arXiv subjects

Shunsuke Yabunaka

Publications and source records attributed to Shunsuke Yabunaka.

27 records · Page 2Linked to original sources

arXiv2017

Cell growth, division and death in cohesive tissues: a thermodynamic approach

Cell growth, division and death are defining features of biological tissues that contribute to morphogenesis. In hydrodynamic descriptions of cohesive tissues, their occurrence implies a non-zero rate of variation of cell density. We show how linear nonequilibrium thermodynamics allows to express this rate as a combination of relevant thermodynamic forces: chemical potential, velocity divergence, and activity. We illustrate the resulting effects of the non-conservation of cell density on simple examples inspired by recent experiments on cell monolayers, considering first the velocity of a spreading front, and second an instability leading to mechanical waves.

q-bio.TO↗

arXiv2016

Collision between chemically-driven self-propelled drops

We consider analytically and numerically head-on collision between two self-propelled drops. Each drop is driven by chemical reactions that produce or consume the concentration isotropically. The isotropic distribution of the concentration field is destabilized by motion of the drop which is itself made by Marangoni flow from concentration-dependent surface tension. This symmetry-breaking self-propulsion is distinct from other self-propulsion mechanisms due to the intrinsic polarity such as squirmers and self-phoretic motion; there is a bifurcation point below which the drop is stationary and above which it moves spontaneously. When two drops moving along the same axis with opposite direction, the interactions arise both from hydrodynamics and concentration overlap. We found that two drops exhibit either elastic collision or fusion depending on the distance from the bifurcation point controlled, for instance, by viscosity. The elastic collision results from the balance between dissipation and energy injection by chemical reactions. We derive the reduced equations for the collision between two drops and analyze the contributions from the two interactions. The concentration-mediated interaction is found to dominate the hydrodynamic interaction.

physics.flu-dyn↗

arXiv2016

The Local Potential Approach to frustrated antiferromagnets

We revisit the critical behavior of classical frustrated systems using the nonperturbative renormalization group (NPRG) equation. Our study is performed within the local potential approximation of this equation to which is added the flow of the field renormalization. Our flow equations are functional to avoid possible artifacts coming from field expansions which consists in keeping only a limited number of coupling constants. We present a simple numerical method to follow the fixed point solution of our equations by changing gradually the dimension d and the number N of spin-components. We explain in details the advantage of this method as well as the numerical difficulties we encounter, which become severe close to d = 2. The function N_c(d) separating the regions of first and second order in the (d,N) plane is computed for d between 4 and 2.2. Our results confirm what was previously found within cruder approximation of the NPRG equation and contradict both the fixed dimension perturbative approach and the results obtained within the conformal bootstrap approach.

cond-mat.stat-mech↗

arXiv2016

Structure Formation due to Antagonistic Salts

Antagonistic salts are composed of hydrophilic and hydrophobic ions. In a mixture solvent (water-oil) such ion pairs are preferentially attracted to water or oil, giving rise to a coupling between the charge density and the composition. First, they form a large electric double layer at a water-oil interface, reducing the surface tension and producing mesophases. Here, the cations and anions are loosely bound by the Coulomb attraction across the interface on the scale of the Debye screening length. Second, on solid surfaces, hydrophilic (hydrophobic) ions are trapped in a water-rich (oil-rich) adsorption layer, while those of the other species are expelled from the layer. This yields a solvation mechanism of local charge separation near a solid. In particular, near the solvent criticality, disturbances around solid surfaces can become oscillatory in space. In mesophases, we calculate periodic structures, which resemble those in experiments.

cond-mat.soft↗

arXiv2015

Hydrodynamics in bridging and aggregation of two colloidal particles in a near-critical binary mixture

We investigate bridging and aggregation of two colloidal particles in a near-critical binary mixture when the fluid far from the particles is outside the coexistence (CX) curve and is rich in the component disfavored by the colloid surfaces. In such situations, the adsorption-induced interaction is enhanced, leading to bridging and aggregation of the particles. We realize bridging firstly by changing the temperature with a fixed interparticle separation and secondly by letting the two particles aggregate. The interparticle attractive force dramatically increases upon bridging. The dynamics is governed by hydrodynamic flow around the colloid surfaces. In aggregation, the adsorption layers move with the particles and squeezing occurs at narrow separation. We take into account the renormalization effect due to the critical fluctuations using the recent local functional theory [J. Chem. Phys. 136, 114704 (2012)].

