Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy

Colour-magnitude diagrams (CMD) of the SMC star cluster NGC419, derived from HST/ACS data, reveal a well-delineated secondary clump located below the classical compact red clump typical of intermediate-age populations. We demonstrate that this feature belongs to the cluster itself, rather than to the underlying SMC field. Then, we use synthetic CMDs to show that it corresponds very well to the secondary clump predicted to appear as a result of He-ignition in stars just massive enough to avoid electron-degeneracy settling in their H-exhausted cores. The main red clump instead is made of the slightly less massive stars which passed through electron-degeneracy and ignited He at the tip of the RGB. In other words, NGC419 is the rare snapshot of a cluster while undergoing the fast transition from classical to degenerate H-exhausted cores. At this particular moment of a cluster's life, the colour distance between the main sequence turn-off and the red clump(s) depends sensitively on the amount of convective core overshooting, Lambda_c. By coupling measurements of this colour separation with fits to the red clump morphology, we are able to estimate simultaneously the cluster mean age (1.35(-0.04,+0.11) Gyr) and overshooting efficiency (Lambda_c=0.47(-0.04,+0.14)). Therefore, clusters like NGC419 may constitute important marks in the age scale of intermediate-age populations. After eye inspection of other CMDs derived from HST/ACS data, we suggest that the same secondary clump may also be present in the LMC clusters NGC1751, 1783, 1806, 1846, 1852, and 1917.Comment: To appear in MNRAS Letters (www.blackwell-synergy.com). Better printed in colou

Star clusters with dual red clumps

A few star clusters in the Magellanic Clouds exhibit composite structures in the red-clump region of their colour-magnitude diagrams. The most striking case is NGC419 in the SMC, where the red clump is composed of a main blob as well as a distinct secondary feature. This structure is demonstrated to be real and corresponds to the simultaneous presence of stars which passed through electron degeneracy after central-hydrogen exhaustion and those that did not. This rare occurrence in a single cluster allows us to set stringent constraints on its age and on the efficiency of convective-core overshooting during main-sequence evolution. We present a more detailed analysis of NGC419, together with a first look at other populous LMC clusters which are apparently in the same phase: NGC1751, NGC1783, NGC1806, NGC1846, NGC1852 and NGC1917. We also compare these Magellanic Cloud cases with their Galactic counterparts, NGC752 and NGC7789. We emphasise the extraordinary potential of these clusters as absolute calibration marks on the age scale of stellar populations.Comment: contributed talk at IAUS 266 'Star clusters: basic galactic building blocks', eds R. de Grijs and J. Lepine. A high resolution version of Fig. 1 is available in http://stev.oapd.inaf.it/~lgirardi/NGC419_hr.pd

The star formation history of the Large Magellanic Cloud star cluster NGC1751

The HST/ACS colour-magnitude diagrams (CMD) of the populous LMC star cluster NGC1751 present both a broad main sequence turn-off and a dual clump of red giants. We show that the latter feature is real and associate it to the first appearance of electron-degeneracy in the H-exhausted cores of the cluster stars. We then apply to the NGC1751 data the classical method of star formation history (SFH) recovery via CMD reconstruction, for different radii corresponding to the cluster centre, the cluster outskirts, and the underlying LMC field. The mean SFH derived from the LMC field is taken into account during the stage of SFH-recovery in the cluster regions, in a novel approach which is shown to significantly improve the quality of the SFH results. For the cluster centre, we find a best-fitting solution corresponding to prolonged star formation for a for a timespan of 460 Myr, instead of the two peaks separated by 200 Myr favoured by a previous work based on isochrone fitting. Remarkably, our global best-fitting solution provides an excellent fit to the data - with chi^2 and residuals close to the theoretical minimum - reproducing all the CMD features including the dual red clump. The results for a larger ring region around the centre indicate even longer star formation, but in this case the results are of lower quality, probably because of the differential extinction detected in the area. Therefore, the presence of age gradients in NGC1751 could not be probed. Together with our previous findings for the SMC cluster NGC419, the present results for the NGC1751 centre argue in favour of multiple star formation episodes (or continued star formation) being at the origin of the multiple main sequence turn-offs in Magellanic Cloud clusters with ages around 1.5 Gyr.Comment: To appear soon in MNRAS. 12 pages, better printed in colou

