Particles on a one-dimensional line exhibit so-called single-file diffusion, which has been investigated as a simple model of diffusion. In single-file diffusion, a constituent particle interacts only with the two neighboring particles, and the order of the particles remains unchanged. This strong constraint makes the analyses of the single particle diffusion to be tractable. When all the particles have the same mass, the dynamics can be largely simplified; the trajectories of particles appear as if they are intersecting with each other. We consider the general cases where the mass of a target particle is different from that of the other particles, and the simple situation mentioned above no longer holds. In this study, we numerically investigate the dynamics of a single target particle with various masses. When the target particle is heavy, the target particle almost shows simple Gaussian diffusion. In contrast, the target particle exhibits anomalous non-Gaussian diffusion when the target particle is sufficiently light. We also perform theoretical analyses to reproduce the mean square displacements in large and small mass cases.

The filament behaviors in liquid dripping flows of semi-dilute polymer (PEO) aqueous solutions with different concentrations of polymers were investigated by using numerical simulations with the FENE-P model. The temporal evolution of the minimum filament radius and the extensional relaxation time agreed with the corresponding experimental results in IC (Inertio-Capillary)/VC (Visco-Capillary) and EC (Elasto-Capillary) regimes. The relation between the extensional relaxation time and the extensibility parameter of polymer was clarified for different solution concentrations. We proposed to determine the extensibility parameter by considering the extensional relaxation times of model solutions, which vary for different solution concentrations, depending on the numerical environment.

This article reviews the 51st volume of Nihon Reoroji Gakkaishi (Journal of the Society of Rheology, Japan), which consists of 5 issues published in 2023. All the papers published in this volume are summarized based on the research topics. The statistics show that the total number of articles is 34, and the ratio of papers in English is 0.53. One special issue has been dedicated to food rheology, in which 4 original articles and a note have been published. The other highlight is the commemorative issue of the 50th anniversary of SRJ, which includes plenty of congratulatory messages from overseas societies of rheology.