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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：66 Percentile：95.03(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.
Matsuya, Yusuke; Sato, Tatsuhiko; Nakamura, Rui*; Naijo, Shingo*; Date, Hiroyuki*
Physics in Medicine & Biology, 65(9), p.095006_1 - 095006_12, 2020/05
Times Cited Count：8 Percentile：39.95(Engineering, Biomedical)Radio-resistance induced under low oxygen pressure plays an important role in malignant progression in fractionated radiotherapy. For the general approach to predict cell killing under hypoxia, cell-killing models (e.g., the Linear-Quadratic model) have to be fitted to 
experimental survival data for both normoxia and hypoxia to obtain the oxygen enhancement ratio (OER). However, model parameters for every oxygen condition needs to be considered by model-fitting approaches. This is inefficient for fractionated irradiation planning. Here, we present an efficient model for fractionated radiotherapy the integrated microdosimetric-kinetic model including cell-cycle distribution and the OER at DNA double-strand break endpoint. The cell survival curves described by this model can reproduce the experimental survival data for both acute and chronic low oxygen concentrations. The OER
used for calculating cell survival agrees well with experimental DSB ratio of normoxia to hypoxia. This work provides biological effective dose (BED) under various oxygen conditions including its uncertainty, which can contribute to creating fractionated regimens for multi-fractionated radiotherapy. If the oxygen concentration in a tumor can be quantified by medical imaging, the present model will make it possible to estimate the cell-killing and BED under hypoxia in more realistic intravital situations.
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：335 Percentile：99.61(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.
Matsuhira, Nobuto*; Komatsu, Ren*; Nakashima, Shinsuke*; Yamashita, Atsushi*; Fukui, Rui*; Takahashi, Hiroyuki*; Shimazoe, Kenji*; Woo, H.*; Tamura, Yusuke*; Takashi, Takayuki*; et al.
no journal, ,
This research aims to develop human resources in the field of remote technology for the decommissioning of the Fukushima Daiichi Nuclear Power Plant. We conduct research on a monitoring platform for fuel debris removal. Here, the developments on prototype experiments were described. We expect to develop research personnel through participation in projects, lectures, and facility tours.
Kawabata, Kuniaki; Matsumoto, Taku; Hanari, Toshihide; Yashiro, Hiroshi*; Goto, Masataka*; Fukui, Rui*; Nakamura, Keita*
no journal, ,
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.
Matsuhira, Nobuto*; Komatsu, Ren*; Nakashima, Shinsuke*; Yamashita, Atsushi*; Fukui, Rui*; Takahashi, Hiroyuki*; Shimazoe, Kenji*; Woo, H.*; Tamura, Yusuke*; Takashi, Takayuki*; et al.
no journal, ,
Matsuhira, Nobuto*; Komatsu, Ren*; Nakashima, Shinsuke*; Yamashita, Atsushi*; Fukui, Rui*; Takahashi, Hiroyuki*; Shimazoe, Kenji*; Woo, H.*; Tamura, Yusuke*; Takashi, Takayuki*; et al.
no journal, ,
Nagasaki, Takao*; Aoki, Takayuki*; Sugihara, Kenta; Nishimura, Masato*; Nakashima, Akira*; Nakamura, Kazuhiro*; Marui, Kentaro*
no journal, ,
Boiling is a gas-liquid two-phase phenomenon of practical importance used in nuclear power generation and equipment cooling. Still, its numerical simulation has not yet been fully developed due to its complex nature involving phase changes. In this study, numerical simulations of pool nucleate boiling, the most basic form of boiling, are performed for a realistic case with many foaming points. The PLIC-VOF method, a sharp interface method, is used because high lattice resolution is required to reproduce the fine boiling structure near the superheated wall, especially for high heat flux boiling. For the solution of the pressure field, a weakly compressible fluid model was used in this study because the Poisson equation solver for the pressure in incompressible flows must be faster and larger in scale. In addition, micro-liquid film evaporation at the bottom of vapor bubbles growing on the wall surface is modeled and incorporated into the calculations. Nucleate boiling was simulated using the above calculation method, and the bubble behavior and wall heat flux were compared with existing experimental results to examine the validity of this simulation.
