255 research outputs found
Using Virtual Observatory Services in Sky View
For over a decade Skyview has provided astronomers and the public with easy access to survey and imaging data from all wavelength regimes. SkyView has pioneered many of the concepts that underlie the Virtual Observatory. Recently SkyView has been released as a distributable package which uses VO protocols to access image and catalog services. This chapter describes how to use the Skyview as a local service and how to customize it to access additional VO services and local data
Running a distributed virtual observatory: US Virtual Astronomical Observatory operations
Operation of the US Virtual Astronomical Observatory shares some issues with
modern physical observatories, e.g., intimidating data volumes and rapid
technological change, and must also address unique concerns like the lack of
direct control of the underlying and scattered data resources, and the
distributed nature of the observatory itself. In this paper we discuss how the
VAO has addressed these challenges to provide the astronomical community with a
coherent set of science-enabling tools and services. The distributed nature of
our virtual observatory-with data and personnel spanning geographic,
institutional and regime boundaries-is simultaneously a major operational
headache and the primary science motivation for the VAO. Most astronomy today
uses data from many resources. Facilitation of matching heterogeneous datasets
is a fundamental reason for the virtual observatory. Key aspects of our
approach include continuous monitoring and validation of VAO and VO services
and the datasets provided by the community, monitoring of user requests to
optimize access, caching for large datasets, and providing distributed storage
services that allow user to collect results near large data repositories. Some
elements are now fully implemented, while others are planned for subsequent
years. The distributed nature of the VAO requires careful attention to what can
be a straightforward operation at a conventional observatory, e.g., the
organization of the web site or the collection and combined analysis of logs.
Many of these strategies use and extend protocols developed by the
international virtual observatory community.Comment: 7 pages with 2 figures included within PD
OMCat: Catalogue of Serendipitous Sources Detected with the XMM-Newton Optical Monitor
The Optical Monitor Catalogue of serendipitous sources (OMCat) contains
entries for every source detected in the publicly available XMM-Newton Optical
Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM
is coaligned and records data simultaneously with the X-ray telescopes on
XMM-Newton, it typically produces images in one or more near-UV/optical bands
for every pointing of the observatory. As of the beginning of 2006, the public
archive had covered roughly 0.5% of the sky in 2950 fields.
The OMCat is not dominated by sources previously undetected at other
wavelengths; the bulk of objects have optical counterparts. However, the OMCat
can be used to extend optical or X-ray spectral energy distributions for known
objects into the ultraviolet, to study at higher angular resolution objects
detected with GALEX, or to find high-Galactic-latitude objects of interest for
UV spectroscopy.Comment: 25 pages, 22 figures, submitted to PAS
Time-Dependence of the Mass Accretion Rate in Cluster Cooling Flows
We analyze two time-dependent cluster cooling flow models in spherical
symmetry. The first assumes that the intracluster gas resides in a static
external potential, and includes the effects of optically thin radiative
cooling and mass deposition. This corresponds to previous steady-state cooling
flow models calculated by White & Sarazin (1987). Detailed agreement is found
between steady-state models and time-dependent models at fixed times in the
simulations. The mass accretion rate is found either to increase or remain
nearly constant once flows reach a steady state. The time rate of change of the
accretion rate is strongly sensitive to the value of the mass deposition
parameter q, but only mildly sensitive to the ratio beta of gravitational
binding energy to gas temperature. We show that previous scaling arguments
presented by Bertschinger (1988) and White (1988) are valid only for mature
cooling flows with weak mass deposition (q ~< 1). The second set of models
includes the effects of a secularly deepening cluster potential and secondary
infall of gas from the Hubble flow. We find that such heating effects do not
prevent the flows from reaching a steady state within an initial central
cooling time.Comment: 22 pages (AASTeX) with 16 EPS figures; accepted for publication in
The Astrophysical Journa
Formation of Cool Cores in Galaxy Clusters via Hierarchical Mergers
We present a new scenario for the formation of cool cores in rich galaxy
clusters based on results from recent high spatial dynamic range, adaptive mesh
Eulerian hydrodynamic simulations of large-scale structure formation. We find
that cores of cool gas, material that would be identified as a classical
cooling flow based on its X-ray luminosity excess and temperature profile, are
built from the accretion of discrete, stable subclusters. Any ``cooling flow''
present is overwhelmed by the velocity field within the cluster - the bulk flow
of gas through the cluster typically has speeds up to about 2,000 km s^-1 and
significant rotation is frequently present in the cluster core. The inclusion
