628 research outputs found
MG1-688432: A Peculiar Variable System
The short period variable star MG1-688432 has been discovered to exhibit
occasional extremely high energy optical outbursts as high as 10^31 joules.
Outbursts are typically of several hours duration. These events are often
highly structured, resembling sequential associated releases of energy. Twenty
years of time sequence photometry is presented, indicating a basic sinusoidal
light curve of mean period 6.65d, with some phase shifting and long-term
temporal trends in amplitude and mean brightness. Spectroscopy reveals a
peculiar star, best resembling a K3 subgiant that has evolved off the main
sequence moderately red-ward of the giant branch. Spectroscopic and radial
velocity analyses indicate a binary system orbiting its barycenter with an
unseen companion to the K3IV primary. This is not an eclipsing system with the
inclination of the orbit precluding eclipse by the secondary. The system is at
a distance of 1.5kpc and analysis of GAIA observations leads to the conclusion
that the HR diagram position of MG1-688432 is established by an intrinsic
feature of the system, most likely either the stellar evolutionary state of the
observed star or the presence of small (non-gray) dust within the system. Two
mechanisms that might give rise to the system are 1) impacts with tidally
disrupted planetary debris, and 2) magnetically induced chromospheric activity.
An intriguing idea that requires further investigation suggests that the unseen
companion is perhaps a white dwarf star which has encountered a planet and
tidally shredded it to produce a debris and dust veil that modulates the
brightness of the primary.Comment: 74 pages, 36 figures, submitted to Astrophysical Journal Supplemen
A stepped wedge cluster randomized control trial of dried blood spot testing to improve the uptake of hepatitis C antibody testing within UK prisons
Background: The prevalence of hepatitis C (HCV) is elevated within prison populations, yet diagnosis in prisons remains low. Dried blood spot testing (DBST) is a simple procedure for the detection of HCV antibodies; its impact on testing in the prison context is unknown. Methods: We carried out a stepped-wedge cluster-randomized control trial of DBST for HCV among prisoners within five male prisons and one female prison. Each prison was a separate cluster. The order in which the intervention (training in use of DBST for HCV testing and logistic support) was introduced was randomized across clusters. The outcome measure was the HCV testing rate by prison. Imputation analysis was carried out to account for missing data. Planned and actual intervention times differed in some prisons; data were thus analysed by intention to treat (ITT) and by observed step times. Results: There was insufficient evidence of an effect of the intervention on testing rate using either the ITT intervention time (OR: 0.84; 95% CI: 0.68�1.03; P = 0.088) or using the actual intervention time (OR: 0.86; 95% CI: 0.71�1.06; P = 0.153). This was confirmed by the pooled results of five imputed data sets. Conclusions: DBST as a stand-alone intervention was insufficient to increase HCV diagnosis within the UK prison setting. Factors such as staff training and allocation of staff time for regular clinics are key to improving service delivery. We demonstrate that prisons can conduct rigorous studies of new interventions, but data collection can be problematic. Trial registration: International Standard Randomized Controlled Trial Number Register (ISRCTN number ISRCTN05628482)
Correlated variability in the blazar 3C 454.3
The blazar 3C 454.3 was revealed by the Fermi Gamma-ray Space Telescope to be
in an exceptionally high flux state in July 2008. Accordingly, we performed a
multi-wavelength monitoring campaign on this blazar using IR and optical
observations from the SMARTS telescopes, optical, UV and X-ray data from the
Swift satellite, and public-release gamma-ray data from Fermi. We find an
excellent correlation between the IR, optical, UV and gamma-ray light curves,
with a time lag of less than one day. The amplitude of the infrared variability
is comparable to that in gamma-rays, and larger than at optical or UV
wavelengths. The X-ray flux is not strongly correlated with either the
gamma-rays or longer wavelength data. These variability characteristics find a
natural explanation in the external Compton model, in which electrons with
Lorentz factor gamma~10^(3-4) radiate synchrotron emission in the
infrared-optical and also scatter accretion disk or emission line photons to
gamma-ray energies, while much cooler electrons (gamma~10^(1-2)) produce X-rays
by scattering synchrotron or other ambient photons.Comment: 7 pages, 3 figures, submitted to ApJ Letter
The Prevalence of Children with a History of Sexual Abuse Hospitalized in the Psychiatric Setting
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72548/1/j.1744-6171.1991.tb00489.x.pd
The Mass-Radius(-Rotation?) Relation for Low-Mass Stars
The fundamental properties of low-mass stars are not as well understood as
those of their more massive counterparts. The best method for constraining
these properties, especially masses and radii, is to study eclipsing binary
systems, but only a small number of late-type (M0 or later) systems have been
identified and well-characterized to date. We present the discovery and
characterization of six new M dwarf eclipsing binary systems. The twelve stars
in these eclipsing systems have masses spanning 0.38-0.59 Msun and orbital
periods of 0.6--1.7 days, with typical uncertainties of ~0.3% in mass and
0.5--2.0% in radius. Combined with six known systems with high-precision
measurements, our results reveal an intriguing trend in the low-mass regime.
