5,594 research outputs found
Critical rainfall thresholds for triggering shallow landslides in the Serchio River Valley (Tuscany, Italy)
Abstract. The Serchio River Valley, in north-western Tuscany, is a well-known tourism area between the Apuan Alps and the Apennines. This area is frequently hit by heavy rainfall, which often triggers shallow landslides, debris flows and debris torrents, sometimes causing damage and death. The assessment of the rainfall thresholds for the initiation of shallow landslides is very important in order to improve forecasting and to arrange efficient alarm systems. With the aim of defining the critical rainfall thresholds for the Middle Serchio River Valley, a detailed analysis of the main rainstorm events was carried out. The hourly rainfall recorded by three rain gauges in the 1935–2010 interval was analysed and compared with the occurrence of shallow landslides. The rainfall thresholds were defined in terms of mean intensity I, rainfall duration D, and normalized using the mean annual precipitation. Some attempts were also carried out to analyze the role of rainfall prior to the damaging events. Finally, the rainfall threshold curves obtained for the study area were compared with the local, regional and global curves proposed by various authors. The results of this analysis suggest that in the study area landslide activity initiation requires a higher amount of rainfall and greater intensity than elsewhere
Evaluation of subsidence induced by long-lasting buildings load using InSAR technique and geotechnical data: The case study of a Freight Terminal (Tuscany, Italy)
This paper shows the results of the comparison between Multi-temporal Synthetic Aperture Radar (MTInSAR) products derived from different sensors (C-band ERS 1/2, Envisat, Sentinel-1 and X-band COSMO-SkyMed) and geotechnical data to investigate the driving factors of subsidence which affect a freight terminal located along the a coastal plain of Tuscany (central Italy). MTInSAR data have been acquired in a very long period, between 1992 and 2018 and were analyzed in terms of subsidence rates and deformation time series at building scale. The obtained results show that the oldest buildings are still affected by a deformation rate close to −5 mm/yr, whereas recent buildings register rates around −40 mm/yr. Time series of deformation suggest that the deformation rates decrease over time following time-dependent trend that approximates the typical consolidation curve for compressible soils. The geotechnical and stratigraphical analysis of the subsurface data (boreholes, cone penetration tests and dilatometer tests) highlights the presence of a 15 m thick layer formed of clay characterized by poor geotechnical characteristics. The comparison among InSAR data, subsurface geological framework and geotechnical reconstruction suggests a possible evaluation of the timing of the primary and secondary consolidation processes
The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence
A numerical model of isotropic homogeneous turbulence with helical forcing is
investigated. The resulting flow, which is essentially the prototype of the
alpha^2 dynamo of mean-field dynamo theory, produces strong dynamo action with
an additional large scale field on the scale of the box (at wavenumber k=1;
forcing is at k=5). This large scale field is nearly force-free and exceeds the
equipartition value. As the magnetic Reynolds number R_m increases, the
saturation field strength and the growth rate of the dynamo increase. However,
the time it takes to built up the large scale field from equipartition to its
final super-equipartition value increases with magnetic Reynolds number. The
large scale field generation can be identified as being due to nonlocal
interactions originating from the forcing scale, which is characteristic of the
alpha-effect. Both alpha and turbulent magnetic diffusivity eta_t are
determined simultaneously using numerical experiments where the mean-field is
modified artificially. Both quantities are quenched in a R_m-dependent fashion.
The evolution of the energy of the mean field matches that predicted by an
alpha^2 dynamo model with similar alpha and eta_t quenchings. For this model an
analytic solution is given which matches the results of the simulations. The
simulations are numerically robust in that the shape of the spectrum at large
scales is unchanged when changing the resolution from 30^3 to 120^3 meshpoints,
or when increasing the magnetic Prandtl number (viscosity/magnetic diffusivity)
from 1 to 100. Increasing the forcing wavenumber to 30 (i.e. increasing the
scale separation) makes the inverse cascade effect more pronounced, although it
remains otherwise qualitatively unchanged.Comment: 21 pages, 26 figures, ApJ (accepted
Real-time evaluation of longitudinal peack systolic strain( speackle tracking measurement) in left and right ventricles of athletes
Evidence for an axion-like particle from PKS 1222+216?
