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Journal Articles

Development of a supplementary outboard side thruster system for dynamic positioning control of autonomous surface vehicle

Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa; Fujii, Shun*

International Journal of Offshore and Polar Engineering, 31(3), p.316 - 324, 2021/09

 Times Cited Count:0

The development of a side thruster system (vehicle (ASV)) that can maintain the direction of travel on the autonomous surface will be explained. Currently, we are working on a mud radioactivity survey in collaboration with Japan Agency for Marine-Earth Science and Technology, Japan Atomic Energy Agency, and Tokyo University of Marine Science and Technology. Deposited at the mouth of Fukushima Prefecture, Japan, the main purpose is to collect unmanned mud using ASV. The Mad Collection has developed a side thruster system and implemented it in ASV. We have confirmed the operation of the ASV with the joystick by using the thruster system for operating the ASV by one person using the joystick.

Journal Articles

Invention of automatic movement and dynamic positioning control method of unmanned vessel for mud mining

Fujii, Shun*; Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa

Proceedings of 26th International Symposium on Artificial Life and Robotics (AROB 26th 2021), p.280 - 285, 2021/01

In recent years, autonomously navigating unmanned vessels have been actively studied, and many of these vessels are designed to perform unmanned operations such as observation and transportation. On the other hand, this study uses an unmanned ship with a moon pool that collects seabed mud, which is difficult for ordinary ships. Vessels used since the area are highly turbulent due to wind, so it is necessary to maintain a fixed point and orientation when removing mud. The ship is equipped with side thrusters to maintain a fixed point and bow direction. In this study, the control method was devised to maintain fixed point and orientation, and the control method is based on robust sliding mode control. The proposed control method was verified by simulation, and the desired behavior was confirmed.

Journal Articles

Development of side thruster system for ASV

Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa

Proceedings of the 30th (2020) International Ocean and Polar Engineering Conference (ISOPE 2020) (USB Flash Drive), p.1255 - 1260, 2020/10

Journal Articles

Visualizing cation vacancies in Ce:Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$ scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.

Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08

 Times Cited Count:1 Percentile:24.67(Physics, Applied)

To clarify the existence of cation vacancies in Ce-doped Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$ (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:Y$$_{3}$$Al$$_{5}$$O$$_{12}$$, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg$$^{2+}$$ ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.

Journal Articles

Temporal change in radiological environments on land after the Fukushima Daiichi Nuclear Power Plant accident

Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Sato, Tetsuro*; Seki, Akiyuki; Sanada, Yukihisa; Wainwright-Murakami, Haruko*; et al.

Journal of Radiation Protection and Research, 44(4), p.128 - 148, 2019/12

Journal Articles

Isotope-selective microscale imaging of radioactive Cs without isobaric interferences using sputtered neutral mass spectrometry with two-step resonant ionization employing newly-developed Ti:Sapphire lasers

Sakamoto, Tetsuo*; Morita, Masato*; Kanenari, Keita*; Tomita, Hideki*; Sonnenschein, V.*; Saito, Kosuke*; Ohashi, Masaya*; Kato, Kotaro*; Iguchi, Tetsuo*; Kawai, Toshihide*; et al.

Analytical Sciences, 34(11), p.1265 - 1270, 2018/11

 Times Cited Count:7 Percentile:39.71(Chemistry, Analytical)

Journal Articles

Investigation of hydrogen gas generation by radiolysis for cement-solidified products of used adsorbents for water decontamination

Sato, Junya; Kikuchi, Hiroshi*; Kato, Jun; Sakakibara, Tetsuro; Matsushima, Ryotatsu; Sato, Fuminori; Kojima, Junji; Nakazawa, Osamu

QST-M-8; QST Takasaki Annual Report 2016, P. 62, 2018/03

no abstracts in English

JAEA Reports

The Catalog of solidification and volume reduction technologies for the treatment of radioactive waste generated by the decommissioning of Fukushima Daiichi Nuclear Power Station

Kato, Jun; Nakagawa, Akinori; Taniguchi, Takumi; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro

JAEA-Review 2017-015, 173 Pages, 2017/07

JAEA-Review-2017-015.pdf:6.67MB

Various radioactive wastes have been generated at the Fukushima Daiichi Nuclear Power Station (1F). To dispose of the wastes underground, it is necessary to make a suitable waste package by the volume reduction and solidification of the wastes. To plan the future decommissioning of 1F, it is also necessary to estimate feasibility of existing treatment technology for those wastes. Therefore the document survey has been performed about volume reduction and solidification technologies that have domestic or foreign experiences of practical treatment for radioactive wastes to assist selection of suitable treatment of the wastes. This report shows the arranged results. The 1F wastes are classified into two groups, homogeneous particulate and liquid wastes and heterogeneous solid wastes. The needful items for the feasibility study such as a technology name, a fundamental principle, treatment efficiency, and characteristic of solidified waste are summarized in each group.

