Fujitani, Youhei

写真a

Affiliation

Faculty of Science and Technology, Department of Applied Physics and Physico-Informatics (Yagami)

Position

Professor
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Career 【 Display / hide 】

  • 1985.05
    -
    Present

    医師国家試験合格（医籍292547）

  • 1994.10
    -
    1995.12

    国立予防衛生研究所 ,主任研究官

  • 1995.01
    -
    1995.12

    東京大学医学部 ,客員研究員

  • 1995.12
    -
    1997.03

    Leiden大学化学研究所物理化学高分子化学研究部門 （オランダ政府奨学生） ,博士研究員

  • 1997.04
    -
    2002.03

    慶應義塾大学理工学部 ,専任講師

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Academic Background 【 Display / hide 】

  • 1985.03

    The University of Tokyo, Faculty of Medicine, 医学科

    University, Graduated

  • 1989.03

    The University of Tokyo, Graduate School, Division of Medicine, 第１基礎医学専攻

    Graduate School, Completed, Doctoral course

  • 1991.03

    The University of Tokyo, Faculty of Science, 物理学科

    University, Graduated

  • 1993.03

    The University of Tokyo, Graduate School, Division of Science, 物理学専攻

    Graduate School, Completed, Master's course

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Academic Degrees 【 Display / hide 】

  • Medicine　, The University of Tokyo, 1989.03

  • Science, The University of Tokyo, 1995.10

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Licenses and Qualifications 【 Display / hide 】

  • 医師免許, 1985

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Papers 【 Display / hide 】

  • Fluctuation amplitudes of a trapped particle in a near-critical binary fluid mixture

    Fujitani Y.

    Physics of Fluids 37 ( 4 )  2025.04

    ISSN  10706631

    　View Summary

    We assume that a binary fluid mixture, lying in the one-phase region near the demixing critical point, contains a Brownian particle trapped by a harmonic potential. A mixture component, preferred by the particle surface via a short-range interaction, concentrates near the surface to generate a thick adsorption layer. This layer, deformed by particle motion, increases the effective mass and restoring force, thereby reducing the equal-time correlation of the fluctuations of the particle position and that of the particle velocity. We calculate these fluctuation amplitudes using the reversible part of hydrodynamics on the basis of the free-energy density of a local functional theory, which is known to describe the critical properties well. The effects of the preferential adsorption are negligible when the stiffness of the trapping potential is sufficiently large. A typical stiffness below which the effects emerge is largely determined by the strength of preferential adsorption and shifts toward larger stiffness as the adsorption is stronger. Plots of the fluctuation amplitudes against the stiffness are approximately independent of the deviation of the temperature from the critical temperature. These properties should facilitate future experimental studies on this phenomenon.

  • Force density induced by preferential adsorption in a near-critical binary fluid mixture subject to the Soret effect

    Fujitani Y.

    Journal of Chemical Physics 161 ( 20 )  2024.11

    ISSN  00219606

    　View Summary

    We assume that two parallel plates are immersed in a binary fluid mixture lying in the one-phase region near the demixing critical point and that the surface of each plate attracts the mixture components differently via short-range interactions. It is known that the composition inhomogeneity caused by the difference can induce a force exerted on the plate at equilibrium. In the present study, we investigate how a temperature gradient imposed vertically on the plates changes the induced force by calculating the composition profile subject to the Soret effect. Numerically solving the derived differential equation, we show that a temperature gradient within the critical regime can change the force distinctly from its equilibrium value and can make the force direction opposite to the one at equilibrium.

  • Thermo-osmosis of a near-critical binary fluid mixture: A general formulation and universal flow direction

    Shunsuke Yabunaka and Youhei Fujitani

    Physical Review E (American Physical Society)  109 ( 6 ) 064610 2024.06

    Research paper (scientific journal), Last author, Corresponding author, Accepted,  ISSN  24700045

    　View Summary

    We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point, and study its transport through a capillary tube linking two large reservoirs. We assume that short-range interactions cause preferential adsorption of one component onto the tube's wall. The adsorption layer can become much thicker than the molecular size, which enables us to apply hydrodynamics based on a coarse-grained free-energy functional. For transport processes induced by gradients of the pressure, composition, and temperature along a cylindrical tube, we obtain the formulas of the Onsager coefficients to extend our previous results on isothermal transport, assuming the critical composition in the middle of each reservoir in the reference equilibrium state. Among the processes, we focus on thermo-osmosis - mass flow due to a temperature gradient. We explicitly derive a formula for the thermal force density, which is nonvanishing in the adsorption layer and causes thermo-osmosis. This formula for a near-critical binary fluid mixture is an extension of the conventional formula for a one-component fluid, expressed in terms of local excess enthalpy. We predict that the direction of thermo-osmotic flow of a mixture near the upper (lower) consolute point is the same as (opposite to) that of the temperature gradient, irrespective of which component is adsorbed on the wall. Our procedure would also be applied to dynamics of a soft material, whose mesoscopic inhomogeneity can be described by a coarse-grained free-energy functional.

