Dependence of the Star Formation Efficiency on the Parameters of Molecular Cloud Formation Simulations

We investigate the response of the star formation efficiency (SFE) to the main parameters of simulations of molecular cloud formation by the collision of warm diffuse medium (WNM) cylindrical streams, neglecting stellar feedback and magnetic fields. The parameters we vary are the Mach number of the inflow velocity of the streams, Msinf, the rms Mach number of the initial background turbulence in the WNM, and the total mass contained in the colliding gas streams, Minf. Because the SFE is a function of time, we define two estimators for it, the "absolute" SFE, measured at t = 25 Myr into the simulation's evolution (sfeabs), and the "relative" SFE, measured 5 Myr after the onset of star formation in each simulation (sferel). The latter is close to the "star formation rate per free-fall time" for gas at n = 100 cm^-3. We find that both estimators decrease with increasing Minf, although by no more than a factor of 2 as Msinf increases from 1.25 to 3.5. Increasing levels of background turbulence similarly reduce the SFE, because the turbulence disrupts the coherence of the colliding streams, fragmenting the cloud, and producing small-scale clumps scattered through the numerical box, which have low SFEs. Finally, the SFE is very sensitive to the mass of the inflows, with sferel decreasing from ~0.4 to ~0.04 as the the virial parameter in the colliding streams increases from ~0.15 to ~1.5. This trend is in partial agreement with the prediction by Krumholz & McKee (2005), since the latter lies within the same range as the observed efficiencies, but with a significantly shallower slope. We conclude that the observed variability of the SFE is a highly sensitive function of the parameters of the cloud formation process, and may be the cause of significant scatter in observational determinations.Comment: 19 pages, submitted to MNRA

High- and Low-Mass Star Forming Regions from Hierarchical Gravitational Fragmentation. High local Star Formation Rates with Low Global Efficiencies

We investigate the properties of "star forming regions" in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. In this simulation, the velocity dispersions at all scales are caused primarily by infall motions rather than by random turbulence. We study the properties (density, total gas+stars mass, stellar mass, velocity dispersion, and star formation rate) of the cloud hosting the first local, isolated "star formation" event in the simulation and compare them with those of the cloud formed by a later central, global collapse event. We suggest that the small-scale, isolated collapse may be representative of low- to intermediate-mass star-forming regions, while the large-scale, massive one may be representative of massive star forming regions. We also find that the statistical distributions of physical properties of the dense cores in the region of massive collapse compare very well with those from a recent survey of the massive star forming region in the Cygnus X molecular cloud. The star formation efficiency per free-fall time (SFE_ff) of the high-mass SF clump is low, ~0.04. This occurs because the clump is accreting mass at a high rate, not because its specific SFR (SSFR) is low. This implies that a low value of the SFE_ff does not necessarily imply a low SSFR, but may rather indicate a large gas accretion rate. We suggest that a globally low SSFR at the GMC level can be attained even if local star forming sites have much larger values of the SSFR if star formation is a spatially intermittent process, so that most of the mass in a GMC is not participating of the SF process at any given time.Comment: Accepted by ApJ. Revised version, according to exchanges with referee. Original results unchanged. Extensive new discussion on the low global efficiency vs. high local efficiency of star formation. Abstract abridge

Molecular Cloud Evolution III. Accretion vs. stellar feedback

We numerically investigate the effect of feedback from the ionizing radiation heating from massive stars on the evolution of giant molecular clouds (GMCs) and their star formation efficiency (SFE). We find that the star-forming regions within the GMCs are invariably formed by gravitational contraction. After an initial period of contraction, the collapsing clouds begin forming stars, whose feedback evaporates part of the clouds' mass, opposing the continuing accretion from the infalling gas. The competition of accretion against dense gas consumption by star formation (SF) and evaporation by the feedback, regulates the clouds' mass and energy balance, as well as their SFE. We find that, in the presence of feedback, the clouds attain levels of the SFE that are consistent at all times with observational determinations for regions of comparable SF rates (SFRs). However, we observe that the dense gas mass is larger in general in the presence of feedback, while the total (dense gas + stars) is nearly insensitive to the presence of feedback, suggesting that the total mass is determined by the accretion, while the feedback inhibits mainly the conversion of dense gas to stars. The factor by which the SFE is reduced upon the inclusion of feedback is a decreasing function of the cloud's mass, for clouds of size ~ 10 pc. This naturally explains the larger observed SFEs of massive-star forming regions. We also find that the clouds may attain a pseudo-virialized state, with a value of the virial mass very similar to the actual cloud mass. However, this state differs from true virialization in that the clouds are the center of a large-scale collapse, continuously accreting mass, rather than being equilibrium entities.Comment: Submitted to ApJ (abstract abridged

The Free-Fall time of finite Sheets and Filaments

Molecular clouds often exhibit filamentary or sheet-like shapes. We compute the free-fall time (\tff) for finite, uniform, self-gravitating circular sheets and filamentary clouds of small but finite thickness, so that their volume density $\rho$ can still be defined. We find that, for thin sheets, the free-fall time is larger than that of a uniform sphere with the same volume density by a factor proportional to $\sqrt{A}$, where the aspect ratio $A$ is given by $A=R/h$, $R$ being the sheet's radius and $h$ is its thickness. For filamentary clouds, the aspect ratio is defined as A=L/\calR, where $L$ is the filament's half length and \calR is its (small) radius, and the modification factor is a more complicated, although in the limit of large $A$ it again reduces to nearly $\sqrt{A}$. We propose that our result for filamentary shapes naturally explains the ubiquitous configuration of clumps fed by filaments observed in the densest structures of molecular clouds. Also, the longer free-fall times for non-spherical geometries in general may contribute towards partially alleviating the "star-formation conundrum", namely, that the star formation rate in the Galaxy appears to be proceeding in a timescale much larger than the total molecular mass in the Galaxy divided by its typical free-fall time. If molecular clouds are in general formed by thin sheets and long filaments, then their relevant free-fall time may have been systematically underestimated, possibly by factors of up to one order of magnitude.Comment: To appear on The Astrophysical Journa

