(11), p.114408_1 - 114408_8, 2022/11

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

$${it S}$$ = 1/2 Heisenberg $${it J}$$$$_{1}$$-$${it J}$$$$_{2}$$ chain antiferromagnets have been investigated extensively due to their exotic magnetic states. Here, we report the magnetic behavior of birchite Cd$$_{2}$$Cu$$_{2}$$(PO$$_{4}$$)$$_{2}$$SO$$_{4}$$$$cdot$$5H$$_{2}$$O and its effective spin model. Experimental studies by magnetic susceptibility, magnetization, heat capacity, and $$mu$$SR measurements indicate the absence of long-range order down to 0.4 K. Theoretical studies reveal that birchite is a model compound for the $${it J}$$$$_{1}$$-$${it J}$$$$_{2}$$ antiferromagnetic chain: the intrachain interactions $${it J}$$$$_{1}$$ and $${it J}$$$$_{2}$$ are antiferromagnetic and their magnitude is about 100 times larger than the interchain interactions. The magnitude of $${it J}$$$$_{2}$$ is two to three times larger than that of $${it J}$$$$_{1}$$, thus the spin gap is expected to be only a few percent of that of $${it J}$$$$_{1}$$. The temperature dependence of the specific heat shows a broad peak at about 1 K ($$simeq$$ 0.036 $${it J}$$$$_{1}$$), which suggests the presence of a spin gap.

Journal Articles

Sodium-cooled Fast Reactors

Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Journal Articles

Gapless spin liquid in a square-kagome lattice antiferromagnet

Fujihara, Masayoshi*; Morita, Katsuhiro*; Mole, R.*; Mitsuda, Setsuo*; Toyama, Takami*; Yano, Shinichiro*; Yu, D.*; Sota, Shigetoshi*; Kuwai, Tomohiko*; Koda, Akihiro*; et al.

Nature Communications (Internet), 11, p.3429_1 - 3429_7, 2020/07

 Times Cited Count:25 Percentile:89.71(Multidisciplinary Sciences)

Journal Articles

Applicability study of nuclear graphite material IG-430 to VHTR

Osaki, Hirotaka; Shimazaki, Yosuke; Sumita, Junya; Shibata, Taiju; Konishi, Takashi; Ishihara, Masahiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 8 Pages, 2015/05

For the design on the VHTR graphite components, it is desirable to employ graphite material with higher strength. IG-430 graphite has been developed as an advanced candidate for VHTR. However, the new developed IG-430 does not have enough databases for the design of HTGR. In this paper, the compressive strength (Cs) of IG-430, one of important strengths for design data, is statistically evaluated. The component reliability is evaluated based on the safety factors defined by the graphite design code, and the applicability as the VHTR graphite material is discussed. It was found that IG-430 has higher strength (about 11%) and lower standard deviation (about 27%) than IG-110 which is one of traditional graphites used for HTGR, because the crack in IG-430 would not easy to propagate rather than IG-110. Since fracture probability for IG-430 is low, the higher reliability of core-component will be achieved using IG-430. It is expected that IG-430 is applicable for VHTR graphite material.

Journal Articles

Production of mutants by ion beam irradiation in ${it Dahlia}$ spp.

Uyama, Yoshihide*; Oya, Hirotaka*; Amano, Yoshinori*; Kashimoto, Koichi*; Hatano, Shoji*; Nozawa, Shigeki; Yoshihara, Ryohei*; Hase, Yoshihiro; Narumi, Issei

JAEA-Review 2012-046, JAEA Takasaki Annual Report 2011, P. 102, 2013/01

Journal Articles

Experimental evidence of nonthermal acceleration of relativistic electrons by an intensive laser pulse

Kuramitsu, Yasuhiro*; Nakanii, Nobuhiko*; Kondo, Kiminori; Sakawa, Yoichi*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; et al.

Physical Review E, 83(2), p.026401_1 - 026401_6, 2011/02

 Times Cited Count:16 Percentile:65.84(Physics, Fluids & Plasmas)

An energy distribution function of energetic particles in the universe or cosmic rays is well represented by a power-law spectrum, therefore, nonthermal acceleration is essential to understand the origin of cosmic rays. A possible candidate for the origin of cosmic rays is wakefield acceleration at relativistic astrophysical perpendicular shocks. Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma.

