arXiv subjects

Hamidreza Khalilian

Publications and source records attributed to Hamidreza Khalilian.

8 recordsLinked to original sources

arXiv2026

Confinement-Induced Optimization of Fluctuation-Induced Forces in Active Fluids

Active matter generates nonequilibrium fluctuations that mediate effective interactions between immersed objects. While fluctuation-induced (FI) forces in active fluids depend on activity, density, and geometry, their dependence on confinement remains poorly understood. We study FI forces between fixed intruders in two-dimensional active fluids composed of self-propelled circular or rodlike particles using Langevin dynamics simulations. We find that the FI force exhibits a pronounced nonmonotonic dependence on intruder separation, reaching a maximum at an optimal gap size well beyond the depletion regime, in contrast to the commonly assumed monotonic decay. This optimal confinement is robust across parameters and is more pronounced for elongated particles. The effect arises from a confinement-controlled balance between particle transport and crowding: narrow gaps hinder exchange between inner and outer regions, whereas large separations effectively decouple the intruders. At intermediate distances, enhanced crowding around the intruders generates maximal collision-rate asymmetries, leading to the strongest effective interactions. These results identify confinement geometry as a key control parameter for FI forces in active matter.

cond-mat.soft↗

arXiv2025

Optimal chirality enhances long-range fluctuation-induced interactions in active fluids

Understanding interactions between chiral active particles -- self-propelling and self-rotating entities -- is crucial for uncovering how chiral active matter self-organizes into dynamic structures. Although fluctuation-induced forces in nonequilibrium active systems can drive structure formation, the role of chirality remains largely unexplored. We investigate effective fluctuation-induced forces between intruders immersed in chiral active fluids and reveal that the impact of chirality depends sensitively on particle shape. For circular particles, increasing the self-rotation to self-propulsion ratio suppresses the interaction, reflecting a transition from rotating flocks to localized spinners. Contrarily, a striking collective behavior emerges for rodlike particles: vortices spontaneously form around the intruders, most pronounced at an optimal chiral angle where the mean curvature of particle trajectories matches the intruder boundary curvature, maximizing the effective force. We map the attractive and repulsive force regimes across chirality, propulsion, and intruder separation, offering new insights and principles for designing and controlling self-assembled active systems.

cond-mat.soft↗

arXiv2024

Structural dynamics and optimal transport of an active polymer

We study the spontaneous configuration transitions of an active semi-flexible polymer between {\it spiral} and {\it non-spiral} states, and show that the configuration dynamics is fully described by a {\it subcritical pitchfork} bifurcation. Exploiting the fact that active polymer barely moves in {\it spiral} states and exhibits net displacements in {\it non-spiral} states, we theoretically prove that the motion of the active polymer is consistent with a {\it run-and-tumble}-like dynamics. Moreover, we find that there exists an {\it optimal} self-propelling {\it force}, at which the probabilities of finding the polymer in the {\it spiral} and {\it non-spiral} state become equal, that maximizes the diffusion coefficient.

cond-mat.soft↗

arXiv2022

Polymer translocation in an environment of active rods

We consider the dynamics of a translocation process of a flexible linear polymer through a nanopore into an environment of active rods in the {\it trans} side. Using Langevin dynamics simulations we find that the rods facilitate translocation to the {\it trans} side even when there are initially more monomers on the {\it cis} than on the {\it trans} side. Structural analysis of the translocating polymer reveals that active rods induce a folded structure to the {\it trans}-side subchain in the case of successful translocation events. By keeping the initial number of monomers on the {\it cis}-side subchain fixed, we map out a state diagram for successful events as a function of the rod number density for a variety of system parameters. This reveals competition between facilitation by the rods at low densities and crowding that hinders translocation at higher densities.

cond-mat.soft↗

arXiv2022

Translocation of an Active Polymer into a Circular Cavity

Translocation dynamics of an active semi-flexible polymer through a nano-pore into a rigid two dimensional circular cavity, and the polymer packing dynamics have been studied by using Langevin dynamics (LD) simulations. The results show that the force exponent $β$, for regime of small cavity radius, i.e. $R \ll R_{\textrm{g}}$, where $R_{\textrm{g}}$ is the gyration radius of the passive semi-flexible polymer in two dimensional free space, is $β=-1$, while for large values of $R \gg R_{\textrm{g}}$ the asymptotic value of the force exponent is $β\approx -0.92$. The force exponent is defined by the scaling form of the average translocation time $\langle τ\rangle \propto F_{\textrm{sp}}^β$, where $F_{\textrm{sp}}$ is the self-propelling force. Moreover, using the definition of the turning number for the polymer inside the cavity, it has been found that at the end of translocation process for small value of $R$ and in the strong force limit the polymer configuration is more regular than the case in which the value of $R$ is large or the force is weak.

cond-mat.soft↗

arXiv2020

Polymer translocation through nanopore assisted by an environment of active rods

We use a combination of computer simulations and iso-flux tension propagation (IFTP) theory to investigate translocation dynamics of a flexible linear polymer through a nanopore into an environment composed of repulsive active rods in 2D. We demonstrate that the rod activity induces a crowding effect on the polymer, leading to a time-dependent net force that facilitates translocation into the active environment. Incorporating this force into the IFTP theory for pore-driven translocation allows us to characterise translocation dynamics in detail and derive a scaling form for the average translocation time as $\tildeτ \sim \tilde{L}_{\textrm{r}}^ν / \tilde{F}_{\textrm{SP}} $, where $\tilde{L}_{\textrm{r}}$ and $\tilde{F}_{\textrm{SP}}$ are the rod length and self-propelling force acting on the rods, respectively, and $ν$ is the Flory exponent.

cond-mat.soft↗

arXiv2015

Obstruction enhances the diffusivity of self-propelled rod-like particles

Diffusion of self-propelled particles in the presence of randomly distributed obstacles in three dimensions is studied using molecular dynamics simulations. It is found that depending on the magnitude of the propelling force and the particle aspect ratio, the diffusion coefficient can be a monotonically decreasing or a non-monotonic concave function of the obstructed volume fraction. Counterintuitive enhancement of the particle diffusivity with increasing the obstacles crowd is shown to be a combinatory effect of the self-propelling force and the anisotropy in the shape of the particle. Regions corresponding to monotonic and non-monotonic dependence of the particle diffusivity on the obstacle density in propelling force-aspect ratio plane are specified theoretically and using the simulation results.

cond-mat.soft↗

arXiv2012

Directed translocation of a flexible polymer through a cone-shaped channel

Entropy-driven directed translocation of a flexible polymer through a cone-shaped channel is studied theoretically and using computer simulation. For a given length of the channel, the effective force of entropic origin acting on the polymer is calculated as a function of the apex angle of the channel. It is found that the translocation time is a non-monotonic function of the apex angle. By increasing the apex angle from zero, the translocation time shows a minimum and then a maximum. Also, it is found that regardless of the value of the apex angle, the translocation time is a uniformly decreasing function of the channel length. The results of the theory and the simulation are in good qualitative agreement.

cond-mat.soft↗