Nov. 2025, Japan Council for Near Infrared Spectroscopy, Awards for supervised students, 41th NIR Forum Student Travel Award
"Particle diameter evaluation of colloidal suspensions by machine learning from light-scattering intensity"
Hiromichi Nozaki;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 42057385

Sep. 2025, Leave a nest Co.,Ltd., Finalist, Foodtech Grand Prix 2025
"Near-infrared scattering spectroscopy for nondestructive evaluation of various food qualities"
Team "ScatLight", Others, Japan

Mar. 2025, Japan Society of Mechanical Engineers Hokkaido Branch, Awards for supervised students, Best Presentation Award
"Interference effects of multiple scattered fields in dense colloidal suspensions using light scattering measurements"
Sou Sasaki;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 42057385

Mar. 2025, Japan Society of Mechanical Engineers Hokkaido Branch, Awards for supervised students, Best Presentation Award
"Numerical study of light scattering in a hollow sphere using Mie theory"
Ryuga Sawada;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 42057385

Feb. 2025, Leave a nest Co.,Ltd., Nipponham Award
"Quantitative relation between meet structure and light scattering for meat quality evaluation"
Hiroyuki Fujii, Publisher, Japan

Nov. 2024, 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"
Koyata Nishikawa;Hiroyuki Fujii;Goro Nishimura;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 42057385

Mar. 2024, The Japan Society of Mechanical Engineers, Awards for supervised students, Miura Award　　　　　　　　　　　　　　　
Hyeonwoo Na

Nov. 2023, 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"
Hiroyuki Fujii, Japan society, Japan, 42057385

Mar. 2023, 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"
Koyata Nishikawa;Hiroyuki Fujii;Goro Nishimura;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 36940960

Mar. 2023, Hokkaido University Faculty of Engineering, The FY2022 Faculty of Engineering Young Faculty Award
Hiroyuki Fujii, Others, Japan

Nov. 2022, 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"
Hyeonwoo Na;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe, Japan society, Japan, 33935141

Jun. 2022, 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"
Hiroyuki Fujii, Publisher, Japan

Mar. 2022, 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"
Hiroyuki Fujii

Nov. 2021, 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"
Iori Terabayashi;Hiroyuki Fujii;Kazumichi Kobayashi;Masao Watanabe, Japan society, 26444760

Oct. 2021, 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"
Yuki Inoue;Hiroyuki Fujii;Goro Nishimura;Toshiaki Aoki;Kazumichi Kobayashi;Masao Watanabe, International society, 26444760

Nov. 2020, Japan Council for Near Infrared Spectroscopy, NIR Advance Award
"Modeling of light scattering in biological tissue, agricultural products, and foods"
Hiroyuki Fujii, Japan society, Japan, 26444760

Minimum thickness of liquid film for the validity of water hammer theory
Kazumichi Kobayashi, Jotaro Akazawa, Kotaro Ohashi, Mikihiro Muramatsu, Takuro Nagakawa, Hiroyuki Fujii, Masao Watanabe
Physics of Fluids, 37, 8, AIP Publishing, 01 Aug. 2025, [Peer-reviewed]
Scientific journal, Systems that clean by high-speed nanodroplet injection have recently been developed; however, elucidating the cleaning mechanism underlying nanodroplet impact is urgently required. In this study, numerical simulations of the high-speed impact phenomenon of two liquid films were performed using the Enskog–Vlasov direct simulation Monte Carlo method. We determine the minimum liquid film thickness for which the water hammer theory is applicable to the maximum pressure generated during liquid film impact. The simulation results show that the water hammer pressure was generated when the liquid film thickness exceeded the compression wavefront thickness generated by the liquid film impact, which is more than ten times the molecular diameter.

Polydisperse stickiness and particle size on light scattering in dense colloidal suspensions: A numerical study using the binary sticky hard-sphere model
Hiroyuki Fujii, Koyata Nishikawa, Hyeonwoo Na, Kazumichi Kobayashi, Masao Watanabe
Results in Physics, 73, 108247, 1, 8, Elsevier BV, Jun. 2025, [Peer-reviewed], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, 42057385

Particle size distribution effects on the light scattering properties in non-diluted colloidal suspensions: A numerical study
Hiroyuki Fujii, Hyeonwoo Na, Jungyun Yi, Kazumichi Kobayashi, Masao Watanabe
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 703, 135208, 1, 9, Elsevier BV, Nov. 2024, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, 42057385

Interference effects on light scattering properties of dense colloidal suspensions: a short review
Hiroyuki Fujii, Hyeonwoo Na, Koyata Nishikawa, Kazumichi Kobayashi, Masao Watanabe
Optical Review, 31, 3, 299, 308, Springer Science and Business Media LLC, 22 May 2024, [Peer-reviewed], [Invited], [Lead author, Corresponding author]
English, Scientific journal, 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., 42057385

Couette flow at high Knudsen number between wall and liquid boundaries
Kazumichi Kobayashi, Kota Aoki, Hirofumi Tabe, Hiroyuki Fujii, Toshiki Nara, Hideyoshi Takashima, Nobuyuki Oshima, Masao Watanabe
Physics of Fluids, 35, 082021, 1, 8, AIP Publishing, 01 Aug. 2023, [Peer-reviewed]
English, Scientific journal, 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.

