1,507 research outputs found
The environment of the wind-wind collision region of Carinae
Carinae is a colliding wind binary hosting two of the most massive
stars and featuring the strongest wind collision mechanical luminosity. The
wind collision region of this system is detected in X-rays and -rays
and offers a unique laboratory for the study of particle acceleration and wind
magneto-hydrodynamics. Our main goal is to use X-ray observations of
Carinae around periastron to constrain the wind collision zone geometry and
understand the reasons for its variability. We analysed 10 Nuclear
Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around
the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV,
which allowed us to grasp the continuum and absorption parameters with very
good accuracy. We were able to identify several physical components and probe
their variability. The X-ray flux varied in a similar way as observed during
previous periastrons and largely as expected if generated in the wind collision
region. The flux detected within ~10 days of periastron is lower than expected,
suggesting a partial disruption of the central region of the wind collision
zone. The Fe K line is likely broadened by the electrons heated along
the complex shock fronts. The variability of its equivalent width indicates
that the fluorescence region has a complex geometry and that the source
obscuration varies quickly with the line of sight.Comment: to be published in A&A, 7 pages, 9 figure
Reflection geometries in absorbed and unabsorbed AGN
The hard X-ray emission of active galactic nuclei (AGN), and in particular,
the reflection component, is shaped by the innermost and outer regions of the
galactic nucleus. Our main goal is to investigate the variation of the Compton
hump amongst a population of sources and correlate it with other spectral
properties to constrain the source geometry. We studied the NuSTAR hard X-ray
spectra of a sample of 83 AGN and performed a detailed spectral analysis of
each of them. Based on their spectral shape, we divided the sample into five
categories and also studied their stacked spectra. We found a stronger
reflection in mildly obscured sources, which verifies the results reported in
previous works. In addition, the reflection behaviour, and probably origin,
varies with absorption. The accretion disc seems to be the main reflector in
unabsorbed sources. A clumpy torus seems to produce most of the reflection in
obscured sources. The filling factor of the clouds surrounding the active
nucleus is a key parameter that drives the appearance of AGN. Finally, we found
that the Fe line and the Compton hump are roughly correlated, as expected.Comment: 16 pages, 9 figures, published by A&
On the detection of myocardial scar based on ECG/VCG analysis
In this paper, we address the problem of detecting the presence of myocardial scar from standard ECG/VCG recordings, giving effort to develop a screening system for the early detection of scar in the point-of-care. Based on the pathophysiological implications of scarred myocardium, which results in disordered electrical conduction, we have implemented four distinct ECG signal processing methodologies in order to obtain a set of features that can capture the presence of myocardial scar. Two of these methodologies: a.) the use of a template ECG heartbeat, from records with scar absence coupled with Wavelet coherence analysis and b.) the utilization of the VCG are novel approaches for detecting scar presence. Following, the pool of extracted features is utilized to formulate an SVM classification model through supervised learning. Feature selection is also employed to remove redundant features and maximize the classifier's performance. Classification experiments using 260 records from three different databases reveal that the proposed system achieves 89.22% accuracy when applying 10- fold cross validation, and 82.07% success rate when testing it on databases with different inherent characteristics with similar levels of sensitivity (76%) and specificity (87.5%)
Genetic Algorithms in Antennas and Smart Antennas Design Overview: Two Novel Antenna Systems for Triband GNSS Applications and a Circular Switched Parasitic Array for WiMax Applications Developments with the Use of Genetic Algorithms
Genetic algorithms belong to a stochastic class of evolutionary techniques, whose robustness and global search of the solutions space have made them extremely popular among researchers. They have been successfully applied to electromagnetic optimization, including antenna design as well as smart antennas design. In this paper, extensive reference to literature related antenna design efforts employing genetic algorithms is taking place and subsequently, three novel antenna systems are designed in order to provide realistic implementations of a genetic algorithm. Two novel antenna systems are presented to cover the new GPS/Galileo band, namely, L5 (1176 MHz), together with the L1 GPS/Galileo and L2 GPS bands (1575 and 1227 MHz). The first system is a modified PIFA and the second one is a helical antenna above a ground plane. Both systems exhibit enhanced performance characteristics, such as sufficient front gain, input impedance matching, and increased front-to-back ratio. The last antenna system is a five-element switched parasitic array with a directional beam with sufficient beamwidth to a predetermined direction and an adequate impedance bandwidth which can be used as receiver for WiMax signals
EDEN: A high-performance, general-purpose, NeuroML-based neural simulator
Modern neuroscience employs in silico experimentation on ever-increasing and
more detailed neural networks. The high modelling detail goes hand in hand with
the need for high model reproducibility, reusability and transparency. Besides,
the size of the models and the long timescales under study mandate the use of a
simulation system with high computational performance, so as to provide an
acceptable time to result. In this work, we present EDEN (Extensible Dynamics
Engine for Networks), a new general-purpose, NeuroML-based neural simulator
that achieves both high model flexibility and high computational performance,
through an innovative model-analysis and code-generation technique. The
simulator runs NeuroML v2 models directly, eliminating the need for users to
learn yet another simulator-specific, model-specification language. EDEN's
functional correctness and computational performance were assessed through
NeuroML models available on the NeuroML-DB and Open Source Brain model
repositories. In qualitative experiments, the results produced by EDEN were
verified against the established NEURON simulator, for a wide range of models.
