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

Interactions between eagles and humans in the James River Bald Eagle Concentration Area

The lower James River supports the largest known concentration of summering eagles in eastern North America. In recent years, both the number of eagles using the river and their distribution along the shoreline appear to have increased substantially. At the same time, an increase in the human population surrounding the lower river has lead to an increase in the use of the river for recreational activities. These trends have heightened concerns within the management community about potential interactions and conflicts between these two user populations. In the summer of 1997, an investigation was initiated to collect data for the purpose of: 1) redefining the boundaries of the James River Bald Eagle concentration area, 2) determining the current level of human use within a section of the lower James River, and 3) investigating potential interactions between the human and eagle populations during the summer months. These objectives were accomplished using a combination of an extended shoreline survey and intensive observations of humans and eagles within the heart of the historic concentration area. The James River Bald Eagle concentration area has expanded well beyond the historic survey area. Elevated numbers of eagles now extend from Jones Neck down river to Fort Eustis, a distance of 140 river kilometers that contains 235 km of primary shoreline. The peak count of 448 eagles on 11 June approaches an average of 2 birds/krn of shoreline for the entire study area. In addition to the expansion of eagles along the shoreline, an increase in both the number and distribution of sites used for nocturnal roosts was documented. Four new communal roost sites spanning the length of the study area were located

"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

Inversion of Ultrasonic Scattering Data to Measure Defect Size, Orientation, and Acoustic Properties

Empirical solutions via the adaptive learning network methodology have been obtained to measure characteristics of three-dimensional defects (spherical and spheroidal) from the analysis of theoretically-modeled scattered waveforms. The solutions have been successfully applied to measure defects from actually observed ultrasonic scattering data. Spherical voids and inclusions in Ti-6-4, varying in diameter from 0.02 em to 0.12 em, and varying In acoustic impedance ratio !with respect to the host alloy (Ti-6-4)] from zero for air cavities to four for tungsten-carbide inclusions, can be directly measured via: (i) The phase cepstrum - which yields an unambiguous measurement of defect diameter and is independent of its acoustic impedance ratio; (ii) Adaptive Learning Networks (ALN) - synthesized from the amplitude spectrum and which yield accurate measurements of defect diameter and the acoustic impedance ratio of the included material. The two empirical solutions. synthesized from the scattering data from an exact model for spheres, yield similar accurate results when applied to actual scattering observed from the defects. Spheroidal defects (oblate spheroids) varying in aspect ratio from 1.67 to 6, varying in volume from 20 to 310 millionths of a cubic centimeter, and varying in orientation from 0°· to 360° in azimuth and 0° to 90° in elevation, can be measured by adaptive learning networks synthesized from scattering data produced by the Born approximation as the theoretical model. Scattering data used to train the ALNs were obtained via computer simulation. As in the case of spheres, the ALNs were trained-using the synthetic waveforms--to predict the defect size and orientation. Once the empirical models were obtained, eight actual defect sizes and orientations were found via the models and these results compare well with the true values. This paper will describe the means by which the inversion of ultrasonic scattering to defect characteristics was accomplished and its NDE implications

Level of understanding of co-trimoxazole use among HIV infected, recurrent pulmonary tuberculosis suspects at a national referral tuberculosis clinic in Kampala, Uganda: a qualitative analysis.

Background: Co-trimoxazole use is the standard of care for preventing Pneumocystis jirovecii pneumonia in sub-Saharan Africa but implementation remains slow. Co-trimoxazole is self- administered with uncertain adherence. Knowledge of co-trimoxazole use among HIV infected persons is unknown.Objectives: To assess knowledge, attitudes and practices of co-trimoxazole use among HIV infected adults evaluated for recurrent PTB in Kampala, Uganda.Methods: A qualitative study utilizing 5 focus group discussions among 30 HIV infected PTB suspects at the national referral tuberculosis treatment centre in Kampala.Results: Males and females had similar median ages. 80% were currently on co-trimoxazole and 50% of participants were on HAART. Majority of participants defined co-trimoxazole as an analgesic. Few noted co-trimoxazole was a drug to treat cough and chest pain. However, few responses revealed that co-trimoxazole prevents opportunistic diseases among PLHIV. Most of participants believed HAART and anti-TB drugs work as co-trimoxazole thus it should not be taken together with them. This belief may lead to increased risk of opportunistic infections, morbidity and mortality.Conclusions: We revealed gaps in understanding of co-trimoxazole use among study participants. We therefore recommend that more facts about co-trimoxazle as prophylaxis against P. jirovecii, bacterial and diarrheal pathogens should be incorporated in VCT fact sheets.Key words: Recurrent tuberculosis; HIV; Co-trimoxazole use; Chemoprophylaxis; Adherenc

