471 research outputs found
Flexural properties of the epoxy resin filled with single and hybrid carbon nanofillers
The aim of this paper was to estimate the effect of moisture and temperature on the
flexural properties of the epoxy filled with single and hybrid carbon nanofillers (CNTs and
CNFs) and to reveal the most environmentally stable NC. Water absorption at 70 °C until
equilibrium moisture content and heating at 70 °C for 4 weeks were followed by freezing at -
20 °C for 8 weeks. Microstructural characterization of optical images revealed homogeneous
dispersion of all carbon nanofillers in the epoxy resin at microscale. Positive nanofiller effects
were found for sorption, flexural and thermophysical characteristics of the epoxy resin. The
most environmentally stable NC was epoxy filled with 0.1 wt. % of CNTs/CNFs hybrid, which
had the lowest effect of temperature and moisture on mechanical characteristics, along with the
lowest equilibrium water content and diffusivity
Phenomenological covariant approach to gravity
We covariantly modify the Einstein-Hilbert action such that the modified
action perturbatively resolves the flat rotational velocity curve of the spiral
galaxies and gives rise to the Tully-Fisher relation, and dynamically generates
the cosmological constant. This modification requires introducing just a single
new universal parameter.Comment: v6: a mistake in deriving the equation of the cosmological constant
corrected, refs adde
Environmental Monitoring of Legionella in Hospitals in the Campania Region: A 5-Year Study
: Legionella is a pathogen that colonizes soils, freshwater, and building water systems. People who are most affected are those with immunodeficiencies, so it is necessary to monitor its presence in hospitals. The purpose of this study was to evaluate the presence of Legionella in water samples collected from hospitals in the Campania region, Southern Italy. A total of 3365 water samples were collected from January 2018 to December 2022 twice a year in hospital wards from taps and showers, tank bottoms, and air-treatment units. Microbiological analysis was conducted in accordance with the UNI EN ISO 11731:2017, and the correlations between the presence of Legionella and water temperature and residual chlorine were investigated. In total, 708 samples (21.0%) tested positive. The most represented species was L. pneumophila 2-14 (70.9%). The serogroups isolated were 1 (27.7%), 6 (24.5%), 8 (23.3%), 3 (18.9%), 5 (3.1%), and 10 (1.1%). Non-pneumophila Legionella spp. represented 1.4% of the total. Regarding temperature, the majority of Legionella positive samples were found in the temperature range of 26.0-40.9 °C. An influence of residual chlorine on the presence of the bacterium was observed, confirming that chlorine disinfection is effective for controlling contamination. The positivity for serogroups other than serogroup 1 suggested the need to continue environmental monitoring of Legionella and to focus on the clinical diagnosis of other serogroups
Newtonian Collapse of Scalar Field Dark Matter
In this letter, we develop a Newtonian approach to the collapse of galaxy
fluctuations of scalar field dark matter under initial conditions inferred from
simple assumptions. The full relativistic system, the so called
Einstein-Klein-Gordon, is reduced to the Schr\"odinger-Newton one in the weak
field limit. The scaling symmetries of the SN equations are exploited to track
the non-linear collapse of single scalar matter fluctuations. The results can
be applied to both real and complex scalar fields.Comment: 4 pages RevTex4 file, 4 eps figure
Spherically Symmetric Solutions in Macroscopic Gravity
Schwarzschild's solution to the Einstein Field Equations was one of the first
and most important solutions that lead to the understanding and important
experimental tests of Einstein's theory of General Relativity. However,
Schwarzschild's solution is essentially based on an ideal theory of
gravitation, where all inhomogeneities are ignored. Therefore, any
generalization of the Schwarzschild solution should take into account the
effects of small perturbations that may be present in the gravitational field.
The theory of Macroscopic Gravity characterizes the effects of the
inhomogeneities through a non-perturbative and covariant averaging procedure.
With similar assumptions on the geometry and matter content, a solution to the
averaged field equations as dictated by Macroscopic Gravity are derived. The
resulting solution provides a possible explanation for the flattening of
galactic rotation curves, illustrating that Dark Matter is not real but may
only be the result of averaging inhomogeneities in a spherically symmetric
background.Comment: 14 pages, added and updated references, some paragraphs rewritten for
clarity, typographical errors fixed, results have not change
Probing the Environment with Galaxy Dynamics
I present various projects to study the halo dynamics of elliptical galaxies.
This allows one to study the outer mass and orbital distributions of
ellipticals in different environments, and the inner distributions of groups
and clusters themselves.Comment: 5 pages, 2 figs, to appear in Proc. ESO Workshop, Groups of Galaxies
in the Nearby Universe (5-9 Dec 2005), eds. I. Saviane, V. Ivanov & J.
