Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25 - 500 solar masses, with H II regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.Comment: 6 pages, 4 figures, accepted for proceedings of HEDLA2010, Caltech, March 15 - 18, 201

Detectability of the First Cosmic Explosions

We present a fully self-consistent simulation of a synthetic survey of the furthermost cosmic explosions. The appearance of the first generation of stars (Population III) in the Universe represents a critical point during cosmic evolution, signaling the end of the dark ages, a period of absence of light sources. Despite their importance, there is no confirmed detection of Population III stars so far. A fraction of these primordial stars are expected to die as pair-instability supernovae (PISNe), and should be bright enough to be observed up to a few hundred million years after the big bang. While the quest for Population III stars continues, detailed theoretical models and computer simulations serve as a testbed for their observability. With the upcoming near-infrared missions, estimates of the feasibility of detecting PISNe are not only timely but imperative. To address this problem, we combine state-of-the-art cosmological and radiative simulations into a complete and self-consistent framework, which includes detailed features of the observational process. We show that a dedicated observational strategy using $\lesssim 8$ per cent of total allocation time of the James Webb Space Telescope mission can provide us up to $\sim 9-15$ detectable PISNe per year.Comment: 9 pages, 8 figures. Minor corrections added to match published versio

Negative emotional reactivity as a marker of vulnerability in the development of borderline personality disorder symptoms

Negative emotionality is a distinguishing feature of borderline personality disorder (BPD). However, this person-level characteristic has not been examined as a marker of vulnerability in the development of this disorder. The current study utilized a multi-method approach to examine the interplay between negative emotional reactivity and cumulative exposure to family adversity on the development of BPD symptoms across three years (ages 16–18) in a diverse, at-risk sample of adolescent girls (N=113). A latent variable of negative emotional reactivity was created from multiple assessments at age 16: (1) self-report, (2) emotion ratings to stressors from ecological assessments across one week, and (3) observer-rated negative affectivity during a mother-daughter conflict discussion task. Exposure to family adversity was measured cumulatively between ages 5 and 16 from annual assessments of family poverty, single parent household, and difficult life circumstances. Results from latent growth curve models demonstrated a significant interaction between negative emotional reactivity and family adversity, such that exposure to adversity strengthened the association between negative emotional reactivity and BPD symptoms. Additionally, family adversity predicted increasing BPD symptoms during late adolescence. These findings highlight negative emotional reactivity as a marker of vulnerability that ultimately increases risk for the development of BPD symptoms

Lifetimes of ultralong-range strontium Rydberg molecules in a dense BEC

The lifetimes and decay channels of ultralong-range Rydberg molecules created in a dense BEC are examined by monitoring the time evolution of the Rydberg population using field ionization. Studies of molecules with values of principal quantum number, $n$, in the range $n=49$ to $n=72$ that contain tens to hundreds of ground state atoms within the Rydberg electron orbit show that their presence leads to marked changes in the field ionization characteristics. The Rydberg molecules have lifetimes of $\sim1-5\,\mu$s, their destruction being attributed to two main processes: formation of Sr$^+_2$ ions through associative ionization, and dissociation induced through $L$-changing collisions. The observed loss rates are consistent with a reaction model that emphasizes the interaction between the Rydberg core ion and its nearest neighbor ground-state atom. The measured lifetimes place strict limits on the time scales over which studies involving Rydberg species in cold, dense atomic gases can be undertaken and limit the coherence times for such measurements.Comment: 9 pages, 8 figure

"I'm a bit concerned" - early actions and psychological constructions in a child protection helpline

This article analyzes early actions in 50 calls reporting cases of abuse to a national child protection helpline in the UK (the National Society for the Prevention of Cruelty to Children Helpline, NSPCC). It focuses on the early turns in the caller's reason for call, in particular, a class of constructions in which the caller describes himself or herself as "concerned about x" (or similar). Analysis of the corpus of calls suggests concern constructions are canonical early elements of the reason-for-call sequence. Concern constructions (a) are oriented to a pre-move in the caller's reason for call, (b) project the unpacking of concerns in a way oriented to the NSPCCs institutional role, (c) attend to epistemological asymmetries between caller and call taker and remove the requirement for disaffiliative next actions such as asking for the basis of claims, (d) provide a way for the Child Protection Officer to take abuse claims seriously while not presupposing their truth, and (e) display an appropriate caller stance. These observations are supported by an analysis of deviant cases. The broader implications of this study for the relation between psychology, interaction, and institutions are discussed

Spacelab energetic ion mass spectrometer

Basic design criteria are given for an ion mass spectrometer for use in studying magnetospheric ion populations. The proposed instrument is composed of an electrostatic analyzer followed by a magnetic spectrometer and simultaneously measures the energy per unit and mass per unit charge of the ion species. An electromagnet is used for momentum analysis to extend the operational energy range over a much wider domain than is possible with the permanent magnets used in previous flights. The energetic ion source regions, ion energization mechanisms, field line tracing, coordinated investigations, and orbit considerations are discussed and operations of the momentum analyzer and of the electrostatic energy analyzer are examined