藤谷 洋平 (フジタニ ヨウヘイ)

Fujitani, Youhei

写真a

所属(所属キャンパス)

理工学部 物理情報工学科 (矢上)

職名

教授

経歴 【 表示 / 非表示

  • 1985年05月
    -
    継続中

    医師国家試験合格(医籍292547)

  • 1994年10月
    -
    1995年12月

    国立予防衛生研究所 ,主任研究官

  • 1995年01月
    -
    1995年12月

    東京大学医学部 ,客員研究員

  • 1995年12月
    -
    1997年03月

    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年04月
    -
    2002年03月

    慶應義塾大学理工学部 ,専任講師

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学歴 【 表示 / 非表示

  • 1985年03月

    東京大学, 医学部, 医学科

    大学, 卒業

  • 1989年03月

    東京大学, 医学研究科, 第1基礎医学専攻

    大学院, 修了, 博士

  • 1991年03月

    東京大学, 理学部, 物理学科

    大学, 卒業

  • 1993年03月

    東京大学, 理学系研究科, 物理学専攻

    大学院, 修了, 修士

学位 【 表示 / 非表示

  • 医学 , 東京大学, 1989年03月

  • 理学 , 東京大学, 1995年10月

免許・資格 【 表示 / 非表示

  • 医師免許, 1985年

 

論文 【 表示 / 非表示

  • 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年06月

    研究論文(学術雑誌), 最終著者, 責任著者, 査読有り

  • 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年05月

    研究論文(学術雑誌), 単著, 筆頭著者, 査読有り,  ISSN  03783812

     概要を見る

    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年09月

    研究論文(学術雑誌), 単著, 筆頭著者, 査読有り

     概要を見る

    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.

  • Diffusiophoresis in a near-critical binary fluid mixture

    藤谷洋平

    Physics of Fluids (Physics of Fluids)  34 ( 4 ) 041701 2022年04月

    査読有り,  ISSN  10706631

     概要を見る

    We consider placing a rigid spherical particle into a binary fluid mixture in the homogeneous phase near the demixing critical point. The particle surface is assumed to have a short-range interaction with each mixture component and to attract one component more than the other. Owing to large osmotic susceptibility, the adsorption layer, where the preferred component is more concentrated, can be of significant thickness. This causes a particle motion under an imposed composition gradient. Thus, diffusiophoresis emerges from a mechanism which has not been considered so far. We calculate how the mobility depends on the temperature and particle size.

  • Isothermal transport of a near-critical binary fluid mixture through a capillary tube with the preferential adsorption

    藪中俊介、藤谷洋平

    Physics of Fluids (Physics of Fluids)  34 ( 5 ) 052012 2022年03月

    研究論文(学術雑誌), 共著, 最終著者, 査読有り,  ISSN  10706631

     概要を見る

    We study isothermal transport of a binary fluid mixture, which lies in the homogeneous phase near the demixing critical point, through a capillary tube. A short-range interaction is assumed between each mixture component and the tube's wall surface, which usually attracts one component more than the other. The resulting preferential adsorption becomes significant owing to large osmotic susceptibility. The mixture flowing out of the tube is rich in the preferred component when flow is driven by the pressure difference between the reservoirs. When flow is driven by the mass-fraction difference, the total mass flow occurs in the presence of the preferential adsorption. These phenomena can be regarded as cross-effects linked by the reciprocal relation. The latter implies that diffusioosmosis arises from the free energy of the bulk of the mixture not involving the surface potential, unlike usual diffusioosmosis far from the critical point. We also study these phenomena numerically by using the hydrodynamics based on the coarse-grained free-energy functional, which was previously obtained to reveal near-critical static properties, and using material constants that were previously obtained in some experimental studies. Influence of the critical enhancement of the transport coefficients is found to be negligible because of off-critical composition in the tube. It is also shown that the conductance, or the total mass flow rate under a given mass-fraction difference, can change non-monotonically with the temperature. The change is well expected to be large enough to be detected experimentally.

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KOARA(リポジトリ)収録論文等 【 表示 / 非表示

研究発表 【 表示 / 非表示

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

    Youhei Fujitani

    7th International Soft Matter Conference (Osaka) , 

    2023年09月

    ポスター発表

  • Diffusiophoresis near a critical point of a binary fluid mixture

    Youhei Fujitani and Shunsuke Yabunaka

    28th International Conference on Statistical Physics (Tokyo) , 

    2023年08月

    口頭発表(一般)

  • 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年09月

    口頭発表(一般), 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年03月

    ポスター発表, 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年03月

    ポスター発表

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Works 【 表示 / 非表示

  • 物理数学の手引き

    藤谷 洋平

    2004年04月
    -
    継続中

    その他, 単独

     発表内容を見る

    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.

 

担当授業科目 【 表示 / 非表示

  • 統計物理

    2024年度

  • 古典流体の緩和過程

    2024年度

  • プレゼンテーション技法

    2024年度

  • 分布系の数理

    2024年度

  • 自然科学実験

    2024年度

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所属学協会 【 表示 / 非表示

  • 日本物理学会, 

    1990年03月
    -
    継続中

委員歴 【 表示 / 非表示

  • 2016年04月
    -
    継続中

    Associate Editor, Journal of the Physical Society of Japan

  • 2011年09月
    -
    2013年03月

    会誌編集委員, 日本物理学会

  • 2006年05月
    -
    2007年04月

    領域12世話人, 日本物理学会