Biomedical subjects

I S Aranson

Publications and source records attributed to I S Aranson.

15 recordsLinked to original sources

PubMed2006

Dynamic self-assembly of magnetic particles on the fluid interface: surface-wave-mediated effective magnetic exchange.

We report on studies of dynamic self-assembled structures induced by a vertical alternating magnetic field in an ensemble of magnetic particles suspended on a liquid surface. We find the formation of nontrivially ordered dynamic snakelike objects in a certain range of field magnitudes and frequencies. In order to probe the properties of the "snakes," we study their magnetic response to in-plane magnetic field applied at different angles with respect to its axis. The segments of the snake exhibit long-range antiferromagnetic ordering mediated by the surface waves, while each segment is composed of ferromagnetically aligned chains of microparticles. We propose a simple phenomenological model where the effect of surface waves is replaced by an effective exchange interaction to describe the observations. In the framework of the proposed model, the effective exchange constant corresponding to different regimes of magnetic driving was extracted from the experimental data.

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PubMed2006

Surface wave assisted self-assembly of multidomain magnetic structures.

An ensemble of magnetic microparticles at the liquid surface displays novel snakelike self-assembled structures induced by an alternating magnetic field. We demonstrate that these structures are directly related to surface waves in the liquid generated by the collective response of magnetic microparticles to the alternating magnetic field. The segments of the "snake" exhibit long-range antiferromagnetic ordering, while each segment is composed of ferromagnetically aligned chains of microparticles. The structures exhibit magnetic hysteretic behavior with respect to an external in-plane magnetic field and logarithmic relaxation of the remanent magnetic moment.

Electromagnetic Fields↗

PubMed2005

Self-diffusion of particles in gas-driven granular layers with periodic flow modulation.

We study self-diffusion of particles in gas-driven granular layers by high-speed fluorescent video microscopy. We show that periodic flow modulation results in an enhancement of the particle's diffusion. The diffusion enhancement, which in turn is an indication of more efficient fluidization of the granular layer, is associated with the onset of disordered subharmonic patterns. Our measurements provide a sensitive characterization method of the fluidization properties of particulate-gas systems.

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PubMed2005

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) nonmagnetic 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(upsilon) approximately exp(-/upsilon/). This behavior is consistent with the 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.

Air Movements↗

PubMed2005

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 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 the low-frequency magnetic excitation favors compact clusters, whereas high frequency driving favors chains and netlike structures. An abrupt phase transition from chains to a network phase was observed for a high density of particles.

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PubMed2005

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

We report an 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 Phys. Rev. E 65, 046117 (2002)] which accounts for the cluster merger.

Journal Article↗

PubMed2004

Self-assembly and vortices formed by microparticles in weak electrolytes.

We carried out experimental studies of the self-assembly of metallic micron-size particles in poorly conducting liquid subject to a constant electric field. Depending on the experimental conditions, the particles self-assemble into long chains directed along the electric field lines and form vortices and other structures. The vortices perform Brownian-type random motion due to self-induced chaotic hydrodynamic flows. We measured the diffusivity constant of the vortices and the conductivity and mechanical stiffness of the chains.

Journal Article↗

PubMed2004

Theory of pattern formation of metallic microparticles in poorly conducting liquids.

We develop a continuum theory of self-assembly and pattern formation in metallic microparticles immersed in a poorly conducting liquid in a dc electric field. The theory is formulated in terms of 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 reproduced the correct topology of the phase diagram and primary patterns observed in the experiment [Phys. Rev. Lett. 90, 114301 (2003)]]: static crystals, honeycombs, dynamic pulsating rings, and rotating multipetal vortices.

Journal Article↗

PubMed2003

Periodic and disordered structures in a modulated gas-driven granular layer.

Experiments with a thin gas-fluidized granular layer revealed a sequence of well-defined transitions as the amplitude and frequency of the gas flow modulation are varied. The observed patterns include subharmonic squares and stripes, quasiperiodic and disordered structures. The wavelength of subharmonic patterns increases with the mean flow rate and decreases with the modulation frequency.

Journal Article↗

PubMed2003

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 a strong dc electric field, self-assemble into a rich variety of novel phases. These phases include static precipitates: honeycombs and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.

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PubMed2003

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 120-microm 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 to (t(0)-t)(2/3) for lower frequencies and S to (t(0)-t) for higher frequencies. We argue that the change in the scaling exponent is related to the transition from three-dimensional (3D) to 2D character of motion in the granular gas.

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PubMed2002

Velocity fluctuations in electrostatically driven granular media.

We study experimentally the particle velocity fluctuations in an electrostatically driven dilute granular gas. The velocity distributions have strong deviations from a Maxwellian form over 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 of most inelastic gases with both short- and long-range interactions.

Journal Article↗

PubMed2002

Phase separation and coarsening in electrostatically driven granular media.

A continuum model for the phase separation and coarsening 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.

Journal Article↗

PubMed2001

Continuum description of avalanches in granular media.

We develop a continuum description of partially fluidized granular flows. Our theory is based on the hydrodynamic equation for the flow coupled with the order parameter equation, which describes the transition between flowing and static components of the granular system. This theory captures important phenomenology recently observed in experiments with granular flows on rough inclined planes [A. Daerr and S. Douady, Nature (London) 399, 241 (1999)]: layer bistability, and transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

Journal Article↗

PubMed1999

Continuum theory of axial segregation in a long rotating drum.

We develop a continuum description for the axial segregation of granular materials in a long rotating drum based on the dynamics of the thin near-surface granular flow coupled to bulk flow. The equations of motion are reduced to the one-dimensional system for two local variables only, the concentration difference and the dynamic angle of repose, or the average slope of the free surface. The parameters of the system are established from comparison with experimental data. The resulting system describes both initial transient traveling wave dynamics and the formation of quasi-stationary bands of segregated materials. A long-term evolution proceeds through slow logarithmic coarsening of the band structure which is analogous to the spinoidal decomposition described by the Cahn-Hilliard equation.

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