Radial Distribution of Production Rates, Loss Rates and Densities Corresponding to Ion Masses <=40 amu in the Inner Coma of Comet Halley: Composition and Chemistry

In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses <=40 amu in the inner coma of the comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion-neutral, electron-neutral, photon-neutral and electron-ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions are discussed in this paper. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km.Comment: pages 42, figures 9 (total 12), tables

Detection of a Hot Gaseous Halo Around the Giant Spiral Galaxy NGC 1961

Hot gaseous halos are predicted around all large galaxies and are critically important for our understanding of galaxy formation, but they have never been detected at distances beyond a few kpc around a spiral galaxy. We used the Chandra ACIS-I instrument to search for diffuse X-ray emission around an ideal candidate galaxy: the isolated giant spiral NGC 1961. We observed four quadrants around the galaxy for 30 ks each, carefully subtracting background and point source emission, and found diffuse emission that appears to extend to 40-50 kpc. We fit $\beta$-models to the emission, and estimate a hot halo mass within 50 kpc of $5\times10^9 M_{\odot}$. When this profile is extrapolated to 500 kpc (the approximate virial radius), the implied hot halo mass is $1-3\times10^{11} M_{\odot}$. These mass estimates assume a gas metallicity of $Z = 0.5 Z_{\odot}$. This galaxy's hot halo is a large reservoir of gas, but falls significantly below observational upper limits set by pervious searches, and suggests that NGC 1961 is missing 75% of its baryons relative to the cosmic mean, which would tentatively place it below an extrapolation of the baryon Tully-Fisher relationship of less massive galaxies. The cooling rate of the gas is no more than 0.4 $M_{\odot}$/year, more than an order of magnitude below the gas consumption rate through star formation. We discuss the implications of this halo for galaxy formation models.Comment: 26 pages, 5 figures, accepted to ApJ. Updated to include journal ref and small changes added in proof

Spontaneous virologic suppression in HIV controllers is independent of delayed-type hypersensitivity test responsiveness

<p>Abstract</p> <p>Background</p> <p>Delayed-type hypersensitivity (DTH) testing, an in vivo assessment of cell-mediated immunity, is a predictor of HIV disease progression beyond CD4 cell count. We investigated whether preserved DTH responsiveness was characteristic of HIV controllers compared to non-controllers and individuals on suppressive HAART.</p> <p>Findings</p> <p>DTH testing consisted of ≥ 3 recall antigens applied approximately every 6 months. DTH responses were classified by the number of positive skin tests: anergic (0), partial anergic (1), or non-anergic (≥ 2). HIV controllers were compared to treatment naïve non-controllers (n = 3822) and a subgroup of non-controllers with VL < 400 copies/mL on their initial HAART regimen (n = 491). The proportion of non-anergic results at first DTH testing was similar for HIV controllers compared to non-controllers (81.9% vs. 77.6%; P = 0.22), but tended to be greater in HIV controllers compared to the HAART subgroup (81.9% vs. 74.5%; P = 0.07). Complete anergy was observed in 14 (10.1%) HIV controllers with CD4 counts ≥ 400 cells/uL. For longitudinal testing, the average percentage of non-anergic DTH determinations per participant was higher in HIV controllers compared to non-controllers (81.2 ± 31.9% vs. 70.7 ± 36.8%; P = 0.0002), however this difference was eliminated with stratification by CD4 count: 200-399 (83.4 ± 35.6% vs. 71.9 ± 40.9%; P = 0.15) and > 400 cells/uL (81.2 ± 31.5% vs. 80.4 ± 32.7%; P = 0.76).</p> <p>Conclusions</p> <p>Spontaneous virologic control was not associated with DTH responsiveness, and several HIV controllers were anergic despite having elevated CD4 counts. These findings suggest that cellular immunity assessed by DTH is not a principal factor contributing to spontaneous virologic suppression in HIV controllers.</p

A cluster randomized controlled trial of a modified vaccination clinical reminder for primary care providers

Objective: Adult vaccination rates in the United States fall short of national goals, and rates are particularly low for Black Americans. We tested a provider-focused vaccination uptake intervention: a modified electronic health record clinical reminder that bundled together three adult vaccination reminders, presented patient vaccination history, and included talking points for providers to address vaccine hesitancy. Method: Primary care teams at the Atlanta Veterans Affairs Medical Center, who saw 28,941 patients during this period, were randomly assigned to receive either the modified clinical reminder (N = 44 teams) or the status quo (N = 40 teams). Results: Uptake of influenza and other adult vaccinations was 1.6 percentage points higher in the intervention group, which was not statistically significant (CI = [-1.3, 4.4], p = 0.28). The intervention had similar effects on Black and White patients and did not reduce the disparity in vaccination rates between these groups. Conclusion: Provider-focused interventions are a promising way to address vaccine hesitancy, but they may need to be more intensive than a modified clinical reminder to have appreciable effects on vaccination uptake

Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418

We present results from a fifteen-month campaign of high-cadence (~ 3 days) mid-infrared Spitzer and optical (B and V ) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 $\mu$m and 4.5 $\mu$m flux variations lag behind those of the optical continuum by $37.2^{+2.4}_{-2.2}$ days and $47.1^{+3.1}_{-3.1}$ days, respectively. We report a cross-correlation time lag between the 4.5 $\mu$m and 3.6 $\mu$m flux of $13.9^{+0.5}_{-0.1}$ days. The lags indicate that the dust emitting at 3.6 $\mu$m and 4.5 $\mu$m is located at a distance of approximately 1 light-month (~ 0.03 pc) from the source of the AGN UV-optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ~ 2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGN. The 3.6 and 4.5 $\mu$m reverberation radii fall above the K-band $\tau \propto L^{0.5}$ size-luminosity relationship by factors $\lesssim 2.7$ and $\lesssim 3.4$, respectively, while the 4.5 $\mu$m reverberation radius is only 27% larger than the 3.6 $\mu$m radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.Comment: 13 pages, 9 figure

Hubble Space Telescope NICMOS Imaging of the Core of M87

We present broad-band 1.1, 1.6 and 2.2 micron images and a 2.37 micron narrow-band image of the inner 19" of the nearby radio galaxy M87, obtained with the Near Infrared Camera and Multi-Object Spectrometer of the Hubble Space Telescope (HST). The isophotes of the broad-band images are almost perfectly circular to within approximately 0.5" (~ 50 pc) of the active nucleus, and an r**1/4 law provides a good fit to the galaxy profile to within the same distance. This result agrees with predictions that the nuclear supermassive black hole will produce a nearly spherical distribution of the surrounding stars within a galaxy crossing time. A difference image formed from the 1.6 micron image and a V-band image obtained with the HST Wide Field Planetary Camera 2 does not show any clear evidence of a physically thick dusty torus around the nucleus, consistent with its lack of strong thermal infrared emission. The images and associated colors also confirm that the regions beyond the nucleus do not contain strongly concentrated dust,in contrast to many other radio galaxies. In combination with other recent observations, these results indicate that M87 represents the dynamically evolved product of past galaxy mergers, and suggest that its nucleus is in the final stages of activity.Comment: Accepted for publication in the Astronomical Journa

New Limits on Sterile Neutrinos from Suzaku Observations of the Ursa Minor Dwarf Spheroidal Galaxy

We present results of our search for X-ray line emission associated with the radiative decay of the sterile neutrino, a well-motivated dark matter candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal galaxy. These data represent the first deep observation of one of these extreme mass-to-light systems and the first dedicated dark matter search using an X-ray telescope. No such emission line is positively detected, and we place new constraints on the combination of the sterile neutrino mass and the active-sterile neutrino oscillation mixing angle. Line flux upper limits are derived using a maximum-likelihood-based approach that, along with the lack of intrinsic X-ray emission, enables us to minimize systematics and account for those that remain. The limits we derive match or approach the best previous results over the entire 1--20 keV mass range from a single Suzaku observation. These are used to place constraints on the existence of sterile neutrinos with given parameters in the general case and in the case where they are assumed to constitute all of the dark matter. The range allowed implies that sterile neutrinos remain a viable candidate to make up some -- or all -- of the dark matter and also explain pulsar kicks and various other astrophysical phenomena.Comment: revised to closely match version to be published in ApJ v. 69

Scattered X-rays in Obscured Active Galactic Nuclei and their Implications for Geometrical Structure and Evolution

We construct a new sample of 32 obscured active galactic nuclei (AGNs) selected from the Second XMM-Newton Serendipitous Source Catalogue to investigate their multiwavelength properties in relation to the "scattering fraction", the ratio of the soft X-ray flux to the absorption-corrected direct emission. The sample covers a broad range of the scattering fraction (0.1%-10%). A quarter of the 32 AGNs have a very low scattering fraction (smaller than 0.5%), which suggests that they are buried in a geometrically thick torus with a very small opening angle. We investigate correlations between the scattering fraction and multiwavelength properties. We find that AGNs with a small scattering fraction tend to have low [O III]lambda5007/X-ray luminosity ratios. This result agrees with the expectation that the extent of the narrow-line region is small because of the small opening angle of the torus. There is no significant correlation between scattering fraction and far-infrared luminosity. This implies that a scale height of the torus is not primarily determined by starburst activity. We also compare scattering fraction with black hole mass or Eddington ratio and find a weak anti-correlation between the Eddington ratio and scattering fraction. This implies that more rapidly growing supermassive black holes tend to have thicker tori.Comment: 13 pages, 10 figures, accepted for publication in Ap

A Retrospective Survey of HIV Drug Resistance Among Patients 1 Year After Initiation of Antiretroviral Therapy at 4 Clinics in Malawi

In 2004, Malawi began scaling up its national antiretroviral therapy (ART) program. Because of limited treatment options, population-level surveillance of acquired human immunodeficiency virus drug resistance (HIVDR) is critical to ensuring long-term treatment success. The World Health Organization target for clinic-level HIVDR prevention at 12 months after ART initiation is ≥ 70%. In 2007, viral load and HIVDR genotyping was performed in a retrospective cohort of 596 patients at 4 ART clinics. Overall, HIVDR prevention (using viral load ≤ 400 copies/mL) was 72% (95% confidence interval [CI], 67%-77%; range by site, 60%-83%) and detected HIVDR was 3.4% (95% CI, 1.8%-5.8%; range by site, 2.5%-4.7%). Results demonstrate virological suppression and HIVDR consistent with previous reports from sub-Saharan Africa. High rates of attrition because of loss to follow-up were noted and merit attention