of consistent initial cosmological conditions for the cluster within its
surrounding supercluster environment is crucial when simulating the evolution
of cool cores in rich galaxy clusters. This new model for the hierarchical
assembly of cool gas naturally explains the high frequency of cool cores in
rich galaxy clusters despite the fact that a majority of these clusters show
evidence of substructure which is believed to arise from recent merger
activity. Furthermore, our simulations generate complex cluster cores in
concordance with recent X-ray observations of cool fronts, cool ``bullets'',
and filaments in a number of galaxy clusters. Our simulations were computed
with a coupled N-body, Eulerian, adaptive mesh refinement, hydrodynamics
cosmology code that properly treats the effects of shocks and radiative cooling
by the gas. We employ up to seven levels of refinement to attain a peak
resolution of 15.6 h^-1 kpc within a volume 256 h-1 Mpc on a side and assume a
standard LambdaCDM cosmology.Comment: To appear in ApJ, 41 pages, 20 Figures and 2 Tables. Full resolution
figures are available at http://casa.colorado.edu/~motl/astro-p
Incorporating statistical uncertainty in the use of physician cost profiles
<p>Abstract</p> <p>Background</p> <p>Physician cost profiles (also called efficiency or economic profiles) compare the costs of care provided by a physician to his or her peers. These profiles are increasingly being used as the basis for policy applications such as tiered physician networks. Tiers (low, average, high cost) are currently defined by health plans based on percentile cut-offs which do not account for statistical uncertainty. In this paper we compare the percentile cut-off method to another method, using statistical testing, for identifying high-cost or low-cost physicians.</p> <p>Methods</p> <p>We created a claims dataset of 2004-2005 data from four Massachusetts health plans. We employed commercial software to create episodes of care and assigned responsibility for each episode to the physician with the highest proportion of professional costs. A physicians' cost profile was the ratio of the sum of observed costs divided by the sum of expected costs across all assigned episodes. We discuss a new method of measuring standard errors of physician cost profiles which can be used in statistical testing. We then assigned each physician to one of three cost categories (low, average, or high cost) using two methods, percentile cut-offs and a t-test (p-value ≤ 0.05), and assessed the level of disagreement between the two methods.</p> <p>Results</p> <p>Across the 8689 physicians in our sample, 29.5% of physicians were assigned a different cost category when comparing the percentile cut-off method and the t-test. This level of disagreement varied across specialties (17.4% gastroenterology to 45.8% vascular surgery).</p> <p>Conclusions</p> <p>Health plans and other payers should incorporate statistical uncertainty when they use physician cost-profiles to categorize physicians into low or high-cost tiers.</p
X-Ray Emission Line Ratios and Multiphase Gas in Elliptical Galaxies and Galaxy Clusters
We examine the K shell emission lines produced by isothermal and simple
multiphase models of the hot gas in elliptical galaxies and galaxy clusters to
determine the most effective means for constraining the width of the
differential emission measure (xi(T)) in these systems which we characterize by
a dimensionless parameter, sigma_xi. Comparison of line ratios of
two-temperature (sigma_xi << 1) and cooling flow (sigma_xi ~1) models is
presented in detail. We find that a two-temperature model can approximate very
accurately a cooling flow spectrum over 0.5-10 keV.
We have re-analyzed the ASCA spectra of three of the brightest galaxy
clusters to assess the evidence for multiphase gas in their cores: M87 (Virgo),
the Centaurus cluster, and the Perseus cluster. K-alpha emission line blends of
Si, S, Ar, Ca, and Fe are detected in each system as is significant Fe K-beta
emission. The Fe K-beta/K-alpha ratios are consistent with optically thin
plasma models and do not suggest resonance scattering in these systems.
Consideration of both the ratios of H-like to He-like K-alpha lines and the
local continuum temperatures clearly rules out isothermal gas in each case. To
obtain more detailed constraints we fitted plasma models over 1.6-9 keV where
the emission is dominated by these K shell lines and by continuum. In each case
the ASCA spectra cannot determine whether the gas emits at only two
temperatures or over a continuous range of temperatures as expected for a
cooling flow. The metal abundances are near solar for all of the multiphase
models. We discuss the implications of these results and examine the prospects
for determining the temperature structure in these systems with upcoming X-ray
missions.Comment: 30 pages (18 figures), To Appear in MNRAS. Major revision of the
initially posted version: (1) The section on ASCA data of ellipticals was
expanded and moved to astro-ph/9811080; (2) The ASCA data of M87, Centaurus,
and Perseus have been re-analyzed. We find evidence for Fe K-beta emission in
these systems, but the Fe K-beta/K-alpha ratios do not suggest resonance
scattering; (3) The metal abundances of the cores of these systems are
consistent with the meteoritic solar value
What Are the Public Health Effects of Direct-to-Consumer Drug Advertising?
