arXiv subjects

Jyothishraj Nambisan

Publications and source records attributed to Jyothishraj Nambisan.

3 recordsLinked to original sources

arXiv2023

First order alignment transition in an interfaced active nematic

We investigate experimentally the dynamic phase transition of a two-dimensional active nematic layer interfaced with a passive liquid crystal. Under a temperature ramp that leads to the transition of the passive liquid into a highly anisotropic lamellar smectic-A phase, and in the presence of a magnetic field, the coupled active nematic reorganizes its flow and orientational patterns from the turbulent into a quasi-laminar regime aligned perpendicularly to the field. Remarkably, while the phase transition of the passive fluid is known to be continuous, our observations reveal intermittent dynamics of the order parameter and the coexistence of aligned and turbulent regions in the active nematic, a signature of discontinuous, or first order, phase transitions.

cond-mat.soft↗

arXiv2022

Physically-informed data-driven modeling of active nematics

A continuum description is essential for understanding a variety of collective phenomena in active matter. However, building quantitative continuum models of active matter from first principles can be extremely challenging due to both the gaps in our knowledge and the complicated structure of nonlinear interactions. Here we use a novel physically-informed data-driven approach to construct a complete mathematical model of an active nematic from experimental data describing kinesin-driven microtubule bundles confined to an oil-water interface. We find that the structure of the model is similar to the Leslie-Ericksen and Beris-Edwards models, but there are significant and important differences. Rather unexpectedly, elastic effects are found to play no role in the experiments considered, with the dynamics controlled entirely by the balance between active stresses and friction stresses.

cond-mat.soft↗

arXiv2020

Phases and excitations of active rod-bead mixtures: simulations and experiments

We present a large-scale numerical study, supplemented by experimental observations, of a quasi-two-dimensional active system of polar rods and spherical beads confined between two horizontal plates and energised by vertical vibration. For low rod concentrations $Φ_r$ we observe a direct phase transition, as bead concentration $Φ_b$ is increased, from the isotropic phase to a homogeneous flock. For $Φ_r$ above a threshold value, an ordered band dense in both rods and beads occurs between the disordered phase and the homogeneous flock, in both experiments and simulations. Within the size ranges accessible we observe only a single band, whose width increases with $Φ_r$. Deep in the ordered state, we observe broken-symmetry "sound" modes and giant number fluctuations. The direction-dependent sound speeds and the scaling of fluctuations are consistent with the predictions of field theories of flocking, but sound damping rates show departures from such theories. At very high densities we see phase separation into rod-rich and bead-rich regions, both of which move coherently.

cond-mat.soft↗