Brownian microhydrodynamics of active filaments

Laskar, Abhrajit; Adhikari, R.

doi:10.1039/c5sm02021b

Cited by 42 publications

(64 citation statements)

References 45 publications

(107 reference statements)

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“…In a future work, we will explore the stochastic aspects more fully, using the Langevin and Smoluchowski description derived in this paper. The formalism can also be extended to study fluctuations in chains of active particles [83][84][85]124]. Applications of our method to collective phenomena in magnetotactic colloids and to active rheology will be presented in forthcoming work as will be the extension to ellipsoidal particles.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…Here  T and  R are 'activity' numbers quantifying the relative importance of active and body terms [83][84][85] while  T and  R are 'Brown' numbers quantifying the relative importance of thermal and active terms We estimate these numbers for two typical active colloidal systems below. Explicit Langevin equations for the velocity and angular velocity are obtained by inverting equation (21).…”

Section: Langevin and Smoluchowski Descriptionsmentioning

confidence: 99%

“…They are related to the slip friction tensors introduced here by using the standard Brownian dynamics integrators, for example that due toErmak and Mc Cammon [93]. We note that the explicit form of the Langevin equation was first obtained in[85] using heuristic arguments.…”

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confidence: 99%

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Generalized Stokes laws for active colloids and their applications

Singh

Adhikari

2018

J. Phys. Commun.

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The force per unit area on the surface of a colloidal particle is a fundamental dynamical quantity in the mechanics and statistical mechanics of colloidal suspensions. Here we compute it in the limit of slow viscous flow for a suspension of N spherical active colloids in which activity is represented by surface slip. Our result is best expressed as a set of linear relations, the 'generalized Stokes laws', between the coefficients of a tensorial spherical harmonic expansion of the force per unit area and the surface slip. The generalized friction tensors in these laws are many-body functions of the colloidal configuration and can be obtained to any desired accuracy by solving a system of linear equations. Quantities derived from the force per unit area-forces, torques and stresslets on the colloids and flow, pressure and entropy production in the fluid-have succinct expressions in terms of the generalized Stokes laws. Most notably, the active forces and torques have a dissipative, long-ranged, many-body character that can cause phase separation, crystallization, synchronization and a variety of other effects observed in active suspensions. We use the results above to derive the Langevin and Smoluchowski equations for Brownian active suspensions, to compute active contributions to the suspension stress and fluid pressure, and to relate the synchrony in a lattice of harmonically trapped active colloids to entropy production. Our results provide the basis for a microscopic theory of active Brownian suspensions that consistently accounts for momentum conservation in the bulk fluid and at fluid-solid boundaries.

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Section: Discussion and Summarymentioning

confidence: 99%

Section: Langevin and Smoluchowski Descriptionsmentioning

confidence: 99%

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Generalized Stokes laws for active colloids and their applications

Singh

Adhikari

2018

J. Phys. Commun.

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“…In the dilute regime, steric interactions play a limited role and insights can be gained by studying individual filaments [40][41][42][43][44] or hydrodynamic equations derived from microscopic models [45][46][47]. Studies of individual active filaments either pivoting or freely swimming showed that activity can drive conformational transformations [48], such as spiralling and spontaneous beating [42,49,50], both in the presence and absence of hydrodynamic interactions.…”

Section: Introductionmentioning

confidence: 99%

Dynamically generated patterns in dense suspensions of active filaments

2018

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We use Langevin dynamics simulations to study dynamical behavior of a dense planar layer of active semiflexible filaments. Using the strength of active force and the thermal persistence length as parameters, we map a detailed phase diagram and identify several nonequilibrium phases in this system. In addition to a slowly flowing melt phase, we observe that, for sufficiently high activity, collective flow accompanied by signatures of local polar and nematic order appears in the system. This state is also characterized by strong density fluctuations. Furthermore, we identify an activity-driven crossover from this state of coherently flowing bundles of filaments to a phase with no global flow, formed by individual filaments coiled into rotating spirals. This suggests a mechanism where the system responds to activity by changing the shape of active agents, an effect with no analog in systems of active particles without internal degrees of freedom.

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“…For simplicity, we assume that all active forces have magnitude F 0 , corresponding to a dipole strength F 0 a. The nature of active forces in our system distinguishes it from past models for active polymers [18][19][20][21], which have typically employed isotropic colored noise to account for activity. The active fluid flow V a (with pressure P a ) satisfies the Stokes equations for viscous hydrodynamics [22]:…”

Section: Model and Simulation Methodsmentioning

confidence: 99%

Extensile motor activity drives coherent motions in a model of interphase chromatin

Saintillan

Shelley

Zidovska

2018

Preprint

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The 3D spatiotemporal organization of the human genome inside the cell nucleus remains a major open question in cellular biology. In the time between two cell divisions, chromatin -the functional form of DNA in cells -fills the nucleus in its uncondensed polymeric form. Recent in-vivo imaging experiments reveal that the chromatin moves coherently, having displacements with long-ranged correlations on the scale of microns and lasting for seconds. To elucidate the mechanism(s) behind these motions, we develop a novel coarse-grained active-polymer model where chromatin is represented as a confined flexible chain acted upon by molecular motors, which perform work by exerting dipolar forces on the system. Numerical simulations of this model account for steric and hydrodynamic interactions as well as internal chain mechanics. These demonstrate that coherent motions emerge in systems involving extensile dipoles and are accompanied by large-scale chain reconfigurations and nematic ordering. Comparisons with experiments show good qualitative agreement and support the hypothesis that self-organizing long-ranged hydrodynamic couplings between chromatinassociated active motor proteins are responsible for the observed coherent dynamics.

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Brownian microhydrodynamics of active filaments

Cited by 42 publications

References 45 publications

Generalized Stokes laws for active colloids and their applications

Generalized Stokes laws for active colloids and their applications

Dynamically generated patterns in dense suspensions of active filaments

Extensile motor activity drives coherent motions in a model of interphase chromatin

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