Numerical study of light scattering and propagation in soymilk: Effects of particle size distributions, concentrations, and medium sizes
Hiroyuki Fujii, Koyata Nishikawa, Hyeonwoo Na, Yuki Inoue, Kazumichi Kobayashi, Masao Watanabe
Infrared Physics & Technology, 132, 104753, 1, 9, Elsevier BV, Aug. 2023, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 42057385

Vapor condensation induced by fast-moving liquid film in the presence of noncondensable gas molecules
Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
International Communications in Heat and Mass Transfer, 142, 106622, 1, 8, Elsevier BV, Mar. 2023, [Peer-reviewed]
English, Scientific journal

Modeling photoacoustic pressure generation in colloidal suspensions at different volume fractions based on a multi-scale approach
Hiroyuki Fujii, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
Photoacoustics, 27, 3, 100368, 1, 10, Elsevier, 01 Sep. 2022, [Peer-reviewed], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, 36096597

Wetting failure in the early stage of water drop impact on a smooth solid surface
Ryunosuke Adachi, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
Physics of Fluids, 34, 062116, 1, 13, AIP Publishing, Jun. 2022, [Peer-reviewed]
English, Scientific journal, 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.

Molecular dynamics simulation of evaporation coefficient of vapor molecules during steady net evaporation in binary mixture system
Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
International Journal of Heat and Mass Transfer, 188, 122663, 122663, Elsevier BV, Jun. 2022, [Peer-reviewed]
English, Scientific journal

Near-infrared scattering properties for binary sticky hard-sphere fluids
Hiroyuki Fujii, Hyeonwoo Na, Toshiaki Aoki, Yuki Inoue, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
Extended abstract of SI-Thru2022, SI-Thru8-02, 1, 3, Apr. 2022, [Peer-reviewed], [Lead author]
English, International conference proceedings, 33935141

Molecular dynamics study of evaporation induced by locally heated argon liquid
Hirofumi Tabe, Kiryu Hiramatsu, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe, Tsuyoshi Totani
Applied Thermal Engineering, 212, 118472, 1, 7, Apr. 2022, [Peer-reviewed], [International Magazine]
English, Scientific journal

Model equations of light scattering properties and a characteristic time of light propagation for polydisperse colloidal suspensions at different volume fractions
Hiroyuki Fujii, Moegi Ueno, Yuki Inoue, Toshiaki Aoki, Kazumichi Kobayashi, Masao Watanabe
Optics Express, 30, 3, 3538, 3538, The Optical Society, 31 Jan. 2022, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, 26444760

Numerical study of near-infrared light propagation in aqueous alumina suspensions using the steady-state radiative transfer equation and dependent scattering theory
Hiroyuki Fujii, Iori Terabayashi, Toshiaki Aoki, Yuki Inoue, Hyeonwoo Na, Kazumichi Kobayashi, Masao Watanabe
Applied Sciences, 12, 3, 1190, 1, 12, MDPI AG, 24 Jan. 2022, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, 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., 33935141

Mean-field kinetic theory analysis of vapor flow between evaporating and condensing interfaces in the presence of non-condensable gas molecules
Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
Physics of Fluids, 33, 12, 122017, 122017, AIP Publishing, Dec. 2021, [Peer-reviewed]
English, Scientific journal

Study on near-infrared light scattering in colloidal suspensions using time-resolved measurements
Yuki Inoue, Hiroyuki Fujii, Goro Nishimura, Toshiaki Aoki, Kazumichi Kobayashi, Masao Watanabe
Extended abstracts of NIR2021, P13, 168, 169, Oct. 2021, [Peer-reviewed], [International Magazine]
English, International conference proceedings, 26444760

Derivation of an extended radiative transfer equation from the electromagnetic wave equation
Toshiaki Aoki, Hiroyuki Fujii, Yuki Inoue, Kazumichi Kobayashi, Masao Watanabe
Extended abstracts of NIR2021, O11, 60, 61, Oct. 2021, [Peer-reviewed]
English, International conference proceedings, 26444760

Numerical Modelling of Initial Photoacoustic Pressure in Colloidal Suspensions for Photoacoustic Imaging
Hiroyuki Fujii, Toshiaki Aoki, Yuki Inoue, Iori Terabayashi, Kazumichi Kobayashi, Masao Watanabe
Technical digest of 26th Microoptics Conference (MOC2021), PO-11, 164, 165, The Japan Society of Applied Physics, Sep. 2021, [Peer-reviewed], [Lead author]
English, International conference proceedings, 26444760

Molecular dynamics study on characteristics of reflection and condensation molecules at vapor–liquid equilibrium state
Hirofumi Tabe, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
PLOS ONE, 16, 3, e0248660, e0248660, Public Library of Science (PLoS), 16 Mar. 2021, [Peer-reviewed]
English, Scientific journal, 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.

