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Search Results: 1 - 10 of 1256 matches for " Koichi Hirabayashi "
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Improvement of Pitting Corrosion Resistance of Type 316L Stainless Steel by Potentiostatic Removal of Surface MnS Inclusions
Nobuyoshi Hara,Koichi Hirabayashi,Yu Sugawara,Izumi Muto
International Journal of Corrosion , 2012, DOI: 10.1155/2012/482730
Abstract: The beneficial effect of the removal of MnS inclusions on the pitting of stainless steels has been demonstrated in two ways. (1) High-purity Type 316L stainless steel with no inclusions was used as a specimen in the measurement of anodic polarization curves in 0.5?M NaCl and (2) commercial Type 316L stainless steel with MnS and slag-related inclusions was first polarized at different potentials for 30 min in 1?M Na2SO4 of pH 3 and then anodic polarization measurements were taken in 0.5?M NaCl. Pitting did not occur in the passive or transpassive region of the high-purity steel. The polarization treatment dissolved MnS and some oxide inclusions (CaO and SiO2) on the surface of the commercial steel. An increase in pitting potential of the commercial steel was noted after treatment at potentials above 0.2?V. At the same time, the number of current spikes due to metastable pits decreased significantly. These results are more likely due to the beneficial effect of removing MnS inclusions from the steel surface rather than the modification effect of the chemical composition of passive films on the surface. 1. Introduction Manganese sulfide (MnS) inclusions are known to act as the initiation sites of pitting corrosion on stainless steels [1–9], while the overall dissolution of the inclusions is not necessary for the formation of pit initiation sites [10–17]. It is therefore expected that the removal of surface MnS inclusions improves the pitting corrosion resistance of stainless steels. The aim of treating the surface of stainless steels with processes like nitric acid passivation (ASTM A380 and ASTM A967) is to form a stable Cr-enriched passive oxide film [18], which plays an important role in providing high corrosion resistance to stainless steels. Such surface treatment has an additional effect of dissolving and removing the MnS inclusions from the surface of stainless steels [19]. Therefore, the improvement of pitting corrosion resistance by passivation treatments can be attributed not only to the modification of the chemical composition of the passive films but also to the removal of MnS from the surface of stainless steels. However, these two effects cannot be distinguished from each other in practice. For the further development of passivation treatments of stainless steels which meet environmental regulations and human safety standards, it is important to understand the intrinsic mechanism of each effect provided by passivation treatments. The purpose of the present study is to examine solely the effect of removing MnS on the pitting corrosion
Structural failure of two-density-layer cohesionless biaxial ellipsoids
Masatoshi Hirabayashi
Physics , 2014, DOI: 10.1016/j.icarus.2014.02.024
Abstract: This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound condition of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.
Failure modes and conditions of a cohesive, spherical body due to YORP spin-up
Masatoshi Hirabayashi
Physics , 2015, DOI: 10.1093/mnras/stv2017
Abstract: This paper presents transition of the failure mode of a cohesive, spherical body due to YORP spin-up. On the assumption that the distribution of materials in the body is homogeneous, failed regions first appearing in the body at different spin rates are predicted by comparing the yield condition of an elastic stress in the body. It is found that as the spin rate increases, the locations of the failed regions move from the equatorial surface to the central region. To avoid such failure modes, the body should have higher cohesive strength. The results by this model are consistent with those by a plastic finite element model. Then, this model and a two-layered-cohesive model first proposed by Hirabayashi et al. are used to classify possible evolution and disruption of a spherical body. There are three possible pathways to disruption. First, because of a strong structure, failure of the central region is dominant and eventually leads to a breakup into multiple components. Second, a weak surface and a weak interior make the body oblate. Third, a strong internal core prevents the body from failing and only allows surface shedding. This implies that observed failure modes may highly depend on the internal structure of an asteroid, which could provide crucial information for giving constraints on the physical properties.
Human Physical Activity Measurement Method Based on Electrostatic Induction  [PDF]
Koichi Kurita
Journal of Sensor Technology (JST) , 2014, DOI: 10.4236/jst.2014.43013
In this study, an effective noncontact and nonattached technique that is based on electrostatic induction current generated during walking motion is proposed for the detection and assessment of human physical activity. In addition, a theoretical model is proposed for the electrostatic induction current generated owing to variation in the electric potential of the human body. The proposed electrostatic induction current model is compared with the theoretical model, and the proposed model is shown to effectively explain the behavior of the electrostatic induction current waveform. The normal walking motions of daily living are recorded with a portable sensor located in a regular house. The obtained results show that detailed information of physical activity such as a gait cycle can be estimated using our proposed technique. Additionally, the walking signal was measured when the subject walked with the ankle and knee fastened to a splint with bandages to simulate a limp. Therefore, the proposed technique, which is based on the detection of signal generated during walking, can be successfully employed to assess human physical activity.
