483 research outputs found
Intercalation-enhanced electric polarization and chain formation of nano-layered particles
Microscopy observations show that suspensions of synthetic and natural
nano-layered smectite clay particles submitted to a strong external electric
field undergo a fast and extended structuring. This structuring results from
the interaction between induced electric dipoles, and is only possible for
particles with suitable polarization properties. Smectite clay colloids are
observed to be particularly suitable, in contrast to similar suspensions of a
non-swelling clay. Synchrotron X-ray scattering experiments provide the
orientation distributions for the particles. These distributions are understood
in terms of competing (i) homogenizing entropy and (ii) interaction between the
particles and the local electric field; they show that clay particles polarize
along their silica sheet. Furthermore, a change in the platelet separation
inside nano-layered particles occurs under application of the electric field,
indicating that intercalated ions and water molecules play a role in their
electric polarization. The resulting induced dipole is structurally attached to
the particle, and this causes particles to reorient and interact, resulting in
the observed macroscopic structuring. The macroscopic properties of these
electro-rheological smectite suspensions may be tuned by controlling the nature
and quantity of the intercalated species, at the nanoscale.Comment: 7 pages, 5 figure
Kinetic Inductance of Josephson Junction Arrays: Dynamic and Equilibrium Calculations
We show analytically that the inverse kinetic inductance of an
overdamped junction array at low frequencies is proportional to the admittance
of an inhomogeneous equivalent impedance network. The bond in this
equivalent network has an inverse inductance
, where is the Josephson
coupling energy of the bond, is the ground-state phase
of the grain , and is the usual magnetic phase factor. We use this
theorem to calculate for square arrays as large as .
The calculated is in very good agreement with the low-temperature
limit of the helicity modulus calculated by conventional equilibrium
Monte Carlo techniques. However, the finite temperature structure of ,
as a function of magnetic field, is \underline{sharper} than the
zero-temperature , which shows surprisingly weak structure. In
triangular arrays, the equilibrium calculation of yields a series of
peaks at frustrations , where is an integer , consistent with experiment.Comment: 14 pages + 6 postscript figures, 3.0 REVTe
Tip-splitting evolution in the idealized Saffman-Taylor problem
We derive a formula describing the evolution of tip-splittings of
Saffman-Taylor fingers in a Hele-Shaw cell, at zero surface tension
Quantum Group, Bethe Ansatz and Bloch Electrons in a Magnetic Field
The wave functions for two dimensional Bloch electrons in a uniform magnetic
field at the mid-band points are studied with the help of the algebraic
structure of the quantum group . A linear combination of its
generators gives the Hamiltonian. We obtain analytical and numerical solutions
for the wave functions by solving the Bethe Ansatz equations, proposed by
Wiegmann and Zabrodin on the basis of above observation. The semi-classical
case with the flux per plaquette is analyzed in detail, by exploring
a structure of the Bethe Ansatz equations. We also reveal the multifractal
structure of the Bethe Ansatz solutions and corresponding wave functions when
is irrational, such as the golden or silver mean.Comment: 30 pages, 11 GIF figures(use xv, or WWW browser
Quasiperiodic Modulated-Spring Model
We study the classical vibration problem of a chain with spring constants
which are modulated in a quasiperiodic manner, {\it i. e.}, a model in which
the elastic energy is , where and is an irrational number. For
, it is shown analytically that the spectrum is absolutely
continuous, {\it i.e.}, all the eigen modes are extended. For ,
numerical scaling analysis shows that the spectrum is purely singular
continuous, {\it i.e.}, all the modes are critical.Comment: REV TeX fil
Nature of Phase Transitions of Superconducting Wire Networks in a Magnetic Field
We study - characteristics of periodic square Nb wire networks as a
function of temperature in a transverse magnetic field, with a focus on three
fillings 2/5, 1/2, and 0.618 that represent very different levels of
incommensurability. For all three fillings, a scaling behavior of -
characteristics is found, suggesting a finite temperature continuous
superconducting phase transition. The low-temperature - characteristics
are found to have an exponential form, indicative of the domain-wall
excitations.Comment: 5 pages, also available at
http://www.neci.nj.nec.com/homepages/tang.htm
Current-voltage scaling of a Josephson-junction array at irrational frustration
Numerical simulations of the current-voltage characteristics of an ordered
two-dimensional Josephson junction array at an irrational flux quantum per
plaquette are presented. The results are consistent with an scaling analysis
which assumes a zero temperature vortex glass transition. The thermal
correlation length exponent characterizing this transition is found to be
significantly different from the corresponding value for vortex-glass models in
disordered two-dimensional superconductors. This leads to a current scale where
nonlinearities appear in the current-voltage characteristics decreasing with
temperature roughly as in contrast with the behavior expected
for disordered models.Comment: RevTex 3.0, 12 pages with Latex figures, to appear in Phys. Rev. B
54, Rapid. Com
Structural Relaxation, Self Diffusion and Kinetic Heterogeneity in the Two Dimensional Lattice Coulomb Gas
We present Monte Carlo simulation results on the equilibrium relaxation
dynamics in the two dimensional lattice Coulomb gas, where finite fraction
of the lattice sites are occupied by positive charges. In the case of high
order rational values of close to the irrational number
( is the golden mean), we find that the system
exhibits, for wide range of temperatures above the first-order transition, a
glassy behavior resembling the primary relaxation of supercooled liquids.
Single particle diffusion and structural relaxation show that there exists a
breakdown of proportionality between the time scale of diffusion and that of
structural relaxation analogous to the violation of the Stokes-Einstein
relation in supercooled liquids. Suitably defined dynamic cooperativity is
calculated to exhibit the characteristic nature of dynamic heterogeneity
present in the system.Comment: 12 pages, 20 figure
Phase Coexistence of a Stockmayer Fluid in an Applied Field
We examine two aspects of Stockmayer fluids which consists of point dipoles
that additionally interact via an attractive Lennard-Jones potential. We
perform Monte Carlo simulations to examine the effect of an applied field on
the liquid-gas phase coexistence and show that a magnetic fluid phase does
exist in the absence of an applied field. As part of the search for the
magnetic fluid phase, we perform Gibbs ensemble simulations to determine phase
coexistence curves at large dipole moments, . The critical temperature is
found to depend linearly on for intermediate values of beyond the
initial nonlinear behavior near and less than the where no
liquid-gas phase coexistence has been found. For phase coexistence in an
applied field, the critical temperatures as a function of the applied field for
two different are mapped onto a single curve. The critical densities
hardly change as a function of applied field. We also verify that in an applied
field the liquid droplets within the two phase coexistence region become
elongated in the direction of the field.Comment: 23 pages, ReVTeX, 7 figure
Current Distribution in the Three-Dimensional Random Resistor Network at the Percolation Threshold
We study the multifractal properties of the current distribution of the
three-dimensional random resistor network at the percolation threshold. For
lattices ranging in size from to we measure the second, fourth and
sixth moments of the current distribution, finding {\it e.g.\/} that
where is the conductivity exponent and is the
correlation length exponent.Comment: 10 pages, latex, 8 figures in separate uuencoded fil
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