4,870 research outputs found
A New Estimate of the Cutoff Value in the Bak-Sneppen Model
We present evidence that the Bak-Sneppen model of evolution on vertices
requires iterates to reach equilibrium. This is substantially more than
previous authors suggested (on the order of ). Based on that estimate, we
present a novel algorithm inspired by previous rank-driven analyses of the
model allowing for direct simulation of the model with populations of up to for iterations. These extensive simulations suggest a
cutoff value of , a value slightly lower than
previously estimated yet still distinctly above . We also study how the
cutoff values at finite approximate the conjectured value at
. Assuming , we find that
, which is significantly lower than previous estimates
().Comment: 18 figures, 12 page
Unveiling the gas kinematics at 10 AU scales in high-mass star-forming regions (Milliarcsecond structure of 6.7 GHz methanol masers)
This work presents a study of the milliarcsecond structure of the 6.7 GHz
methanol masers at high-velocity resolution (0.09 km s^(-1)) in four high-mass
star-forming regions: G16.59-0.05, G23.01-0.41, IRAS20126+4104, and AFGL5142.
We studied these sources by means of multi-epoch VLBI observations in the 22
GHz water and 6.7 GHz methanol masers, to determine the 3-D gas kinematics
within a few thousand AU from the (proto)star. The present work exploits the
6.7 GHz maser data collected so far to investigate the milliarcsecond structure
of this maser emission at high-velocity resolution. Most of the detected 6.7
GHz maser features present an ordered (linear, or arc-like) distribution of
maser spots on the plane of the sky, together with a regular variation in the
spot LSR velocity (V_LSR) with position. Typical values for the amplitude of
the V_LSR gradients (defined in terms of the derivative of the spot V_LSR with
position) are found to be 0.1-0.2 km s^(-1) mas^(-1). In each of the four
target sources, the orientation and the amplitude of most of the feature V_LSR
gradients remain remarkably stable in time, on timescales of (at least) several
years. We also find that the data are consistent with having the V_LSR
gradients and proper motion vectors in the same direction on the sky,
considered the measurement uncertainties. The time persistency, the ordered
angular and spatial distribution, and the orientation generally similar to the
proper motions, altogether suggest a kinematical interpretation for the origin
of the 6.7 GHz maser V_LSR gradients. This work shows that the organized
motions (outflow, infall, and rotation) revealed by the (22 GHz water and 6.7
GHz methanol) masers on large scales (~100-1000 AU) also persist to very small
(~10 AU) scales.Comment: 14 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics Journa
New Records of Hyperiidea (Crustacea: Amphipoda) from the North Central Gulf of Mexico
Records of 54 species of amphipods of the suborder Hyperiidea from the Gulf of Mexico are presented. Forty-seven species are recorded from the Gulf for the first time. Previous records of occurrence in the Gulf of Mexico, Caribbean Sea, and associated North Atlantic waters are provided for each species
New Records of Hyperiidea (Crustacea: Amphipoda) from the North Central Gulf of Mexico
Records of 54 species of amphipods of the suborder Hyperiidea from the Gulf of Mexico are presented. Forty-seven species are recorded from the Gulf for the first time. Previous records of occurrence in the Gulf of Mexico, Caribbean Sea, and associated North Atlantic waters are provided for each species
A combinatorial approach to knot recognition
This is a report on our ongoing research on a combinatorial approach to knot
recognition, using coloring of knots by certain algebraic objects called
quandles. The aim of the paper is to summarize the mathematical theory of knot
coloring in a compact, accessible manner, and to show how to use it for
computational purposes. In particular, we address how to determine colorability
of a knot, and propose to use SAT solving to search for colorings. The
computational complexity of the problem, both in theory and in our
implementation, is discussed. In the last part, we explain how coloring can be
utilized in knot recognition
Interpretation and the Constraints on International Courts
This paper argues that methodologies of interpretation do not do what they promise – they do not constrain interpretation by providing neutral steps that one can follow in finding out a meaning of a text – but nevertheless do their constraining work by being part of what can be described as the legal practice
VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41
The present paper focuses on the high-mass star-forming region G23.01-0.41.
Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced
observations of the three most powerful maser species in G23.01-0.41: H2O at
22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1
epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (<
0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3
and 3.6 cm. Results: We have detected H2O, CH3OH, and OH maser emission
clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW,
from which emerges a massive 12CO outflow, elongated NE-SW, extended up to the
pc-scale. Although the three maser species show a clearly different spatial and
velocity distribution and sample distinct environments around the massive YSO,
the spatial symmetry and velocity field of each maser specie can be explained
in terms of expansion from a common center, which possibly denotes the position
of the YSO driving the maser motion. Water masers trace both a fast shock (up
to 50 km/s) closer to the YSO, powered by a wide-angle wind, and a slower (20
km/s) bipolar jet, at the base of the large-scale outflow. Since the compact
free-free emission is found offset from the putative location of the YSO along
a direction consistent with that of the maser jet axis, we interpret the radio
continuum in terms of a thermal jet. The velocity field of methanol masers can
be explained in terms of a composition of slow (4 km/s in amplitude) motions of
radial expansion and rotation about an axis approximately parallel to the maser
jet. Finally, the distribution of line of sight velocities of the hydroxyl
masers suggests that they can trace gas less dense (n(H2) < 10^6 cm^-3) and
more distant from the YSO than that traced by the water and methanol masers,
which is expanding toward the observer. (Abridged)Comment: 23 pages, 8 figures, 4 tables, accepted by Astronomy and Astrophysic
Severe Coronavirus Disease 2019 Infection in an Adolescent Patient After Hematopoietic Stem Cell Transplantation
© 2020 American College of Chest Physicians Infection with the severe acute respiratory syndrome coronavirus 2 causes severe acute lung injury in approximately 5% of infected adults, but few reports have been made of severe pediatric disease. We present an adolescent patient who contracted severe acute respiratory syndrome coronavirus 2 one week after a paternal haplo-identical hematopoietic stem cell transplant, with development of severe hyperferritinemic acute lung injury and macrophage activation-like syndrome. We present her case and a comparison of her laboratory data with those of a cohort of pediatric patients with coronavirus disease 2019 without severe disease
Observing---and Imaging---Active Galactic Nuclei with the Event Horizon Telescope
Originally developed to image the shadow region of the central black hole in
Sagittarius A* and in the nearby galaxy M87, the Event Horizon Telescope (EHT)
provides deep, very high angular resolution data on other AGN sources too. The
challenges of working with EHT data have spurred the development of new image
reconstruction algorithms. This work briefly reviews the status of the EHT and
its utility for observing AGN sources, with emphasis on novel imaging
techniques that offer the promise of better reconstructions at 1.3 mm and other
wavelengths.Comment: 10 pages, proceedings contribution for Blazars through Sharp
Multi-Wavelength Eyes, submitted to Galaxie
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