381 research outputs found
Fluorescent Ly-alpha emission from the high-redshift intergalactic medium
We combine a high-resolution hydro-simulation of the LambdaCDM cosmology with
two radiative transfer schemes (for continuum and line radiation) to predict
the properties, spectra and spatial distribution of fluorescent Ly-alpha
emission at z~3. We focus on line radiation produced by recombinations in the
dense intergalactic medium ionized by UV photons. In particular, we consider
both a uniform background and the case where gas clouds are illuminated by a
nearby quasar. We find that the emission from optically thick regions is
substantially less than predicted from the widely used static, plane-parallel
model. The effects induced by a realistic velocity field and by the complex
geometric structure of the emitting regions are discussed in detail. We make
predictions for the expected brightness and size distributions of the
fluorescent sources.Our results account for recent null detections and can be
used to plan new observational campaigns both in the field (to measure the
intensity of the diffuse UV background) and in the proximity of bright quasars
(to understand the origin of high colum-density absorbers).Comment: 15 pages, 12 figures, accepted for publication in Ap
Deeper Chandra Follow-up of Cygnus TeV Source Perpetuates Mystery
A 50 ksec Chandra observation of the unidentified TeV source in Cygnus
reported by the HEGRA collaboration reveals no obvious diffuse X-ray
counterpart. However, 240 Pointlike X-ray sources are detected within or nearby
the extended TeV J2032+4130 source region, of which at least 36 are massive
stars and 2 may be radio emitters. That the HEGRA source is a composite, having
as counterpart the multiple point-like X-ray sources we observe, cannot be
ruled out. Indeed, the distribution of point-like X-ray sources appears
non-uniform and concentrated broadly within the extent of the TeV source
region. We offer a hypothesis for the origin of the very high energy gamma-ray
emission in Cyg OB2 based on the local acceleration of TeV range cosmic rays
and the differential distribution of OB vs. less massive stars in this
association.Comment: Substantially revised version; incorporates referee suggestions &
expanded discussio
Computer-aided diagnosis of emphysema in COPD patients: neural-network-based analysis of lung shape in digital chest radiographs.
Careggi Smart Hospital: A mobile app for patients, citizens and healthcare staff
This paper presents a mobile app called âCareggi Smart Hospitalâ which has been developed for the Careggi Polyclinic in Florence. The application is designed for Android smartphones and tablets and it is freely downloadable from the Google Play Store. It provides various useful tools to the hospital's users such as personnel and structures finding, way-finding and the possibility to access personal medical records collected on regional electronic health record
Accretion Shocks in Clusters of Galaxies and their SZ Signature from Cosmological Simulations
Cold dark matter (CDM) hierarchical structure formation models predict the
existence of large-scale accretion shocks between the virial and turnaround
radii of clusters of galaxies. Kocsis et al. (2005) suggest that the
Sunyaev-Zel'dovich (SZ) signal associated with such shocks might be observable
with the next generation radio interferometer, ALMA. We study the
three--dimensional distribution of accretion shocks around individual clusters
of galaxies drawn from adaptive mesh refinement (AMR) and smoothed particle
hydrodynamics (SPH) simulations of LCDM (dark energy dominated CDM) models. In
relaxed clusters, we find two distinct sets of shocks. One set ("virial
shocks"), with Mach numbers of 2.5-4, is located at radii 0.9-1.3 Rvir, where
Rvir is the spherical infall estimate of the virial radius, covering about
40-50% of the total surface area around clusters at these radii. Another set of
stronger shocks ("external shocks") is located farther out, at about 3 Rvir,
with large Mach numbers (~100), covering about 40-60% of the surface area. We
simulate SZ surface brightness maps of relaxed massive galaxy clusters drawn
from high resolution AMR runs, and conclude that ALMA should be capable of
detecting the virial shocks in massive clusters of galaxies. More simulations
are needed to improve estimates of astrophysical noise and to determine optimal
observational strategies.Comment: 41 pages including 11 figures and 2 tables; ApJ, in pres
UHECR Acceleration in Dark Matter Filaments of Cosmological Structure Formation
A mechanism for proton acceleration to ~10^21eV is suggested. It may operate
in accretion flows onto thin dark matter filaments of cosmic structure
formation. The flow compresses the ambient magnetic field to strongly increase
and align it with the filament. Particles begin the acceleration by the ExB
drift with the accretion flow. The energy gain in the drift regime is limited
by the conservation of the adiabatic invariant p_perp^2/B. Upon approaching the
filament, the drift turns into the gyro-motion around the filament so that the
particle moves parallel to the azimuthal electric field. In this 'betatron'
regime the acceleration speeds up to rapidly reach the electrodynamic limit
for an accelerator with magnetic field and the orbit radius
(Larmor radius). The periodic orbit becomes unstable and the particle
slings out of the filament to the region of a weak (uncompressed) magnetic
field, which terminates the acceleration.