A comparative study of the delta-Eddington and Galerkin quadrature methods for highly forward scattering of photons in random media
Hiroyuki Fujii, Go Chiba, Yukio Yamada, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
Journal of Computational Physics, 423, 109825, 1, 14, Sep. 2020, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, 11969653

Photon transport model for dense polydisperse colloidal suspensions using the radiative transfer equation combined with the dependent scattering theory
Hiroyuki Fujii, Leung Tsang, Jiyue Zhu, Koki Nomura, Kazumichi Kobayashi, Masao Watanabe
Optics Express, 28, 15, 22962, 22977, The Optical Society, 10 Jul. 2020, [Peer-reviewed], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, 26444760

Evaporation coefficient and condensation coefficient of vapor under high gas pressure conditions
Kotaro Ohashi, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
Scientific Reports, 10, 8143, 18 May 2020, [Peer-reviewed]
English, Scientific journal

Analysis of interference effects on light scattering in colloidal suspensions
Koki Nomura, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe, Goro Nishimura
Proceeding of the 7th Asian NIR symposium (ANS2020), 2020, AFI-0006, 12, 13, Feb. 2020, [Peer-reviewed], [Corresponding author]
English, International conference proceedings, 10990287

Finite element investigation of light propagationin the human neck using the time-dependent radiative transfer theory
Shigeki Endo, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe
Proceeding of the 7th Asian NIR symposium (ANS2020), 2020, NRT-0008, 60, 61, Feb. 2020, [Peer-reviewed], [Corresponding author]
English, International conference proceedings, 11969653

Numerical study on light propagation in a white bread loaf
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, Feb. 2020, [Peer-reviewed], [Lead author], [International Magazine]
English, International conference proceedings, 13396474

Characteristic length and time scales of the highly forward scattering of photons in random media
Hiroyuki Fujii, Moegi Ueno, Kazumichi Kobayashi, Masao Watanabe
Applied Sciences, 10, 93, 1, 16, Feb. 2020, [Peer-reviewed], [Lead author, Corresponding author]
English

Hidden prompt splashing by corona splashing at drop impact on a smooth dry surface
Taku Ashida, Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada
Physical Review Fluids, 5, 011601, 1, 9, American Physical Society (APS), Jan. 2020, [Peer-reviewed]
English, Scientific journal

Levitation mechanism of impacting nanodroplet on heated wall
Hirofumi Tabe, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii, Masao Watanabe
International Journal of Thermal Sciences, 150, 106203, 1, 10, Elsevier BV, Jan. 2020, [Peer-reviewed]
English, Scientific journal

Numerical treatment of highly forward scattering on radiative transfer using the delta-M approximation and Galerkin quadrature method
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, Sep. 2019, [Peer-reviewed]
English, International conference proceedings

Finite element investigation of a void region on light propagation in scattering media using the radiative transfer equation
Kosuke Tabayashi, Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe
AIP Conference Proceedings (ICNAAM2018), 2116, 450052, 1, 4, Jul. 2019, [Peer-reviewed]
English, International conference proceedings

Time-domain diffuse optical tomography with lp sparsity regularization for thyroid cancer imaging
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, Jul. 2019, [Peer-reviewed]
English, International conference proceedings

Numerical errors of light propagation in the two-dimensional human neck model using the time-dependent radiative transfer equation with renormalized phase functions
Hiroyuki Fujii, Yamada Yukio, Hoshi Yoko, Kobayashi Kazumichi, Watanabe Masao
AIP Conference Proceedings (ICNAAM2018), 2116, 450037, 1, 4, Jul. 2019, [Peer-reviewed]
English, International conference proceedings

Influence of a small amount of noncondensable gas on shock wave generation inside a collapsing vapor bubble
Kyohei Yamamoto, Kazumichi Kobayashi, Masao Watanabe, Hiroyuki Fujii, Misaki Kon, Hiroyuki Takahira
Physical Review Fluids, 4, 063603, 1, 10, Jun. 2019, [Peer-reviewed]
English, Scientific journal

Light propagation models of the human neck for photoacoustic imaging of thyroid cancer
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, May 2019, [Peer-reviewed]
English, International conference proceedings

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, Apr. 2019, [Peer-reviewed]
English, Scientific journal

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, 993, 1003, Springer Science and Business Media LLC, Apr. 2019, [Peer-reviewed]
English, Scientific journal

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, [Peer-reviewed]

Molecular gas dynamics analysis on condensation coefficient of vapour during gas–vapour bubble collapse
Kazumichi Kobayashi, Takahiro Nagayama, Masao Watanabe, Hiroyuki Fujii, Misaki Kon
Journal of Fluid Mechanics, 856, 10, 1045, 1063, Dec. 2018, [Peer-reviewed]
English, Scientific journal

Accurate and efficient computation of the 3D radiative transfer equation in highly forward-peaked scattering media using a renormalization approach
Hiroyuki Fujii, Yukio Yamada, Go Chiba, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe
Journal of Computational Physics, 374, 591, 604, Dec. 2018, [Peer-reviewed]
English, Scientific journal

Light propagation model of titanium dioxide suspensions in water using the radiative transfer equation
Hiroyuki Fujii, Yukio Yamada, Yoko Hoshi, Shinpei Okawa, Kazumichi Kobayashi, Masao Watanabe
Reaction Kinetics, Mechanisms and Catalysis, 123, 2, 439, 453, Springer Netherlands, 01 Apr. 2018, [Peer-reviewed]
English, Scientific journal

