Papers by Author: Yukichi Umakoshi

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Authors: Takuya Ishimoto, Takayoshi Nakano, Yukichi Umakoshi, Masaya Yamamoto, Yasuhiko Tabata
Abstract: Bone mechanical function is given as a result of the material and structural parameters of bone tissue. We previously reported that the material parameter of regenerated bone can be evaluated dominantly using two indices of the density and the preferred orientation degree of biological apatite (BAp). In addition, bone morphology remarkably changes during bone regeneration, which may lead to a dynamic change in the mechanical function of whole bone. In this study, therefore, material and structural parameters of regenerated bone are analyzed separately. A 5-mm-long defect was introduced in rabbit ulna and spontaneously regenerated, and then a three-point bending test was conducted at the regenerated portion. The important parameter which dominantly controls the whole bone mechanical function shifts from a structural to material parameter during bone regeneration. Moreover, it was statistically demonstrated that the increase in the material parameter is strongly determined by recovery of the orientation degree of the BAp c-axis.
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Authors: Yuichiro Koizumi, Yoritoshi Minamino, Takayoshi Nakano, Yukichi Umakoshi
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Authors: Yukichi Umakoshi, Hiroyuki Y. Yasuda, Toshiya Sakata
Abstract: Crystallographic relation between NiAl (β ) grains and Ni3Al (γ ' ) precipitate was examined using Ni-38at%Al bicrystals with an oriented grain boundary. Microstructure and texture in B2 type intermetallic compounds such as NiAl and FeAl were controlled by a thermomechanical process focusing on obtaining highly developed <111> texture and improving ductility.
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Authors: Takayoshi Nakano, Takuya Ishimoto, Jee Wook Lee, Yukichi Umakoshi, Masaya Yamamoto, Yasuhiko Tabata, Akio Kobayashi, Hiroyoshi Iwaki, Kunio Takaoka, Mariko Kawai, Toshio Yamamoto
Abstract: A dominant inorganic substance in hard tissue is known to be a biological apatite (BAp)^nano-crystal which basically crystallizes in an anisotropic hcp lattice, and the BAp c-axis is parallel to extended collagen fibrils. We applied the microbeam X-ray diffractometer system with an incident beam spot 100µm or 50µm in diameter to the original, regenerated and pathological hard tissues in order to analyze the preferential alignment of the BAp c-axis as a parameter of bone quality closely relating to the mechanical function. We conclude that the BAp orientational distribution in the hard tissues is a new measure to evaluate stress distribution in vivo, nano-scale microstructure and the related mechanical function, healing process of the regenerated bone and progress of the bone diseases.
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Authors: Yukichi Umakoshi, Koji Hagihara, Takayoshi Nakano
Abstract: Plastic deformation behavior including anomalous strengthening of Ni3X-type compounds with D019, D0a and D024 structure were examined and summarized, focusing on the correlation between deformation characteristics and features of their crystal structures.
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Authors: Akihiro Nino, Takeshi Nagase, Yukichi Umakoshi
Abstract: Formation of a nanocrystalline structure through rapid solidification, thermal crystallization and electron irradiation induced crystallization was investigated in Fe-Nd-B alloys. A nanocrystalline structure was obtained by rapid quenching of the melt in a Fe86Nd9B5 alloy, while an amorphous single phase was formed in a Fe77Nd4.5B18.5 alloy. In the latter alloy, a nanocrystalline structure was obtained by thermal crystallization and electron irradiation induced crystallization of the amorphous phase. The average grain size of the precipitate obtained by irradiation at 298 K was about 8 nm, which is much smaller than that obtained during thermal crystallization. Results indicate that electron irradiation is effective for obtaining a novel nanocrystalline structure in Fe-Nd-B alloys.
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Authors: Hiroyuki Y. Yasuda, T. Kase, S. Minamiguchi, A. Yokoyama, Yukichi Umakoshi, P.M. Bronsveld, Jeff T.M. de Hosson
Abstract: The pseudoelastic behavior of Fe3Al single crystals doped with an extra element (e.g. Ti, V, Cr, Mn, Co, Ni, Si, Ga, Ge) was investigated. In binary Fe-23.0at.%Al crystals with the D03 structure, 1/4[111] superpartial dislocations moved independently dragging the nearest-neighbor anti-phase boundaries (NNAPB) during loading. During unloading, the NNAPB pulled back the superpartials decreasing its energy resulting in a giant pseudoelasticity of which the recoverable strain is about 5 %. Addition of a third element significantly affected the pseudoelastic behavior of Fe3Al single crystals. Mn- or Ga-doped crystal demonstrated a giant pseudoelasticity. In particular, Ga-doping was found to be effective in the enhancement of the pseudoelasticity. On the other hand, the amount of strain recovery decreased upon doping of the other elements. The frictional stress of the superpartials, the back stress of the NNAPB and ordered domain structure in the crystals changed upon doping, which was closely related to the pseudoelastic behavior.
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Authors: J.P. Chu, S.H. Chen, Hiroyuki Y. Yasuda, Yukichi Umakoshi, Kanryu Inoue
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Authors: Jee Wook Lee, Takayoshi Nakano, Satoru Toyosawa, Yasuhiko Tabata, Yukichi Umakoshi
Abstract: Bone microstructure and its functions are maintained by the activity of bone cells such as osteoclast for bone resorption and osteoblast for bone formation. In this study, we examined the role of osteoclast on the formation of the preferential orientation of biological apatite (BAp) as a bone quality parameter using OPG-KO and op/op mouse models in which the expression of osteoclast increases for osteoporosis and decreases for osteopetrosis. The orientation degree of the BAp c-axis was analyzed by a microbeam X-ray diffraction system. We found more decrease in the preferential alignment of the BAp c-axis along the longitudinal direction of bone in the femoral bones of both OPG-KO and op/op mice at 12 weeks compared with normal control mice. We concluded that changes in the amount and activity of osteoclast affect BAp alignment, resulting in the degradation of bone microstructure in osteoporosis and osteopetrosis.
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