Faculty Profiles - Obayashi Ippei

Papers - Obayashi Ippei

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Disappearance of chaotic attractor of passive dynamic walking by stretch-bending deformation in basin of attraction Reviewed

Kota Okamoto, Shinya Aoi, Ippei Obayashi, Hiroshi Kokubu, Kei Senda, Kazuo Tsuchiya

2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) 2020.10

Inferring fracture forming processes by characterizing fracture network patterns with persistent homology Reviewed

A. Suzuki, M. Miyazawa, A. Okamoto, H. Shimizu, I. Obayashi, Y. Hiraoka, T. Tsuji, P. K. Kang, T. Ito

Computers and Geosciences 143 104550 - 104550 2020.10

Publishing type：Research paper (scientific journal) Publisher：Elsevier BV

© 2020 The Author(s) Persistent homology is a mathematical method to quantify topological features of shapes, such as connectivity. This study applied persistent homology to analyze fracture network patterns in rocks. We show that persistent homology can detect paths connecting from one boundary to the other boundary constituting fractures, which is useful for understanding relationships between fracture patterns and flow phenomena. In addition, complex fracture network patterns so-called mesh textures in serpentine were analyzed by persistent homology. In previous studies, fracture network patterns for different flow conditions were generated by a hydraulic–chemical–mechanical simulation and classified based on additional data and on expert's experience and knowledge. In this study, image analysis based on persistent homology alone was able to characterize fracture patterns. Similarities and differences of fracture network patterns between natural serpentinite and simulation were quantified and discussed. The data-driven approach combining with the persistent homology analysis helps to infer fracture forming processes in rocks. The results of persistent homology analysis provide critical topological information that cannot be obtained by geometric analysis of image data only.

DOI： 10.1016/j.cageo.2020.104550

Scopus

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Fractal mechanism of basin of attraction in passive dynamic walking Reviewed

Kota Okamoto, Shinya Aoi, Ippei Obayashi, Hiroshi Kokubu, Kei Senda, Kazuo Tsuchiya

Bioinspiration & Biomimetics 15 ( 5 ) 055002 - 055002 2020.7

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

Abstract

Passive dynamic walking is a model that walks down a shallow slope without any control or input. This model has been widely used to investigate how humans walk with low energy consumption and provides design principles for energy-efficient biped robots. However, the basin of attraction is very small and thin and has a fractal-like complicated shape, which makes producing stable walking difficult. In our previous study, we used the simplest walking model and investigated the fractal-like basin of attraction based on dynamical systems theory by focusing on the hybrid dynamics of the model composed of the continuous dynamics with saddle hyperbolicity and the discontinuous dynamics caused by the impact upon foot contact. We clarified that the fractal-like basin of attraction is generated through iterative stretching and bending deformations of the domain of the Poincaré map by sequential inverse images. However, whether the fractal-like basin of attraction is actually fractal, i.e., whether infinitely many self-similar patterns are embedded in the basin of attraction, is dependent on the slope angle, and the mechanism remains unclear. In the present study, we improved our previous analysis in order to clarify this mechanism. In particular, we newly focused on the range of the Poincaré map and specified the regions that are stretched and bent by the sequential inverse images of the Poincaré map. Through the analysis of the specified regions, we clarified the conditions and mechanism required for the basin of attraction to be fractal.

DOI： 10.1088/1748-3190/ab9283

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Other Link： https://iopscience.iop.org/article/10.1088/1748-3190/ab9283/pdf

Very sharp diffraction peak in non-glass forming liquid with the formation of distorted tetraclusters Reviewed

C. Koyama, S. Tahara, S. Kohara, Y. Onodera, D. R. Småbråten, S. M. Selbach, J. Akola, T. Ishikawa, A. Masuno, A. Mizuno, J. T. Okada, Y. Watanabe, Y. Nakata, K. Ohara, H. Tamaru, H. Oda, I. Obayashi, Y. Hiraoka, O. Sakata

NPG Asia Materials 12 ( 1 ) 43-1 - 43-11 2020.6

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Understanding the liquid structure provides information that is crucial to uncovering the nature of the glass-liquid transition. We apply an aerodynamic levitation technique and high-energy X-rays to liquid (l)-Er(2)O(3)to discover its structure. The sample densities are measured by electrostatic levitation at the International Space Station. Liquid Er(2)O(3)displays a very sharp diffraction peak (principal peak). Applying a combined reverse Monte Carlo - molecular dynamics approach, the simulations produce an Er-O coordination number of 6.1, which is comparable to that of another nonglass-forming liquid,l-ZrO2. The atomic structure ofl-Er(2)O(3)comprises distorted OEr4 tetraclusters in nearly linear arrangements, as manifested by a prominent peak observed at similar to 180 degrees in the Er-O-Er bond angle distribution. This structural feature gives rise to long periodicity corresponding to the sharp principal peak in the X-ray diffraction data. A persistent homology analysis suggests thatl-Er(2)O(3)is homologically similar to the crystalline phase. Moreover, electronic structure calculations show thatl-Er(2)O(3)has a modest band gap of 0.6 eV that is significantly reduced from the crystalline phase due to the tetracluster distortions. The estimated viscosity is very low above the melting point forl-ZrO2, and the material can be described as an extremely fragile liquid.

