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Last Updated :2024/11/10

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Master

Affiliation (Master)

  • Faculty of Engineering　Mechanical and Aerospace Engineering　Thermal and Fluid Systems

Affiliation (Master)

  • Faculty of Engineering　Mechanical and Aerospace Engineering　Thermal and Fluid Systems

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Hiroyuki

  • Name (Kana)

    Fujii

  • Name

    201301096907506744

Alternate Names

Achievement

Research Interests

  • Light scattering and propagation   Radiative transfer   Electromagnetic scattering   Modeling and simulation   Near-infrared spectroscopy   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Thermal engineering / Radiative transfer; light scattering

Research Experience

  • 2023/04 - Today Hokkaido University Faculty of Engineering Division of Mechanical and Space Engineering Associate Professor (tenure track)
  • 2024/08 - 2024/12 University of Michigan Electrical Engineering and Computer Science Visiting Scholar
  • 2023/08 - 2023/09 Roskilde University Department of Science and Environment Mathematics and Physics (IMFUFA) Visiting researcher
  • 2019/04 - 2023/03 Hokkaido University Faculty of Engineering Mechanical and space engineering Assistant professor (tenure)
  • 2019/09 - 2019/12 University of Michigan Electrical engineering and computer science Visiting scholar
  • 2014/04 - 2019/03 Hokkaido University Faculty of Engineering, Division of Mechanical and Space Engineering Assistant Professor (tenure track)
  • 2012/04 - 2014/03 Tokyo Metropolitan Institute of Medical Science Integrated Neuroscience Research Project Post Doctral Researcher (JST researcher)

Education

  • 2009/04 - 2012/03  Tohoku University  Mechanical Engineering  Ph.D course
  • 2007/04 - 2009/03  Tohoku University  Mechanical Engineering  Master course
  • 2003/04 - 2007/03  University of Tsukuba  First Cluster of Colleges,College of Natural Sciences

Committee Memberships

  • 2024/05 - Today   The Heat Transfer Society of Japan   Councilor of the 63rd Executives   https://www.htsj.or.jp/en/about/2618.html
  • 2022/04 - Today   Fluids Engineering Division of the Japan Society of Mechanical Engineers   Secretary, Technical Meeting of Hokkaido Branch
  • 2022/04 - Today   Consortium of Industry-Academia Collaboration on Bio-Optical Imaging and Spectroscopy   Committee member   https://cboi.jp/
  • 2021/04 - Today   Japan council for near infrared spectroscopy   Officier   http://jcnirs.org/yakuin.html
  • 2023/06 -2024/07   The fifth International Workshop on Nano-Micro Thermal Radiation, Nanorad 2024   Second Secretary General   https://nanorad2024.org/index.html
  • 2022/04 -2024/03   Thermal Engineering Division of the Japan Society of Mechanical Engineers   Public relations, News letter
  • 2015/04 -2017/03   Fluids Engineering Division of the Japan Society of Mechanical Engineers   Public relations, News letter
  • 2015/01 -2015/10   Japan Society of Mechanical Engineers   Committee member of the annual workshop

Awards

  • 2024/11 Japan Council for Near Infrared Spectroscopy (JCNIRS) Awards for supervised students, 40th NIR Forum Student Travel Award
     "Light scattering properties for a coagulation state in soy milk" 
    受賞者: Koyata Nishikawa;Hiroyuki Fujii;Goro Nishimura;Kazumichi Kobayashi;Masao Watanabe
  • 2024/03 The Japan Society of Mechanical Engineers Awards for supervised students, Miura Award
     
    受賞者: Hyeonwoo Na
  • 2023/11 The Optical Society of Japan Optical Paper Award 2023
     "Model equations of light scattering properties and a characteristic time of light propagation for polydisperse colloidal suspensions at different volume fractions" 
    受賞者: Hiroyuki Fujii
  • 2023/03 Japan Society of Mechanical Engineers Hokkaido Branch Awards for supervised students, Best presentation award
     "Light scattering properties for monitoring of a coagulation process in soymilk" 
    受賞者: Koyata Nishikawa;Hiroyuki Fujii;Goro Nishimura;Kazumichi Kobayashi;Masao Watanabe
  • 2023/03 Hokkaido University Faculty of Engineering The FY2022 Faculty of Engineering Young Faculty Award
     
    受賞者: Hiroyuki Fujii
  • 2022/11 Japan Council for Near Infrared Spectroscopy (JCNIRS) Awards for supervised students, 38th NIR Forum Student Travel Award
     "Numerical study of the near-infrared light scattering properties by molecular dynamics simulations and electromagnetic theory" 
    受賞者: Hyeonwoo Na;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe
  • 2022/06 Japan Association for Chemical Innovation 11th JACI Prize for Encouraging Young Researcher
     "Development of near-infrared spectroscopy to evaluate the dispersion stability in colloidal suspensions" 
    受賞者: Hiroyuki Fujii
  • 2022/03 Konica Minolta Science and Technology Foundation Konica Minolta Imaging Science Encouragement Award FY2021
     "Non-destructive evaluation of the particle size distribution for dense colloidal suspension using scattered light" 
    受賞者: Hiroyuki Fujii
  • 2021/11 Japan Council for Near Infrared Spectroscopy (JCNIRS) Awards for supervised students, 37th NIR Forum Student Travel Award
     "Multiphysics model of photoacoustic waves induced by near-infrared laser" 
    受賞者: Iori Terabayashi;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe
  • 2021/10 The International Council for NIR Spectroscopy (ICNIRS) Awards for supervised students, Best Poster Award of NIR2021
     "Study on near-infrared light scattering in colloidal suspensions using time-resolved measurements" 
    受賞者: Yuki Inoue;Hiroyuki Fujii;Goro Nishimura;Toshiaki Aoki;Kazumichi Kobayashi;Masao Watanabe
  • 2020/11 Japan Council for Near Infrared Spectroscopy NIR Advance Award
     "Modeling of light scattering in biological tissue, agricultural products, and foods" 
    受賞者: Hiroyuki Fujii

Published Papers

  • Hiroyuki Fujii, Hyeonwoo Na, Jungyun Yi, Kazumichi Kobayashi, Masao Watanabe
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 703 (135208) 1 - 9 0927-7757 2024/11 [Refereed][Not invited]
  • Hiroyuki Fujii, Hyeonwoo Na, Koyata Nishikawa, Kazumichi Kobayashi, Masao Watanabe
    Optical Review Springer Science and Business Media LLC 31 (3) 299 - 308 1340-6000 2024/05/22 [Refereed][Invited]
     
    Abstract Near-infrared spectroscopy and imaging using scattered light potentially evaluate the structural properties of the medium, like the average particle size, based on a relation between its structure and light scattering. A qualitative understanding of light scattering is crucial for developing optical imaging techniques. The scattering properties of dense colloidal suspensions have been extensively investigated using the electromagnetic theory (EMT). The colloidal suspensions are widely used in liquid tissue phantoms for optical imaging techniques and are encountered in various fields, such as the food and chemical industries. The interference between electric fields scattered by colloidal particles significantly influences the scattering properties, so-called the interference effects. Despite many efforts since the 1980s, a complete understanding of the interference effects has still not been achieved. The main reason is the complicated dependence of the interference on the optical wavelength, particle size, and so on. This paper briefly reviews numerical and theoretical studies of the interference effect based on the dependent scattering theory, one of the EMTs, and model equations.
  • Kazumichi Kobayashi, Kota Aoki, Hirofumi Tabe, Hiroyuki Fujii, Toshiki Nara, Hideyoshi Takashima, Nobuyuki Oshima, Masao Watanabe
    Physics of Fluids 35 (082021) 1 - 8 1070-6631 2023/08/01 [Refereed]
     
