134 research outputs found
`Oumuamua as a messenger from the Local Association
7 pages, one table, two figures, accepted for publication by ApJL. © 2018. The American Astronomical Society. All rights reserved.With a hyperbolic trajectory around the Sun, 'Oumuamua is the first confirmed interstellar object. However, its origin is poorly known. By simulating the orbits of 0.23 million local stars, we find 109 encounters with periastron less than 5 pc. 'Oumuamua's low peculiar velocity is suggestive of its origin from a young stellar association with similar velocity. In particular, we find that 'Oumuamua would have had slow encounters with at least five young stars belonging to the Local Association, thus suggesting these as plausible sites for formation and ejection. In addition to an extremely elongated shape, the available observational data for 'Oumuamua indicates a red color, suggestive of a potentially organic-rich and activity-free surface. These characteristics seem consistent with formation through energetic collisions between planets and debris objects in the middle part of a young stellar system. We estimate an abundance of at least 6.0 × 10 -3 au -3 for such interstellar objects with mean diameter larger than 100 m and find that it is likely that most of them will be ejected into the Galactic halo. Our Bayesian analysis of the available light curves indicates a rotation period of 6.96 +1.45 -0.39, which is consistent with the estimation by Meech et al. and shorter than those in other literature. The codes and results are available on GitHub (https://github.com/phillippro/Oumuamua).Peer reviewe
1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales
Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic
Center, can be studied on Schwarzschild radius scales with (sub)millimeter
wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm
wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on
Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the
CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator
1924-292 were observed over three consecutive nights, and both sources were
clearly detected on all baselines. For the first time, we are able to extract
1.3 mm VLBI interferometer phase information on Sgr A* through measurement of
closure phase on the triangle of baselines. On the third night of observing,
the correlated flux density of Sgr A* on all VLBI baselines increased relative
to the first two nights, providing strong evidence for time-variable change on
scales of a few Schwarzschild radii. These results suggest that future VLBI
observations with greater sensitivity and additional baselines will play a
valuable role in determining the structure of emission near the event horizon
of Sgr A*.Comment: 8 pages, submitted to ApJ
MUSTANG 3.3 Millimeter Continuum Observations of Class 0 Protostars
We present observations of six Class 0 protostars at 3.3 mm (90 GHz) using
the 64-pixel MUSTANG bolometer camera on the 100-m Green Bank Telescope. The
3.3 mm photometry is analyzed along with shorter wavelength observations to
derive spectral indices (S_nu ~ nu^alpha) of the measured emission. We utilize
previously published dust continuum radiative transfer models to estimate the
characteristic dust temperature within the central beam of our observations. We
present constraints on the millimeter dust opacity index, beta, between 0.862
mm, 1.25 mm, and 3.3 mm. Beta_mm typically ranges from 1.0 to 2.4 for Class 0
sources. The relative contributions from disk emission and envelope emission
are estimated at 3.3 mm. L483 is found to have negligible disk emission at 3.3
mm while L1527 is dominated by disk emission within the central beam. The
beta_mm^disk <= 0.8 - 1.4 for L1527 indicates that grain growth is likely
occurring in the disk. The photometry presented in this paper may be combined
with future interferometric observations of Class 0 envelopes and disks.Comment: 19 pages, 3 figures, AJ accepted, in pres
Year 1 of the Legacy Survey of Space and Time (LSST): Recommendations for Template Production to Enable Solar System Small Body Transient and Time Domain Science
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will discover ~6 million solar system planetesimals, providing in total over a billion photometric and astrometric measurements in 6 broad-band filters. Rubin Observatory's automated data reduction pipelines will employ difference imaging; templates representing the static sky will be subtracted from the nightly LSST observations in order to identify transient sources, including solar system moving objects. These templates are expected to be generated by coadding high quality images of the same pointing from the previous year's survey observations. The first year of LSST operations will require a different method for generating templates, if solar system discoveries are to be reported daily like Year 2 and beyond. We make recommendations for template production in the LSST's first year and present the opportunities for solar system small body transient and time domain science enhanced by this change
Canine Leptospirosis, United States, 2002–2004
The proportion of positive Leptospira microscopic agglutination tests for 23,005 dogs significantly increased from 2002 to 2004 (p<0.002) regardless of the positive cutoff titer used and was highest (p<0.05) for serovars Autumnalis and Grippotyphosa. The strongest positive serologic correlation (r = 0.72) was between serovars Autumnalis and Pomona
Photon-induced near-field electron microscopy (PINEM) of eukaryotic cells
Photon-induced near-field electron microscopy (PINEM) is a technique to produce and then image evanescent electromagnetic fields on the surfaces of nanostructures. Most previous applications of PINEM have imaged surface plasmon-polariton waves on conducting nanomaterials. Here, the application of PINEM on whole human cancer cells and membrane vesicles isolated from them is reported. We show that photons induce time-, orientation-, and polarization-dependent evanescent fields on the surfaces of A431 cancer cells and isolated membrane vesicles. Furthermore, the addition of a ligand to the major surface receptor on these cells and vesicles (Epidermal Growth Factor Receptor, EGFR) reduces the intensity of these fields in both preparations. In the absence of plasmon waves in biological samples, we propose these evanescent fields reflect the changes of EGFR kinase domain polarization upon ligand binding
The Contribution of Social Networks to the Health and Self-Management of Patients with Long-Term Conditions: A Longitudinal Study
Evidence for the effectiveness of patient education programmes in changing individual self-management behaviour is equivocal. More distal elements of personal social relationships and the availability of social capital at the community level may be key to the mobilisation of resources needed for long-term condition self-management to be effective.
Aim: To determine how the social networks of people with long-term conditions (diabetes and heart disease) are associated with health-related outcomes and changes in outcomes over time.
Methods: Patients with chronic heart disease (CHD) or diabetes (n = 300) randomly selected from the disease registers of 19 GP practices in the North West of England. Data on personal social networks collected using a postal questionnaire, alongside face-to-face interviewing. Follow-up at 12 months via postal questionnaire using a self-report grid for network members identified at baseline.
Analysis: Multiple regression analysis of relationships between health status, self-management and health economics outcomes, and characteristics of patients’ social networks.
Results: Findings indicated that: (1) social involvement with a wider variety of people and groups supports personal self-management and physical and mental well-being; (2) support work undertaken by personal networks expands in accordance with health needs helping people to cope with their condition; (3) network support substitutes for formal care and can produce substantial saving in traditional health service utilisation costs. Health service costs were significantly (p0.01) reduced for patients receiving greater levels of illness work through their networks.
Conclusions: Support for self-management which achieves desirable policy outcomes should be construed less as an individualised set of actions and behaviour and more as a social network phenomenon. This study shows the need for a greater focus on harnessing and sustaining the capacity of networks and the importance of social involvement with community groups and resources for producing a more desirable and cost-effective way of supporting long term illness management
Rebounding from disruptive events: Business recovery following the Northridge earthquake
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