215 research outputs found
Improved WKB approximation for quantum tunneling: Application to heavy ion fusion
In this paper we revisit the one-dimensional tunneling problem. We consider
Kemble's approximation for the transmission coefficient. We show how this
approximation can be extended to above-barrier energies by performing the
analytical continuation of the radial coordinate to the complex plane. We
investigate the validity of this approximation by comparing their predictions
for the cross section and for the barrier distribution with the corresponding
quantum mechanical results. We find that the extended Kemble's approximation
reproduces the results of quantum mechanics with great accuracy.Comment: 8 pages, 6 figures, in press, in European. Phys. Journal A (2017
Approximate transmission coefficients in heavy ion fusion
In this paper we revisit the one-dimensional tunnelling problem. We consider
different approximations for the transmission through the Coulomb barrier in
heavy ion collisions at near-barrier energies. First, we discuss approximations
of the barrier shape by functional forms where the transmission coefficient is
known analytically. Then, we consider Kemble's approximation for the
transmission coefficient. We show how this approximation can be extended to
above-barrier energies by performing the analytical continuation of the radial
coordinate to the complex plane. We investigate the validity of the different
approximations considered in this paper by comparing their predictions for
transmission coefficients and cross sections of three heavy ion systems with
the corresponding quantum mechanical results.Comment: 12 pages, 6 figure
Is there an excess of black holes around ? Optimising the complexity of population models with the use of reversible jump MCMC
Some analyses of the third gravitational wave catalogue released by the
LIGO-Virgo-KAGRA collaboration (LVK) suggest an excess of black holes around
. In order to investigate this feature, we introduce two
flexible population models, a semi-parametric one and a non-parametric one.
Both make use of reversible jump Markov chain Monte-Carlo to optimise their
complexity. We also illustrate how the latter can be used to efficiently
perform model selection. Our parametric model broadly agrees with the fiducial
analysis of the LVK, but finds a peak of events at slightly larger masses. Our
non-parametric model shows this same displacement. Moreover, it also suggests
the existence of an excess of black holes around . We assess the
robustness of this prediction by performing mock injections and running
hierarchical analyses on those. We find that such a feature might be due to
statistical fluctuations, given the small number of events observed so far,
with a probability. We estimate that with a few hundreds of observations,
as expected for O4, our non-parametric model will, be able to robustly
determine the presence of this excess. It will then allow for an efficient
agnostic inference of the properties of black holes.Comment: correct typo in equation
The lure of sirens: joint distance and velocity measurements with third generation detectors
The next generation of detectors will detect gravitational waves from binary neutron stars at cosmological distances, for which around a thousand electromagnetic follow-ups may be observed per year. So far, most work devoted to the expected cosmological impact of these standard sirens employed them only as distance indicators. Only recently their use as tracers of clustering, similar to what already proposed for supernovae, has been studied. Focusing on the expected specifications of the Einstein Telescope (ET), we forecast here the performance on cosmological parameters of future standard sirens as both distance and density indicators, with emphasis on the linear perturbation growth index and on spatial curvature. We improve upon previous studies in a number of ways: a more detailed analysis of available telescope time, the inclusion of more cosmological and nuisance parameters, the Alcock-Paczynski correction, the use of sirens also as both velocity and density tracers, and a more accurate estimation of the distance posterior. We find that the analysis of the clustering of sirens improves the constraints on by 30% and on by over an order of magnitude, with respect to their use merely as distance indicators. With 5 years of joint ET and Rubin Observatory follow-ups we could reach precision of 0.1 km/s/Mpc in and 0.02 in using only data in the range . We also find that the use of sirens as tracers of density, and not only velocity, yields good improvements on the growth of structure constraints
Measuring source properties and quasi-normal-mode frequencies of heavy massive black-hole binaries with LISA
The laser-interferometer space antenna (LISA) will be launched in the mid
2030s. It promises to observe the coalescence of massive black-hole (BH)
binaries with signal-to-noise ratios (SNRs) reaching thousands. Crucially, it
will detect some of these binaries with high SNR both in the inspiral and the
merger-ringdown stages. Such signals are ideal for tests of General Relativity
(GR) using information from the whole waveform. Here, we consider
astrophysically motivated binary systems at the high-mass end of the population
observable by LISA, and simulate their LISA signals using the newly developed
parametrised, multipolar, aligned-spin effective-one-body model: pSEOBNRv5HM.