Role of age and comorbidities in mortality of patients with infective endocarditis

Purpose: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. Methods: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015. Patients were stratified into three age groups:<65 years, 65 to 80 years, and = 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. Results: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 = 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients =80 years who underwent surgery were significantly lower compared with other age groups (14.3%, 65 years; 20.5%, 65-79 years; 31.3%, =80 years). In-hospital mortality was lower in the <65-year group (20.3%, <65 years;30.1%, 65-79 years;34.7%, =80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%, =80 years; p = 0.003).Independent predictors of mortality were age = 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI = 3 (HR:1.62; 95% CI:1.39–1.88), and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared, the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. Conclusion: There were no differences in the clinical presentation of IE between the groups. Age = 80 years, high comorbidity (measured by CCI), and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Escucha México, Estrategias Gráficas y Cultura Auditiva. Otoño 2022

Este reporte del PAP Escucha México, perteneciente al trabajo realizado durante el periodo de Otoño 2022, cuenta con información detallada sobre los resultados alcanzados en cada uno de los proyectos que integran esta organización en el período anteriormente establecido. Para este proceso en específico, se buscó enfocar la mayor cantidad de esfuerzos posibles a que el 4to Encuentro Internacional de Cultura Auditiva se desarrollara de la mejor forma posible, sin descuidar el trabajo que se siguió realizando en el resto de proyectos. Como resumen general, todos presentaron resultados positivos, pues se tuvo presencia importante en redes sociales, mejor que en periodos anteriores, además de que se combinaron esfuerzos para que el 4to Encuentro tuviera una difusión adecuada y alcanzara a la mayor cantidad de personas posibles, lo que a su vez resultó en eventos llenos de gente interesada en aprender sobre Cultura Auditiva y Discapacidad, ejes temáticos centrales de este PAP.ITESO, A.C

First measurement of Ξc0 production in pp collisions at s=7 TeV

The production of the charm-strange baryon Csi0c is measured for the first time at the LHC via its semileptonic decay into e+Csi-νe in pp collisions at sqrt(s) = 7 TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1 &lt; pT &lt; 8 GeV/c at mid-rapidity, |y| &lt; 0.5. The transverse momentum dependence of the Csi0c baryon production relative to the D0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross- section ratio.The production of the charm-strange baryon Csi0c is measured for the first time at the LHC via its semileptonic decay into e+Csi-νe in pp collisions at sqrt(s) = 7 TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1 &lt; pT &lt; 8 GeV/c at mid-rapidity, |y| &lt; 0.5. The transverse momentum dependence of the Csi0c baryon production relative to the D0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross- section ratio

Inclusive J/ψ production at forward and backward rapidity in p-Pb collisions at √sNN=8.16 TeV

Inclusive J/psi production is studied in p-Pb interactions at a centre-of-mass energy per nucleon-nucleon collision sqrt(s_NN) = 8.16TeV, using the ALICE detector at the CERN LHC. The J/psi meson is reconstructed, via its decay to a muon pair, in the centre-of-mass rapidity intervals 2.03 < ycms < 3.53 and -4.46 < ycms < -2.96, where positive and negative ycms refer to the p-going and Pb-going direction, respectively. The transverse momentum coverage is pT < 20 GeV/c. In this paper, ycms- and pT-differential cross sections for inclusive J/psi production are presented, and the corresponding nuclear modification factors RpPb are shown. Forward results show a suppression of the J/psi yield with respect to pp collisions, concentrated in the region pT < 5 GeV/c. At backward rapidity no significant suppression is observed. The results are compared to previous measurements by ALICE in p-Pb collisions at sqrt(s_NN) = 5.02TeV and to theoretical calculations. Finally, the ratios RFB between forward- and backward-ycms RpPb values are shown and discussed

Energy dependence and fluctuations of anisotropic flow in Pb-Pb collisions at √sNN=5.02 and 2.76 TeV

Measurements of anisotropic flow coefficients with two- and multi-particle cumulants for inclusive charged particles in Pb-Pb collisions at sqrt(s_NN) = 5.02 and 2.76TeV are reported in the pseudorapidity range |eta|< 0.8 and transverse momentum 0.2 < pT < 50 GeV/c. The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) ub^-1 in the centrality range 0-80%, is analysed. Flow coefficients up to the sixth flow harmonic (v6) are reported and a detailed comparison among results at the two energies is carried out. The pT dependence of anisotropic flow coefficients and its evolution with respect to centrality and harmonic number n are investigated. An approximate power-law scaling of the form vn(pT) ~ pT^(n/3) is observed for all flow harmonics at low pT (0.2 < pT < 3 GeV/c). At the same time, the ratios vn/vm^(n/m) are observed to be essentially independent of pT for most centralities up to about pT = 10 GeV/c. Analysing the differences among higher-order cumulants of elliptic flow (v2), which have different sensitivities to flow fluctuations, a measurement of the standardised skewness of the event-by-event v2 distribution P(v2) is reported and constraints on its higher moments are provided. The Elliptic Power distribution is used to parametrise P(v2), extracting its parameters from fits to cumulants. The measurements are compared to different model predictions in order to discriminate among initial-state models and to constrain the temperature dependence of the shear viscosity to entropy-density ratio