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, [Peer-reviewed]
English, International conference proceedings

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, Oct. 2017, [Peer-reviewed]
English, International conference proceedings

Influence of condensation coefficient o spherical bubble collapse with evaporation and condensation
Shotaro Morikawa, Yuki Tatekura, Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe, Koichi Sasaki
Nagare, 36, 105, 108, May 2017, [Peer-reviewed]
Japanese, Scientific journal

Modeling of light propagation in the human neck for diagnoses of thyroid cancers by diffuse optical tomography
Hiroyuki Fujii, Yukio Yamada, Kazumichi Kobayashi, Masao Watanabe, Yoko Hoshi
International Journal for Numerical Methods in Biomedical Engineering, 33, 5, 1, 12, May 2017, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal

Kinetic boundary conditions for vapor-gas binary mixture
Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
MICROFLUIDICS AND NANOFLUIDICS, 21, 3, 1, 13, Mar. 2017, [Peer-reviewed]
English, Scientific journal

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, [Peer-reviewed]
English, International conference proceedings

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, [Peer-reviewed]
English, International conference proceedings

Renormalization of the highly forward-peaked phase function using the double exponential formula for radiative transfer
Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
Journal of Mathematical Chemistry, 54, 10, 2048, 2061, Nov. 2016, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal

Early stage of nanodroplet impact on solid wall
Kazumichi Kobayashi, Kazuki Konno, Hisao Yaguchi, Hiroyuki Fujii, Toshiyuki Sanada, Masao Watanabe
Physics of Fluids, 28, 3, 1, 10, Mar. 2016, [Peer-reviewed]
English, Scientific journal

Quantitative method to determine the optical properties of melons by the photon diffusion equation
Kiyohito Hattori, Hiroyuki Fujii, Goro Nishimura, Kazumichi Kobayashi, Masao Watanabe
Proceeding of the 5th Asian NIR symposium (ANS2016), 2016, O-6, 72, 73, 2016, [Peer-reviewed]
English, International conference proceedings

Near-infrared optical properties of white bread using the light propagation model
Hiroyuki Fujii, Goro Nishimura, Kiyohito Hattori, Kazumichi Kobayashi, Masao Watanabe
Proceeding of the 5th Asian NIR symposium (ANS2016), 2016, P-86, 288, 289, 2016, [Peer-reviewed]
English, International conference proceedings

Molecular Dynamics Simulation on Kinetic Boundary Conditions of Gas-Vapor Binary Mixture
Kazumichi Kobayashi, Kiyofumi Sasaki, Misaki Kon, Hiroyuki Fujii, Masao Watanabe
30TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS (RGD 30), 1786, 110002, 1, 9, 2016, [Peer-reviewed]
English, International conference proceedings

Numerical study of photon migration in the presence of a void region using the radiative transfer and diffusion equations
Erina Miyakawa, Hiroyuki Fujii, Kiyohito Hattori, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
AIP Conference Proceedings (ICCMSE2016), 1790, 050003, 1, 4, 2016, [Peer-reviewed]
English, International conference proceedings

Normalization method of highly forward-peaked scattering phase function using the double exponential formula for radiative transfer
Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
AIP Conference Proceedings (ICCMSE2016), 1790, 050002, 1, 4, 2016, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

Numerical modeling of photon migration in human neck based on the radiative transport equation
Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe
Journal of Applied Nonlinear Dynamics, 5, 1, 117, 125, L and H Scientific Publishing, LLC, 2016, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal

A coupling model of the radiative transport equation for calculating photon migration in biological tissue
Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi, Masao Watanabe
Proceedings of SPIE for Biophotonics Japan 2015, 9792, SPIE, 2015, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

Numerical study of light propagation in agricultural products for non-destructive assessment of food quality
Kiyohito Hattori, Hiroyuki Fujii, Yuki Tatekura, Kazumichi Kobayashi, Masao Watanabe
Proceedings of SPIE for Biophotonics Japan 2015, 9792, SPIE, 2015, [Peer-reviewed]
English, International conference proceedings

Numerical modeling of photon migration in the cerebral cortex of the living rat using the radiative transport equation
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, SPIE, 2015, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

Hybrid model of light propagation in random media based on the time-dependent radiative transfer and diffusion equations
Hiroyuki Fujii, Shinpei Okawa, Yukio Yamada, Yoko Hoshi
Journal of Quantitative Spectroscopy & Radiative Transfer, 147, 145, 154, Nov. 2014, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal

Mathematical modeling and image reconstruction in biomedical optical imaging
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, Japan Soc. of Med. Electronics and Biol. Engineering, 17 Aug. 2014, [Peer-reviewed]
Japanese, Scientific journal

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, Feb. 2014, [Peer-reviewed], [Lead author]
English, International conference proceedings

Numerical modeling of photon propagation in biological tissue based on the radiative transfer equation
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, 2013, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

Hybrid model for photon propagation in random media based on the radiative transfer and diffusion equations
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, 2013, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

A coupling model of light propagation based on the radiative transfer and diffusion equations
Hiroyuki Fujii, Yoko Hoshi, Shinpei Okawa, Tetsuya Yoshinaga, Satoru Kohno, Yukio Yamada
AIP Conference Proceedings (ICNAAM2013), 1558, 2528, 2531, 2013, [Peer-reviewed], [Lead author, Corresponding author]
English, International conference proceedings

