1,680 research outputs found
Light storage protocols in Tm:YAG
We present two quantum memory protocols for solids: A stopped light approach
based on spectral hole burning and the storage in an atomic frequency comb.
These procedures are well adapted to the rare-earth ion doped crystals. We
carefully clarify the critical steps of both. On one side, we show that the
slowing-down due to hole-burning is sufficient to produce a complete mapping of
field into the atomic system. On the other side, we explain the storage and
retrieval mechanism of the Atomic Frequency Comb protocol. This two important
stages are implemented experimentally in Tm- doped
yttrium-aluminum-garnet crystal
The 1980 earthquake in southern Italy: rescue of trapped victims and mortality.
A retrospective survey was undertaken on the health effects of the 1980 earthquake in southern Italy. The study population included 3619 people living in 7 villages situated near the epicentre of the disaster. The overall casualty rate (dead and injured) was 19.7%. Nearly all the deaths (192/202) occurred among trapped people who died before they could be rescued. Eighty per cent of all the trapped people were extricated within 2 days, mostly without the use of sophisticated means. The probability of survival decreased sharply, the longer the time before extrication. The crude mortality during the 18 months following the earthquake was 19.0 per thousand among the injured people who received treatment, and 14.1 per thousand among non-injured people. After age standardization, there was no significant difference between these two figures and the expected mortality figures for the Italian population in normal times (14.4 per thousand). These results stress the importance of providing rescue activities in the first 48 hours after the impact. Strengthening the self-reliance of the community in disaster preparedness is suggested as the best way to improve the effectiveness of relief operations. In disaster-prone areas, training and education in methods of rescue should be an integral part of any primary health care programme
Inhomogeneous Superconductivity in Comb-Shaped Josephson Junction Networks
We show that some of the Josephson couplings of junctions arranged to form an
inhomogeneous network undergo a non-perturbative renormalization provided that
the network's connectivity is pertinently chosen. As a result, the zero-voltage
Josephson critical currents turn out to be enhanced along directions
selected by the network's topology. This renormalization effect is possible
only on graphs whose adjacency matrix admits an hidden spectrum (i.e. a set of
localized states disappearing in the thermodynamic limit). We provide a
theoretical and experimental study of this effect by comparing the
superconducting behavior of a comb-shaped Josephson junction network and a
linear chain made with the same junctions: we show that the Josephson critical
currents of the junctions located on the comb's backbone are bigger than the
ones of the junctions located on the chain. Our theoretical analysis, based on
a discrete version of the Bogoliubov-de Gennes equation, leads to results which
are in good quantitative agreement with experimental results.Comment: 4 pages, 2 figures, revte
COVID-19 Vaccines and Atrial Fibrillation: Analysis of the Post-Marketing Pharmacovigilance European Database
Atrial fibrillation (AF) has been described in COVID-19 patients. Recently, some case reports and US pharmacovigilance analyses described AF onset as a rare adverse event following COVID-19 vaccination. The possible correlation is unclear. We systematically analyzed the reports of AF related to COVID-19 vaccines collected in the European pharmacovigilance database, EudraVigilance (EV), from 2020 to November 2022. We carried out descriptive and disproportionality analyses. Moreover, we performed a sensitivity analysis, excluding the reports describing other possible alternative AF causes (pericarditis, myocarditis, COVID-19, or other drugs that may cause/exacerbate AF). Overall, we retrieved 6226 reports, which represented only 0.3% of all those related to COVID-19 vaccines collected in EV during our study period. AF reports mainly referred to adults (in particular, >65 years old), with an equal distribution in sex. Reports were mainly related to tozinameran (54.04%), elasomeran (28.3%), and ChAdOx1-S (14.32%). The reported AF required patient hospitalization in 35% of cases and resulted in a life-threatening condition in 10% of cases. The AF duration (when reported) was highly variable, but the majority of the events had a short duration (moda = 24 h). Although an increased frequency of AF reporting with mRNA vaccines emerges from our study, other investigations are required to investigate the possible correlation between COVID-19 vaccination and the rare AF occurrence
Stochastic collective dynamics of charged--particle beams in the stability regime
We introduce a description of the collective transverse dynamics of charged
(proton) beams in the stability regime by suitable classical stochastic
fluctuations. In this scheme, the collective beam dynamics is described by
time--reversal invariant diffusion processes deduced by stochastic variational
principles (Nelson processes). By general arguments, we show that the diffusion
coefficient, expressed in units of length, is given by ,
where is the number of particles in the beam and the Compton
wavelength of a single constituent. This diffusion coefficient represents an
effective unit of beam emittance. The hydrodynamic equations of the stochastic
dynamics can be easily recast in the form of a Schr\"odinger equation, with the
unit of emittance replacing the Planck action constant. This fact provides a
natural connection to the so--called ``quantum--like approaches'' to beam
dynamics. The transition probabilities associated to Nelson processes can be
exploited to model evolutions suitable to control the transverse beam dynamics.
In particular we show how to control, in the quadrupole approximation to the
beam--field interaction, both the focusing and the transverse oscillations of
the beam, either together or independently.Comment: 15 pages, 9 figure
Spherically symmetric solutions in f(R)-gravity via Noether Symmetry Approach
We search for spherically symmetric solutions of f(R) theories of gravity via
the Noether Symmetry Approach. A general formalism in the metric framework is
developed considering a point-like f(R)-Lagrangian where spherical symmetry is
required. Examples of exact solutions are given.Comment: 17 pages, to appear in Class. Quant. Gra
Towards an eficient atomic frequency comb quantum memory
We present an efficient photon-echo experiment based on atomic frequency
combs [Phys. Rev. A 79, 052329 (2009)]. Echoes containing an energy of up to
35% of that of the input pulse are observed in a Pr3+-doped Y2SiO5 crystal.
This material allows for the precise spectral holeburning needed to make a
sharp and highly absorbing comb structure. We compare our results with a simple
theoretical model with satisfactory agreement. Our results show that atomic
frequency combs has the potential for high-efficiency storage of single photons
as required in future long-distance communication based on quantum repeaters.Comment: 10 pages, 5 figure
Tracker fields from nonminimally coupled theory
We extend the concept of quintessence to a flat nonminimally coupled scalar -
tensor theories of gravity. By means of Noether's symmetries for the
cosmological pointlike Lagrangian L, it is possible to exhibit exact solutions
for a class of models depending on a free parameter s. This parameter comes out
in the relationship existing between the coupling F(\phi) and the potential
V(\phi) because of such a symmetry for L. When inverse power law potentials are
taken in account, a whole family of exact solutions parametrized by such an s
is proposed as a class of tracker fields, and some considerations are made
about them.Comment: 17 pages, submitted to Physical Review
Conceivable security risks and authentication techniques for smart devices
With the rapidly escalating use of smart devices and fraudulent transaction of users’ data from their devices, efficient and reliable techniques for authentication of the smart devices have become an obligatory issue. This paper reviews the security risks for mobile devices and studies several authentication techniques available for smart devices. The results from field studies enable a comparative evaluation of user-preferred authentication mechanisms and their opinions about reliability, biometric authentication and visual authentication techniques
- …