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Search Results: 1 - 10 of 350576 matches for " Robert S. Hill "
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Evolutionary History of Hunter-Gatherer Marriage Practices
Robert S. Walker,Kim R. Hill,Mark V. Flinn,Ryan M. Ellsworth
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0019066
Abstract: The universality of marriage in human societies around the world suggests a deep evolutionary history of institutionalized pair-bonding that stems back at least to early modern humans. However, marriage practices vary considerably from culture to culture, ranging from strict prescriptions and arranged marriages in some societies to mostly unregulated courtship in others, presence to absence of brideservice and brideprice, and polyandrous to polygynous unions. The ancestral state of early human marriage is not well known given the lack of conclusive archaeological evidence.
UIT Astro-2 Observations of NGC 4449
Robert S. Hill,Michael N. Fanelli,Denise A. Smith,Theodore P. Stecher,the UIT Team
Physics , 1996, DOI: 10.1063/1.52826
Abstract: The bright Magellanic irregular galaxy NGC 4449 was observed by the Ultraviolet Imaging Telescope (UIT) during the Astro-2 Spacelab mission in March, 1995. Far ultraviolet (FUV) images at a spatial resolution of ~3 arcsec show bright star-forming knots that are consistent with the general optical morphology of the galaxy and are often coincident with bright H II regions. Comparison of FUV with H-alpha shows that in a few regions, sequential star formation may have occurred over the last few Myr. The bright star forming complexes in NGC 4449 are superposed on a smooth, diffuse FUV background that may be associated with the H-alpha "froth."
Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density
Harry I. Teplitz,Nicholas R. Collins,Jonathan P. Gardner,Robert S. Hill,Jason Rhodes
Physics , 2002, DOI: 10.1086/374659
Abstract: We present the luminosity function of [OII]-emitting galaxies at a median redshift of z=0.9, as measured in the deep spectroscopic data in the STIS Parallel Survey (SPS). The luminosity function shows strong evolution from the local value, as expected. By using random lines of sight, the SPS measurement complements previous deep single field studies. We calculate the density of inferred star formation at this redshift by converting from [OII] to H-alpha line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014 Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46
GSH 006-15+7: A local Galactic supershell featuring transition from HI emission to absorption
Vanessa A. Moss,Naomi M. McClure-Griffiths,Robert Braun,Alex S. Hill,Greg J. Madsen
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20538.x
Abstract: We report on the discovery of a new Galactic supershell, GSH 006-15+7, from the Galactic All Sky Survey data. Observed and derived properties are presented and we find that GSH 006-15+7 is one of the nearest physically large supershells known, with dimensions of ~ 780 x 520 pc at a distance of ~ 1.5 kpc. The shell wall appears in HI emission at b <~ -6.5 deg and in HI self-absorption (HISA) at b >~ -6.5 deg. We use this feature along with HISA diagnostics to estimate an optical depth of tau ~ 3, a spin temperature of ~ 40 K and a swept-up mass of M ~ 3e6 solar masses. We also investigate the origin of GSH 006-15+7, assessing the energy contribution of candidate powering sources and finding evidence in favour of a formation energy of ~ 1e52 ergs. We find that this structure provides evidence for the transfer of mass and energy from the Galactic disk into the halo.
Halpha and [S II] emission from warm ionized gas in the Scutum-Centaurus Arm
Alex S. Hill,Robert A. Benjamin,L. Matthew Haffner,Martin Gostisha,Kathleen A. Barger
Physics , 2014, DOI: 10.1088/0004-637X/787/2/106
Abstract: We present Wisconsin H-Alpha Mapper [S II] {\lambda}6716 and H{\alpha} spectroscopic maps of the warm ionized medium (WIM) in the Scutum-Centaurus Arm at Galactic longitudes 310{\deg} < l < 345{\deg}. Using extinction-corrected H{\alpha} intensities (IH{\alpha}c), we measure an exponential scale height of electron density-squared in the arm of H_ne^2 = 0.30 kpc (assuming a distance of 3.5 kpc), intermediate between that observed in the inner Galaxy and in the Perseus Arm. The [S II]/H{\alpha} line ratio is enhanced at large |z| and in sightlines with faint IH{\alpha}c. We find that the [S II]/H{\alpha} line ratio has a power law relationship with IH{\alpha}c from a value of ~=1.0 at IH{\alpha}c < 0.2 R (Rayleighs) to a value of ~=0.08 at IH{\alpha}c >= 100 R. The line ratio is better correlated with H{\alpha} intensity than with height above the plane, indicating that the physical conditions within the WIM vary systematically with electron density. We argue that the variation of the line ratio with height is a consequence of the decrease of electron density with height. Our results reinforce the well-established picture in which the diffuse H{\alpha} emission is due primarily to emission from in situ photoionized gas, with scattered light only a minor contributor.
