arXiv subjects

I. S. Aranson

Publications and source records attributed to I. S. Aranson.

At least 19 recordsLinked to original sources

arXiv2013

Viscosity control of the dynamic self-assembly in ferromagnetic suspensions

Recent studies of dynamic self-assembly in ferromagnetic colloids suspended in liquid-air or liquid-liquid interfaces revealed a rich variety of dynamic structures ranging from linear snakes to axisymmetric asters, which exhibit novel morphology of the magnetic ordering accompanied by large-scale hydrodynamic flows. Based on controlled experiments and first principle theory, we argue that the transition from snakes to asters is governed by the viscosity of the suspending liquid where less viscous liquids favor snakes and more viscous, asters. By obtaining analytic solutions of the time-averaged Navier-Stokes equations, we gain insights into the role of mean hydrodynamic flows and an overall balance of forces governing the self-assembly. Our results illustrate that the viscosity can be used to control the outcome of the dynamic self-assembly in magnetic colloidal suspensions.

cond-mat.soft↗

arXiv2011

Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a BCS-BEC Crossover

We study the spontaneous formation of vortices during the superfluid condensation in a trapped fermionic gas subjected to a rapid thermal quench via evaporative cooling. Our work is based on the numerical solution of the time dependent crossover Ginzburg-Landau equation coupled to the heat diffusion equation. We quantify the evolution of condensate density and vortex length as a function of a crossover phase parameter from BCS to BEC. The more interesting phenomena occur somewhat nearer to the BEC regime and should be experimentally observable; during the propagation of the cold front, the increase in condensate density leads to the formation of supercurrents towards the center of the condensate as well as possible condensate volume oscillations.

cond-mat.quant-gas↗

arXiv2010

Model for Dynamic Self-Assembled Magnetic Surface Structures

We propose a first-principles model for self-assembled magnetic surface structures on the water-air interface reported in earlier experiments \cite{snezhko2,snezhko4}. The model is based on the Navier-Stokes equation for liquids in shallow water approximation coupled to Newton equations for interacting magnetic particles suspended on the water-air interface. The model reproduces most of the observed phenomenology, including spontaneous formation of magnetic snake-like structures, generation of large-scale vortex flows, complex ferromagnetic-antiferromagnetic ordering of the snake, and self-propulsion of bead-snake hybrids. The model provides valuable insights into self-organization phenomena in a broad range of non-equilibrium magnetic and electrostatic systems with competing interactions.

cond-mat.soft↗

arXiv2005

Velocity Distributions of Granular Gases with Drag and with Long-Range Interactions

We study velocity statistics of electrostatically driven granular gases. For two different experiments: (i) non-magnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(v) ~ exp(-|v|). This behavior is consistent with kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction.

cond-mat.soft↗

arXiv2004

Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders

We report the first experimental study of cluster size distributions in electrostatically driven granular submonolayers. The cluster size distribution in this far-from-equilibrium process exhibits dynamic scaling behavior characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the attachment and detachment of the "gas" particles. The scaled size distribution, however, is different from the classical Wagner distribution obtained in the limit of a vanishingly small area fraction of the clusters. A much better agreement is found with the theory of Conti et al. [Phys. Rev. E 65, 046117 (2002)] which accounts for the cluster merger.

cond-mat.soft↗

arXiv2004

Structure formation in electromagnetically driven granular media

We report structure formation in submonolayers of magnetic microparticles subjected to periodic electrostatic and magnetic excitations. Depending on the excitation parameters, we observe the formation of a rich variety of structures: clusters, rings, chains, and networks. The growth dynamics and shapes of the structures are strongly dependent on the amplitude and frequency of the external magnetic field. We find that for pure ac magnetic driving at low densities of particles, the low-frequency magnetic excitation favors clusters while high frequency excitation favors chains and net-like structures. An abrupt phase transition from chains to a network phase was observed for a high density of particles.

nlin.PS↗

arXiv2003

Theory of pattern-formation of metallic microparticles in poorly conducting liquid

We develop continuum theory of self-assembly and pattern formation in metallic microparticles immersed in a poorly conducting liquid in DC electric field. The theory is formulated in terms of two conservation laws for the densities of immobile particles (precipitate) and bouncing particles (gas) coupled to the Navier-Stokes equation for the liquid. This theory successfully reproduces correct topology of the phase diagram and primary patterns observed in the experiment [Sapozhnikov et al, Phys. Rev. Lett. v. 90, 114301 (2003)]: static crystals and honeycombs and dynamic pulsating rings and rotating multi-petal vortices.

cond-mat.mtrl-sci↗

arXiv2003

Partially fluidized shear granular flows: Continuum theory and MD simulations

The continuum theory of partially fluidized shear granular flows is tested and calibrated using two dimensional soft particle molecular dynamics simulations. The theory is based on the relaxational dynamics of the order parameter that describes the transition between static and flowing regimes of granular material. We define the order parameter as a fraction of static contacts among all contacts between particles. We also propose and verify by direct simulations the constitutive relation based on the splitting of the shear stress tensor into a``fluid part'' proportional to the strain rate tensor, and a remaining ``solid part''. The ratio of these two parts is a function of the order parameter. The rheology of the fluid component agrees well with the kinetic theory of granular fluids even in the dense regime. Based on the hysteretic bifurcation diagram for a thin shear granular layer obtained in simulations, we construct the ``free energy'' for the order parameter. The theory calibrated using numerical experiments with the thin granular layer is applied to the surface-driven stationary two dimensional granular flows in a thick granular layer under gravity.

