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Journal Articles

Temporal variability of $$^{137}$$Cs concentrations in coastal sediments off Fukushima

Suzuki, Shotaro*; Amano, Yosuke*; Enomoto, Masahiro*; Matsumoto, Akira*; Morioka, Yoshiaki*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Kaeriyama, Hideki*; Miura, Hikaru*; Tsumune, Daisuke*; et al.

Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07

 Times Cited Count:2 Percentile:32.35(Environmental Sciences)

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:30 Percentile:96.87(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

Pulsed neutron imaging based crystallographic structure study of a Japanese sword made by Sukemasa in the Muromachi period

Oikawa, Kenichi; Kiyanagi, Yoshiaki*; Sato, Hirotaka*; Omae, Kazuma*; Pham, A.*; Watanabe, Kenichi*; Matsumoto, Yoshihiro*; Shinohara, Takenao; Kai, Tetsuya; Harjo, S.; et al.

Materials Research Proceedings, Vol.15, p.207 - 213, 2020/02

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:233 Percentile:99.74(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

Probing strongly correlated 4$$f$$-orbital symmetry of the ground state in Yb compounds by linear dichroism in core-level photoemission

Mori, Takeo*; Kitayama, Satoshi*; Kanai, Yuina*; Naimen, Sho*; Fujiwara, Hidenori*; Higashiya, Atsushi*; Tamasaku, Kenji*; Tanaka, Arata*; Terashima, Kensei*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 83(12), p.123702_1 - 123702_5, 2014/12

 Times Cited Count:15 Percentile:68.66(Physics, Multidisciplinary)

We show that the strongly correlated 4$$f$$-orbital symmetry of the ground state is revealed by linear dichroism in core-level photoemission spectra, as we have discovered for YbRh$$_{2}$$Si$$_{2}$$ and YbCu$$_{2}$$Si$$_{2}$$. Theoretical analysis shows us that the linear dichroism reflects the anisotropic charge distributions resulting from a crystalline electric field. We have successfully determined the ground-state 4$$f$$ symmetry for both compounds from the polarization-dependent angle resolved core-level spectra at a temperature well below the first excitation energy. The excited-state symmetry is also probed by temperature dependence of the linear dichroism where the high measurement temperatures are on the order of the crystal-field-splitting energies.

Journal Articles

Hydrogen removal from hydrogenated diamond-like carbon films by exposure to photon and energetic atomic oxygen beams

Yokota, Kumiko*; Tagawa, Masahito*; Matsumoto, Koji*; Furuyama, Yuichi*; Kitamura, Akira*; Kanda, Kazuhiro*; Tode, Mayumi; Yoshigoe, Akitaka; Teraoka, Yuden

Protection of Materials and Structures from the Space Environment; Astrophysics and Space Science Proceedings, Vol.32, p.531 - 539, 2012/08

Journal Articles

Resonant angle-resolved photoelectron spectroscopy of substitutional solid solutions of CeRu$$_2$$Si$$_2$$

Okane, Tetsuo; Kawasaki, Ikuto; Yasui, Akira; Okochi, Takuo*; Takeda, Yukiharu; Fujimori, Shinichi; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Matsumoto, Yuji*; et al.

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA060_1 - SA060_3, 2011/07

 Times Cited Count:1 Percentile:11.37(Physics, Multidisciplinary)

Journal Articles

Estimation of heat transfer coefficient and flow characteristics on heat transfer tube in sodium-water reaction

Matsumoto, Toshinori*; Takata, Takashi*; Yamaguchi, Akira*; Kurihara, Akikazu; Ohshima, Hiroyuki

Journal of Nuclear Science and Technology, 48(3), p.315 - 321, 2011/03

 Times Cited Count:1 Percentile:10.77(Nuclear Science & Technology)

In the steam generator of a sodium-cooled fast reactor, when the tube fails, water leaks into the sodium stream and sodium-water reaction is initiated. In the present study, a numerical analysis has been carried out to determine the heat transfer coefficient from temperature data obtained in a sodium-water reaction experiment. By updating the heat transfer coefficient, an inverse problem of heat transfer has been solved in the analysis based on the result of the SWAT-1R experiment. It is found that the heat transfer coefficient fluctuates largely during the reaction. The heat transfer coefficient is affected by the flow characteristics. Hence, we characterize the flow pattern near the heat transfer tube at typical periods in the phenomenon progression.

