arXiv subjects

Shambhavi Dikshit

Publications and source records attributed to Shambhavi Dikshit.

5 recordsLinked to original sources

arXiv2025

Competing effect of disorder on phase separation in active systems

We investigate the impact of random pinned disorder on a collection of self propelled particles. To achieve this, we construct a continuum model by formulating the coupled hydrodynamic equations for slow variables, local density and momentum density of particles. The disorder in the system acts as pinning sites, effectively immobilizing the particles that come into contact with them. Our numerical results reveal that weak disorder leads to phase separation in the system at density and activity lower than the typical values for motility induced phase separation. We construct a phase diagram using numerical simulations as well as linearized approximation in the plane of activity and packing fraction of particles at weak disorder densities. On increasing disorder density the system shows the Micro phase separation, while at large disorder densities, the system becomes heterogeneous and eventually undergoes kinetic arrest. The structure factor tail deviates from the Porods law, indicating increased roughness at domain interfaces under strong disorder. Furthermore, we analyze the fractal dimension of the interface as a function of disorder density, highlighting the increasing irregularity of phase separated domains. We also found that disorder significantly suppresses number fluctuations in the system.

cond-mat.soft↗

arXiv2024

Domain growth kinetics of active model B with thermal fluctuations

We perform a comprehensive study on the role of thermal noise on the ordering kinetics of a collection of active Brownian particles modeled using coarse-grained conserved active model B (AMB). The ordering kinetics of the system is studied for the critical mixture when quenched from high to a low temperature. The structure of the growing domains changes from isolated droplet type for AMB without noise to bi-continuous type for active model B with noise (AMBN). Unlike the passive counterpart of the AMB, the noise is relevant for the growth kinetics of the AMB. We use extensive numerical study, as well as dynamic scaling hypothesis to characterize the kinetics of the system. We find that the asymptotic growth law for AMBN is diffusive Lifshitz-Slyozov (LS) type, whereas it was reported previously that the asymptotic growth law for the AMB without noise is slower, with a growth exponent 4. Moreover, the kinetics of the growing domains show a strong time dependent growth for AMBN. The growth law shows a crossover from early time 1/3 value to intermediate time 1/4 value, and it again traverses from 1/4 to 1/3 asymptotically. The two different scaling functions are found for intermediate time and late time with growth law 1/4 and 1/3 respectively.

cond-mat.stat-mech↗

arXiv2023

Ordering kinetics in active polar fluid

We model the active polar fluid as a collection of orientable objects supplied with active stresses and momentum damping coming from the viscosity of bulk fluid medium. The growth kinetics of local orientation field is studied. The effect of active fluid is contractile or extensile depending upon the sign of the active stress. We explore the growth kinetics for different activities. We observe that for both extensile and contractile cases the growth is altered by a prefactor when compared to the equilibrium Model A. We find that the extensile fluid enhances the domain growth whereas the contractile fluid supresses it. The asymptotic growth becomes pure algebraic for large magnitudes of activity. We also find that the domain morphology remains unchanged due to activity and system shows the good dynamic scaling for all activities. Our study provides the understanding of ordering kinetics in active polar gel.

cond-mat.soft↗

arXiv2021

Activity Driven Phase Separation and Ordering Kinetics of Passive Particles

The steady state and phase ordering kinetics in a pure active Borwnian particle system are studied in recent years. In binary mixture of active and passive Brownian particles passive particles are used as probe to understand the properties of active medium. In our present study we study the mixture of passive and active Brownian particles. Here we aim to understand the steady state and kinetics of small passive particles in the mixture. In our system,the passive particles are small in size and large in number, whereas ABPs are large in size and small in number. The system is studied on a two-dimensional substrate using overdamp Langevin dynamic simulation. The steady state and kinetics of passive particles are studied for various size and activity of active particles. Passive particles are purely athermal in nature and have dynamics only due to bigger ABPs. For small size ratio and activity the passive particles remain homogeneous in the system, whereas on increasing size ratio and activity they form periodic hexagonal close pack (HCP) spanning clusters in the system. We have also studied the kinetics of growing passive particle clusters. The mass of the largest cluster shows a much slower growth kinetics in contrast to conserved growth kinetics in ABP system. Our study provides an understanding of steady state and kinetics of passive particles in the presence of bigger active particles. The mixture can be thought of as effect of big microorganism moving in passive medium.

cond-mat.soft↗

arXiv2021

Dynamics of a collection of active particles on a two-dimensional periodic undulated surface

We study the dynamics of circular active particles (AP) on a two dimensional periodic undulated surface. Each particle has an internal energy mechanism which is modeled by an active friction force and it is controlled by an activity parameter $v_0$. It acts as negative friction if the speed of the particle is smaller than $v_0$ and normal friction otherwise. Surface undulation is modeled by the periodic undulation of fixed amplitude and wavelength and is measured in terms of a dimensionless ratio of amplitude and wavelength, $\bar{h}$. The dynamics of the particle is studied for different activities, $v_0$ and surface undulations (SU), $\bar{h}$. Three types of particle dynamics are observed on varying activity and SU. For small $v_0 \lesssim 0.1$ and $\bar{h}$ $\gtrsim 0.8$, particles remain confined in a surface minimum, for moderate $v_0 \lesssim \bar{h}$, dynamics of particle shows an intermediate subdiffusion to late time diffusion and for large $v_0 \gtrsim \bar{h}$, it shows initial superdiffusion to late time diffusion. For all $v_0$'s and $\bar{h} \lesssim 0.2$, the dynamics of particle, satisfies the Green-Kubo relation between the effective diffusivity and velocity auto-correlation function. Systematic deviation is found on increasing $\bar{h}$. Hence, an effective equilibrium can be established for a range of system parameters in this nonequilibirum system.

cond-mat.soft↗