589 research outputs found
r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers
We consider hot accretion disk outflows from black hole - neutron star
mergers in the context of the nucleosynthesis they produce. We begin with a
three dimensional numerical model of a black hole - neutron star merger and
calculate the neutrino and antineutrino fluxes emitted from the resulting
accretion disk. We then follow the element synthesis in material outflowing the
disk along parameterized trajectories. We find that at least a weak r-process
is produced, and in some cases a main r-process as well. The neutron-rich
conditions required for this production of r-process nuclei stem directly from
the interactions of the neutrinos emitted by the disk with the free neutrons
and protons in the outflow.Comment: 10 pages, 4 figures, one table and additional references adde
Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. II. The reverse shock in two-dimensional simulations
After the initiation of the explosion of core-collapse supernovae, neutrinos
emitted from the nascent neutron star drive a supersonic baryonic outflow. This
neutrino-driven wind interacts with the more slowly moving, earlier supernova
ejecta forming a wind termination shock (or reverse shock), which changes the
local wind conditions and their evolution. Important nucleosynthesis processes
(alpha-process, charged-particle reactions, r-process, and vp-process) occur or
might occur in this environment. The nucleosynthesis depends on the long-time
evolution of density, temperature, and expansion velocity. Here we present
two-dimensional hydrodynamical simulations with an approximate description of
neutrino-transport effects, which for the first time follow the post-bounce
accretion, onset of the explosion, wind formation, and the wind expansion
through the collision with the preceding supernova ejecta. Our results
demonstrate that the anisotropic ejecta distribution has a great impact on the
position of the reverse shock, the wind profile, and the long-time evolution.
This suggests that hydrodynamic instabilities after core bounce and the
consequential asymmetries may have important effects on the
nucleosynthesis-relevant conditions in the neutrino-heated baryonic mass flow
from proto-neutron stars.Comment: 13 pages, 8 figures, accepted for publication in A&
The influence of collective neutrino oscillations on a supernova r-process
Recently, it has been demonstrated that neutrinos in a supernova oscillate
collectively. This process occurs much deeper than the conventional
matter-induced MSW effect and hence may have an impact on nucleosynthesis. In
this paper we explore the effects of collective neutrino oscillations on the
r-process, using representative late-time neutrino spectra and outflow models.
We find that accurate modeling of the collective oscillations is essential for
this analysis. As an illustration, the often-used "single-angle" approximation
makes grossly inaccurate predictions for the yields in our setup. With the
proper multiangle treatment, the effect of the oscillations is found to be less
dramatic, but still significant. Since the oscillation patterns are sensitive
to the details of the emitted fluxes and the sign of the neutrino mass
hierarchy, so are the r-process yields. The magnitude of the effect also
depends sensitively on the astrophysical conditions - in particular on the
interplay between the time when nuclei begin to exist in significant numbers
and the time when the collective oscillation begins. A more definitive
understanding of the astrophysical conditions, and accurate modeling of the
collective oscillations for those conditions, is necessary.Comment: 27 pages, 10 figure
Peritonitis secondary to traumatic duodenal laceration in the presence of a large pancreatic pseudocyst: a case report
<p>Abstract</p> <p>Introduction</p> <p>A pancreatic pseudocyst is a common sequela of severe acute pancreatitis. Commonly, it presents with abdominal pain and a mass in the epigastrium several weeks after the acute episode and can be managed conservatively, endoscopically or surgically. We report a patient with a pancreatic pseudocyst awaiting endoscopic therapy who developed a life-threatening complication following a rather innocuous trauma to the abdomen.</p> <p>Case presentation</p> <p>A 23-year-old Asian male student presented as an emergency with an acute abdomen a week after a minor trauma to his upper abdomen. The injury occurred when he was innocently punched in the abdomen by a friend. He experienced only moderate discomfort briefly at the time. His past medical history included coeliac disease and an admission four months previously with severe acute pancreatitis. He was hospitalized for 15 days; his pancreatitis was thought to be due to alcohol binge drinking on weekends. Ultrasound scanning showed no evidence of gallstone disease. Five days after the trauma, he became anorexic, lethargic and feverish and started vomiting bilious content. Seven days post-trauma, he presented to our emergency department with severe abdominal pain. An emergency laparotomy was performed where a transverse linear duodenal laceration was found at the junction of the first and second part of his duodenum, with generalized peritonitis. His stomach and duodenum were stretched over a large pancreatic pseudocyst posterior to his stomach. It was postulated that an incomplete duodenal injury (possibly a serosal tear) occurred following the initial minor trauma, which was followed by local tissue necrosis at the injury site resulting in a delayed presentation of generalized peritonitis.