Severe and polytraumatic injuries among recreational skiers and snowboarders: incidence, demographics and injury patterns in South Tyrol

Background Alpine skiing and snowboarding are popular winter sports. The practice of these sports is related to traumatic injuries, some of which are severe and/or life threatening. Objectives To identify the incidence, injury patterns and associated risk factors of severe and polytraumatic injuries in South Tyrol. Materials and methods During four consecutive winter seasons (2001-2005), data of every patient referred to our emergency department (Bolzano-Bozen) after a skiing or snowboarding accident were collected. One hundred and five patients with an Injury Severity Score of 16 or higher were identified (90 skiers, 15 snowboarders). Statistical descriptive analyses were carried out by producing frequency tables. Chi-square test was performed to verify possible association between injury severity and type of sport. Risk factors for severe injuries were evaluated using logistic regression with robust variance estimators. Results Traumatic brain injury was the most common injury observed (51 cases), followed by vertebral injury (45 cases); 63% of the patients reported two or more associated injuries. We observed significant associations between severe spine injuries and the following risk factors: snowboarders who reported more severe injuries than skiers [odds ratio = 5.89, 95% confidence interval (CI) = 1.31, 26.44], age classes of 40-50 years and over 60 years showed an OR of 8.10 (95% CI = 1.87, 35.06) and 5.16 (95% CI = 1.27, 21.01), respectively, with respect to age class (20-40 years). Conclusion Severe traumatic injuries occur among skiers and snowboarders, and preventive measures such as the use of helmets and educational programs, are necessary. European Journal of Emergency Medicine 19: 69-72 (C) 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

The star formation history of the SMC star cluster NGC419

The rich SMC star cluster NGC419 has recently been found to present both a broad main sequence turn-off and a dual red clump of giants, in the sharp colour-magnitude diagrams (CMD) derived from the High Resolution Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope. In this work, we apply to the NGC419 data the classical method of star formation history (SFH) recovery via CMD reconstruction, deriving for the first time this function for a star cluster with multiple turn-offs. The values for the cluster metallicity, reddening, distance and binary fraction, were varied within the limits allowed by present observations. The global best-fitting solution is an excellent fit to the data, reproducing all the CMD features with striking accuracy. The corresponding star formation rate is provided together with estimates of its random and systematic errors. Star formation is found to last for at least 700 Myr, and to have a marked peak at the middle of this interval, for an age of 1.5 Gyr. Our findings argue in favour of multiple star formation episodes (or continued star formation) being at the origin of the multiple main sequence turn-offs in Magellanic Cloud clusters with ages around 1 Gyr. It remains to be tested whether alternative hypotheses, such as a main sequence spread caused by rotation, could produce similarly good fits to the data.Comment: 10 pages, MNRAS in pres

Detraining effects prevention: a new rising challenge for athletes

[no abstract available

Ag-Vanadates/GO Nanocomposites by Aerosol-Assisted Spray Pyrolysis: Preparation and Structural and Electrochemical Characterization of a Versatile Material

In this article, we describe the deposition by aerosol-assisted spray pyrolysis of different types of silver vanadate nanocomposites with and without graphene oxide (GO) on different substrates (carbon paper (CP) and fluorine-doped tin oxide (FTO)). When deposited on CP, different amounts of GO were added to the Ag and V precursor solution to study the effect of GO on the physicochemical properties of the resulting Ag-vanadate. It is shown that the addition of GO leads mainly to the formation of nanoparticles of the Ag2V4O11 phase, whereas Ag2V4O11 and Ag3VO4 are obtained without the addition of GO. The morphology and chemical properties of the composites were determined by scanning and transmission electron microscopies, X-ray diffraction, X-ray photoemission spectroscopy, and UV\u2013visible and Raman spectroscopies. In addition, the photoelectrochemical (PEC) properties of such composites were studied by CV, linear sweep voltammetry, and electrochemical impedance spectroscopy. The ideal AgxVOy and GO ratio was optimized for obtaining higher photocurrent values and a good stability. The results showed that the presence of GO improves the electrical conductivity of the catalyst layer as well as the electron injection from the oxide to the electrode surface. The deposition of pure Ag2V4O11 on FTO does not lead to samples with stable PEC performances. Samples grown on CP supports showed an efficient electrochemical detection of small amounts of ethylenediamine in water solution

