２０１９年５月９日 立木佑弥氏

日時：２０１９年５月９日（木）　１１：３０〜１３：００
場所：首都大学東京　８号館３０７号室
講師：立木佑弥氏（首都大学東京）
題目：数理的アプローチと実証的アプローチの融合による生態学現象の理解

要旨：一般に科学的な議論は、仮説を検証するために実験や観察によってデータを得て、それを評価することで進められる。自然科学の一分野である生態学も然りである。自然に存在する膨大な情報には一般にノイズや不確定要素が伴うため、仮説を検証するために現象を抽象化し、精緻な実験系・観察系を組み立てる。これは模型化（モデリング）と呼ばれ、自然に存在するノイズを除去し、現象の原因と結果を浮き彫りにするための努力である。一方、現象を数学的に記述する数理モデリングも現象からコアを抜き出す努力の一つであり、論理的に構築された数理モデルを用いて議論することで、現象に対する見通しが良くなる。本講演では、ササ類の一斉開花現象、イモリ-カエル被食捕食系、サケ科魚類生活史意思決定を対象に、生態学的現象を読み解くためのアプローチとして、数理モデルを用いた理論と野外観察と実験による実証の融合アプローチを紹介し、その有用性について議論する。

２０１９年３月４日 Prof. Bruce Law

日時：２０１９年３月４日（月）　１４：３０〜１６：００
場所：首都大学東京　８号館３０１号室
講師：Prof. Bruce Law (Kansas State University)
題目：Particles at liquid surfaces: mechanics and thermodynamics

要旨：Particle adsorption and self-assembly, at a liquid surface, determines the surfactant behavior of these particles in Pickering emulsions and governs the flotation process, used extensively in the mining industry, to separate valuable minerals and metals in the ground from other residual materials. The physics of particles at liquid surfaces is still incompletely understood and is a subject of continuing current interest. In this seminar we review recent developments. The physics, which is applicable, depends upon particle size. For sufficiently large particles, of order microns, surface and line interactions determine the particle behavior as required by mechanical equilibrium. For sufficiently small particles, of order nanometers, both mechanical and thermodynamic equilibrium of the particle at the liquid surface must be considered. For these nanometer-sized particles finite-size line tension effects, originating from the van der Waals interaction, are found to play an important role.

２０１９年２月１５日 Prof. Michael Elbaum

日時：２０１９年２月１５日（金）　１１：００〜１２：３０
場所：首都大学東京　８号館３０２号室
講師：Prof. Michael Elbaum (Weizmann Institute of Science)
題目：Cellular imaging in 3D with cryo-STEM tomography

要旨：Cryo-electron microscopy has achieved unprecedented resolution in recent years with new technological breakthroughs. However its practice is traditionally restricted to the study of ultra-thin specimens. While tomography introduced a view in three dimensions, the thickness limitations of traditional imaging modalities remain. We have introduced the method of scanning transmission electron microscopy (STEM) for cryo-tomography of biological specimens. STEM is inherently suited to thicker samples, in some cases reaching intact cells. Moreover, the image contrast based on electron scattering can be interpreted quantitatively. The talk will describe the methodology and a number of applications to intracellular crystallization and self-assembly.

２０１９年１月３０日 Prof. Kuo-An Wu

日時：２０１９年１月３０日（水）　１１：００〜１２：３０
場所：首都大学東京　８号館３０２号室
講師：Prof. Kuo-An Wu (National Tsing Hua University)
題目：Pattern formation theory in tackling challenges in condensed matter at the nanoscale

要旨：The Swift-Hohenberg equation has been widely used to model formation of patterns seen in nonlinear systems at the macroscopic scale. The phenomenological model can be recast into an atomistic continuum model, namely the phase field crystal model, to describe material systems where the self-organized patterns represent crystal lattice structures. Besides its close relation to the Swift-Hohenberg equation, the phase field crystal approach has its roots in the classical density functional theory of freezing, and it bridges the molecular simulations and macroscopic continuum models. In this talk, I will briefly discuss how the lattice pattern at the atomistic scale naturally gives rise to anisotropies in surface energies and kinetic coefficients which are main determinants of morphology of crystals at the macroscopic scale. In addition, the simple phase field crystal model is capable of describing elasticity, plasticity, and discrete dislocations that enables us to study fundamental mechanisms of nanocrystalline grain growth and grain boundary grooving. I will discuss how discrete structures, such as dislocations and grain boundaries (usually omitted in classical theory), drastically change predictions of classical theory.

２０１９年１月１７日 Mr. Sami Al-Izzi

日時：２０１９年１月１７日（木）　１１：００〜１２：３０
場所：首都大学東京　８号館３０１号室
講師：Mr. Sami Al-Izzi (University of Warwick)
題目：Hydro-osmotic instabilities in active membrane tubes

要旨：We study a membrane tube with unidirectional ion pumps driving an osmotic pressure difference [1]. A pressure-driven peristaltic instability is identified, qualitatively distinct from similar tension-driven Rayleigh-type instabilities on membrane tubes. We discuss how this instability could be related to the function and biogenesis of membrane bound organelles, in particular, the contractile vacuole complex. The unusually long natural wavelength of this instability is in agreement with that observed in cells.

[1] S. C. Al-Izzi, G. Rowlands, P. Sens, and M. S. Turner, Phys. Rev. Lett. 120, 138102 (2018).