The statistical features of the radiation emitted by Free-Electron Lasers (FELs), either by Self-Amplified Spontaneous Emission (SASE-FELs) or by seeded emission (seeded-FELs), are attracting ...increasing attention because of the use of such light in probing high energy states of matter and their dynamics. While the experimental studies conducted so far have mainly concentrated on correlation functions, here we shift the focus towards reconstructing the distribution of the occupation numbers of the radiation energy states. In order to avoid the various drawbacks related to photon counting techniques when large numbers of photons are involved, we propose a Maximum Likelihood reconstruction of the diagonal elements of the FEL radiation states in the energy eigenbasis based on the statistics of no-click events. The ultimate purpose of such a novel approach to FEL radiation statistics is the experimental confirmation that SASE-FEL radiation exhibits thermal occupation number statistics, while seeded-FEL light Poissonian statistics typical of coherent states and thus of laser light. In this framework, it is interesting to note that the outcome of this work can be extended to any process of harmonic generation from a coherent light pulse, unlocking the gate to the study of the degree to which the original distinctive quantum features deduced from the statistical photon number fluctuations are preserved in non-linear optical processes.
Understanding how a spin current flows across metal-semiconductor interfaces at pico- and femtosecond timescales has implications for ultrafast spintronics, data processing and storage applications. ...However, the possibility to directly access the propagation of spin currents on such time scales has been hampered by the simultaneous lack of both ultrafast element specific magnetic sensitive probes and tailored metal-semiconductor interfaces. Here, by means of free electron laser-based element sensitive Kerr spectroscopy, we report direct experimental evidence of spin currents across a Ni/Si interface in the form of different magnetodynamics at the Ni M2,3 and Si L2,3 absorption edges. This further allows us to calculate the propagation velocity of the spin current in silicon, which is on the order of 0.2 nm/fs.
The most common cause of hospitalization for children younger than age one is bronchiolitis. Several prenatal and environmental risk factors may affect the incidence of hospitalization for ...bronchiolitis. The aim of this study was to investigate the relation between exposure to vehicular traffic and the incidence of hospitalization for bronchiolitis in children during their first year of life in Italy.
A multicenter prospective birth cohort study, where equal numbers of newborns of 33-34, 35-37 and ≥38 wGA were recruited at birth (1814 children) in 30 Italian neonatology units. Two interviewer-administered questionnaires were used to collect data. The first interview was carried out at the end of the Italian epidemic season. The second interview was carried out when the child was one year old. Data on possible prenatal, perinatal, and postnatal/environmental risk factors and on vehicular traffic density in the zone of residence were collected. On each interview, parents were also asked about any hospitalizations of the child. The outcome measure was the hospitalization for bronchiolitis (International Health Service ICD-9 code 466).
Univariate analysis demonstrated that exposure to air pollution due to vehicular traffic, was significantly associated with an increased risk of hospitalization for bronchiolitis. The adjusted risk from logistic regression model confirmed that children exposed to air pollution due to vehicular traffic were at increased risk of hospitalization for bronchiolitis.
Exposure to air pollution due to vehicular traffic may increase the risk of hospitalization for bronchiolitis in the first year of life.