cond-mat.mtrl-sci↗

arXiv2002

Coarsening of granular clusters: two types of scaling behaviors

We report on an experimental study of small cluster dynamics during the coarsening process in driven granular submonolayers of 120mkm bronze particles. The techniques of electrostatic and vertical mechanical vibration were employed to excite the granular gas. We measure the scaling exponent for the evaporation of small clusters during coarsening. It was found that the surface area of small clusters S vs time t behaves as S ~ (t_0-t)^(2/3) for lower frequencies and S ~ (t_0-t) for higher frequencies. We argue that the change in the scaling exponent is related to the transition from three dimensional to two dimensional character of motion in the granular gas.

cond-mat.stat-mech↗

arXiv2002

Dynamic self-assembly and patterns in electrostatically driven granular media

We show that granular media consisting of metallic microparticles immersed in a poorly conducting liquid in strong DC electric field self-assemble a rich variety of novel phases. These phases include static precipitate: honeycombs and Wigner crystals; and novel dynamic condensate: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.

cond-mat.stat-mech↗

arXiv2002

Velocity Fluctuations in Electrostatically Driven Granular Media

We study experimentally the particle velocity fluctuations in an electrostatically driven dilute granular gas. The experimentally obtained velocity distribution functions have strong deviations from Maxwellian form in a wide range of parameters. We have found that the tails of the distribution functions are consistent with a stretched exponential law with typical exponents of the order 3/2. Molecular dynamic simulations shows qualitative agreement with experimental data. Our results suggest that this non-Gaussian behavior is typical for most inelastic gases with both short and long range interactions.

cond-mat.stat-mech↗

arXiv2001

Phase Separation and Coarsening in Electrostatically Driven Granular Media

A continuum model for the phase separation and coarsening, observed in electrostatically driven granular media, is formulated in terms of a Ginzburg-Landau equation subject to conservation of the total number of grains. In the regime of well-developed clusters, the continuum model is used to derive "sharp-interface" equations that govern the dynamics of the interphase boundary. The model captures the essential physics of this system.

cond-mat.soft↗

arXiv2001

Stick-slip friction and nucleation dynamics of ultra-thin liquid films

We develop the theory for stick-slip motion in ultra-thin liquid films confined between two moving atomically-flat surfaces. Our model is based on hydrodynamic equation for the flow coupled to the dynamic order parameter field describing the ``shear melting and freezing'' of the confined fluid. This model successfully accounts for observed phenomenology of friction in ultra-thin films, including periodic and chaotic sequences of slips, transitions from stick-slip motion to steady sliding.

cond-mat.mtrl-sci↗

arXiv2000

Dynamics of electrostatically-driven granular media. Effects of Humidity

We performed experimental studies of the effect of humidity on the dynamics of electrostatically-driven granular materials. Both conducting and dielectric particles undergo a phase transition from an immobile state (granular solid) to a fluidized state (granular gas) with increasing applied field. Spontaneous precipitation of solid clusters from the gas phase occurs as the external driving is decreased. The clustering dynamics in conducting particles is primarily controlled by screening of the electric field but is aided by cohesion due to humidity. It is shown that humidity effects dominate the clustering process with dielectric particles.

cond-mat.soft↗

arXiv2000

Resonances, instabilities, and structure selection of driven Josephson lattice in layered superconductors

We investigate dynamics of Josephson vortex lattice in layered high T$_{c}$ superconductors at high magnetic fields. It is shown that the average electric current depends on the lattice structure and is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode. We find the stability regions of moving lattice. It is shown that a specific lattice structure at given velocity is uniquely selected by the boundary conditions: at small velocities periodic triangular lattice is stable and looses its stability at some critical velocity. At even higher velocities a structure close to a rectangular lattice is restored.

cond-mat.supr-con↗

arXiv2000

Oscillations and defect turbulence in a shallow fluidized bed

We report an experimental study of the dynamics of an air-fluidized thin granular layer. Near-onset behavior of this shallow fluidized bed was described in the earlier paper (Tsimring et al, 1999). Above the threshold of fluidization the system exhibits a Hopf bifurcation as the layer starts to oscillate at a certain frequency due to a feedback between the layer dilation and the airflow drag force. After application of temporal band-pass filtering of this frequency we discovered the spatio-temporal dynamics in the form of defect turbulence. This type of dynamics is natural for spatio-temporal systems close to the threshold of a Hopf bifurcation. At high flow rates, low-frequency short-wavelength structures appear in addition to the long-wavelength excitations. A simple model describing the instability and occurrence of oscillations in a shallow fluidized bed, is proposed.

nlin.PS↗

arXiv2000

Continuum field description of crack propagation

We develop continuum field model for crack propagation in brittle amorphous solids. The model is represented by equations for elastic displacements combined with the order parameter equation which accounts for the dynamics of defects. This model captures all important phenomenology of crack propagation: crack initiation, propagation, dynamic fracture instability, sound emission, crack branching and fragmentation.

cond-mat.mtrl-sci↗

arXiv1999

High-Acceleration Patterns in Thin Vibrated Granular Layers

Theoretical and experimental study of high-acceleration patterns in vibrated granular layers is presented. The order parameter model based on parametric Ginzburg-Landau equation is used to describe strongly nonlinear excitations including hexagons, interface between flat anti-phase domains and new localized objects, super-oscillons. The experiments confirmed the existence of super-oscillons and bound states of super-oscillons and interfaces. On the basis of order parameter model we predict analytically and confirm experimentally that the additional subharmonic driving results in controlled motion of the interfaces.

cond-mat.soft↗