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Journal Articles

Coherent eddies transporting passive scalars through the plant canopy revealed by Large-Eddy simulations using the lattice Boltzmann method

Watanabe, Tsutomu*; Takagi, Marie*; Shimoyama, Ko*; Kawashima, Masayuki*; Onodera, Naoyuki; Inagaki, Atsushi*

Boundary-Layer Meteorology, 181(1), p.39 - 71, 2021/10

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.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

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:140 Percentile:99.81(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.

Journal Articles

Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS$$_{2}$$

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:45 Percentile:86.42(Physics, Multidisciplinary)

We investigate LiVS$$_{2}$$ and LiVSe$$_{2}$$ with a triangular lattice as itinerant analogues of LiVO$$_{2}$$ known for the formation of a valence-bond solid (VBS) state out of an S = 1 frustrated magnet. LiVS$$_{2}$$, 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$$_{c}$$ $$sim$$ 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$$_{2}$$ has a pseudogap, likely originating from the VBS fluctuation. LiVSe$$_{2}$$ was found to be a paramagnetic metal down to 2 K.

Journal Articles

Progress in physics and technology developments for the modification of JT-60

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:6.89(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-$$beta$$. 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.

Journal Articles

Objectives and design of the JT-60 superconducting tokamak

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

Journal Articles

Objectives and design of the JT-60 superconducting tokamak

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:71.47(Physics, Fluids & Plasmas)

no abstracts in English

Oral presentation

New strategy on rare earth in advanced nuclear fuel cycle

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 $$^{233}$$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.

Oral presentation

Feasibility study on material creation and new-type fuel utilization by using HTTR, 1; Outline of feasibility study

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.

Oral presentation

Feasibility Study on material creation and new-type fuel utilization by using HTTR, 5; Study on thorium fuel utilization

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).

Oral presentation

Feasibility Study on material development and new-type fuel utilization by using HTTR, 4; Feasibility study on development of irradiation capsule and irradiation method

Shinohara, Masanori; Shibata, Taiju; Katayama, Masaharu*; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*

no journal, , 

no abstracts in English

Oral presentation

Feasibility study on a wide-variety of fuel utilization by using HTTR, 3; Nuclear characteristics of thorium loaded core

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).

Oral presentation

Feasibility study on a wide-variety of fuel utilization by using HTTR, 1; Outline of feasibility study

Katayama, Masaharu*; Takamatsu, Kuniyoshi; Sawa, Kazuhiro; Takagi, Naoyuki*; Ooka, Yasunori*; Yamasaki, Masatoshi*

no journal, , 

no abstracts in English

Oral presentation

Feasibility study on a wide-variety of fuel utilization by using HTTR, 4; Study on thorium fuel utilization

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.

13 (Records 1-13 displayed on this page)
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