Journal Articles

Model experiment of cosmic ray acceleration due to an incoherent wakefield induced by an intense laser pulse

Kuramitsu, Yasuhiro*; Nakanii, Nobuhiko*; Kondo, Kiminori; Sakawa, Yoichi*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; et al.

Physics of Plasmas, 18(1), p.010701_1 - 010701_4, 2011/01

 Times Cited Count:19 Percentile:62.63(Physics, Fluids & Plasmas)

Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma. An intensive laser pulse was propagated in a plasma tube created by imploding a hollow polystyrene cylinder, as the large amplitude light waves propagated in the upstream plasma at an astrophysical shock. Nonthermal electrons were generated, and the energy distribution functions of the electrons have a power-law component with an index of 2.

JAEA Reports

Probabilistic safety assessment on experimental fast reactor Joyo; Level1 PSA for internal events

Ishikawa, Koki; Takamatsu, Misao; Kawahara, Hirotaka; Mihara, Takatsugu; Kurisaka, Kenichi; Terano, Toshihiro; Murakami, Takanori; Noritsugi, Akihiro; Iseki, Atsushi; Saito, Takakazu; et al.

JAEA-Technology 2009-004, 140 Pages, 2009/05

JAEA-Technology-2009-004.pdf:2.0MB

Probabilistic safety assessment (PSA) has been applied to nuclear plants as a method to achieve effective safety regulation and safety management. In order to establish the PSA standard for fast breeder reactor (FBR), the FBR-PSA for internal events in rated power operation is studied by Japan Atomic Energy Agency (JAEA). The level1 PSA on the experimental fast reactor Joyo was conducted to investigate core damage probability for internal events with taking human factors effect and dependent failures into account. The result of this study shows that the core damage probability of Joyo is 5.0$$times$$10$$^{-6}$$ per reactor year (/ry) and that the core damage probability is smaller than the safety goal for existed plants (10 ry) and future plants (10$$^{-5}$$/ry) in the IAEA INSAG-12 (International Nuclear Safety Advisory Group) basic safety principle.

Journal Articles

Spectrum modulation of relativistic electrons by laser wakefield

Nakanii, Nobuhiko*; Kondo, Kiminori; Kuramitsu, Yasuhiro*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; Tanimoto, Tsuyoshi*; et al.

Applied Physics Letters, 93(8), p.081501_1 - 081501_3, 2008/08

 Times Cited Count:4 Percentile:18.82(Physics, Applied)

Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum.

Journal Articles

Chemistry in mega-gravity; Preparation of molecular-scaled graded materials from radical copolymerization

Ihara, Hirotaka; Abe, Yasuyuki*; Miyamoto, Akihiro*; Nishihara, Masamichi*; Takafuji, Makoto*; Ono, Masao; Okayasu, Satoru; Mashimo, Tsutomu

Chemistry Letters, 37(2), p.200 - 201, 2008/02

 Times Cited Count:1 Percentile:7.47(Chemistry, Multidisciplinary)

The molecular-graded structures have been realized through direct copolymerization of halogenated styrene and 2-ethylhexyl methacrylate under ultra-strong gravitational field. The graded structures were clearly confirmed by EPMA and NMR spectroscopy.

Journal Articles

Overview of national centralized tokamak program; Mission, design and strategy to contribute ITER and DEMO

Ninomiya, Hiromasa; Akiba, Masato; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hayashi, Nobuhiko; Hosogane, Nobuyuki; Ikeda, Yoshitaka; Inoue, Nobuyuki; et al.

Journal of the Korean Physical Society, 49, p.S428 - S432, 2006/12

To contribute DEMO and ITER, the design to modify the present JT-60U into superconducting coil machine, named National Centralized Tokamak (NCT), is being progressed under nationwide collaborations in Japan. Mission, design and strategy of this NCT program is summarized.

Journal Articles

Overview of the national centralized tokamak programme

Kikuchi, Mitsuru; Tamai, Hiroshi; Matsukawa, Makoto; Fujita, Takaaki; Takase, Yuichi*; Sakurai, Shinji; Kizu, Kaname; Tsuchiya, Katsuhiko; Kurita, Genichi; Morioka, Atsuhiko; et al.

