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Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Keikinzoku, 73(11), p.530 - 536, 2023/11
In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.
Komatsu, Yuya*; Shimizu, Ryota*; Wilde, M.*; Kobayashi, Shigeru*; Sasahara, Yuki*; Nishio, Kazunori*; Shigematsu, Kei*; Otomo, Akira*; Fukutani, Katsuyuki; Hitosugi, Taro*
Crystal Growth & Design, 20(9), p.5903 - 5907, 2020/09
Times Cited Count：5 Percentile：46.4(Chemistry, Multidisciplinary)
VAl Heusler alloy thin films; Appearance of antiferromagnetism and exchange bias in a layered structure with FeTsuchiya, Tomoki*; Kobayashi, Ryota*; Kubota, Takahide*; Saito, Kotaro*; Ono, Kanta*; Ohara, Takashi; Nakao, Akiko*; Takanashi, Koki*
Journal of Physics D; Applied Physics, 51(6), p.065001_1 - 065001_7, 2018/02
Times Cited Count：10 Percentile：45.99(Physics, Applied)Suzuki, Ryota*; Kobayashi, Yoshinori*; Kuno, Yoshinori*; Yamada, Taichi; Yamazaki, Keiichi*; Yamazaki, Akiko*
International Journal on Artificial Intelligence Tools, 25(5), p.1640005_1 - 1640005_19, 2016/10
Times Cited Count：1 Percentile：10.6(Computer Science, Artificial Intelligence)To meet the demands of an aging society, research on intelligent/robotic wheelchairs have been receiving a lot of attention. In elderly care facilities, care workers are required to communicate with the elderly in order to maintain both their mental and physical health. While this is regarded as important, having a conversation with someone on a wheelchair while pushing it from behind in a traditional setting would interfere with their smooth and natural conversation. So we are developing a robotic wheelchair system which allows companions and wheelchair users to move in a natural formation. This paper reports on an investigation to learn the patterns of human behavior when the wheelchair users and their companions communicate while walking together. The ethnographic observation reveals a natural formation of positioning for both companions and wheelchair users. Based on this investigation, we propose a multiple robotic wheelchair system which can maintain desirable formations for communication between wheelchairs.
Aoyagi, Yoshiteru*; Kobayashi, Ryotaro*; Kaji, Yoshiyuki; Shizawa, Kazuyuki*
International Journal of Plasticity, 47, p.13 - 28, 2013/08
Times Cited Count：25 Percentile：71.33(Engineering, Mechanical)In this study, we derive reaction-diffusion equations for dislocation patterning of dislocation cell structures and subgrains. In order to express the generation of dislocation pattern responding to deformation progress, information of slip rate and stress and effect of interactions between slip systems on formation of cell structures are introduced into the reaction rate coefficients of reaction-diffusion equations. Moreover, we propose a multiscale crystal plasticity model based on dislocation patterning. Then we carry out pseudo-three-dimensional FE-FD hybrid simulation for severe compression of FCC polycrystal using the present model. Some processes of ultra fine-graining, i.e., generation of dislocation cell structures, subgrains, dense dislocation walls and lamella subdivisions with high angle boundaries are numerically reproduced, and we investigate the effect of dislocation behavior on the processes of ultrafine-graining.
KM1Okazaki, Nobuo; Tamada, Taro; Feese, M. D.*; Kato, Masaru*; Miura, Yutaka*; Komeda, Toshihiro*; Kobayashi, Kazuo*; Kondo, Keiji*; Blaber, M.*; Kuroki, Ryota
Protein Science, 21(4), p.539 - 552, 2012/04
Times Cited Count：3 Percentile：6.67(Biochemistry & Molecular Biology)Aoyagi, Yoshiteru; Kobayashi, Ryotaro*; Shizawa, Kazuyuki*
Nihon Kikai Gakkai Rombunshu, A, 77(775), p.448 - 461, 2011/03
Ultrafine-grained metals whose grain size is less than one micron have attracted interest as high strength materials. However, a mechanism of ultrafine-graining based on evolution of dislocation structures has not been clarified. In this study, we derive reaction-diffusion equations for dislocation patterning of dislocation cell structures and subgrains. In order to express the generation of dislocation pattern responding to deformation progress, information of slip rate and stress and effect of interactions between slip systems on formation of cell structures are introduced into the reaction rate coefficients of reaction-diffusion equations. Moreover, we propose a multiscale crystal plasticity model based on dislocation patterning. Then we carry out two-dimensional FE-FD simulation for severe compression of FCC polycrystal using the present model. Some processes of ultrafine-graining, i.e., generation of dislocation cell structures, subgrains, dense dislocation walls and lamella subdivisions with high angle boundary is numerically reproduced, and we investigate the effect of dislocation behaviors on the processes of ultrafine-graining.
