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2011

Soft condensed matter

Articles 1 - 5 of 5

Full-Text Articles in Physics

Generic Phases Of Cross-Linked Active Gels: Relaxation, Oscillation And Contractility, Shiladitya Banerjee, Tanniemola B. Liverpool, M. C. Marchetti Oct 2011

Generic Phases Of Cross-Linked Active Gels: Relaxation, Oscillation And Contractility, Shiladitya Banerjee, Tanniemola B. Liverpool, M. C. Marchetti

Physics - All Scholarship

We study analytically and numerically a generic continuum model of an isotropic active solid with internal stresses generated by non-equilibrium `active' mechano-chemical reactions. Our analysis shows that the gel can be tuned through three classes of dynamical states by increasing motor activity: a constant unstrained state of homogeneous density, a state where the local density exhibits sustained oscillations, and a steady-state which is spontaneously contracted, with a uniform mean density.


Substrate Rigidity Deforms And Polarizes Active Gels, Shiladitya Banerjee, M. C. Marchetti Aug 2011

Substrate Rigidity Deforms And Polarizes Active Gels, Shiladitya Banerjee, M. C. Marchetti

Physics - All Scholarship

We present a continuum model of the coupling between cells and substrate that accounts for some of the observed substrate-stiffness dependence of cell properties. The cell is modeled as an elastic active gel, adapting recently developed continuum theories of active viscoelastic fluids. The coupling to the substrate enters as a boundary condition that relates the cell's deformation field to local stress gradients. In the presence of activity, the coupling to the substrate yields spatially inhomogeneous contractile stresses and deformations in the cell and can enhance polarization, breaking the cell's front-rear symmetry.


Active Jamming: Self-Propelled Soft Particles At High Density, Silke Henkes, Yaouen Fily, M. Christina Marchetti Jul 2011

Active Jamming: Self-Propelled Soft Particles At High Density, Silke Henkes, Yaouen Fily, M. Christina Marchetti

Physics - All Scholarship

We study numerically the phases and dynamics of a dense collection of self-propelled particles with soft repulsive interactions in two dimensions. The model is motivated by recent in vitro experiments on confluent monolayers of migratory epithelial and endothelial cells. The phase diagram exhibits a liquid phase with giant number fluctuations at low packing fraction and high self-propulsion speed and a jammed phase at high packing fraction and low self-propulsion speed. The dynamics of the jammed phase is controlled by the low frequency modes of the jammed packing.


Cooperative Self-Propulsion Of Active And Passive Rotors, Yaouen Fily, Aparna Baskaran, M. Cristina Marchetti Jul 2011

Cooperative Self-Propulsion Of Active And Passive Rotors, Yaouen Fily, Aparna Baskaran, M. Cristina Marchetti

Physics - All Scholarship

Using minimal models for low Reynolds number passive and active rotors in a fluid, we characterize the hydrodynamic interactions among rotors and the resulting dynamics of a pair of interacting rotors. This allows us to treat in a common framework passive or externally driven rotors, such as magnetic colloids driven by a rotating magnetic field, and active or internally driven rotors, such as sperm cells confined at boundaries. The hydrodynamic interaction of passive rotors contains an azimuthal component 1/r2 to dipolar order that can yield the recently discovered “cooperative self-propulsion” of a pair of rotors of opposite vorticity. While this …


Polar Patterns In Active Fluids, Luca Giomi, M. Cristina Marchetti Jun 2011

Polar Patterns In Active Fluids, Luca Giomi, M. Cristina Marchetti

Physics - All Scholarship

We study the spatio-temporal dynamics of a model of polar active fluid in two dimensions. The system exhibits a transition from an isotropic to a polarized state as a function of density. The uniform polarized state is, however, unstable above a critical value of activity. Upon increasing activity, the active fluids displays increasingly complex patterns, including traveling bands, traveling vortices and chaotic behavior. The advection arising from the particles self-propulsion and unique to polar fluids yields qualitatively new behavior as compared to that obtain in active nematic, yielding traveling-wave structures. We show that the nonlinear hydrodynamic equations can be mapped …