47 research outputs found
Broad-band properties of the hard X-ray cataclysmic variables IGR J00234+6141 and 1RXS J213344.1+510725
A significant number of cataclysmic variables were detected as hard X-ray
sources in the INTEGRAL survey, most of them of the magnetic intermediate polar
type. We present a detailed X-ray broad-band study of two new sources, IGR
J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure
members of the intermediate polar class. Timing and spectral analysis of IGR
J00234+6141 are based on a XMM-Newton observation and INTEGRAL publicly
available data. For 1RXS J213344.1+510725 we use XMM-Newton and Suzaku
observations at different epochs, as well as INTEGRAL publicly available data.
We determine a spin period of 561.64 +/- 0.56 s for the white dwarf in IGR
J00234+6141. The X-ray pulses are observed up to about 2 keV. From XMM-Newton
and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period
of 570.862 +/- 0.034 s. The observations span three epochs where the pulsation
is observed to change at different energies both in amplitude and shape. In
both objects, the spectral analysis spanned over a wide energy range, from 0.3
to 100 keV, shows the presence of multiple emission components absorbed by
dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a
multi-temperature plasma with a maximum temperature of about 50 keV. In 1RXS
J213344.1+510725, multiple optically thin components are inferred, as well as
an optically thick (blackbody) soft X-ray emission with a temperature of about
100 eV. This latter adds 1RXS J213344.1+510725 to the growing group of soft
X-ray intermediate polars. (abridged)Comment: 12 pages, 8 figures, 5 tables. Accepted for publication in A&
Wavelet and R/S analysis of the X-ray flickering of cataclysmic variables
Recently, wavelets and R/S analysis have been used as statistical tools to
characterize the optical flickering of cataclysmic variables. Here we present
the first comprehensive study of the statistical properties of X-ray flickering
of cataclysmic variables in order to link them with physical parameters. We
analyzed a sample of 97 X-ray light curves of 75 objects of all classes
observed with the XMM-Newton space telescope. By using the wavelets analysis,
each light curve has been characterized by two parameters, alpha and Sigma,
that describe the energy distribution of flickering on different timescales and
the strength at a given timescale, respectively. We also used the R/S analysis
to determine the Hurst exponent of each light curve and define their degree of
stochastic memory in time. The X-ray flickering is typically composed of long
time scale events (1.5 < alpha < 3), with very similar strengths in all the
subtypes of cataclysmic variables (-3 < Sigma < -1.5). The X-ray data are
distributed in a much smaller area of the alpha-Sigma parameter space with
respect to those obtained with optical light curves. The tendency of the
optical flickering in magnetic systems to show higher Sigma values than the
non-magnetic systems is not encountered in the X-rays. The Hurst exponents
estimated for all light curves of the sample are larger than those found in the
visible, with a peak at 0.82. In particular, we do not obtain values lower than
0.5. The X-ray flickering presents a persistent memory in time, which seems to
be stronger in objects containing magnetic white dwarf primaries. The
similarity of the X-ray flickering in objects of different classes together
with the predominance of a persistent stochastic behavior can be explained it
terms of magnetically-driven accretion processes acting in a considerable
fraction of the analyzed objects.Comment: 10 pages, 3 figures, 2 tables. Language revision. Accepted for
publication in A&
Effects of Bariatric Surgery on COVID-19: a Multicentric Study from a High Incidence Area
Introduction: The favorable effects of bariatric surgery (BS) on overall pulmonary function and obesity-related comorbidities could influence SARS-CoV-2 clinical expression. This has been investigated comparing COVID-19 incidence and clinical course between a cohort of patients submitted to BS and a cohort of candidates for BS during the spring outbreak in Italy. Materials and Methods: From April to August 2020, 594 patients from 6 major bariatric centers in Emilia-Romagna were administered an 87-item telephonic questionnaire. Demographics, COVID-19 incidence, suggestive symptoms, and clinical outcome parameters of operated patients and candidates to BS were compared. The incidence of symptomatic COVID-19 was assessed including the clinical definition of probable case, according to World Health Organization criteria. Results: Three hundred fifty-three operated patients (Op) and 169 candidates for BS (C) were finally included in the statistical analysis. While COVID-19 incidence confirmed by laboratory tests was similar in the two groups (5.7% vs 5.9%), lower incidence of most of COVID-19-related symptoms, such as anosmia (p: 0.046), dysgeusia (p: 0.049), fever with rapid onset (p: 0.046) were recorded among Op patients, resulting in a lower rate of probable cases (14.4% vs 23.7%; p: 0.009). Hospitalization was more frequent in C patients (2.4% vs 0.3%, p: 0.02). One death in each group was reported (0.3% vs 0.6%). Previous pneumonia and malignancies resulted to be associated with symptomatic COVID-19 at univariate and multivariate analysis. Conclusion: Patients submitted to BS seem to develop less severe SARS-CoV-2 infection than subjects suffering from obesity
Characterization of new hard X-ray Cataclysmic Variables
We aim at characterizing a sample of 9 new hard X-ray selected Cataclysmic
Variable (CVs), to unambiguously identify them as magnetic systems of the
Intermediate Polar (IP) type. We performed timing and spectral analysis by
using X-ray, and simultaneous UV and optical data collected by XMM-Newton,
complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse
arrival time were used to estimate the orbital periods. The X-ray spectra were
fitted using composite models consisting of different absorbing columns and
emission components. Strong X-ray pulses at the White Dwarf (WD) spin period
are detected and found to decrease with energy. Most sources are spin-dominated
systems in the X-rays, though four are beat dominated at optical wavelengths.
