横山悦郎（よこやまえつろう）[教授]

Etsuro Yokoyama [Professor]

【略歴】
　1989年　日本学術振興会特別研究員PD
　1990年　アメリカ合衆国カーネギ・メロン大学物理学科博士研究員
　1992年　九州工業大学情報工学部助手
　1993年　山口大学工学部助教授
　2002年　現職に至る

理学博士（北海道大学)

【専門分野】
結晶成長理論　Crystal Growth (Theory)

【担当授業科目】
初等情報処理１・２
マルチメディア論１・２
数値解析及び計算機II（物理学科開講）
現代科学（理学部開講）

【研究概要】
主な研究テーマは，様々な環境条件に応じて千差万別に成長する結晶の形態（パターン）が出来る上がる仕組を， 数理モデルを作って理論的・数値解析的に解明することである． 特色としては，実験グループと積極的に共同研究を進める． 例えば，宇宙ステーション「きぼう」における微小重力環境を使った過冷却水中での氷結晶の形態形成，隕石中に含まれるコンドリュールという鉱物の形成などの共同研究を行ってきた。 また情報系の研究者とは画像解析の新しい手法・開発などの共同研究も行ってきた． 更に、数学者との共同研究では，分子的尺度で平坦な結晶面（ファセット面）において不均一な過飽和度が存在する場合の安定な成長の厳密な取り扱いを数学的・数値解析的に考察した． その他、結晶成長の分野にとどまらず，ろうそくの炎の振動現象など，様々な振動現象・パターン形成の数理モデル確立も研究テーマのひとつである．

[Research Interests]
The morphological prediction of a crystal is interdisciplinary and is related to various subjects, transport and diffusion phenomena, physical chemistry of surface and interface, nucleation, chemical reactions, convection surrounding a crystal, and phase transformation, which involves a lot of mathematical problems. The formation of patterns during the growth of a crystal is a free-boundary problem in which the interface that separates the crystal from a nutrient phase moves under the influence of nonequilibrium conditions. The resulting patterns depend markedly on conditions in the nutrient phase, e.g. temperature and concentration, which influence the growth speed of each element of the interface. Furthermore, the growth speed of each element also depends on the local geometry of the interface, specifically on the interface curvature and the orientation of the interface relative to the crystal axes.

My recent subjects are as follows:

  1. We study the appearance of an asymmetrical pattern for a disk crystal of ice growing from supercooled water by using an analysis of growth rates for radius and thickness. The growth of the radius is controlled by transport of latent heat and is calculated by solving the diffusion equation for the temperature field surrounding the disk. The growth of the thickness is governed by the generation of steps. Symmetry breaking with respect to the basal plane of an ice disk crystal can be observed when the thickness reaches a critical value; then one basal face becomes larger than the other and the disk loses its cylindrical shape. Subsequently, morphological instability occurs at the edge of the larger basal face of the asymmetrical shape We show that the critical thickness is related to the critical condition for the stable growth of a basal face.
  2. We study the time dependent behavior of local slope density on the growing macroscopically flat facet under a given nonuniformity in supersaturation along the surface by means of the characteristics for a first order partial differential equation of growing surface and show that the asymptotic behavior of local slope density can be determined by the variation of reciprocal of supersaturation under the conditions of stability.
  3. We propose a model of self-oscillatory growth to explain the appearance of patterns with period structures during growth of a crystal under constant external conditions, such as temperature, concentration and convection. The model takes into account a hysteresis behavior of interface kinetic processes at a rate determined by the deviation from the local equilibrium temperature. Self-oscillatory growth occurs because of the coupling of interface kinetics to the transport of latent heat from the interface under constant growth conditions.
  4. Chondrules are small particles of silicate material of the order of a few millimeters in radius, and are the main component of chondritic meteorite. We present a model of the growth starting from a seed crystal at the location of an outer part of pure melt droplet into spherical single crystal corresponding to a chondrule. The formation of rims surrounding a chondrule during solidification is simulated by using the phase field model in three dimensions. Our results display a well developed rim structure when we choose the initial temperature of a melt droplet more than the melting point under the condition of larger supercooling. Furthermore, we show that the size of a droplet plays an important role in the formation of rims during solidification.
【発表論文・著書】2002年学習院大学赴任以降
  1. S. Ibaraki, R. Ise, K. Ishimori, Y. Oaki, G. Sazak, E. Yokoyama, K. Tsukamoto and H. Imai,
    Oscillatory growth for twisting crystals
    Chemical Communications, 51(2015)8516--8519.
  2. Y. Furukawa, E. Yokoyama, I. Yoshizaki, H. Tamaru, T. Shimaoka and T. Sone,
    Crystal Growth Experiments of Ice in Kibo of ISS,
    International Journal of Microgravity Science Application, 31(2014)93--99.
  3. H. Asakawa, G. Sazaki, E. Yokoyama, K. Nagashima, S. Nakatsubo and Y. Furukawa,
    Roles of Surface/Volume Diffusion in the Growth Kinetics of Elementary Spiral Steps on Ice Basal Faces Grown from Water Vapor,
    Crystal Growth \& Design, 14(2014)3210--3220.
  4. K. Murayama, K. Tsukamoto, A. Srivastava, H. Miura, E. Yokoyama and Y. Kimura,
    Measurement of two-dimensional distribution of surface supersaturation over a sodium chlorate crystal surface using multidirectional interferometry,
    Crystal Research \& Technology, 49(2014) 315--322.
  5. 横山悦郎, 古川義純,
    多面体結晶の形態安定性の観点からみた氷円盤結晶の成長不安定,
    日本マイクログラビティ応用学会誌, 30(2013)19--23.
  6. I. Yoshizaki, T. Ishikawa, S. Adachi, E. Yokoyama and Y. Furukawa,
    Precise measurements of dendrite growth of ice crystals in microgravity,
    Microgravity Science and Technology, 24(2012)245--253.
  7. H. Miura, E. Yokoyama, K. Nagashima, K. Tsukamoto and A. Srivastava,
    A new constraint for chondrule formation: condition for the rim formation of barred-olivine textures,
    Earth Planets and Space, 63(2011)1087-1096.
  8. S. Adachi, I. Yoshizaki, T. Ishikawa, E. Yokoyama, Y. Furukawa and T. Shimaoka,
    Stable growth mechanisms of ice disk crystals in heavy water,
    Physical Review E, 84(2011) 051605-1--051605-9.
  9. E. Yokoyama, I. Yoshizaki, T. Shimaoka, T. Sone, T. Kiyota and Y. Furukawa,
    Measurements of Growth Rates of an Ice Crystal from Supercooled Heavy Water under Microgravity Conditions: Basal Face Growth Rate and Tip Velocity of a Dendrite,
    Journal of Physical Chemistry B, 115(2011) 8739--8745.
  10. H. Miura, E. Yokoyama, K. Nagashima, K. Tsukamoto and A. Srivastava,
    Phase-field simulation for crystallization of a highly supercooled forsterite-chondrule melt droplet,
    Journal of Applied Physics 108(2010) 114912--114912-12.
  11. G. Sazaki, S. Zepeda, S. Nakatsubo, E. Yokoyama and Y. Furukawa,
    Elementary steps at the surface of ice crystals visualized by advanced optical microscopy,
    Proceedings of the National Academy of Sciences, 107(2010) 19702--19707.
  12. A. Srivastava, K. Tsukamoto, E. Yokoyama, K. Murayama and M. Fukuyama,
    Fourier analysis based phase shift interferometric tomography for three-dimensional reconstruction of concentration field,
    Journal of Crystal Growth, 312(2010) 2254--2262.
  13. 古川義純, 横山悦郎,吉崎泉, 依田眞一，田中哲夫，島岡太郎, 曽根武彦, 友部俊之,
    氷の結晶成長における形態不安定化--ISS「きぼう」実験の概要,
    日本マイクログラビティ応用学会誌, 27(2010)24--31.
  14. H. Kitahata, J. Taguchi, M. Nagayama, T. Sakurai, Y. Ikura, A. Osa, Y. Sumino, M. Tanaka, E. Yokoyama and H. Miike,
    Oscillation and Synchronization in the Combustion of Candles
    , Journal of Physical Chemistry A, 113(2009) 8164--8168.
  15. E. Yokoyama, R. F. Sekerka and Y. Furukawa,
    Growth of Ice Disk : Dependence of critical thickness for ice disk instability on supercooling of water,
    Journal of Physical Chemistry B, 113(2009) 4733--4738.
  16. S. Zepeda, E. Yokoyama Y. Uda, C. Katagiri and Y. Furukawa,
    In Situ observation of antifreeze glycoprotein kinetics at the ice interface reveals a two-step reversible adsorption mechanism,
    Crystal Growth \& Design, 8(2008)2845--2855.
  17. E. Yokoyama, Y. Giga and P. Rybka,
    A microscopic time scale approximation to the behavior of the local slope on the faceted surface under a nonuniformity in supersaturation,
    Physica D, 237(2008)3666--3672.
  18. K. Matsumoto, T. Irisawa, E. Yokoyama and M. Kitamura,
    Growth of a binary ideal solid solution crystal studied by Monte Carlo simulation,
    Journal of Crystal Growth, 310(2008)646--654.
  19. 古川義純, 横山悦郎,吉崎泉, 足立聡, 島岡太郎, 曽根武彦, 友部俊之,
    「きぼう」における氷の円盤結晶の形態不安定化実験,
    日本マイクログラビティ応用学会誌, 25(2008)680--682.
  20. 塚本勝男, 西村良浩, 横山悦郎,
    微小重力での結晶成長 その場"観察,
    可視化情報, 25(2005)156--163.
  21. Y. Furukawa, E. Yokoyama and W. Shimada,
    Morphological instability on an ice crystal growing in supercooled water,
    Studies on Crystal Growth Under Microgravity,
    Editors Y. Hayakawa and Y. Furukawa, Research Signpost, ISBN: 81-308-0025-X (2005) 165-186.
  22. K. Matsumoto, T. Irisawa, M. Kitamura, E. Yokoyama, Y. Kumagai and A. Koukitu,
    Effective distribution coefficients of an ideal solid solution crystal: Monte Carlo simulation,
    Journal of Crystal Growth, 276(2005)635--642.
  23. Y. Furukawa, N. Inohara and E. Yokoyama,
    Growth patterns and interfacial kinetic supercooling at ice/water interfaces at which anti-freeze glycoprotein molecules are adsorbed,
    Journal of Crystal Growth 275(2005)167--174.
  24. 古川義純、横山悦郎,
    マクロ分子の界面吸着が関与する結晶成長機構―氷結晶と不凍タンパク質―,
    Space Utilization Research, 21(2005)102--104.
  25. 横山悦郎,
    雪結晶の形と結晶サイズ,
    形の科学辞典, 「形の科学辞典」編集委員会編, 朝倉書店（2004)340-341.
  26. Y. Furukawa and E. Yokoyama,
    Morphological instability on an ice disk,
    Journal of the Japan Society of Microgravity Application, 21(2004)217--223.
  27. Y. Furukawa, E. Yokoyama, Y. Nishimura, J. Ohtsubo, N. Inohara and S. Nakatusbo,
    Visualization of a thermal diffusion field around a single ice crystal growing in supercooled water under a short-term microgravity condition,
    Journal of the Japan Society of Microgravity Application, 21(2004)196--201.
  28. 岡田 耕一, 横山 悦郎, 三池 秀敏,
    逆余弦関数による干渉じま解析法の提案,
    電子情報通信学会論文誌, J86-D-II(2003)1420--1430.
  29. 小畠秀和, 塚本勝男, 横山悦郎, 佐藤久夫, 野沢純,
    微小重力を利用した惑星起源物質の形成シミュレーション,
    日本マイクログラビティ応用学会誌, 20 (2003)137--144.
  30. 古川義純, 西村良弘, 横山悦郎, 猪原直美,
    氷の結晶成長ダイナミクスに対する凍結抑制タンパク質の効果,
    日本結晶成長学会誌,30 (2003)21--31.
  31. 古川義純, 西村良浩,横山悦郎,
    氷の海に住む魚はなぜ凍らないか？−氷の結晶成長抑制機能をもつたんぱく質,
    固体物理, 37(2002)396--402.