Dynamics of a single atom in ternary metallic glass-forming Cu60TixZr40-x melts by molecular-dynamics simulations
Hiroyuki Fujii, Michio Tokuyama
Physical Review E, 83, 2, 1, 8, Feb. 2011, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal

Simulation study of transport phenomena in supercooled Cu-Ti-Zr liquids
Hiroyuki Fujii, Michio Tokuyama
Proceedings of Eighth International Conference on Flow Dynamics, OS12-72, 618, 619, 2011, [Peer-reviewed]
English, International conference proceedings

Modeling light scattering of colloidal suspensions
Hiroyuki Fujii, えんじにあRing（北海道大学大学院工学研究院・工学院広報誌），特集「工学部100周年記念・未来のエンジニアリング ─100年後に向けて─」, 436, 03, Dec. 2024, [Invited], [Domestic magazines]
Hokkaido University Faculty of Engineering, Japanese, Introduction research institution, 42057385

Light scattering and propagation of biological tissues, agricultural products, and foods
Hiroyuki Fujii, えんじにあRing（北海道大学大学院工学研究院・工学院広報誌），特集「工学研究院若手教員奨励賞受賞者紹介」, Aug. 2023, [Invited], [Domestic magazines]
Hokkaido University Faculty of Engineering, Japanese, Introduction research institution

エタノール液滴のスプラッシュ発生に及ぼす蒸気の凝縮効果
澤井 冴, 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之, 流体工学部門講演会講演論文集, 2018, OS2-17, May 2019, [Peer-reviewed]
Japanese, Summary national conference

単一液滴衝突時に取り込まれる空気膜の観察
Riichiro Endo, Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, 流体工学部門講演会講演論文集, 2018, OS2-5, May 2019, [Peer-reviewed]
Japanese, Summary national conference

炉物理コードシステムCBZへのガラーキン求積法の実装
千葉豪, 藤井宏之, 日本原子力学会秋の大会予稿集(CD-ROM), 2018, ROMBUNNO.2M20, 20 Aug. 2018
Japanese

生体における光の輸送現象：輻射輸送方程式の数値計算と光トモグラフィへの応用に向けて
藤井 宏之, 第50回炉物理夏期セミナーテキスト, 39, 64, Aug. 2018
Japanese, Lecture materials

Numerical study of light scattering in the human neck for diagnosis of thyroid cancers by optical tomography
Fujii Hiroyuki, Yamada Yukio, Hoshi Yoko, Kobayashi Kazumichi, Watanabe Masao, Extended abstract of the 12th CME International Conference, OS12, 2, 2018
English, Summary international conference

分子動力学法を用いた高温壁へ衝突するナノ液滴の浮遊メカニズム解析
田部 広風海, 小林 一道, 矢口 久雄, 藤井 宏之, 渡部 正夫, マイクロ・ナノ工学シンポジウム, 2018.9, 30pm4PN16, 2018, [Peer-reviewed]
Japanese, Summary national conference

高温壁へ衝突する液滴の浮遊メカニズムに関する分子動力学解析
田部 広風海, 小林 一道, 矢口 久雄, 藤井 宏之, 渡部 正夫, 流体工学部門講演会講演論文集, 2018, OS2-1, 2018, [Peer-reviewed]
Japanese, Summary national conference

粘弾性乳液滴と固体表面の高速衝突の観察
伊藤 一樹, 芦田 拓, 渡部 正夫, 小林 一道, 藤井 宏之, 吉岡 孝一郎, 大井 航, 髙野 真, 流体工学部門講演会講演論文集, 2018, OS2-23, 2018, [Peer-reviewed]
Japanese, Summary national conference

低圧環境下における高速液滴衝突直後に発生するsplashの観察
芦田 拓, 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之, 流体工学部門講演会講演論文集, 2018, OS2-9, 2018, [Peer-reviewed]
Japanese, Summary national conference

Fine Droplets Generation Induced by Interactions between Focused Ultrasound and a Liquid Surface
Kazuya Seko, Kazumichi Kobayashi, Fujii Hiroyuki, Masao Watanabe, Japanese Journal of Multiphase Flow, 32, 1, 60, 64, 2018
Japanese, Introduction scientific journal

Numerical Calculation Of Time-resolved Light Reflectance From Biological Tissue Using The Radiative Transfer Equation
Hiroyuki Fujii, Yukio Yamada, Yoko Hoshi, Kazumichi Kobayashi, Masao Watanabe, Extended abstract of The International Conference on Mathematics in (bio)Chemical Kinetics and Engineering (MaCKiE) 2017, 2017
English, Summary international conference

拡散光による甲状腺腫瘍診断のためのヒト頸部内における光伝播の数値解析
藤井 宏之, 山田 幸生, 星 詳子, 小林 一道, 渡部 正夫, 第３３回近赤外フォーラム 講演論文集, I, 07, 2017
Japanese, Summary national conference

