355 research outputs found
Effect of the Heart Rate Variability Representations on the Quantification of the Cardiorespiratory Interactions during Autonomic Nervous System Blockade
The Heart Rate Variability (HRV) is a noninvasive tool to evaluate the activity of the autonomic nervous system. To study the HRV, different mathematical representations can be used. The selection of a representation might have an effect on the evaluation of the mechanisms that modulate the Heart Rate (HR). One of these mechanisms is the Respiratory Sinus Arrhythmia (RSA), i.e. an increased HR during inhalation and a decreased HR during exhalation. Different methods exist to quantify the RSA. A common approach is to calculate the power in the High Frequency (HF, 0.15 - 0.4 Hz) band of the spectrum of the HRV representation. More recently proposed methods use the respiratory signals to estimate the strength of the RSA.This paper studies the effect of the HRV representations on the quantification of the RSA. To this end, an experiment is used in which the sympathetic and parasympathetic branches of the autonomic nervous system are selectively blocked. Three different HRV representations are considered. Afterwards, the strength of the RSA is estimated using three approaches, namely the spectral content in the HF band of the HRV representations, orthogonal subspace projections and a time-frequency representation.The results suggest that the selection of an HRV representation does not have a significant impact on the RSA estimates in a healthy population
The properties of the clumpy torus and BLR in the polar-scattered Seyfert 1 galaxy ESO 323-G77 through X-ray absorption variability
We report results from multi-epoch X-ray observations of the polar-scattered
Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral
variability from months to years timescales. The observed spectral variability
is entirely due to variations of the column density of a neutral absorber
towards the intrinsic nuclear continuum. The column density is generally
Compton-thin ranging from a few times 10 cm to a few times
10 cm. However, one observation reveals a Compton-thick state
with column density of the order of 1.5 10 cm. The
observed variability offers a rare opportunity to study the properties of the
X-ray absorber(s) in an active galaxy. We identify variable X-ray absorption
from two different components, namely (i) a clumpy torus whose individual
clumps have a density of 1.7 10 cm and an average
column density of 4 10 cm, and (ii) the broad
line region (BLR), comprising individual clouds with density of 0.1-8
10 cm and column density of 10-10 cm. The
derived properties of the clumpy torus can also be used to estimate the torus
half-opening angle, which is of the order of 47 . We also confirm the
previously reported detection of two highly ionized warm absorbers with outflow
velocities of 1000-4000 km s. The observed outflow velocities are
consistent with the Keplerian/escape velocity at the BLR. Hence, the warm
absorbers may be tentatively identified with the warm/hot inter-cloud medium
which ensures that the BLR clouds are in pressure equilibrium with their
surroundings. The BLR line-emitting clouds may well be the cold, dense clumps
of this outflow, whose warm/hot phase is likely more homogeneous, as suggested
by the lack of strong variability of the warm absorber(s) properties during our
monitoring.Comment: 15 pages, 4 tables, and 9 figures. Accepted for publication in MNRA
Locating privileged spreaders on an Online Social Network
Social media have provided plentiful evidence of their capacity for
information diffusion. Fads and rumors, but also social unrest and riots travel
fast and affect large fractions of the population participating in online
social networks (OSNs). This has spurred much research regarding the mechanisms
that underlie social contagion, and also who (if any) can unleash system-wide
information dissemination. Access to real data, both regarding topology --the
network of friendships-- and dynamics --the actual way in which OSNs users
interact--, is crucial to decipher how the former facilitates the latter's
success, understood as efficiency in information spreading. With the
