35 research outputs found
Elastic Effects in Disordered Nematic Networks
Elastic effects in a model of disordered nematic elastomers are numerically
investigated in two dimensions. Networks crosslinked in the isotropic phase
exhibit unusual soft mechanical response against stretching. It arises from
gradual alignment of orientationally correlated regions that are elongated
along the director. A sharp crossover to a macroscopically aligned state is
obtained on further stretching. The effect of random internal stress is also
discussed.Comment: 5 pages, 5 figure
Synchronization in A Carpet of Hydrodynamically Coupled Rotors with Random Intrinsic Frequency
We investigate synchronization caused by long-range hydrodynamic interaction
in a two-dimensional, substrated array of rotors with random intrinsic
frequencies. The rotor mimics a flagellated bacterium that is attached to the
substrate ("bacterial carpet") and exerts an active force on the fluid.
Transition from coherent to incoherent regimes is studied numerically, and the
results are compared to a mean-field theory. We show that quite a narrow
distribution of the intrinsic frequency is required to achieve collective
motion in realistic cases. The transition is gradual, and the critical behavior
is qualitatively different from that of the conventional globally coupled
oscillators. The model not only serves as a novel example of non-locally
coupled oscillators, but also provides insights into the role of intrinsic
heterogeneities in living and artificial microfluidic actuators.Comment: 5 pages, 5 figure
Generic Conditions for Hydrodynamic Synchronization
Synchronization of actively oscillating organelles such as cilia and flagella
facilitates self-propulsion of cells and pumping fluid in low Reynolds number
environments. To understand the key mechanism behind synchronization induced by
hydrodynamic interaction, we study a model of rigid-body rotors making fixed
trajectories of arbitrary shape under driving forces that are arbitrary
functions of the phases. For a wide class of geometries, we obtain the
necessary and sufficient conditions for synchronization of a pair of rotors. We
also find a novel synchronized pattern with a time-dependent phase shift. Our
results shed light on the role of hydrodynamic interactions in biological
systems, and could help in developing efficient mixing and transport strategies
in microfluidic devices.Comment: 4 pages, 3 figure
Dynamics of Orientational Phase Ordering Coupled to Elastic Degrees of Freedom
Slow dynamics in complex systems : 3rd International Symposium on Slow Dynamics in Complex Systems, Sendai, Japan, 3-8 November 2003 / editors, Tokuyama Michio, Irwin Oppenheim ; sponsoring organizations, Institute of Fluid Science, Tohoku University Ministry of Education, Culture, Sports, Science and Technology of Japa
Anomalous elasticity of disordered nematic gels
Statistical physics : third Tohwa University international conference : Fukuoka, Japan 8-12 November 1999 / editor Michio Tokuyama, H. Eugene Stanle
Synchronization and Collective Dynamics in a Carpet of Microfluidic Rotors
We study synchronization of an array of rotors on a substrate that are
coupled by hydrodynamic interaction. The rotors that are modeled by an
effective rigid body, are driven by an internal torque and exerts an active
force on the surrounding fluid. The long-ranged nature of the hydrodynamic
interaction between the rotors causes a rich pattern of dynamical behaviors
including phase ordering and turbulent spiral waves. The model provides a novel
example of coupled oscillators with long-range interaction. Our results suggest
strategies for designing controllable microfluidic mixers using the emergent
behavior of hydrodynamically coupled active components.Comment: 4 pages, 3 figure
Numerical simulation of the twist-grain-boundary phase of chiral liquid crystals
We study the core structure of the twist-grain-boundary (TGB) phase of chiral
liquid crystals by numerically minimizing the Landau-de Gennes free energy. We
analyze the morphology of layers at the grain boundary, to better understand
the mechanism of frustration between the smectic layer order and chirality. As
the chirality increases, the effective bending rigidity of layers is reduced
due to unlocking of the layer orientation and the director. This results in
large deviation of the layer morphology from that of Scherk's first minimal
surface and linear stack of screw dislocations (LSD).Comment: 4 pages and 6 figure
Vortex phase matching of a self-propelled model of fish with autonomous fin motion
It has been a long-standing problem how schooling fish optimize their motion
by exploiting the vortices shed by the others. A recent experimental study
showed that a pair of fish reduce energy consumption by matching the phases of
their tailbeat according to their distance. In order to elucidate the dynamical
mechanism by which fish control the motion of caudal fins via vortex-mediated
hydrodynamic interactions, we introduce a new model of a self-propelled swimmer
with an active flapping plate. The model incorporates the role of the central
pattern generator network that generates rhythmic but noisy activity of the
caudal muscle, in addition to hydrodynamic and elastic torques on the fin. For
a solitary fish, the model reproduces a linear relation between the swimming
speed and tailbeat frequency, as well as the distributions of the speed,
tailbeat amplitude, and frequency. For a pair of fish, both the distribution
function and energy dissipation rate exhibit periodic patterns as functions of
the front-back distance and phase difference of the flapping motion. We show
that a pair of fish spontaneously adjust their distance and phase difference
via hydrodynamic interaction to reduce energy consumption.Comment: 18 pages, 11 figure