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

  title={Phases and excitations of active rod-bead mixtures: simulations and experiments.},
  author={Harsh Soni and Nitin Kumar and Jyothishraj Nambisan and Rahul K Gupta and A. K. Sood and Sriram Ramaswamy},
  journal={Soft matter},
We present a large-scale numerical study, supplemented by experimental observations, on a quasi-two-dimensional active system of polar rods and spherical beads confined between two horizontal plates and energised by vertical vibration. For a low rod concentration Φr, our observations are consistent with a direct phase transition, as bead concentration Φb is increased, from the isotropic phase to a homogeneous flock. For Φr above a threshold value, an ordered band dense in both rods and beads… 

Algebraic correlations and anomalous fluctuations in ordered flocks of Janus particles fueled by an AC electric field

We study the polar collective dynamics of Janus colloidal particles fueled by an AC electric field. When the density is high enough, the polar interactions between the particles induce a polar

Hohenberg-Mermin-Wagner-Type Theorems for Equilibrium Models of Flocking.

It is proved that two-dimensional Vicsek type models do not spontaneously break the rotational symmetry in their equilibrium states at any nonzero temperature, and suggests that the origin of the symmetry breaking should be sought in the absence of a detailed balance condition, or, equivalently, in nonequilibrium nature.

Heterogeneous bacterial swarms with mixed lengths.

The results suggest a physical advantage for the spontaneous heterogeneity of bacterial swarm populations, particularly around which aggregates of short, rapidly moving cells can form, resulting in enhanced swarming speeds.

Mechanically driven active and passive grains as models for egress dynamics

Passages of people or cattle through narrow entrances or exits occur in manifold situations. They are difficult to study experimentally, because one has to carefully separate objective, physical

Polar swimmers induce several phases in active nematics.

A minimal model for the mixture of polar particles in active nematics is developed and it is found that theActive nematics in such a mixture are highly sensitive to the presence of Polar particles and show the formation of large scale higher order structures for a relatively low polar particle density.



Swimmer Suspensions on Substrates: Anomalous Stability and Long-Range Order.

It is shown that, depending on the sign of a single parameter, a state with polar orientational order is anomalously stable (or anomalously unstable), with a nonzero relaxation rate for angular fluctuations, not parallel to the ordering direction, at zero wave number.

Nonequilibrium steady states in a vibrated-rod monolayer: tetratic, nematic, and smectic correlations

We study experimentally the nonequilibrium phase behaviour of a horizontal monolayer of macroscopic rods. The motion of the rods in two dimensions is driven by vibrations in the vertical direction.

Flocking at a distance in active granular matter

It is reported here that millimetre-sized tapered rods, rendered motile by contact with an underlying vibrated surface and interacting through a medium of spherical beads, undergo a phase transition to a state of spontaneous alignment of velocities and orientations above a threshold bead area fraction.

Low-noise phase of a two-dimensional active nematic system.

This work systematically study the two-dimensional fluctuating ordered phase in a coarse-grained hydrodynamic description involving both the nematic director and the conserved density field, showing that the system always displays only quasi-long-ranged orientational order beyond a crossover scale.

Vibrated polar disks: spontaneous motion, binary collisions, and collective dynamics

We study the spontaneous motion, binary collisions, and collective dynamics of “polar disks”, i.e. specially designed particles which, when vibrated between two horizontal plates, move coherently

Long-range ordering of vibrated polar disks.

This work presents a model reproducing quantitatively the single, binary, and collective properties of this granular system usingibrated polar disks, and shows in silico that true long-range order is possible in the experimental system.

Defect Unbinding in Active Nematics.

It is shown that activity, within perturbation theory, lowers the defect-unbinding transition temperature, determining a critical line in the temperature-activity plane that separates the quasi-long-range ordered (nematic) and disordered (isotropic) phases.

The low noise phase of a 2d active nematic

We consider a collection of self-driven apolar particles on a substrate that organize into an active nematic phase at sufficiently high density or low noise. Using the dynamical renormalization

Active nematics on a substrate: Giant number fluctuations and long-time tails

We construct the equations of motion for the coupled dynamics of order parameter and concentration for the nematic phase of driven particles on a solid surface, and show that they imply i) giant

Sounds and hydrodynamics of polar active fluids

It is demonstrated that two mixed modes, coupling density and velocity fluctuations, propagate along all directions in colloidal-roller fluids and it is shown how the six material constants defining the linear hydrodynamics of these active liquids can be measured from their spontaneous fluctuation spectrum, while being out of reach of conventional rheological methods.