4,139 research outputs found
Properties of Resolved Star Clusters in M51
We present a study of compact star clusters in the nearby pair of interacting
galaxies NGC 5194/95 (M51), based on multifilter Hubble Space Telescope WFPC2
archival images. We have detected ~400 isolated clusters. Our requirement that
clusters be detected based only on their morphology results in the selection of
relatively isolated objects, and we estimate that we are missing the majority
(by a factor 4-6) of <10 Myr clusters due to crowding. Hence we focus on the
cluster population older than 10 Myr. An age distribution shows a broad peak
between 100-500 Myr, which is consistent with the crossing times of NGC 5195
through the NGC 5194 disk estimated in both single and multiple-passage
dynamical models. We estimate that the peak contains approximately 2.2-2.5
times more clusters than expected from a constant rate of cluster formation
over this time interval. We estimate the effective radii of our sample clusters
and find a median value of 3-4 pc. Additionally, we see correlations of
increasing cluster size with cluster mass (with a best fit slope of
0.14\pm0.03) at the 4sigma level, and with cluster age (0.06\pm0.02) at the
3sigma level. Finally, we report for the first time the discovery of faint,
extended star clusters in the companion, NGC 5195, an SB0 galaxy. These have
red [(V-I)>1.0] colors, effective radii >7 pc, and are scattered over the disk
of NGC 5195. Our results indicate that NGC 5195 is therefore currently the
third known barred lenticular galaxy to have formed so-called "faint fuzzy"
star clusters. (abridged)Comment: 15 pages, 12 figures, 1 table; to appear in A
The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space Telescope Imaging
We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of
five (M81, M83, NGC 6946, M101, and M51) low inclination, nearby spiral
galaxies to study ancient star cluster populations. M81 globular clusters (GC)
have an intrinsic color distribution which is very similar to those in the
Milky Way and M31, with ~40% of the clusters having colors expected for a
metal-rich population. On the other hand, the GC system in M51 appears almost
exclusively blue and metal poor. This lack of metal-rich GCs associated with
the M51 bulge indicates that the bulge formation history of this Sbc galaxy may
have differed significantly from that of our own. Ancient clusters in M101, and
possibly in NGC 6946, appear to have luminosity distributions which continue to
rise to our detection limit (M_V ~ -6.0), well beyond the expected turnover
(M_V ~ -7.4) in the luminosity function. This is reminiscent of the situation
in M33, a Local Group galaxy of similar Hubble type. The faint ancient cluster
candidates in M101 and NGC 6946 have colors and radii similar to their more
luminous counterparts, and we suggest that these are either intermediate age
(3-9 Gyr) disk clusters or the low mass end of the original GC population. If
the faint, excess GC candidates are excluded, we find that the specific
frequency (S_N) of ancient clusters formed in later-type spirals is roughly
constant, with S_N=0.5 +- 0.2. By combining the results of this study with
literature values for other systems, we find that the total GC specific
frequencies in spirals appear to correlate best with Hubble type and
bulge/total ratio, rather than with galaxy luminosity or galaxy mass
(abridged).Comment: 31 pages, 11 tables, 10 figure
RIVET: Rapid Interactive Visualization for Extensible Training
The new NASA mandate calls for missions of unprecedented remoteness and duration while human capabilities remain relatively fixed. The RIVET team (Penn, Orbitec, and NASA JSC) is to develop computer based integrated training and instruction tools that are visually intuitive, easily authorable, and adaptable to user skill level and context. The goal is to improve reliability in executing instructions by a crew with limited training, especially for critical tasks in nominal and emergency situations
Medical Tourism in the Tropics: New Regulation is Needed to Tackle Equity and Quality Concerns in Barbados
Medical tourism is on the rise as many patients travel overseas to seek private medical care that is either more expensive, unavailable or requires long waiting periods in their home country. Barbados, a small Caribbean island actively planning for medical tourism industry development, faces common challenges affecting destination countries such as degraded local access to healthcare, and possible brain drain of domestic medical workers. To address such concerns, the government must navigate both legal and ethical obstacles to develop effective regulatory mechanisms for their emerging medical tourism sector.
 
Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83
We use new WFC3 observations of the nearby grand design spiral galaxy M83 to
develop two independent methods for estimating the ages of young star clusters.
