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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.
Nagao, Keisuke*; Okazaki, Ryuji*; Nakamura, Tomoki*; Miura, Yayoi*; Osawa, Takahito; Bajo, Kenichi*; Matsuda, Shintaro*; Ebihara, Mitsuru*; Ireland, T.*; Kitajima, Fumio*; et al.
Science, 333(6046), p.1128 - 1131, 2011/08
Times Cited Count：130 Percentile：95.22(Multidisciplinary Sciences)A steroid surface materials record regolith processes and a history of cosmic-ray irradiation. Noble gas isotopes in three rocky grains from Itokawa have been determined. High concentrations of solar He, Ne, and Ar, as high as those in lunar soils, are released at variable temperatures from each sample. The isotopic compositions are essentially identical to those of solar wind but distinguishable in He relative abundance. These noble gas characteristics can be explained by repeated implantation and preferential loss of solar He by removal of weathered He-rich rim on the grain surface through friction among regolith grains on Itokawa. Residence time of regolith materials on Itokawa is alculated to be shorter than 10 Myr, suggesting that regolith materials of small asteroids would escape easily to space.
) and Cs(7
) by femtosecond laser pulsesYamada, Hidetaka; Yokoyama, Keiichi; Teranishi, Yoshiaki*; Sugita, Akihiro; Shirai, Toshizo*; Aoyama, Makoto; Akahane, Yutaka; Inoue, Norihiro*; Ueda, Hideki*; Yamakawa, Koichi; et al.
Physical Review A, 72(6), p.063404_1 - 063404_5, 2005/12
Times Cited Count：6 Percentile：31.21(Optics)A demonstration of coherent quantum control for ultrafast precise selection of closely-lying states is reported. A phase-locked pair of femtosecond laser pulses is generated through a pulse shaper to excite the ground-state cesium atom to the Cs(7) and Cs(7) states by two-photon absorption. The excited state population is measured by detecting fluorescence from each spin-orbit state. By controlling the phase-difference of the pulse pair, an ultrafast precise selection is accomplished. The contrast ratio of the maximal to minimal selection ratio exceeds 10
with the delay less than 400 fs.
Yokoyama, Keiichi; Teranishi, Yoshiaki; Toya, Yukio; Shirai, Toshizo; Fukuda, Yuji; Aoyama, Makoto; Akahane, Yutaka; Inoue, Norihiro*; Ueda, Hideki; Yamakawa, Koichi; et al.
Journal of Chemical Physics, 120(20), p.9446 - 9449, 2004/05
Times Cited Count：6 Percentile：18.77(Chemistry, Physical)Optimal laser control for ultrafast selection of closely-lying excited states, whose energy separation is smaller than the laser bandwidth, is reported on the two-photon transition of atomic cesium; Cs(6S 
7D
, J = 5/2 and 3/2). Selective excitation was carried out by pulse shaping of ultrashort laser pulses which were adaptively modulated in a closed-loop learning system handling eight parameters representing the electric field. Two-color fluorescence from the respective excited states was monitored to measure the selectivity. The fitness used in the learning algorithm was evaluated from the ratio of the fluorescence yield. After fifty generations, a pair of nearly transform-limitted pulses were obtained as an optimal pulse shape, proving the effectiveness of "Ramsey fringes" mechanism. The contrast of the selection ratio was improved by 
30 % from the simple "Ramsey fringes" experiment.
Nakamura, Yukiharu; Tsutsui, Hiroaki*; Takei, Nahoko*; Shirai, Hiroshi; Sugihara, Masayoshi; Gribov, Y.*; Ozeki, Takahisa; Tobita, Kenji; Iio, Shunji*; Jardin, S. C.*
Journal of Plasma and Fusion Research SERIES, Vol.6, p.196 - 198, 2004/00
no abstracts in English
Shirai, Hiroshi; Shimizu, Katsuhiro; Hayashi, Nobuhiko; Itakura, Hirofumi*; Takase, Keizo*
JAERI-Data/Code 2000-040, 214 Pages, 2001/01
JAERI-Data-Code-2000-040.pdf:7.89MB
no abstracts in English
Takenaga, Hidenobu; Nagashima, Keisuke; Sakasai, Akira; Asakura, Nobuyuki; Shimizu, Katsuhiro; Kubo, Hirotaka; Higashijima, Satoru; Oikawa, Toshihiro; Shirai, Hiroshi; Fujita, Takaaki; et al.
