harsh soni | Indian Institute of Science (original) (raw)
Papers by harsh soni
Physical Review E
We present a theory for the interaction between motile particles in an elastic medium on a substr... more We present a theory for the interaction between motile particles in an elastic medium on a substrate, relying on two arguments: a moving particle creates a conspicuously fore-aft asymmetric distortion in the the elastic medium; this strain field reorients other particles. We show that this leads to sensing, attraction and pursuit, with a non-reciprocal character, between a pair of motile particles. We confirm the predicted distortion fields and non-mutual trail-following in our experiments and simulations on polar granular rods made motile by vibration, moving through a dense monolayer of beads in its crystalline phase. Our theory should be of relevance to the interaction of motile cells in the extracellular matrix or in a supported layer of gel or tissue.
Bulletin of the American Physical Society, 2019
Bulletin of the American Physical Society, 2018
We show, through experiments and simulations, that geometrically polar granular rods, rendered ac... more We show, through experiments and simulations, that geometrically polar granular rods, rendered active by the transduction of vertical vibration, undergo a collective trapping phase transition in the presence of a V-shaped obstacle when the opening angle drops below a threshold value thetac\theta_cthetac. We propose a theoretical explanation for the phenomenon, based on a competition between motility-induced phase separation (MIPS) and the collective expulsion of smectic tilt-boundary structures that form inside the wedge. Our numerical experiments support the resulting predictions that thetac\theta_cthetac decreases with increasing angular noise and that aggregate growth saturates at a horizon radius. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Bulletin of the American Physical Society, 2016
We report experiments and simulations on collective trapping in a horizontal monolayer of tapered... more We report experiments and simulations on collective trapping in a horizontal monolayer of tapered granular rods rendered motile by mechanical vibration. A macroscopic fraction of the particles are trapped by a V-shaped obstacle if its opening angle is less than a threshold value of about 120 degrees, consistent with active Brownian simulations [PRL 108, 268307 (2012)]. the transition between trapped and untrapped states becomes sharper with increasing system size in our numerical studies. We offer a theoretical understanding of this nonequilibrium phase transition based on collective noise suppression and an analysis of fluxes. We show also that the trap can serve to separate particles based on their motility and rotational diffusivity.
Physical review. E, 2016
We show, through experiments and simulations, that geometrically polar granular rods, rendered ac... more We show, through experiments and simulations, that geometrically polar granular rods, rendered active by the transduction of vertical vibration, undergo a collective trapping phase transition in the presence of a V-shaped obstacle when the opening angle drops below a threshold value. We propose a mechanism that accounts qualitatively for the transition, based on the cooperative reduction of angular noise with increasing area fraction. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Soft Matter
We present a large-scale numerical study, supplemented by experimental observations, of a quasi-t... more We present a large-scale numerical study, supplemented by experimental observations, of a quasi-two-dimensional active system of polar rods and spherical beads confined between two horizontal plates and energised by vertical...
Physical Review E, 2016
Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is... more Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is subject to compression. Motivated by recent experiments [Agrawal et al., Soft Matter 8, 7138 (2012)] that show how wrinkle morphology can be controlled by using a nematic elastomer substrate, we develop the theory of small-amplitude wrinkles of an isotropic film atop a nematic elastomer. The directors of the nematic elastomer are assumed to lie in a plane parallel to the plane of the undeformed film. For uniaxial compression of the film along the direction perpendicular to the elastomer directors, the system behaves as a compressed film on an isotropic substrate. When the uniaxial compression is along the direction of nematic order, we find that the soft elasticity characteristic of liquid crystal elastomers leads to a critical stress for wrinkling which is very small compared to the case of an isotropic substrate. We also determine the wavelength of the wrinkles at the critical stress, and show how the critical stress and wavelength depend on substrate depth and the anisotropy of the polymer chains in the nematic elastomer.