cond-mat.soft↗

arXiv2014

Geometric pumping induced by shear flow in dilute liquid crystalline polymer solutions

We investigate nonlinear rheology of dilute liquid crystalline polymer solutions under time dependent two-directional shear flow. We analyze the Smoluchowski equation, which describes the dynamics of the orientation of a liquid crystalline polymer, by employing technique of the full counting statistics. In the adiabatic limit, we derive the expression for time integrated currents generated by a Berry-like curvature. Using this expression, it is shown that the expectation values of the time-integrated angular velocity of a liquid crystalline polymer and the time-integrated stress tensor are generally not zero even if the time average of the shear rate is zero. The validity of the theoretical calculations is confirmed by direct numerical simulations of the Smoluchowski equation. Nonadiabatic effects are also investigated by simulations and it is found that the time-integrated stress tensor depends on the speed of the modulation of the shear rate if we adopt the isotropic distribution as an initial state.

cond-mat.soft↗

arXiv2013

Phase separation in a binary mixture confined between symmetric parallel plates: Capillary condensation transition near the bulk critical point

We investigate phase separation of near-critical binary mixtures between parallel symmetric walls in the strong adsorption regime. We take into account the renormalization effect due to the critical fluctuations using the recent local functional theory [J. Chem. Phys. 136, 114704 (2012)]. In statics, a van der Waals loop is obtained in the relation between the average order parameter $ $ in the film and the chemical potential when the temperature $T$ is lower than the film critical temperature $T_c^{ca}$ (in the case of an upper critical solution temperature). In dynamics, we lower $T$ below the capillary condensation line from above $T_c^{ca}$. We calculate the subsequent time-development assuming no mass exchange between the film and the reservoir. In the early stage, the order parameter $psi$ changes only in the direction perpendicular to the walls. For sufficiently deep quenching, such one-dimensional profiles become unstable with respect to the fluctuations varying in the lateral directions. The late-stage coarsening is then accelerated by the hydrodynamic interaction. A pancake domain of the phase disfavored by the walls finally appears in the middle of the film.

cond-mat.soft↗

arXiv2012

Self-propelled motion of a fluid droplet under chemical reaction

We study self-propelled dynamics of a droplet due to a Marangoni effect and chemical reactions in a binary fluid with a dilute third component of chemical product which affects the interfacial energy of a droplet. The equation for the migration velocity of the center of mass of a droplet is derived in the limit of an infinitesimally thin inter- face. We found that there is a bifurcation from a motionless state to a propagating state of droplet by changing the strength of the Marangoni effect.

nlin.PS↗

arXiv2011

Polydomain growth at isotropic-nematic transitions in liquid crystalline polymers

We studied the dynamics of isotropic-nematic transitions in liquid crystalline polymers by integrating time-dependent Ginzburg-Landau equations. In a concentrated solution of rodlike polymers, the rotational diffusion constant Dr of the polymer is severely suppressed by the geometrical constraints of the surrounding polymers, so that the rodlike molecules diffuse only along their rod directions. In the early stage of phase transition, the rodlike polymers with nearly parallel orientations assemble to form a nematic polydomain. This polydomain pattern with characteristic length l, grows with self-similarity in three dimensions (3D) over time with a l~1/4 scaling law. In the late stage, the rotational diffusion becomes significant, leading a crossover of the growth exponent from 1/4 to 1/2. This crossover time is estimated to be of the order t~1/Dr. We also examined time evolution of a pair of disclinations placed in a confined system, by solving the same time-dependent Ginzburg-Landau equations in two dimensions (2D). If the initial distance between the disclinations is shorter than some critical length, they approach and annihilate each other; however, at larger initial separations they are stabilized.

cond-mat.soft↗