298 research outputs found
Electromagnetic precursor flares from the late inspiral of neutron star binaries
The coalescence of two neutron stars is accompanied by the emission of
gravitational waves, and can also feature electromagnetic counterparts powered
by mass ejecta and the formation of a relativistic jet after the merger. Since
neutron stars can feature strong magnetic fields, the non-trivial interaction
of the neutron star magnetospheres might fuel potentially powerful
electromagnetic transients prior to merger. A key process powering those
precursor transients is relativistic reconnection in strong current sheets
formed between the two stars. In this work, we provide a detailed analysis of
how the twisting of the common magnetosphere of the binary leads to an emission
of electromagnetic flares, akin to those produced in the solar corona. By means
of relativistic force-free electrodynamics simulations, we clarify the role of
different magnetic field topologies in the process. We conclude that flaring
will always occur for suitable magnetic field alignments, unless one of the
neutron stars has a magnetic field significantly weaker than the other.Comment: 19 pages, 10 figure
Reconnection-powered fast radio transients from coalescing neutron star binaries
It is an open question whether and how gravitational wave events involving
neutron stars can be preceded by electromagnetic counterparts. This work shows
that the collision of two neutron stars with magnetic fields well below
magnetar-level strengths can produce millisecond Fast-Radio-Burst-like
transients. Using global force-free electrodynamics simulations, we demonstrate
that electromagnetic flares, produced by overtwisted common flux tubes in the
binary magnetosphere, collide with the orbital current sheet and compress it,
resulting in enhanced magnetic reconnection. As a result, the current sheet
fragments into a sequence of plasmoids, which collide with each other leading
to the emission of coherent electromagnetic waves. The resulting
millisecond-long burst of radiation should have frequencies in the range of
for magnetic fields of at the
stellar surfaces.Comment: 10 pages, 4 figures, version accepted by PR
Electromagnetic precursors to black hole - neutron star gravitational wave events: Flares and reconnection-powered fast-radio transients from the late inspiral
The presence of magnetic fields in the late inspiral of black hole -- neutron
star binaries could lead to potentially detectable electromagnetic precursor
transients. Using general-relativistic force-free electrodynamics simulations,
we investigate pre-merger interactions of the common magnetosphere of black
hole -- neutron star systems. We demonstrate that these systems can feature
copious electromagnetic flaring activity, which we find depends on the magnetic
field orientation but not on black hole spin. Due to interactions with the
surrounding magnetosphere, these flares could lead to Fast Radio Burst-like
transients and X-ray emission, with as an upper bound for
the luminosity, where is the magnetic field strength on the surface of
the neutron star.Comment: 13 pages, 6 figures; accepted version, to appear in ApJ
Electrical Grid Anomaly Detection via Tensor Decomposition
Supervisory Control and Data Acquisition (SCADA) systems often serve as the
nervous system for substations within power grids. These systems facilitate
real-time monitoring, data acquisition, control of equipment, and ensure smooth
and efficient operation of the substation and its connected devices. Previous
work has shown that dimensionality reduction-based approaches, such as
Principal Component Analysis (PCA), can be used for accurate identification of
anomalies in SCADA systems. While not specifically applied to SCADA,
non-negative matrix factorization (NMF) has shown strong results at detecting
anomalies in wireless sensor networks. These unsupervised approaches model the
normal or expected behavior and detect the unseen types of attacks or anomalies
by identifying the events that deviate from the expected behavior. These
approaches; however, do not model the complex and multi-dimensional
interactions that are naturally present in SCADA systems. Differently,
non-negative tensor decomposition is a powerful unsupervised machine learning
(ML) method that can model the complex and multi-faceted activity details of
SCADA events. In this work, we novelly apply the tensor decomposition method
Canonical Polyadic Alternating Poisson Regression (CP-APR) with a probabilistic
framework, which has previously shown state-of-the-art anomaly detection
results on cyber network data, to identify anomalies in SCADA systems. We
showcase that the use of statistical behavior analysis of SCADA communication
with tensor decomposition improves the specificity and accuracy of identifying
anomalies in electrical grid systems. In our experiments, we model real-world
SCADA system data collected from the electrical grid operated by Los Alamos
National Laboratory (LANL) which provides transmission and distribution service
through a partnership with Los Alamos County, and detect synthetically
generated anomalies.Comment: 8 pages, 2 figures. In IEEE Military Communications Conference,
Artificial Intelligence for Cyber Workshop (MILCOM), 202
Magnetar bursts due to Alfv\'{e}n wave nonlinear breakout
The most common form of magnetar activity is short X-ray bursts, with
durations from milliseconds to seconds, and luminosities ranging from
to . Recently, an X-ray burst from the
galactic magnetar SGR 1935+2154 was detected to be coincident with two fast
radio burst (FRB) like events from the same source, providing evidence that
FRBs may be linked to magnetar bursts. Using fully 3D force-free
electrodynamics simulations, we show that such magnetar bursts may be produced
by Alfv\'{e}n waves launched from localized magnetar quakes: a wave packet
propagates to the outer magnetosphere, becomes nonlinear, and escapes the
magnetosphere, forming an ultra-relativistic ejecta. The ejecta pushes open the
magnetospheric field lines, creating current sheets behind it. Magnetic
reconnection can happen at these current sheets, leading to plasma energization
and X-ray emission. The angular size of the ejecta can be compact,
sr if the quake launching region is small, sr at the stellar
surface. We discuss implications for the FRBs and the coincident X-ray burst
from SGR 1935+2154.Comment: 14 pages, 11 figures, accepted for publication in Ap
1000 Genomes-based meta-analysis identifies 10 novel loci for kidney function
