2,563 research outputs found
Radiation spectra and polarization in magnetar bursts
We present Monte Carlo simulations of radiative transfer in magnetar
atmospheres. We include the effects of vacuum polarization, electron and proton
scattering, and free-free absorption. Simulations are performed for the
atmosphere model with the magnetic field perpendicular and also tilted with
respect to the neutron star surface, and we show that the average spectrum does
not strongly depend on the orientation of the magnetic field. We investigate
the region of the parameter space where the vacuum absorption-like feature
appears in the spectrum and we analyze the shape of the proton cyclotron line.
Our results indicate that the existence of the vacuum polarization feature
should be a general attribute of soft gamma-ray repeaters burst spectra,
provided that the energy release takes place at the sufficiently dense region,
and the atmosphere scaleheight is large enough. We discuss the existence of
such a feature in recent observational data on these sources.Comment: submitted to Ap
Can attention to the intestinal microbiota improve understanding and treatment of anorexia nervosa?
Anorexia nervosa (AN) is characterized by severe dietary restriction or other weight loss behaviors and exhibits the highest mortality rate of any psychiatric disorder. Therapeutic renourishment in AN is founded primarily on clinical opinion and guidelines, with a weak evidence base. Genetic factors do not fully account for the etiology of AN, and non-genetic factors that contribute to the onset and persistence of this disease warrant investigation. Compelling evidence that the intestinal microbiota regulates adiposity and metabolism, and more recently, anxiety behavior, provides a strong rationale for exploring the role of this complex microbial community in the onset, maintenance of, and recovery from AN. This review explores the relationship between the intestinal microbiota and AN and a potential role for this enteric microbial community as a therapy for this severe illness
Double Compact Objects III: Gravitational Wave Detection Rates
The unprecedented range of second-generation gravitational-wave (GW)
observatories calls for refining the predictions of potential sources and
detection rates. The coalescence of double compact objects (DCOs)---i.e.,
neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black
hole-black hole (BH-BH) binary systems---is the most promising source of GWs
for these detectors. We compute detection rates of coalescing DCOs in
second-generation GW detectors using the latest models for their cosmological
evolution, and implementing inspiral-merger-ringdown (IMR) gravitational
waveform models in our signal-to-noise ratio calculations. We find that: (1)
the inclusion of the merger/ringdown portion of the signal does not
significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by
a factor for BH-BH systems; (2) in almost all of our models BH-BH
systems yield by far the largest rates, followed by NS-NS and BH-NS systems,
respectively, and (3) a majority of the detectable BH-BH systems were formed in
the early Universe in low-metallicity environments. We make predictions for the
distributions of detected binaries and discuss what the first GW detections
will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure
Genetic epidemiology of eating disorders
We capture recent findings in the field of genetic epidemiology of eating disorders. As analytic techniques evolve for twin, population, and molecular genetics, new findings emerge at an accelerated pace. We present the current status of knowledge regarding the role of genetic and environmental factors that influence risk for eating disorders
Distribution of compact object mergers around galaxies
Compact object mergers are one of the currently favored models for the origin
of GRBs. The discovery of optical afterglows and identification of the nearest,
presumably host, galaxies allows the analysis of the distribution of burst
sites with respect to these galaxies. Using a model of stellar binary evolution
we synthesize a population of compact binary systems which merge within the
Hubble time. We include the kicks in the supernovae explosions and calculate
orbits of these binaries in galactic gravitational potentials. We present the
resulting distribution of merger sites and discuss the results in the framework
of the observed GRB afterglows.Comment: 8 pages, 5 figures, submitted to MNRA
Initial Populations of Black Holes in Star Clusters
Using an updated population synthesis code we study the formation and
evolution of black holes (BHs) in young star clusters following a massive
starburst. This study continues and improves on the initial work described by
Belczynski, Sadowski & Rasio (2004). In our new calculations we account for the
possible ejections of BHs and their progenitors from clusters because of natal
kicks imparted by supernovae and recoil following binary disruptions. The
results indicate that the properties of both retained BHs in clusters and
ejected BHs (forming a field population) depend sensitively on the depth of the
cluster potential. In particular, most BHs ejected from binaries are also
ejected from clusters with central escape speeds Vesc < 100 km/s. Conversely,
most BHs remaining in binaries are retained by clusters with Vesc > 50 km/s.
BHs from single star evolution are also affected significantly: about half of
the BHs originating from primordial single stars are ejected from clusters with
Vesc < 50 km/s. Our results lay a foundation for theoretical studies of the
formation of BH X-ray binaries in and around star clusters, including possible
ultra-luminous sources, as well as merging BH--BH binaries detectable with
future gravitational-wave observatories.Comment: 35 pages, 8 tables, 17 figures; resubmitted to ApJ (revised version
The Gut-Brain Axis in Healthy Females: Lack of Significant Association between Microbial Composition and Diversity with Psychiatric Measures
This study examined associations between the composition and diversity of the intestinal microbiota and measures of depression, anxiety, eating disorder psychopathology, stress, and personality in a group of healthy adult females
Black hole - neutron star mergers: the first mass gap and kilonovae
Observations of X-ray binaries indicate a dearth of compact objects in the
mass range from and the existence of this (first mass)
gap has been used to advance our understanding of the engines behind
core-collapse supernovae. LIGO/Virgo observations provide an independent
measure of binary compact remnant masses and several candidate first mass gap
objects (either NS or BH) were observed in the O3 science run. We study the
formation of BH-NS mergers in the framework of isolated classical binary
evolution. We use population synthesis method to evolve binary stars
(Population I and II) across cosmic time. The predicted BH-NS mergers from the
isolated classical binary evolution are sufficiently abundant (
) in the local Universe () to produce the observed
LIGO/Virgo candidates. We present results on the NS to BH mass ratios
( ) in merging systems, showing that although systems
with a mass ratio as low as can exist, only a small fraction () of LIGO/Virgo detectable BH-NS mergers have mass ratios below
. We find that with appropriate constraints on the (delayed) supernova
engine of LIGO/Virgo BH-NS mergers may host at least one compact
object in the gap. The uncertainties in the processes behind compact object
formation imply that the fraction of BH-NS systems ejecting mass during the
merger is . In our reference we find that only of
BH-NS mergers will have any mass ejection, and about the same percentage would
produce kilonova bright enough to have a chance to be detected even with a
large (Subaru-class) m telescope. Interestingly, all these mergers will have
both BH and NS in the first mass gap.Comment: 14 pages, 12 figure
Prospective associations between childhood social communication processes and adolescent eating disorder symptoms in an epidemiological sample
Deficits in social cognition and communication, the processes associated with human social behavior and interaction, have been described in individuals with eating disorder psychopathology. The current study examined whether social communication characteristics present in middle childhood (ages 8–14) were associated with eating disorder behaviors, cognitions, and diagnoses across adolescence (ages 14–18) in a large, population-based sample. Participants (N = 4864) were children enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC), a population-based, prospective study of women and their children. Regression methods tested prospective associations between social functioning using a facial emotion recognition task and parentally reported social communication symptoms (or difficulties), measured by the Social Communication Disorder Checklist (SCDC), with eating disorder symptoms and diagnoses. Misattribution of faces as sad or angry at age 8.5 was associated with purging and anorexia nervosa diagnosis at age 14, respectively, among girls. Furthermore, autistic-like social communication difficulties during middle childhood were associated with bulimia nervosa symptoms during adolescence among both girls and boys. Results did not support global associations between measured social communication deficits and eating disorder risk in this sample, but specific difficulties with facial emotion recognition and social communication may enhance the risk for disordered eating behaviors
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