Nuclear Fusion, 46(3), p.S29 - S38, 2006/03

 Times Cited Count:13 Percentile:41.84(Physics, Fluids & Plasmas)

The National Centralized Tokamak (NCT) facility program is a domestic research program for advanced tokamak research to succeed JT-60U incorporating Japanese university accomplishments. The mission of NCT is to establish high beta steady-state operation for DEMO and to contribute to ITER. The machine flexibility and mobility is pursued in aspect ratio and shape controllability, feedback control of resistive wall modes, wide current and pressure profile control capability for the demonstration of the high-b steady state.

Journal Articles

Engineering design and control scenario for steady-state high-beta operation in national centralized tokamak

Tsuchiya, Katsuhiko; Akiba, Masato; Azechi, Hiroshi*; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; et al.

Fusion Engineering and Design, 81(8-14), p.1599 - 1605, 2006/02

 Times Cited Count:1 Percentile:9.98(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Design study of national centralized tokamak facility for the demonstration of steady state high-$$beta$$ plasma operation

Tamai, Hiroshi; Akiba, Masato; Azechi, Hiroshi*; Fujita, Takaaki; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; Hosogane, Nobuyuki; Ichimura, Makoto*; et al.

Nuclear Fusion, 45(12), p.1676 - 1683, 2005/12

 Times Cited Count:15 Percentile:45.55(Physics, Fluids & Plasmas)

Design studies are shown on the National Centralized Tokamak facility. The machine design is carried out to investigate the capability for the flexibility in aspect ratio and shape controllability for the demonstration of the high-beta steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor, and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced in consistent with the sufficient divertor pumping. Evaluations of the plasma performance towards the determination of machine design are presented.

Journal Articles

Advanced high-temperature ultracentrifuge apparatus for mega-gravity materials science

Mashimo, Tsutomu; Huang, X.; Osakabe, Toyotaka; Ono, Masao*; Nishihara, Masamichi*; Ihara, Hirotaka*; Sueyoshi, Masanori*; Shibasaki, Koji*; Shibasaki, Shiro*; Mori, Nobuo*

Review of Scientific Instruments, 74(1), p.160 - 163, 2003/01

 Times Cited Count:53 Percentile:89.01(Instruments & Instrumentation)

An ultracentrifuge apparatus, which could generate an ultra-strong gravitational field of even $$>$$1,000,000 (1 million) G (1G = 9.8 m/s$$^{2}$$) in a wide temperature range up to $$>$$ 500$$^{circ}$$C with high stability controls, was developed for new materials science research. The system consisted of an air turbine motor with ceramic ball bearings and dumper section, a sample rotor with an outer diameter up to 160 mm, a vacuum chamber and a heating system. The ultracentrifuge experiments using the 70 and 80 mm-diam rotors made of titanium alloy with rotational speeds of up to 170,000 rpm at temperatures of even over 200$$^{circ}$$C for 100 hours with the ripples of $$<$$ 0.05% and $$<$$ 1 degree, respectively, were successfully performed, where the maximum gravitational field at sample was $$>$$1,000,000 G, and the potential energy and sample volume were larger than those of the Kumamoto University one (Rev. Sci. Instr. 67, 3170 (1996)) by $$>$$ 1.9 and $$>$$ 4 times, respectively.

Journal Articles

Initial results of helium ash experiment in the JT-60 lower divertor

Nakamura, Hiroo; Tobita, Kenji; Hirayama, Toshio; Koide, Yoshihiko; Arai, Takashi; Kuriyama, Masaaki; Kubo, Hirotaka; Kusama, Yoshinori; Sugie, Tatsuo; Sugihara, Masayoshi; et al.

Fusion Technology, 18, p.578 - 582, 1990/12

no abstracts in English

Oral presentation

Zn(II) adsorption behavior of bifunctional chelating fiber having aminomethylphosphonate and sulfonate groups

Shibata, Yoshikazu*; Matsuura, Hirotaka*; Ihara, Toshihiro*; Jo, Akinori*; Katakai, Akio; Tamada, Masao

no journal, , 

no abstracts in English

34 (Records 1-20 displayed on this page)