Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Okuma, Ryutaro*; Kofu, Maiko; Asai, Shinichiro*; Avdeev, M.*; Koda, Akihiro*; Okabe, Hirotaka*; Hiraishi, Masatoshi*; Takeshita, Soshi*; Kojima, Kenji*; Kadono, Ryosuke*; et al.
Nature Communications (Internet), 12, p.4382_1 - 4382_7, 2021/07
Times Cited Count：7 Percentile：60.19(Multidisciplinary Sciences)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：44 Percentile：97.1(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.
Shinohara, Takenao; Kai, Tetsuya; Oikawa, Kenichi; Nakatani, Takeshi; Segawa, Mariko; Hiroi, Kosuke; Su, Y. H.; Oi, Motoki; Harada, Masahide; Iikura, Hiroshi; et al.
Review of Scientific Instruments, 91(4), p.043302_1 - 043302_20, 2020/04
Times Cited Count：51 Percentile：96.53(Instruments & Instrumentation)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：262 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.
Oikawa, Kenichi; Su, Y. H.; Kiyanagi, Ryoji; Kawasaki, Takuro; Shinohara, Takenao; Kai, Tetsuya; Hiroi, Kosuke; Harjo, S.; Parker, J. D.*; Matsumoto, Yoshihiro*; et al.
Physica B; Condensed Matter, 551, p.436 - 442, 2018/12
Times Cited Count：6 Percentile：38.09(Physics, Condensed Matter)Oba, Yojiro; Shinohara, Takenao; Sato, Hirotaka*; Onodera, Yohei*; Hiroi, Kosuke; Su, Y. H.; Sugiyama, Masaaki*
Journal of the Physical Society of Japan, 87(9), p.094004_1 - 094004_5, 2018/09
Times Cited Count：1 Percentile：11.83(Physics, Multidisciplinary)no abstracts in English
Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.
Space Science Reviews, 208(1-4), p.317 - 337, 2017/07
Times Cited Count：54 Percentile：71.62(Astronomy & Astrophysics)NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.
Su, Y. H.; Oikawa, Kenichi; Shinohara, Takenao; Kai, Tetsuya; Hiroi, Kosuke; Harjo, S.; Kawasaki, Takuro; Gong, W.; Zhang, S. Y.*; Parker, J. D.*; et al.
Physics Procedia, 88, p.42 - 49, 2017/06
Times Cited Count：4 Percentile：84.9(Instruments & Instrumentation)Oikawa, Kenichi; Su, Y. H.; Tomota, Yo*; Kawasaki, Takuro; Shinohara, Takenao; Kai, Tetsuya; Hiroi, Kosuke; Zhang, S.*; Parker, J. D.*; Sato, Hirotaka*; et al.
Physics Procedia, 88, p.34 - 41, 2017/00
Times Cited Count：5 Percentile：88.97(Instruments & Instrumentation)Time of flight Bragg edge transmission (BET) imaging was adopted to the plastically bent plates of a ferritic steel and a duplex stainless steel, and the obtained results were validated using neutron diffraction method and electron backscatter diffraction (EBSD) observations. The BET imaging results of texture distribution and phase volume fractions showed good agreements with those obtained by neutron diffraction and EBSD. The crystallite size evaluation using extinction correction was succeeded by the RITS code where Sabine's primary extinction function was applied, however, the crystallite size was not obtained by the Rietveld refinement where the same function was used for the evaluation. In this study, we comparatively reinvestigate the crystallite size and the dislocation density of the plastically bent steel plates by the use of Pawley analysis on the diffraction data and grain analysis on EBSD data.
Su, Y. H.; Oikawa, Kenichi; Harjo, S.; Shinohara, Takenao; Kai, Tetsuya; Harada, Masahide; Hiroi, Kosuke; Zhang, S.*; Parker, J. D.*; Sato, Hirotaka*; et al.
