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Full-Text Articles in Physics
Instabilities And Oscillations In Isotropic Active Gels, Shiladitya Banerjee, M. Cristina Marchetti
Instabilities And Oscillations In Isotropic Active Gels, Shiladitya Banerjee, M. Cristina Marchetti
Physics - All Scholarship
We present a generic formulation of the continuum elasticity of an isotropic crosslinked active gel. The gel is described by a two-component model consisting of an elastic network coupled frictionally to a permeating fluid. Activity is induced by active crosslinkers that undergo an ATP-activated cycle and transmit forces to the network. The on/off dynamics of the active crosslinkers is described via rate equations for unbound and bound motors. For large activity motors yield a contractile instability of the network. At smaller values of activity, the on/off motor dynamics provides an effective inertial drag on the network that opposes elastic restoring …
Fluctuations And Pattern Formation In Self-Propelled Particles, Shradha Mishra, Aparna Baskaran, M. Cristina Marchetti
Fluctuations And Pattern Formation In Self-Propelled Particles, Shradha Mishra, Aparna Baskaran, M. Cristina Marchetti
Physics - All Scholarship
We consider a coarse-grained description of a system of self-propelled particles given by hydrodynamic equations for the density and polarization fields. We find that the ordered moving or flocking state of the system is unstable to spatial fluctuations beyond a threshold set by the self-propulsion velocity of the individual units. In this region, the system organizes itself into an inhomogeneous state of well-defined propagating stripes of flocking particles interspersed with low density disordered regions. Further, we find that even in the regime where the homogeneous flocking state is stable, the system exhibits large fluctuations in both density and orientational order. …
Paraboloidal Crystals, Mark Bowick, Luca Giomi
Paraboloidal Crystals, Mark Bowick, Luca Giomi
Physics - All Scholarship
The interplay between order and geometry in soft condensed matter systems is an active field with many striking results and even more open problems. Ordered structures on curved surfaces appear in multi-electron helium bubbles, viral and bacteriophage protein capsids, colloidal self-assembly at interfaces and in physical membranes. Spatial curvature can lead to novel ground state configurations featuring arrays of topological defects that would be excited states in planar systems. We illustrate this with a sequence of images showing the Voronoi lattice (in gold) and the corresponding Delaunay triangulations (in green) for ten low energy configurations of a system of classical …
Nonequilibrium Statistical Mechanics Of Self-Propelled Hard Rods, Aparna Baskaran, M. Cristina Marchetti
Nonequilibrium Statistical Mechanics Of Self-Propelled Hard Rods, Aparna Baskaran, M. Cristina Marchetti
Physics - All Scholarship
Using tools of nonequilibirum mechanics, we study a model of self-propelled hard rods on a substrate in two dimensions to quantify the interplay of self-propulsion and excluded-volume effects. We derive of a Smoluchowski equation for the configurational probability density of self-propelled rods that contains several modifications as compared to the familiar Smoluchowski equation for thermal rods. As a side-product of out work, we also present a purely dynamical derivation of the Onsager form of the mean field excluded volume interaction among thermal hard rods.
Sheared Active Fluids: Thickening, Thinning And Vanishing Viscosity, Luca Giomi, Tanniemola B. Liverpool, M. Cristina Marchetti
Sheared Active Fluids: Thickening, Thinning And Vanishing Viscosity, Luca Giomi, Tanniemola B. Liverpool, M. Cristina Marchetti
Physics - All Scholarship
We analyze the behavior of a suspension of active polar particles under shear. In the absence of external forces, orientationally ordered active particles are known to exhibit a transition to a state of non-uniform polarization and spontaneous flow. Such a transition results from the interplay between elastic stresses, due to the liquid crystallinity of the suspension, and internal active stresses. In the presence of an external shear we find an extremely rich variety of phenomena, including an effective reduction (increase) in the apparent viscosity depending on the nature of the active stresses and the flow-alignment property of the particles, as …