- Hiizu Nakanish, Professor
- Kiyohide Nomura, Associate Professor
- Takahiro Sakaue, Assistant Professor
- Our group studies equilibrium and non-equilibrium statistical physics theoretically on various systems. Recent research topics include granular media, polymer physics, stochastic processes, bio-physics, low-dimensional quantum systems, application of quantum field theory on statistical physics.
- Shear thickening in granular-fluid mixture
- Non-equilibrium dynamics of single polymers
- Statistical mechanics of ring polymer solutions
- Electro-rheological effect in binary fluids
- Low dimensional quantum systems
1. Shear thickening in granular-fluid mixture:
Dense granule-fluid mixture is called dilatant fluid and often shows severe shear thickening; its viscosity discontinuously increases by orders of magnitude under shear stress. We have developed a phenomenological model for its macroscopic behavior and found that the medium may show shear thickening oscillation, namely, the oscillation between thickened and relaxed states under a constant external state in a certain range. This oscillation had never been reported, thus we constructed a experimental setup for this purpose and demonstrated the medium actually shows the oscillation as we predicted. We also demonstrated that the thickening appear in the region of tensile stress.
 H. Nakanishi, S. Nagahiro, and N. Mitarai, Phys. Rev. E 85, 011401 (2012).
 S. Nagahiro, H. Nakanishi and N. Mitarai, EPL 104 (2013) 28002.
 S. Nagahiro and H. Nakanishi, submitted. arXiv:1511.05250
2. Non-equilibrium dynamics of single polymers:
We study the dynamic of a long flexible polymer driven by various external forces. A key example is the translocation of biopolymers, i.e., the threading of DNA, RNA and proteins through a narrow pore. We have pointed out that in typical experiments, the translocation process takes place in the condition far-from-equilibrium accompanying of large conformational distortion (Fig. 1). We elucidated the underlying physics in term of the tension propagation along the chain backbone, and constructed a basic framework to describe such a highly non-equilibrium process .
The concept of tension propagation is important in various problems in polymer dynamics, including a stretching process by tensile force  and a rotation around a bar driven by torque . A conceptually similar dynamics can be seen in the compression dynamics of nano-channel confined DNA, where the stress propagation manifests itself as the development of concentration shock wave .
 T. Sakaue, Phys. Rev. E. vol. 76 (2007) 021803; ibid, vol. 81 (2010) 041808.
 T. Sakaue. T. Saito and H. Wada, Phys. Rev. E. vol. 86 (2012) 011804.
 M. Laleman et al., Macromolecules. vol. 49 (2016) 405.
 A. Khorshid et al. Phys. Rev. Lett. vol. 113 (2014) 268104.