quantitative analysis that stems from complex network theory, we discuss who
(and why) has privileged spreading capabilities when it comes to information
diffusion. This is done considering the evolution of an episode of political
protest which took place in Spain, spanning one month in 2011.Comment: 7 pages, 4 figure
Obstructive sleep apnoea-related respiratory events and desaturation severity are associated with the cardiac response
Obstructive sleep apnoea (OSA) causes, among other things, intermittent blood oxygen desaturations, increasing the sympathetic tone. Yet the effect of desaturations on heart rate variability (HRV), a simple and noninvasive method for assessing sympathovagal balance, has not been comprehensively studied. We aimed to study whether desaturation severity affects the immediate HRV.MethodsWe retrospectively analysed the electrocardiography signals in 5-min segments (n=39 132) recorded during clinical polysomnographies of 642 patients with suspected OSA. HRV parameters were calculated for each segment. The segments were pooled into severity groups based on the desaturation severity (i.e.the integrated area under the blood oxygen saturation curve) and the respiratory event rate within the segment. Covariate-adjusted regression analyses were performed to investigate possible confounding effects.ResultsWith increasing respiratory event rate, the normalised high-frequency band power (HFNU) decreased from 0.517 to 0.364 (p<0.01), the normalised low-frequency band power (LFNU) increased from 0.483 to 0.636 (p<0.01) and the mean RR interval decreased from 915 to 869 ms (p<0.01). Similarly, with increasing desaturation severity, the HFNUdecreased from 0.499 to 0.364 (p<0.01), the LFNUincreased from 0.501 to 0.636 (p<0.01) and the mean RR interval decreased from 952 to 854 ms (p<0.01). Desaturation severity-related findings were confirmed by considering the confounding factors in the regression analyses.ConclusionThe short-term HRV response differs based on the desaturation severity and the respiratory event rate in patients with suspected OSA. Therefore, a more detailed analysis of HRV and desaturation characteristics could enhance OSA severity estimation
Engulfing a radio pulsar: the case of PSR J1023+0038
The binary millisecond radio pulsar PSR J1023+0038 has been recently the
subject of multiwavelength monitoring campaigns which revealed that an
accretion disc has formed around the neutron star (since 2013 June). We present
here the results of X-ray and UV observations carried out by the Swift
satellite between 2013 October and 2014 May, and of optical and NIR
observations performed with the REM telescope, the Liverpool Telescope, the
2.1-m telescope at the San Pedro M\'artir Observatory and the 1.52-m telescope
at the Loiano observing station. The X-ray spectrum is well described by an
absorbed power law, which is softer than the previous quiescent epoch (up to
2013 June). The strong correlation between the X-ray and the UV emissions
indicates that the same mechanism should be responsible for part of the
emission in these bands. Optical and infrared photometric observations show
that the companion star is strongly irradiated. Double-peaked emission lines in
the optical spectra provide compelling evidence for the presence of an outer
accretion disc too. The spectral energy distribution from IR to X-rays is well
modelled if the contributions from the companion, the disc and the intra-binary
shock emission are all considered. Our extensive data set can be interpreted in
terms of an engulfed radio pulsar: the radio pulsar is still active, but
undetectable in the radio band due to a large amount of ionized material
surrounding the compact object. X-rays and gamma-rays are produced in an
intra-binary shock front between the relativistic pulsar wind and matter from
the companion and an outer accretion disc. The intense spin-down power
irradiates the disc and the companion star, accounting for the UV and optical
emissions.Comment: 11 pages, 8 figures, 5 tables; accepted for publication on MNRA
Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined properties, we measure global
temperatures in the range ,
bolometric X-ray luminosities of , and estimate masses,
as derived from , of .
