arXiv subjects

Isamu Sou

Publications and source records attributed to Isamu Sou.

9 recordsLinked to original sources

arXiv2023

Odd elasticity of a catalytic micromachine

We perform numerical simulations of a model micromachine driven by catalytic chemical reactions. Our model includes a mechano-chemical coupling between the structural variables and the nonequilibrium variable describing the catalytic reactions. The time-correlation functions of the structural variables are calculated and further analyzed in terms of odd Langevin dynamics. We obtain the effective odd elastic constant that manifests the broken time-reversal symmetry of a catalytic micromachine. Within the simulation, we separately estimate the quantity called nonreciprocality and show that its behavior is similar to that of the odd elasticity.Our approach suggests a new method to extract the nonequilibrium properties of a micromachine only by measuring its structural dynamics.

cond-mat.soft↗

arXiv2023

Simulations of Odd Microswimmers

We perform numerical simulations of odd microswimmers consisting of three spheres and two odd springs. To describe the hydrodynamic interaction, both the Oseen-type and the Rotne-Prager-Yamakawa (RPY)-type mobilities are used. For the Oseen-type mobility, the simulation results quantitatively reproduce the asymptotic expression of the average velocity. For the RPY-type mobility, on the other hand, the average velocity is smaller than that of the Oseen-type mobility and the deviation is more pronounced for larger spheres. We also perform simulations of microswimmers having different sphere sizes and show that the average velocity becomes smaller than that of the equal size case. The size of the middle sphere plays an important role in determining the average velocity.

cond-mat.soft↗

arXiv2022

Time-correlation functions for odd Langevin systems

We investigate the statistical properties of fluctuations in active systems that are governed by non-symmetric responses. Both an underdamped Langevin system with an odd resistance tensor and an overdamped Langevin system with an odd elastic tensor are studied. For a system in thermal equilibrium, the time-correlation functions should satisfy time-reversal symmetry and the anti-symmetric parts of the correlation functions should vanish. For the odd Langevin systems, however, we find that the anti-symmetric parts of the time-correlation functions can exist and that they are proportional to either the odd resistance coefficient or the odd elastic constant. This means that the time-reversal invariance of the correlation functions is broken due to the presence of odd responses in active systems. Using the short-time asymptotic expressions of the time-correlation functions, one can estimate an odd elastic constant of an active material such as an enzyme or a motor protein.

cond-mat.soft↗

arXiv2021

The Onsager-Machlup Integral for Non-reciprocal Systems with Odd Elasticity

The variational principle of the Onsager-Machlup integral is used to describe the stochastic dynamics of a micromachine, such as an enzyme, characterized by odd elasticity. The obtained most probable path is found to become non-reciprocal in the presence of odd elasticity and is further related to the entropy production.

cond-mat.soft↗

arXiv2021

Odd Microswimmer

We propose a model for a thermally driven microswimmer in which three spheres are connected by two springs with odd elasticity. We demonstrate that the presence of odd elasticity leads to the directional locomotion of the stochastic microswimmer.

cond-mat.soft↗

arXiv2020

Irreversibility and entropy production of a thermally driven micromachine

We discuss the non-equilibrium properties of a thermally driven micromachine consisting of three spheres which are in equilibrium with independent heat baths characterized by different temperatures. Within the framework of a linear stochastic Langevin description, we calculate the time-dependent average irreversibility that takes a maximum value for a finite time. This time scale is roughly set by the spring relaxation time. The steady-state average entropy production rate is obtained in terms of the temperatures and the friction coefficients of the spheres. The average entropy production rate depends on thermal and/or mechanical asymmetry of a three-sphere micromachine. We also obtain the center of mass diffusion coefficient of a thermally driven three-sphere micromachine as a function of different temperatures and friction coefficients. With the results of the total entropy production rate and the diffusion coefficient, we finally discuss the efficiency of a thermally driven micromachine.

cond-mat.stat-mech↗

arXiv2019

Non-equilibrium probability flux of a thermally driven micromachine

We discuss the non-equilibrium statistical mechanics of a thermally driven micromachine consisting of three spheres and two harmonic springs [Y. Hosaka et al., J. Phys. Soc. Jpn. 86, 113801 (2017)]. We obtain the non-equilibrium steady state probability distribution function of such a micromachine and calculate its probability flux in the corresponding configuration space. The resulting probability flux can be expressed in terms of a frequency matrix that is used to distinguish between a non-equilibrium steady state and a thermal equilibrium state satisfying detailed balance. The frequency matrix is shown to be proportional to the temperature difference between the spheres. We obtain a linear relation between the eigenvalue of the frequency matrix and the average velocity of a thermally driven micromachine that can undergo a directed motion in a viscous fluid. This relation is consistent with the scallop theorem for a deterministic three-sphere microswimmer.

cond-mat.stat-mech↗

arXiv2017

Thermally Driven Elastic Micromachines

We discuss the directional motion of an elastic three-sphere micromachine in which the spheres are in equilibrium with independent heat baths having different temperatures. Even in the absence of prescribed motion of springs, such a micromachine can gain net motion purely because of thermal fluctuations. A relation connecting the average velocity and the temperatures of the spheres is analytically obtained. This velocity can also be expressed in terms of the average heat flows in the steady state. Our model suggests a new mechanism for the locomotion of micromachines in nonequilibrium biological systems.

cond-mat.soft↗

arXiv2017

Coexistences of lamellar phases in ternary surfactant solutions

We theoretically investigate the coexistences of lamellar phases both in binary and ternary surfactant solutions. The previous free energy of a lamellar stack is extended to take into account the translational entropy of membrane segments. The obtained phase diagram for binary surfactant solutions (surfactant/water mixtures) shows a phase separation between two lamellar phases and also exhibits a critical point. For lamellar phases in ternary surfactant solutions (surfactant/surfactant/water mixtures), we explore possible phase behaviors and show that the phase diagrams exhibit various three-phase regions as well as two-phase regions in which different lamellar phases coexist. We also find that finite surface tension suppresses undulation fluctuations of membranes and leads to a wider three-phase and two-phase coexistence regions.

cond-mat.soft↗