98 research outputs found
Soft-core baryon-baryon potentials for the complete baryon octet
SU(3) symmetry relations on the recently constructed hyperon-nucleon
potentials are used to develop potential models for all possible baryon-baryon
interaction channels. The main focus is on the interaction channels with total
strangeness S=-2, -3, and -4, for which no experimental data exist yet. The
potential models for these channels are based on SU(3) extensions of potential
models for the S=0 and S=-1 sectors, which are fitted to experimental data.
Although the SU(3) symmetry is not taken to be exact, the S=0 and S=-1 sectors
still provide the necessary constraints to fix all free parameters. The
potentials for the S=-2, -3, and -4 sectors, therefore, do not contain any
additional free parameters, which makes them the first models of this kind.
Various properties of the potentials are illustrated by giving results for
scattering lengths, bound states, and total cross sections.Comment: 22 pages RevTex, 6 postscript figure
Constraints on cosmic hemispherical power anomalies from quasars
Recent analyses of the cosmic microwave background (CMB) maps from the WMAP
satellite have uncovered evidence for a hemispherical power anomaly, i.e. a
dipole modulation of the CMB power spectrum at large angular scales with an
amplitude of +/-14 percent. Erickcek et al have put forward an inflationary
model to explain this anomaly. Their scenario is a variation on the curvaton
scenario in which the curvaton possesses a large-scale spatial gradient that
modulates the amplitude of CMB fluctuations. We show that this scenario would
also lead to a spatial gradient in the amplitude of perturbations sigma_8, and
hence to a dipole asymmetry in any highly biased tracer of the underlying
density field. Using the high-redshift quasars from the Sloan Digital Sky
Survey, we find an upper limit on such a gradient of |nabla
sigma_8|/sigma_8<0.027/r_{lss} (99% posterior probability), where r_{lss} is
the comoving distance to the last-scattering surface. This rules out the
simplest version of the curvaton spatial gradient scenario.Comment: matches JCAP accepted version (minor revisions
A systematic cross-search for radio/infrared counterparts of XMM-Newton sources
We present a catalog of cross-correlated radio, infrared and X-ray sources
using a very restrictive selection criteria with an IDL-based code developed by
us. The significance of the observed coincidences was evaluated through Monte
Carlo simulations of synthetic sources following a well-tested protocol. We
found 3320 coincident radio/X-ray sources with a high statistical significance
characterized by the sum of error-weighted coordinate differences. For 997 of
them, 2MASS counterparts were found. The percentage of chance coincidences is
less than 1%. X-ray hardness ratios of well-known populations of objects were
used to provide a crude representation of their X-ray spectrum and to make a
preliminary diagnosis of the possible nature of unidentified X-ray sources. The
results support the fact that the X-ray sky is largely dominated by Active
Galactic Nuclei at high galactic latitudes (|b| >= 10^\circ). At low galactic
latitudes (|b| <= 10^\circ) most of unidentified X-ray sources (~94%) lie at
|b| <= 2^\circ. This result suggests that most of the unidentified sources
found toward the Milky Way plane are galactic objects. Well-known and
unidentified sources were classified in different tables with their
corresponding radio/infrared and X-ray properties. These tables are intended as
a useful tool for researchers interested in particular identifications.Comment: Accepted for publication in Ap&SS. 47 pages, 10 figures. On-line
material: figures and table
An analysis of the FIR/RADIO Continuum Correlation in the Small Magellanic Cloud
The local correlation between far-infrared (FIR) emission and radio-continuum
(RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales
from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ~15 pc.
