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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

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:21 Percentile:98.04(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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

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:181 Percentile:99.77(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

An Evaluation method of reflectance spectra to be obtained by Hayabusa2 Near-Infrared Spectrometer (NIRS3) based on laboratory measurements of carbonaceous chondrites

Matsuoka, Moe*; Nakamura, Tomoki*; Osawa, Takahito; Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Nakauchi, Yusuke*; Arai, Takehiko*; Komatsu, Mutsumi*; Hiroi, Takahiro*; et al.

Earth, Planets and Space (Internet), 69(1), p.120_1 - 120_12, 2017/09

AA2017-0327.pdf:1.53MB

 Times Cited Count:5 Percentile:23.35(Geosciences, Multidisciplinary)

We have conducted ground-based performance evaluation tests of the Near-Infrared Spectrometer (NIRS3) onboard Hayabusa2 spacecraft and established a method for evaluating its measured reflectance spectra. Reflectance spectra of nine powdered carbonaceous chondrite samples were measured by both NIRS3 and a FT-IR spectrometer. Since raw data obtained by NIRS3 had considerable spectral distortion caused by systematic offsets in sensitivity of individual pixels, we have established two methods for correcting the NIRS3 data by comparing them with the corresponding FT-IR data. In order to characterize the absorption bands in NIRS3 spectra, the depth of each band component D$$lambda$$ is defined for each wavelength $$lambda$$ ($$mu$$m). Reflectance spectra of asteroid Ryugu, the target asteroid of Hayabusa2, to be recorded by the NIRS3 are expected to reveal the characteristics of the surface materials by using the evaluation technique.

Journal Articles

NIRS3; The Near Infrared Spectrometer on Hayabusa2

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:40 Percentile:70.46(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.

Journal Articles

Development of constitutive models for fast reactor design

Tsukimori, Kazuyuki; Iwata, Koji*; Kawasaki, Nobuchika*; Okajima, Satoshi; Yada, Hiroki; Kasahara, Naoto*

Nuclear Engineering and Design, 269, p.23 - 32, 2014/04

 Times Cited Count:1 Percentile:9.92(Nuclear Science & Technology)

R&D to enable a practical fast breeder reactor plant is proceeding in Japan, which is called "FaCT" (Fast reactor Cycle Technology development). One of the key issues of R&D is to realize a reasonably compact reactor vessel by eliminating the wall protection equipment which is installed inside the vessel in order to reduce thermal loading in the conventional design. Most important concern is the amount of the inelastic strain of the vessel accumulated around the liquid sodium surface which moves upward and downward cyclically with start-up and shut-down. The aim of this study is to develop rational constitutive models that enable prediction of this kind of complex inelastic behaviors precisely and to prepare the design guide based on inelastic analysis. We developed a high accuracy plasticity model and a simplified plasticity model and valuated them by organized experiments.

Journal Articles

Development of constitutive models for fast reactor design

Tsukimori, Kazuyuki; Iwata, Koji*; Kawasaki, Nobuchika*; Kasahara, Naoto*

Transactions of 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT-21) (CD-ROM), 8 Pages, 2011/11

Journal Articles

A Temperature dependent multi-linear cyclic plasticity model

Iwata, Koji

Nihon Kikai Gakkai M&M 2011 Zairyo Rikigaku Kanfarensu Koen Rombunshu (CD-ROM), 3 Pages, 2011/07

no abstracts in English

Journal Articles

Development of constitutive models for fast reactor design; Strategy of the study and results in the first half stage

Tsukimori, Kazuyuki; Iwata, Koji; Kawasaki, Nobuchika; Yada, Hiroki; Kasahara, Naoto

Transactions of 20th International Conference on Structural Mechanics in Reactor Technology (SMiRT-20) (CD-ROM), 10 Pages, 2009/08

R&D to enable a practical fast breeder reactor plant is proceeding in Japan, which is called "FaCT (Fast reactor Cycle Technology development)". One of the key issues of R&D is to realize a reasonably small reactor vessel by eliminating the thermal liner which is installed inside the vessel in order to reduce thermal loading in the conventional design. Most important concern is the amount of the inelastic strain of the vessel accumulated around the liquid sodium surface which moves up and downward cyclically with start-up and shut-down. The aim of this study is to develop rational constitutive models that enable prediction of this kind of complex inelastic behaviors precisely and to prepare the design guide based on inelastic analysis. In this paper, the framework and strategy of the R&D and the results in the first half stage are introduced.

Journal Articles

A Temperature dependent two-surface cyclic plasticity model

Iwata, Koji

Nihon Kikai Gakkai M&M 2009 Zairyo Rikigaku Kanfarensu Koen Rombunshu (CD-ROM), p.138 - 140, 2009/07

A two-surface cyclic plasticity model which enables precise prediction of inelastic behaviors of cyclically loaded metallic materials under non-isothermal conditions is presented. A concept of generic stress-strain relation, which is generated from monotonic and cyclic stable stress-strain curves, is introduced in the model to represent cyclic hardening. Temperature dependent material properties are taken into account in the rate form constitutive equation. The functional capability of the model is verified through its application to basic uniaxial material tests with/without varying temperature.