Materials Science & Engineering A, 675, p.19 - 31, 2016/10
Times Cited Count：23 Percentile：72.27(Nanoscience & Nanotechnology)Hiroi, Hiroshi*; Arai, Masanobu; Kisohara, Naoyuki
Dai-21-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (USB Flash Drive), 3 Pages, 2016/06
The purpose of fast breeder reactors (FBR) and the role of Monju were discussed in Ministry of education, culture, sports science and technology-Japan (MEXT) after the Fukushima NNP accident. The discussion has concluded that FBRs contribute to energy security and reduction of high-level radioactive waste, and that Monju is to be utilized to demonstrate these usefulness and to implement international contributions. This paper addresses anticipated R&D results from Monju on the basis of the enforcement of new nuclear regulation, the energy situations in Japan and the international status of FBR development and collaborations.
Kurihara, Akikazu; Yatabe, Toshio; Hiroi, Hiroshi; Tanabe, Hiromi
JNC TN9400 2003-060, 236 Pages, 2003/07
JNC-TN9400-2003-060.pdf:7.91MB
Large leak sodium-water reaction tests were carried out using SWAT-1 rig and SWAT-3 facility in Power Reactor and Nuclear Fuel Development Corporation (PNC) O-arai Engineering Center to obtain the data on the design of the prototype LMFBR Monju steam generator against a large leak accident.This report provides the results of SWAT-3 Runs 1 and 2.In Runs 1 and 2, the heat transfer tube bundle of the evaporator, fabricated by TOSHIBA/IHI, were used, and the pressure relief line was located at the top of evaporator.The water injection rates in the evaporator were 6.7kg/s and 14.2 (initial) - 9.7kg/s in Runs 1 and 2 respectively, which corresponded to 3.3 tubes and 7.1 (initial) - 4.8 tubes failure in actual size system according to iso-velocity modeling.Approximately two hundreds of measurement points were provided to collect data such as pressure,Temperature, strain,sodium level, void, thrust load, acceleration, displacement, flow rate, and so on in each run.Initial spike pressures were 1.13MPa and 2.62MPa nearest to injection point in Runs 1 and 2 respectively, and the maximum quasi-steady pressures in evaporator were 0.49MPa and 0.67MPa in Runs 1 and 2. No secondary tube failure was observed. The rupture disc of evaporator (RD601) burst at 1.1s in Run-1 and at 0.7s in Run-2 after water injected, and the pressure relief system was well-functioned though a few items for improvement were found.
Suzuki, Soju; Ito, Chikara; Aoyama, Takafumi; Hiroi, Hiroshi
no journal, ,
no abstracts in English
Kawamura, Hiroshi; Niimi, Motoji; Kusunoki, Tsuyoshi; Nagao, Yoshiharu; Hiroi, Hiroshi
no journal, ,
no abstracts in English
Kai, Tetsuya; Shinohara, Takenao; Oikawa, Kenichi; Nakatani, Takeshi; Segawa, Mariko; Hiroi, Kosuke; Su, Y. H.; Hayashida, Hirotoshi*; Parker, J. D.*; Matsumoto, Yoshihiro*; et al.
no journal, ,
no abstracts in English
Su, Y. H.; Oikawa, Kenichi; Harjo, S.; Shinohara, Takenao; Kai, Tetsuya; Harada, Masahide; Hiroi, Kosuke; Zhang, S.*; Parker, J. D.*; Sato, Hirotaka*; et al.
no journal, ,
Shinohara, Takenao; Kai, Tetsuya; Oikawa, Kenichi; Nakatani, Takeshi; Segawa, Mariko; Harada, Masahide; Hiroi, Kosuke; Su, Y. H.; Aizawa, Kazuya; Hayashida, Hirotoshi*; et al.
no journal, ,
no abstracts in English
Shinohara, Takenao; Kai, Tetsuya; Oikawa, Kenichi; Nakatani, Takeshi; Hiroi, Kosuke; Su, Y. H.; Hayashida, Hirotoshi*; Parker, J. D.*; Matsumoto, Yoshihiro*; Zhang, S.*; et al.
no journal, ,
no abstracts in English
Su, Y. H.; Oikawa, Kenichi; Shinohara, Takenao; Kai, Tetsuya; Hiroi, Kosuke; Hayashida, Hirotoshi*; Zhang, S.*; Parker, J. D.*; Matsumoto, Yoshihiro*; Sato, Hirotaka*; et al.
no journal, ,