The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is
shown to be greatest in the most active star forming regions with a power law
slope of ~1.14 indicating that the RC emission increases faster than the FIR
emission. The slope of the other regions and the SMC are much flatter and in
the range of 0.63-0.85. The slopes tend to follow the thermal fractions of the
regions which range from 0.5 to 0.95. The thermal fraction of the RC emission
alone can provide the expected FIR/RC correlation. The results are consistent
with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray
electrons (CRe-s) diffusing away from the star forming regions. Since the CRe-s
appear to escape the SMC so readily, the results here may not provide support
for coupling between the local gas density and the magnetic field intensity.Comment: 19 pages, 7 Figure
Relativistic models of two low-luminosity radio jets: B2 0326+39 and B2 1553+24
We apply the intrinsically symmetrical, decelerating relativistic jet model
developed by Laing & Bridle for 3C 31 to deep, full-synthesis 8.4-GHz VLA
imaging of the two low-luminosity radio galaxies B2 0326+39 and B2 1553+24.
After some modifications to the functional forms used to describe the geometry,
velocity, emissivity and magnetic-field structure, these models can accurately
fit our data in both total intensity and linear polarization. We conclude that
the jets in B2 0326+39 and B2 1553+24 are at angles of 64 +/- 5 deg and 7.7 +/-
1.3 deg to the line of sight, respectively. In both objects, we find that the
jets decelerate from 0.7 - 0.8c to <0.2c over a distance of approximately 10
kpc, although in B2 1553+24 this transition occurs much further from the
nucleus than in B2 0326+39 or 3C 31. The longitudinal emissivity profiles can
be divided into sections, each fit accurately by a power law; the indices of
these power laws decrease with distance from the nucleus. The magnetic fields
in both objects are dominated by the longitudinal component in the
high-velocity regions close to the nucleus and by the toroidal component
further out, but B2 0326+39 also has a significant radial component at large
distances, whereas B2 1553+24 does not. Simple adiabatic models fail to fit the
emissivity variations in the regions of high velocity but provide good
descriptions of the emissivity after the jets have decelerated. Given the small
angle to the line of sight inferred for B2 1553+24, there should be a
significant population of similar sources at less extreme orientations. Such
objects should have long (>200 kpc), straight, faint jets and we show that
their true sizes are likely to have been underestimated in existing images.
(Slightly abridged.)Comment: 27 pages, 21 figures, accepted for publication in MNRA
Supermassive Black Hole Binaries: The Search Continues
Gravitationally bound supermassive black hole binaries (SBHBs) are thought to
be a natural product of galactic mergers and growth of the large scale
structure in the universe. They however remain observationally elusive, thus
raising a question about characteristic observational signatures associated
with these systems. In this conference proceeding I discuss current theoretical
understanding and latest advances and prospects in observational searches for
SBHBs.Comment: 17 pages, 4 figures. To appear in the Proceedings of 2014 Sant Cugat
Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
Global CO2 emissions from dry inland waters share common drivers across ecosystems
Many inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey covering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle
A Person-Centered Approach to Poststroke Care: The COMprehensive Post-Acute Stroke Services Model
Many individuals who have had a stroke leave the hospital without postacute care services in place. Despite high risks of complications and readmission, there is no standard in the United States for postacute stroke care after discharge home. We describe the rationale and methods for the development of the COMprehensive Post-Acute Stroke Services (COMPASS) care model and the structure and quality metrics used for implementation. COMPASS, an innovative, comprehensive extension of the TRAnsition Coaching for Stroke (TRACS) program, is a clinician-led quality improvement model providing early supported discharge and transitional care for individuals who have had a stroke and have been discharged home. The effectiveness of the COMPASS model is being assessed in a cluster-randomized pragmatic trial in 41 sites across North Carolina, with a recruitment goal of 6,000 participants. The COMPASS model is evidence based, person centered, and stakeholder driven. It involves identification and education of eligible individuals in the hospital; telephone follow-up 2, 30, and 60 days after discharge; and a clinic visit within 14 days conducted by a nurse and advanced practice provider. Patient and caregiver self-reported assessments of functional and social determinants of health are captured during the clinic visit using a web-based application. Embedded algorithms immediately construct an individualized care plan. The COMPASS model's pragmatic design and quality metrics may support measurable best practices for postacute stroke care
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