Nuclear Fusion, 39(11Y), p.1917 - 1928, 1999/11
Times Cited Count：22 Percentile：57.71(Physics, Fluids & Plasmas)no abstracts in English
Asakura, Nobuyuki; Hosogane, Nobuyuki; Itami, Kiyoshi; Sakasai, Akira; Sakurai, Shinji; Shimada, Michiya; Kubo, Hirotaka; Higashijima, Satoru; Shimizu, Katsuhiro; Takenaga, Hidenobu; et al.
Journal of Nuclear Materials, 266-269, p.182 - 188, 1999/00
Times Cited Count：66 Percentile：96.68(Materials Science, Multidisciplinary)no abstracts in English
Tobita, Kenji; Nishitani, Takeo; Harano, Hideki*; Tani, Keiji; Isobe, Mitsutaka*; Fujita, Takaaki; Kusama, Yoshinori; G.A.Wurden*; Shirai, Hiroshi; Oikawa, Toshihiro; et al.
Fusion Energy 1996, Vol.1, p.497 - 505, 1997/00
no abstracts in English
Tobita, Kenji; Harano, Hideki*; Nishitani, Takeo; Fujita, Takaaki; Tani, Keiji; Oikawa, Toshihiro; Shirai, Hiroshi; Kusama, Yoshinori
Nuclear Fusion, 37(11), p.1583 - 1592, 1997/00
Times Cited Count：26 Percentile：64.72(Physics, Fluids & Plasmas)no abstracts in English
system with the trajectory-surface-hopping modelIchihara, Akira; Shirai, Toshizo; Yokoyama, Keiichi
Journal of Chemical Physics, 105(5), p.1857 - 1861, 1996/08
Times Cited Count：38 Percentile：78.01(Chemistry, Physical)no abstracts in English
Shirai, Hiroshi; Takizuka, Tomonori; Kikuchi, Mitsuru; Mori, Masahiro; Nishitani, Takeo; Ishida, Shinichi; Kamada, Yutaka; Sato, Masayasu; Isei, Nobuaki; Koide, Yoshihiko; et al.
IAEA-CN-60/A2-17, 0, p.355 - 364, 1995/00
no abstracts in English
Nagashima, Keisuke; Koide, Yoshihiko; Shirai, Hiroshi
Nuclear Fusion, 34(3), p.449 - 454, 1994/00
Times Cited Count：67 Percentile：94.74(Physics, Fluids & Plasmas)no abstracts in English
Shirai, Hiroshi; Hirayama, Toshio; Shimizu, Katsuhiro; Tani, Keiji; Azumi, Masafumi; Hirai, Kenichiro*; Konno, Satoshi*; Takase, Keizo*
JAERI-M 93-026, 97 Pages, 1993/02
no abstracts in English
Nagashima, Keisuke; Koide, Yoshihiko; Shirai, Hiroshi; Azumi, Masafumi
ISPP-14; Local transport studies in fusion plasmas, 0, p.75 - 80, 1993/00
no abstracts in English
Shimizu, Katsuhiro; Hirayama, Toshio; Shirai, Hiroshi; Tani, Keiji; *; Azumi, Masafumi
JAERI-M 89-146, 53 Pages, 1989/10
no abstracts in English
Koide, Yoshihiko; Hirayama, Toshio; Sugie, Tatsuo; Sakasai, Akira; Kubo, Hirotaka; Akaoka, Nobuo*; Nishitani, Takeo; Nagashima, Keisuke; Shirai, Hiroshi; Takeuchi, Hiroshi; et al.
Nuclear Fusion, 28(10), p.1835 - 1844, 1988/10
Times Cited Count：5 Percentile：26.43(Physics, Fluids & Plasmas)no abstracts in English
Hirayama, Toshio; Shimizu, Katsuhiro; Tani, Keiji; Shirai, Hiroshi; Kikuchi, Mitsuru
JAERI-M 88-043, 35 Pages, 1988/03
no abstracts in English
Yoshida, Hidetoshi; Shimizu, Katsuhiro; Shirai, Hiroshi; Tobita, Kenji; Kusama, Yoshinori; Kubo, Hirotaka; Koide, Yoshihiko; Sakasai, Akira; Fukuda, Takeshi; Nagashima, Keisuke; et al.
15th European Conf. on Controlled Fusion and Plasma Heating, Vol. 12, Pt. 1, p.163 - 166, 1988/00
no abstracts in English