We estimated the orbital period in all system (except for IGR J16500-3307),
providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR
J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX
J0636+3535 posses a soft X-ray optically thick component at kT 80 eV. An
intense K_alpha Fe line at 6.4 keV is detected in all sources. An absorption
edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and
lower limits to the accretion rates are estimated. We found all sources to be
IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors,
while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535
display a disc-overflow accretion mode. All sources show a temperature gradient
in the post-shock regions and a highly absorbed emission from material located
in the pre-shock flow which is also responsible for the X-ray pulsations.
Reflection at the WD surface is likely the origin of the fluorescent iron line.
There is an increasing evidence for the presence of a warm absorber in IPs. The
addition of 2 systems to the subgroup of soft X-ray IPs confirms a \sim 30%
incidence.Comment: 23 pages, 11 figures, 7 tables, accepter for publication in A&A in
April 201
Fast optical source for quantum key distribution based on semiconductor optical amplifiers
A novel integrated optical source capable of emitting faint pulses with
different polarization states and with different intensity levels at 100 MHz
has been developed. The source relies on a single laser diode followed by four
semiconductor optical amplifiers and thin film polarizers, connected through a
fiber network. The use of a single laser ensures high level of
indistinguishability in time and spectrum of the pulses for the four different
polarizations and three different levels of intensity. The applicability of the
source is demonstrated in the lab through a free space quantum key distribution
experiment which makes use of the decoy state BB84 protocol. We achieved a
lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error
ratio as low as while the lower bound secure key rate
became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this
is the fastest polarization encoded QKD system which has been reported so far.
The performance, reduced size, low power consumption and the fact that the
components used can be space qualified make the source particularly suitable
for secure satellite communication
Anthropogenic disturbance in tropical forests can double biodiversity loss from deforestation
© 2016 Macmillan Publishers Limited. All rights reserved. Concerted political attention has focused on reducing deforestation, and this remains the cornerstone of most biodiversity conservation strategies. However, maintaining forest cover may not reduce anthropogenic forest disturbances, which are rarely considered in conservation programmes. These disturbances occur both within forests, including selective logging and wildfires, and at the landscape level, through edge, area and isolation effects. Until now, the combined effect of anthropogenic disturbance on the conservation value of remnant primary forests has remained unknown, making it impossible to assess the relative importance of forest disturbance and forest loss. Here we address these knowledge gaps using a large data set of plants, birds and dung beetles (1,538, 460 and 156 species, respectively) sampled in 36 catchments in the Brazilian state of Pará. Catchments retaining more than 69-80% forest cover lost more conservation value from disturbance than from forest loss. For example, a 20% loss of primary forest, the maximum level of deforestation allowed on Amazonian properties under Brazil's Forest Code, resulted in a 39-54% loss of conservation value: 96-171% more than expected without considering disturbance effects. We extrapolated the disturbance-mediated loss of conservation value throughout Pará, which covers 25% of the Brazilian Amazon. Although disturbed forests retained considerable conservation value compared with deforested areas, the toll of disturbance outside Pará's strictly protected areas is equivalent to the loss of 92,000-139,000 km2 of primary forest. Even this lowest estimate is greater than the area deforested across the entire Brazilian Amazon between 2006 and 2015 (ref. 10). Species distribution models showed that both landscape and within-forest disturbances contributed to biodiversity loss, with the greatest negative effects on species of high conservation and functional value. These results demonstrate an urgent need for policy interventions that go beyond the maintenance of forest cover to safeguard the hyper-diversity of tropical forest ecosystems
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A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network
Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazonia Sustentavel, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.Keywords: Social–ecological systems, Tropical forests, Land use, Interdisciplinary research, Sustainability, Trade-off