Journal Articles

Beam cooling experiment at ion storage ring, S-LSR

Shirai, Toshiyuki*; Tanabe, Mikio*; Soda, Hikaru*; Ikegami, Masahiro*; Fujimoto, Shinji*; Tongu, Hiromu*; Noda, Akira*; Noda, Koji*; Shibuya, Shinji*; Fujimoto, Tetsuya*; et al.

Proceedings of 9th Symposium on Accelerator and Related Technology for Application, p.19 - 22, 2007/06

Journal Articles

PHITS; Benchmark of partial charge-changing cross sections for intermediate-mass systems

Mancusi, D.*; Sihver, L.*; Gustafsson, K.*; La Tessa, C.*; Guetersloh, S.*; Zeitlin, C.*; Miller, J.*; Heilbronn, L.*; Niita, Koji*; Sato, Tatsuhiko; et al.

Nuclear Instruments and Methods in Physics Research B, 254(1), p.30 - 38, 2007/01

 Times Cited Count:17 Percentile:75.49(Instruments & Instrumentation)

The PHITS code is a three-dimensional Monte Carlo code that is able to simulate the transport of nuclei and other particles in complicated geometries. As a part of a comprehensive benchmarking program, we have investigated the possibility of using PHITS to calculate partial charge-changing cross sections and we have compared the results with measurements. The results suggest that the current reaction-cross-section models might be inadequate for use in space radiation protection: We therefore claim the need for a thorough benchmarking of the models and for new reaction-cross-section measurements and experimental techniques.

JAEA Reports

FINAS Example Manual (Second Edition)

Iwata, Koji; Tsukimori, Kazuyuki; Chiba, Takahisa*; Sakai, Shinkichi*; Uenom, M.*; Sakai, Tetsuya*; Sakai, Hikaru*

JNC TN9520 2003-006, 569 Pages, 2003/09

JNC-TN9520-2003-006.pdf:9.55MB

FINAS is a general purpose structural analysis computer program developed by Japan Nuclear Cycle Development Institute for the calculation of static, dynamic and thermal responses of elastic and inelastic structures by the finite element method. This document contains typical analysis examples that illustrate applications of FINAS to a number of structural engineering problems. The first part of this document presents fundamental examples in which numerical solutions by FINAS are compared with some analytical reference solutions, and the second part of this document presents more complex examples intended for practical application. All of the input data image and principal results for each problem are included in this document for beginners convenience. All the analyses are performed using the Version 13.0 of FINAS

Journal Articles

Beam-palarization asymmetries for the $$p$$($$overrightarrow{gamma}$$,$$K$$$$^{+}$$)$$Lambda$$ and $$p$$($$overrightarrow{gamma}$$,$$K$$$$^{+}$$)$$Sigma$$$$^{0}$$ reactions for $$E$$$$_{gamma}$$=1.5-2.4 GeV

Zegers, R. G. T.*; Sumihama, Mizuki*; Ahn, D. S.*; Ahn, J. K.*; Akimune, Hidetoshi*; Asano, Yoshihiro; Chang, W. C.*; Dat$'e$, S.*; Ejiri, Hiroyasu*; Fujimura, Hisako*; et al.

Physical Review Letters, 91(9), p.092001_1 - 092001_4, 2003/08

 Times Cited Count:128 Percentile:95.13(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Evidence for a narrow $$S$$ = +1 Baryon resonance in photoproduction from the neutron

Nakano, Takashi*; Ahn, D. S.*; Ahn, J. K.*; Akimune, Hidetoshi*; Asano, Yoshihiro; Chang, W. C.*; Date, S.*; Ejiri, Hiroyasu*; Fujimura, Hisako*; Fujiwara, Mamoru; et al.

Physical Review Letters, 91(1), p.012002_1 - 012002_4, 2003/07

 Times Cited Count:998 Percentile:99.88(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

The CEA-JNC Seminar on Simulation Code Development for Fast Reactor Cycle Technology

; Iwata, Koji

Saikuru Kiko Giho, (20), p.95 - 98, 2003/00

Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.

Journal Articles

None

Iwata, Koji

Saikuru Kiko Giho, (16), p.221 - 225, 2002/09

None

Journal Articles

None

Iwata, Koji

Saikuru Kiko Giho, (15), p.195 - 196, 2002/06

None

Journal Articles

Experimental Study on the Avoidance and Suppression Criteria for the Vortex-Induced Vibration of a Cantilever Cylinder

Sakai, Takaaki; Morishita, Masaki; Iwata, Koji; Kitamura, Seiji

Journal of Pressure Vessel Technology, 124(2), p.187 - 195, 2002/05

 Times Cited Count:1 Percentile:12.79(Engineering, Mechanical)

None

Journal Articles

None

Iwata, Koji

Saikuru Kiko Giho, (14), p.256 - 257, 2002/03

None

Journal Articles

Vortex-Induced Vibration of a Cantilever Circular Cylinder in Super-Critical Reynolds Number Flow and Its Suppression by Structure Damping

Sakai, Takaaki; Iwata, Koji; Morishita, Masaki; Kitamura, Seiji

JSME International Journal, Series B, 44(4), p.712 - 720, 2001/11

None

85 (Records 1-20 displayed on this page)