1,869 research outputs found
Semiclassical Propagation of Coherent States for the Hartree equation
In this paper we consider the nonlinear Hartree equation in presence of a
given external potential, for an initial coherent state. Under suitable
smoothness assumptions, we approximate the solution in terms of a time
dependent coherent state, whose phase and amplitude can be determined by a
classical flow. The error can be estimated in by C \sqrt {\var}, \var
being the Planck constant. Finally we present a full formal asymptotic
expansion
Revisiting Kepler-444. II. Rotational, orbital and high-energy fluxes evolution of the system
Context. Kepler-444 is one of the oldest planetary systems known thus far.
Its peculiar configuration consisting of five sub-Earth-sized planets orbiting
the companion to a binary stellar system makes its early history puzzling.
Moreover, observations of HI-Ly- variations raise many questions
about the potential presence of escaping atmospheres today. Aims. We aim to
study the orbital evolution of Kepler-444-d and Kepler-444-e and the impact of
atmospheric evaporation on Kepler-444-e. Methods. Rotating stellar models of
Kepler-444-A were computed with the Geneva stellar evolution code and coupled
to an orbital evolution code, accounting for the effects of dynamical,
equilibrium tides and atmospheric evaporation. The impacts of multiple stellar
rotational histories and extreme ultraviolet (XUV) luminosity evolutionary
tracks are explored. Results. Using detailed rotating stellar models able to
reproduce the rotation rate of Kepler-444-A, we find that its observed rotation
rate is perfectly in line with what is expected for this old K0-type star,
indicating that there is no reason for it to be exceptionally active as would
be required to explain the observed HI-Ly- variations from a
stellar origin. We show that given the low planetary mass ( 0.03 M) and relatively large orbital distance ( 0.06 AU) of
Kepler-444-d and e, dynamical tides negligibly affect their orbits, regardless
of the stellar rotational history considered. We point out instead how
remarkable the impact is of the stellar rotational history on the estimation of
the lifetime mass loss for Kepler-444-e. We show that, even in the case of an
extremely slow rotating star, it seems unlikely that such a planet could retain
a fraction of the initial water-ice content if we assume that it formed with a
Ganymede-like composition
Constraints on planetary tidal dissipation from a detailed study of Kepler 91b
Context. With the detection of thousands of exoplanets, characterising their
dynamical evolution in detail represents a key step in the understanding of
their formation. Studying the dissipation of tides occurring both in the host
star and in the planets is of great relevance in order to investigate the
distribution of the angular momentum occurring among the objects populating the
system and to studying the evolution of the orbital parameters. From a
theoretical point of view, the dissipation of tides throughout a body may be
studied by relying on the so-called phase or time-lag equilibrium tides model
in which the reduced tidal quality factor Q'p, or equivalently the product
between the love number and the time lag (k2DeltaT), describe how efficiently
tides are dissipated within the perturbed body. Constraining these factors by
looking at the current configuration of the exoplanetary system is extremely
challenging, and simulations accounting for the evolution of the system as a
whole might help to shed some light on the mechanisms governing this process.
Aims. We aim to constrain the tidal dissipation factors of hot-Jupiter-like
planets by studying the orbital evolution of Kepler-91b. Methods. We firstly
carried out a detailed asteroseismc characterisation of Kepler-91 and computed
a dedicated stellar model using both classical and astereoseismic constraints.
We then coupled the evolution of the star to the one of the planets by means of
our orbital evolution code and studied the evolution of the system by
accounting for tides dissipated both in the planet and in the host star.
Results. We found that the maximum value for k2DeltaT (or equivalently the
minimum value for Q'p) determining the efficiency of equilibrium tides
dissipation occurring within Kepler-91b is 0.4 pm 0.25 s (4.5+5.8 * 10^5).Comment: accepted for publication in Astronomy & Astrophysic
High prevalence of anti-hepatitis e virus antibodies among blood donors in central Italy, february to march 2014
Prevalence of anti-hepatitis E virus (HEV) antibodies is highly variable in developed countries, which seems partly due to differences in assay sensitivity. Using validated sensitive assays, we tested 313 blood donors attending a hospital transfusion unit in central Italy in January and February 2014 for anti-HEV IgG and IgM and HEV RNA. Data on HEV exposure were collected from all donors. Overall anti-HEV IgG prevalence was 49% (153/313). Eating raw dried pig-liver sausage was the only independent predictor of HEV infection (adjusted prevalence rate ratio = 2.14; 95% confidence interval: 1.23–3.74). Three donors were positive for either anti-HEV IgM (n = 2; 0.6%) or HEV RNA (n = 2; 0.6%); they were completely asymptomatic, without alanine aminotransferase (ALT) abnormalities. Of the two HEV RNA-positive donors (both harbouring genotype 3), one was anti-HEV IgG- and IgM-positive, the other was anti-HEV IgG- and IgM-negative. The third donor was positive for anti-HEV IgG and IgM but HEV RNA-negative. HEV infection is therefore hyperendemic among blood donors (80% men 18–64 years-old) from central Italy and associated with local dietary habits. Nearly 1% of donors have acute or recent infection, implying potential transmission to blood recipients. Neither ALT nor anti-HEV IgM testing seems useful to prevent transfusion-transmitted HEV infection. © 2016, European Centre for Disease Prevention and Control
Quantum Kinetic Evolution of Marginal Observables
We develop a rigorous formalism for the description of the evolution of
observables of quantum systems of particles in the mean-field scaling limit.
