1,022 research outputs found
Realistic Ionizing Fluxes for Young Stellar Populations from 0.05 to twice solar metallicity
We present a new grid of ionizing fluxes for O and Wolf-Rayet stars for use
with evolutionary synthesis codes and single star H II region analyses. A total
of 230 expanding, non-LTE, line-blanketed model atmospheres have been
calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 solar) using the
WM-basic code of Pauldrach et al. (2001) and the CMFGEN code of Hillier &
Miller (1998). The stellar wind parameters are scaled with metallicity for both
O and W-R stars. We incorporate the new models into Starburst99 (Leitherer et
al. 1999) and compare the ionizing outputs with Schaerer & Vacca (1998) and
Leitherer et al. (1999). The changes in the output ionizing fluxes are
dramatic, particularly below 228 A. We also find lower fluxes in the He I
continuum for Z > 0.4 solar and ages < 7 Myr because of the increased line
blanketing. We test the accuracy of the new models by constructing
photoionization models. We show that for the dwarf O star grid, He I 5876/H
beta decreases between Z = 1 and twice solar in a similar manner to
observations (e.g. Bresolin et al. 1999) due to the increased effect of line
blanketing. We therefore suggest that a lowering of the upper mass limit at
high abundances is not required to explain the observations. For the case of an
instantaneous burst, we plot the softness parameter "eta prime" against the
abundance indicator R_23. The new models are coincident with the data of
Bresolin et al. (1999), particularly during the W-R phase, unlike previous
models which over-predict the hardness of the ionizing radiation.Comment: 21 pages, 15 postscript colour figures, includes mn2e.cls. To be
published in MNRAS. Revised version containing modifications to Tables 1-
Hematochezia in a patient with liver cirrhosis
Although commonly detectable in patients with cirrhosis, rectal varices only infrequently cause significant hematochezia (0.5ā3.6%). While they may be expected to resolve with treatment of the concomitant portal hypertension, there is currently no standardized approach to their management in isolation. Therefore many authorities recommend transjugular intrahepatic portosystemic shunting (TIPS) as a means of alleviating otherwise recalcitrant bleeding. Conceptually, however, rectal varices should be as amenable to local therapies as are their counterparts occurring at the esophagogastric junction. In this report, we describe the use of endoscopic banding per ano to alleviate significant rectal bleeding in a patient with poorly controlled portal hypertension. This allowed medical optimisation so that the underlying pathology could be controlled without recourse to TIPS or other means of creating a formal portosystemic shunt
The Skyās the Limit: Scholarly Communication, Digital Initiatives, Institutional Repositories, and Subject Librarians
The University of Central Floridaās institutional repository, Showcase of Text, Archives, Research, and Scholarship (STARS), has presented new opportunities for collaboration among the Librariesā Office of Scholarly Communication, Digital Initiatives, Research Services, and subject librarians. Building on efforts to proactively promote scholarly communication initiatives to the university community, these four units have used the institutional repository as a foundation for collaboration, outreach, marketing, and educational efforts. This article will give an overview of a panel presentation given by members of these four units on STARS and highlight the role the institutional repository has in increasing the collaborative efforts of these four units. Additionally, it will highlight four different perspectives and discuss strategies designed to generate institutional repository interest from the university community. Successful ventures and lessons learned will provide insight into creating a productive interdepartmental framework that is geared toward supporting students and faculty institutional repository projects
Century-scale records of land-based activities recorded in Mesoamerican coral cores
Author Posting. Ā© The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Pollution Bulletin 58 (2009): 1835-1842, doi:10.1016/j.marpolbul.2009.07.024.The Mesoamerican Reef, the second-largest barrier reef in the world, is located in the
western Caribbean Sea off the coasts of Mexico, Belize, Guatemala, and Honduras.
Particularly in the south, the surrounding watersheds are steep and the climate is
extremely wet. With development and agricultural expansion, the potential for negative
impacts to the reef from land-based runoff becomes high. We constructed annually
resolved century-scale records of metal/calcium ratios in coral skeletons collected from
four sites experiencing a gradient of land-based runoff. Our proxy data indicate that
runoff onto the reef has increased relatively steadily over time at all sites, consistent with
land use trends from historical records. Sediment supply to the reef is greater in the south,
and these more exposed reefs will probably benefit most immediately from management
that targets runoff reduction. However, because runoff at all sites is steadily increasing,
even distal sites will benefit from watershed management.This research was supported by funds from the PADI Foundation, B. Katz, two
anonymous donors and the Edna Bailey Sussman Foundation to J.C
Lithium abundances in CEMP stars
Carbon-enhanced metal-poor (CEMP) stars are believed to show the chemical
imprints of more massive stars (M > 0.8 Msun) that are now extinct. In
particular, it is expected that the observed abundance of Li should deviate in
these stars from the standard Spite lithium plateau. We study here a sample of
11 metal-poor stars and a double-lined spectroscopic binary with -1.8 <[Fe/H]<
-3.3 observed with VLT/UVES spectrograph. Among these 12 metal-poor stars,
there are 8 CEMP stars for which we measure or constrain the Li abundance. In
contrast to previous arguments, we demonstrate that an appropriate regime of
dilution permits the existence of "Li-Spite plateau and C-rich" stars, whereas
some of the "Li-depleted and C-rich" stars call for an unidentified additional
depletion mechanism that cannot be explained by dilution alone. We find
evidence that rotation is related to the Li depletion in some CEMP stars.