    This paper presents molecular dynamics simulations of the Couette flow of a rarefied gas between the liquid and wall boundaries and, in particular, investigates the boundary conditions for the Boltzmann equation at the liquid interface. The simulation results for various Knudsen numbers show that the slip velocity decreases at the liquid boundary and increases at the smooth wall as the Knudsen number increases, indicating that the velocity profile of the rarefied Couette flow is asymmetric. One reason for this is backscattering, in which molecules are reflected in the opposite direction to the mainstream flow, owing to molecular-scale roughness at the liquid boundary. It has also been suggested that the backscattering effect decreases when the gas density increases. This can be understood using the local Knudsen numbers near the liquid boundary.
  • Hiroyuki Fujii, Koyata Nishikawa, Hyeonwoo Na, Yuki Inoue, Kazumichi Kobayashi, Masao Watanabe
    Infrared Physics & Technology 132 (104753) 1 - 9 1350-4495 2023/08 [Refereed][Not invited]
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    International Communications in Heat and Mass Transfer 142 (106622) 1 - 8 0735-1933 2023/03 [Refereed][Not invited]
  • Hiroyuki Fujii, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
    Photoacoustics Elsevier 27 (3) 100368, 1 - 10 2022/09/01 [Refereed]
  • Ryunosuke Adachi, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
    Physics of Fluids 34 (062116) 1 - 13 1070-6631 2022/06 [Refereed][Not invited]
     
    A water drop impacting a dry solid surface can eject a thin liquid sheet, which is forced to expand on the surface to wet the solid surface. Wetting failure, which produces defects in applications based on the impact of drops, including coating, cooling, cleaning, and printing, may occur with a sufficiently large liquid-sheet velocity. However, the exact onset of wetting failure when a drop impacts the surface has yet to be determined. Therefore, we examine the dependence of rim instability immediately after liquid-sheet ejection on the static contact angle of the solid surface at the instant of water drop impact. This study is the first attempt to solve this problem and is made possible only by using an ultra-high-speed camera. We revealed that wetting failure can occur by investigating the rim instability of the liquid sheet.
  • Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    International Journal of Heat and Mass Transfer 188 122663 - 122663 0017-9310 2022/06 [Refereed]
  • Hiroyuki Fujii, Hyeonwoo Na, Toshiaki Aoki, Yuki Inoue, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
    Extended abstract of SI-Thru2022 (SI-Thru8-02) 1 - 3 2022/04 [Refereed][Not invited]
  • Hirofumi Tabe, Kiryu Hiramatsu, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe, Tsuyoshi Totani
    Applied Thermal Engineering 212 (118472) 1 - 7 1359-4311 2022/04 [Refereed]
     
    In this study, we conducted molecular dynamics simulations of the evaporation of locally heated argon liquid to construct the kinetic boundary condition (KBC) for the evaporation. The KBC denotes the boundary condition of the Boltzmann equation, and the mass, momentum, and heat fluxes through the interface can be determined by solving the Boltzmann equation with the KBC. From the results, we established a method for constructing the KBC for the evaporation of locally heated argon liquid. Furthermore, we found that the velocity distribution of the KBC immediately after liquid heating becomes anisotropic, which means that the normal and tangential temperatures composed of outgoing molecules from the liquid phase to the gas phase take different values when the liquid interface is heated momentarily. From the present study, we can elucidate the mechanism of the occurrence of net evaporation mass flux due to the locally heated liquid film, e.g., the spot heating by infrared radiation.
  • Hiroyuki Fujii, Moegi Ueno, Yuki Inoue, Toshiaki Aoki, Kazumichi Kobayashi, Masao Watanabe
    Optics Express 30 (3) 3538 - 3538 2022/01/31 [Refereed]
  • Hiroyuki Fujii, Iori Terabayashi, Toshiaki Aoki, Yuki Inoue, Hyeonwoo Na, Kazumichi Kobayashi, Masao Watanabe
    Applied Sciences 12 (3) 1190, 1 - 12 2022/01/24 [Refereed]
     
    Understanding light propagation in liquid phantoms, such as colloidal suspensions, involves fundamental research of near-infrared optical imaging and spectroscopy for biological tissues. Our objective is to numerically investigate light propagation in the alumina colloidal suspensions with the mean alumina particle diameter of 55 nm at the volume fraction range 1–20%. We calculated the light scattering properties using the dependent scattering theory (DST) on a length scale comparable to the optical wavelength. We calculated the steady-state radiative transfer and photon diffusion equations (RTE and PDE) using the DST results based on the finite difference method in a length scale of the mean free path. The DST calculations showed that the scattering and reduced scattering coefficients become more prominent at a higher volume fraction. The anisotropy factor is almost zero at all the volume fractions, meaning the scattering is isotropic. The comparative study of the RTE with the PDE showed that the diffusion approximation holds at the internal region with all the volume fractions and the boundary region with the volume fraction higher than 1%. Our findings suggest the usefulness of the PDE as a light propagation model for the alumina suspensions rather than the RTE, which provides accurate but complicated computation.
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    Physics of Fluids 33 (12) 122017 - 122017 1070-6631 2021/12 [Refereed]
  • Yuki Inoue, Hiroyuki Fujii, Goro Nishimura, Toshiaki Aoki, Kazumichi Kobayashi, Masao Watanabe
    Extended abstracts of NIR2021 P13 168 - 169 2021/10 [Refereed][Not invited]
  • Toshiaki Aoki, Hiroyuki Fujii, Yuki Inoue, Kazumichi Kobayashi, Masao Watanabe
    Extended abstracts of NIR2021 O11 60 - 61 2021/10 [Refereed][Not invited]
  • Hiroyuki Fujii, Toshiaki Aoki, Yuki Inoue, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
    Technical digest of 26th Microoptics Conference (MOC2021) 日本応用物理学会 PO-11 164 - 165 2021/09 [Refereed]
  • Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    PLOS ONE 16 (3) e0248660 - e0248660 2021/03/16 [Refereed]
     
    The kinetic boundary condition (KBC) represents the evaporation or condensation of molecules at the vapor–liquid interface for molecular gas dynamics (MGD). When constructing the KBC, it is necessary to classify molecular motions into evaporation, condensation, and reflection in molecular-scale simulation methods. Recently, a method that involves setting the vapor boundary and liquid boundary has been used for classifying molecules. The position of the vapor boundary is related to the position where the KBC is applied in MGD analyses, whereas that of the liquid boundary has not been uniquely determined. Therefore, in this study, we conducted molecular dynamics simulations to discuss the position of the liquid boundary for the construction of KBCs. We obtained some variables that characterize molecular motions such as the positions that the molecules reached and the time they stayed in the vicinity of the interface. Based on the characteristics of the molecules found from these variables, we investigated the valid position of the liquid boundary. We also conducted an investigation on the relationship between the condensation coefficient and the molecular incident velocity from the vapor phase to the liquid phase. The dependence of the condensation coefficient on the incident velocity of molecules was confirmed, and the value of the condensation coefficient becomes small in the low-incident-velocity range. Furthermore, we found that the condensation coefficient in the non-equilibrium state shows almost the same value as that in the equilibrium state, although the corresponding velocity distribution functions of the incident velocity significantly differ from each other.
  • Hiroyuki Fujii, Go Chiba, Yukio Yamada, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
    Journal of Computational Physics 423 (109825) 1 - 14 0021-9991 2020/09 [Refereed][Not invited]
     