Journal Articles

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure study on oxidative etching of diamond-like carbon films by hyperthermal atomic oxygen

Tagawa, Masahito*; Yokota, Kumiko*; Kitamura, Akira*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden; Kanda, Kazuhiro*; Niibe, Masahito*

Applied Surface Science, 256(24), p.7678 - 7683, 2010/10

 Times Cited Count:13 Percentile:50.91(Chemistry, Physical)

Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption fine structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp$$^{2}$$ structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp$$^{3}$$-rich region remained at the topmost DLC surface. The formation of an sp$$^{3}$$-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface.

Journal Articles

C-axis critical current of a PrFeAsO$$_{0.7}$$ single crystal

Kashiwaya, Hiromi*; Shirai, Kazumi*; Matsumoto, Tetsuro*; Shibata, Hajime*; Kambara, Hiroshi*; Ishikado, Motoyuki; Eisaki, Hiroshi*; Iyo, Akira*; Shamoto, Shinichi; Kurosawa, Itaru*; et al.

Applied Physics Letters, 96(20), p.202504_1 - 202504_3, 2010/05

 Times Cited Count:28 Percentile:71.55(Physics, Applied)

The ${it c}$-axis transport properties of a high-pressure synthesized PrFeAsO$$_{0.7}$$ single crystal are studied using s-shaped junctions. Resistivity anisotropy of about 120 detected at 50 K shows the presence of strong anisotropy in the electronic states. The obtained critical current density for the ${it c}$-axis of 2.9 $$times$$ 10$$^{5}$$ A/cm$$^{2}$$ is two orders of magnitude larger than that in Bi$$_{2}$$Sr$$_{1.6}$$La$$_{0.4}$$CuO$$_{6+delta}$$. The appearance of a hysteresis in the current-voltage curve below ${it T}$ $$_{c}$$ is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (${it I}$ $$_{c}$$ ${it R}$ $$_{n}$$) product is explained by an inspecular transport in ${it s}$ $$_{pm}$$ -wave pair potential.

Journal Articles

Recent progress in the energy recovery linac project in Japan

Sakanaka, Shogo*; Akemoto, Mitsuo*; Aoto, Tomohiro*; Arakawa, Dai*; Asaoka, Seiji*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.2338 - 2340, 2010/05

Future synchrotron light source using a 5-GeV energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting R&D efforts for that. We are developing high-brightness DC photocathode guns, two types of cryomodules for both injector and main superconducting (SC) linacs, and 1.3 GHz high CW-power RF sources. We are also constructing the Compact ERL (cERL) for demonstrating the recirculation of low-emittance, high-current beams using above-mentioned critical technologies.

Journal Articles

Catalytic effect of Pt and Ag-loaded $$gamma$$-Al$$_{2}$$O$$_{3}$$ on the oxidation of xylene in air at low temperature under electron-beam irradiation

Hakoda, Teruyuki; Matsumoto, Kanae*; Mizuno, Akira*; Hirota, Koichi

International Journal of Plasma Environmental Science & Technology, 4(1), p.65 - 70, 2010/03

The catalytic effect of Pt/Al$$_{2}$$O$$_{3}$$ and Ag/Al$$_{2}$$O$$_{3}$$ on the oxidation of xylene in air was studied at a constant temperature of 373 K, when they were combined with electron-beam (EB)-induced non-thermal plasmas (NTPs). The presence of a catalyst bed was found to enhance the oxidation of the irradiation products of xylene. However, the degree of catalytic oxidation was different depending on the type of loaded metal and the position of the catalyst bed. Compared with a Al$$_{2}$$O$$_{3}$$ bed, a Pt/Al$$_{2}$$O$$_{3}$$ bed in the NTP space suppressed oxidation, while an Ag/Al$$_{2}$$O$$_{3}$$ bed downstream of the NTP space enhanced it. Under low temperature conditions, Pt/Al$$_{2}$$O$$_{3}$$ was not a suitable catalyst for the oxidation of organics in combination with the NTP process. On the other hand, the Ag/Al$$_{2}$$O$$_{3}$$ catalyst was a preferable catalyst for the NTP-induced oxidation of organics under such low temperature conditions.

