935 research outputs found
Common envelope ejection in massive binary stars - Implications for the progenitors of GW150914 and GW151226
The recently detected gravitational wave signals (GW150914 and GW151226) of
the merger event of a pair of relatively massive stellar-mass black holes (BHs)
calls for an investigation of the formation of such progenitor systems in
general. We analyse the common envelope (CE) stage of the "traditional"
formation channel in binaries where the first-formed compact object undergoes
an in-spiral inside the envelope of its evolved companion star and ejects the
envelope in that process. We calculate envelope binding energies of donor stars
with initial masses between 4 and 115 Msun for metallicities of Z=Zsun/2 and
Z=Zsun/50, and derive minimum masses of in-spiralling objects needed to eject
these envelopes. We find that CE evolution, besides from producing WD-WD and
NS-NS binaries, may, in principle, also produce massive BH-BH systems with
individual BH component masses up to ~50-60 Msun, in particular for donor stars
evolved to giants. However, the physics of envelope ejection of massive stars
remains uncertain. We discuss the applicability of the energy-budget formalism,
the location of the bifurcation point, the recombination energy and the
accretion energy during in-spiral as possible energy sources, and also comment
on the effect of inflated helium cores. Massive stars in a wide range of
metallicities and with initial masses up to at least 115 Msun may possibly shed
their envelopes and survive CE evolution, depending on their initial orbital
parameters, similarly to the situation for intermediate mass and low-mass stars
with degenerate cores. We conclude that based on stellar structure
calculations, and in the view of the usual simple energy budget analysis,
events like GW150914 and GW151226 could possibly be produced from the CE
channel. Calculations of post-CE orbital separations, however, and thus the
estimated LIGO detection rates, remain highly uncertain. [Abridged]Comment: 13 pages, 7 figures, A&A accepte
Ultra-stripped Type Ic supernovae from close binary evolution
Recent discoveries of weak and fast optical transients raise the question of
their origin. We investigate the minimum ejecta mass associated with
core-collapse supernovae (SNe) of Type Ic. We show that mass transfer from a
helium star to a compact companion can produce an ultra-stripped core which
undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In
this Letter, a detailed example is presented in which the pre-SN stellar mass
is barely above the Chandrasekhar limit, resulting in the ejection of only
~0.05-0.20 M_sun of material and the formation of a low-mass neutron star. We
compute synthetic light curves of this case and demonstrate that SN 2005ek
could be explained by our model. We estimate that the fraction of such
ultra-stripped to all SNe could be as high as 0.001-0.01. Finally, we argue
that the second explosion in some double neutron star systems (for example, the
double pulsar PSR J0737-3039B) was likely associated with an ultra-stripped SN
Ic.Comment: ApJ Letters, in press, 6 pages, 5 figures (emulateapj style). Very
minor changes to match printed version. Follow DOI link below for online
published versio
Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?
The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors
of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose
angular momentum due to their intense stellar winds. We investigate whether the
tidal interaction of a Wolf-Rayet star with a compact object in a binary system
can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the
evolution of close Wolf-Rayet binaries, including tidal angular momentum
exchange, differential rotation of the Wolf-Rayet star, internal magnetic
fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is
approximated as a point mass. We then employ a population synthesis code to
infer the occurrence rates of the various relevant binary evolution channels.
