A CFD-based Approach to Predict Explosion Overpressure: A Comparison to Current Methods

A CFD-based approach has been developed in this work to predict the overpressure produced during an explosion. An adiabatic exothermal reaction allows computing the explosion energy release. To validate the proposed CFD approach, overpressure predictions based on this methodology are compared with results produced with the TNObased method. It is demonstrated that the physics adopted in our model produces satisfactory predictions in the open area. The CFD simulations were carried out in the ANSYS CFX tool. The source of energy corresponds to the one produced by a stoichiometric proportion in reactants without energy generation. The explosion analysis considered that explosion occurs geometrically as a sequence of control volumes. Thus, the explosion in a volume is assumed to occur when the maximum pressure is achieved in the previous control volume. This way, the explosion is propagated and it is shown that it is equivalent to conventional predicting methods

The Age, Stellar Content and Star Formation Timescale of the B59 Dense Core

We have used moderate resolution, near-infrared spectra from the SpeX spectrograph on the NASA Infrared Telescope facility to characterize the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Measuring luminosity and temperature sensitive features in the spectra of 20 candidate YSOs, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. We find that B59 is composed of late type (K4-M6) low-mass (0.9--0.1 M_sun) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the Rho Oph, Taurus, and Chameleon star forming regions. Deriving absolute age estimates from pre-main sequence models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6+/-0.8 Myrs. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6+4.1/-2.6 Myrs. We also find that the relative age orderings implied by pre-main sequence evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependencies. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggest that the B59 dense core has been stable against global collapse for roughly 6 dynamical timescales, and is actively forming stars with a star formation efficiency per dynamical time of ~6%. This maximum likelihood value agrees well with recent star formation simulations that incorporate various forms of support against collapse, such as sub-critical magnetic fields, outflows, and radiative feedback from protostellar heating. [abridged]Comment: 20 pages, 12 figures, accepted for publication in the Astrophysical Journal; updated to amend acknowledgment

The molecular gas content of the Pipe Nebula I. Direct evidence of outflow-generated turbulence in B59?

The Pipe Nebula is a molecular cloud hosting the B59 region as its only active star-forming clump. While the particular importance of outflows in active star forming regions is subject of debate, the quiet nature of the gas in B59 makes it a good site to directly see the impact of protostellar feedback on the quiescent dense gas. Using HARP at the JCMT, we mapped the B59 region with the J=3-2 transition of 12CO to study the kinematics and energetics of the outflows, and 13CO and C18O to study the overall dynamics of the ambient cloud, the physical properties of the gas, and the hierarchical structure of the region. The B59 region has a total of 30Msun of cold and quiescent material, mostly gravitationally bound, with narrow line widths throughout. Such low levels of turbulence in non-star-forming sites of B59 are indicative of the intrinsic initial conditions of the cloud. On the other hand, close to the forming protostars the impact of the outflows is observed as a localised increase of both line widths from 0.3 to 1 km/s, and 13CO excitation temperatures by 2-3K. The impact of the outflows is also evident in the low column density material which shows signs of being pushed, shaped and carved by the outflow bow shocks as they pierce their way out of the cloud. Much of this structure is readily apparent in a dendrogram analysis of the cloud. The low mass of B59 together with its intrinsically quiescent gas and small number of protostars, allows the identification of specific regions where the outflows from the embedded sources interact the dense gas. Our study suggests that outflows are an important mechanism for injecting and sustaining supersonic turbulence at sub-parsec size scales. We find that less than half of the outflow energy is deposited as turbulent energy of the gas, however this turbulent energy is sufficient to slow down the collapse of the region.Comment: Accepted for publication in A&

Does opening a milk bank in a neonatal unit change infant feeding practices? A before and after study

<p>Abstract</p> <p>Background</p> <p>Donor human milk banks are much more than simple centers for collection, storage, processing, and distribution of donor human milk, as they cover other aspects and represent a real opportunity to promote and support breastfeeding. The aim of our study is to assess the impact that opening a human milk bank has had on the proportion of infants receiving exclusive breast milk at discharge and other aspects related to feeding children with birth weight < or = 1500 g or < 32 weeks gestation admitted to the neonatal unit.</p> <p>Methods</p> <p>The study included babies of < or = 1500 g or < 32 weeks gestation. Fifty infants born from February to July in 2006, before the opening of the human milk bank, and 54 born from February to July in 2008, after its opening, met inclusive criteria. We collected data about days of hospital stay, hours of life when feeding was started, hours of life when full enteral feeding was attained, the type of milk received during admission, and the type of feeding on discharge.</p> <p>Results</p> <p>Children born in 2008 commenced feeding 16 hours earlier than those born in 2006 (p = 0.00). The proportion of infants receiving exclusive breast milk at discharge was 54% in 2006 and 56% in 2008 (p = 0.87). The number of days they received their mother's own milk during the first 28 days of life was 24.2 days in 2006, compared to 23.7 days in 2008 (p = 0.70). In 2006, 60% of infants received infant formula at least once in the first 28 days of life, compared to 37% in 2008 (p = 0.01).</p> <p>Conclusions</p> <p>The opening of a donor human milk bank in a neonatal unit did not reduce the proportion of infants exclusively fed with breast milk at discharge, but did reduce the proportion of infants that received infant formula during the first four weeks of life. Also, having donor human milk available enables commencement of enteral feeding earlier.</p

Elaboración de modelos de informe para la asignatura de Laboratorio de Óptica

Memoria ID-0195. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2014-2015

Elaboración de un archivo fotográfico de fenómenos ópticos y experiencias sencillas con luz. Edición de informe didáctico

Memoria ID-0199. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2014-2015

Cluster-formation in the Rosette molecular cloud at the junctions of filaments

For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. The Rosette molecular cloud, irradiated by the NGC2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peaked PDF we interprete as caused by shock compression. The deviations of the PDF from the log-normal shape typically associated with low- and high-mass star-forming regions at Av~3-4m and 8-10m, respectively, are found here within the very same cloud. This shows that there is no fundamental difference in the density structure of low- and high-mass star-forming regions. We conclude that star-formation in Rosette - and probably in high-mass star-forming clouds in general - is not globally triggered by the impact of UV-radiation. Moreover, star formation takes place in filaments that arose from the primordial turbulent structure built up during the formation of the cloud. Clusters form at filament mergers, but star formation can be locally induced in the direct interaction zone between an expanding HII--region and the molecular cloud.Comment: A&A Letter, in pres

Actividades para la captación de estudiantes para el Máster en Física y Tecnología de los Láseres

Memoria ID-0250. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2015-2016

Encuentros de divulgación en óptica entre estudiantes y profesores

Memoria ID-0046. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2017-2018

Actividades para la captación de estudiantes para el Máster en Física y Tecnología de los Láseres

Memoria ID-212. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2013-2014