</p> <p>Conclusion</p> <p>This is the first reported case of a traumatic duodenal laceration following minor blunt trauma in the presence of a large pancreatic pseudocyst. Minor blunt abdominal trauma in a normal healthy adult would not be expected to result in a significant duodenal injury. In the presence of a large pseudocyst, however, the stretching of the duodenum over the pseudocyst had probably predisposed the duodenum to this injury. Patients awaiting therapeutic interventions for their pancreatic pseudocysts should be warned about this unusual but life-threatening risk following minor blunt abdominal trauma.</p
Simulation of merging binary neutron stars in full general relativity: case
We have performed 3D numerical simulations for merger of equal mass binary
neutron stars in full general relativity. We adopt a -law equation of
state in the form where P, , \varep and
are the pressure, rest mass density, specific internal energy, and the
adiabatic constant with . As initial conditions, we adopt models of
corotational and irrotational binary neutron stars in a quasi-equilibrium state
which are obtained using the conformal flatness approximation for the three
geometry as well as an assumption that a helicoidal Killing vector exists. In
this paper, we pay particular attention to the final product of the
coalescence. We find that the final product depends sensitively on the initial
compactness parameter of the neutron stars : In a merger between sufficiently
compact neutron stars, a black hole is formed in a dynamical timescale. As the
compactness is decreased, the formation timescale becomes longer and longer. It
is also found that a differentially rotating massive neutron star is formed
instead of a black hole for less compact binary cases, in which the rest mass
of each star is less than 70-80% of the maximum allowed mass of a spherical
star. In the case of black hole formation, we roughly evaluate the mass of the
disk around the black hole. For the merger of corotational binaries, a disk of
mass may be formed, where M_* is the total rest mass of the
system. On the other hand, for the merger of irrotational binaries, the disk
mass appears to be very small : < 0.01M_*.Comment: 27 pages, to appear in Phys. Rev.
Organotypical tissue cultures from adult murine colon as an in vitro model of intestinal mucosa
Together with animal experiments, organotypical cell cultures are important models for analyzing cellular interactions of the mucosal epithelium and pathogenic mechanisms in the gastrointestinal tract. Here, we introduce a three-dimensional culture model from the adult mouse colon for cell biological investigations in an in vivo-like environment. These explant cultures were cultured for up to 2Â weeks and maintained typical characteristics of the intestinal mucosa, including a high-prismatic epithelium with specific epithelial cell-to-cell connections, a basal lamina and various connective tissue cell types, as analyzed with immunohistological and electron microscopic methods. The function of the epithelium was tested by treating the cultures with dexamethasone, which resulted in a strong upregulation of the serum- and glucocorticoid-inducible kinase 1 similar to that found in vivo. The culture system was investigated in infection experiments with the fungal pathogen Candida albicans. Wildtype but not Îcph1/Îefg1-knockout Candida adhered to, penetrated and infiltrated the epithelial barrier. The results demonstrate the potential usefulness of this intestinal in vitro model for studying epithelial cell-cell interactions, cellular signaling and microbiological infections in a three-dimensional cell arrangement
Airway branching morphogenesis in three dimensional culture