Oka, Toshitaka; Oshima, Akihiro*; Motohashi, Ryota*; Seto, Naoto*; Watanabe, Yuji*; Kobayashi, Ryoji*; Saito, Koki*; Kudo, Hisaaki*; Murakami, Takeshi*; Washio, Masakazu*; et al.
Radiation Physics and Chemistry, 80(2), p.278 - 280, 2011/02
Times Cited Count：7 Percentile：48.91(Chemistry, Physical)The chemical structures of various ion-beam irradiated isotactic-polypropylene samples were studied. Results of micro-Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy suggest not only the linear energy transfer, but also the fluence is effective in local transformation of the isotactic-polypropylene.
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.
Okazaki, Nobuo; Tamada, Taro; Kato, Masaru*; Miura, Yutaka*; Kobayashi, Kazuo*; Kuroki, Ryota
no journal, ,
We successed crystallization of glycosyltransferase (GTSase) from Sulfolobus shibatae DSM5389, and determined crystal structure with data which was collected at SPring-8 BL41XU. The enzyme has 729 amino acids and five domains. Domain A is major domain which has (
/
)8 barrel catalytic domain as in the usual alpha-amylase family enzymes. The catalytic center is located in the center of the (/)8 barrel. In the near (/)8 barrel, electric density of Mg
ion is observed. Some hydrogen bonding network is observed, too.
Oka, Toshitaka; Oshima, Akihiro*; Motohashi, Ryota*; Seto, Naoto*; Watanabe, Yuji*; Kobayashi, Ryoji*; Kudo, Hisaaki*; Murakami, Takeshi*; Washio, Masakazu*; Hama, Yoshimasa*
no journal, ,
Okazaki, Nobuo; Tamada, Taro; Miura, Yutaka*; Feese, M. D.*; Kato, Masaru*; Komeda, Toshihiro*; Takehara, Kyoko*; Kobayashi, Kazuo*; Kondo, Keiji*; Kuroki, Ryota
no journal, ,
The crystal structure of glycosyltrehalose synthase (GTSase) from the hyperthermophilic archaeum Sulfolobus shibatae DSM5389 has been determined to 2.3 A resolution by X-ray crystallography. GTSase converts the glucosidic bond between the last two glucose residues of amylose from an alpha-1,4 bond to an alpha-1,1 bond, making a non-reducing glycosyl trehaloside in the first step of the biosynthesis of trehalose. The structure of GTSase can be divided into five domains. The central domain has the (beta/alpha)8 barrel fold which is conserved in the alpha-amylase family as the catalytic domain. Three invariant catalytic carboxylic amino acids in the alpha-amylase family are also found in GTSase at positions Asp241, Glu269 and Asp460 in the (beta/alpha)8 domain. Our previous study with KM1-GTSase has been shown that the maltooligosaccharides are converted to glycosyltrehalose by an intramolecular transglycosylation mechanism.
Adachi, Motoyasu; Okazaki, Nobuo*; Tamada, Taro; Kato, Masaru*; Kobayashi, Kazuo*; Blaber, M.; Kuroki, Ryota
no journal, ,
Maltooligosyl trehalose synthase (MTSase) and maltooligosyl trehalose trehalohydrolase (MTHase) are key enzymes for effective production of trehalose which is a useful compound as a preservative for foods. To understand the catalytic mechanism of MTSase, the crystal structure of MTSase derived from the hyperthermophilic archaeum Sulfolobus shibatae DSM5389 has been determined to 2.3 
resolution by X-ray crystallography. Three invariant catalytic carboxylic amino acids in the -amylase family are found in MTSase at positions Asp241, Glu269 and Asp460 in the (/)8 domain.
Yamasaki, Ryota; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu
no journal, ,
no abstracts in English