The surprising discovery by MAGIC of an intense, rapidly varying emission in
the energy range 70 - 400 GeV from the flat spectrum radio quasar PKS 1222+216
represents a challenge for all interpretative scenarios. Indeed, in order to
avoid absorption of \gamma rays in the dense ultraviolet radiation field of the
broad line region (BLR), one is forced to invoke some unconventional
astrophysical picture, like for instance the existence of a very compact (r\sim
10^{14} cm) emitting blob at a large distance (R \sim10^{18} cm) from the jet
base. We offer the investigation of a scenario based on the standard blazar
model for PKS 1222+216 where \gamma rays are produced close to the central
engine, but we add the new assumption that inside the source photons can
oscillate into axion-like particles (ALPs), which are a generic prediction of
several extensions of the Standard Model of elementary particle interactions.
As a result, a considerable fraction of very-high-energy photons can escape
absorption from the BLR through the mechanism of photon-ALP oscillations much
in the same way as they largely avoid absorption from extragalactic background
light when propagating over cosmic distances in the presence of large-scale
magnetic fields in the nG range. In addition we show that the above MAGIC
observations and the simultaneous Fermi/LAT observations in the energy range
0.3 - 3 GeV can both be explained by a standard spectral energy distribution
for experimentally allowed values of the model parameters. In particular, we
need a very light ALP just like in the case of photon-ALP oscillations in
cosmic space. Moreover, we find it quite tantalizing that the most favorable
value of the photon-ALP coupling happens to be the same in both situations.
Although our ALPs cannot contribute to the cold dark matter, they are a viable
candidate for the quintessential dark energy. [abridged]Comment: 32 pages, 10 figures, accepted for publication in Physical Review
Coherent vortex structures and 3D enstrophy cascade
Existence of 2D enstrophy cascade in a suitable mathematical setting, and
under suitable conditions compatible with 2D turbulence phenomenology, is known
both in the Fourier and in the physical scales. The goal of this paper is to
show that the same geometric condition preventing the formation of
singularities - 1/2-H\"older coherence of the vorticity direction - coupled
with a suitable condition on a modified Kraichnan scale, and under a certain
modulation assumption on evolution of the vorticity, leads to existence of 3D
enstrophy cascade in physical scales of the flow.Comment: 15 pp; final version -- to appear in CM
Cocirculation of Hajj and non-Hajj strains among serogroup W meningococci in Italy, 2000 to 2016
In Italy, B and C are the predominant serogroups among meningococci causing invasive diseases. Nevertheless, in the period from 2013 to 2016, an increase in serogroup W Neisseria meningitidis (MenW) was observed. This study intends to define the main characteristics of 63 MenW isolates responsible of invasive meningococcal disease (IMD) in Italy from 2000 to 2016. We performed whole genome sequencing on bacterial isolates or single gene sequencing on culturenegative samples to evaluate molecular heterogeneity. Our main finding was the cocirculation of the Hajj and the South American sublineages belonging to MenW/ clonal complex (cc)11, which gradually surpassed the MenW/cc22 in Italy. All MenW/cc11 isolates were fully susceptible to cefotaxime, ceftriaxone, ciprofloxacin, penicillin G and rifampicin. We identified the fulllength NadA protein variant 2/3, present in all the MenW/cc11. We also identified the fHbp variant 1, which we found exclusively in the MenW/cc11/Hajj sublineage. Concern about the epidemic potential of MenW/cc11 has increased worldwide since the year 2000. Continued surveillance, supported by genomic characterisation, allows high-resolution tracking of pathogen dissemination and the detection of epidemicassociated strains
Classroom characteristic and implementation of a substance use prevention curriculum in European countries
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