Factors affecting injury severity among recreational skiers and snowboarders: an epidemiology study

Different results have been reported for skiing and snowboarding injuries worldwide. Few studies consider the injury severity score (ISS) for the evaluation of differences among injured skiers–snowboarders. The aim of this study is to identify possible risk factors that affect the severity of skiing and snowboarding injuries in three winter seasons (2002–2005) in South Tyrol. For every injured skier or snowboarder referred to our emergency department in three consecutive seasons, the following data were collected: date of birth, gender, self-declared technical skills level, place of residence (local/non-local), as well as the date, time, and place of the accident. Type of injury and ISS were retrospectively assigned. Data concerning the snowfall in the last 24 h, average snow level, and outdoor air temperature values were obtained from four weather stations that were located inside the ski resorts. A multiple linear regression model was used to evaluate the association between ISS and potential determinants. In the analyzed seasons, 2,511 injured skiers and 843 injured snowboarders were evaluated at our emergency department. There was a significant change in the ISS value for subjects with different self-reported skills levels (P.001). Men and non-local residents experienced more severe injuries than women and local residents, respectively (P.013, P.001). The ISS was higher for people aged over 60 (P.001). Snowfalls brought about a decrease in accident severity (P = 0.009). The severity of the injuries increases with age. Prevention and information programs should be targeted to people who are at high risk of severe injury. A 24-h fresh snowfall seems to reduce the severity of injuries. Very little is known about snow conditions and winter sports injury. Further studies are needed to explore this field

A Framework for the Design and Simulation of Embedded Vision Applications Based on OpenVX and ROS

Customizing computer vision applications for embedded systems is a common and widespread problem in the cyber-physical systems community. Such a customization means parametrizing the algorithm by considering the external environment and mapping the Software application to the heterogeneous Hardware resources by satisfying non-functional constraints like performance, power, and energy consumption. This work presents a framework for the design and simulation of embedded vision applications that integrates the OpenVX standard platform with the Robot Operating System (ROS). The paper shows how the framework has been applied to tune the ORB-SLAM application for an NVIDIA Jetson TX2 board by considering different environment contexts and different design constraints

Clusters in Various Cosmological Models: Abundance and Evolution

The combination of measurements of the local abundance of rich clusters of galaxies and its evolution to higher redshift offers the possibility of a direct measurement of $\Omega_0$ with little contribution from other cosmological parameters. We investigate the significance of recent claims that this evolution indicates that $\Omega_0$ must be small. The most recent cluster velocity dispersion function from a compilation including the ESO Northern Abell Cluster Survey (ENACS) results in a significantly higher normalization for models, corresponding to $\sigma_8\approx 0.6$ for $\Omega_0=1$, compared to the Eke, Cole, & Frenk result of $\sigma_8=0.52\pm 0.04$. Using the ENACS data for a $z=0$ calibration results in strong evolution in the abundance of clusters, and we find that the velocity dispersion function is consistent with $\Omega_0=1$. The results are dependent upon the choice and analysis of low-redshift and high-redshift data, so at present, the data is not good enough to determine $\Omega_0$ unambiguously.Comment: 4 pages Latex using sprocl.sty, 1 figure. To appear in Proceedings of 12th Potsdam Cosmology Workshop, "Large-Scale Structure: Tracks and Traces" Sept. 15-19, 199