We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally
spun up and producing a collapsar -- does not occur at solar metallicity and
may only occur with low probability at low metallicity. It is limited by the
widening of the binary orbit induced by the strong Wolf-Rayet wind or by the
radius evolution of the Wolf-Rayet star that most often leads to a binary
merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with
black holes such that it becomes comparable to the occurrence rate of long
gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&
Fast-growing pancreatic neuroendocrine carcinoma in a patient with multiple endocrine neoplasia type 1: a case report
<p>Abstract</p> <p>Introduction</p> <p>Predictive genetic screening and regular screening programs in patients with multiple endocrine neoplasia type 1 are intended to detect and treat malignant tumors at the earliest stage possible. Malignant neuroendocrine pancreatic tumors are the most frequent cause of death in these patients. However, the extent and intervals of screening in patients with multiple endocrine neoplasia type 1 are controversial as neuroendocrine tumors are usually slow growing. Here we report the case of a patient who developed a fast-growing neuroendocrine carcinoma within 15 months of a laparoscopic distal pancreatic resection.</p> <p>Case presentation</p> <p>We followed a group of 45 patients with multiple endocrine neoplasia type 1 by an annual screening program in the Department of Visceral, Thoracic, and Vascular Surgery at the University Hospital Marburg in cooperation with the Department of Radiology and the Division of Endocrinology. A man with multiple endocrine neoplasia type 1 who was diagnosed with a recurrent primary hyperparathyroidism underwent a distal pancreatic resection for a non-functional neuroendocrine tumor. In the context of our regular screening program, a large non-functional neuroendocrine tumor was diagnosed in the pancreatic head 15 months after the first pancreatic surgery. Therefore, we performed an enucleation and regional lymph node resection. At histology, the diagnosis of a neuroendocrine carcinoma with one lymph node metastasis was established. There was no evidence of recurrence 9 months after re-operation.</p> <p>Conclusion</p> <p>Fast-growing neuroendocrine tumors are rare in patients with multiple endocrine neoplasia type 1. The intervals, both postoperative and in newly diagnosed pancreatic lesions, in patients with multiple endocrine neoplasia type 1 should be reduced to 6 months to establish the early diagnosis of rapidly progressive disease in a small subset of patients.</p
Global microRNA depletion suppresses tumor angiogenesis
MicroRNAs delicately regulate the balance of angiogenesis. Here we show that depletion of all microRNAs suppresses tumor angiogenesis. We generated microRNA-deficient tumors by knocking out Dicer1. These tumors are highly hypoxic but poorly vascularized, suggestive of deficient angiogenesis signaling. Expression profiling revealed that angiogenesis genes were significantly down-regulated as a result of the microRNA deficiency. Factor inhibiting hypoxia-inducible factor 1 (HIF-1), FIH1, is derepressed under these conditions and suppresses HIF transcription. Knocking out FIH1 using CRISPR/Cas9-mediated genome engineering reversed the phenotypes of microRNA-deficient cells in HIF transcriptional activity, VEGF production, tumor hypoxia, and tumor angiogenesis. Using multiplexed CRISPR/Cas9, we deleted regions in FIH1 3âČ untranslated regions (UTRs) that contain microRNA-binding sites, which derepresses FIH1 protein and represses hypoxia response. These data suggest that microRNAs promote tumor responses to hypoxia and angiogenesis by repressing FIH1.Swedish Research CouncilHoward Hughes Medical Institute (International Student Research Fellowship)National Institutes of Health (U.S.) (grant number R01-CA133404)MIT-Harvard Center of Cancer Nanotechnology Excellence (grant no. U54-CA151884)David H. Koch Institute for Integrative Cancer Research at MIT (Marie D. and Pierre Casimir-Lambert Fund)National Cancer Institute (U.S.) (Koch Institute Support (core) Grant P30-CA14051))National Institutes of Health (U.S.) (grant EB016101-01A1)Damon Runyon Cancer Research Foundation (Research Fellow (DRG-2117-12)
Unraveling the Landau's consistence criterion and the meaning of interpenetration in the "Two-Fluid" Model
In this letter we show that it is possible to unravel both the physical
origin of the Landau's consistence criterion and the specific and subtle
meaning of interpenetration of the "two fluids" if one takes into account that
in the hydrodynamic regime one needs a coarse-graining in time to bring the
system into local equilibrium. That is, the fuzziness in time is relevant for
the phenomenological Landau's consistency criterion and the meaning of
interpenetration. Note also that we are not questioning the validity of the
"Two-Fluid" Model.Comment: 8 pages, affiliation added, typos corrected, final version published
in Eur. Phys. J.