    A versatile and accurate treatment for the highly forward-peaked phase function in the three-dimensional (3D) radiative transfer equation (RTE) based on the discrete ordinates method (DOM) is crucial for biomedical optics. Our first objective was to compare the delta-Eddington (dE) and Galerkin quadrature (GQ) methods. The dE method decomposes the phase function into a purely forward-peaked component and the other component, and expands the other component by Legendre polynomials as well as the finite order Legendre expansion (FL) method does. The GQ method conducts the weighting procedure in addition to the Legendre expansion. Although it was reported that both methods can provide the accurate results for calculations of the RTE, the versatility of both methods is still unclear. The second objective was to examine a possibility of a conjunction of the GQ method with the dE method, called as the GQ-dE method, which has the advantages of both methods. We examined numerical errors in the moment conditions of the phase function using the FL, dE, GQ and GQ-dE methods at various types and orders of the quadrature sets, mainly in the region of the errors induced by the angular discretization using the DOM. The errors were reduced by the dE method from those by the FL method, however the error reduction depended on the types and orders of the quadrature sets. Meanwhile, the errors were significantly reduced by the GQ and GQ-dE methods, regardless of the quadrature sets. We also verified the numerical calculations of the time-dependent 3D RTE by the analytical solution of the RTE for homogeneous media in the region of the scattering length scale, where the highly forward-peaked phase function strongly influences the RTE-results. The errors in the RTE-results were similar to those in the moment conditions. Our results suggest the higher versatility and accuracy of the GQ and GQ-dE methods than those of the FL and dE methods. (C) 2020 Elsevier Inc. All rights reserved.
  • Hiroyuki Fujii, Leung Tsang, Jiyue Zhu, Koki Nomura, Kazumichi Kobayashi, Masao Watanabe
    Optics Express 28 (15) 22962 - 22977 2020/07/10 [Refereed][Not invited]
  • Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
    Scientific Reports 10 8143  2020/05/18 [Refereed][Not invited]
  • Koki Nomura, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe, Goro Nishimura
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 (AFI-0006) 12 - 13 2020/02 [Refereed][Not invited]
  • Shigeki Endo, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 (NRT-0008) 60 - 61 2020/02 [Refereed][Not invited]
  • Hiroyuki Fujii, Goro Nishimura, Shigeki Endo, Koki Nomura, Kazumichi Kobayashi, Masao Watanabe
    Proceeding of the 7th Asian NIR symposium (ANS2020) 2020 (AFI-0007) 14 - 15 2020/02 [Refereed][Not invited]
  • Hiroyuki Fujii, Moegi Ueno, Kazumichi Kobayashi, Masao Watanabe
    Applied Sciences 10 (93) 1 - 16 2020/02 [Refereed][Not invited]
  • Taku Ashida, Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada
    Physical Review Fluids 5 (011601) 1 - 9 2020/01 [Refereed][Not invited]
  • Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    International Journal of Thermal Sciences 150 (106203) 1 - 10 1290-0729 2020/01 [Refereed][Not invited]
  • Hiroyuki Fujii, Go Chiba, Yukio Yamada, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
    Proceedings of the 9th International Symposium on Radiative Transfer, RAD-19 (SM05) 261 - 268 2019/09 [Refereed][Not invited]
  • Kosuke Tabayashi, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe
    AIP Conference Proceedings (ICNAAM2018) 2116 (450052) 1 - 4 2019/07 [Refereed][Not invited]
  • Shinpei Okawa, Tetsuya Mimura, Hiroyuki Fujii, Hiroshi Kawaguchi, Yukari Tanikawa, Manabu Machida, Eiji Okada, Yoko Hoshi
    Proceedings of SPIE, Diffuse Optical Spectroscopy and Imaging VII 11074 (1107407) 1 - 4 2019/07 [Refereed][Not invited]
  • Hiroyuki Fujii, Yamada Yukio, Hoshi Yoko, Kobayashi Kazumichi, Watanabe Masao
    AIP Conference Proceedings (ICNAAM2018) 2116 (450037) 1 - 4 2019/07 [Refereed][Not invited]
  • Kyohei Yamamoto, Kazumichi Kobayashi, Masao Watanabe, Hiroyuki Fujii, Misaki Kon, Hiroyuki Takahira
    Physical Review Fluids 4 (063603) 1 - 10 2019/06 [Refereed][Not invited]
  • Kosuke Tabayashi, Hiroyuki Fujii, Shinpei Okawa, Kazumichi Kobayashi, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    CMBE Proceedings (6th International Conference on Computational & Mathematical Biomedical Engineering) (A5) 161 - 164 2227-9385 2019/05 [Refereed][Not invited]
  • Correction to: Influence of liquid–solid intermolecular force on levitation of impacting nanodroplet
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Heat and Mass Transfer 55 (4) 1005 - 1005 2019/04 [Refereed][Not invited]
  • Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Heat and Mass Transfer 55 (4) 993 - 1003 0947-7411 2019/04 [Refereed][Not invited]
  • Molecular Dynamics Study on Influence of Liquid-solid Intermolecular Force on Levitating Mechanism of Impacting Nanodroplet on Heated Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Surface Wettability Effects on Phase Change Phenomena(SWEP) 2019 [Refereed][Not invited]
  • Kazumichi Kobayashi, Takahiro Nagayama, Masao Watanabe, Hiroyuki Fujii, Misaki Kon
    Journal of Fluid Mechanics 856 (10) 1045 - 1063 2018/12 [Refereed][Not invited]
  • Hiroyuki Fujii, Yukio Yamada, Go Chiba, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
    Journal of Computational Physics 374 591 - 604 2018/12 [Refereed][Not invited]
  • Hiroyuki Fujii, Yukio Yamada, Yoko Hoshi, Shinpei Okawa, Kazumichi Kobayashi, Masao Watanabe
    Reaction Kinetics, Mechanisms and Catalysis 123 (2) 439 - 453 1878-5204 2018/04/01 [Refereed][Not invited]
     
    Constructions of numerical schemes for solving the radiative transfer equation (RTE) are crucial to evaluate light propagation inside photocatalytic systems. We develop accurate and efficient schemes of the three-dimensional and time-dependent RTE for numerical phantoms modeling aqueous titanium dioxide suspensions, in which the anisotropy of the forward-directed scattering varies and the strength of absorption is comparable to that of scattering. To improve the accuracy and efficiency of the numerical solutions, the forward-directed phase function is renormalized in the zeroth or first order with a small number of discrete angular directions. Then, we investigate the influences of the forward-directed scattering on the numerical solutions by comparing with the analytical solutions. The investigation shows that with the anisotropy factor less than approximately 0.7 corresponding to the moderate forward-directed scattering, the numerical solutions of the RTE using the both of the zeroth and first order renormalization approaches are accurate due to the reductions of the numerical errors of the phase function. With the anisotropy factor more than approximately 0.7 corresponding to the highly forward-directed scattering, the first order renormalization approach still provides the accurate results, while the zeroth order approach does not due to the large errors of the phase function. These results suggest that the developed scheme using the first order renormalization can provide accurate and efficient calculations of light propagation in photocatalytic systems.
  • Influence of surface roughness of high temperature wall on levitation of impacting droplet based on molecular dynamics simulation
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Surface Wettability Effects on Phase Change Phenomena (SWEP) workshop 2018 [Refereed][Not invited]
  • Numerical investigation of light and pressure propagation in biological tissue for model-based photoacoustic tomography
    Kosuke Tabayashi, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe
    Extended Abstracts of The 9th JSME-KSME Thermal and Fluids Engineering Conference (TFEC9-1526) 1 - 4 2017/10 [Refereed][Not invited]
  • Shotaro Morikawa, Yuki Tatekura, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe, Koichi Sasaki
    Nagare 36 105 - 108 2017/05 [Refereed][Not invited]
  • Hiroyuki Fujii, Yukio Yamada, Kazumichi Kobayashi, Masao Watanabe, Yoko Hoshi
    International Journal for Numerical Methods in Biomedical Engineering 33 (5) 1 - 12 2040-7939 2017/05 [Refereed][Not invited]
     
