Star Formation in the Starburst Cluster in NGC 3603

We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (~ 1 - 3 M_sun) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ~ 2 to ~ 30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East - North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.Comment: 21 pages, 19 figures, accepted for publication in Astrophysics & Space Scienc

Multiple Facets of Biodiversity Drive the Diversity-Stability Relationship

A significant body of evidence has demonstrated that biodiversity stabilizes ecosystem functioning over time in grassland ecosystems. However, the relative importance of different facets of biodiversity underlying the diversity–stability relationship remains unclear. Here we used data from 39 biodiversity experiments and structural equation modeling to investigate the roles of species richness, phylogenetic diversity, and both the diversity and community-weighted mean of functional traits representing the ‘fast–slow’ leaf economics spectrum in driving the diversity–stability relationship. We found that high species richness and phylogenetic diversity stabilize biomass production via enhanced asynchrony. Contrary to our hypothesis, low phylogenetic diversity also enhances ecosystem stability directly, albeit weakly. While the diversity of fast–slow functional traits has a weak effect on ecosystem stability, communities dominated by slow species enhance ecosystem stability by increasing mean biomass production relative to the standard deviation of biomass over time. Our results demonstrate that biodiversity influences ecosystem stability via a variety of facets, thus highlighting a more multicausal relationship than has been previously acknowledged

A new frontier for quality of care in gynecologic oncology surgery: Multi-institutional assessment of short-term outcomes for ovarian cancer using a risk-adjusted model

Objective - To test the feasibility and utility of a risk-adjusted, multicenter outcomes model for ovarian cancer surgery as a tool for quality improvement. Methods - Patient characteristics, intra-operative findings, procedures, and outcomes were assessed in primary advanced stage ovarian cancer cases from 3 independent centers. A surgical complexity score (SCS) was developed to adjust for extent of surgery. Outcomes measures were: 30-day morbidity (sepsis, thrombo-embolic, cardiac, readmission or re-operation), 3-month mortality, length of stay (LOS), and ability to receive chemotherapy. A multivariable risk-adjusted model was developed for all the outcomes. Observed-to-expected (O/E) outcome ratios were calculated from all data. Results - 564 consecutive patients from 3 centers were analyzed. The strongest predictors of 30-day morbidity were endogenous [albumin (p < 0.001) and ASA (p = 0.008)] and complexity of surgery [SCS (p < 0.001)]. Age (p = 0.002) and ASA (p = 0.001) independently predicted mortality. LOS independently correlated with age (p = 0.007), albumin (p = 0.004), SCS (p = 0.002), and stage (p = 0.024). ASA (p < 0.001) and SCS (p = 0.003) both impacted ability to receive chemotherapy. Observed to expected (O/E) ratios for dependent outcome variables were similar for all 3 institutions. Conclusions - We demonstrate the benefits of a national system for studying outcomes in gynecologic surgery using a risk-adjusted model. We specifically find that endogenous patient factors and complexity of surgery are primary drivers of morbidity in ovarian cancer surgery. These data can successfully be used to formulate expected, risk-adjusted rates of complications thus providing a meaningful mechanism to identify areas ripe for quality improvement