For stars with M=0.35-0.80 Msun, components in short-period binary systems (P<1
day; 12 stars) have radii which are inflated by up to 10% (mean=4.8+/-1.0%)
with respect to evolutionary models for low-mass main-sequence stars, whereas
components in longer-period systems (>1.5 days; 12 stars) tend to have smaller
radii (mean=1.7+/-0.7%). This trend supports the hypothesis that short-period
systems are inflated by the influence of the close companion, most likely
because they are tidally locked into very high rotation speeds that enhance
activity and inhibit convection. In summary, very close binary systems are not
representative of typical M dwarfs, but our results for longer-period systems
indicate that the evolutionary models are broadly valid in the M~0.35-0.80 Msun
regime.Comment: Accepted to ApJ; 21 pages, 10 figures, 8 tables in emulateapj format.
The full contents of Table 4 are included in the submission as tab4.tx
Centennial-scale reductions in nitrogen availability in temperate forests of the United States
Forests cover 30% of the terrestrial Earth surface and are a major component of the global carbon
(C) cycle. Humans have doubled the amount of global reactive nitrogen (N), increasing deposition of N onto forests worldwide. However, other global changes—especially climate change and elevated atmospheric carbon dioxide concentrations—are increasing demand for N, the element limiting primary productivity in temperate forests, which could be reducing N availability. To determine the long-term, integrated effects of global changes on forest N cycling, we measured stable N isotopes in wood, a proxy for N supply relative to demand, on large spatial and temporal scales across the continental U.S.A. Here, we show that forest N availability has generally declined across much of the U.S. since at least 1850 C.E. with cool, wet forests demonstrating the greatest declines. Across sites, recent trajectories of N availability were independent of recent atmospheric N deposition rates, implying a minor role for modern N deposition on the trajectory of N status of North American forests. Our results demonstrate that current trends of global changes are likely to be consistent with forest oligotrophication into theforeseeable future, further constraining forest C fixation and potentially storage
The moisture response of soil heterotrophic respiration: Interaction with soil properties
Soil moisture is of primary importance for predicting the evolution of soil carbon stocks and fluxes, both because it strongly controls organic matter decomposition and because it is predicted to change at global scales in the following decades. However, the soil functions used to model the heterotrophic respiration response to moisture have limited empirical support and introduce an uncertainty of at least 4% in global soil carbon stock predictions by 2100. The necessity of improving the representation of this relationship in models has been highlighted in recent studies. Here we present a data-driven analysis of soil moisture-respiration relations based on 90 soils. With the use of linear models we show how the relationship between soil heterotrophic respiration and different measures of soil moisture is consistently affected by soil properties. The empirical models derived include main effects and moisture interaction effects of soil texture, organic carbon content and bulk density. When compared to other functions currently used in different soil biogeochemical models, we observe that our results can correct biases and reconcile differences within and between such functions. Ultimately, accurate predictions of the response of soil carbon to future climate scenarios will require the integration of soil-dependent moisture-respiration functions coupled with realistic representations of soil water dynamic
Convergence Of Soil Nitrogen Isotopes Across Global Climate Gradients
Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems, and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the N-15 : N-14 ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling. In synthesizing data from over 6000 soil samples, we show strong global relationships among soil N isotopes, mean annual temperature (MAT), mean annual precipitation (MAP), and the concentrations of organic carbon and clay in soil. In both hot ecosystems and dry ecosystems, soil organic matter was more enriched in N-15 than in corresponding cold ecosystems or wet ecosystems. Below a MAT of 9.8 degrees C, soil delta N-15 was invariant with MAT. At the global scale, soil organic C concentrations also declined with increasing MAT and decreasing MAP. After standardizing for variation among mineral soils in soil C and clay concentrations, soil delta N-15 showed no consistent trends across global climate and latitudinal gradients. Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss.
- …