To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldBACKGROUND: Lungs develop from the fetal digestive tract where epithelium invades the vascular rich stroma in a process called branching morphogenesis. In organogenesis, endothelial cells have been shown to be important for morphogenesis and the maintenance of organ structure. The aim of this study was to recapitulate human lung morphogenesis in vitro by establishing a three dimensional (3D) co-culture model where lung epithelial cells were cultured in endothelial-rich stroma. METHODS: We used a human bronchial epithelial cell line (VA10) recently developed in our laboratory. This cell line cell line maintains a predominant basal cell phenotype, expressing p63 and other basal markers such as cytokeratin-5 and -14. Here, we cultured VA10 with human umbilical vein endothelial cells (HUVECs), to mimic the close interaction between these cell types during lung development. Morphogenesis and differentiation was monitored by phase contrast microscopy, immunostainings and confocal imaging. RESULTS: We found that in co-culture with endothelial cells, the VA10 cells generated bronchioalveolar like structures, suggesting that lung epithelial branching is facilitated by the presence of endothelial cells. The VA10 derived epithelial structures display various complex patterns of branching and show partial alveolar type-II differentiation with pro-Surfactant-C expression. The epithelial origin of the branching VA10 colonies was confirmed by immunostaining. These bronchioalveolar-like structures were polarized with respect to integrin expression at the cell-matrix interface. The endothelial-induced branching was mediated by soluble factors. Furthermore, fibroblast growth factor receptor-2 (FGFR-2) and sprouty-2 were expressed at the growing tips of the branching structures and the branching was inhibited by the FGFR-small molecule inhibitor SU5402. DISCUSSION: In this study we show that a human lung epithelial cell line can be induced by endothelial cells to form branching bronchioalveolar-like structures in 3-D culture. This novel model of human airway morphogenesis can be used to study critical events in human lung development and suggests a supportive role for the endothelium in promoting branching of airway epithelium
Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
Aims. A transient astrophysical event observed in both gravitational wave
(GW) and electromagnetic (EM) channels would yield rich scientific rewards. A
first program initiating EM follow-ups to possible transient GW events has been
developed and exercised by the LIGO and Virgo community in association with
several partners. In this paper, we describe and evaluate the methods used to
promptly identify and localize GW event candidates and to request images of
targeted sky locations.
Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to
Oct 20 2010), a low-latency analysis pipeline was used to identify GW event
candidates and to reconstruct maps of possible sky locations. A catalog of
nearby galaxies and Milky Way globular clusters was used to select the most
promising sky positions to be imaged, and this directional information was
delivered to EM observatories with time lags of about thirty minutes. A Monte
Carlo simulation has been used to evaluate the low-latency GW pipeline's
ability to reconstruct source positions correctly.
Results. For signals near the detection threshold, our low-latency algorithms
often localized simulated GW burst signals to tens of square degrees, while
neutron star/neutron star inspirals and neutron star/black hole inspirals were
localized to a few hundred square degrees. Localization precision improves for
moderately stronger signals. The correct sky location of signals well above
threshold and originating from nearby galaxies may be observed with ~50% or
better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not
included in v1. Accepted for publication in Astronomy & Astrophysic
Swift follow-up observations of candidate gravitational-wave transient events
We present the first multi-wavelength follow-up observations of two candidate
gravitational-wave (GW) transient events recorded by LIGO and Virgo in their
2009-2010 science run. The events were selected with low latency by the network
of GW detectors and their candidate sky locations were observed by the Swift
observatory. Image transient detection was used to analyze the collected
electromagnetic data, which were found to be consistent with background.
Off-line analysis of the GW data alone has also established that the selected
GW events show no evidence of an astrophysical origin; one of them is
consistent with background and the other one was a test, part of a "blind
injection challenge". With this work we demonstrate the feasibility of rapid
follow-ups of GW transients and establish the sensitivity improvement joint
electromagnetic and GW observations could bring. This is a first step toward an
electromagnetic follow-up program in the regime of routine detections with the
advanced GW instruments expected within this decade. In that regime
multi-wavelength observations will play a significant role in completing the
astrophysical identification of GW sources. We present the methods and results
from this first combined analysis and discuss its implications in terms of
sensitivity for the present and future instruments.Comment: Submitted for publication 2012 May 25, accepted 2012 October 25,
published 2012 November 21, in ApJS, 203, 28 (
http://stacks.iop.org/0067-0049/203/28 ); 14 pages, 3 figures, 6 tables;
LIGO-P1100038; Science summary at
http://www.ligo.org/science/Publication-S6LVSwift/index.php ; Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p110003
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