DOI： 10.1038/s41427-020-0220-0

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Protein-Folding Analysis Using Features Obtained by Persistent Homology Reviewed

Takashi Ichinomiya, Ippei Obayashi, Yasuaki Hiraoka

Biophysical Journal 118 ( 12 ) 2926 - 2937 2020.6

Origin of the mixed alkali effect in silicate glass Reviewed

Yohei Onodera, Yasuyuki Takimoto, Hiroyuki Hijiya, Taketoshi Taniguchi, Shingo Urata, Seiji Inaba, Sanae Fujita, Ippei Obayashi, Yasuaki Hiraoka, Shinji Kohara

NPG Asia Materials 11 ( 1 ) 75 - 11 2019.12

Understanding diffraction patterns of glassy, liquid and amorphous materials via persistent homology analyses Reviewed

Y. Onodera, S. Kohara, S. Tahara, A. Masuno, H. Inoue, M. Shiga, A. Hirata, K. Tsuchiya, Y. Hiraoka, I. Obayashi, K. Ohara, A. Mizuno, O. Sakata

Journal of the Ceramic Society of Japan 127 ( 12 ) 853 - 863 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

The structure of glassy, liquid, and amorphous materials is still not well understood, due to the insufficient structural information from diffraction data. In this article, attempts are made to understand the origin of diffraction peaks, particularly of the first sharp diffraction peak (FSDP, Q(1)), the principal peak (PP, Q(2)), and the third peak (Q(3)), observed in the measured diffraction patterns of disordered materials whose structure contains tetrahedral motifs. It is confirmed that the FSDP (Q(1)) is not a signature of the formation of a network, because an FSDP is observed in tetrahedral molecular liquids. It is found that the PP (Q(2)) reflects orientational correlations of tetrahedra. Q(3), that can be observed in all disordered materials, even in common liquid metals, stems from simple pair correlations. Moreover, information on the topology of disordered materials was revealed by utilizing persistent homology analyses. The persistence diagram of silica (SiO2) glass suggests that the shape of rings in the glass is similar not only to those in the crystalline phase with comparable density (alpha-cristobalite), but also to rings present in crystalline phases with higher density (alpha-quartz and coesite); this is thought to be the signature of disorder. Furthermore, we have succeeded in revealing the differences, in terms of persistent homology, between tetrahedral networks and tetrahedral molecular liquids, and the difference/similarity between liquid and amorphous (glassy) states. Our series of analyses demonstrated that a combination of diffraction data and persistent homology analyses is a useful tool for allowing us to uncover structural features hidden in halo pattern of disordered materials. (C) 2019 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.19143

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Persistent Homology and Structural Analysis in Materials Science Invited

Yasuaki Hiraoka, Ippei Obayashi, Kazuto Akagi

Artificial Intelligence 34 ( 3 ) 330 - 338 2019.5

Visualization of Topological Defect in Labyrinth Magnetic Domain by Using Persistent Homology Reviewed

T. YAMADA, Y. SUZUKI, C. MITSUMATA, K. ONO, T. UENO, I. OBAYASHI, Y. HIRAOKA, M. KOTSUGI

Vacuum and Surface Science 62 ( 3 ) 153 - 160 2019.3

Language：Japanese Publisher：Surface Science Society Japan

<p>We executed the topological data analysis of labyrinth magnetic domain structure to visualize pinning site during the magnetization reversal process. We utilized persistent homology to extract the topological feature of the magnetic domain structure, and principal component analysis was used to construct the correlation between persistence diagram and magnetic hysteresis loop. As a result, we could automatically visualize the pinning site as topological defect on the original magnetic domain structure.</p>

DOI： 10.1380/vss.62.153

CiNii Article

CiNii Books

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Visualization of Topological Defect in Labyrinth Magnetic Domain by Using Persistent Homology Invited Reviewed

YAMADA T., SUZUKI Y., MITSUMATA C., ONO K., UENO T., OBAYASHI I., HIRAOKA Y., KOTSUGI M.