Bulletin of the American Physical Society, Mar 2, 2015
Submitted for the MAR15 Meeting of The American Physical Society Flocking at a distance in granul... more Submitted for the MAR15 Meeting of The American Physical Society Flocking at a distance in granular matter HARSH SONI, Indian Institute of Science, SRIRAM RAMASWAMY, TIFR Hyderabad-A mixture of polar granular rods and spherical beads on a vibrated plate undergoes a phase transition to an orientationally ordered state above a critical bead concentration. We study this system using large scale numerical simulations with periodic boundary conditions. We find an intermediate state with banded structures between the disordered and the globally ordered state. We observe a single band whose width increases with rod concentration. We find that at high densities the rods and the beads phase separate. We also test the various theoretical predictions of the hydrodynamic theory in the ordered state. Our results, which are in good agreement with the theory, are following: We see a highly anisotropic dispersion relation are exhibited with two sound modes in all directions except along the flock. Further the rods are super diffusive in the transverse direction and exhibit large number fluctuations.
Nature Communications, 2014
The Isometric Fluctuation Relation (IFR) [P.I. Hurtado et al., PNAS 108, 7704 (2011)] relates the... more The Isometric Fluctuation Relation (IFR) [P.I. Hurtado et al., PNAS 108, 7704 (2011)] relates the relative probability of current fluctuations of fixed magnitude in different spatial directions. We test its validity in an experiment on a tapered rod, rendered motile by vertical vibration and immersed in a sea of spherical beads. We analyse the statistics of the velocity vector of the rod and show that they depart significantly from the IFR of Hurtado et al. Aided by a Langevin-equation model we show that our measurements are largely described by an anisotropic generalization of the IFR [R. Villavicencio et al., EPL 105, 30009 (2014)], with no fitting parameters, but with a discrepancy in the prefactor whose origin may lie in the detailed statistics of the microscopic noise. The experimentally determined Large-Deviation Function of the velocity vector has a kink on a curve in the plane.
Soft Matter
We study the linear stability of an isotropic active fluid in three different geometries: a film ... more We study the linear stability of an isotropic active fluid in three different geometries: a film of active fluid on a rigid substrate, a cylindrical thread of fluid, and a spherical fluid droplet.
Physical Review Letters
We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. ... more We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. Activity changes the effective shear viscosity, reducing it to zero at a critical value of activity. Expanding in the sheet amplitude, we find that the correction to the swimming speed due to activity is inversely proportional to the effective shear viscosity. Our perturbative calculation becomes invalid near the critical value of activity; using numerical methods to probe this regime, we find that activity enhances the swimming speed by an order of magnitude compared to the passive case.
Physical Review E
We present an experimental realization of the collective trapping phase transition [Kaiser et al.... more We present an experimental realization of the collective trapping phase transition [Kaiser et al., Phys. Rev. Lett. 108, 268307 (2012)], using motile polar granular rods in the presence of a Vshaped obstacle. We offer a theory of this transition based on the interplay of motility-induced condensation and liquid-crystalline ordering and show that trapping occurs when persistent influx overcomes the collective expulsion of smectic defect structures. In agreement with the theory, our experiments find that a trap fills to the brim when the trap angle θ is below a threshold θc, while all particles escape for θ > θc. Our simulations support a further prediction, that θc goes down with increasing rotational noise. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Applied Physics Letters, 2009
We report that the average rotation speed of optically trapped crenated erythrocytes is direct si... more We report that the average rotation speed of optically trapped crenated erythrocytes is direct signature of their membrane deformability. When placed in hypertonic buffer, discocytic erythrocytes are subjected to crenation. The deformation of cells brings in chirality and asymmetry in shape that make them rotate under the scattering force of a linearly polarized optical trap. A change in the deformability of the erythrocytes, due to any internal or environmental factor, affects the rotation speed of the trapped crenated cells. Here we show how the increment in erythrocyte membrane rigidity with adsorption of Ca ++ ions can be exhibited through this approach.