Attractor-Based Simultaneous Design of the Minimum Set of Control Nodes and Controllers in Boolean Networks  [PDF]
Koichi Kobayashi
Applied Mathematics (AM) , 2016, DOI: 10.4236/am.2016.714131
Abstract: Design of control strategies for gene regulatory networks is a challenging and important topic in systems biology. In this paper, the problem of finding both a minimum set of control nodes (control inputs) and a controller is studied. A control node corresponds to a gene that expression can be controlled. Here, a Boolean network is used as a model of gene regulatory networks, and control specifications on attractors, which represent cell types or states of cells, are imposed. It is important to design a gene regulatory network that has desired attractors and has no undesired attractors. Using a matrix-based representation of BNs, this problem can be rewritten as an integer linear programming problem. Finally, the proposed method is demonstrated by a numerical example on a WNT5A network, which is related to melanoma.
Possible Effect of Pressure Solution on the Movement of a Canister in the Buffer of Geological Disposal System  [PDF]
Koichi Shin
International Journal of Geosciences (IJG) , 2017, DOI: 10.4236/ijg.2017.82006
Abstract: One of the major concepts of the geological disposal of high level radioactive waste is to enclose a metallic container with bentonite buffer which is considered to be impermeable and chemically stable. Since the average density of the container is around 6 to 7 and very heavy compared to bentonite, the scenario of container sinking has been evaluated because excess sinking makes short the pathway of nuclide migration in the bentonite and is detrimental to the safety of the disposal system. Previous considerations on container sinking have been made from the viewpoint of mechanical deformation of the bentonite. In this paper, a chemical deformation process is presented as another mechanism of container sinking, which has not been previously considered for the container sinking in the field of radioactive waste disposal. The chemical deformation mentioned in this paper is the deformation through the process of pressure solution of minerals constituting the buffer, transportation by diffusion and precipitation. That such chemical deformation is a ubiquitous phenomenon occurring in various scales in the crust of the earth will be shown through the review of previous works. Then, some future research topics will be suggested which would be required in order to evaluate the container sinking in the safety case for radioactive waste disposal.
Regeneration Traits of Four Dominant Species in a Cool-Temperate Conifer-Hardwood Mixed Forest, Northern Japan  [PDF]
Koichi Takahashi
American Journal of Plant Sciences (AJPS) , 2017, DOI: 10.4236/ajps.2017.813223
Abstract: Regeneration traits of four dominant species were studied during a decade in a cool-temperate conifer-hardwood mixed forest, northern Japan. Dominant species were three canopy species (Tilia japonica, Acer mono and Abies sachalinensis) and a subcanopy species Prunus ssiori. Regeneration traits differed among the four dominant species. The regeneration of a conifer Abies sachalinensis largely depends on major disturbances because its size structure was a bell-shaped pattern. The growth rate of the sub-canopy species Prunus ssiori increased faster with tree size than the other three species, and therefore, this species can reach reproductive stage faster. Although the number of recruits of Tilia japonica was less than the other three dominant species, about one-fourth of Tilia japonica regenerated by the sprouts. Thus, vegetative reproduction is important for the regeneration of Tilia japonica. On the contrary, many recruits were observed in Acer mono, and its recruits and saplings concentrated in canopy gaps, suggesting that the regeneration of Acer mono restricted to canopy gaps. Thus, clear differences in the regeneration traits were recognized in the four dominant species. This study suggests that the species-specific regeneration traits contribute to the species coexistence of the four dominant species through different regeneration niches.
Two Types of Laminoplasty for Cervical Spondylotic Myelopathy at Multiple Levels
Shigeru Hirabayashi,Takashi Matsushita
ISRN Orthopedics , 2011, DOI: 10.5402/2011/637185
Coulomb-assisted $\bmΣ^-$-nucleus bound states in the ($K^-$, $π^+$) reaction
Toru Harada,Yoshiharu Hirabayashi
Physics , 2009, DOI: 10.1016/j.nuclphysa.2009.08.005
Abstract: We study a production of Coulomb-assisted $\Sigma^-$-nucleus bound states by nuclear ($K^-$, $\pi^+$) reactions within a distorted-wave impulse approximation, so as to examine several types of the $\Sigma$-nucleus potentials that are consistent with the available $\Sigma^-$ atomic X-ray data and nuclear ($\pi^-$, $K^+$) data. We theoretically demonstrate the inclusive ($K^-$, $\pi^+$) spectra of the $\Sigma^-$ unstable bound states on $^{28}$Si, $^{58}$Ni, and $^{208}$Pb targets at incident $K^-$ lab momenta $p_{K}= 400\text{--}800$ MeV/c. The results show that the near-recoilless ($K^-$, $\pi^+$) reaction on the $^{58}$Ni target gives a clear candidate to confirm properties of the $\Sigma$-nucleus potentials having a repulsion inside the nuclear surface and an attraction outside the nucleus with a sizable absorption, whereas details of the repulsion of the potential at the nuclear center cannot be determined by the inclusive spectra. This is a promising attempt to extract properties of the $\Sigma$-nucleus potential in the nucleus at forthcoming J-PARC experiments, as a full complement to the analyses of the $\Sigma^-$ atomic and ($\pi^-$, $K^+$) data.
Magnetic Reconnection under Anisotropic MHD Approximation
K. Hirabayashi,M. Hoshino
Physics , 2013, DOI: 10.1063/1.4831754
Abstract: We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. Our results showed that once magnetic reconnection takes place, a firehose-sense pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10-30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system, and is consistent with the satellite observation in the Earth's magnetosphere.
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