The Effects of Binary Evolution on the Dynamics of Core Collapse and Neutron-Star Kicks
We systematically examine how the presence in a binary affects the final core
structure of a massive star and its consequences for the subsequent supernova
explosion. Interactions with a companion star may change the final rate of
rotation, the size of the helium core, the strength of carbon burning and the
final iron core mass. Stars with initial masses larger than \sim 11\Ms that
experiece core collapse will generally have smaller iron cores at the time of
the explosion if they lost their envelopes due to a previous binary
interaction. Stars below \sim 11\Ms, on the other hand, can end up with larger
helium and metal cores if they have a close companion, since the second
dredge-up phase which reduces the helium core mass dramatically in single stars
does not occur once the hydrogen envelope is lost. We find that the initially
more massive stars in binary systems with masses in the range 8 - 11\Ms are
likely to undergo an electron-capture supernova, while single stars in the same
mass range would end as ONeMg white dwarfs. We suggest that the core collapse
in an electron-capture supernova (and possibly in the case of relatively small
iron cores) leads to a prompt explosion rather than a delayed neutrino-driven
explosion and that this naturally produces neutron stars with low-velocity
kicks. This leads to a dichotomous distribution of neutron star kicks, as
inferred previously, where neutron stars in relatively close binaries attain
low kick velocities. We illustrate the consequences of such a dichotomous kick
scenario using binary population synthesis simulations and discuss its
implications. This scenario has also important consequences for the minimum
initial mass of a massive star that becomes a neutron star. (Abbreviated.)Comment: 8 pages, 3 figures, submitted to ApJ, updated versio
Will the starless cores in Chamaeleon I and III turn prestellar?
The nearby Chamaeleon molecular cloud complex is a good laboratory to study
the process of low-mass star formation since it consists of three clouds with
very different properties. Cha III does not show any sign of star formation,
while star formation has been very active in Cha I and may already be
finishing. Our goal is to determine whether star formation can proceed in Cha
III, and to compare the results to our recent survey of Cha I. We used the
Large APEX Bolometer Array (LABOCA) to map Cha III in dust continuum emission
at 870 micron. 29 sources are extracted from the map, all of them being
starless. The starless cores are found down to a visual extinction of 1.9 mag,
in marked contrast with other molecular clouds, including Cha I. Apart from
this difference, the Cha III starless cores share very similar properties with
those found in Cha I. At most two sources have a mass larger than the critical
Bonnor-Ebert mass, which suggests that the fraction of prestellar cores is very
low, even lower than in Cha I. Only the most massive sources are candidate
prestellar cores, in agreement with the correlation found earlier in the Pipe
nebula. The mass distribution of the 85 starless cores of Cha I and III that
are not candidate prestellar cores is consistent with a single power law down
to the 90% completeness limit, with an exponent close to the Salpeter value. A
fraction of the starless cores in Cha I and III may still grow in mass and
become gravitationally unstable. Based on predictions of numerical simulations
of turbulent molecular clouds, we estimate that at most 50% and 20% of the
starless cores of Cha I and III, respectively, may form stars. The LABOCA
survey reveals that Cha III, and Cha I to some extent too, is a prime target to
study the formation of prestellar cores, and thus the onset of star formation.
(abridged).Comment: Accepted for publication in A&A. 22 pages, 16 figures, 4 tables. A
version with high-resolution figures is available on request to the first
autho
Regular dendritic patterns induced by non-local time-periodic forcing
The dynamic response of dendritic solidification to spatially homogeneous
time-periodic forcing has been studied. Phase-field calculations performed in
two dimensions (2D) and experiments on thin (quasi 2D) liquid crystal layers
show that the frequency of dendritic side-branching can be tuned by oscillatory
pressure or heating. The sensitivity of this phenomenon to the relevant
parameters, the frequency and amplitude of the modulation, the initial
undercooling and the anisotropies of the interfacial free energy and molecule
attachment kinetics, has been explored. It has been demonstrated that besides
the side-branching mode synchronous with external forcing as emerging from the
linear Wentzel-Kramers-Brillouin analysis, modes that oscillate with higher
harmonic frequencies are also present with perceptible amplitudes.Comment: 15 pages, 23 figures, Submitted to Phys. Rev.
The role of the pathologist in tissue banking: European Consensus Expert Group Report
Human tissue biobanking encompasses a wide range of activities and study designs and is critical for application of a wide range of new technologies (-âomicsâ) to the discovery of molecular patterns of disease and for implementation of novel biomarkers into clinical trials. Pathology is the cornerstone of hospital-based tissue biobanking. Pathologists not only provide essential information identifying the specimen but also make decisions on what should be biobanked, making sure that the timing of all operations is consistent with both the requirements of clinical diagnosis and the optimal preservation of biological products. This document summarizes the conclusions of a Pathology Expert Group Meeting within the European Biological and Biomolecular Research Infrastructure (BBMRI) Program. These recommendations are aimed at providing guidance for pathologists as well as for institutions hosting biobanks on how to better integrate and support pathological activities within the framework of biobanks that fulfill international standards
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