1,839 research outputs found
A Search for Companions to Brown Dwarfs in the Taurus and Chamaeleon Star Forming Regions
We present the results of a search for companions to young brown dwarfs in
the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used
WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these
regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional
late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with
adaptive optics at Keck Observatory. We have applied PSF subtraction to the
primaries and have searched the resulting images for objects that have colors
and magnitudes that are indicative of young low-mass objects. Through this
process, we have identified promising candidate companions to 2MASS
J04414489+2301513 (rho=0.105"/15 AU), 2MASS J04221332+1934392 (rho=0.05"/7 AU),
and ISO 217 (rho=0.03"/5 AU). We reported the discovery of the first candidate
in a previous study, showing that it has a similar proper motion as the primary
through a comparison of astrometry measured with WFPC2 and Gemini adaptive
optics. We have collected an additional epoch of data with Gemini that further
supports that result. By combining our survey with previous high-resolution
imaging in Taurus, Chamaeleon, and Upper Sco (10 Myr), we measure binary
fractions of 14/93 = 0.15+0.05/-0.03 for M4-M6 (0.1-0.3 Msun) and 4/108 =
0.04+0.03/-0.01 for >M6 (10 AU. Given the youth
and low density of these three regions, the lower binary fraction at later
types is probably primordial rather than due to dynamical interactions among
association members. The widest low-mass binaries (>100 AU) also appear to be
more common in Taurus and Chamaeleon than in the field, which suggests that the
widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or
that field brown dwarfs have been born predominantly in denser clusters where
wide systems are disrupted or inhibited from forming.Comment: Astrophysical Journal, in pres
Structural defects induced by Fe-ion implantation in TiO2
X-ray photoelectron spectroscopy (XPS) and resonant x-ray emission
spectroscopy (RXES) measurements of pellet and thin film forms of TiO with
implanted Fe ions are presented and discussed. The findings indicate that
Fe-implantation in a TiO pellet sample induces heterovalent cation
substitution (Fe Ti) beneath the surface region. But
in thin film samples, the clustering of Fe atoms is primarily detected. In
addition to this, significant amounts of secondary phases of Fe are
detected on the surface of all doped samples due to oxygen exposure. These
experimental findings are compared with density functional theory (DFT)
calculations of formation energies for different configurations of structural
defects in the implanted TiO:Fe system. According to our calculations, the
clustering of Fe-atoms in TiO:Fe thin films can be attributed to the
formation of combined substitutional and interstitial defects. Further, the
differences due to Fe doping in pellet and thin film samples can ultimately be
attributed to different surface to volume ratios.Comment: 7+ pages, 3 Figure, to appear in J. Appl. Phy
Combining Slaughterhouse Surveillance Data with Cattle Tracing Scheme and Environmental Data to Quantify Environmental Risk Factors for Liver Fluke in Cattle.
Liver fluke infection causes serious disease (fasciolosis) in cattle and sheep in many regions of the world, resulting in production losses and additional economic consequences due to condemnation of the liver at slaughter. Liver fluke depends on mud snails as an intermediate host and infect livestock when ingested through grazing. Therefore, environmental factors play important roles in infection risk and climate change is likely to modify this. Here, we demonstrate how slaughterhouse data can be integrated with other data, including animal movement and climate variables to identify environmental risk factors for liver fluke in cattle in Scotland. We fitted a generalized linear mixed model to the data, with exposure-weighted random and fixed effects, an approach which takes into account the amount of time cattle spent at different locations, exposed to different levels of risk. This enabled us to identify an increased risk of liver fluke with increased animal age, rainfall, and temperature and for farms located further to the West, in excess of the risk associated with a warmer, wetter climate. This model explained 45% of the variability in liver fluke between farms, suggesting that the unexplained 55% was due to factors not included in the model, such as differences in on-farm management and presence of wet habitats. This approach demonstrates the value of statistically integrating routinely recorded slaughterhouse data with other pre-existing data, creating a powerful approach to quantify disease risks in production animals. Furthermore, this approach can be used to better quantify the impact of projected climate change on liver fluke risk for future studies
QSO 2237+0305 VR light curves from Gravitational Lenses International Time Project optical monitoring
We present VR observations of QSO 2237+0305 conducted by the GLITP
collaboration from 1999 October 1 to 2000 February 3. The observations were
made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos
Observatory, La Palma (Spain). The PSF fitting method and an adapted version of
the ISIS subtraction method have been used to derive the VR light curves of the
four components (A-D) of the quasar. The mean errors range in the intervals
0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the
faintest component (D) having the largest uncertainties. We address the
relatively good agreement between the A-D light curves derived using different
filters, photometric techniques, and telescopes. The new VR light curves of
component A extend the time coverage of a high magnification microlensing peak,
which was discovered by the OGLE team.Comment: 15 pages, 3 figures, ApJ accepted (Feb 19
Predicting the band gap of ternary oxides containing 3d(10) and 3d(0) metals
We present soft x-ray spectroscopy measurements and electronic structure calculations of ZnTiO 3, a ternary oxide that is related to wurtzite ZnO and rutile TiO 2. The electronic structure of ZnTiO 3 was calculated using a variety of exchange-correlation functionals, and we compare the predicted band gaps of this material obtained from each functional with estimates from our experimental data and optical gaps quoted from the literature. We find that the main hybridizations in the electronic structure of ZnTiO 3 can be predicted from the electronic structures of the two binary oxides. We further find that ZnTiO 3 has weaker O 2p-Zn 3d repulsion than in ZnO, resulting in a relatively lower valence band maximum and consequently a larger band gap. Although we find a significant core hole shift in the measured O K XAS of ZnTiO 3, we provide a simple empirical scheme for estimating the band gap that may prove to be applicable for any d10-d0 ternary oxide, and could be useful in finding a ternary oxide with a band gap tailored to a specific energy. © 2012 American Physical Society
Treating patients as persons : a capabilities approach to support delivery of person-centered care
Peer reviewedPublisher PD
Galaxies in Southern Bright Star Fields I. Near-infrared imaging
As a prerequisite for cosmological studies using adaptive optics techniques,
we have begun to identify and characterize faint sources in the vicinity of
bright stars at high Galactic latitudes. The initial phase of this work has
been a program of K_s imaging conducted with SOFI at the ESO NTT. From
observations of 42 southern fields evenly divided between the spring and autumn
skies, we have identified 391 additional stars and 1589 galaxies lying at
separations 60" from candidate guide stars in the magnitude range 9.0 R 12.4.
When analyzed as a "discrete deep field" with 131 arcmin^2 area, our dataset
gives galaxy number counts that agree with those derived previously over the
range 16 K_s 20.5. This consistency indicates that in the aggregate, our fields
should be suitable for future statistical studies. We provide our source
catalogue as a resource for users of large telescopes in the southern
hemisphere.Comment: 10 pages, 7 figures, accepted by A&A; Table 3 is available at
http://www.rzg.mpg.de/~ajb/data.html pending upload to CD
Stable spinning optical solitons in three dimensions
We introduce spatiotemporal spinning solitons (vortex tori) of the
three-dimensional nonlinear Schrodinger equation with focusing cubic and
defocusing quintic nonlinearities. The first ever found completely stable
spatiotemporal vortex solitons are demonstrated. A general conclusion is that
stable spinning solitons are possible as a result of competition between
focusing and defocusing nonlinearities.Comment: 4 pages, 6 figures, accepted to Phys. Rev. Let
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