The first method uses the physical extent and morphology of Halpha emission to
estimate the ages of clusters younger than tau ~10 Myr. It is based on the
simple premise that the gas in very young (tau < few Myr) clusters is largely
coincident with the cluster stars, is in a small, ring-like structure
surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in
a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The
second method is based on an observed relation between pixel-to-pixel flux
variations within clusters and their ages. This method relies on the fact that
the brightest individual stars in a cluster are most prominent at ages around
10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older
than about 100 Myr. These two methods are the basis for a new morphological
classification system which can be used to estimate the ages of star clusters
based on their appearance. We compare previous age estimates of clusters in M83
determined from fitting UBVI Halpha measurements using predictions from stellar
evolutionary models with our new morphological categories and find good
agreement at the ~95% level. The scatter within categories is ~0.1 dex in log
tau for young clusters (10 Myr) clusters. A
by-product of this study is the identification of 22 "single-star" HII regions
in M83, with central stars having ages ~4 Myr.Comment: 33 pages, 10 figures, 3 tables; published in March Ap
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Inbound Medical Tourism to Barbados: A Qualitative Examination of Local Lawyers’ Prospective Legal and Regulatory Concerns
Background
Enabled by globalizing processes such as trade liberalization, medical tourism is a practice that involves patients’ intentional travel to privately obtain medical care in another country. Empirical legal research on this issue is limited and seldom based on the perspectives of destination countries receiving medical tourists. We consulted with diverse lawyers from across Barbados to explore their views on the prospective legal and regulatory implications of the developing medical tourism industry in the country.
Methods
We held a focus group in February 2014 in Barbados with lawyers from across the country. Nine lawyers with diverse legal backgrounds participated. Focus group moderators summarized the study objective and engaged participants in identifying the local implications of medical tourism and the anticipated legal and regulatory concerns. The focus group was transcribed verbatim and analyzed thematically.
Results
Five dominant legal and regulatory themes were identified through analysis: (1) liability; (2) immigration law; (3) physician licensing; (4) corporate ownership; and (5) reputational protection.
Conclusions
Two predominant legal and ethical concerns associated with medical tourism in Barbados were raised by participants and are reflected in the literature: the ability of medical tourists to recover medical malpractice for adverse events; and the effects of medical tourism on access to health care in the destination country. However, the participants also identified several topics that have received much less attention in the legal and ethical literature. Overall this analysis reveals that lawyers, at least in Barbados, have an important role to play in the medical tourism sector beyond litigation – particularly in transactional and gatekeeper capacities. It remains to be seen whether these findings are specific to the ecology of Barbados or can be extrapolated to the legal climate of other medical tourism destination countries
Double-Stranded RNA-Dependent Protein Kinase (PKR) is Downregulated by Phorbol Ester
The double-stranded RNA-dependent protein kinase (PKR) is one of the key mediators of interferon (IFN) action against certain viruses. PKR also plays an important role in signal transduction and immunomodulation. Understanding the regulation of PKR activity is important for the use of PKR as a tool to discover and develop novel therapeutics for viral infections, cancer and immune dysfunction. We found that phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinase C (PKC), decreased the level of autophosphorylated PKR in a dose- and time-dependent manner in IFN-treated mouse fibroblast cells. Polyinosinic–polycytidylic acid (poly I:C) treatment enhanced the activity of PKR induced by IFN, but did not overcome the PMA-induced reduction of PKR autophosphorylation. Western blot analysis with a monoclonal antibody to mouse PKR revealed that the decrease of PKR autophosphorylation in cells by PMA was a result of PKR protein degradation. Selective PKC inhibitors blocked the degradation of PKR stimulated by PMA, indicating that PKC activity was required for the effect. Furthermore, we also found that proteasome inhibitors prevented PMA-induced down regulation of PKR, indicating that an active proteasome is required. Our results identify a novel mechanism for the post-translational regulation of PKR
Double-Stranded RNA-Dependent Protein Kinase (PKR) is Downregulated by Phorbol Ester
The double-stranded RNA-dependent protein kinase (PKR) is one of the key mediators of interferon (IFN) action against certain viruses. PKR also plays an important role in signal transduction and immunomodulation. Understanding the regulation of PKR activity is important for the use of PKR as a tool to discover and develop novel therapeutics for viral infections, cancer and immune dysfunction. We found that phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinase C (PKC), decreased the level of autophosphorylated PKR in a dose- and time-dependent manner in IFN-treated mouse fibroblast cells. Polyinosinic–polycytidylic acid (poly I:C) treatment enhanced the activity of PKR induced by IFN, but did not overcome the PMA-induced reduction of PKR autophosphorylation. Western blot analysis with a monoclonal antibody to mouse PKR revealed that the decrease of PKR autophosphorylation in cells by PMA was a result of PKR protein degradation. Selective PKC inhibitors blocked the degradation of PKR stimulated by PMA, indicating that PKC activity was required for the effect. Furthermore, we also found that proteasome inhibitors prevented PMA-induced down regulation of PKR, indicating that an active proteasome is required. Our results identify a novel mechanism for the post-translational regulation of PKR
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