51 research outputs found
Phase separation and large deviations of lattice active matter
Off-lattice active Brownian particles form clusters and undergo phase
separation even in the absence of attractions or velocity-alignment mechanisms.
Arguments that explain this phenomenon appeal only to the ability of particles
to move persistently in a direction that fluctuates, but existing lattice
models of hard particles that account for this behavior do not exhibit phase
separation. Here we present a lattice model of active matter that exhibits
motility-induced phase separation in the absence of velocity alignment. Using
direct and rare-event sampling of dynamical trajectories we show that
clustering and phase separation are accompanied by pronounced fluctuations of
static and dynamic order parameters. This model provides a complement to
off-lattice models for the study of motility-induced phase separation.Comment: Submitted along with arXiv:1709.03951 as a joint work to PRE and PR
Statistical Mechanics of Transport Processes in Active Fluids II: Equations of Hydrodynamics for Active Brownian Particles
We perform a coarse-graining analysis of the paradigmatic active matter
model, Active Brownian Particles, yielding a continuum description in terms of
balance laws for mass, linear and angular momentum, and energy. The derivation
of the balance of linear momentum reveals that the active force manifests
itself directly as a continuum-level body force proportional to an order
parameter-like director field, which therefore requires its own evolution
equation to complete the continuum description of the system. We derive this
equation, demonstrating in the process that bulk currents may be sustained in
homogeneous systems only in the presence of inter-particle aligning
interactions. Further, we perform a second coarse-graining of the balance of
linear momentum and derive the expression for active or swim pressure in the
case of mechanical equilibrium.Comment: 9 pages, 3 appendices with derivation
Entropy production fluctuations encode collective behavior in active matter
We derive a general lower bound on distributions of entropy production in
interacting active matter systems. The bound is tight in the limit that
interparticle correlations are small and short-ranged, which we explore in four
canonical active matter models. In all models studied, the bound is weak where
collective fluctuations result in long-ranged correlations, which subsequently
links the locations of phase transitions to enhanced entropy production
fluctuations. We develop a theory for the onset of enhanced fluctuations and
relate it to specific phase transitions in active Brownian particles. We also
derive optimal control forces that realize the dynamics necessary to tune
dissipation and manipulate the system between phases. In so doing, we uncover a
general relationship between entropy production and pattern formation in active
matter, as well as ways of controlling it
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