Predicting the outcomes of treatment to eradicate the latent reservoir for HIV-1
Alison L. Hill,Daniel I. S. Rosenbloom,Feng Fu,Martin A. Nowak,Robert F. Siliciano
Quantitative Biology , 2014, DOI: 10.1073/pnas.1406663111
Abstract: Massive research efforts are now underway to develop a cure for HIV infection, allowing patients to discontinue lifelong combination antiretroviral therapy (ART). New latency-reversing agents (LRAs) may be able to purge the persistent reservoir of latent virus in resting memory CD4+ T cells, but the degree of reservoir reduction needed for cure remains unknown. Here we use a stochastic model of infection dynamics to estimate the efficacy of LRA needed to prevent viral rebound after ART interruption. We incorporate clinical data to estimate population-level parameter distributions and outcomes. Our findings suggest that approximately 2,000-fold reductions are required to permit a majority of patients to interrupt ART for one year without rebound and that rebound may occur suddenly after multiple years. Greater than 10,000-fold reductions may be required to prevent rebound altogether. Our results predict large variation in rebound times following LRA therapy, which will complicate clinical management. This model provides benchmarks for moving LRAs from the lab to the clinic and can aid in the design and interpretation of clinical trials. These results also apply to other interventions to reduce the latent reservoir and can explain the observed return of viremia after months of apparent cure in recent bone marrow transplant recipients and an immediately-treated neonate.
HST Observations of New Horizontal Branch Structures in the Globular Cluster omega Centauri
Noella L. D'Cruz,Robert W. O'Connell,Robert T. Rood,Jonathan H. Whitney,Ben Dorman,Wayne B. Landsman,Robert S. Hill,Theodore P. Stecher,Ralph C. Bohlin
Physics , 1999, DOI: 10.1086/308375
Abstract: The globular cluster omega Centauri contains the largest known population of very hot horizontal branch (HB) stars. We have used the Hubble Space Telescope to obtain a far-UV/optical color-magnitude diagram of three fields in omega Cen. We find that over 30% of the HB objects are ``extreme'' HB or hot post-HB stars. The hot HB stars are not concentrated toward the cluster center, which argues against a dynamical origin for them. A wide gap in the color distribution of the hot HB stars appears to correspond to gaps found earlier in several other clusters. This suggests a common mechanism, probably related to giant branch mass loss. The diagram contains a significant population of hot sub-HB stars, which we interpret as the ``blue-hook'' objects predicted by D'Cruz et al. (1996a). These are produced by late He-flashes in stars which have undergone unusually large giant branch mass loss. omega Cen has a well-known spread of metal abundance, and our observations are consistent with a giant branch mass loss efficiency which increases with metallicity.
Magnetized Gas in the Smith High Velocity Cloud
Alex S. Hill,S. A. Mao,Robert A. Benjamin,Felix J. Lockman,Naomi M. McClure-Griffiths
Physics , 2013, DOI: 10.1088/0004-637X/777/1/55
Abstract: We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures towards extragalactic radio sources behind the Smith Cloud, new HI observations from the Green Bank Telescope, and a spectroscopic map of H{\alpha} from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure of approximately 100 rad m^(-2) which are generally well correlated with decelerated H{\alpha} emission. We estimate a lower limit on the line-of-sight component of the field of approximately 8 {\mu}G along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by HI or H{\alpha} at the velocity of the Smith Cloud. The smooth H{\alpha} morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (approximately 1 Rayleigh) H{\alpha} intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas.
Electrical Transport in Thick Film Resistors
Robert M. Hill
Active and Passive Electronic Components , 1980, DOI: 10.1155/apec.6.141
Abstract:
Ultraviolet Imaging of the Irregular Galaxy NGC 4449 with UIT: Photometry and Recent Star-Formation History
Robert S. Hill,Michael N. Fanelli,Denise A. Smith,Ralph C. Bohlin,Susan G. Neff,Robert W. O'Connell,Morton S. Roberts,Andrew M. Smith,Theodore P. Stecher
Physics , 1998, DOI: 10.1086/306302
Abstract: The bright Magellanic irregular galaxy NGC 4449 was observed during the Astro-2 Space Shuttle mission by the Ultraviolet Imaging Telescope (UIT), which obtained images of a ~40 arcmin field centered on the galaxy in two broad far-ultraviolet (FUV) bands centered at 1520 A and 1620 A, with 3 arcsec - 5 arcsec spatial resolution. Together with H-alpha and H-beta fluxes from ground-based Fabry-Perot images, these data are analyzed in order to explore the recent star formation history of NGC 4449. Maps of the flux ratios H-alpha/FUV and FUV/blue continuum are presented and interpreted using evolutionary synthesis models. Photometry is presented both for 22 apertures containing large OB complexes and for 57 small apertures containing compact FUV-emitting knots. The OB complexes along the northern edge of the visible system have high H-alpha/FUV ratios, and thus appear to be more dominated by the current generation of stars than are other parts of the galaxy. However, young sources do exist elsewhere and are particularly conspicuous along the bar. The small aperture analysis shows three candidate regions for sequential star formation. Surface brightness profiles are consistent with an exponential disk in both the FUV and the optical continuum.
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