378 research outputs found
The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight
The limiting magnitude of the HST data set used by Cochran et al. (1995) to
detect small objects in the Kuiper belt is reevaluated, and the methods used
are described in detail. It is shown, by implanting artificial objects in the
original HST images, and re-reducing the images using our original algorithm,
that the limiting magnitude of our images (as defined by the 50% detectability
limit) is . This value is statistically the same as the value found in
the original analysis. We find that of the moving Kuiper belt objects
with are detected when trailing losses are included. In the same data
in which these faint objects are detected, we find that the number of false
detections brighter than is less than one per WFPC2 image. We show
that, primarily due to a zero-point calibration error, but partly due to
inadequacies in modeling the HST'S data noise characteristics and Cochran et
al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects
in the HST dataset by over a factor of 2, and their conclusions are therefore
invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe
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A qualitative study of health information technology in the Canadian public health system
Background: Although the adoption of health information technology (HIT) has advanced in Canada over the past decade, considerable challenges remain in supporting the development, broad adoption, and effective use of HIT in the public health system. Policy makers and practitioners have long recognized that improvements in HIT infrastructure are necessary to support effective and efficient public health practice. The objective of this study was to identify aspects of health information technology (HIT) policy related to public health in Canada that have succeeded, to identify remaining challenges, and to suggest future directions to improve the adoption and use of HIT in the public health system. Methods: A qualitative case study was performed with 24 key stakeholders representing national and provincial organizations responsible for establishing policy and strategic direction for health information technology. Results: Identified benefits of HIT in public health included improved communication among jurisdictions, increased awareness of the need for interoperable systems, and improvement in data standardization. Identified barriers included a lack of national vision and leadership, insufficient investment, and poor conceptualization of the priority areas for implementing HIT in public health. Conclusions: The application of HIT in public health should focus on automating core processes and identifying innovative applications of HIT to advance public health outcomes. The Public Health Agency of Canada should develop the expertise to lead public health HIT policy and should establish a mechanism for coordinating public health stakeholder input on HIT policy
Random and ordered phases of off-lattice rhombus tiles
We study the covering of the plane by non-overlapping rhombus tiles, a
problem well-studied only in the limiting case of dimer coverings of regular
lattices. We go beyond this limit by allowing tiles to take any position and
orientation on the plane, to be of irregular shape, and to possess different
types of attractive interactions. Using extensive numerical simulations we show
that at large tile densities there is a phase transition from a fluid of
rhombus tiles to a solid packing with broken rotational symmetry. We observe
self-assembly of broken-symmetry phases, even at low densities, in the presence
of attractive tile-tile interactions. Depending on tile shape and interactions
the solid phase can be random, possessing critical orientational fluctuations,
or crystalline. Our results suggest strategies for controlling tiling order in
experiments involving `molecular rhombi'.Comment: Supp. Info. and version with high-res figures at
http://nanotheory.lbl.gov/people/rhombus_paper/rhombus.htm
Blueschist from the Mariana forearc records long-lived residence of material in the subduction channel
From ca. 50 Ma to present, the western Pacific plate has been subducting under the Philippine Sea plate, forming the oceanic Izu-Bonin-Mariana (IBM) subduction system. It is the only known location where subduction zone products are presently being transported to the surface by serpentinite-mud volcanoes. A large serpentine mud āvolcanoā forms the South Chamorro Seamount and was successfully drilled by ODP during Leg 195. This returned mostly partially serpentinized harzburgites enclosed in serpentinite muds. In addition, limited numbers of small (1 mmā1 cm) fragments of rare blueschists were also discovered. UāPb dating of zircon and rutile from one of these blueschist clasts give ages of 51.1 Ā± 1.2 Ma and 47.5 Ā± 2.0 Ma, respectively. These are interpreted to date prograde high-pressure metamorphism. Mineral equilibria modelling of the blueschist clast suggests the mineral assemblage formed at conditions of ā¼1.6 GPa and ā¼590 Ā°C. We interpret that this high-pressure assemblage formed at a depth of ā¼50 km within the subduction channel and was subsequently exhumed and entrained into the South Chamorro serpentinite volcano system at depths of ā¼27 km. Consequently, we propose that the material erupted from the South Chamarro Seamount may be sampling far greater depths within the Mariana subduction system than previously thought. The apparent thermal gradient implied by the pressureātemperature modelling (ā¼370 Ā°C/GPa) is slightly warmer than that predicted by typical subduction channel numerical models and other blueschists worldwide. The age of the blueschist suggests it formed during the arc initiation stages of the proto-Izu-Bonin-Mariana arc, with the PāT conditions recording thermally elevated conditions during initial stages of western Pacific plate subduction. This indicates the blueschist had prolonged residence time in the stable forearc as the system underwent east-directed rollback. The Mariana blueschist shows that subduction products can remain entrained in subduction channels for many millions of years prior to exhumation
Palaeoproterozoic eclogites: exhumation and burial convolution of P-t histories
Dillon Brown, RenƩe Tamblyn, Martin Hand, and Laura Morrisse
Results from a Near Infrared Search for Emission-line Stars in the Inner Galaxy: Spectra of New Wolf-Rayet Stars
We present follow-up spectroscopy of emission line candidates detected on
near-infrared narrow band images in the inner Galaxy (Homeier et al. 2003). The
filters are optimized for the detection of Wolf-Rayet stars and other objects
which exhibit emission--lines in the 2 m region. Approximately three
square degrees along the Galactic plane have been analyzed in seven
narrow--filters (four emission--lines and three continuum). We have discovered
4 new Wolf-Rayet stars and present coordinates, finding charts, and K-band
spectra.Comment: To appear in Astronomy & Astrophysic
Relating Energy Level Alignment and Amine-Linked Single Molecule Junction Conductance
Using photoemission spectroscopy, we determine the relationship between
electronic energy level alignment at a metal-molecule interface and
single-molecule junction transport data. We measure the position of the highest
occupied molecular orbital (HOMO) relative to the Au metal Fermi level for
three 1,4-benzenediamine derivatives on Au(111) and Au(110) with ultraviolet
and resonant x-ray photoemission spectroscopy. We compare these results to
scanning tunnelling microscope based break-junction measurements of single
molecule conductance and to first-principles calculations. We find that the
energy difference between the HOMO and Fermi level for the three molecules
adsorbed on Au(111) correlate well with changes in conductance, and agree well
with quasiparticle energies computed from first-principles calculations
incorporating self-energy corrections. On the Au(110) which present Au atoms
with lower-coordination, critical in break-junction conductance measurements,
we see that the HOMO level shifts further from the Fermi level. These results
provide the first direct comparison of spectroscopic energy level alignment
measurements with single molecule junction transport data
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