Laboratory of Fluid Dynamics, Division of Mechanical and Space Engineering, Faculty of Engineering, Hokkaido University
渡部 正夫, 小林 一道, 藤井 宏之, 混相流 = Japanese journal of multiphase flow, 30, 4, 408, 411, Dec. 2016
日本混相流学会, Japanese

Construction of an anatomical neck model for diffuse optical imaging
Naoyoshi Wakabayashi, Ken Nadamoto, Kazuki Kurihara, Shinpei Okawa, Koh Hashimoto, Hiroshi Kawaguchi, Yukari Tanikawa, Hiroyuki Fujii, Satoru Kohno, Yoko Hoshi, Eiji Okada, Optics InfoBase Conference Papers, 3, 18 Apr. 2016
OSA - The Optical Society, English

拡散光トモグラフィ－：現状と展望
Yoko Hoshi, Fujii Hiroyuki, Koh Hashimoto, The Review of Laser Engineering, 44, 4, 230, 234, Apr. 2016, [Peer-reviewed], [Invited]
レーザー学会, Japanese, Introduction scientific journal

Visualization of the Interior of the Human Body by Simulating Light Propagation
Hiroyuki Fujii, えんじにあRing（北海道大学大学院工学研究院・工学院広報誌），特集「命そして人間らしい生活を守る」, 405, 03, Jan. 2016, [Invited], [Domestic magazines]
Hokkaido University Faculty of Engineering, Japanese, Introduction research institution

蒸気と気体で満たされた球形気泡の収縮・膨張運動に関する分子気体力学解析
永山 貴大, 今 美沙紀, 小林 一道, 渡部 正夫, 藤井 宏之, 高比良 裕之, 流体工学部門講演会講演論文集, 2016, 0727, 2016, [Peer-reviewed]
Japanese, Summary national conference

Numerical analysis of photon migration in three-dimensional turbid media using the delta-Eddington approximation
Hiroyuki Fujii, Shinpei Okawa, Ken Nadamoto, Eiji Okada, Yukio Yamada, Yoko Hoshi, Masao Watanabe, Extended abstract of the 9th CME International Conference, OS6, 4, 2015
English, Summary international conference

反射衝撃波によって誘起される非凝縮性気体を伴う蒸気の凝縮現象に関する分子気体力学に基づく数値計算
永山 貴大, 藤井 宏之, 小林 一道, 渡部 正夫, 日本機械学会年次大会, 2015, J0540205, 2015
Japanese, Summary national conference

シリンジを用いた高速液滴射出装置の開発および液滴衝突の観察
片岡 豊, 堀 優作, 渡部 正夫, 小林 一道, 藤井 宏之, 日本機械学会年次大会, 2015, G0500203, 2015
Japanese, Summary national conference

異なる境界条件を課した生体モデルにおける光伝播の数値解析
服部 聖仁, 藤井 宏之, 小林 一道, 渡部 正夫, 日本機械学会年次大会, 2015, J2410103, 2015
Japanese, Summary national conference

固体壁面の濡れ性が液滴衝突により発生する流れの進展挙動に与える影響の観察
山口 陽平, 渡部 正夫, 小林 一道, 藤井 宏之, 真田 俊之, 流体工学部門講演会講演論文集, 2015, 317, 2015, [Peer-reviewed]
Japanese, Summary national conference

低圧環境下での高速液滴衝突によるSplash発生の観察
東 稜, 渡部 正夫, 小林 一道, 藤井 宏之, 流体工学部門講演会講演論文集, 2015, 318, 2015, [Peer-reviewed]
Japanese, Summary national conference

シリンジを用いた高速微細液滴射出装置の開発
堀 優作, 片岡 豊, 渡部 正夫, 小林 一道, 藤井 宏之, 流体工学部門講演会講演論文集, 2015, 319, 2015, [Peer-reviewed]
Japanese, Summary national conference

エタノール液滴と固体壁の衝突現象に周囲気体種が及ぼす影響
磯野 俊悠, 渡部 正夫, 小林 一道, 藤井 宏之, 日本機械学会年次大会, 2015, G0500202, 2015
Japanese, Summary national conference

生体光イメージングのためのヒト頸部内光伝播モデルの構築
藤井 宏之, 大川 晋平, 灘本 健, 岡田 英史, 山田 幸生, 星 詳子, 渡部 正夫, バイオエンジニアリング講演会講演論文集, 2015.27, 1G21, Jan. 2015
Japanese, Summary national conference

ヒト生体イメージングを目指した革新的バイオフォトニクス技術の構築
岡田英史, 大川晋平, 谷川ゆかり, 吉永哲哉, 藤井宏之, 藤本憲市, 橋本康, 岩瀬正, 河野理, 星詳子, 日本生体医工学会大会プログラム・論文集(CD-ROM), 53rd, ROMBUNNO.SY3-02-2, 2014
Japanese

拡散光トモグラフィのための輻射輸送方程式及び拡散方程式を用いた光学特性値再構成アルゴリズムの開発
Hiroyuki Fujii, Yoko Hoshi, Shinpei Okawa, Tomoya Kosuge, Satoru Kohno, 理論応用力学講演会 講演論文集, 62, OS05-08, Mar. 2013, [Peer-reviewed]
Japanese, Summary national conference