Brain connectivity networks at the basis of human attention components: An EEG study
The Attention Network Task (ANT) was developed to disentangle the three components of attention identified in the Posner's theoretical model (alerting, orienting and executive control) and to measure the corresponding behavioral efficiency. Several fMRI studies have already provided evidences on the anatomical separability and interdependency of these three networks, and EEG studies have also unveiled the associated brain rhythms. What is still missing is a characterization of the brain circuits subtending the attentional components in terms of directed relationships between the brain areas and their frequency content. Here, we want to exploit the high temporal resolution of the EEG, improving its spatial resolution by means of advanced source localization methods, and to integrate the resulting information by a directed connectivity analysis. The results showed in the present study demonstrate the possibility to associate a specific directed brain circuit to each attention component and to identify synthetic indices able to selectively describe their neurophysiological, spatial and spectral properties
Estimating brain connectivity when few data points are available: Perspectives and limitations
Methods based on the use of multivariate autoregressive modeling (MVAR) have proved to be an accurate and flexible tool for the estimation of brain functional connectivity. The multivariate approach, however, implies the use of a model whose complexity (in terms of number of parameters) increases quadratically with the number of signals included in the problem. This can often lead to an underdetermined problem and to the condition of multicollinearity. The aim of this paper is to introduce and test an approach based on Ridge Regression combined with a modified version of the statistics usually adopted for these methods, to broaden the estimation of brain connectivity to those conditions in which current methods fail, due to the lack of enough data points. We tested the performances of this new approach, in comparison with the classical approach based on ordinary least squares (OLS), by means of a simulation study implementing different ground-truth networks, under different network sizes and different levels of data points. Simulation results showed that the new approach provides better performances, in terms of accuracy of the parameters estimation and false positives/false negatives rates, in all conditions related to a low data points/model dimension ratio, and may thus be exploited to estimate and validate estimated patterns at single-trial level or when short time data segments are available
Profundidade de semeadura na emergência do capim colchão.
Para a elaboração de estratégias racionais de manejo das plantas daninhas o conhecimento científico sobre a biologia dessas espécies relacionada à profundidade máxima de emergência proporciona a interpretação do comportamento ecológicos das espécies no campo, permitindo a adoção de práticas adequadas de manejo, incluindo práticas não-químicas. Deste modo, o trabalho objetivou avaliar a emergência de plântulas de Digitaria ciliares L., conhecido como capim-colchão, em diferentes profundidades de semeadura. O experimento foi desenvolvido em casa de vegetação da Universidade do Estado de Mato Grosso (UNEMAT) onde os tratamentos consistiram em diferentes profundidades de semeadura (0, 0,5, 1,0, 2,0, 4,0, 8,0 e 10 cm). O delineamento experimental utilizado foi o inteiramente ao acaso, sendo três repetições e sete tratamentos. Cada parcela foi composta por um vaso com capacidade de 2,5 L de capacidade, preenchido com Latossolo Vermelho Amarelo distrófico de textura argilosa, acrescida de 25 sementes distribuídas nas profundidades pré-determinadas. As avaliações de emergência das plântulas foram realizadas diariamente durante 28 dias, sendo avaliado o índice de velocidade de emergência (IVE) e a porcentagem de emergência, sendo todos os dados submetidos à aplicação do teste ?F? na análise da variância e as médias analisadas e comparadas por meio do teste de ?Tukey? a 5% de probabilidade. A emergência das plântulas de capim-colchão é influenciada de forma exponencial decrescente pela profundidade de semeadura dos propágulos no substrato, havendo alta emergência das plântulas quando as sementes foram depositadas na superfície e baixa emergência quando submetidas de 0,5 a 10 cm de profundidade. Em superfície (0 cm) a emergência das plântulas foi favorecida, de maneira que as médias atingiram cerca de 86% de emergência, entretanto nas demais profundidades os valores foram abaixo de 21%. Conclui-se que o capimcolchão (D. ciliaris L.) apresenta maior emergência em superfície