arXiv subjects

Abhishek Chaudhuri

Publications and source records attributed to Abhishek Chaudhuri.

46 records · Page 3Linked to original sources

arXiv2011

Effect of interactions on the cellular uptake of nanoparticles

We present a simple two-state model to understand the size-dependent endocytosis of nanoparticles. Using this model, we elucidate the relevant energy terms required to understand the size-dependent uptake mechanism and verify it by correctly predicting the behavior at large and small particle sizes. In the absence of interactions between the nanoparticles we observe an asymmetric distribution of sizes with maximum uptake at intermediate sizes and a minimum size cut-off below which there can be no endocytosis. Including the effect of interactions in our model has remarkable effects on the uptake characteristics. Attractive interactions shift the minimum size cut-off and increase the optimal uptake while repulsive interactions make the distribution more symmetric lowering the optimal uptake.

cond-mat.soft↗

arXiv2010

Heat conduction and phonon localization in disordered harmonic crystals

We investigate the steady state heat current in two and three dimensional isotopically disordered harmonic lattices. Using localization theory as well as kinetic theory we estimate the system size dependence of the current. These estimates are compared with numerical results obtained using an exact formula for the current given in terms of a phonon transmission function, as well as by direct nonequilibrium simulations. We find that heat conduction by high-frequency modes is suppressed by localization while low-frequency modes are strongly affected by boundary conditions. Our {\color{black}heuristic} arguments show that Fourier's law is valid in a three dimensional disordered solid except for special boundary conditions. We also study the pinned case relevant to localization in quantum systems and often used as a model system to study the validity of Fourier's law. Here we provide the first numerical verification of Fourier's law in three dimensions. In the two dimensional pinned case we find that localization of phonon modes leads to a heat insulator.

cond-mat.dis-nn↗

arXiv2009

Heat transport and phonon localization in mass-disordered harmonic crystals

We investigate the steady state heat current in two and three dimensional disordered harmonic crystals in a slab geometry, connected at the boundaries to stochastic white noise heat baths at different temperatures.The disorder causes short wavelength phonon modes to be localized so the heat current in this system is carried by the extended phonon modes which can be either diffusive or ballistic. Using ideas both from localization theory and from kinetic theory we estimate the contribution of various modes to the heat current and from this we obtain the asymptotic system size dependence of the current. These estimates are compared with results obtained from a numerical evaluation of an exact formula for the current, given in terms of a frequency transmission function, as well as from direct nonequilibrium simulations. These yield a strong dependence of the heat flux on boundary conditions. Our analytical arguments show that for realistic boundary conditions the conductivity is finite in three dimensions but we are not able to verify this numerically, except in the case where the system is subjected to an external pinning potential. This case is closely related to the problem of localization of electrons in a random potential and here we numerically verify that the pinned three dimensional system satisfies Fourier's law while the two dimensional system is a heat insulator. We also investigate the inverse participation ratio of different normal modes.

cond-mat.dis-nn↗

arXiv2007

Driving particle current through narrow channels using classical pump

We study a symmetric exclusion process in which the hopping rates at two chosen adjacent sites vary periodically in time and have a relative phase difference. This mimics a colloidal suspension subjected to external space and time dependent modulation of the diffusion constant. The two special sites act as a classical pump by generating an oscillatory current with a nonzero ${\cal DC}$ value whose direction depends on the applied phase difference. We analyze various features in this model through simulations and obtain an expression for the $\cal{DC}$ current via a novel perturbative treatment.

cond-mat.stat-mech↗

arXiv2007

Growing smooth interfaces with inhomogeneous, moving external fields: dynamical transitions, devil's staircases and self-assembled ripples

We study the steady state structure and dynamics of an interface in a pure Ising system on a square lattice placed in an inhomogeneous external field. The field has a profile with a fixed shape designed to stabilize a flat interface, and is translated with velocity v_e. For small v_e, the interface is stuck to the profile, is macroscopically smooth, and is rippled with a periodicity in general incommensurate with the lattice parameter. For arbitrary orientations of the profile, the local slope of the interface locks in to one of infinitely many rational values (devil's staircase) which most closely approximates the profile. These ``lock-in'' structures and ripples dissappear as v_e increases. For still larger v_e the profile detaches from the interface which is now characterized by standard Kardar-Parisi-Zhang (KPZ) exponents.

cond-mat.soft↗

arXiv2007

Stress relaxation in a perfect nanocrystal by coherent ejection of lattice layers