HapMap imputed genome-wide association studies (GWAS) have revealed > 50 loci at which common variants with minor allele frequency > 5% are associated with kidney function. GWAS using more complete reference sets for imputation, such as those from The 1000 Genomes project, promise to identify novel loci that have been missed by previous efforts. To investigate the value of such a more complete variant catalog, we conducted a GWAS meta-analysis of kidney function based on the estimated glomerular filtration rate (eGFR) in 110,517 European ancestry participants using 1000 Genomes imputed data. We identified 10 novel loci with p-value < 5 x 10(-8) previously missed by HapMap-based GWAS. Six of these loci (HOXD8, ARL15, PIK3R1, EYA4, ASTN2, and EPB41L3) are tagged by common SNPs unique to the 1000 Genomes reference panel. Using pathway analysis, we identified 39 significant (FDR < 0.05) genes and 127 significantly (FDR < 0.05) enriched gene sets, which were missed by our previous analyses. Among those, the 10 identified novel genes are part of pathways of kidney development, carbohydrate metabolism, cardiac septum development and glucose metabolism. These results highlight the utility of re-imputing from denser reference panels, until wholegenome sequencing becomes feasible in large samples
Is surgery in acute aortic dissection type A still contraindicated in the presence of preoperative neurological symptoms?†
OBJECTIVES Severe neurological deficit (ND) due to acute aortic dissection type A (AADA) was considered a contraindication for surgery because of poor prognosis. Recently, more aggressive indication for surgery despite neurological symptoms has shown acceptable postoperative clinical results. The aim of this study was to evaluate early and mid-term outcomes of patients with AADA presenting with acute ND. METHODS Data from 53 patients with new-onset ND who received surgical repair for AADA between 2005 and 2012 at our institution were retrospectively reviewed. ND was defined as focal motor or sensory deficit, hemiplegia, paraplegia, convulsions or coma. Neurological symptoms were evaluated preoperatively using the Glasgow Coma Scale (GCS) and modified Rankin Scale (mRS), and at discharge as well as 3-6 months postoperatively using the mRS and National Institutes of Health Stroke Scale. Involvement of carotid arteries was assessed in the pre- and postoperative computed tomography. Logistic regression analysis was performed to detect predictive factors for recovery of ND. RESULTS Of the 53 patients, 29 (54.7%) showed complete recovery from focal ND at follow-up. Neurological symptoms persisted in 24 (45.3%) patients, of which 8 (33%) died without neurological assessment at follow-up. Between the two groups (patients with recovery and those with persisting ND), there was no significant difference regarding the duration of hypothermic circulatory arrest (28 ± 14 vs 36 ± 20 min) or severely reduced consciousness (GCS <8). Multivariate analysis showed significant differences for the preoperative mRS between the two groups (P < 0.007). A high preoperative mRS was associated with persistence of neurological symptoms (P < 0.02). Cardiovascular risk factors, age or involvement of supra-aortic branches were not predictive for persistence of ND. CONCLUSION More than half of our patients recovered completely from ND due to AADA after surgery. Severity of clinical symptoms had a predictive value. Patients suffering from AADA and presenting with ND before surgery should not be excluded from emergency surger
Political opportunity structures, democracy, and civil war
Theories of mobilization suggest that groups are more likely to resort to violence in the presence of political opportunity structures that afford greater prospects for extracting concessions from the government or better opportunities to topple ruling governments. However, existing efforts to consider the possible influences of political opportunity structures on incentives for violence and civil war empirically have almost invariably relied upon measures of democracy to proxy for the hypothesized mechanisms, most notably the argument that the opposing effects of political accommodation and repression will give rise to an inverted U-shaped relationship between democracy and the risk of civil war. The authors detail a number of problems with measures of democracy as proxies for political opportunity structures and develop alternative measures based on the likely risks that political leaders will lose power in irregular challenges and their implications for the incentives for resort to violence. The authors evaluate empirically how the security with which leaders hold office influences the prospects of violent civil conflict. The findings indicate that recent irregular leader entry and transitions indeed increase the risk of conflict onset, while democratic institutions are found to decrease the risk of civil war, after controlling for the new measures of state weakness. </jats:p
The impact of donor and recipient common clinical and genetic variation on estimated glomerular filtration rate in a European renal transplant population
Genetic variation across the HLA is known to influence renal‐transplant outcome. However, the impact of genetic variation beyond the HLA is less clear. We tested the association of common genetic variation and clinical characteristics, from both the donor and recipient, with post‐transplant eGFR at different time‐points, out to 5‐years post‐transplantation.
We conducted GWAS meta‐analyses across 10,844 donors and recipients from five European ancestry cohorts. We also analysed the impact of polygenic risk scores (PRS), calculated using genetic variants associated with non‐transplant eGFR, on post‐transplant eGFR.
PRS calculated using the recipient genotype alone, as well as combined donor and recipient genotypes were significantly associated with eGFR at 1‐year post‐transplant. 32% of the variability in eGFR at 1‐year post‐transplant was explained by our model containing clinical covariates (including weights for death/graft‐failure), principal components and combined donor‐recipient PRS, with 0.3% contributed by the PRS. No individual genetic variant was significantly associated with eGFR post‐transplant in the GWAS.
This is the first study to examine PRS, composed of variants that impact kidney function in the general population, in a post‐transplant context. Despite PRS being a significant predictor of eGFR post‐transplant, the effect size of common genetic factors is limited compared to clinical variables
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