Borissova (Springer-Verlag
A New Approach to Searching for Dark Matter Signals in Fermi-LAT Gamma Rays
Several cosmic ray experiments have measured excesses in electrons and
positrons, relative to standard backgrounds, for energies from ~ 10 GeV - 1
TeV. These excesses could be due to new astrophysical sources, but an
explanation in which the electrons and positrons are dark matter annihilation
or decay products is also consistent. Fortunately, the Fermi-LAT diffuse gamma
ray measurements can further test these models, since the electrons and
positrons produce gamma rays in their interactions in the interstellar medium.
Although the dark matter gamma ray signal consistent with the local electron
and positron measurements should be quite large, as we review, there are
substantial uncertainties in the modeling of diffuse backgrounds and,
additionally, experimental uncertainties that make it difficult to claim a dark
matter discovery. In this paper, we introduce an alternative method for
understanding the diffuse gamma ray spectrum in which we take the intensity
ratio in each energy bin of two different regions of the sky, thereby canceling
common systematic uncertainties. For many spectra, this ratio fits well to a
power law with a single break in energy. The two measured exponent indices are
a robust discriminant between candidate models, and we demonstrate that dark
matter annihilation scenarios can predict index values that require "extreme"
parameters for background-only explanations.Comment: v1: 11 pages, 7 figures, 1 table, revtex4; v2: 13 pages, 8 figures, 1
table, revtex4, Figure 4 added, minor additions made to text, references
added, conclusions unchanged, published versio
Robust implications on Dark Matter from the first FERMI sky gamma map
We derive robust model-independent bounds on DM annihilations and decays from
the first year of FERMI gamma-ray observations of the whole sky. These bounds
only have a mild dependence on the DM density profile and allow the following
DM interpretations of the PAMELA and FERMI electron/positron excesses: primary
channels mu+ mu-, mu+ mu-mu+mu- or e+ e- e+ e-. An isothermal-like density
profile is needed for annihilating DM. In all such cases, FERMI gamma spectra
must contain a significant DM component, that may be probed in the future.Comment: 16 pages, 8 figures. Final versio
Implications of the Fermi-LAT diffuse gamma-ray measurements on annihilating or decaying Dark Matter
We analyze the recently published Fermi-LAT diffuse gamma-ray measurements in
the context of leptonically annihilating or decaying dark matter (DM) with the
aim to explain simultaneously the isotropic diffuse gamma-ray and the PAMELA,
Fermi and HESS (PFH) anomalous data. Five different DM
annihilation/decay channels , , , , or (the latter
two via an intermediate light particle ) are generated with PYTHIA. We
calculate both the Galactic and extragalactic prompt and inverse Compton (IC)
contributions to the resulting gamma-ray spectra. To find the Galactic IC
spectra we use the interstellar radiation field model from the latest release
of GALPROP. For the extragalactic signal we show that the amplitude of the
prompt gamma-emission is very sensitive to the assumed model for the
extragalactic background light. For our Galaxy we use the Einasto, NFW and
Isothermal DM density profiles and include the effects of DM substructure
assuming a simple subhalo model. Our calculations show that for the
annihilating DM the extragalactic gamma-ray signal can dominate only if rather
extreme power-law concentration-mass relation is used, while more
realistic relations make the extragalactic component comparable or
subdominant to the Galactic signal. For the decaying DM the Galactic signal
always exceeds the extragalactic one. In the case of annihilating DM the PFH
favored parameters can be ruled out only if power-law relation is
assumed. For DM decaying into or the PFH favored DM parameters
are not in conflict with the Fermi gamma-ray data. We find that, due to the
(almost) featureless Galactic IC spectrum and the DM halo substructure,
annihilating DM may give a good simultaneous fit to the isotropic diffuse
gamma-ray and to the PFH data without being in clear conflict with the
other Fermi-LAT gamma-ray measurements.Comment: Accepted for publication in JCAP, added missing references, new Figs.
9 \& 10, 35 page
Seismological monitoring of Campi Flegrei caldera
Campi Flegrei is an active volcanic area posing a serious threat over Naples. Half of
the city lies inside the caldera rim. The volcano has shown in the last 30 years different
episodes of unrest, the most recent is still ongoing. For this reason the monitoring of
this volcano is a fundamental task. The current seismic network consists of 8 short
period and 5 broadband stations. The seismic monitoring is complemented by 2 infrasonic
sensors and 3 dilatometers. The recent seismicity has been characterized by
swarms of volcano-tectonic and long-period events. The network geometry allows an
accurate location of VT events with a detection threshold of magnitudes less than 1.0
Some VT events have been recorder also by the infrasonic sensors showing interesting
similarities. LP events have been recorded by both short period and broadband
stations. The polarization analysis performed over the broadband recordings is an important
tool for the real time detection of such events, related to the dynamics of the
hydrothermal system. The ongoing developments consists in a progressive increasing
of the number of broadband digital stations and infrasonic sensors, in improving the
accuracy of hypocenter locations by using a 3D velocity model and in the implementation
of new automatic techniques aimed at the detection, classification and analysis
of seismic events.PublishedVienna, Austria1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveope
- …