119 research outputs found
Effective temperature and glassy dynamics of active matter
A systematic expansion of the many-body master equation for active matter, in
which motors power configurational changes as in the cytoskeleton, is shown to
yield a description of the steady state and responses in terms of an effective
temperature. The effective temperature depends on the susceptibility of the
motors and a Peclet number which measures their strength relative to thermal
Brownian diffusion. The analytic prediction is shown to agree with previous
numerical simulations and experiments. The mapping also establishes a
description of aging in active matter that is also kinetically jammed.Comment: 2 figure
Tensegrity and Motor-Driven Effective Interactions in a Model Cytoskeleton
Actomyosin networks are major structural components of the cell. They provide
mechanical integrity and allow dynamic remodeling of eukaryotic cells,
self-organizing into the diverse patterns essential for development. We provide
a theoretical framework to investigate the intricate interplay between local
force generation, network connectivity and collective action of molecular
motors. This framework is capable of accommodating both regular and
heterogeneous pattern formation, arrested coarsening and macroscopic
contraction in a unified manner. We model the actomyosin system as a motorized
cat's cradle consisting of a crosslinked network of nonlinear elastic filaments
subjected to spatially anti-correlated motor kicks acting on motorized (fibril)
crosslinks. The phase diagram suggests there can be arrested phase separation
which provides a natural explanation for the aggregation and coalescence of
actomyosin condensates. Simulation studies confirm the theoretical picture that
a nonequilibrium many-body system driven by correlated motor kicks can behave
as if it were at an effective equilibrium, but with modified interactions that
account for the correlation of the motor driven motions of the actively bonded
nodes. Regular aster patterns are observed both in Brownian dynamics
simulations at effective equilibrium and in the complete stochastic
simulations. The results show that large-scale contraction requires correlated
kicking.Comment: 38 pages, 13 figure
Immune cells use active tugging forces to distinguish affinity and accelerate evolution
Cells are known to exert forces to sense their physical surroundings for
guidance of motion and fate decisions. Here, we propose that cells might do
mechanical work to drive their own evolution, taking inspiration from the
adaptive immune system. Growing evidence indicates that immune B cells -
capable of rapid Darwinian evolution - use cytoskeletal forces to actively
extract antigen from other cells' surface. To elucidate the evolutionary
significance of force usage, we develop a theory of tug-of-war antigen
extraction that maps receptor binding characteristics to clonal reproductive
fitness, revealing physical determinants of selection strength. This framework
unifies mechanosensing and affinity-discrimination capabilities of evolving
cells: pulling against stiff antigen tethers enhances discrimination stringency
at the expense of absolute extraction. As a consequence, active force usage can
accelerate adaptation but may also cause extinction of cell populations,
resulting in an optimal range of pulling strength that matches molecular
rupture forces observed in cells. Our work suggests that nonequilibrium,
physical extraction of environmental signals can make biological systems more
evolvable at a moderate energy cost.Comment: 14 pages, 6 figure
Entanglement tongue and quantum synchronization of disordered oscillators
We study the synchronization of dissipatively-coupled van der Pol oscillators
in the quantum limit, when each oscillator is near its quantum ground state.
Two quantum oscillators with different frequencies exhibit an entanglement
tongue, which is the quantum analogue of an Arnold tongue. It means that the
oscillators are entangled in steady state when the coupling strength is greater
than a critical value, and the critical coupling increases with detuning. An
ensemble of many oscillators with random frequencies still exhibits a
synchronization phase transition in the quantum limit, and we analytically
calculate how the critical coupling depends on the frequency disorder. Our
results can be experimentally observed with trapped ions or neutral atoms.Comment: 11 pages, 5 figure
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