Physical Review E
We present a theory for the interaction between motile particles in an elastic medium on a substr... more We present a theory for the interaction between motile particles in an elastic medium on a substrate, relying on two arguments: a moving particle creates a conspicuously fore-aft asymmetric distortion in the the elastic medium; this strain field reorients other particles. We show that this leads to sensing, attraction and pursuit, with a non-reciprocal character, between a pair of motile particles. We confirm the predicted distortion fields and non-mutual trail-following in our experiments and simulations on polar granular rods made motile by vibration, moving through a dense monolayer of beads in its crystalline phase. Our theory should be of relevance to the interaction of motile cells in the extracellular matrix or in a supported layer of gel or tissue.
Bulletin of the American Physical Society, 2019
Bulletin of the American Physical Society, 2018
We show, through experiments and simulations, that geometrically polar granular rods, rendered ac... more We show, through experiments and simulations, that geometrically polar granular rods, rendered active by the transduction of vertical vibration, undergo a collective trapping phase transition in the presence of a V-shaped obstacle when the opening angle drops below a threshold value thetac\theta_cthetac. We propose a theoretical explanation for the phenomenon, based on a competition between motility-induced phase separation (MIPS) and the collective expulsion of smectic tilt-boundary structures that form inside the wedge. Our numerical experiments support the resulting predictions that thetac\theta_cthetac decreases with increasing angular noise and that aggregate growth saturates at a horizon radius. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Bulletin of the American Physical Society, 2016
We report experiments and simulations on collective trapping in a horizontal monolayer of tapered... more We report experiments and simulations on collective trapping in a horizontal monolayer of tapered granular rods rendered motile by mechanical vibration. A macroscopic fraction of the particles are trapped by a V-shaped obstacle if its opening angle is less than a threshold value of about 120 degrees, consistent with active Brownian simulations [PRL 108, 268307 (2012)]. the transition between trapped and untrapped states becomes sharper with increasing system size in our numerical studies. We offer a theoretical understanding of this nonequilibrium phase transition based on collective noise suppression and an analysis of fluxes. We show also that the trap can serve to separate particles based on their motility and rotational diffusivity.
Physical review. E, 2016
We show, through experiments and simulations, that geometrically polar granular rods, rendered ac... more We show, through experiments and simulations, that geometrically polar granular rods, rendered active by the transduction of vertical vibration, undergo a collective trapping phase transition in the presence of a V-shaped obstacle when the opening angle drops below a threshold value. We propose a mechanism that accounts qualitatively for the transition, based on the cooperative reduction of angular noise with increasing area fraction. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Soft Matter
We present a large-scale numerical study, supplemented by experimental observations, of a quasi-t... more We present a large-scale numerical study, supplemented by experimental observations, of a quasi-two-dimensional active system of polar rods and spherical beads confined between two horizontal plates and energised by vertical...
Physical Review E, 2016
Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is... more Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is subject to compression. Motivated by recent experiments [Agrawal et al., Soft Matter 8, 7138 (2012)] that show how wrinkle morphology can be controlled by using a nematic elastomer substrate, we develop the theory of small-amplitude wrinkles of an isotropic film atop a nematic elastomer. The directors of the nematic elastomer are assumed to lie in a plane parallel to the plane of the undeformed film. For uniaxial compression of the film along the direction perpendicular to the elastomer directors, the system behaves as a compressed film on an isotropic substrate. When the uniaxial compression is along the direction of nematic order, we find that the soft elasticity characteristic of liquid crystal elastomers leads to a critical stress for wrinkling which is very small compared to the case of an isotropic substrate. We also determine the wavelength of the wrinkles at the critical stress, and show how the critical stress and wavelength depend on substrate depth and the anisotropy of the polymer chains in the nematic elastomer.