    Diffuse optical tomography using near-infrared light in a wavelength range from 700 to 1000nm has the potential to enable non-invasive diagnoses of thyroid cancers; some of which are difficult to detect by conventional methods such as ultrasound tomography. Diffuse optical tomography needs to be based on a physically accurate model of light propagation in the neck, because it reconstructs tomographic images of the optical properties in the human neck by inverse analysis. Our objective here was to investigate the effects of three factors on light propagation in the neck using the 2D time-dependent radiative transfer equation: (1) the presence of the trachea, (2) the refractive-index mismatch at the trachea-tissue interface, and (3) the effect of neck organs other than the trachea (spine, spinal cord, and blood vessels). There was a significant influence of reflection and refraction at the trachea-tissue interface on the light intensities in the region between the trachea and the front of the neck surface. Organs other than the trachea showed little effect on the light intensities measured at the front of the neck surface although these organs affected the light intensities locally. These results indicated the necessity of modeling the refractive-index mismatch at the trachea-tissue interface and the possibility of modeling other neck organs simply as a homogeneous medium when the source and detectors were far from large blood vessels.
  • Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
    MICROFLUIDICS AND NANOFLUIDICS 21 (3) 1 - 13 1613-4982 2017/03 [Refereed][Not invited]
     
    Using molecular dynamics simulations, the present study investigated the precise characteristics of the binary mixture of condensable gas (vapor) and noncondensable gas (NC gas) molecules creating kinetic boundary conditions (KBCs) at a gas-liquid interface in equilibrium. We counted the molecules utilizing the improved two-boundary method proposed in previous studies by Kobayashi et al. (Heat Mass Trans 52: 1851-1859, 2016. doi: 10.1007/s00231-015-1700-6). In this study, we employed Ar for the vapor molecules, and Ne for the NC gas molecules. The present method allowed us to count easily the evaporating, condensing, degassing, dissolving, and reflecting molecules in order to investigate the detailed motion of the molecules, and also to evaluate the velocity distribution function of the KBCs at the interface. Our results showed that the evaporation and condensation coefficients for vapor and NC gas molecules decrease with the increase in the molar fraction of the NC gas molecules in the liquid. We also found that the KBCs can be specified as a function of the molar fraction and liquid temperature. Furthermore, we discussed the method to construct the KBCs of vapor and NC gas molecules.
  • Molecular Dynamics Study of Droplet Impact on High-Temperature Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    The 7th East Asia Mechanical and Aerospace Engineering Workshop 2017 [Refereed][Not invited]
  • Molecular Dynamics Simulation of the Role of the Wettability in the Droplet Impact on a High-temperature Wall
    Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
    Extended Abstracts of the 9th JSME-KSME Thermal and Fluids Engineering Conference TFEC9-1492 2017 [Refereed][Not invited]
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Journal of Mathematical Chemistry 54 (10) 2048 - 2061 0259-9791 2016/11 [Refereed][Not invited]
     
    Numerical calculation of photon migration in biological tissue using the radiative transfer equation (RTE) has attracted great interests in biomedical optics and imaging. Because biological tissue is a highly forward-peaked scattering medium, renormalization of the phase function in numerical calculation of the RTE is crucial. This paper proposes a simple approach of renormalizing the phase function by the double exponential formula, which was heuristically modified from the original one. Firstly, the validity of the proposed approach was tested by comparing numerical results for an average cosine of the polar scattering angle calculated by the proposed approach with those by the conventional approach in highly forward-peaked scattering. The results show that calculation of the average cosine converged faster using the proposed approach than using the conventional one as a total number of discrete angular directions increases. Next, the accuracy of the numerical solutions of the RTE using the proposed approach was examined by comparing the numerical solutions with the analytical solutions of the RTE in a homogeneous medium with highly forward-peaked scattering. It was found that the proposed approach reduced the errors of the numerical solutions from those using the conventional one especially at a small value of the total number of the directions. This result suggests that the proposed approach has a possibility to improve the accuracy for the numerical results of the RTE in the highly scattering medium.
  • Kazumichi Kobayashi, Kazuki Konno, Hisao Yaguchi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
    Physics of Fluids 28 (3) 1 - 10 1070-6631 2016/03 [Refereed][Not invited]
     
    In this study, we investigated nanodroplet spreading at the early stage after the impact using molecular dynamics simulations by changing the magnitude of the intermolecular force between the liquid and wall molecules. We showed that the droplet deformation after the impact greatly depends on the intermolecular force. The temporal evolution of the spreading diameters was measured by the cylindrical control volume for several molecular layers in the vicinity of the wall. At the early stage of the nanodroplet impact, the normalized spreading radius of the droplet is proportional to the square root of the normalized time, (t) over cap. This result is understood by the geometrical consideration presented by Rioboo et al. ["Time evolution of liquid drop impact onto solid, dry surfaces," Exp. Fluids 33, 112-124 (2002)]. In addition, we found that as the intermolecular force between the liquid and wall becomes stronger, the normalized spreading diameter of the first molecular layer on the wall remains less dependent on the impact velocity. Furthermore, the time evolution of the droplet spreading changes from root(t) over cap to log (t) over cap with time. (C) 2016 AIP Publishing LLC.
  • Kiyohito Hattori, Hiroyuki Fujii, Goro Nishimura, Kazumichi Kobayashi, Masao Watanabe
    Proceeding of the 5th Asian NIR symposium (ANS2016) 2016 (O-6) 72 - 73 2016 [Refereed][Not invited]
  • Hiroyuki Fujii, Goro Nishimura, Kiyohito Hattori, Kazumichi Kobayashi, Masao Watanabe
    Proceeding of the 5th Asian NIR symposium (ANS2016) 2016 (P-86) 288 - 289 2016 [Refereed][Not invited]
  • Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
    30TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS (RGD 30) 1786 (110002) 1 - 9 0094-243X 2016 [Refereed][Not invited]
     
    The aim of this study is to construct the kinetic boundary condition for Ar-Ne binary mixture in equilibrium using molecular dynamics (MD) simulations. The temperature of the MD simulation system is 85 K; Ar molecules behave as condensable gas (vapor), and Ne molecules behave as non-condensable gas (gas). In this simulation, we utilize the two-boundary method improved by our previous study to investigate behaviors of Ar and Ne molecules at the interface. From the results, we can obtain the molecular mass fluxes at the interface, and evaluate the values of evaporation and condensation coefficients of Ar (vapor) and Ne (gas) molecules.
  • Erina Miyakawa, Hiroyuki Fujii, Kiyohito Hattori, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
    AIP Conference Proceedings (ICCMSE2016) 1790 (050003) 1 - 4 0094-243X 2016 [Refereed][Not invited]
     