Vacuum and Surface Science 62 ( 3 ) 153 - 160 2019.3

Language：Japanese Publisher：The Japan Society of Vacuum and Surface Science

DOI： 10.1380/vss.62.153

CiNii Article

CiNii Books

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Persistent Homology and Its Applications to Materials Science Reviewed

Yasuaki Hiraoka, Ippei Obayashi

Materia Japan 58 ( 1 ) 17 - 22 2019.1

Ultrahigh-pressure form of SiO2 glass with dense pyrite-type crystalline homology Reviewed

M. Murakami, S. Kohara, N. Kitamura, J. Akola, H. Inoue, A. Hirata, Y. Hiraoka, Y. Onodera, I. Obayashi, J. Kalikka, N. Hirao, T. Musso, A. S. Foster, Y. Idemoto, O. Sakata, Y. Ohishi

Physical Review B 99 ( 4 ) 2019.1

パーシステントホモロジーの基礎と材料工学への適用例 Invited Reviewed

平岡裕章, 大林一平

日本金属学会会報「まてりあ」 58 ( 1 ) 17 - 22 2019

Hepatic tumor classification using texture and topology analysis of non-contrast-enhanced three-dimensional T1-weighted MR images with a radiomics approach Reviewed International journal

A. Oyama, Y. Hiraoka, I. Obayashi, Y. Saikawa, S. Furui, K. Shiraishi, S. Kumagai, T. Hayashi, J. Kotoku

Scientific Reports 9 ( 1 ) 8764 - 8764 2019

Language：English Publishing type：Research paper (scientific journal)

The purpose of this study is to evaluate the accuracy for classification of hepatic tumors by characterization of T1-weighted magnetic resonance (MR) images using two radiomics approaches with machine learning models: texture analysis and topological data analysis using persistent homology. This study assessed non-contrast-enhanced fat-suppressed three-dimensional (3D) T1-weighted images of 150 hepatic tumors. The lesions included 50 hepatocellular carcinomas (HCCs), 50 metastatic tumors (MTs), and 50 hepatic hemangiomas (HHs) found respectively in 37, 23, and 33 patients. For classification, texture features were calculated, and also persistence images of three types (degree 0, degree 1 and degree 2) were obtained for each lesion from the 3D MR imaging data. We used three classification models. In the classification of HCC and MT (resp. HCC and HH, HH and MT), we obtained accuracy of 92% (resp. 90%, 73%) by texture analysis, and the highest accuracy of 85% (resp. 84%, 74%) when degree 1 (resp. degree 1, degree 2) persistence images were used. Our methods using texture analysis or topological data analysis allow for classification of the three hepatic tumors with considerable accuracy, and thus might be useful when applied for computer-aided diagnosis with MR images.

DOI： 10.1038/s41598-019-45283-z

PubMed

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Volume-Optimal Cycle: Tightest Representative Cycle of a Generator in Persistent Homology Reviewed

Obayashi, I.

SIAM Journal on Applied Algebra and Geometry 2 ( 4 ) 508 - 534 2018.10

Non-Empirical Identification of Trigger Sites in Image Data using Persistent Homology: Crack Formation during Heterogeneous Reduction of Iron-Ore Sinters Reviewed

M. Kimura, I. Obayashi, Y. Takeichi, R. Murao, Y. Hiraoka

Microscopy and Microanalysis 24 ( S2 ) 540 - 541 2018.8

Persistence diagrams with linear machine learning models Reviewed

Obayashi, I., Hiraoka, Y., Kimura, M.

Journal of Applied and Computational Topology 1 ( 3-4 ) 421 - 449 2018.5

Non-empirical identification of trigger sites in heterogeneous processes using persistent homology Reviewed

Masao Kimura, Ippei Obayashi, Yasuo Takeichi, Reiko Murao, Yasuaki Hiraoka

Scientific Reports 8 ( 1 ) 2018.2

Persistent homology analysis of craze formation Reviewed

Takashi Ichinomiya, Ippei Obayashi, Yasuaki Hiraoka

PHYSICAL REVIEW E 95 ( 1 ) 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We apply a persistent homology analysis to investigate the behavior of nanovoids during the crazing process of glassy polymers. We carry out a coarse-grained molecular dynamics simulation of the uniaxial deformation of an amorphous polymer and analyze the results with persistent homology. Persistent homology reveals the void coalescence during craze formation, and the results suggest that the yielding process is regarded as the percolation of nanovoids created by deformation.

DOI： 10.1103/PhysRevE.95.012504

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Chemical state mapping of heterogeneous reduction of iron ore sinter Reviewed

M. Kimura, Y. Takeichi, R. Murao, I. Obayashi, Y. Hiraoka, Y. Liu

X-RAY MICROSCOPY CONFERENCE 2016 (XRM 2016) 849 012015 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Iron ore sinter constitutes the major component of the iron-bearing burden in blast furnaces, and its reduction mechanism is one of the keys to improving the productivity of ironmaking. Iron ore sinter is composed of multiple iron oxide phases and calcium ferrites (CFs), and their heterogeneous reduction was investigated in terms of changes in iron chemical state: Fe-III, Fe-II, and Fe-0 were examined macroscopically by 2D X-ray absorption and microscopically by 3D transmission X-ray microscopy (TXM). It was shown that the reduction starts at iron oxide grains rather than at calcium ferrite (CF) grains, especially those located near micropores. The heterogeneous reduction causes crack formation and deteriorates the mechanical strength of the sinter. These results help us to understand the fundamental aspects of heterogeneous reduction schemes in iron ore sinter.

DOI： 10.1088/1742-6596/849/1/012015

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