431 research outputs found
Ferret brain possesses young interneuron collections equivalent to human postnatal migratory streams.
The human early postnatal brain contains late migratory streams of immature interneurons that are directed to cortex and other focal brain regions. However, such migration is not observed in rodent brain, and whether other small animal models capture this aspect of human brain development is unclear. Here, we investigated whether the gyrencephalic ferret cortex possesses human-equivalent postnatal streams of doublecortin positive (DCX+) young neurons. We mapped DCX+ cells in the brains of ferrets at P20 (analogous to human term gestation), P40, P65, and P90. In addition to the rostral migratory stream, we identified three populations of young neurons with migratory morphology at P20 oriented toward: (a) prefrontal cortex, (b) dorsal posterior sigmoid gyrus, and (c) occipital lobe. These three neuronal collections were all present at P20 and became extinguished by P90 (equivalent to human postnatal age 2 years). DCX+ cells in such collections all expressed GAD67, identifying them as interneurons, and they variously expressed the subtype markers SP8 and secretagogin (SCGN). SCGN+ interneurons appeared in thick sections to be oriented from white matter toward multiple cortical regions, and persistent SCGN-expressing cells were observed in cortex. These findings indicate that ferret is a suitable animal model to study the human-relevant process of late postnatal cortical interneuron integration into multiple regions of cortex
Impact of Medicaid expansion on smoking prevalence and quit attempts among those newly eligible, 2011–2019
Introduction: Low-income populations have higher rates of smoking and are disproportionately affected by smoking-related illnesses. This study assessed the long-term impact of increased coverage for tobacco cessation through Medicaid expansion on past-year quit attempts and prevalence of cigarette smoking.
Methods: Using data from CDC's annual Behavioral Risk Factor Surveillance System 2011-2019, we conducted difference-in-difference regression analyses to compare changes in smoking prevalence and past-year quit attempts in expansion states versus non-expansion states. Our sample included non-pregnant adults (18-64 years old) without dependent children with incomes at or below 100% of the Federal Poverty Level (FPL).
Results: Regression analyses indicate that Medicaid expansion was associated with reduced smoking prevalence in the first two years post-expansion (β=-0.019, p=0.04), but that this effect was not maintained at longer follow-up periods (β=-0.006, p=0.49). Results of regression analyses also suggest that Medicaid expansion does not significantly impact quit attempts in the short-term (β=-0.013, p=0.52) or at longer term follow-up (β=-0.026, p=0.08).
Conclusions: Expanded coverage for tobacco cessation services through Medicaid alone may not be enough to increase quit-attempts or sustain a reduction in overall prevalence of smoking in newly eligible populations over time. Medicaid programs should consider additional strategies, such as public education campaigns and removal of barriers, to support cessation among enrollees
Plane waves with weak singularities
We study a class of time dependent solutions of the vacuum Einstein equations
which are plane waves with weak null singularities. This singularity is weak in
the sense that though the tidal forces diverge at the singularity, the rate of
divergence is such that the distortion suffered by a freely falling observer
remains finite. Among such weak singular plane waves there is a sub-class which
do not exhibit large back reaction in the presence of test scalar probes.