Journal Articles

Band structures of CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$ studied by resonant soft X-ray ARPES

Okane, Tetsuo; Okochi, Takuo*; Takeda, Yukiharu; Fujimori, Shinichi; Yasui, Akira; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Matsumoto, Yuji*; Sugi, Motoki*; et al.

Physica Status Solidi (B), 247(3), p.397 - 399, 2010/03

Journal Articles

Numerical study on correlation of heat transfer coefficient with void fraction at heat transfer tube surface in sodium water reaction

Matsumoto, Toshinori*; Takata, Takashi*; Yamaguchi, Akira*; Kurihara, Akikazu; Ohshima, Hiroyuki

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 10 Pages, 2009/09

When a heat transfer tube fails in steam generator (SG) of sodium-cooled fast reactor (SFR), sodium-water reaction (SWR) would take place. It is significant for estimation of the heat transfer from the fluid to the tube wall during SWR region to evaluate the possibility of the secondary tube failure in case of overheating rupture. In the present study, thermal hydraulics simulation of the fluid around the tube is conducted. The heat transfer coefficient is computed, the correlation diagram between the heat transfer coefficient and the void fraction has been obtained. The void fraction around the heat transfer tube in the SWR has been evaluated.

Journal Articles

Si-doping for the protection of hydrogenated diamond-like carbon films in a simulated atomic oxygen environment in low earth orbit

Yokota, Kumiko*; Tagawa, Masahito*; Kitamura, Akira*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden; Fontaine, J.*; Belin, M.*

Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan (Internet), 7(ists26), p.Pc_37 - Pc_42, 2009/06

The effect of hyperthermal atomic oxygen (AO) exposure on a surface property of Si-doped DLC was investigated. Two types of DLC were tested which contain Si atoms approximately 10 at% and 20 at%. Surface analytical results of high-resolution X-ray photoelectron spectroscopy using synchrotron radiation (synchrotron radiation photoemission spectroscopy; SR-PES) as well as Rutherford backscattering spectroscopy (RBS) have been used for characterization of the AO-exposed Si-doped DLC. It was identified by SR-PES that the SiO$$_{2}$$ layer was formed by the hyperthermal AO exposure at the Si-doped DLC surface. RBS data indicates that AO exposure leads to severe thickness loss on the non-dope DLC, in contrast, SiO$$_{2}$$ layer formed by the hyperthermal atomic oxygen reaction at the Si-doped DLC protects the DLC underneath the SiO$$_{2}$$ layer.

Journal Articles

4$$f$$-derived Fermi surfaces of CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$ near the quantum critical point; Resonant soft-X-ray ARPES study

Okane, Tetsuo; Okochi, Takuo*; Takeda, Yukiharu; Fujimori, Shinichi; Yasui, Akira; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Matsumoto, Yuji*; Sugi, Motoki*; et al.

Physical Review Letters, 102(21), p.216401_1 - 216401_4, 2009/05

 Times Cited Count:27 Percentile:77.18(Physics, Multidisciplinary)

Journal Articles

Role of metals loaded on a TiO$$_{2}$$ Surface in the oxidation of xylene in air using an electron beam irradiation/catalytic process

Hakoda, Teruyuki; Matsumoto, Kanae*; Mizuno, Akira*; Hirota, Koichi

Applied Catalysis A; General, 357(2), p.244 - 249, 2009/04

 Times Cited Count:16 Percentile:38.2(Chemistry, Physical)