The corresponding asymptotics of a solution of the initial-value problem of the
dual quantum BBGKY hierarchy is constructed. Moreover, links of the evolution
of marginal observables and the evolution of quantum states described in terms
of a one-particle marginal density operator are established. Such approach
gives the alternative description of the kinetic evolution of quantum
many-particle systems to generally accepted approach on basis of kinetic
equations.Comment: 18 page
Meningococcal C conjugate vaccine effectiveness before and during an outbreak of invasive meningococcal disease due to Neisseria meningitidis serogroup C/cc11, Tuscany, Italy
Introduction: In Tuscany, Italy, where a universal immunization program with monovalent meningococcal C conjugate vaccine (MCC) was introduced in 2005, an outbreak of invasive meningococcal disease (IMD) due to the hypervirulent strain of Neisseria meningitidis C/cc11 occurred in 2015–2016, leading to an immunization reactive campaign using either the tetravalent (ACWY) meningococcal conjugate or the MCC vaccine. During the outbreak, IMD serogroup C (MenC) cases were also reported among vaccinated individuals. This study aimed to characterize meningococcal C conjugate vaccines (MenC-vaccines) failures and to estimate their effectiveness since the introduction (2005–2016) and during the outbreak (2015–2016). Methods: MenC cases and related vaccine-failures were drawn from the National Surveillance System of Invasive Bacterial Disease (IBD) for the period 2006–2016. A retrospective cohort-study, including the Tuscany' population of the birth-cohorts 1994–2014, was carried out. Based on annual reports of vaccination, person-years of MenC-vaccines exposed and unexposed individuals were calculated by calendar-year, birth-cohort, and local health unit. Adjusted (by birth-cohort, local health unit, and calendar-year) risk-ratios (ARR) of MenC invasive disease for vaccinated vs unvaccinated were estimated by the Poisson model. Vaccine-effectiveness (VE) was estimated as: VE = 1-ARR. Results: In the period 2006–2016, 85 MenC-invasive disease cases were reported; 61 (71.8%) from 2015 to 2016. Twelve vaccine failures occurred, all of them during the outbreak. The time-interval from immunization to IMD onset was 20 days in one case, from 9 months to 3 years in six cases, and ≥7 years in five cases. VE was, 100% (95%CI not estimable, p = 0.03) before the outbreak (2006–2014) and 77% (95%CI 36–92, p < 0.01) during the outbreak; VE was 80% (95%CI 54–92, p < 0.01) during the overall period. Conclusions: In Tuscany, MenC-vaccine failures occurred exclusively during the 2015–2016 outbreak. Most of them occurred several years after vaccination. VE during the outbreak-period was rather high supporting an effective protection induced by MenC-vaccines
Novel plasmid-mediated colistin resistance mcr-4 gene in Salmonella and Escherichia coli, Italy 2013, Spain and Belgium, 2015 to 2016
A novel mcr colistin resistance gene was identified in a strain of Salmonella enterica, monophasic variant of serovar Typhimurium (4,5,12:i:- ), isolated from a pig at slaughter in Italy in 2013, and in Escherichia coli strains collected during routine diagnostic of postweaning diarrhoea in pigs from Spain and Belgium in 2015 and 2016. Immediate implementation of mcrscreening including this novel gene variant is required for Salmonella and E. coli from humans and food-producing animals in Europe. © 2017, European Centre for Disease Prevention and Control (ECDC). All rights reserved
New method to measure thermal shock resistance in ceramics using a piezo-spectroscopic technique
A new method for assessing the critical temperature in thermally shocked ceramics is proposed. It is based on the measurement of stress relaxation of residual stresses as a consequence of thermal shock. The change in the stress-field is determined by piezo-spectroscopic technique. The technique is described and the results analyzed. The values obtained are compared with those obtained by the conventional method based on strength degradation measured on test pieces quenched at different temperatures. The agreement among the data is very good
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