3,315 research outputs found
On the Spin of the X(3872)
Whether the much studied X(3872) is an axial or tensor resonance makes an
important difference to its interpretation. A recent paper by the BaBar
collaboration raised the viable hypothesis that it might be a 2-+ state based
on the 3 pions spectrum in the X -> J/psi omega decays. Furthermore, the Belle
collaboration published the 2 pions invariant mass and spin-sensitive angular
distributions in X -> J/psi rho decays. Starting from a general parametrization
of the decay amplitudes for the axial and tensor quantum numbers of the X, we
re-analyze the whole set of available data. The level of agreement of the two
spin hypotheses with data is interpreted with a rigorous statistical approach
based on Monte Carlo simulations in order to be able to combine all the
distributions regardless of their different levels of sensitivity to the spin
of the X. Our analysis returns a probability of 5.5% and 0.1% for the agreement
with data of the 1++ and 2-+ hypotheses, respectively, once we combine the
whole information (angular and mass distributions) from both channels. On the
other hand, the separate analysis of J/psi rho (angular and mass distributions)
and J/psi omega (mass distribution) indicates that the 2-+ assignment is
excluded at the 99.9% C.L. by the former case, while the latter excludes at the
same level the 1++ hypothesis. There are therefore indications that the two
decay modes behave in a different way.Comment: 12 pages, 9 figures, 2 tables. Added angular distributions, which
lead to different conclusion
Reply to Marchi's comment on "Geomorphic hazards and intense rainfall: the case study of the Recco Stream catchment (Eastern Liguria, Italy)" by Faccini et al. (2012)
No abstract available
Geomorphological hazard and tourist vulnerability along Portofino Park trails (Italy)
International audienceThe many trails existing in the coastal area of Portofino Promontory are used by tourists for trekking or as pathways to small villages and beaches. The aim of this paper is to define geomorphological hazard and tourist vulnerability in this area, within the framework of the management and planning of hiking activities in Portofino Natural Park. In particular, processes triggered by gravity, running waters and wave motion, affecting the slopes and the cliff, are considered. The typology of the trails and trail maintenance are also taken into account in relation to weather conditions that can make the excursion routes dangerous for tourists. In conclusion, an operative model is applied for the definition of possible risk scenarios. This model is founded on an inventory and the quantification of geomorphological hazards and tourist vulnerability, in comparison with trail rescue data. The model can be applied to other environments and tourist areas
Geomorphic hazards and intense rainfall: the case study of the Recco Stream catchment (Eastern Liguria, Italy)
Abstract. A critical pluviometric event occurred in the central-eastern Ligurian Riviera, 15 km from Genoa, on 1 June 2007. This event caused landslides and hydraulic problems between Sori and Camogli and in the inland area of the Recco Valley. An analysis of the heavy rainfall was conducted. Hourly precipitation data revealed a critical event between 04:00 a.m. and 07:00 a.m. local time, with more than 220 mm of precipitation over three hours. Slope movements were mainly debris flows that detached from the lateral valleys of the Recco Stream catchment and from well-maintained, wooded slopes that were also characterised by cultivated terraces. Numerous slide planes corresponded to the interface between the surface cover and the underlying bedrock, which presents an unfavourable geologic structure in terms of stability assessment. In most cases, the displaced material had a limited thickness. Debris cover was rapidly channelled along small valleys, which controlled the critical hydraulic conditions in the secondary drainage network. Man-made drainage systems were partially or totally blocked in a very short time and, like the natural watercourses, accumulated thick and extensive alluvial fans. Most of the instability phenomena occurred in areas that had been designated medium or low-risk areas during land planning, and in sectors that were defined as stable, because they lacked geomorphic indicators connected to landslide risks. The above considerations highlight some gaps of the Recco Stream Master Plan. Therefore, to update this land planning tool, it is necessary to extensively investigate local geomorphological characteristics and to adopt a different method for assigning weights to the geohazard maps
The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group
We present a detailed study of the stellar and HI structure of the dwarf
irregular galaxies SextansA and SextansB, members of the NGC3109 association.