We show that a small crystal trapped within a potential well and in contact with its own fluid, responds to large compressive stresses by a novel mechanism -- the transfer of complete lattice layers across the solid-fluid interface. Further, when the solid is impacted by a momentum impulse set up in the fluid, a coherently ejected lattice layer carries away a definite quantity of energy and momentum, resulting in a sharp peak in the calculated phonon absorption spectrum. Apart from its relevance to studies of stability and failure of small sized solids, such coherent nanospallation may be used to make atomic wires or monolayer films.

cond-mat.soft↗

arXiv2007

Heat conduction through a trapped solid: effect of structural changes on thermal conductance

We study the conduction of heat across a narrow solid strip trapped by an external potential and in contact with its own liquid. Structural changes, consisting of addition and deletion of crystal layers in the trapped solid, are produced by altering the depth of the confining potential. Nonequilibrium molecular dynamics simulations and, wherever possible, simple analytical calculations are used to obtain the thermal resistance in the liquid, solid and interfacial regions (Kapitza or contact resistance). We show that these layering transitions are accompanied by sharp jumps in the contact thermal resistance. Dislocations, if present, are shown to increase the thermal resistance of the strip drastically.

cond-mat.soft↗

arXiv2007

Novel Fluctuations at a Constrained Liquid-Solid Interface

We study the interface between a solid trapped within a bath of liquid by a suitably shaped non-uniform external potential. Such a potential may be constructed using lasers, external electric or magnetic fields or a surface template. We study a two dimensional case where a thin strip of solid, created in this way, is surrounded on either side by a bath of liquid with which it can easily exchange particles. Since height fluctuations of the interface cost energy, this interface is constrained to remain flat at all length scales. However, when such a solid is stressed by altering the depth of the potential; beyond a certain limit, it responds by relieving stress by novel interfacial fluctuations which involve addition or deletion of entire lattice layers of the crystal. This ``layering'' transition is a generic feature of the system regardless of the details of the interaction potential. We show how such interfacial fluctuations influence mass, momentum and energy transport across the interface. Tiny momentum impulses produce weak shock waves which travel through the interface and cause the spallation of crystal layers into the liquid. Kinetic and energetic constraints prevent spallation of partial layers from the crystal, a fact which may be of some practical use. We also study heat transport through the liquid-solid interface and obtain the resistances in liquid, solid and interfacial regions (Kapitza resistance) as the solid undergoes such layering transitions. Heat conduction, which shows strong signatures of the structural transformations, can be understood using a free volume calculation.

cond-mat.soft↗

arXiv2004

A Kinetics Driven Commensurate - Incommensurate Transition

The steady state structure of an interface in an Ising system on a square lattice placed in a {\em non-uniform} external field, shows a commensurate -incommensurate transition driven by the velocity of the interface. The non-uniform field has a profile with a fixed shape which is designed to stabilize a flat interface, and is translated with velocity $v_{e}$. For small velocities the interface is stuck to the profile and is rippled with a periodicity which may be either commensurate or incommensurate with the lattice parameter of the square lattice. For a general orientation of the profile, the local slope of the interface locks in to one of infinitely many rational directions producing a devil's staircase structure. These ``lock-in'' or commensurate structures dissappear as $v_e$ increases through a kinetics driven commensurate - incommensurate transition. For large $v_e$ the interface becomes detached from the field profile and coarsens with Kardar-Parisi-Zang exponents. The complete phase-diagram and the multifractal spectrum corresponding to these structures have been obtained numerically together with several analytic results concerning the dynamics of the rippled phases. Our work has technological implications in crystal growth and the production of surfaces with various desired surface morphologies.

cond-mat.stat-mech↗

arXiv2002

Profile driven interfaces in 1 + 1 dimensions : periodic steady states, dynamical melting and detachment

We study the steady state structure and dynamics of a 2-d Ising interface placed in an inhomogeneous external field with a sigmoidal profile which moves with velocity $v_{e}$. In the strong coupling limit the problem maps onto an assymmetric exclusion process involving motion of particles in 1-d with position dependent right and left jump probabilities. For small $v_{e}$, the interface is stuck to the field profile. As $v_{e}$ increases the profile detaches from the interface. At the transition point(and beyond), the interfacial structure and dynamics is characterized by KPZ exponents. For small $v_{e}$, on the other hand, the interface is macroscopically smooth with a vanishing roughness exponent $α$. The interfacial structure is periodic with a periodicity which depends on the orientation of the interface. For a fixed orientation this periodic structure ``melts'' as $v_e$ is increased. We determine the dynamical ``phase - diagram'' of this system in the $v_e$ - orientation plane.

cond-mat.soft↗