Background to the debate: Only two industrialized countries, the United States and New Zealand, allow direct-to-consumer advertising (DTCA) of prescription medicines, although New Zealand is planning a ban [ 1]. The challenge for these governments is ensuring that DTCA is more beneficial than harmful. Proponents of DTCA argue that it helps to inform the public about available treatments and stimulates appropriate use of drugs for high-priority illnesses (such as statin use in people with ischemic heart disease). Critics argue that the information in the adverts is often biased and misleading, and that DTCA raises prescribing costs without net evidence of health benefits
Regulation of cell survival by sphingosine-1-phosphate receptor S1P1 via reciprocal ERK-dependent suppression of bim and PI-3-kinase/protein kinase C-mediated upregulation of Mcl-1
Although the ability of bioactive lipid sphingosine-1-phosphate (S1P) to positively regulate anti-apoptotic/pro-survival responses by binding to S1P1 is well known, the molecular mechanisms remain unclear. Here we demonstrate that expression of S1P1 renders CCL39 lung fibroblasts resistant to apoptosis following growth factor withdrawal. Resistance to apoptosis was associated with attenuated accumulation of pro-apoptotic BH3-only protein Bim. However, although blockade of extracellular signal-regulated kinase (ERK) activation could reverse S1P1-mediated suppression of Bim accumulation, inhibition of caspase-3 cleavage was unaffected. Instead S1P1-mediated inhibition of caspase-3 cleavage was reversed by inhibition of phosphatidylinositol-3-kinase (PI3K) and protein kinase C (PKC), which had no effect on S1P1 regulation of Bim. However, S1P1 suppression of caspase-3 was associated with increased expression of anti-apoptotic protein Mcl-1, the expression of which was also reduced by inhibition of PI3K and PKC. A role for the induction of Mcl-1 in regulating endogenous S1P receptor-dependent pro-survival responses in human umbilical vein endothelial cells was confirmed using S1P receptor agonist FTY720-phosphate (FTY720P). FTY720P induced a transient accumulation of Mcl-1 that was associated with a delayed onset of caspase-3 cleavage following growth factor withdrawal, whereas Mcl-1 knockdown was sufficient to enhance caspase-3 cleavage even in the presence of FTY720P. Consistent with a pro-survival role of S1P1 in disease, analysis of tissue microarrays from ER+ breast cancer patients revealed a significant correlation between S1P1 expression and tumour cell survival. In these tumours, S1P1 expression and cancer cell survival were correlated with increased activation of ERK, but not the PI3K/PKB pathway. In summary, pro-survival/anti-apoptotic signalling from S1P1 is intimately linked to its ability to promote the accumulation of pro-survival protein Mcl-1 and downregulation of pro-apoptotic BH3-only protein Bim via distinct signalling pathways. However, the functional importance of each pathway is dependent on the specific cellular context
Runx1 deficiency protects against adverse cardiac remodeling following myocardial infarction
Background: Myocardial infarction (MI) is a leading cause of heart failure and death worldwide. Preservation of contractile function and protection against adverse changes in ventricular architecture (cardiac remodeling) are key factors to limiting progression of this condition to heart failure. Consequently, new therapeutic targets are urgently required to achieve this aim. Expression of the Runx1 transcription factor is increased in adult cardiomyocytes after MI; however, the functional role of Runx1 in the heart is unknown.
Methods: To address this question, we have generated a novel tamoxifen-inducible cardiomyocyte-specific Runx1-deficient mouse. Mice were subjected to MI by means of coronary artery ligation. Cardiac remodeling and contractile function were assessed extensively at the whole-heart, cardiomyocyte, and molecular levels.
Results: Runx1-deficient mice were protected against adverse cardiac remodeling after MI, maintaining ventricular wall thickness and contractile function. Furthermore, these mice lacked eccentric hypertrophy, and their cardiomyocytes exhibited markedly improved calcium handling. At the mechanistic level, these effects were achieved through increased phosphorylation of phospholamban by protein kinase A and relief of sarco/endoplasmic reticulum Ca2+-ATPase inhibition. Enhanced sarco/endoplasmic reticulum Ca2+-ATPase activity in Runx1-deficient mice increased sarcoplasmic reticulum calcium content and sarcoplasmic reticulum–mediated calcium release, preserving cardiomyocyte contraction after MI.
Conclusions: Our data identified Runx1 as a novel therapeutic target with translational potential to counteract the effects of adverse cardiac remodeling, thereby improving survival and quality of life among patients with MI
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