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 】

  • Drag coefficient of a liquid domain with distinct viscosity in a fluid membrane

    TANI HISASI, FUJITANI YOUHEI

    Journal of Fluid Mechanics （Journal of Fluid Mechanics)  836   910 - 931 2018.02

    Research paper (scientific journal), Joint Work, Accepted,  ISSN  00221120

    　View Summary

    © 2017 Cambridge University Press. We calculate the drag coefficient of a circular liquid domain in a flat fluid membrane surrounded by three-dimensional fluids on both sides. The coefficient of a rigid disk is well known, while that of a circular liquid domain is also well known when the membrane viscosity inside the domain equals the one outside the domain. As the ratio of the former viscosity to the latter increases to infinity, the drag coefficient of a liquid domain should approach that of the disk of the same size in the same ambient viscosities. This approach has not yet been shown explicitly, however. When the ratio is not unity, the continuity of the stress makes the velocity gradient discontinuous across the domain perimeter in the membrane. On the other hand, the velocity gradient is continuous in the ambient fluids, whose velocity field should agree with that of the membrane as the spatial point approaches the membrane. This means that we need to assume dipole singularity along the domain perimeter in solving the governing equations unless the ratio is unity. In the present study, we take this singularity into account and obtain the drag coefficient of a liquid domain as a power series with respect to a dimensionless parameter, which equals zero when the ratio is unity and approaches unity when the ratio tends to infinity. As the parameter increases to unity, the sum of the series is numerically shown to approach the drag coefficient of the disk.

  • Osmotic effects on dynamics of a colloidal rigid sphere in a near-critical binary fluid mixture

    Fujitani Y.

    Journal of the Physical Society of Japan （Journal of the Physical Society of Japan)  87 （ 8 ）  2018

    ISSN  00319015

    　View Summary

    ©2018 The Physical Society of Japan. When a rigid spherical particle is put in a binary fluid mixture lying in the homogeneous phase near the demixing critical point, one of the fluid components is expected to be significantly concentrated around the particle because it is attracted preferentially by the particle surface. The resultant gradient of the mixture composition causes an additional pressure including osmotic pressure. We study how this pressure changes the particle motion by using the Gaussian free-energy functional for the mixture and assuming a correlation length much smaller than the particle size. The drag coefficient in this situation was calculated in the regime of sufficiently weak preferential attraction in a previous study [R. Okamoto, Y. Fujitani, and S. Komura, J. Phys. Soc. Jpn. 82, 084003 (2013)]. We here devise a new procedure beyond the regime to calculate the drag coefficient and the long-time tail of the velocity correlation of the particle. Our results cannot be explained totally by effective enlargement of the particle due to the layer rich in the preferred component.

  • Drag coefficient of a circular inclusion in a near-critical binary fluid membrane

    Tani H., Fujitani Y.

    Journal of the Physical Society of Japan （Journal of the Physical Society of Japan)  87 （ 10 ）  2018

    ISSN  00319015

    　View Summary

    © 2018 The Physical Society of Japan. We calculate the drag coefficient of a circular liquid domain, which is placed in a flat fluid membrane composed of a binary fluid mixture lying in the homogeneous phase near the demixing critical point. Assuming a sufficiently small correlation length, we regard the domain dynamics as independent of the critical fluctuation and use the Gaussian free-energy functional for the mixture. Because of the near-criticality, the preferential attraction between the domain component and one of the mixture components generates a significant composition gradient outside the domain, which can affect the drag coefficient. We first consider a domain having the same membrane viscosity as the domain exterior. The drag coefficient is expanded with respect to a dimensionless strength of the preferential attraction. It is numerically shown that the magnitude of the expansion coefficient markedly decreases as the order of the strength increases and that the first-order term of the series usually gives a good approximation for practical material constants. The effect of the preferential attraction is shown to be able to become significantly large in practice. We secondly consider cases where the membrane viscosities of the domain interior and exterior are different. The first-order term of the expansion series decreases to approach zero as the domain viscosity increases to infinity. This agrees with previous numerical results showing that the hydrodynamics makes the effect of the preferential attraction negligibly small for a rigid disk.

  • Osmotic suppression of positional fluctuation of a trapped particle in a near-critical binary fluid mixture in the regime of the Gaussian model

    FUJITANI YOUHEI

    Journal of the Physical Society of Japan 86   114602 2017.11

    Research paper (scientific journal), Single Work, Accepted

  • Undulation Amplitude of a Fluid Membrane in a Near-Critical Binary Fluid Mixture Calculated beyond the Gaussian Model Supposing Weak Preferential Attraction

    FUJITANI YOUHEI

    Journal of the Physical Society of Japan （日本物理学会)  86   044602 2017

    Research paper (scientific journal), Single Work, Accepted

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

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Presentations 【 Display / hide 】

  • 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 (general)

  • 臨界点近くの2成分混合系中のコロイドの抵抗係数

    薮中俊介、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, Oral Presentation(general)

  • Drag coefficient of a Circular Liquid Domain in a Near-Critical Binary Fluid Membrane

    Youhei Fujitani

    Soft matter physics; from the perspective of the essential heterogeneity (Nishijin Plaza, Kyushuu University) , 2018.12, Oral Presentation(general)

  • 相分離臨界点近くの一様相にある二成分流体におけるコロイド粒子の動力学への浸透圧の影響

    FUJITANI YOUHEI

    日本物理学会年次大会 (東京理科大（野田）) , 2018.03, Poster (general)

  • 壁に囲まれた三次元流体中の流体膜において内外の膜粘性の異なる円形液体領域の抵抗係数

    TANI HISASIFUJITANI YOUHEI

    日本物理学会秋季大会 (岩手大学) , 2017.09, Poster (general)

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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 】

  • THERMAL PHYSICS

    2021

  • STATISTICALMECHANICS

    2021

  • PRESENTATION TECHNIQUE

    2021

  • MATHEMATICAL METHODS IN THE PHYSICAL SCIENCES

    2021

  • INDEPENDENT STUDY ON FUNDAMENTAL SCIENCE AND TECHNOLOGY

    2021

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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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