1,420 research outputs found
Vision Problems In Ecuador: Developing A Clinical Trial to Test Visual Acuity In Rural Populations
In many developing countries, access to medical care and screenings are difficult, and this is especially true for countries with large rural populations, such as Ecuador. There are many groups and non-governmental organizations (NGOs) that contribute time and money to educational systems and other basic infrastructure, but not necessarily medical screenings. In the case of eyesight, without proper screening an individual may fall behind academically or even withdraw from education simply because they cannot see. The simple addition of corrective lenses could be the difference between a life of poverty, and a life of wellbeing for many of these individuals. Visual acuity is a good indicator of eye health, and can be used to quickly screen large populations and identify those with vision problems. Working with Dr. Kass we have developed a program that uses an “open door” method to determine visual acuity. The acuity results from this program can be compared to results from a standard Landolt C eye chart to determine if the program accurately predicts visual acuity. Ecuador is an excellent country to use as a trial for this program, and successful implementation can lead the way for implementation in other countries
Spectral Statistics for the Dirac Operator on Graphs
We determine conditions for the quantisation of graphs using the Dirac
operator for both two and four component spinors. According to the
Bohigas-Giannoni-Schmit conjecture for such systems with time-reversal symmetry
the energy level statistics are expected, in the semiclassical limit, to
correspond to those of random matrices from the Gaussian symplectic ensemble.
This is confirmed by numerical investigation. The scattering matrix used to
formulate the quantisation condition is found to be independent of the type of
spinor. We derive an exact trace formula for the spectrum and use this to
investigate the form factor in the diagonal approximation
Intermediate statistics for a system with symplectic symmetry: the Dirac rose graph
We study the spectral statistics of the Dirac operator on a rose-shaped
graph---a graph with a single vertex and all bonds connected at both ends to
the vertex. We formulate a secular equation that generically determines the
eigenvalues of the Dirac rose graph, which is seen to generalise the secular
equation for a star graph with Neumann boundary conditions. We derive
approximations to the spectral pair correlation function at large and small
values of spectral spacings, in the limit as the number of bonds approaches
infinity, and compare these predictions with results of numerical calculations.
Our results represent the first example of intermediate statistics from the
symplectic symmetry class.Comment: 26 pages, references adde
Carbon and Strontium Abundances of Metal-Poor Stars
We present carbon and strontium abundances for 100 metal-poor stars measured
from R7000 spectra obtained with the Echellette Spectrograph and Imager
at the Keck Observatory. Using spectral synthesis of the G-band region, we have
derived carbon abundances for stars ranging from [Fe/H] to
[Fe/H]. The formal errors are dex in [C/Fe]. The strontium
abundance in these stars was measured using spectral synthesis of the resonance
line at 4215 {\AA}. Using these two abundance measurments along with the barium
abundances from our previous study of these stars, we show it is possible to
identify neutron-capture-rich stars with our spectra. We find, as in other
studies, a large scatter in [C/Fe] below [Fe/H]. Of the stars with
[Fe/H], 94% can be classified as carbon-rich metal-poor stars. The Sr
and Ba abundances show that three of the carbon-rich stars are
neutron-capture-rich, while two have normal Ba and Sr. This fraction of carbon
enhanced stars is consistent with other studies that include this metallicity
range.Comment: ApJ, Accepte
Level spacings and periodic orbits
Starting from a semiclassical quantization condition based on the trace
formula, we derive a periodic-orbit formula for the distribution of spacings of
eigenvalues with k intermediate levels. Numerical tests verify the validity of
this representation for the nearest-neighbor level spacing (k=0). In a second
part, we present an asymptotic evaluation for large spacings, where consistency
with random matrix theory is achieved for large k. We also discuss the relation
with the method of Bogomolny and Keating [Phys. Rev. Lett. 77 (1996) 1472] for
two-point correlations.Comment: 4 pages, 2 figures; major revisions in the second part, range of
validity of asymptotic evaluation clarifie
Beyond the Heisenberg time: Semiclassical treatment of spectral correlations in chaotic systems with spin 1/2
The two-point correlation function of chaotic systems with spin 1/2 is
evaluated using periodic orbits. The spectral form factor for all times thus
becomes accessible. Equivalence with the predictions of random matrix theory
for the Gaussian symplectic ensemble is demonstrated. A duality between the
underlying generating functions of the orthogonal and symplectic symmetry
classes is semiclassically established
5-Bromopyrimidin-2(1H)-one
The geometric parameters of the title compound, C4H3BrN2O, are in the usual ranges. The crystal packing is characterized by N—H⋯N and C—H⋯O hydrogen bonds and short O⋯Br contacts
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