Conference and Seminar


International conference From Soft Matter to Protocell


日時: 平成25年6月3日(月)10:30-11:45
講演タイトル: Volume transition of inflating balloon
講演者: 土井正男 先生
所属: 北京航空航天大学
場所: 東北大学大学院理学研究科合同B棟 745室

When a cylindrical balloon is inflated, inflation often takes place non-uniformly; an inflated part is created, and the size of the inflated increases as the balloon is inflated. This behavior is discussed based on the theory of rubber elasticity. Its relevance to osmotic swelling is also discussed.

日時: 平成25年4月26日(金)16:30-18:00
講演タイトル:Active Polar Two-Fluid Macroscopic Dynamics:
講演者: Prof. Harald Pleiner,
所属: Max Planck Institute for Polymer Research,
場所: 東北大学大学院理学研究科合同B棟 743室

We study the dynamics of systems with a polar dynamic preferred direction. Examples include shoals of fish, flocks of birds, migrating insects, and pattern-forming growth of bacteria. Due to the fact that the preferred direction only exists dynamically, but not statically, the macroscopic variable of choice is the macroscopic velocity associated with the motion of the active units, which are typically biological in nature. We derive the macroscopic equations for such a system and discuss novel static, reversible and irreversible cross-couplings connected to a second velocity as a variable. We analyze in detail how the macroscopic behavior of an active system with a polar dynamic preferred direction compares to other systems with two velocities including immiscible liquids and electrically neutral quantum liquids. We critically discuss differences in the normal mode spectrum compared to other orientationally ordered systems. We investigate the influence of chirality on the macroscopic behavior of such active media.

日時: 平成24年8月22日(水)16:30-
タイトル: Collective Motion of Self-Propelled Soft Particles
講師: Takao Ohta (Department of Physics, Kyoto University)
場所: 東北大学 理学研究科 合同B棟745室

We investigate dynamics of deformable self-propelled particles based on the model equations for a single soft particle which has a coupling between migration and shape deformation [1]. The dynamics is governed by the time-evolution equations of the center of mass and the deformation tensor. Two models are introduced to study the collective motions of interacting particles. The first one (model I) has a repulsive interacting potential whose magnitude depends on the relative direction of elongation of a pair of particles [2, 3]. The force from other particles as well as a noise term are added to the equation for the center of mass. The other model (model II) has also a repulsive pair-wise potential but without an explicit alignment mechanism. This force enters both in the equation of the center of mass and in the equation for the deformation tensor so that existence of other particles causes directly shape deformation [4]. Numerical simulations are carried out in two dimensions by changing the noise intensity, the interaction strength and the particle density to obtain the phase diagram of the ordered and the disordered states. We show by a mean field analysis of model I that deformability is a favorable origin for the transitionat high density [2, 3].

[1] T. Ohta and T. Ohkuma, Phys. Rev. Lett. 102, 154101 (2009).
[2] Y. Itino, T. Ohkuma and T. Ohta: J. Phys. Soc. Jpn. 80 033001 (2011).
[3] Y. Itino, and T. Ohta: J. Phys. Soc. Jpn. submitted.
[4] A. Menzel and T. Ohta: Europhys. Letters (in press).