Journal Articles

The Hydrogen gas generation by electron-beam irradiation from ALPS adsorbents solidified by several inorganic materials

Sato, Junya; Suzuki, Shinji*; Kato, Jun; Sakakibara, Tetsuro; Meguro, Yoshihiro; Nakazawa, Osamu

QST-M-2; QST Takasaki Annual Report 2015, P. 87, 2017/03

no abstracts in English

Journal Articles

The Hydrogen gas generation by gamma-ray irradiation from ALPS adsorbents solidified by several inorganic materials

Sato, Junya; Suzuki, Shinji*; Kato, Jun; Sakakibara, Tetsuro; Meguro, Yoshihiro; Nakazawa, Osamu

QST-M-2; QST Takasaki Annual Report 2015, P. 88, 2017/03

no abstracts in English

Journal Articles

Progress of the general control system for the Materials and Life Science Experimental Facility in J-PARC

Sakai, Kenji; Oi, Motoki; Watanabe, Akihiko; Kai, Tetsuya; Kato, Yuko; Meigo, Shinichiro; Takada, Hiroshi

JAEA-Conf 2015-002, p.593 - 598, 2016/02

For safe and stable beam operation, a MLF general control system (GCS) consists of several subsystems such as an integral control, interlock, server, network, and timing distribution systems. Since the first beam injection in 2008, the GCS has operated stably without any serious troubles in comparison with upgrade of target devices for ramping up beam power and increment of user apparatuses year by year. In recent years, however, it has been improved significantly in view of sustainable long-term operation and maintenance. The monitor and operation system of the GCS has been upgraded by changing its framework software to improve potential flexibility in its maintenance. Its interlock system was also modified in accordance with the re-examination of the risk management system of J-PARC. This paper reports recent progress of the MLF-GCS.

JAEA Reports

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2014

Hama, Katsuhiro; Mikake, Shinichiro; Ishibashi, Masayuki; Sasao, Eiji; Kuwabara, Kazumichi; Ueno, Tetsuro; Onuki, Kenji*; Beppu, Shinji; Onoe, Hironori; Takeuchi, Ryuji; et al.

JAEA-Review 2015-024, 122 Pages, 2015/11

JAEA-Review-2015-024.pdf:80.64MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technical basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase III, as the Phase II was concluded for a moment with the completion of the excavation of horizontal tunnels at GL-500m level in February 2014. This report presents the results of the investigations, construction and collaboration studies in fiscal year 2014.

Journal Articles

Soft X-ray laser observation of femtosecond-laser-driven ablation of tungsten

Nishikino, Masaharu; Hasegawa, Noboru; Ishino, Masahiko; Ochi, Yoshihiro; Kawachi, Tetsuya; Yamagiwa, Mitsuru; Kato, Yoshiaki*

Chinese Optics Letters, 13(7), p.070002_1 - 070002_3, 2015/07

 Times Cited Count:1 Percentile:8.29(Optics)

Journal Articles

Development of prediction technology of two-phase flow dynamics under earthquake acceleration, 16; Experimental and numerical study of pressure fluctuation effects on bubble motion

Kato, Yuki; Yoshida, Hiroyuki; Yokoyama, Ryotaro*; Kanagawa, Tetsuya*; Kaneko, Akiko*; Monji, Hideaki*; Abe, Yutaka*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 8 Pages, 2015/05

Journal Articles

Spatial distributions of radionuclides deposited onto ground soil around the Fukushima Dai-ichi Nuclear Power Plant and their temporal change until December 2012

Mikami, Satoshi; Maeyama, Takeshi*; Hoshide, Yoshifumi*; Sakamoto, Ryuichi*; Sato, Shoji*; Okuda, Naotoshi*; Demongeot, S.*; Gurriaran, R.*; Uwamino, Yoshitomo*; Kato, Hiroaki*; et al.

