61 research outputs found
Effective interactions of colloids on nematic films
The elastic and capillary interactions between a pair of colloidal particles
trapped on top of a nematic film are studied theoretically for large
separations . The elastic interaction is repulsive and of quadrupolar type,
varying as . For macroscopically thick films, the capillary interaction
is likewise repulsive and proportional to as a consequence of
mechanical isolation of the system comprised of the colloids and the interface.
A finite film thickness introduces a nonvanishing force on the system (exerted
by the substrate supporting the film) leading to logarithmically varying
capillary attractions. However, their strength turns out to be too small to be
of importance for the recently observed pattern formation of colloidal droplets
on nematic films.Comment: 13 pages, accepted by EPJ
Nonprofit governance: Improving performance in troubled economic times
Nonprofit management is currently pressured to perform effectively in a weak economy. Yet, nonprofit governance continues to suffer from unclear conceptions of the division of labor between board of directors and executive directors. This online survey of 114 executive directors aims to provide clarification and recommendations for social administration
Topological Defects in Nematic Droplets of Hard Spherocylinders
Using computer simulations we investigate the microscopic structure of the
singular director field within a nematic droplet. As a theoretical model for
nematic liquid crystals we take hard spherocylinders. To induce an overall
topological charge, the particles are either confined to a two-dimensional
circular cavity with homeotropic boundary or to the surface of a
three-dimensional sphere. Both systems exhibit half-integer topological point
defects. The isotropic defect core has a radius of the order of one particle
length and is surrounded by free-standing density oscillations. The effective
interaction between two defects is investigated. All results should be
experimentally observable in thin sheets of colloidal liquid crystals.Comment: 13 pages, 16 figures, Phys. Rev.
Topological Defects and Interactions in Nematic Emulsions
Inverse nematic emulsions in which surfactant-coated water droplets are
dispersed in a nematic host fluid have distinctive properties that set them
apart from dispersions of two isotropic fluids or of nematic droplets in an
isotropic fluid. We present a comprehensive theoretical study of the
distortions produced in the nematic host by the dispersed droplets and of
solvent mediated dipolar interactions between droplets that lead to their
experimentally observed chaining. A single droplet in a nematic host acts like
a macroscopic hedgehog defect. Global boundary conditions force the nucleation
of compensating topological defects in the nematic host. Using variational
techniques, we show that in the lowest energy configuration, a single water
droplet draws a single hedgehog out of the nematic host to form a tightly bound
dipole. Configurations in which the water droplet is encircled by a
disclination ring have higher energy. The droplet-dipole induces distortions in
the nematic host that lead to an effective dipole-dipole interaction between
droplets and hence to chaining.Comment: 17 double column pages prepared by RevTex, 15 eps figures included in
text, 2 gif figures for Fig. 1
Alabama Veterans Rural Health Initiative: A Preliminary Evaluation of Unmet Health Care Needs
The Alabama Veterans Rural Health Initiative aims to better understand the health care needs, health status, and barriers to care for rural veterans. Following extensive community outreach, Veteran Community Outreach Health Workers assessed 203 veterans residing in rural counties of Alabama who either: 1) had never enrolled in VA health services, or 2) had not used those services in at least two years. While 71.4 percent of participants reported having utilized non-VHA primary care within the past year, 33.5 percent reported an inability or delay in obtaining needed health care for one or more services: primary care, specialty care, mental health care, addictions treatment, dental care, or prescription medication. The most commonly cited barrier was cost. Among all participants, 56 percent screened positive for at least one Axis I mental disorder. Rurally residing, non-VHA utilizing veterans appear to have fairly good access to primary care, but need dental care, prescription medication, and mental health care
A new citrus-feeding psyllid from the Comoro Islands, with a review of the Diaphorina amoena species group (Homoptera)
Discriminative Analysis for Image-Based Studies
In this paper, we present a methodology for performing statistical analysis for image-based studies of differences between populations and describe our experience applying the technique in several different population comparison experiments. Unlike traditional analysis tools, we consider all features simultaneously, thus accounting for potential correlations between the features. The result of the analysis is a classifier function that can be used for labeling new examples and a map over the original features indicating the degree to which each feature participates in estimating the label for any given example. Our experiments include shape analysis of subcortical structures in schizophrenia, cortical thinning in healthy aging and Alzheimer’s disease and comparisons of fMRI activations in response to different visual stimuli
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