arXiv subjects

A. Alexander-Katz

Publications and source records attributed to A. Alexander-Katz.

3 recordsLinked to original sources

arXiv2026

Topology of Nonequilibrium Currents Controls Active Transport

Structured environments repeatedly redirect active particles, producing transport pathways that cannot be readily inferred from individual trajectories. Here, we show that the large-scale organization of these transport pathways is governed by topological constraints. Hydrodynamic scattering generates nonequilibrium current fields whose defect structure, characterized by integer indices, constrain transport pathways and renders them robust to smooth perturbations. This principle is demonstrated with rotating colloids in obstacle arrays and extended to stokeslet and force-dipole flows, thereby linking microscale transport to the topology of hydrodynamically generated nonequilibrium currents.

cond-mat.soft↗

arXiv2015

Elasticity Induced Force Reversal Between Active Spinning Particles in Dense Passive Media

The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here, we study the interactions between active agents in a dense non-active medium. Our system consists of actuated spinning (active) particles embedded in a dense monolayer of passive (non-active) particles. We demonstrate that the presence of the passive monolayer alters dramatically the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a new mechanism for the interaction between active agents in complex and structured media, opening up new opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

cond-mat.soft↗

arXiv2007

Motion-reversal in a simple microscopic swimmer

We study the motion of a microscopic swimmer composed of a semiflexible polymer anchored at the surface of a magnetic sphere using hydrodynamic simulations and scaling arguments. The swimmer is driven by a rotating magnetic field, and displays forward and backward motion depending on the value of the rotational frequency. In particular, the system exhibits forward thrust for frequencies below a critical frequency $ω^*$, while above $ω^*$ the motion is reversed.

cond-mat.soft↗