The mechanism requires pre-acceleration that is likely to occur in structure
formation shocks upstream or nearby the filament accretion flow. Previous
studies identify such shocks as efficient proton accelerators to a firm upper
limit ~10^19.5 eV placed by the catastrophic photo-pion losses. The present
mechanism combines explosive energy gain in its final (betatron) phase with
prompt particle release from the region of strong magnetic field. It is this
combination that allows protons to overcome both the photo-pion and the
synchrotron-Compton losses and therefore attain energy 10^21 eV. A requirement
on accelerator to reach a given E_max placed by the accelerator energy
dissipation \propto E_{max}^{2}/Z_0 due to the finite vacuum impedance Z_0 is
circumvented by the cyclic operation of the accelerator.Comment: 34 pages, 10 figures, to be published in JCA
Energy Dissipation in Interstellar Cloud Collisions
We present a study of the kinetic energy dissipation in interstellar cloud
collisions. The main aim is to understand the dependence of the elasticity
(defined as the ratio of the final to the initial kinetic energy of the clouds)
on the velocity and mass ratio of the colliding clouds, magnetic field
strength, and gas metallicity for head-on collisions. The problem has been
studied both analytically and via numerical simulations. We have derived handy
analytical relationships that well approximate the analogous numerical results.
The main findings of this work are: (i) the kinetic energy dissipation in cloud
collisions is minimum (i.e. the collision elasticity is maximum) for a cloud
relative velocity ; (ii) the above minimum value is
proportional , where is the metallicity and is the cloud
size: the larger is the more dissipative (i.e. inelastic) the
collision will be; (iii) in general, we find that the energy dissipation
decreases when the magnetic field strength, and mass ratio of the clouds are
increased and the metallicity is decreased, respectively. We briefly discuss
the relevance of this study to the global structure of the interstellar medium
and to galaxy formation and evolution.Comment: 16 pages, aasms LaTeX, 7 figures. ApJ, accepte
Integrated HTA and FMECA methodology for the evaluation of robotic surgery
Robotic surgery has been strongly improved since the beginning of the twenty-first century and chased important level of technical and clinical performances. Within the robotic area, the most worldwide used surgical robot is the da VinciÂź system made by Intuitive Surgical Inc.
The aim of this study was to evaluate at the hospital scale the robotic surgery (Hospital âBased Health Technology Assessment) in comparison to the open and laparoscopic procedures yet combining a FMECA analysis to accurately assess all those aspects involving patient and staff safety.
The total number of robotic procedures directly observed by the surgical department and reported in the following study was 44, including 28 urology interventions and 16 general surgeries. The study confirmed clinical benefits carried out with the robot but bigger complexity in managing the whole surgical system in terms of structural needs, staff and technology.
For the future, further steps regard the necessity to dispose of a wider number of robotic procedures in order to strength the analysis reliability and complete the socio-economic assessment with medium and long terms observation. Finally a new FMECA application will be essential to monitor the real effects of the suggested actions on the evaluated risks according to the already known and new failure modes
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