    Diffuse optical tomography (DOT), which is still under development, has a potential to enable non-invasive diagnoses of thyroid cancers in the human neck using the near-infrared light. This modality needs a photon migration model because scattered light is used. There are two types of photon migration models: the radiative transport equation (RTE) and diffusion equation (DE). The RTE can describe photon migration in the human neck with accuracy, while the DE enables an efficient calculation. For developing the accurate and efficient model of photon migration, it is crucial to investigate a condition where the DE holds in a scattering medium including a void region under the refractive-index mismatch at the void boundary because the human neck has a trachea (void region) and the refractive indices are different between the human neck and trachea. Hence, in this paper, we compare photon migration using the RTE with that using the DE in the medium. The numerical results show that the DE is valid under the refractive-index match at the void boundary even though the void region is near the source and detector positions. Under the refractive-index mismatch at the boundary, the numerical results using the DE disagree with those using the RTE when the void region is near the source and detector positions. This is probably because the anisotropy of the light scattering remains around the void boundary.
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    AIP Conference Proceedings (ICCMSE2016) 1790 (050002) 1 - 4 0094-243X 2016 [Refereed][Not invited]
     
    Numerical calculation of photon migration in biological tissue using the radiative transfer equation (RTE) has attracted great interests in biomedical optics and imaging. Because biological tissue is a highly forward-peaked scattering medium, a normalization of scattering phase function in the RTE is crucial. This paper proposes a simple way of normalizing the phase function by the double exponential formula, which is heuristically modified from the original one. The proposed method is validated by the agreement between the numerical solution of the RTE with the proposed method and analytical solution of the RTE for the case of a highly forward-peaked scattering medium, while the numerical solutions with conventional normalization methods disagree with the analytical solution. This result suggests the proposed method is accurate in numerical calculation of the RTE.
  • Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Journal of Applied Nonlinear Dynamics 5 (1) 117 - 125 2164-6473 2016 [Refereed][Not invited]
     
    Biomedical optical imaging has a possibility of a comprehensive di- agnosis of thyroid cancer in conjunction with ultrasound imaging. For improvement of the optical imaging, this study develops a higher order scheme for solving the time-dependent radiative transport equa- tion (RTE) by use of the finite-difference and discrete-ordinate meth- ods. The accuracy and efficiency of the developed scheme are ex- amined by comparison with the analytical solutions of the RTE in homogeneous media. Then, the developed scheme is applied to de- scribing photon migration in the human neck model. The numerical simulations show complex behaviors of photon migration in the hu- man neck model due to multiple diffusive reflection near the trachea.
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Proceedings of SPIE for Biophotonics Japan 2015 9792 1605-7422 2015 [Refereed][Not invited]
     
    Development of a physically accurate and computationally efficient photon migration model for turbid media is crucial for optical computed tomography such as diffuse optical tomography. For the development, this paper constructs a space-time coupling model of the radiative transport equation with the photon diffusion equation. In the coupling model, a space-time regime of the photon migration is divided into the ballistic and diffusive regimes with the interaction between the both regimes to improve the accuracy of the results and the efficiency of computation. The coupling model provides an accurate description of the photon migration in various turbid media in a wide range of the optical properties, and reduces computational loads when compared with those of full calculation of the RTE.
  • Kiyohito Hattori, Hiroyuki Fujii, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
    Proceedings of SPIE for Biophotonics Japan 2015 9792 1605-7422 2015 [Refereed][Not invited]
     
    An accurate determination of optical properties of agricultural products is crucial for non-destructive assessment of food quality. For the determination, light intensity is measured at the surface of the product then, inverse analysis is employed based on a light propagation model such as the radiative transfer equation (RTE). The inverse analysis requires high computational loads because the light intensity is numerically calculated using the model every time the optical properties are changed. For the calculation, we propose an efficient technique by combining a numerical solution with an analytical solution of the RTE, and investigate the validity of the technique in a two-dimensional homogeneous circular medium which is regarded as a light propagation model with optical properties of kiwifruit. The proposed technique can provide accurate results of the light intensity in change of the optical properties, and the accuracy is less dependent on the boundary conditions and source-detector angles. In addition, the technique can reduce computation time compared with that for numerical calculation of the RTE. These results indicate usefulness of the proposed technique for the inverse analysis.
  • Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
    Proceedings of SPIE for Biomedical Applications of Light Scattering IX 9333 1605-7422 2015 [Refereed][Not invited]
     
    Accurate modeling and efficient calculation of photon migration in biological tissues is requested for determination of the optical properties of living tissues by in vivo experiments. This study develops a calculation scheme of photon migration for determination of the optical properties of the rat cerebral cortex (ca 0.2 cm thick) based on the three-dimensional time-dependent radiative transport equation assuming a homogeneous object. It is shown that the time-resolved profiles calculated by the developed scheme agree with the profiles measured by in vivo experiments using near infrared light. Also, an efficient calculation method is tested using the delta-Eddington approximation of the scattering phase function.
  • Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi
    Journal of Quantitative Spectroscopy & Radiative Transfer 147 145 - 154 0022-4073 2014/11 [Refereed][Not invited]
     
    Numerical modeling of light propagation in random media has been an important issue for biomedical imaging, including diffuse optical tomography (DOT). For high resolution DOT, accurate and fast computation of light propagation in biological tissue is desirable. This paper proposes a space-time hybrid model for numerical modeling based on the radiative transfer and diffusion equations (RTE and DE, respectively) in random media under refractive-index mismatching. In the proposed model, the RTE and DE regions are separated into space and time by using a crossover length and the time from the ballistic regime to the diffusive regime, rho(DA) similar to 10/mu(t)' and t(DA) similar to 20/v mu(t)' where mu(t)' and v represent a reduced transport coefficient and light velocity, respectively. The present model succeeds in describing light propagation accurately and reduces computational load by a quarter compared with full computation of the RTE. (C) 2014 Elsevier Ltd. All rights reserved.
  • Eiji Okada, Shinpei Okawa, Yukari Tanikwa, Tetsuya Yoshinaga, Hiroyuki Fujii, Ken’ichi Fujimoto, Kou Hashimoto, Tadashi Iwase, Satoru Kohno, Yoko Hoshi
    Transactions of Japanese Society for Medical and Biological Engineering 52 52 - SY-53 1347-443X 2014/08/17 [Refereed][Not invited]
     
    Diffuse optical tomography (DOT) has potential to provide clinically important functional information which is cannot measured by X-ray CT and MRI. The light is scattered by tissue and an adequate mathematical model is essential for DOT. In this project, we establish the forward model and image reconstruction algorithm based on the radiative transfer equation (RTE), which is more accurate but complicated than the conventionally used diffusion equation (DE), and a time-resolved system to measure the optical properties of tissue. A hybrid RTE-DE algorithm is developed to reduce the computational cost however keeping the high accuracy. The image reconstruction based on the RTE is evaluated by simulation and the results are clearly improved compared with that based on the DE. The feasibility study has been started to assess the applicability of RTE-based DOT to the brain and thyroid gland in which light propagation is affected by low- or non-scattering regions.
  • Image errors of time-resolved optical tomography based on the radiative transfer and diffusion equations
    Hiroyuki Fujii, Shinpei Okawa, Tetsuya Yoshinaga, Yukio Yamada, Yoko Hoshi
    ODF'14 Technical Digest (9th International Conference on Optics-photonics Design and Fabrication) 13PDb-20 1 - 2 2014/02 [Refereed][Not invited]
  • Hiroyuki Fujii, Yoko Hoshi, Shinpei Okawa, Tomoya Kosuge, Satoru Kohno
    AIP Conference Proceedings (4th International Symposium on Slow Dynamics in Complex Systems) 1518 579 - 585 0094-243X 2013 [Refereed][Not invited]
     
