803 research outputs found
An Experiment Combining Specialization with Abstract Interpretation
It was previously shown that control-flow refinement can be achieved by a
program specializer incorporating property-based abstraction, to improve
termination and complexity analysis tools. We now show that this purpose-built
specializer can be reconstructed in a more modular way, and that the previous
results can be achieved using an off-the-shelf partial evaluation tool, applied
to an abstract interpreter. The key feature of the abstract interpreter is the
abstract domain, which is the product of the property-based abstract domain
with the concrete domain. This language-independent framework provides a
practical approach to implementing a variety of powerful specializers, and
contributes to a stream of research on using interpreters and specialization to
achieve program transformations.Comment: In Proceedings VPT/HCVS 2020, arXiv:2008.0248
Racial Disparities in Drug Court Graduation Rates: The Role of Recovery Support Groups and Environments
There are more than 3,000 drug courts in the United States, and research has demonstrated that, in some drug courts, African American participants are less likely to graduate than their White counterparts. Quantitative studies have documented the problem, but qualitative studies are needed to develop an in-depth understanding of this phenomenon through participants’ experiences. This qualitative study asked African American participants (n = 31) about their lived experiences in drug court to develop insight into the factors that might contribute to racial disparities in drug court outcomes. African Americans had favorable views toward both mandated and natural recovery support groups, and they felt that participating in these support groups increased their likelihood of graduating drug court. Conversely, African Americans felt that a barrier to graduating drug court was their environments, mainly risk factors posed by family, neighborhoods, and peers. Implications for drug court practice are discussed
Evidence of a vertical kinematic oscillation beyond the Radcliffe Wave
The Radcliffe Wave (RW) is a recently discovered sinusoidal vertical feature
of dense gas in the proximity of the Sun. In the disk plane, it is aligned with
the Local Arm. However, the origin of its vertical undulation is still unknown.
This study constrains the kinematics of the RW, using young stars and open
clusters as tracers, and explores the possibility of this oscillation being
part of a more extended vertical mode. We study the median vertical velocity
trends of the young stars and clusters along with the RW and extend it further
to the region beyond it. We discover a kinematic wave in the Galaxy, distinct
from the warp, with the amplitude of oscillation depending on the age of the
stellar population. We perform a similar analysis in the N-body simulation of a
satellite as massive as the Sagittarius dwarf galaxy impacting the galactic
disk. When projected in the plane, the spiral density wave induced by the
satellite impact is aligned with the RW, suggesting that both may be the
response of the disk to an external perturbation. However, the observed
kinematic wave is misaligned. It appears as a kinematic wave travelling
radially, winding up faster than the density wave matched by the RW,
questioning its origin. If a satellite galaxy is responsible for this kinematic
wave, we predict the existence of a vertical velocity dipole that should form
across the disk and this may be measurable with the upcoming Gaia DR3 and DR4.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Supernova Remnants in the Fossil Starburst in M82
We report the discovery of ten compact H-alpha-bright sources in the
post-starburst region northeast of the center of M82, ``M82 B.'' These objects
have H alpha luminosities and sizes consistent with Type II supernova remnants
(SNRs). They fall on the same H alpha surface brightness-diameter (Sigma-D)
relation defined by SNRs in other nearby star-forming galaxies, with the M82
candidates lying preferentially at the small diameter end. These are the first
candidates for optically-visible SNRs in M82 outside the heavily obscured
central starburst within ~250 pc from the galactic center. If these sources are
SNRs, they set an upper limit to the end of the starburst in region ``B2,''
about 500 pc from the galaxy's core, of ~50 Myr. Region ``B1,'' about 1000 pc
from the core, lacks good SNR candidates and is evidently somewhat older. This
suggests star formation in the galaxy has propagated inward toward the
present-day intense starburst core.Comment: Re-submitted to AJ, referee's comments taken into account, 15 pages
LaTeX preprint style, 4 postscript figures; full-resolution figures available
from http://www.astro.virginia.edu/~rd7a/snrs/ Changes: minor textual changes
and orientation/axes of Fig.
The Milky Way's Kiloparsec Scale Wind: A Hybrid Cosmic-Ray and Thermally Driven Outflow
We apply a wind model, driven by combined cosmic-ray and thermal-gas
pressure, to the Milky Way, and show that the observed Galactic diffuse soft
X-ray emission can be better explained by a wind than by previous static gas
models. We find that cosmic-ray pressure is essential to driving the observed
wind. Having thus defined a "best-fit" model for a Galactic wind, we explore
variations in the base parameters and show how the wind's properties vary with
changes in gas pressure, cosmic-ray pressure and density. We demonstrate the
importance of cosmic rays in launching winds, and the effect cosmic rays have
on wind dynamics. In addition, this model adds support to the hypothesis of
Breitschwerdt and collaborators that such a wind may help explain the
relatively small gradient observed in gamma-ray emission as a function of
galactocentric radius.Comment: 14 pages, 11 figures; Accepted to Ap
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