22 research outputs found
Glassy swirls of active dumbbells
The dynamics of a dense binary mixture of soft dumbbells, each subject to an
active propulsion force and thermal fluctuations, shows a sudden arrest, first
to a translational then to a rotational glass, as one reduces temperature
or the self-propulsion force . Is the temperature-induced glass different
from the activity-induced glass? To address this question, we monitor the
dynamics along an iso-relaxation-time contour in the plane. We find
dramatic differences both in the fragility and in the nature of dynamical
heterogeneity which characterise the onset of glass formation - the
activity-induced glass exhibits large swirls or vortices, whose scale is set by
activity, and appears to diverge as one approaches the glass transition. This
large collective swirling movement should have implications for collective cell
migration in epithelial layers.Comment: 13 pages, 11 figure
Odd elasticity in driven granular matter
Odd elasticity describes the unusual elastic response of solids whose
stress-strain relationship is not compatible with an elastic potential. Here,
we present a study of odd elasticity in a driven granular matter system
composed of grains with ratchet-like interparticle friction and activated by
oscillatory shear. We find that the system permits a time-averaged elasticity
theory featuring nonzero odd elastic coefficients. These coefficients are
explicitly measured using molecular dynamics simulations and can be predicted
and tuned from microscopics. In the presence of disorder, our driven granular
material displays distinctive properties ranging from self-healing grain
boundaries in polycrystalline systems to chiral plastic vortices and force
chain deflection in amorphous packings. Beyond granular matter, our work
motivates the search for microscopic transduction mechanisms that convert
periodic nonuniform drive into uniform elastic properties of active solids.Comment: See supplementary movies at
https://home.uchicago.edu/~vitelli/videos.htm
Robustness of travelling states in generic non-reciprocal mixtures
Emergent non-reciprocal interactions violating Newton's third law are
widespread in out-of-equilibrium systems. It has been demonstrated recently
that phase separating mixtures with such non-reciprocal interactions between
components exhibit travelling states that have no equilibrium counterpart.
Using extensive Brownian dynamics simulations, we investigate the existence and
stability of such travelling states in the collective dynamics of a generic
non-reciprocal particle system. By varying a broad range of parameters
including aggregate state of the mixture components, diffusivity, degree of
non-reciprocity, effective spatial dimension and density, we determine that
these dynamic travelling states exist only in a relatively narrow region of
parameter space. Our work also sheds light on the physical mechanisms for the
disappearance of travelling states when relevant parameters are being varied.
Our results have implications for a range of non-equilibrium systems including
non-reciprocal phase separating mixtures, non-equilibrium pattern formation and
predator-prey models.Comment: 6 pages, 5 figure
Activity controls fragility: A Random First Order Transition Theory for an active glass
How does nonequilibrium activity modify the approach to a glass? This is an
important question, since many experiments reveal the near-glassy nature of the
cell interior, remodelled by activity. However, different simulations of dense
assemblies of active particles, parametrised by a self-propulsion force, ,
and persistence time, , appear to make contradictory predictions about
the influence of activity on characteristic features of glass, such as
fragility. This calls for a broad conceptual framework to understand active
glasses; here we extend the Random First-Order Transition (RFOT) theory to a
dense assembly of self-propelled particles. We compute the active contribution
to the configurational entropy using an effective medium approach - that of a
single particle in a caging-potential. This simple active extension of RFOT
provides excellent quantitative fits to existing simulation results. We find
that whereas always inhibits glassiness, the effect of is more
subtle and depends on the microscopic details of activity. In doing so, the
theory automatically resolves the apparent contradiction between the simulation
models. The theory also makes several testable predictions, which we verify by
both existing and new simulation data, and should be viewed as a step towards a
more rigorous analytical treatment of active glass