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Dive into the research topics where Barath Ezhilan is active.

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Featured researches published by Barath Ezhilan.


Physics of Fluids | 2013

Instabilities and nonlinear dynamics of concentrated active suspensions

Barath Ezhilan; Michael Shelley; David Saintillan

Suspensions of active particles, such as motile microorganisms and artificial microswimmers, are known to undergo a transition to complex large-scale dynamics at high enough concentrations. While a number of models have demonstrated that hydrodynamic interactions can in some cases explain these dynamics, collective motion in experiments is typically observed at such high volume fractions that steric interactions between nearby swimmers are significant and cannot be neglected. This raises the question of the respective roles of steric vs hydrodynamic interactions in these dense systems, which we address in this paper using a continuum theory and numerical simulations. The model we propose is based on our previous kinetic theory for dilute suspensions, in which a conservation equation for the distribution function of particle configurations is coupled to the Stokes equations for the fluid motion [D. Saintillan and M. J. Shelley, “Instabilities, pattern formation, and mixing in active suspensions,” Phys. Flu...


Scientific Reports | 2015

Vapor-Driven Propulsion of Catalytic Micromotors.

Renfeng Dong; Jinxing Li; Isaac Rozen; Barath Ezhilan; Tailin Xu; Caleb Christianson; Wei Gao; David Saintillan; Biye Ren; Joseph Wang

Chemically-powered micromotors offer exciting opportunities in diverse fields, including therapeutic delivery, environmental remediation, and nanoscale manufacturing. However, these nanovehicles require direct addition of high concentration of chemical fuel to the motor solution for their propulsion. We report the efficient vapor-powered propulsion of catalytic micromotors without direct addition of fuel to the micromotor solution. Diffusion of hydrazine vapor from the surrounding atmosphere into the sample solution is instead used to trigger rapid movement of iridium-gold Janus microsphere motors. Such operation creates a new type of remotely-triggered and powered catalytic micro/nanomotors that are responsive to their surrounding environment. This new propulsion mechanism is accompanied by unique phenomena, such as the distinct off-on response to the presence of fuel in the surrounding atmosphere, and spatio-temporal dependence of the motor speed borne out of the concentration gradient evolution within the motor solution. The relationship between the motor speed and the variables affecting the fuel concentration distribution is examined using a theoretical model for hydrazine transport, which is in turn used to explain the observed phenomena. The vapor-powered catalytic micro/nanomotors offer new opportunities in gas sensing, threat detection, and environmental monitoring, and open the door for a new class of environmentally-triggered micromotors.


Journal of Fluid Mechanics | 2015

On the distribution and swim pressure of run-and-tumble particles in confinement

Barath Ezhilan; Roberto Alonso-Matilla; David Saintillan

The spatial and orientational distribution in a dilute active suspension of non-Brownian run-and-tumble spherical swimmers confined between two planar hard walls is calculated theoretically. Using a kinetic model based on coupled bulk/surface probability density functions, we demonstrate the existence of a concentration wall boundary layer with thickness scaling with the run length, the absence of polarization throughout the channel, and the presence of sharp discontinuities in the bulk orientation distribution in the neighborhood of orientations parallel to the wall in the near-wall region. Our model is also applied to calculate the swim pressure in the system, which approaches the previously proposed ideal-gas behavior in wide channels but is found to decrease in narrow channels as a result of confinement. Monte-Carlo simulations are also performed for validation and show excellent quantitative agreement with our theoretical predictions.


Physics of Fluids | 2012

Chaotic dynamics and oxygen transport in thin films of aerotactic bacteria

Barath Ezhilan; Amir Alizadeh Pahlavan; David Saintillan

A kinetic model and three-dimensional numerical simulations are applied to study the dynamics in suspensions of run-and-tumble aerotactic bacteria confined in free-standing liquid films surrounded by air. In thin films, oxygen and bacterial concentration profiles approach steady states. In thicker films, a transition to chaotic dynamics is shown to occur and is characterized by unsteady correlated motions, the formation of bacterial plumes, and enhanced oxygen transport and consumption. This transition, also observed in previous experiments, arises as a result of the coupling between the aerotactic response of the bacteria and the flow fields they generate via hydrodynamic interactions.


Biomicrofluidics | 2016

Microfluidic rheology of active particle suspensions: Kinetic theory

Roberto Alonso-Matilla; Barath Ezhilan; David Saintillan

We analyze the effective rheology of a dilute suspension of self-propelled slender particles confined between two infinite parallel plates and subject to a pressure-driven flow. We use a continuum kinetic model to describe the configuration of the particles in the system, in which the disturbance flows induced by the swimmers are taken into account, and use it to calculate estimates of the suspension viscosity for a range of channel widths and flow strengths typical of microfluidic experiments. Our results are in agreement with previous bulk models, and in particular, demonstrate that the effect of activity is strongest at low flow rates, where pushers tend to decrease the suspension viscosity whereas pullers enhance it. In stronger flows, dissipative stresses overcome the effects of activity leading to increased viscosities followed by shear-thinning. The effects of confinement and number density are also analyzed, and our results confirm the apparent transition to superfluidity reported in recent experiments on pusher suspensions at intermediate densities. We also derive an approximate analytical expression for the effective viscosity in the limit of weak flows and wide channels, and demonstrate good agreement between theory and numerical calculations.


Nanoscale | 2015

Motion-based threat detection using microrods: experiments and numerical simulations

Barath Ezhilan; Wei Gao; Allen Pei; Isaac Rozen; Renfeng Dong; Beatriz Jurado-Sánchez; Joseph Wang; David Saintillan


Journal of Fluid Mechanics | 2015

Transport of a dilute active suspension in pressure-driven channel flow

Barath Ezhilan; David Saintillan


Bulletin of the American Physical Society | 2015

Spontaneous ordering and vortex states of active fluids in circular confinement

Maxime Theillard; Barath Ezhilan; David Saintillan


Bulletin of the American Physical Society | 2014

Effect of hydrodynamic interactions in confined active suspensions

Barath Ezhilan; David Saintillan


Bulletin of the American Physical Society | 2012

Concentrated active suspensions: Kinetic theory, linear stability and numerical simulations

Barath Ezhilan; Michael Shelley; David Saintillan

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Amir Alizadeh Pahlavan

Massachusetts Institute of Technology

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Isaac Rozen

University of California

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Joseph Wang

University of California

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Michael Shelley

Courant Institute of Mathematical Sciences

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Renfeng Dong

University of California

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Wei Gao

University of California

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