We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the
Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0
mag/arcsec^2. We find that both galaxies are significantly more extended than
what previously traced with surface photometry, out to ~4 kpc from their
centers along their major axis. Older stars are found to have more extended
distribution with respect to younger populations. We obtain the first estimate
of the mean metallicity for the old stars in SexB, from the color distribution
of the Red Giant Branch, =-1.6. The SB profiles show significant
changes of slope and cannot be fitted with a single Sersic model. Both galaxies
have HI discs as massive as their respective stellar components. In both cases
the HI discs display solid-body rotation with maximum amplitude of ~50 km/s
(albeit with significant uncertainty due to the poorly constrained
inclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratio
M/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of the
stellar components is more extended than the gaseous disc in both galaxies. We
find that the main, approximately round-shaped, stellar body of Sex~A is
surrounded by an elongated low-SB stellar halo that can be interpreted as a
tidal tail, similar to that found in another member of the same association
(Antlia). We discuss these, as well as other evidences of tidal disturbance, in
the framework of a past passage of the NGC3109 association close to the Milky
Way, that has been hypothesized by several authors and is also supported by the
recently discovered filamentary configuration of the association itself.Comment: Accepted for publication by A&A. PdfLateX, 16 pages, 11 figures, 2
appendice
High-resolution lightning detection and possible relationship with rainfall events over the Central Mediterranean area
Lightning activity is usually associated with precipitations events and represents a possible indicator of climate change, even contributing to its increase with the production of NOx gases. The study of lightning activity on long temporal periods is crucial for fields related to atmospheric phenomena from intense rain-related hazard processes to long-term climate changes. This study focuses on 19 years of lightning-activity data, recorded from Italian Lightning Detection Network SIRF, part of the European network EUCLID (European Cooperation for Lightning Detection). Preliminary analysis was dedicated to the spatial and temporal assessment of lightning through detection in the Central Mediterranean area, focusing on yearly and monthly data. Temporal and spatial features have been analyzed, measuring clustering through the application of global Moran’s I statistics and spatial local autocorrelation; a Mann–Kendall trend test was performed on monthly series aggregating the original data on a 5 × 5 km cell. A local statistically significant trend emerged from the analysis, suggesting a possible linkage between surface warming and lightning activity
A spatial multicriteria prioritizing approach for geo-hydrological risk mitigation planning in small and densely urbanized Mediterranean basins
Landslides and floods, particularly flash floods, occurred recently in many
Mediterranean catchments as a consequence of heavy rainfall events, causing
damage and sometimes casualties. The high hazard is often associated with
high vulnerability deriving from intense urbanization, in particular along
the coastline where streams are habitually culverted. The necessary risk
mitigation strategies should be applied at the catchment scale with a holistic
approach, avoiding spot interventions.
In the present work, a high-risk area, hit in the past by several floods and
concurrent superficial landslides due to extremely localized and intense
rain events, has been studied. A total of 21 small catchments have been identified:
only some of them have been hit by extremely damaging past events, but all
lie in the intense-rain high-hazard area and are strongly urbanized in the
lower coastal zone. The question is what would happen if an intense rain
event should strike one of the not previously hit catchments; some situations
could be worse or not, so attention has been focused on the comparison
among catchments. The aim of the research has been identifying a priority
scale among catchments, pointing out the more critical ones and giving a
quantitative comparison tool for decision makers to support strong
scheduling of long-time planning interventions at the catchment scale. The past
events' effects and the geomorphic process analysis together with the field
survey allowed us to select three sets of parameters: one describing the
morphometric–morphological features related to flood and landslide hazard,
another describing the degree of urbanization and of anthropogenic
modifications at the catchment scale and the last related to the elements that
are exposed to risk. The realized geodatabase allowed us to apply the spatial
multicriteria analysis technique (S-MCA) to the descriptive parameters and
to obtain a priority scale among the analyzed catchments. The scale can be
used to plan risk mitigation interventions starting from the more critical
catchments, then focusing economic resources primarily on them and obtaining
an effective prevention strategy. The methodology could be useful even to
check how the priority scale is modified during the progress of the
mitigation work realization.
In addition, this approach could be applied in a similar context, even among
sub-catchments, after identifying a suitable set of descriptive parameters
depending on the active geomorphological processes and the kind of
anthropogenic modification. The prioritization would allow to invest
economic resources in risk mitigation interventions priory in the more
critical catchments.</p
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