Additionally, we report on a newly recognized double-lined spectroscopic binary
star in our sample. For this star, we develop a new technique from which
estimates of stellar parameters and luminosity ratios can be derived based on a
high-resolution spectrum alone, without the need for input from evolutionary
models.Comment: 62 pages, 16 figures, accepted for publication in Ap
A fiberāmounted, micromachined photoconductive probe with 15 nV/Hz1/2 sensitivity
We report the performance of a micromachined, photoconductiveāsampling probe that is fabricated on lowātemperatureāgrown GaAs and mounted on a singleāmode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 Ī¼m, and a sensitivity of 15 nV/(Hz)1/2 when integrated with a high impedance, junction fieldāeffect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probeās compact cross section makes it ideal for applications as an internalānode, picosecondāresponse, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits. Ā© 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70779/2/APPLAB-69-13-1843-1.pd
A fieldāsensitive photoconductive probe for sampling through passivation layers
A fieldāsensitive photoconductive sampling technique has been demonstrated in measurements performed through an insulating layer without the need for conductive contact. Sampled signals are sensed by a virtualāground, floatingāgate amplifier without draining charge from the device under test or the photoconductive switch. The minimum detectable signal is 2.5 Ī¼V/Hz1/2 with a spatial resolution of 7 Ī¼m, while the sampling bandwidth is essentially that observed using photoconductive sampling with a conductive contact to the device under test. The photovoltaic and shot current noise are negligible in comparison with the lockāin amplifier noise since the current flowing in this highāimpedance, floatingāgate probe is negligible. Ā© 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70307/2/APPLAB-69-15-2211-1.pd
Fully automated 3D segmentation of dopamine transporter SPECT images using an estimation-based approach
Quantitative measures of uptake in caudate, putamen, and globus pallidus in
dopamine transporter (DaT) brain SPECT have potential as biomarkers for the
severity of Parkinson disease. Reliable quantification of uptake requires
accurate segmentation of these regions. However, segmentation is challenging in
DaT SPECT due to partial-volume effects, system noise, physiological
variability, and the small size of these regions. To address these challenges,
we propose an estimation-based approach to segmentation. This approach
estimates the posterior mean of the fractional volume occupied by caudate,
putamen, and globus pallidus within each voxel of a 3D SPECT image. The
estimate is obtained by minimizing a cost function based on the binary
cross-entropy loss between the true and estimated fractional volumes over a
population of SPECT images, where the distribution of the true fractional
volumes is obtained from magnetic resonance images from clinical populations.
The proposed method accounts for both the sources of partial-volume effects in
SPECT, namely the limited system resolution and tissue-fraction effects. The
method was implemented using an encoder-decoder network and evaluated using
realistic clinically guided SPECT simulation studies, where the ground-truth
fractional volumes were known. The method significantly outperformed all other
considered segmentation methods and yielded accurate segmentation with dice
similarity coefficients of ~ 0.80 for all regions. The method was relatively
insensitive to changes in voxel size. Further, the method was relatively robust
up to +/- 10 degrees of patient head tilt along transaxial, sagittal, and
coronal planes. Overall, the results demonstrate the efficacy of the proposed
method to yield accurate fully automated segmentation of caudate, putamen, and
globus pallidus in 3D DaT-SPECT images
Local Stressors Reduce Coral Resilience to Bleaching
Coral bleaching, during which corals lose their symbiotic dinoflagellates, typically corresponds with periods of intense heat stress, and appears to be increasing in frequency and geographic extent as the climate warms. A fundamental question in coral reef ecology is whether chronic local stress reduces coral resistance and resilience from episodic stress such as bleaching, or alternatively promotes acclimatization, potentially increasing resistance and resilience. Here we show that following a major bleaching event, Montastraea faveolata coral growth rates at sites with higher local anthropogenic stressors remained suppressed for at least 8 years, while coral growth rates at sites with lower stress recovered in 2ā3 years. Instead of promoting acclimatization, our data indicate that background stress reduces coral fitness and resilience to episodic events. We also suggest that reducing chronic stress through local coral reef management efforts may increase coral resilience to global climate change
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