1,039 research outputs found
Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gas
We have considered the processes which lead to elastic scattering between two
far ultraviolet or X--ray photons while they propagate inside a solid, modeled
as a simple electron gas. The new ingredient, with respect to the standard
theory of photon--photon scattering in vacuum, is the presence of low--energy,
nonrelativistic electron--hole excitations. Owing to the existence of
two--photon vertices, the scattering processes in the metal are predominantly
of second order, as opposed to fourth order for the vacuum case. The main
processes in second order are dominated by exchange of virtual plasmons between
the two photons. For two photons of similar energy , this gives
rise to a cross section rising like up to maximum of around
~cm, and then decreasing like . The maximal cross
section is found for the photon wavevector , the Fermi surface
size, which typically means a photon energy in the keV range.
Possible experiments aimed at checking the existence of these rare but
seemingly measurable elastic photon--photon scattering processes are discussed,
using in particular intense synchrotron sources.Comment: 33 pages, TeX, Version 3.1, S.I.S.S.A. preprint 35/93/C
Uncertainty Quantification in Bayesian Reduced-Rank Sparse Regressions
Reduced-rank regression recognises the possibility of a rank-deficient matrix
of coefficients, which is particularly useful when the data is
high-dimensional. We propose a novel Bayesian model for estimating the rank of
the rank of the coefficient matrix, which obviates the need of post-processing
steps, and allows for uncertainty quantification. Our method employs a mixture
prior on the regression coefficient matrix along with a global-local shrinkage
prior on its low-rank decomposition. Then, we rely on the Signal Adaptive
Variable Selector to perform sparsification, and define two novel tools, the
Posterior Inclusion Probability uncertainty index and the Relevance Index. The
validity of the method is assessed in a simulation study, then its advantages
and usefulness are shown in real-data applications on the chemical composition
of tobacco and on the photometry of galaxies
Towards a direct measurement of vacuum magnetic birefringence: PVLAS achievements
Nonlinear effects in vacuum have been predicted but never observed yet
directly. The PVLAS collaboration has long been working on an apparatus aimed
at detecting such effects by measuring vacuum magnetic birefringence.
Unfortunately the sensitivity has been affected by unaccounted noise and
systematics since the beginning. A new small prototype ellipsometer has been
designed and characterized at the Department of Physics of the University of
Ferrara, Italy entirely mounted on a single seismically isolated optical bench.
With a finesse F = 414000 and a cavity length L = 0.5 m we have reached the
predicted sensitivity of psi = 2x10^-8 1/sqrt(Hz) given the laser power at the
output of the ellipsomenter of P = 24 mW. This record result demonstrates the
feasibility of reaching such sensitivities and opens the way to designing a
dedicated apparatus for a first detection of vacuum magnetic birefringence
Evidence-based practice among Italian osteopaths: a national cross-sectional survey.
BackgroundWhile evidence-based practice (EBP) is widely accepted across healthcare professions, research investigating its implementation in manual therapy professions such as osteopathy is limited. The primary aim of this study was to investigate Italian osteopaths' attitudes, skills, and use of EBP. A secondary purpose was to understand the obstacles and enablers to EBP adoption in the Italian osteopathic context.MethodsA cross-sectional national survey was conducted (April to June 2020) among a sample of Italian osteopaths. Eligible participants were invited to complete the Italian-translated Evidence-Based practice Attitude and Utilization Survey (EBASE) anonymously online using various recruitment strategies, including email and social media campaigns. In addition to the three EBASE sub-scores (attitudes, skills and use), the demographic characteristics of the sample were considered.ResultsA total of 473 osteopaths responded to the survey. The sample appeared to represent the Italian osteopathic profession. The majority of participants had a favorable attitude toward EBP. Eighty-eight percent of respondents agreed that EBP was necessary for osteopathy practice and that scientific literature and research findings were beneficial to their clinical scenario (95%). Perceived skill levels in EBP were rated as moderate, with the lowest scores for items relating to clinical research and systematic review conduct. Apart from reading/reviewing scientific literature and using online search engines to locate relevant research papers, participant engagement in all other EBP-related activities was generally low. Clinical practice was perceived to be based on a very small proportion of clinical research evidence. The primary obstacles to EBP implementation were a dearth of clinical evidence in osteopathy, and poor skills in applying research findings. The primary enablers of EBP adoption were access to full-text articles, internet connectivity at work, and access to online databases.ConclusionsItalian osteopaths were largely supportive of evidence-based practice but lacked basic skills in EBP and rarely engaged in EBP activities. The updating of osteopathic training curriculum and professional formal regulation in Italy could provide a suitable framework to improve EBP skills and use