  • Preferential adsorption in a near-critical binary fluid mixture as analyzed in the framework of the non-random two-liquid model

    Youhei Fujitani

    Fluid Phase Equilibria (Elsevier)  580   114050 2024.05

    Research paper (scientific journal), Single Work, Lead author, Accepted,  ISSN  03783812

    　View Summary

    We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point. Short-range interactions between the mixture components and a solid surface in contact with the mixture can make the mixture composition inhomogeneous significantly near the surface. This inhomogeneity has been shown to cause various phenomena by using the renormalized local functional theory. In its free-energy density, the order-parameter field is coarse-grained without rescaled and only the most singular part is specified. In the present study, on the basis of the crossover theory, we introduce a square-gradient term to the free-energy density of the extended non-random two-liquid model, which includes more than the most singular part. Thanks to similarity between the renormalized local functional theory and the crossover theory, the relationship between the two free-energy densities can be clarified. Supposing a mixture of nitroethane and 3-methylpentane and a mixture of 2,6-lutidine and water, we use the proposed free-energy density to calculate the inhomogeneous composition profile numerically. The free-energy density also enables us to calculate excess densities of entropy and enthalpy, unlike that of the renormalized local functional theory. We also find that the magnitude of the thermal force density, which is induced by a temperature gradient to cause flow in thermoosmosis, can depend on the calculation procedures significantly.

  • Effects of the preferential adsorption in a near-critical binary fluid mixture on dynamics of a droplet

    Youhei Fujitani

    Physics of Fluids (American Institute of Physics)  34 ( 9 ) 092007 2022.09

    Research paper (scientific journal), Single Work, Lead author, Accepted,  ISSN  10706631

    　View Summary

    A binary fluid mixture in the homogeneous phase near the demixing critical point can include a small spherical droplet of a third fluid-component confined by a sharp interface. Conversely, a droplet consisting of the mixture can be included in the third fluid-component. The third component is assumed to attract one mixture component more than the other via short-range interactions. The adsorption layer, enriched with the preferred component, appears on the mixture side of the interface and can thicken significantly. The preferential adsorption causes the drag coefficient to deviate. We use the hydrodynamics based on a coarse-grained free-energy functional to calculate the deviation, neglecting the weak singularity of mixture viscosity. When the mixture lies inside the droplet, the ratio of the deviation changes nonmonotonically as the ratio of the ambient viscosity to the droplet viscosity increases. When the mixture lies outside, the former ratio increases with the latter ratio and can be considerably larger for a droplet than for a rigid sphere. Then, if a composition gradient is imposed, a force-free droplet undergoes diffusiophoresis, whose mobility can be considerably larger in magnitude than that of a rigid sphere. We also discuss probable power-law dependences of the drag coefficient and the mobility on the reduced temperature. The suggested power for the mobility is connected with the universal order-parameter profile in the surface critical behavior.

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Papers, etc., Registered in KOARA 【 Display / hide 】

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Presentations 【 Display / hide 】

  • Diffusiophoresis of a colloidal particle in a near-critical binary fluid mixture

    Youhei Fujitani

    7th International Soft Matter Conference (Osaka) , 

    2023.09
    , 

    Poster presentation

  • Diffusiophoresis near a critical point of a binary fluid mixture

    Youhei Fujitani and Shunsuke Yabunaka

    28th International Conference on Statistical Physics (Tokyo) , 

    2023.08
    , 

    Oral presentation (general)

  • 相分離臨界点近くの一様相にある二成分流体中のコロイド粒子の拡散泳動

    藤谷洋平、藪中俊介

    日本物理学会年秋季大会 (東京) , 

    2022.09
    , 

    Oral presentation (general), 日本物理学会

  • 相分離臨界点近くの二成分流体において選択的親和性のないコロイド剛体球の自己拡散係数

    藤谷洋平

    日本物理学会年次大会 (福岡) , 

    2020.03
    , 

    Poster presentation, 日本物理学会

  • 相分離臨界点近くの二成分流体膜にあって膜粘性の異なる円形液体領域の抵抗係数

    谷文之、藤谷洋平

    日本物理学会第74回年次大会 (九州大学伊都キャンパス) , 

    2019.03
    , 

    Poster presentation

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Works 【 Display / hide 】

  • 物理数学の手引き

    FUJITANI YOUHEI

    2004.04
    -
    Present
    , 

    Other, Single

    　View Details

    学部講義「数理物理」・大学院講義「応用数理解析」の講義ノートを拡張して，180ページあまりの冊子としTex製本して，講義に活用した．ただし，出版社を介してはおらず非売品である．

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Courses Taught 【 Display / hide 】

  • STATISTICALMECHANICS

    2025

  • PRESENTATION TECHNIQUE

    2025

  • MATHEMATICS OF DISTRIBUTED SYSTEMS

    2025

  • LABORATORY IN SCIENCE

    2025

  • INDEPENDENT STUDY ON FUNDAMENTAL SCIENCE AND TECHNOLOGY

    2025

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Memberships in Academic Societies 【 Display / hide 】

  • 日本物理学会, 

    1990.03
    -
    Present
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Committee Experiences 【 Display / hide 】

  • 2016.04
    -
    Present

    Associate Editor, Journal of the Physical Society of Japan

  • 2011.09
    -
    2013.03

    会誌編集委員, 日本物理学会

  • 2006.05
    -
    2007.04

    領域12世話人, 日本物理学会

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