The Molecular Hydrogen Deficit in Gamma-Ray Burst Afterglows

Recent analysis of five gamma-ray burst (GRB) afterglow spectra reveal the absence of molecular hydrogen absorption lines, a surprising result in light of their large neutral hydrogen column densities and the detection of H$_2$ in similar, more local star-forming regions like 30 Doradus in the Large Magellanic Cloud (LMC). Observational evidence further indicates that the bulk of the neutral hydrogen column in these sight lines lies 100 pc beyond the progenitor and that H$_2$ was absent prior to the burst, suggesting that direct flux from the star, FUV background fields, or both suppressed its formation. We present one-dimensional radiation hydrodynamical models of GRB host galaxy environments, including self-consistent radiative transfer of both ionizing and Lyman-Werner photons, nine-species primordial chemistry with dust formation of H$_2$, and dust extinction of UV photons. We find that a single GRB progenitor is sufficient to ionize neutral hydrogen to distances of 50 - 100 pc but that a galactic Lyman-Werner background is required to dissociate the molecular hydrogen in the ambient ISM. Intensities of 0.1 - 100 times the Galactic mean are necessary to destroy H$_2$ in the cloud, depending on its density and metallicity. The minimum radii at which neutral hydrogen will be found in afterglow spectra is insensitive to the mass of the progenitor or the initial mass function (IMF) of its cluster, if present.Comment: 12 pages, 7 figures, accepted for Ap

Activation of p44/42 MAPK plays a role in the TBT-induced loss of human natural killer (NK) cell function

Natural killer (NK) cells destroy (lyse) tumor cells, virally infected cells, and antibody-coated cells. Previous studies indicated that exposure to the environmental contaminant tributyltin (TBT) decreases the lytic function of NK cells and activates mitogen-activated protein kinases (MAPK), including p44/42 (Aluoch and Whalen Toxicology 209:263–277, 2005). If activation of p44/42 is required for TBT-induced decreases of lytic function, then activation of p44/42 to similar extents by pharmacological agents such as phorbol 12-myristate 13-acetate (PMA) should mimic to some extent changes induced in NK cells with TBT exposures. NK cells were exposed to PMA concentrations between 0.25 and 10 nM for 10 min, 1 h, and 6 h before determining the lytic function (51Cr release assay) and phosphorylation state of MAPKs (Western blot). A 1-h exposure of NK cells to 5 nM PMA resulted in a loss of lytic function of 47%. Western blot analysis showed that a 1-h exposure to 5 nM PMA caused a sixfold increase in phospho-p44/42 levels. Previous studies showed a fivefold increase in phospho-p44/42 in response to a 1-h exposure to 300 nM TBT. Exposure to 300 nM TBT caused about a 40% decrease in lytic function. This study supports the hypothesis that p44/42 activation (as seen with TBT exposures) can cause a loss of NK-cell lytic function

The First Stars

We review recent theoretical results on the formation of the first stars in the universe, and emphasize related open questions. In particular, we discuss the initial conditions for Population III star formation, as given by variants of the cold dark matter cosmology. Numerical simulations have investigated the collapse and the fragmentation of metal-free gas, showing that the first stars were predominantly very massive. The exact determination of the stellar masses, and the precise form of the primordial initial mass function, is still hampered by our limited understanding of the accretion physics and the protostellar feedback effects. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times. We show how complementary observations, both at high redshifts and in our local cosmic neighborhood, can be utilized to probe the first epoch of star formation.Comment: 38 pages, 10 figures, draft version for 2004 Annual Reviews of Astronomy and Astrophysics, high-resolution version available at http://cfa-www.harvard.edu/~vbromm