Limits on the violation of g-universality with a Galileo-type experiment
Abstract We present new results for a Galilean experiment using two masses of copper and tungsten in simultaneous free fall. The experiment searches for a possible difference in the free-fall acceleration Î g and it is sensitive to any composition-dependent interaction between the test masses and the earth, whose range exceeds 10 km. The results show no evidence for any composition-dependent gravity-like interaction within Îg ÎŒ Gal
Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas
Low energy non linear QED effects in vacuum have been predicted since 1936
and have been subject of research for many decades. Two main schemes have been
proposed for such a 'first' detection: measurements of ellipticity acquired by
a linearly polarized beam of light passing through a magnetic field and direct
light-light scattering. The study of the propagation of light through an
external field can also be used to probe for new physics such as the existence
of axion-like particles and millicharged particles. Their existence in nature
would cause the index of refraction of vacuum to be different from unity in the
presence of an external field and dependent of the polarization direction of
the light propagating. The major achievement of reaching the project
sensitivities in gravitational wave interferometers such as LIGO an VIRGO has
opened the possibility of using such instruments for the detection of QED
corrections in electrodynamics and for probing new physics at very low
energies. In this paper we discuss the difference between direct birefringence
measurements and index of refraction measurements. We propose an almost
parasitic implementation of an external magnetic field along the arms of the
VIRGO interferometer and discuss the advantage of this choice in comparison to
a previously proposed configuration based on shorter prototype interferometers
which we believe is inadequate. Considering the design sensitivity in the
strain, for the near future VIRGO+ interferometer, of in the range 40 Hz Hz leads to a variable
dipole magnet configuration at a frequency above 20 Hz such that Tm/ for a `first' vacuum non linear QED detection
Precise mirror alignment and basic performance of the RICH detector of the NA62 experiment at CERN
The Ring Imaging Cherenkov detector is crucial for the identification of
charged particles in the NA62 experiment at the CERN SPS. The detector
commissioning was completed in 2016 by the precise alignment of mirrors using
reconstructed tracks. The alignment procedure and measurement of the basic
performance are described. Ring radius resolution, ring centre resolution,
single hit resolution and mean number of hits per ring are evaluated for
positron tracks. The contribution of the residual mirror misalignment to the
performance is calculated.Comment: 13 pages, 10 figure
The Casimir force and the quantum theory of lossy optical cavities
We present a new derivation of the Casimir force between two parallel plane
mirrors at zero temperature. The two mirrors and the cavity they enclose are
treated as quantum optical networks. They are in general lossy and
characterized by frequency dependent reflection amplitudes. The additional
fluctuations accompanying losses are deduced from expressions of the optical
theorem. A general proof is given for the theorem relating the spectral density
inside the cavity to the reflection amplitudes seen by the inner fields. This
density determines the vacuum radiation pressure and, therefore, the Casimir
force. The force is obtained as an integral over the real frequencies,
including the contribution of evanescent waves besides that of ordinary waves,
and, then, as an integral over imaginary frequencies. The demonstration relies
only on general properties obeyed by real mirrors which also enforce general
constraints for the variation of the Casimir force.Comment: 18 pages, 6 figures, minor amendment
Light Detection System and Time Resolution of the NA62 RICH
A large RICH detector is used in NA62 to suppress the muon contamination in
the charged pion sample by a factor of 100 in the momentum range between 15 and
35 GeV/c. Cherenkov light is collected by 1952 photomultipliers placed at the
upstream end. In this paper the characterization of the photomultipliers and
the dedicated Frontend and Data Acquisition electronics are described, the time
resolution and the light detection efficiency measurement are presented.Comment: 15 pages, 11 figure
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