1,237 research outputs found
High-speed Photometric Observations of ZZ Ceti White Dwarf Candidates
We present high-speed photometric observations of ZZ Ceti white dwarf
candidates drawn from the spectroscopic survey of bright DA stars from the
Villanova White Dwarf Catalog by Gianninas et al., and from the recent
spectroscopic survey of white dwarfs within 40 parsecs of the Sun by Limoges et
al. We report the discovery of six new ZZ Ceti pulsators from these surveys,
and several photometrically constant DA white dwarfs, which we then use to
refine the location of the ZZ Ceti instability strip.Comment: 4 pages, 1 table, 2 figures, to appear in "19th European White Dwarf
Workshop" in the ASP Conference Serie
Finding apparent horizons and other two-surfaces of constant expansion
Apparent horizons are structures of spacelike hypersurfaces that can be
determined locally in time. Closed surfaces of constant expansion (CE surfaces)
are a generalisation of apparent horizons. I present an efficient method for
locating CE surfaces. This method uses an explicit representation of the
surface, allowing for arbitrary resolutions and, in principle, shapes. The CE
surface equation is then solved as a nonlinear elliptic equation.
It is reasonable to assume that CE surfaces foliate a spacelike hypersurface
outside of some interior region, thus defining an invariant (but still
slicing-dependent) radial coordinate. This can be used to determine gauge modes
and to compare time evolutions with different gauge conditions. CE surfaces
also provide an efficient way to find new apparent horizons as they appear e.g.
in binary black hole simulations.Comment: 21 pages, 8 figures; two references adde
Aspirin and its Metabolites Enhance the Expression of Vascular Endothelial Growth Factor in Retinal Pigment Epithelial Cell Cultures – Implications in the Pathophysiology of Age-Related Macular Degeneration
Purpose: An estimated 19.3% of adults, especially the elderly in the United States regularly use Aspirin for cardioprotection. Recently, multiple cohort studies have concluded that regular aspirin use for 10-15 years was associated with a statistically significant increase in the risk of incident age-related and neovascular acute macular degeneration. It has been hypothesized
that aspirin or its metabolites induce the expression of vascular endothelial growth factor (VEGF).
Materials & Methods: Retinal pigment epithelial cells, ARPE-19 (ATCC®CRL-2302™) were cultured. The cells were grown to achieve 95% confluence and then the media was changed. Cells cultured under blue light, red light, or darkness
were subjected to a challenge with high dose aspirin (0.925 mg/dL), low dose aspirin (0.325 mg/dL), or hippuric acid (0.325 mg/dL). Light was generated using 2 red or blue LEDs powered by 3v CR2032 batteries. The 24-well plate was incubated with or without drugs in blue light, red light or darkness at 37C for 16 hours. The supernatants were harvested, and VEGF was quantified. One-way ANOVA using Dunnett’s multiple comparison test was performed to analyze statistical significance.
Results: Cells exposed to blue light or darkness and hippuric acid showed a statistically significant increase in VEGF secretion (P=0.0012). However, cells exposed to red light with hippuric acid challenge showed no significant difference from the mean of cells exposed to darkness and sham control.
Conclusions: Retinal pigment epithelial cells challenged with oxidative stress provided by blue light or darkness in the presence of hippuric acid increased VEGF secretion, suggesting a possible cause for neovascularization in age-related macular degeneration. RPE cells exposed to red light, known to abrogate oxidative stress, had decreased levels of VEGF induction by hippuric acid
Mg(, )Na reaction study for spectroscopy of Na
The Mg(, )Na reaction was measured at the Holifield
Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to
better constrain spins and parities of energy levels in Na for the
astrophysically important F()Ne reaction rate
calculation. 31 MeV proton beams from the 25-MV tandem accelerator and enriched
Mg solid targets were used. Recoiling He particles from the
Mg(, )Na reaction were detected by a highly segmented
silicon detector array which measured the yields of He particles over a
range of angles simultaneously. A new level at 6661 5 keV was observed in
the present work. The extracted angular distributions for the first four levels
of Na and Distorted Wave Born Approximation (DWBA) calculations were
compared to verify and extract angular momentum transfer.Comment: 11 pages, 6 figures, proceedings of the 18th International Conference
on Accelerators and Beam Utilization (ICABU2014
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