    Recently, numerical models for photon propagation inside the living tissues have extensively been discussed based on the radiative transfer (RTE) and diffusion equations (DE). In this paper, we propose a hybrid model based on the RTE and DE for photon propagation in a turbid medium with an anisotropic source and refractive-index-mismatched boundaries. At first, we examine the validity of the diffusion approximation by comparing calculated fluence rates between the RTE and DE. The accuracy of the diffusion approximation is confirmed when the detector is placed far from the source and boundaries. These length scales are estimated at similar to 10/mu(t) from the source and similar to 3/mu(t) from the boundaries with the transport coefficient These length scales are estimated at similar to 10/mu(t) from the source and similar to 3/mu(t) from the boundaries with the transport coefficient mu(t). By using the two length scales, we can construct a hybrid model successfully. Our hybrid model recovers photon propagation based on the RTE, and effectively reduces computation costs by approximately half.
  • Hiroyuki Fujii, Yoko Hoshi, Shinpei Okawa, Tomoya Kosuge, Satoru Kohno
    Proceedings of SPIE for Optical Tomography and Spectroscopy of Tissue X 8578 (857835) 1 - 7 1605-7422 2013 [Refereed][Not invited]
     
    For improvement of diffuse optical tomography, one needs a numerical model to compute photon propagation accurately and efficiently. Thus, in the paper, we construct a hybrid model based on the radiative transfer equation (RTE) and diffusion equation (DE) in the time domain under the refractive-index- mismatching at boundary. At first, a fictive interface between the RTE and DE regions is determined, which is characterized by a length scale ρDA. By comparing the fluence rate calculated based on the RTE to that on the DE, we estimate ρDA at ∼10/μt, where μt denotes the extinction coefficient. Next, we determine a coefficient representing the reflectivity in the Robin boundary condition of the DE by analyzing the fluence rates in the domain outside ρDA. Then, the hybrid model is constructed by using the determinations. The fluence rates based on this hybrid algorithm is consistent with those on the RTE in a whole range of the medium and computational costs are reduced efficiently. © 2013 Copyright SPIE.
  • Hiroyuki Fujii, Yoko Hoshi, Shinpei Okawa, Tetsuya Yoshinaga, Satoru Kohno, Yukio Yamada
    AIP Conference Proceedings (ICNAAM2013) 1558 2528 - 2531 0094-243X 2013 [Refereed][Not invited]
     
    Recently, transport phenomena of photon energy have been attractive topics due to the applications of the biomedical imaging such as diffuse optical tomography (DOT). For improvement of numerical modeling in DOT, accurate and fast calculations of light propagations in biological tissues are necessary. This paper proposes a light propagation model based on the radiative transfer and diffusion equations (RTE and DE) in random media. Numerical calculations of light propagation using the both equations provide the condition for the DE to be valid. Length and time scales for the validity of the DE are estimated to be about 10l(m) and 20l(m)/v, respectively, where l(m) is the mean free path of photon and v is the light velocity. The proposed model can provide accurate descriptions of spatial and temporal profiles of light propagation in random media subject to the refractive-index mismatched boundary condition. Also, it can appropriately reduce computation time by an order of magnitude when compared with that fully computing the RTE.
  • Hiroyuki Fujii, Michio Tokuyama
    Physical Review E 83 (2) 1 - 8 1539-3755 2011/02 [Refereed][Not invited]
     
    The recently proposed universality near the glass transition [M. Tokuyama, Phys. Rev. E 80, 031503 (2009)] is tested for the dynamics of a single atom in ternary metallic glass-forming Cu60TixZr40-x melts by using molecular-dynamics simulations for different compositions, x = 10, 20, and 30. First, a master curve for the dynamics of the atom, such as the mean-square and mean-fourth displacements, is shown to exist independently of x if the long-time self-diffusion coefficient D-S(L) has the same value. Second, a master curve for the temperature dependence of D-S(L) is shown to exist independently of x. Finally, master curves for characteristic length and time scales of the atom are also shown to exist independently of x.
  • Hiroyuki Fujii, Michio Tokuyama
    Proceedings of Eighth International Conference on Flow Dynamics OS12-72 618 - 619 2011 [Refereed][Not invited]

MISC

Books etc

  • Hiroyuki Fujii (Joint workSections 1.3 and 2.5)
    NTS Inc. 2021/12 (ISBN: 9784860437299) 
    生体に安全で優しい“光イメージング”!! ―それは、光の波動性・粒子性の特性を正しく理解し、光の 安全性を最大限利用することが肝要。 この分野における、日本に蓄積されたさまざまな技術リソースと アカデミアでの研究成果の融合により、生体への応用も格段の 進化を遂げる！

Teaching Experience

  • Advanced Fluids EngineeringAdvanced Fluids Engineering Hokkaido University
  • Mechatoronics exerciseMechatoronics exercise Hokkaido University

Association Memberships

  • The Optical Society of Japan   The Heat Transfer Society of Japan   THE JAPAN SOCIETY OF MECHANICAL ENGINEERS   THE PHYSICAL SOCIETY OF JAPAN   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2024/04 -2028/03 
    Author : 小林 一道, 藤井 宏之, 渡部 正夫
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2024/04 -2026/03 
    Author : 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2026/03 
    Author : Hiroyuki Fujii
  • NAKATANI Foundation：Research grant
    Date (from‐to) : 2023/04 -2025/03 
    Author : Hiroyuki Fujii
  • Hokkaido University：Consortium-forming Robust Agriculture, Forestry and Fisheries Engineering Research Program
    Date (from‐to) : 2023/04 -2024/03
  • The Public Foundation of Elizabeth Arnold一Fuji：Research fund
    Date (from‐to) : 2022/08 -2023/07 
    Author : Hiroyuki Fujii
  • Takano Life Science Research Foundation：Research promotion
    Date (from‐to) : 2022/06 -2023/04 
    Author : Hiroyuki Fujii
  • The Uehara Memorial Foundation：Research promotion
    Date (from‐to) : 2022/02 -2023/04 
    Author : Hiroyuki Fujii
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2023/03 
    Author : 小林 一道, 藤井 宏之, 渡部 正夫
     
    本提案研究は，混合気体に接した気液界面における気体論境界条件を構築し，様々な分野に本研究成果を展開することである．2021年度は主に以下の３つの研究を行った． １．分子計算（分子運動論および分子動力学シミュレーション）を用いて，非平衡気液界面における気体論境界条件の構築を行った．その結果，気体論境界条件に含まれる二つの未知パラメータ（蒸発係数および凝縮係数）を決定した．本結果より，非平衡気液界面における蒸発係数と凝縮係数の値は，平衡状態および非平衡状態においてほぼ変わらないことが明らかとなった．これにより，初期液体温度などの条件にもよるが，平衡状態の蒸発係数および凝縮係数を求めておけば気体論境界条件を構築できることが示唆された． ２．分子動力学解析を用いて，固体壁と液体に挟まれた気体のクエット流れについて解析を行った．この研究より，気液界面における気体論境界条件の位置を検証した．本研究より，１の研究で指定していた気体論境界条件の位置は妥当であることが示唆された．また，高クヌーセン数流れになるほど，気液界面の境界条件が平衡状態の関数形から異なることが示唆された．これについてはさらなる検討が必要である． ３．分子動力学解析を用いて，混合液体（エタノール・イソオクタン）の蒸発について検証した．分子動力学計算を用いてエタノール・イソオクタンの気液平衡系を作り出し，１の研究で提案した方法によって，液体から蒸発する分子の成分について調べた．その結果，エタノールの濃度が低い混合液体においても，蒸発するエタノール分子の割合は高くなることが示された．今後はこの知見を用いて実験結果を整理する予定である．
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2020/04 -2023/03 
    Author : 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之
     
