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Watanabe, Tsutomu*; Takagi, Marie*; Shimoyama, Ko*; Kawashima, Masayuki*; Onodera, Naoyuki; Inagaki, Atsushi*
Boundary-Layer Meteorology, 181(1), p.39 - 71, 2021/10
Times Cited Count：6 Percentile：47.35(Meteorology & Atmospheric Sciences)A double-distribution-function lattice Boltzmann model for large-eddy simulations of a passive scalar field is described within and above a plant canopy. For a top-down scalar, for which the plant canopy serves as a distributed sink, the flux of the scalar near the canopy top are predominantly determined by sweep motions originating far above the canopy. By contrast, scalar ejection events are induced by coherent eddies generated near the canopy top. In this paper, the generation of such eddies is triggered by the downward approach of massive sweep motions to existing wide regions of weak ejective motions from inside to above the canopy.
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：43 Percentile：96.93(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 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 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.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count：259 Percentile：99.73(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Katayama, Naoyuki*; Uchida, Masaya*; Hashizume, Daisuke*; Niitaka, Seiji*; Matsuno, Jobu*; Matsumura, Daiju; Nishihata, Yasuo; Mizuki, Junichiro; Takeshita, Nao*; Gauzzi, A.*; et al.
Physical Review Letters, 103(14), p.146405_1 - 146405_4, 2009/10
Times Cited Count：59 Percentile：88.48(Physics, Multidisciplinary)We investigate LiVS and LiVSe with a triangular lattice as itinerant analogues of LiVO known for the formation of a valence-bond solid (VBS) state out of an S = 1 frustrated magnet. LiVS, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at T
305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS has a pseudogap, likely originating from the VBS fluctuation. LiVSe was found to be a paramagnetic metal down to 2 K.
Tamai, Hiroshi; Matsukawa, Makoto; Kurita, Genichi; Hayashi, Nobuhiko; Urata, Kazuhiro*; Miura, Yushi; Kizu, Kaname; Tsuchiya, Katsuhiko; Morioka, Atsuhiko; Kudo, Yusuke; et al.
Plasma Science and Technology, 6(1), p.2141 - 2150, 2004/02
Times Cited Count：2 Percentile：6.49(Physics, Fluids & Plasmas)The dominant issue for the the modification program of JT-60 (JT-60SC) is to demonstrate the steady state reactor relevant plasma operation. Physics design on plasma parameters, operation scenarios, and the plasma control method are investigated for the achievement of high-
. Engineering design and the R&D on the superconducting magnet coils, radiation shield, and vacuum vessel are performed. Recent progress in such physics and technology developments is presented.
Ishida, Shinichi; Abe, Katsunori*; Ando, Akira*; Chujo, T.*; Fujii, Tsuneyuki; Fujita, Takaaki; Goto, Seiichi*; Hanada, Kazuaki*; Hatayama, Akiyoshi*; Hino, Tomoaki*; et al.
Nuclear Fusion, 43(7), p.606 - 613, 2003/07
no abstracts in English
Ishida, Shinichi; Abe, Katsunori*; Ando, Akira*; Cho, T.*; Fujii, Tsuneyuki; Fujita, Takaaki; Goto, Seiichi*; Hanada, Kazuaki*; Hatayama, Akiyoshi*; Hino, Tomoaki*; et al.
Nuclear Fusion, 43(7), p.606 - 613, 2003/07
Times Cited Count：33 Percentile：69.14(Physics, Fluids & Plasmas)no abstracts in English
Ozawa, Masaki; Suzuki, Tatsuya*; Shinoda, Yoshihiko; Takagi, Naoyuki*
no journal, ,
Toward the ultimate minimization of radioactive wastes, a new fuel cycle paradigm has been proposed as Advanced ORIENT Cycle strategy. The strategy will cover the recycle of some specific fission products (i.e., rare metals) as well as enhanced P and T of all of actinides and long-lived fission products. The paper will particularly discuss, with focusing on rare earths in the spent nuclear fuel, the radiochemical properties and separation chemistry of inter- and intra-group separations of 4f/5f elements by tertiary pyridine resin. Furthermore, incineration possibility of Th separated from rare earth ore is evaluated as source of 
U, new nuclear fuel. New ideas of thorium utilization as nuclear fuels and of active creation of artificial rare elements in a fission reactor will also be introduced.
Katayama, Masaharu*; Takamatsu, Kuniyoshi; Sawa, Kazuhiro; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*
no journal, ,
As collaborative research project by Japan Atomic Energy Agency, Toyota Tsusho Corporation and Nuclear Fuel Industries, Ltd., new utilizations of HTGR and new R&D of a cooperative relationship between car industries and HTGR are presented. Specifically, we showed the results of feasibility study on material creation and new-type fuel utilization by using HTTR.
Ooka, Yasunori*; Tanaka, Hideki*; Yamasaki, Masatoshi*; Goto, Minoru; Ueta, Shohei; Takagi, Naoyuki*; Katayama, Masaharu*
no journal, ,
The usage of thorium as nuclear fuel has been focused, which is produced with mining rare metal. The study on thorium fuel utilization is conducted for high temperature gas-cooled reactor (HTGR). We reported about the evaluations on the nuclear characteristics and on manufacturing of the thorium fuel for irradiation test using the High Temperature engineering Test Reactor (HTTR).
Shinohara, Masanori; Shibata, Taiju; Katayama, Masaharu*; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*
no journal, ,
no abstracts in English
Goto, Minoru; Ueta, Shohei; Katayama, Masaharu*; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*
no journal, ,
To utilize thorium in a high temperature gas-cooled reactor (HTGR), calculation of its nuclear characteristics with high accuracy is important subject. Criticality, which is one of the important nuclear characteristics, was measured for thorium loaded core by using critical assemblies, and comparisons between the measurements and calculations were reported. While measurement of criticality of thorium loaded core using actual reactor is almost not published. This paper described about measurement of nuclear characteristics of thorium loaded core using a High Temperature Engineering Test Reactor (HTTR).
Katayama, Masaharu*; Takamatsu, Kuniyoshi; Sawa, Kazuhiro; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*
no journal, ,
no abstracts in English
Ueta, Shohei; Goto, Minoru; Katayama, Masaharu*; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*
no journal, ,
For the feasibility study on a wide-variety of fuel utilization of the high temperature gas-cooled reactor (HTGR) in order to confirm the integrity and the irradiation performance of thorium as the fuel, the irradiation test with thorium-uranium mixed dioxide fuel (denoted as thorium fuel) by the High temperature engineering test reactor (HTTR) of Japan Atomic Energy Agency (JAEA) has been reviewed, and its neutronic characteristics has been evaluated. With regard to the license, the HTTR and the fuel fabrication plant of Nuclear Fuel Industries, Ltd. have been permitted to treat thorium as the fuel. During the irradiation, the integrity of the fuel specimen can be monitored continuously by the fuel failure detection (FFD) system installed in the HTTR. After the irradiation, the fuel sample is dismantled from the core and post-irradiation examinations are carried out to confirm the integrity and to evaluate the irradiance of the test fuel. The irradiance of the thorium fuel sample have been estimated in case of the irradiation test with three block of the thorium fuel in 4 of thorium to uranium mixed ratio and in 20% of enrichment of uranium-235. As the result, the burnup of the thorium fuel specimens will be approximately 21 GWd/t with 30 MW of reactor power in 660 days of the irradiation duration.
Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.
no journal, ,
JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.