Catalytic oxidation of xylene in air was performed under electron beam (EB) irradiation using pure TiO$$_{2}$$ as well as TiO$$_{2}$$ loaded with Ag, Pt, Au, and Mn to clarify the role of loaded metal in the enhancement of oxidation of xylene and its irradiation byproducts to CO$$_{2}$$ in EB-induced non-thermal plasma. EB irradiation experiments were performed with the catalyst bed placed in both irradiated and non-irradiated spaces. The highest conversion percentage of decomposed xylene to CO$$_{2}$$ was obtained by irradiation/catalytic oxidation using an Ag/TiO$$_{2}$$ bed placed in a non-irradiated space. The greater enhancement of CO$$_{2}$$ production on an Ag/TiO$$_{2}$$ pellet surface compared to that on other metal-loaded TiO$$_{2}$$ pellet surfaces was due to the synergetic effect of strong adsorption of the byproducts on the Ag loaded on TiO$$_{2}$$ and production of active oxygen from decomposition of O$$_{3}$$ in the presence of Ag.

Journal Articles

Hydrogen desorption from a diamond-like carbon film by hyperthermal atomic oxygen exposure

Yokota, Kumiko*; Tagawa, Masahito*; Kitamura, Akira*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden

Applied Surface Science, 255(13-14), p.6710 - 6714, 2009/04

 Times Cited Count:13 Percentile:50.32(Chemistry, Physical)

The densities of hydrogen and carbon atoms in a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy and elastic recoil detection analysis. The hydrogen density in DLC decreased upon atomic oxygen exposure with collision energy as low as 2 eV, whereas an exposure greater than 3 eV was necessary to remove carbon atoms. A high collision energy also led to hydrogen desorption in the deeper region of DLC. The surface density of hydrogen decreased 6% by atomic oxygen exposure, and was independent of the collision energy. Additionally, the non-bonded hydrogen, which could diffuse in DLC, was desorbed by the energy transfer from the atomic oxygen collisions.

Journal Articles

Interlaboratory comparison of positron annihilation lifetime measurements

Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.

Materials Science Forum, 607, p.248 - 250, 2009/00

So far no standard procedure for the positron annihilation lifetime (PAL) technique has been established. A lack of the standards has led to difficulty in ensuring the equivalency and reliability of data from different laboratories. As a first, we conducted an interlaboratory comparison of PAL measurements for metal, polymer and silica glass with agreed procedures for data recording and analysis. The PAL data recorded at different laboratories were analyzed with a single lifetime component for the metal sample and with three components for the others, respectively. Based on the results of the reported positron and ortho-positronium lifetimes, the possible sources of the uncertainties in the PAL measurements are discussed. To reduce the effect of scattered $$gamma$$ rays, a lead shield was placed between the detectors. The uncertainty was significantly decreased, signifying that placing lead shields between the detectors effectively reduced the false signals due to the scattered $$gamma$$ rays.

Journal Articles

Oxidation process of xylene in air using Ag/TiO$$_{2}$$ under electron beam irradiation

Hakoda, Teruyuki; Matsumoto, Kanae; Mizuno, Akira*; Narita, Tadashi*; Kojima, Takuji; Hirota, Koichi

IEEE Transactions on Industry Applications, 44(6), p.1950 - 1956, 2008/11

 Times Cited Count:3 Percentile:34.24(Engineering, Multidisciplinary)

Oxidation of xylene and its irradiation-induced organic byproducts in air using Ag-loaded TiO$$_{2}$$ (Ag/TiO$$_{2}$$) beds was studied under electron beam (EB) irradiation. The Ag/TiO$$_{2}$$ beds were placed in an irradiation or a non-irradiation space in order to identify the oxidation of xylene/its byproducts by EB irradiation, by catalytic process, and by a combination of the two. Placement of the Ag/TiO$$_{2}$$ bed to the irradiation space resulted in the suppression of xylene decomposition. On the other hand, production of CO$$_{2}$$ was observed in the gas phase of the irradiation space and on the surface of the Ag/TiO$$_{2}$$ pellets placed both in the irradiation and non-irradiation spaces. The concentration of CO$$_{2}$$ became higher when the layer was placed in the non-irradiation space. The production of CO$$_{2}$$ was enhanced by loading of Ag to the TiO$$_{2}$$ pellet surface. The highest concentration of CO$$_{2}$$ was obtained for Ag/TiO$$_{2}$$ with Ag contents greater than 5wt%.

61 (Records 1-20 displayed on this page)