【主要発表論文５編】2002年学習院大学赴任以前
  1. Etsuro Yokoyama, Robert F. Sekerka and Yoshinori Furukawa,
    Growth trajectories of disk crystals of ice growing from supercooled water,
    Journal of Physical Chemistry B, 104(2000)65--67.
  2. Tatsunari Sakurai, Etsuro Yokoyama and Hidetoshi Miike,
    Propagation of surface deformation coupled with convection waves under the excitation of a chemical wave train,
    Physical Revierw E, 56(1997)R2367--R2370.
  3. Hidetoshi Miike, Tatsunari Sakurai, Atsushi Osa and Etsuro Yokoyama,
    Observation of two-dimensional Brownian motion by microscope image sequence processing,
    Journal of the Physical Society of Japan, 66(1997)1647--1655.
  4. Etsuro Yokoyama and Robert F. Sekerka,
    A numerical study of the combined effect of anisotropic surafce tension and interface kinetics on pattern formation during the growth of two-dimensional crystals,
    Journal of Crystal Growth, 125(1992)389--403.
  5. Etsuro Yokoyama and Toshio Kuroda,
    Pattern formation in growth of snow crystals occuring in the surface kinetic process and the diffuison process,
    Physical Review A, 41(1990)2038--2049.

【その他教育実績】
  1. 東京大学大学院数理科学研究科　客員教授 2006/4/1-2011/3/31, 2015/4/1 -- 現在
  2. 学習院グリーン元気プロジェクト　モンゴル国 企画・引率 2014/08/08 - 2014/08/22
  3. 学習院グリーン元気プロジェクト　中国内モンゴル自治区 企画・引率 2013/08/08 - 2012/08/22
  4. 日中国交回復40周年記念学生交流フォーラム 企画・引率 （北京）2012/11/01 - 2012/11/05
  5. 日中国交回復40周年記念学生交流フォーラム 企画・引率 （東京）2012/08/29 - 2012/08/30
  6. 学習院グリーン元気プロジェクト　ペルー 企画・引率 2012/08/08 - 2012/08/22
  7. 学習院グリーン元気プロジェクト　中国内モンゴル自治区 企画・引率 2011/08/08 - 2011/08/22
  8. 学習院大学東日本大震災ボランティア　岩手県久慈市・野田村・宮古市　企画・参加・引率 2011/07/17 - 2011/07/23
  9. 学習院グリーン元気プロジェクト　中国内モンゴル自治区 企画・引率 2010/08/08 - 2010/08/23
  10. 学習院グリーン元気プロジェクト　小笠原父島 企画・引率 2009/08/14 - 2009/08/22
  11. 学習院元気プロジェクト　サハリン引率 2008/08/04 - 2008/08/13

5April2016