Mass Loss From Planetary Nebulae in Elliptical Galaxies

Early-type galaxies possess a dilute hot (2-10E6 K) gas that is probably the thermalized ejecta of the mass loss from evolving stars. We investigate the processes by which the mass loss from orbiting stars interacts with the stationary hot gas for the case of the mass ejected in a planetary nebula event. Numerical hydrodynamic simulations show that at first, the ejecta expands nearly symmetrically, with an upstream bow shock in the hot ambient gas. At later times, the flow past the ejecta creates fluid instabilities that cause about half of the ejecta to separate and the other half to flow more slowly downstream in a narrow wake. When radiative cooling is included, most of the material in the wake (>80%) remains below 1E5 K while the separated ejecta is hotter (1E5-1E6 K). The separated ejecta is still less than one-quarter the temperature of the ambient medium and the only way it will reach the temperature of the ambient medium is through turbulent mixing (after the material has left the grid). These calculations suggest that a significant fraction of the planetary nebula ejecta may not become part of the hot ambient material. This is in contrast to our previous calculations for continuous mass loss from giant stars in which most of the mass loss became hot gas. We speculate that detectable OVI emission may be produced, but more sophisticated calculations will be required to determine the emission spectrum and to better define the fraction of cooled material.Comment: 34 pages with 20 figures. Higher quality figures are in the ApJ versio

Six-year mortality in a street-recruited cohort of homeless youth in San Francisco, California.

Objectives. The mortality rate of a street-recruited homeless youth cohort in the United States has not yet been reported. We examined the six-year mortality rate for a cohort of street youth recruited from San Francisco street venues in 2004. Methods. Using data collected from a longitudinal, venue-based sample of street youth 15-24 years of age, we calculated age, race, and gender-adjusted mortality rates. Results. Of a sample of 218 participants, 11 died from enrollment in 2004 to December 31, 2010. The majority of deaths were due to suicide and/or substance abuse. The death rate was 9.6 deaths per hundred thousand person-years. The age, race and gender-adjusted standardized mortality ratio was 10.6 (95% CI [5.3-18.9]). Gender specific SMRs were 16.1 (95% CI [3.3-47.1]) for females and 9.4 (95% CI [4.0-18.4]) for males. Conclusions. Street-recruited homeless youth in San Francisco experience a mortality rate in excess of ten times that of the states general youth population. Services and programs, particularly housing, mental health and substance abuse interventions, are urgently needed to prevent premature mortality in this vulnerable population

Using Generalizability Theory to Investigate Sources of Variance of the Autism Diagnostic Observation Schedule-2 with Trainees

Autism Spectrum Disorder (ASD) can be considered a serious developmental concern, which, complicated by its rising rate, creates a challenge for psychologists in properly and consistently diagnosing the disorder. Various types of assessments such as reporting measures, observation systems, and standardized assessments are currently used in the identification of ASD. Any one instrument typically examines multiple domains of functioning such as intellectual, neuropsychological (including adaptive, attention, sensory, motor, language, memory, executive functioning, academic, and social/emotional), and behavior (social and repetitive/restricted). Often, evaluators combine assessments that were not originally meant to detect ASD with those that were intended for that purpose. The most respected method of diagnosis of ASD at this time includes direct assessments as well as indirect in an attempt to maximize accuracy of clinical judgment. However, this method is not reflected in common identification practice for ASD; instead, many clinicians are relying on rating scales. Unfortunately, there are not a sufficient amount of studies examining the reliability of some of the available measures, especially with trainees. In particular, studies examining the sources of variance on the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) are limited in quantity and depth. The conceptual framework for this study will be Generalizability (G) Theory. This study is designed to expand upon currently available information regarding the interrater reliability of the ADOS-2 by using techniques available in G Theory in order to understand multiple sources of variance associated with the instrument, in particular with relation to coding by trainees

The Fate of Stellar Mass Loss in Central Cluster Galaxies

Star formation within the central galaxies of galaxy clusters is often interpreted as being fueled by cooling of the hot intracluster medium. However, the star-forming gas is dusty, and Spitzer spectra show that the dust properties are similar to those in more normal star-forming environments, in which the dust has come from the winds of dying stars. Here we consider whether the primary source of the star-forming gas in central cluster galaxies could be normal stellar mass loss. We show that the overall stellar mass-loss rate in a large central galaxy (~4-8 solar masses per year) is at least as large as the observed star-formation rates in all but the most extreme cases and must be included in any assessment of the gas-mass budget of a central cluster galaxy. We also present arguments suggesting that the gas shed by stars in galaxy clusters with high core pressures and short central cooling times may remain cool and distinct from its hot surroundings, thereby preserving the dust within it.Comment: ApJ Letters, in press, 4 pages, 1 figur

The 2016 US Presidential Election on Facebook: An Exploratory Analysis of Sentiments

Social media platforms are valuable tools for political campaigns. In this study, we analyze a dataset representing over 22 thousand Facebook posts by candidates and over 48 million comments to understand the nature of online discourse. Specifically, we study the interaction between political candidates and the public during the 2016 presidential elections in the United States. We outline a novel method to classify commentators into four groups: strong supporters, supporters, dissenters, and strong dissenters. Comments by each group on policy-related topics are analyzed using sentiment analysis. Finally, we discuss avenues for future research to study the dynamics of social media platforms and political campaigns

Nonlocal boundary conditions for corrugated acoustic metasurface with strong near field interactions

The propagation of long-wavelength sound in the presence of a metasurface made by arranging acoustic resonators periodically upon or slightly above an impervious substrate is studied. The method of two-scale asymptotic homogenization is used to derive effective boundary conditions, which account for both the surface corrugation and the low-frequency resonance. This method is applied to periodic arrays of resonators of any shape operating in the long-wavelength regime. The approach relies on the existence of a locally periodic boundary layer developed in the vicinity of the metasurface, where strong near-field interactions of the resonators with each other and with the substrate take place. These local effects give rise to an effective surface admittance supplemented by nonlocal contributions from the simple and double gradients of the pressure at the surface. These phenomena are illustrated for the periodic array of cylindrical Helmholtz resonators with an extended inner duct. Effects of the centre-to-centre spacing and orientation of the resonators' opening on the nonlocality and apparent resonance frequency are studied. The model could be used to design metasurfaces with specific effective boundary conditions required for particular applications