The merger-ringdown signal in this model depends on the binary properties
(masses and spins), and also on parameters that describe fractional deviations
from the GR quasi-normal-mode frequencies of the remnant BH. Performing full
Bayesian analyses, we assess to which accuracy LISA will be able to constrain
deviations from GR in the ringdown signal when using information from the whole
signal. We find that these deviations can typically be constrained to within
and in the best cases to within . We also show that we can measure
the binary masses and spins with great accuracy even for very massive BH
systems with low SNR in the inspiral: individual source-frame masses can
typically be constrained to within and as precisely as , and
individual spins can typically be constrained to within and as precisely
as . Finally, we probe the accuracy of the SEOBNRv5HM waveform family by
performing synthetic injections of GR numerical-relativity waveforms. For the
source parameters considered, we measure erroneous deviations from GR due to
systematics in the waveform model. These results confirm the need for improving
waveform models to perform tests of GR with binary BHs at high SNR with LISA.Comment: 15 pages, 18 with appendices, 19 figure
Observing GW190521-like binary black holes and their environment with LISA
Binaries of relatively massive black holes like GW190521 have been proposed to form in dense gas environments, such as the disks of Active Galactic Nuclei (AGNs), and they might be associated with transient electromagnetic counterparts. The interactions of this putative environment with the binary could leave a significant imprint at the low gravitational wave frequencies observable with the Laser Interferometer Space Antenna (LISA). We show that LISA will be able to detect up to ten GW190521-like black hole binaries, with sky position errors deg. Moreover, it will measure directly various effects due to the orbital motion around the supermassive black hole at the center of the AGN, especially the Doppler modulation and the Shapiro time delay. Thanks to a careful treatment of their frequency domain signal, we were able to perform the full parameter estimation of Doppler and Shapiro-modulated binaries as seen by LISA. We find that the Doppler and Shapiro effects will allow for measuring the AGN parameters (radius and inclination of the orbit around the AGN, central black hole mass) with up to percent-level precision. Properly modeling these low-frequency environmental effects is crucial to determine the binary formation history, as well as to avoid biases in the reconstruction of the source parameters and in tests of general relativity with gravitational waves. <br
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Kawasaki-like multisystem inflammatory syndrome in children during the covid-19 pandemic in Paris, France: prospective observational study.
OBJECTIVES: To describe the characteristics of children and adolescents affected by an outbreak of Kawasaki-like multisystem inflammatory syndrome and to evaluate a potential temporal association with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. DESIGN: Prospective observational study. SETTING: General paediatric department of a university hospital in Paris, France. PARTICIPANTS: 21 children and adolescents (aged ≤18 years) with features of Kawasaki disease who were admitted to hospital between 27 April and 11 May 2020 and followed up until discharge by 15 May 2020. MAIN OUTCOME MEASURES: The primary outcomes were clinical and biological data, imaging and echocardiographic findings, treatment, and outcomes. Nasopharyngeal swabs were prospectively tested for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR) and blood samples were tested for IgG antibodies to the virus. RESULTS: 21 children and adolescents (median age 7.9 (range 3.7-16.6) years) were admitted with features of Kawasaki disease over a 15 day period, with 12 (57%) of African ancestry. 12 (57%) presented with Kawasaki disease shock syndrome and 16 (76%) with myocarditis. 17 (81%) required intensive care support. All 21 patients had noticeable gastrointestinal symptoms during the early stage of illness and high levels of inflammatory markers. 19 (90%) had evidence of recent SARS-CoV-2 infection (positive RT-PCR result in 8/21, positive IgG antibody detection in 19/21). All 21 patients received intravenous immunoglobulin and 10 (48%) also received corticosteroids. The clinical outcome was favourable in all patients. Moderate coronary artery dilations were detected in 5 (24%) of the patients during hospital stay. By 15 May 2020, after 8 (5-17) days of hospital stay, all patients were discharged home. CONCLUSIONS: The ongoing outbreak of Kawasaki-like multisystem inflammatory syndrome among children and adolescents in the Paris area might be related to SARS-CoV-2. In this study an unusually high proportion of the affected children and adolescents had gastrointestinal symptoms, Kawasaki disease shock syndrome, and were of African ancestry
Detecting the start of an influenza outbreak using exponentially weighted moving average charts
Background. Influenza viruses cause seasonal outbreaks in temperate climates, usually during winter and early spring, and are endemic in tropical climates. The severity and length of influenza outbreaks vary from year to year. Quick and reliable detection of the start of an outbreak is needed to promote public health measures. Methods. We propose the use of an exponentially weighted moving average (EWMA) control chart of laboratory confirmed influenza counts to detect the start and end of influenza outbreaks. Results. The chart is shown to provide timely signals in an example application with seven years of data from Victoria, Australia. Conclusions. The EWMA control chart could be applied in other applications to quickly detect influenza outbreaks
Challenges of keyword-based location disclosure
A practical solution to location privacy should be incremen-tally deployable. We claim it should hence reconcile the eco-nomic value of location to aggregators, usually ignored by prior works, with a user’s control over her information. Loca-tion information indeed is being collected and used by many mobile services to improve revenues, and this gives rise to a heated debate: Privacy advocates ask for stricter regula-tion on information collection, while companies argue that it would jeopardize the thriving economy of the mobile web. We describe a system that gives users control over their information and does not degrade the data given to aggre-gators. Recognizing that the first challenge is to express lo-cations in a way that is meaningful for advertisers and users, we propose a keyword based design. Keywords characterize locations, let the users inform the system about their sen-sitivity to disclosure, and build information directly usable by an advertiser’s targeting campaign. Our work makes two main contributions: we design a market of location infor-mation based on keywords and we analyze its robustness to attacks using data from ad-networks, geo-located services, and cell networks. Categories and Subject Descriptors Security and Privacy [Human and societal aspects of security and privacy]: Usability in security and privac
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