At the same time, computational-performance benchmarks reveal that EDEN runs up
to 2 orders-of-magnitude faster than NEURON on a typical desktop computer, and
does so without additional effort from the user. Finally, and without added
user effort, EDEN has been built from scratch to scale seamlessly over multiple
CPUs and across computer clusters, when available.Comment: 29 pages, 9 figure
Undifferentiated embryonal sarcoma of the liver mimicking acute appendicitis. Case report and review of the literature
BACKGROUND: Undifferentiated embryonal sarcoma (UES) of liver is a rare malignant neoplasm, which affects mostly the pediatric population accounting for 13% of pediatric hepatic malignancies, a few cases has been reported in adults. CASE PRESENTATION: We report a case of undifferentiated embryonal sarcoma of the liver in a 20-year-old Caucasian male. The patient was referred to us for further investigation after a laparotomy in a district hospital for spontaneous abdominal hemorrhage, which was due to a liver mass. After a through evaluation with computed tomography scan and magnetic resonance imaging of the liver and taking into consideration the previous history of the patient, it was decided to surgically explore the patient. Resection of I–IV and VIII hepatic lobe. Patient developed disseminated intravascular coagulation one day after the surgery and died the next day. CONCLUSION: It is a rare, highly malignant hepatic neoplasm, affecting almost exclusively the pediatric population. The prognosis is poor but recent evidence has shown that long-term survival is possible after complete surgical resection with or without postoperative chemotherapy
Anxiety, insomnia and family support in nurses, two years after the onset of the pandemic crisis
Introduction:
The Covid-19 pandemic continues to cause serious physical and mental problems for health professionals, particularly nurses.
Aim:
To estimate the prevalence of anxiety and insomnia and to evaluate their possible association with family support received by nurses two years after the onset of the pandemic.
Materials and methods:
In total, the study participants were 404 nurses (335 females and 69 males) with a mean age of 42.88 (SD = 10.9) years and a mean of 17.96 (SD = 12) years working as nurses. Nurses from five tertiary hospitals in Athens constituted the study population who completed the questionnaires State-Trait Anxiety Inventory (STAI), Athens Insomnia Scale (AIS) and Family Support Scale (FSS), in the months of November and December 2021. Regarding demographic and occupational characteristics, gender, age and years of experience as nurses were recorded.
Results:
60.1% of the nurses showed abnormal scores in state anxiety, with 46.8% in trait anxiety, and 61.4% showed insomnia. Women showed higher scores on the two subscales of anxiety and the insomnia scale compared to men (p 0.05). Positive correlations (p < 0.01) were found between the State Anxiety Inventory, Trait Anxiety Inventory and AIS, while all of them showed a high negative correlation with FSS (p < 0.01). Age showed a negative correlation with Trait Anxiety Inventory (p < 0.05). As shown by the mediation analysis, the relationship between state anxiety and insomnia was mediated by trait anxiety, whereas state anxiety appeared to be dependent on family support.
Conclusions:
Nurses continue to experience high levels of anxiety and insomnia and feel less supported by their families than in the first year of the pandemic. Insomnia appears to be dependent on state anxiety, with a significant indirect effect of trait anxiety, while family support seems to affect state anxiety
X-ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing
UV and optical continuum reverberation mapping is powerful for probing the
accretion disk and inner broad-line region. However, recent reverberation
mapping campaigns in the X-ray, UV, and optical have found lags consistently
longer than those expected from the standard disk reprocessing picture. The
largest discrepancy to-date was recently reported in Mrk 335, where UV/optical
lags are up to 12 times longer than expected. Here, we perform a
frequency-resolved time lag analysis of Mrk 335, using Gaussian processes to
account for irregular sampling. For the first time, we compare the Fourier
frequency-resolved lags directly to those computed using the popular
Interpolated Cross-Correlation Function (ICCF) method applied to both the
original and detrended light curves. We show that the anticipated disk
reverberation lags are recovered by the Fourier lags when zeroing in on the
short-timescale variability. This suggests that a separate variability
component is present on long timescales. If this separate component is modeled
as reverberation from another region beyond the accretion disk, we constrain a
size-scale of roughly 15 light-days from the central black hole. This is
consistent with the size of the broad line region inferred from H
reverberation lags. We also find tentative evidence for a soft X-ray lag, which
we propose may be due to light travel time delays between the hard X-ray corona
and distant photoionized gas that dominates the soft X-ray spectrum below 2
keV.Comment: Accepted for publication in ApJ, 8 figure
- …