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems.Comment: 17 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Twitter-based analysis of the dynamics of collective attention to political parties
Large-scale data from social media have a significant potential to describe
complex phenomena in real world and to anticipate collective behaviors such as
information spreading and social trends. One specific case of study is
represented by the collective attention to the action of political parties. Not
surprisingly, researchers and stakeholders tried to correlate parties' presence
on social media with their performances in elections. Despite the many efforts,
results are still inconclusive since this kind of data is often very noisy and
significant signals could be covered by (largely unknown) statistical
fluctuations. In this paper we consider the number of tweets (tweet volume) of
a party as a proxy of collective attention to the party, identify the dynamics
of the volume, and show that this quantity has some information on the
elections outcome. We find that the distribution of the tweet volume for each
party follows a log-normal distribution with a positive autocorrelation of the
volume over short terms, which indicates the volume has large fluctuations of
the log-normal distribution yet with a short-term tendency. Furthermore, by
measuring the ratio of two consecutive daily tweet volumes, we find that the
evolution of the daily volume of a party can be described by means of a
geometric Brownian motion (i.e., the logarithm of the volume moves randomly
with a trend). Finally, we determine the optimal period of averaging tweet
volume for reducing fluctuations and extracting short-term tendencies. We
conclude that the tweet volume is a good indicator of parties' success in the
elections when considered over an optimal time window. Our study identifies the
statistical nature of collective attention to political issues and sheds light
on how to model the dynamics of collective attention in social media.Comment: 16 pages, 7 figures, 3 tables. Published in PLoS ON
Detection of blueshifted emission and absorption and a relativistic Iron line in the X-ray spectrum of ESO 323-G077
We report on the X-ray observation of the Seyfert 1 ESO323-G077 performed
with XMM-Newton. The spectra show a complex spectrum with conspicuous
absorption and emission features. The continuum emission can be modelled with a
power law with an index of 1.99+/-0.02 in the whole XMM-Newton energy band,
marginally consistent with typical values of Type-I objects. An absorption
component with an uncommonly high equivalent Hydrogen column,
n_H=5.82(+0.12/-0.11)x10^22 cm-2, is affecting the soft part of the spectrum.
Additionally, two warm absorption components are also present. The lower
ionised one has an ionisation parameter of Log(U)=2.14(+0.06/-0.07) and an
outflowing velocity of v=3200(+600/-200) km/s. Two absorption lines located at
~6.7 and ~7.0 keV can be modelled with the highly ionised absorber. The
ionisation parameter and outflowing velocity of the gas measured are
Log(U)=3.26(+0.19/-0.15) and v=1700(+600/-400) km/s, respectively. Four
emission lines were also detected in the soft energy band. The most likely
explanation for these emission lines is that they are associated with an
outflowing gas with a velocity of ~2000 km/s. The data suggest that the same
gas which is causing the absorption could also being responsible of these
emission features. Finally, the spectrum shows the presence of a relativistic
iron emission line likely originated in the accretion disc of a Kerr BH with an
inclination of ~25 deg. We propose a model to explain the observed X-ray
properties which invokes the presence of a two-phase outflow with cone-like
structure and a velocity of the order of 2,000-4,000 km/s. The inner layer of
the cone would be less ionised, or even neutral, than the outer layer. The
inclination angle would be lower than the opening angle of the outflowing cone.Comment: 11 pages, accepted in MNRA
Refining the associations of the Fermi Large Area Telescope Source Catalogs
The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released
in February 2010 and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in
April 2012, based on data from 24 months of operation. Since their releases,
many follow up observations of unidentified gamma-ray sources (UGSs) were
performed and new procedures to associate gamma-ray sources with potential
counterparts at other wavelengths were developed. Here we review and
characterize all the associations as published in the 1FGL and 2FGL catalog on
the basis of multifrequency archival observations. In particular we located 177
spectra for the low-energy counterparts that were not listed in the previous
Fermi catalogs, and in addition we present new spectroscopic observations of 8
gamma-ray blazar candidates. Based on our investigations, we introduce a new
counterpart category of "candidate associations" and propose a refined
classification for the candidate low-energy counterparts of the Fermi sources.
We compare the 1FGL-assigned counterparts with those listed in the 2FGL to
determine which unassociated sources became associated in later releases of the
Fermi catalogs. We also search for potential counterparts to all the remaining
unassociated Fermi sources. Finally, we prepare a refined and merged list of
all the associations of the 1FGL plus 2FGL catalogs that includes 2219 unique
Fermi objects. This is the most comprehensive and systematic study of all the
associations collected for the gamma-ray sources available to date. We conclude
that 80% of the Fermi sources have at least one known plausible gamma-ray
emitter within their positional uncertainty regions.Comment: 26 pages, 24 figures, 7 tables, ApJS accepted for publication
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