    本研究の目的は，「高Oh液滴の固体面衝突直後に発生するcorona splashとprompt splashの発生条件を明らかにし，二つのsplashの発生メカニズムを説明する理論モデルを構築すること」である．この目的を達成するために，本年度は以下の２項目について研究を行った． １．固体表面に滴衝する高Oh液滴の観察：自由落下するシリコンオイルを用いて衝突実験を行い，高Oh液滴のsplash発生条件を探索した．高粘度液滴衝突ではあるOhを閾値としてsplashとreceding break-upの２種類の不安定性が観察されること, 閾値Oh数以上ではreceding break-upのみが観察されさらにOh数を大きくすると不安定性が観察されないこと，receding break-upはある衝突速度以上では観察されないことを明らかにした． ２．粗い表面に衝突する液滴の観察：低圧力環境下の高速液滴衝突 (50m/s程度) 実現を行い，固体表面粗さの効果を検討するために，減圧チャンバ内での粗い固体表面への高速液滴衝突を観察した．平滑表面および粗い固体表面においてsplashの発生閾値を検討した．低Oh液滴衝突においては，これまで観察されていたcorona splashとprompt splashに加えて衝突直後極短時間にのみ観察されるsplashが存在することが発見され，これまでに提案されたsplash発生閾値モデルは，粗い表面には適用できないことを明らかにした． ３．高速度カラー光干渉計による気液界面計測システムによる観察：固体表面に衝突する液滴の固体面衝突直前に，固体表面と液滴との間に形成される薄空気膜はsplash発生に大きな影響を与える．この薄空気膜厚さの空間分布の時間変化が，固体表面電位と液体の誘電率によって大きく変化することを明らかにした．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2023/03 
    Author : 西村 吾朗, 藤井 宏之
     
    散乱体に埋め込まれた蛍光体に関して、その時間応答関数に関して、研究協力者と検討した。特に、S/Nが最も良くなる時間応答関数が最大値を取る時間を、点蛍光体に関して解析的に導出し、厳密な証明を与えた。これらの結果を投稿論文としてまとめ投稿した。 時間応答関数を観測する上で、検出条件が与える影響を評価するために、MCシミュレーションを行った。特に、検出方向の境界面に対する角度依存性を検討した。検出方向の方位角を4分割、極角を10分割しそれぞれの方向で検出される光子数に関してシミュレーションを行った。入射点と検出点を結ぶ方向に対し直角となる方位角で検出する場合の極角に対する依存性は、界面のフレネル反射と拡散反射のみで説明可能であった。一方、入射点と検出点を結ぶ方向では、入射点方向から離れる方向では強度が大きくなる一方、逆の方向では強度が小さくなり、直角方向のそれとの違いはほぼ対称的であった。この結果は、拡散近似に含まれる流れの項で説明できることがわかった。その一方、時間応答の速い時間ではそれらからずれ、拡散近似の破れが現れた。これらの結果は、10月に行われた国内学会、4月に行われた国際会議で報告した。 散乱体濃度に対して時間応答特性がどのように変化するか、特にその波長依存性に関して、共同研究者とより詳細に解析を進めた。その結果、濃度に対する散乱係数の依存性の非線形性が、波長が長くなるにつれより薄い濃度で現れることが明らかになった。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/06 -2023/03 
    Author : 渡部 正夫, 小林 一道, 藤井 宏之
     
    本研究の目的は，アクティブマターを用いたマイクロ流体システムを開発するために，アクティブマターのメカニズムを解明することである．液滴アクティブマターのメカニズムを解明するためには，分散質（液滴）と分散媒との固体表面上での挙動を解明する必要がある．液滴と分散媒が混和性の場合には，移流による物質移動と相互拡散による物質移動が発生するため，個体表面極近傍での液滴と分散媒の濃度分布を計測することが必要不可欠となる．そのため，以下の２事項に着目して検討した． １．表面プラズモン共鳴観察による濃度分布計測システムの構築：固体表面極近傍での液滴・分散媒の濃度分布を計測するために，表面プラズモン共鳴観察による濃度分布計測システムを構築した．表面プラズモン共鳴の共鳴条件が，基板表面の状態に敏感に変化することを利用して，基板表面への赤色光入射角を固定することで，基板表面極近傍の液滴・分散媒濃度分布を反射率の関数として 光強度分布として定量化可能である．今年度は，液滴として水，分散媒としてエタノールを用いた．基板表面への入射光角度を水の表面プラズモン共鳴角度に固定して，固体表面極近傍における水・エタノール混合溶液の水平方向濃度分布の時間変化を高速度カメラで撮影することに成功した． ２．エタノール薄液膜に衝突する水液滴挙動の固体表面極近傍での観察：底面を金薄膜を蒸着したスライドガラスとするアクリル製の検査容器を作成しプリズム上に設置し，容器の中にエタノール薄液膜を形成した．直径2mm程度の水液滴を自由落下させエタノール薄液膜に衝突させた．エタノール薄液膜厚さと水液滴落下高さとをパラメータとして，衝突後の水液滴とエタノールの混合溶液の固体表面極近傍での挙動を検討するために，表面プラズモン共鳴観察を行い，固体極近傍での水平方向濃度分布を高速度カメラを用いて観察した．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/10 -2023/03 
    Author : Hiroyuki Fujii
     
    本研究の目的は、生体ファントムであるコロイド溶液における、光の散乱、光の揺らぎ、コロイド粒子の拡散運動に関するマルチフィジックスモデルを構築し、光の揺らぎのメカニズムを統一的に理解することである。拡散相関分光法は、光強度の揺らぎの時間相関関数を計測することで、媒体深部の拡散係数を評価する。この分光法では、光の散乱、光の揺らぎ、粒子の拡散運動のモデル化が必要であるが、先行研究では別々にモデル化が行われていた。本研究では、３つの物理現象が密接に関係していることに着目する。電磁波散乱理論、輻射(ふく射)輸送論、ブラウン動力学シミュレーションに基づいたマルチフィジックスモデルを構築し、光の時間相関関数などを数値計算した上で一連の物理現象における特性時間や特性長を評価する。特性時間や特性長を無次元解析し、光の散乱と粒子の拡散運動に起因した光の揺らぎのメカニズムについて、普遍性の観点より明らかにする。この目的を達成するため、本年度は以下の２項目について研究を実施した。 １．ブラウン動力学シミュレーションを実行する計算コードを作成した。分子動力学シミュレーションと構造特性の結果を比較し、溶媒粒子による構造特性への影響は小さいことを確認することができた。シミュレーション結果より得る構造特性の妥当性を、様々な計算手法による結果を比較して、検証した。少ない粒子数であっても、バルク系を再現する計算コードを構築した。 ２．シミュレーションで得た構造特性の結果を、電磁波理論の一つである干渉散乱理論に組み込み、光散乱特性を世界に先駆けて計算した。粘着性剛体球モデルの結果と比較し、光散乱特性に粒子間の引力相互作用が強く影響を及ぼすことを明らかにした。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2023/03 
    Author : Hiroyuki Fujii
     
