25,403 research outputs found
Factors contributing to household food insecurity in a rural upstate New York County
In order to identify factors that contribute to household food insecurity in a rural county in upstate New York, we conducted two personal interviews with 193 women who were between the ages of 20 and 40 years, had less than 16 years of education, and had children living at home. Data were collected on sociodemographic characteristics, risk factors for food insecurity, food program participation, and the Radimer/Cornell hunger and food insecurity measures; in addition, each household's food supplies were inventoried. Regression analyses and tree-based partitioning were used to identify the risk factors. The variables significantly (p
Vortex Molecular Crystal and Vortex Plastic Crystal States in Honeycomb and Kagome Pinning Arrays
Using numerical simulations, we investigate vortex configurations and pinning
in superconductors with honeycomb and kagome pinning arrays. We find that a
variety of novel vortex crystal states can be stabilized at integer and
fractional matching field densities. The honeycomb and kagome pinning arrays
produce considerably more pronounced commensuration peaks in the critical
depinning force than triangular pinning arrays, and also cause additional peaks
at noninteger matching fields where a portion of the vortices are located in
the large interstitial regions of the pinning lattices. For the honeycomb
pinning array, we find matching effects of equal strength at most fillings
B/B_\phi=n/2 for n>2, where n is an integer, in agreement with recent
experiments. For kagome pinning arrays, pronounced matching effects generally
occur at B/B_\phi=n/3 for n>3, while for triangular pinning arrays pronounced
matching effects are observed only at integer fillings B/B_\phi=n. At the
noninteger matching field peaks in the honeycomb and kagome pinning arrays, the
interstitial vortices are arranged in dimer, trimer, and higher order n-mer
states that have an overall orientational order. We call these n-mer states
"vortex molecular crystals" and "vortex plastic crystals" since they are
similar to the states recently observed in colloidal molecular crystal systems.
We argue that the vortex molecular crystals have properties in common with
certain spin systems such as Ising and n-state Potts models. We show that
kagome and honeycomb pinning arrays can be useful for increasing the critical
current above that of purely triangular pinning arrays.Comment: 19 pages, 22 postscript figures. Version to appear in Phys. Rev.
Jamming in Granular Polymers
We examine the jamming transition in a two-dimensional granular polymer
system using compressional simulations. The jamming density \phi_c decreases
with increasing length of the granular chain due to the formation of loop
structures, in excellent agreement with recent experiments. The jamming density
can be further reduced in mixtures of granular chains and granular rings, also
as observed in experiment. We show that the nature of the jamming in granular
polymer systems has pronounced differences from the jamming behavior observed
for polydisperse two-dimensional disk systems at Point J. This result provides
further evidence that there is more than one type of jamming transition.Comment: 5 pages, 7 postscript figures, version to appear in PR
Viscous Decoupling Transitions for Individually Dragged Particles in Systems with Quenched Disorder
We show that when an individual particle is dragged through an assembly of
other particles in the presence of quenched disorder, a viscous decoupling
transition occurs between the dragged particle and the surrounding particles
which is controlled by the quenched disorder. A counterintuitive consequence of
this transition is that the velocity of the dragged particle can be increased
by increasing the strength or density of the quenched disorder. The decoupling
transition can also occur when the external drive on the dragged particle is
increased, and is observable as a clear signature in the velocity-force
response.Comment: 4 pages, 3 postscript figure
Remote sensing of changes in morphology and physiology of trees under stress Annual progress report
Remote sensing of morphological and physiological changes in trees under stres
Charge Transport Transitions and Scaling in Disordered Arrays of Metallic Dots
We examine the charge transport through disordered arrays of metallic dots
using numerical simulations. We find power law scaling in the current-voltage
curves for arrays containing no voids, while for void-filled arrays charge
bottlenecks form and a single scaling is absent, in agreement with recent
experiments. In the void-free case we also show that the scaling exponent
depends on the effective dimensionality of the system. For increasing applied
drives we find a transition from 2D disordered filamentary flow near threshold
to a 1D smectic flow which can be identified experimentally using
characteristics in the transport curves and conduction noise.Comment: 4 pages, 4 postscript figure
Devil's Staircase and Disordering Transitions in Sliding Vortices and Wigner Crystals on Random Substrates with Transverse Driving
Using numerical simulations we show that, in the presence of random quenched
disorder, sliding superconducting vortices and Wigner crystals pass through a
variety of dynamical phases when an additional transverse driving force is
applied. If the disorder is weak, the driven particles form a moving lattice
and the transverse response shows a devil's staircase structure as the net
driving force vector locks with the symmetry directions of the moving lattice,
in agreement with the predictions of Le Doussal and Giamarchi. For strong
disorder, and particularly for smoothly varying potential landscapes, the
transverse response consists of a sequence of disordering transitions with an
intervening formation of stable channel structures.Comment: 7 pages, 6 postscript figures. Version to appear in Phys. Rev.
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