輻射輸送方程式を用いた生体内光伝搬の数理モデル構築
藤井 宏之, 星 詳子, 大川 晋平, 小菅 朋也, 河野 理, 日本物理学会講演概要集, 67.2.2, 20pAK-9, 2012
Japanese, Summary national conference

28aPS-76 Study of Displacement-Displacement Correlation Function on Mettalic-Glass Former Cu_<60>Ti_<20>Zr_<20>
Fujii H., Tokuyama M., Meeting abstracts of the Physical Society of Japan, 64, 2, 238, 238, 18 Aug. 2009
The Physical Society of Japan (JPS), Japanese

Biomedical Optical Imaging -Fundamentals and Clinical Applications
Hiroyuki Fujii, Sections 1.3 and 2.5
NTS Inc., Dec. 2021, 9784860437299, Japanese, Scholarly book, 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！, [Peer-reviewed], [Joint work]

Advanced Fluids Engineering　　　　　　　　　　　　　　　
Hokkaido University
Jun. 2023 - Present, Postgraduate courses

Mechatoronics exercise　　　　　　　　　　　　　　　
Hokkaido University
Oct. 2021 - Present

ラボラトリーセミナー　　　　　　　　　　　　　　　
北海道大学
2015 - Present

熱流体力学演習Ⅱ　　　　　　　　　　　　　　　
北海道大学
2015 - Present

応用数学演習Ⅱ　　　　　　　　　　　　　　　
北海道大学
2016 - 2020

工学的創成実験　　　　　　　　　　　　　　　
北海道大学
2015 - 2016

計測工学実験　　　　　　　　　　　　　　　
北海道大学
2014 - 2015

Apr. 2022 - Present
The Optical Society of Japan

Apr. 2020 - Present
The Heat Transfer Society of Japan　　　　　　　　　　　　　　　

May 2014 - Present
THE JAPAN SOCIETY OF MECHANICAL ENGINEERS　　　　　　　　　　　　　　　

Second-by-second coagulation control system for highly concentrated colloids based on multiple light scattering and fluorescence response
Grants-in-Aid for Scientific Research
Apr. 2025 - Mar. 2028
Yoshito Saito, Hiroyuki Fujii
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Niigata University, Coinvestigator, 25K02127

Evaporation coefficient of nanoparticle suspension
Grants-in-Aid for Scientific Research
Apr. 2024 - Mar. 2028
Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Coinvestigator, 24K00797

Elucidation of the mechanism of splash suppression due to the condensation effect when a droplet impinges on a solid surface in a vapor
Grants-in-Aid for Scientific Research
Apr. 2024 - Mar. 2026
Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Coinvestigator, 23K26027

Interference effects caused by multiple scattering of the near-infrared electric fields in super-concentrated solutions
Grants-in-Aid for Scientific Research
Apr. 2023 - Mar. 2026
Hiroyuki Fujii
Japan Society for the Promotion of Science, Fund for the Promotion of Joint International Research (Fostering Joint International Research (A)), Hokkaido University, Principal investigator, 22KK0243

Model equations for extracting optical absorption components from photoacoustic signals
Research grant
Apr. 2023 - Mar. 2025
Hiroyuki Fujii
NAKATANI Foundation, Hokkaido University, Principal investigator, Competitive research funding

Near-infrared spectroscopy using scattered light for non-destructive evaluation of food qualities
Consortium-forming Robust Agriculture, Forestry and Fisheries Engineering Research Program
Apr. 2023 - Mar. 2024
Hiroyuki Fujii, Goro Nishimura
Hokkaido University, Public offering, Hokkaido University, Principal investigator

Nondestructive measurement of ingredients inside stuffed bread using light
Research fund
Aug. 2022 - Jul. 2023
Hiroyuki Fujii
The Public Foundation of Elizabeth Arnold一Fuji, Hokkaido University, Principal investigator

Study of the c orrelation between structural and light scattering properties in soybean curd for nondestructive monitoring
Research promotion
Jun. 2022 - Apr. 2023
Hiroyuki Fujii
Takano Life Science Research Foundation, Principal investigator, Competitive research funding

Numerical study of light and photoacoustic propagation in the human neck for photoacoustic imaging
Research promotion
Feb. 2022 - Apr. 2023
Hiroyuki Fujii
The Uehara Memorial Foundation, Principal investigator

Multiphysics modeling of light scattering, light fluctuation, and particle diffusion in colloidal suspensions
Grants-in-Aid for Scientific Research
Oct. 2021 - Mar. 2023
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, Grant-in-Aid for Transformative Research Areas (A) (Publicly Offered Research), Hokkaido University, Principal investigator, Competitive research funding, 21H05577

Elucidation of non-equilibrium phase change at gas-liquid interface mechanism for mixture gas and its application to molecular multi-phase fluid dynamics
Grants-in-Aid for Scientific Research
Apr. 2020 - Mar. 2023
Kazumichi Kobayashi, Hiroyuki Fujii, Masao Watanabe
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．
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Coinvestigator, 20K04277

Similarity of a splash at high Ohnesorge liquid drop impact on a solid surface
Grants-in-Aid for Scientific Research
Apr. 2020 - Mar. 2023
Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii, Toshiyuki Sanada
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, Grant-in-Aid for Scientific Research (B), Hokkaido University, Coinvestigator, 20H02061