String propagation in these backgrounds is smooth and there is a natural way to
continue the metric beyond the singularity. This continued metric admits string
propagation without the string becoming infinitely excited. We construct a one
parameter family of smooth metrics which are at a finite distance in the space
of metrics from the extended metric and a well defined operator in the string
sigma model which resolves the singularity.Comment: 22 pages, Added references and clarifying comment
Jet substructure at the Large Hadron Collider
Jet substructure has emerged to play a central role at the Large Hadron Collider, where it has provided numerous innovative ways to search for new physics and to probe the standard model, particularly in extreme regions of phase space. This review focuses on the development and use of state-of-the-art jet substructure techniques by the ATLAS and CMS experiments
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
We propose a cosmological scenario in which the hot big bang universe is
produced by the collision of a brane in the bulk space with a bounding orbifold
plane, beginning from an otherwise cold, vacuous, static universe. The model
addresses the cosmological horizon, flatness and monopole problems and
generates a nearly scale-invariant spectrum of density perturbations without
invoking superluminal expansion (inflation). The scenario relies, instead, on
physical phenomena that arise naturally in theories based on extra dimensions
and branes. As an example, we present our scenario predominantly within the
context of heterotic M-theory. A prediction that distinguishes this scenario
from standard inflationary cosmology is a strongly blue gravitational wave
spectrum, which has consequences for microwave background polarization
experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde
Phase Structure and Compactness
In order to study the influence of compactness on low-energy properties, we
compare the phase structures of the compact and non-compact two-dimensional
multi-frequency sine-Gordon models. It is shown that the high-energy scaling of
the compact and non-compact models coincides, but their low-energy behaviors
differ. The critical frequency at which the sine-Gordon model
undergoes a topological phase transition is found to be unaffected by the
compactness of the field since it is determined by high-energy scaling laws.
However, the compact two-frequency sine-Gordon model has first and second order
phase transitions determined by the low-energy scaling: we show that these are
absent in the non-compact model.Comment: 21 pages, 5 figures, minor changes, final version, accepted for
publication in JHE
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The DEEP Groth Strip Galaxy Redshift Survey. VIII. The Evolution of Luminous Field Bulges at Redshift z ~ 1
We present a sample of over 50 luminous field bulges (including ellipticals)
found in the Groth Strip Survey (GSS), with 0.73< z < 1.04 and with bulge
magnitudes I <= 23. The exponential disk light is removed via decomposition of
HST images using GIM2D. We find that 85% of these bulges are nearly as red as
local E/S0's and have a shallow slope and a small color dispersion in the
color-luminosity relation, suggesting roughly coeval formation. The surface
brightnesses of these bulges are about 1 mag higher than local bulges. These
results are explained adopting a "drizzling" scenario where a metal-rich early
formation is later polluted by small amounts of additional star formation.
Almost all disks have the same or bluer colors than their accompanying bulges,
regardless of the bulge-disk ratio and bulge luminosity, as expected from
semi-analytic hierarchical galaxy formation models. We present evidence that
the few blue bulge candidates are not likely to be genuine blue ellipticals or
bulges. Our deeper, more extensive, and less disk-contaminated observations
challenge prior claims that 30% to 50% of field bulges or ellipticals are in a
blue, star-forming phase at z < 1. We conclude that field bulges and
ellipticals at z ~ 1, like luminous early- type cluster galaxies at the same
redshift, are already dominated by metal-rich, old stellar populations that
have been fading from a formation epoch earlier than z ~ 1.5. (abridged)Comment: ApJS accepted, 106 pages, 10 figures. Figure 14 in JPEG format. Full
version available at http://deep.ucolick.org/publications.htm
The NANOGrav 11-Year Data Set: Arecibo Observatory Polarimetry And Pulse Microcomponents
We present the polarization pulse profiles for 28 pulsars observed with the
Arecibo Observatory by the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz.
These profiles represent some of the most sensitive polarimetric millisecond
pulsar profiles to date, revealing the existence of microcomponents (that is,
pulse components with peak intensities much lower than the total pulse peak
intensity). Although microcomponents have been detected in some pulsars
previously, we present microcomponents for PSRs B1937+21, J1713+0747, and
J2234+0944 for the first time. These microcomponents can have an impact on
pulsar timing, geometry, and flux density determination. We present rotation
measures for all 28 pulsars, determined independently at different observation
frequencies and epochs, and find the Galactic magnetic fields derived from
these rotation measures to be consistent with current models. These
polarization profiles were made using measurement equation template matching,
which allows us to generate the polarimetric response of the Arecibo
Observatory on an epoch-by-epoch basis. We use this method to describe its time
variability, and find that the polarimetric responses of the Arecibo
Observatory's 1.4 and 2.1 GHz receivers vary significantly with time.Comment: 41 pages, 20 figure
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