Bulletin of the American Physical Society, Mar 2, 2015
Submitted for the MAR15 Meeting of The American Physical Society Flocking at a distance in granul... more Submitted for the MAR15 Meeting of The American Physical Society Flocking at a distance in granular matter HARSH SONI, Indian Institute of Science, SRIRAM RAMASWAMY, TIFR Hyderabad-A mixture of polar granular rods and spherical beads on a vibrated plate undergoes a phase transition to an orientationally ordered state above a critical bead concentration. We study this system using large scale numerical simulations with periodic boundary conditions. We find an intermediate state with banded structures between the disordered and the globally ordered state. We observe a single band whose width increases with rod concentration. We find that at high densities the rods and the beads phase separate. We also test the various theoretical predictions of the hydrodynamic theory in the ordered state. Our results, which are in good agreement with the theory, are following: We see a highly anisotropic dispersion relation are exhibited with two sound modes in all directions except along the flock. Further the rods are super diffusive in the transverse direction and exhibit large number fluctuations.
Nature Communications, 2014
The Isometric Fluctuation Relation (IFR) [P.I. Hurtado et al., PNAS 108, 7704 (2011)] relates the... more The Isometric Fluctuation Relation (IFR) [P.I. Hurtado et al., PNAS 108, 7704 (2011)] relates the relative probability of current fluctuations of fixed magnitude in different spatial directions. We test its validity in an experiment on a tapered rod, rendered motile by vertical vibration and immersed in a sea of spherical beads. We analyse the statistics of the velocity vector of the rod and show that they depart significantly from the IFR of Hurtado et al. Aided by a Langevin-equation model we show that our measurements are largely described by an anisotropic generalization of the IFR [R. Villavicencio et al., EPL 105, 30009 (2014)], with no fitting parameters, but with a discrepancy in the prefactor whose origin may lie in the detailed statistics of the microscopic noise. The experimentally determined Large-Deviation Function of the velocity vector has a kink on a curve in the plane.
Soft Matter
We study the linear stability of an isotropic active fluid in three different geometries: a film ... more We study the linear stability of an isotropic active fluid in three different geometries: a film of active fluid on a rigid substrate, a cylindrical thread of fluid, and a spherical fluid droplet.
Physical Review Letters
We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. ... more We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. Activity changes the effective shear viscosity, reducing it to zero at a critical value of activity. Expanding in the sheet amplitude, we find that the correction to the swimming speed due to activity is inversely proportional to the effective shear viscosity. Our perturbative calculation becomes invalid near the critical value of activity; using numerical methods to probe this regime, we find that activity enhances the swimming speed by an order of magnitude compared to the passive case.
Physical Review E
We present an experimental realization of the collective trapping phase transition [Kaiser et al.... more We present an experimental realization of the collective trapping phase transition [Kaiser et al., Phys. Rev. Lett. 108, 268307 (2012)], using motile polar granular rods in the presence of a Vshaped obstacle. We offer a theory of this transition based on the interplay of motility-induced condensation and liquid-crystalline ordering and show that trapping occurs when persistent influx overcomes the collective expulsion of smectic defect structures. In agreement with the theory, our experiments find that a trap fills to the brim when the trap angle θ is below a threshold θc, while all particles escape for θ > θc. Our simulations support a further prediction, that θc goes down with increasing rotational noise. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
Applied Physics Letters, 2009
We report that the average rotation speed of optically trapped crenated erythrocytes is direct si... more We report that the average rotation speed of optically trapped crenated erythrocytes is direct signature of their membrane deformability. When placed in hypertonic buffer, discocytic erythrocytes are subjected to crenation. The deformation of cells brings in chirality and asymmetry in shape that make them rotate under the scattering force of a linearly polarized optical trap. A change in the deformability of the erythrocytes, due to any internal or environmental factor, affects the rotation speed of the trapped crenated cells. Here we show how the increment in erythrocyte membrane rigidity with adsorption of Ca ++ ions can be exhibited through this approach.