Interference effects on radiative transfer in dense colloidal suspensions
Grants-in-Aid for Scientific Research
Apr. 2020 - Mar. 2023
Hiroyuki Fujii, Kazumichi Kobayashi, Masao Watanabe, Goro Nishimura
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。
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Principal investigator, 20H02076

A high-sensitive time-domain method to identify fluorescence targets in thick biological tissue
Grants-in-Aid for Scientific Research
Apr. 2019 - Mar. 2023
Goro Nishimura, Hiroyuki Fujii
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, Grant-in-Aid for Scientific Research (C), Hokkaido University, Coinvestigator, 19K04421

Investigation of active matter mechanics by surface plasmon resonance observation
Grants-in-Aid for Scientific Research
Jun. 2018 - Mar. 2023
Masao Watanabe, Kazumichi Kobayashi, Hiroyuki Fujii
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, Grant-in-Aid for Challenging Research (Exploratory), Hokkaido University, Coinvestigator, 18K18816

Modeling of light and pressure propagation in biological tissue volumes for photoacoustic imaging
研究助成（一般）
Jul. 2020 - Mar. 2021
Hiroyuki Fujii
The AKIYAMA LIFE SCIENCE FOUNDATION, Principal investigator

Study of interference of the radiative transfer induced by local and global structures of biological tissues and development of theoretical calculations of the light scattering properties
Grants-in-Aid for Scientific Research
Apr. 2018 - Mar. 2021
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, Grant-in-Aid for Early-Career Scientists, Hokkaido University, Principal investigator, 18K13694

Surrounding gas effects on instability at solid-gas-liquid three-phase contact line in high-speed liqdui film flow
Grants-in-Aid for Scientific Research
Apr. 2017 - Mar. 2020
Watanabe Masao, Toshiyuki Sanada, Kazumichi Kobayashi, Hiroyuki Fujii
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Coinvestigator, 17H03168

Nondestructive measurement of bread qualities using the near-infrared light
Research fund
Jul. 2019 - Feb. 2020
Hiroyuki Fujii
THE PUBLIC FOUNDATION OF ELIZABETH ARNOLD‐FUJI, Principal investigator, Competitive research funding

Improvement of light propagation model for thyroid cancer diagnosis by optical computed tomography
The 2017 Research Grant
Mar. 2018 - Mar. 2019
Fujii Hiroyuki
The Okawa Foundation for Information and Telecommunications, Principal investigator, Competitive research funding

Determination of kinetic boundary conditions for gas-vapor binary mixture and its application
Grants-in-Aid for Scientific Research
Apr. 2016 - Mar. 2019
Kobayashi Kazumichi, Hiroyuki Fujii, Masao Watanabe, 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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Coinvestigator, 16K06064

Development of monitoring system of oxygenated hemoglobin supply to fetus and placenta based on propagation of light and acoustic wave
Grants-in-Aid for Scientific Research
Apr. 2015 - Mar. 2018
Okawa Shinpei, Hiroyuki Fujii, Hirasawa Takeshi, 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, Grant-in-Aid for Scientific Research (C), National Defense Medical College, Coinvestigator, 15K06125

Determination of optical properties for biological tissue based on radiative transport model in fine structure of biological tissue
Grants-in-Aid for Scientific Research
Apr. 2015 - Mar. 2018
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, Principal investigator, 15K17980

Non-destructive evaluation of the white bread qualities using diffuse optical tomography
Research Grant / Funabashi Shigeaki Memorial Encouragement Grant
Jul. 2016 - Apr. 2017
Fujii Hiroyuki
THE PUBLIC FOUNDATION OF ELIZABETH ARNOLD‐FUJI, Hokkaido University, Principal investigator, Competitive research funding

Examination of the relation between light scattering and structures for agricultural products by diffuse optical tomography
Research grant
Jul. 2016 - Mar. 2017
Fujii Hiroyuki
The AKIYAMA LIFE SCIENCE FOUNDATION, Principal investigator, Competitive research funding

Condensation effect on high-speed liquid-film flow instability at a liquid-droplet impact on a solid surface in a vaporous environment
Grants-in-Aid for Scientific Research
Apr. 2014 - Mar. 2017
Masao Watanabe, Toshiyuki Sanada, Kazumichi Kobayashi, Hisao Yaguchi, Hiroyuki Fujii
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Coinvestigator, 26289031

Study of unsteady heat and mass transfer at the strong non-equilibrium interface ugin mean-field kinetic theory
Grants-in-Aid for Scientific Research
Apr. 2014 - Mar. 2016
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, Coinvestigator, 26630043

Non-destructive evaluation of the melon qualities by near-infrared imaging
フードイノベーション創造支援事業
Jul. 2015 - Feb. 2016
藤井 宏之
Northern Advancement Center for Science & Technology, Principal investigator, Competitive research funding

Cancer detection of the human neck by noninvasive optical imaging
Promotion for Young Research Talent and Network
Aug. 2014 - Feb. 2015
Fujii Hiroyuki
Northern Advancement Center for Science & Technology, Principal investigator, Competitive research funding