762 research outputs found
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.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
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.Comment: 5 pages, to appear in PR
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.Comment: 4 pages, 3 figure
ETEKOS experimental ecological system
The problem of changes in the ecology resulting, for example, in increases in water temperature because of discharges from large thermal power plants is considered. An experiment creating a model of such an ecological system is described
Investigation of radiation effects in water solutions during exposure with laser or LEDs light
Abstract only.The installation for gamma-, X-ray and neutron registration in water solutions (600 ml LiOH, or NaOH, or Na2CO3) during exposure with red light (λ=645+/-20 nm) of laser or light-emission devises (LEDs) was created. The laser light power was 5 mW and the LEDs - from 600 mW up to 10 W. Neutrons were measured with help of tow 3He counters, placed in paraphine barrel. Small neutron emission (up to 100 neutrons) has been registered in the form of series of short (ms) bursts during some minutes. Tritium production has also been detected in water solution probes. The gamma-ray and X-ray radiation measured by NaI scintillation detector & Geiger counters was not detected. Received results are discussed
Cellular Models for River Networks
A cellular model introduced for the evolution of the fluvial landscape is
revisited using extensive numerical and scaling analyses. The basic network
shapes and their recurrence especially in the aggregation structure are then
addressed. The roles of boundary and initial conditions are carefully analyzed
as well as the key effect of quenched disorder embedded in random pinning of
the landscape surface. It is found that the above features strongly affect the
scaling behavior of key morphological quantities. In particular, we conclude
that randomly pinned regions (whose structural disorder bears much physical
meaning mimicking uneven landscape-forming rainfall events, geological
diversity or heterogeneity in surficial properties like vegetation, soil cover
or type) play a key role for the robust emergence of aggregation patterns
bearing much resemblance to real river networks.Comment: 7 pages, revtex style, 14 figure
Features of combining of scanning probe microscopy with optical and scanning electron microscopy
Interacting circular nanomagnets
Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in
diameter) were prepared by the method of the electron lithography. The
magnetization curves were studied by Hall magnetometry with the compensation
technique for different external field orientations at 4.2K and 77K. The shape
of hysteresis curves indicates that there is magnetostatic interaction between
the particles. The main peculiarity is the existence of remanent magnetization
perpendicular to easy plain. By numerical simulation it is shown, that the
character of the magnetization reversal is a result of the interplay of the
interparticle interaction and the magnetization distribution within the
particles (vortex or uniform).Comment: 16 pages, 8 figure
The influence of defects on magnetic properties of fcc-Pu
The influence of vacancies and interstitial atoms on magnetism in Pu has been
considered in frames of the Density Functional Theory (DFT). The relaxation of
crystal structure arising due to different types of defects was calculated
using the molecular dynamic method with modified embedded atom model (MEAM).
The LDA+U+SO (Local Density Approximation with explicit inclusion of Coulomb
and spin-orbital interactions) method in matrix invariant form was applied to
describe correlation effects in Pu with these types of defects. The
calculations show that both vacancies and interstitials give rise to local
moments in -shell of Pu in good agreement with experimental data for
annealed Pu. Magnetism appears due to destroying of delicate balance between
spin-orbital and exchange interactions.Comment: 13 pages, 4 figure
A hysteresis model with dipole interaction: one more devil-staircase
Magnetic properties of 2D systems of magnetic nanoobjects (2D regular
lattices of the magnetic nanoparticles or magnetic nanostripes) are considered.
The analytical calculation of the hysteresis curve of the system with
interaction between nanoobjects is provided. It is shown that during the
magnetization reversal system passes through a number of metastable states. The
kinetic problem of the magnetization reversal was solved for three models. The
following results have been obtained. 1) For 1D system (T=0) with the
long-range interaction with the energy proportional to , the
staircase-like shape of the magnetization curve has self-similar character. The
nature of the steps is determined by interplay of the interparticle interaction
and coercivity of the single nanoparticle. 2) The influence of the thermal
fluctuations on the kinetic process was examined in the framework of the
nearest-neighbor interaction model. The thermal fluctuations lead to the
additional splitting of the steps on the magnetization curve. 3) The
magnetization curve for system with interaction and coercivity dispersion was
calculated in mean field approximation. The simple method to experimentally
distinguish the influence of interaction and coercivity dispersion on the
magnetization curve is suggested.Comment: 22 pages, 8 figure
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