    本研究の目的は、「生体を模擬した高密度なコロイド溶液に対して、輻射（ふくしゃ）の干渉効果を組み込んだ輻射輸送モデル(輸送モデル)を新たに構築した上で、干渉効果が及ぼす光伝播への影響を明らかにすること」である。生体光イメージングや光治療において、生体内の光伝播を定量的に把握することが必要であり、光を輻射と捉えた輸送モデルが活用されている。しかし、従来の輸送モデルには、生体のような高密度な散乱媒体において重要となる干渉効果が考慮されていない。本研究では電磁波の散乱理論より干渉効果を考慮した散乱特性を計算し、輸送モデルに組み込んだ上で光強度の時間分解波形を数値計算する。また、短パルスレーザー光源による光強度計測も実施する。干渉効果が光伝播へ影響を及ぼす時空間スケールについて、散乱係数などで表される無次元数を用いて解析し、理論、数値計算、実験より体系的に明らかにする。この目的を達成するため、本年度は以下の３項目について研究を実施した。 １．光散乱特性を簡潔に記述するモデル式を開発した。モデル式により、単一散乱の寄与と干渉効果の寄与を分離して評価することに初めて成功した。 ２．分担研究者の西村吾朗助教の波長可変の光計測システムを利用して、コロイド溶液（脂質エマルジョン）において、濃度20%まで21条件、720 nmから860 nmまでの6条件で光計測を実施した。光計測データを逆解析することで算出した光学特性値をモデル式より解析し、干渉効果の波長依存性を明らかにした。 ３．分子動力学シミュレーションにより構造特性を計算し、干渉散乱理論に組み込んで散乱特性を計算した。粒子間の引力相互作用が散乱特性に強く影響を及ぼすことを明らかにした。
  • The AKIYAMA LIFE SCIENCE FOUNDATION：研究助成（一般）
    Date (from‐to) : 2020/07 -2021/03 
    Author : Hiroyuki Fujii
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2021/03 
    Author : Fujii Hiroyuki
     
    This study considered dense colloidal suspensions in water as optical phantoms of biological tissues, and examined the light scattering properties in the colloidal suspensions by numerical calculations for the electromagnetic scattering and radiative transfer theories, and by light reflectance measurements based on the time-correlated single photon counting system. Especially, we investigated the light interference effects on the scattering properties in the suspensions at different volume fractions from 0.1 to 20%. We developed a theory of the interference effects in polydisperse systems based on the electromagnetic theory, while a conventional theory of the interference effects can not fully treat the polydispersity. Our numerical calculations showed conditions where the interference strongly influences the scattering properties. Time-resolved light reflectance measurements supported our numerical results.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Watanabe Masao
     
    Liquid droplet impacts on solid surface are key elements in technical applications, such as rapid spray cooling, ink-jet printing and semiconductor cleaning. Although the broad varieties of parameters that control splash formation after the droplet impact, are proposed, they are not thoroughly explored; hence, dynamics of the droplet after the impact are yet fully understood. After droplet impacts on solid surface, characteristic film flow is developed; then splash which consists of the secondary droplets ejected from the edge of the lamella may be generated. We investigated the surrounding-gas effects on the instability in the vicinity of the solid-gas-liquid triple-phase contact line of the ejected fast liquid film flow. We conducted four types of experiments: observation of thin-gas layer by color interferometry, droplet impact on solid surface with various wettability, high-speed droplet impact in the reduced pressure chamber, droplet impact in the condensable surrounding gas.
  • THE PUBLIC FOUNDATION OF ELIZABETH ARNOLD‐FUJI：Research fund
    Date (from‐to) : 2019/07 -2020/02 
    Author : Hiroyuki Fujii
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2019/03 
    Author : Kobayashi Kazumichi, KON Misaki
     
    The aim of this study is to determine the kinetic boundary conditions for vapor (condensable gas) - gas (non-condensable gas) binary mixture. We also apply the boundary conditions for multi phase flow, especially for the analysis of bubble collapse problem.
    In the present study period, molecular dynamics method was used to construct the kinetic boundary conditions for vapor-gas mixture at equilibrium. We also solved the problem of the bubble collapse using the boundary conditions obtained from the molecular dynamics simulation. As a result, it was suggested that a thin layer composed of non-condensable gas is formed in the vicinity of the gas-liquid interface when the bubble collapses, and it was indicated that the condensation coefficient becomes extremely low due to the influence of this layer. It was also revealed that the internal temperature field when bubble collapses was affected by a small amount of non-condensable gas contained in the bubble.
  • The Okawa Foundation for Information and Telecommunications：The 2017 Research Grant
    Date (from‐to) : 2018/03 -2019/03 
    Author : Fujii Hiroyuki
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2018/03 
    Author : Okawa Shinpei, SEI Kiguna
     
    To develop the method to monitor the oxygenated hemoglobin supply to fetus and placenta by using photoacoustic wave which is the ultrasound induced by the pulsed laser light, the estimation of the tissue optical properties such as scattering and absorption coefficients from measured photoacoustic wave, the development of the images reconstruction for quantitative photoacoustic tomography, and the photoacoustic imaging of the placenta of rabbits were conducted.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2018/03 
    Author : Fujii Hiroyuki
     
    The objectives of this study were to examine light propagation in biological tissue with fine structure using the radiative transfer equation, and to determine the optical properties of the tissues using an inverse algorithm. Firstly, an accurate and efficient numerical scheme was developed for solving the radiative transfer equation in highly forward-directed scattering media such as biological tissue.From the numerical results of the RTE, the transition length and time from ballistic light to diffusive light were evaluated as a function of the optical properties. Secondly,the time-resolved profiles of light in agricultural and food products were measured and the in-vivo and ex-vivo optical properties of them were evaluated using the inverse analysis. It was suggested the optical properties were related with the structural properties.
  • THE PUBLIC FOUNDATION OF ELIZABETH ARNOLD‐FUJI：Research Grant / Funabashi Shigeaki Memorial Encouragement Grant
    Date (from‐to) : 2016/07 -2017/04 
    Author : Fujii Hiroyuki
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2017/03 
    Author : WATANABE MASAO
     
    Droplet impacts on solid surface are key elements in technical applications, such as rapid spray cooling, ink-jet printing and semiconductor cleaning. Although the broad varieties of parameters that control splash formation after the droplet impact, are proposed, they are not thoroughly explored; hence, dynamics of the droplet after the impact are yet fully understood. After droplet impacts on solid surface, characteristic film flow is developed; then splash may be generated. In this study, we examine the effects of the temperature of surrounding gas, which is either condensable or non-condensable, on ethanol droplet impact. We found that splash can be suppressed with the increase of the surrounding gas temperature. We measured the splash threshold pressure for a splash to appear as a function of the temperature. The results show that the splash threshold pressure is a monotonically increasing function of the surrounding gas temperature.
  • The AKIYAMA LIFE SCIENCE FOUNDATION：Research grant
    Date (from‐to) : 2016/07 -2017/03 
    Author : Fujii Hiroyuki
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2016/03 
    Author : Watanabe Masao, KOBAYASHI KAZUMICHI, YAGUCHI HISAO, HIROYUKI FUJII
     
    The aim of this study is to examine a kinetic boundary condition that depends on liquid temperature for the Boltzmann equation in a vapor-liquid two-phase system during unsteady net evaporation/condensation in a strong non-equilibrium status.We carried out numerical simulations of the unsteady heat and mass transfer in the vicinity of interface at the strong non-equilibrium status by using EV-DSMC method; then, we constructed the kinetic boundary condition that can prescribe the heat and mass transfer in the vicinity of the interface in the frame work of the macroscopic fluid mechanics. We proposed a novel model of the bubble dynamics with phase change taken into consideration. We also investigated the bubble dynamics with phase change.
  • Northern Advancement Center for Science & Technology：フードイノベーション創造支援事業
    Date (from‐to) : 2015/07 -2016/02 
    Author : 藤井 宏之
  • Northern Advancement Center for Science & Technology：Promotion for Young Research Talent and Network
    Date (from‐to) : 2014/08 -2015/02 
    Author : Fujii Hiroyuki

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