Journal of Environmental Radioactivity, 139, p.320 - 343, 2015/01

 Times Cited Count:70 Percentile:94.06(Environmental Sciences)

Journal Articles

High order harmonics from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Faenov, A. Y.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; Koga, J. K.; Mori, Michiaki; Kawase, Keigo*; et al.

RAL-TR-2015-025, P. 22, 2015/00

Journal Articles

High order harmonics from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; et al.

New Journal of Physics (Internet), 16(9), p.093003_1 - 093003_30, 2014/09

 Times Cited Count:25 Percentile:81.51(Physics, Multidisciplinary)

Journal Articles

Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

Kato, Aitaro*; Saiga, Atsushi; Takeda, Tetsuya*; Iwasaki, Takaya*; Matsuzawa, Toru*

Earth, Planets and Space (Internet), 66, p.86_1 - 86_8, 2014/08

 Times Cited Count:17 Percentile:54.31(Geosciences, Multidisciplinary)

To understand the mechanism of an intensive non-volcanic seismic swarm in the Kii Peninsula, Japan, we used a dense seismic linear array to measure fine-scale variations of seismic velocities and converted teleseismic waves. A low-velocity anomaly confined to just beneath the seismic swarm area is clearly imaged, which spatially correlates with an uplifted surface area, and a highly conductive and strong attenuative body. These results suggest that fluids such as partial melt or water are present beneath this non-volcanic seismic swarm area. It is notable that the island arc Moho below the seismic swarm area is at depths of ca. 32 km in the northern part of the seismic swarm area, and shallows to ca. 20 km towards the south, due to an upwardly raised structure of serpentinized mantle wedge. In addition, we show that hydrated oceanic crust of the subducting Philippine Sea slab is characterized by low-velocities with a high Poisson's ratio at depths shallower than 40 km. Water released from the subducting oceanic crust could cause serpentinization of the mantle wedge and infiltration into the forearc base of the overlying plate. The interaction between dehydration of the subducting oceanic crust and hydration of the mantle wedge and overlying plate exerts an important role in driving the non-volcanic seismic swarm activity in the Kii Peninsula.

Journal Articles

Preparation of tungsten carbide nanoparticles by ion implantation and electrochemical etching

Kato, Sho; Yamaki, Tetsuya; Yamamoto, Shunya; Hakoda, Teruyuki; Kawaguchi, Kazuhiro; Kobayashi, Tomohiro*; Suzuki, Akihiro*; Terai, Takayuki*

Nuclear Instruments and Methods in Physics Research B, 314, p.149 - 152, 2013/11

 Times Cited Count:0 Percentile:0.01(Instruments & Instrumentation)

We implanted 100 keV W$$^+$$ in unpolished GC substrates at nominal fluences up to $$1.7times10^{17}$$ ions/cm$$^2$$. The implanted samples were electrochemically anodized in a NaOH aqueous solution to etch the surface layer. The analyses were performed by X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). XPS W 4f spectra indicated the formation of carbides as reported previously. The electrochemical etching clearly increased the W concentration on the surface. According to the RBS results, half of the implanted W atoms were retained in the substrate, while the rest should escape to the etching solution. The cross-sectional TEM image revealed a uniform distribution of WC particles with a diameter of less than 10 nm just near the surface region.

Journal Articles

A Study of the regional stress and the stress state in the galleries of the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Tsusaka, Kimikazu; Tokiwa, Tetsuya; Kondo, Keiji; Inagaki, Daisuke; Kato, Harumi*

Proceedings of 6th International Symposium on In-situ Rock Stress (RS 2013) (CD-ROM), p.331 - 338, 2013/08

In a high-level radioactive waste disposal, initial stress state is important for designing support and layout of repository. Based on the background, objectives of this paper is to investigate the state of regional stress in detail and change of initial stress state along construction of the Underground Research Laboratory (URL). Hydraulic fracturing tests and observation of the borehole breakouts through borehole televiewer logging have been conducted in the boreholes around the Horonobe URL and in the galleries of the URL. As a result, the values of the stress measured in the boreholes around the URL increased along depth and the orientations of the maximum horizontal stress were different between a map scale fault. In addition, values of initial stresses measured in the galleries were less than those of boreholes around the URL and orientation of the maximum horizontal stress were different in each depth of the gallery. These results suggest that measurements of the stress in the galleries are important for modification of the layout designed before construction of the URL.

324 (Records 1-20 displayed on this page)