## Conference and Seminar

#### Conference

**International conference From Soft Matter to Protocell**

#### Seminar

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

abstract：

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

abstract：

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

abstract：

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).