16,687 research outputs found
Dynamics, Rectification, and Fractionalization for Colloids on Flashing Substrates
We show that a rich variety of dynamic phases can be realized for mono- and
bidisperse mixtures of interacting colloids under the influence of a symmetric
flashing periodic substrate. With the addition of dc or ac drives, phase
locking, jamming, and new types of ratchet effects occur. In some regimes we
find that the addition of a non-ratcheting species increases the velocity of
the ratcheting particles. We show that these effects occur due to the
collective interactions of the colloids.Comment: 4 pages, 4 postscript figures. Version to appear in Phys. Rev. Let
Ordering and Melting in Colloidal Molecular Crystal Mixtures
We show in simulations that a rich variety of novel orderings such as
pinwheel and star states can be realized for colloidal molecular crystal
mixtures at rational ratios of the number of colloids to the number of minima
from an underlying periodic substrate. These states can have multi-step melting
transitions and also show coexistence in which one species disorders while the
other species remains orientationally disordered. For other mixtures, only
partially ordered or frustrated states form.Comment: 4 pages, 4 postscript figure
Nutritional Consequences of Food Insecurity in a Rural New York State County
This study of women with children in a rural county of upstate New York examined the relationships of food insecurity and income with two nutritional consequences (adiposity and fruit and vegetables consumption), and assessed whether disordered eating patterns is a mediator for the effects of food insecurity and income on these nutritional consequences. Each of 193 respondents was interviewed twice in her home. Data were collected on household food stores, socioeconomic and demographic characteristics, methods of obtaining food, food program participation, household expenditures, food intake, the Radimer/Cornell hunger and food insecurity items, height, weight, frequency of fruit and vegetable consumption, and disordered eating patterns. Regression analysis was used to analyze the relationships of body mass index and an obesity classification with height, income, education, single parenthood, employment, food insecurity, disordered eating, and frequency of fruit and vegetable consumption. Regression analysis was also used to examine the relationships of disordered eating and frequency of fruit and vegetable consumption with the other variables. Lower income and unemployment were related to higher adiposity. The effects of income on adiposity were not mediated through disordered eating patterns or through fruit and vegetable consumption. Food insecurity was related to adiposity, and part of this effect of food insecurity was mediated through disordered eating. This mediating effect of disordered eating partially explained why those experiencing the least severe food insecurity were more likely to be overweight than those who were food secure, but those experiencing the most severe food insecurity were less likely to be overweight than those who were food secure. Food insecurity was related to lower fruit and vegetable consumption, but this did not translate into effects on adiposity.
Multiscaling at Point J: Jamming is a Critical Phenomenon
We analyze the jamming transition that occurs as a function of increasing
packing density in a disordered two-dimensional assembly of disks at zero
temperature for ``Point J'' of the recently proposed jamming phase diagram. We
measure the total number of moving disks and the transverse length of the
moving region, and find a power law divergence as the packing density increases
toward a critical jamming density. This provides evidence that the T = 0
jamming transition as a function of packing density is a {\it second order}
phase transition. Additionally we find evidence for multiscaling, indicating
the importance of long tails in the velocity fluctuations.Comment: 4 pages, 5 figures; extensive new numerical data; final version in
press at PR
Estimating the prevalence of hunger and food insecurity: The validity of questionnaire-based measures for the identification of households
This study had three objectives: (1) to assess the validity of questionnaire-based measures in identifying households experiencing hunger and food insecurity, (2) to examine the interrelationships of different questionnaire-based measures, and (3) to examine the construction of a continuous food insecurity scale intended to differentiate three levels of food insecurity within households. A 1993 survey of 193 randomly sampled rural households with women and children living at home provided data on demographics, risk factors for food insecurity, Radimer/Cornell, CCHIP, and NHANES III hunger and food insecurity items, coping strategies, fruit and vegetable consumption, disordered eating behaviors, height, weight, dietary recall, and household food-stores inventory. This information was used to develop a definitive criterion measure for hunger and food insecurity, against which the Radimer/Cornell and CCHIP questionnaire-based measures, the NHANES III item, and the continuous food insecurity scale were tested for their specificity and sensitivity in measuring levels of food insecurity.
Develop and test fuel cell powered on site integrated total energy sysems: Phase 3: Full-scale power plant development
A 25-cell stack of the 13 inch x 23 inch cell size (about 4kW) remains on test after 8300 hours, using simulated reformate fuel. A similar stack was previously shut down after 7000 hours on load. These tests have been carried out for the purpose of assessing the durability of fuel cell stack components developed through the end of 1983. A 25kW stack containing 175 cells of the same size and utilizing a technology base representative of the 25-cell stacks has been constructed and is undergoing initial testing. A third 4kW stack is being prepared, and this stack will incorporate several new technology features
Nonlinear dynamics, rectification, and phase locking for particles on symmetrical two-dimensional periodic substrates with dc and circular ac drives
We investigate the dynamical motion of particles on a two-dimensional
symmetric periodic substrate in the presence of both a dc drive along a
symmetry direction of the periodic substrate and an additional circular ac
drive. For large enough ac drives, the particle orbit encircles one or more
potential maxima of the periodic substrate. In this case, when an additional
increasing dc drive is applied in the longitudinal direction, the longitudinal
velocity increases in a series of discrete steps that are integer multiples of
the lattice constant of the substrate times the frequency. Fractional steps can
also occur. These integer and fractional steps correspond to distinct stable
dynamical orbits. A number of these phases also show a rectification in the
positive or negative transverse direction where a non-zero transverse velocity
occurs in the absence of a dc transverse drive. We map out the phase diagrams
of the regions of rectification as a function of ac amplitude, and find a
series of tongues. Most of the features, including the steps in the
longitudinal velocity and the transverse rectification, can be captured with a
simple toy model and by arguments from nonlinear maps. We have also
investigated the effects of thermal disorder and incommensuration on the
rectification phenomena, and find that for increasing disorder, the
rectification regions are gradually smeared and the longitudinal velocity steps
are no longer flat but show a linearly increasing velocity.Comment: 14 pages, 17 postscript figure
Simulations of Spinodal Nucleation in Systems with Elastic Interactions
Systems with long-range interactions quenched into a metastable state near
the pseudospinodal exhibit nucleation that is qualitatively different than the
classical nucleation observed near the coexistence curve. We have observed
nucleation droplets in our Langevin simulations of a two-dimensional model of
martensitic transformations and have determined that the structure of the
nucleating droplet differs from the stable martensite structure. Our results,
together with experimental measurements of the phonon dispersion curve, allow
us to predict the nature of the droplet. These results have implications for
nucleation in many solid-solid transitions and the structure of the final
state
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