1,341 research outputs found
Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources
The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show
anisotropies on all scales, from just above the experimental angular resolution
up to medium scales and dipole anisotropies. We find that a global comparison
of the two-point auto-correlation function of the data with the one of
catalogues of potential sources is a powerful diagnostic tool. In particular,
this method is far less sensitive to unknown deflections in magnetic fields
than cross-correlation studies while keeping a strong discrimination power
among source candidates. We illustrate these advantages by considering ordinary
galaxies, gamma ray bursts and active galactic nuclei as possible sources.
Already the sparse publicly available data suggest that the sources of UHECRs
may be a strongly clustered sub-sample of galaxies or of active galactic
nuclei. We present forecasts for various cases of source distributions which
can be checked soon by the Pierre Auger Observatory.Comment: 11 pages, 8 figures, 4 tables; minor changes, matches published
versio
The GZK horizon and constraints on the cosmic ray source spectrum from observations in the GZK regime
We discuss the GZK horizon of protons and present a method to constrain the
injection spectrum of ultrahigh energy cosmic rays (UHECRs) from supposedly
identified extragalactic sources. This method can be applied even when only one
or two events per source are observed and is based on the analysis of the
probability for a given source to populate different energy bins, depending on
the actual CR injection spectral index. In particular, we show that for a
typical source density of , a data set of 100 events
above eV allows one in 97% of all cases to distinguish a
source spectrum from one with at 95%
confidence level.Comment: v2: 5 pages, 3 figures; shortened, title changed, matches version to
be publishe
Tracing groundwater circulation in a valuable mineral water basin with geochemical and isotopic tools: the case of FERRARELLE, Riardo basin, Southern Italy
The Riardo basin hosts groundwater exploited for the production of high quality, naturally sparkling, bottled water (e.g., Ferrarelle water), and circulating in a system constituted by highly fractured Mesozoic carbonates, overlain by more impervious volcanic rocks of the Roccamonfina complex. The two formations are locally in hydraulic connection and dislocated by deep-rooted faults. The study aimed at elucidating groundwater origin and circulation, using isotopic tracers (δ18O, δ2H, δ11B and 87Sr/86Sr) coupled to groundwater dating (Tritium, CFCs and SF6). Besides recharge by local precipitation over the Riardo hydrogeological basin, stable isotope ratios in water indicated an extra-basin recharge, likely from the elevated surrounding carbonate reliefs (e.g., Maggiore and Matese Mts.). The mineralization process, promoted by the deep CO2 flux, controls the B and Sr contents. However, their isotopic ratios did not allow discriminating between circulation in the volcanic and in the carbonate aquifers, as in the latter the isotopic composition differed from the original marine signature. Groundwater model ages ranged from ~ 30 years for the volcanic endmember to > 70 years for the deep, mineralized end-member, with longer circuits recharged at higher elevations. Overall, the results of this study were particularly relevant for mineral water exploitation. A recharge from outside the hydrogeological basin could be evidenced, especially for the more mineralized and valuable groundwater, and an active recent recharge was detected for the whole Riardo system. Both findings will contribute to the refinement of the hydrogeological model and water budget, and to a sustainable development of the resource
On line power spectra identification and whitening for the noise in interferometric gravitational wave detectors
In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
Least Squares ones.Comment: 28 pages, 21 figures, uses iopart.cls accepted for pubblication on
Classical and Quantum Gravit
Spin-orbital polarization of Majorana edge states in oxides nanowires
We investigate a paradigmatic case of topological superconductivity in a
one-dimensional nanowire with orbitals and a strong interplay of
spin-orbital degrees of freedom due to the competition of orbital Rashba
interaction, atomic spin-orbit coupling, and structural distortions. We
demonstrate that the resulting electronic structure exhibits an orbital
dependent magnetic anisotropy which affects the topological phase diagram and
the character of the Majorana bound states (MBSs). The inspection of the
electronic component of the MBSs reveals that the spin-orbital polarization
generally occurs along the direction of the applied Zeeeman magnetic field, and
transverse to the magnetic and orbital Rashba fields. The competition of
symmetric and antisymmetric spin-orbit coupling remarkably leads to a
misalignment of the spin and orbital moments transverse to the orbital Rashba
fields, whose manifestation is essentially orbital dependent. The behavior of
the spin-orbital polarization along the applied Zeeman field reflects the
presence of multiple Fermi points with inequivalent orbital character in the
normal state. Additionally, the response to variation of the electronic
parameters related with the degree of spin-orbital entanglement leads to
distinctive evolution of the spin-orbital polarization of the MBSs. These
findings unveil novel paths to single-out hallmarks relevant for the
experimental detection of MBSs.Comment: 14 pages, 8 figure
Sensitivity of a VIRGO pair to stochastic GW backgrounds
The sensitivity of a pair of VIRGO interferometers to gravitational waves
backgrounds (GW) of cosmological origin is analyzed for the cases of maximal
and minimal overlap of the two detectors. The improvements in the detectability
prospects of scale-invariant and non-scale-invariant logarithmic energy spectra
of relic GW are discussed.Comment: 25 pages in RevTex style with 6 figure
Temperature dependence of optical spectral weights in quarter-filled ladder systems
The temperature dependence of the integrated optical conductivity I(T)
reflects the changes of the kinetic energy as spin and charge correlations
develop. It provides a unique way to explore experimentally the kinetic
properties of strongly correlated systems. We calculated I(T) in the frame of a
t-J-V model at quarter-filling for ladder systems, like NaV_2O_5, and show that
the measured strong T dependence of I(T) for NaV_2O_5 can be explained by the
destruction of short range antiferromagnetic correlations. Thus I(T) provides
detailed information about super-exchange and magnetic energy scales.Comment: 4 pages, 5 figure
Groundwater mixing in a heterogeneous multilayer aquifer driven by geogenic CO2 fluxes: Evidence from chemical and isotopic composition of Ferrarelle waters (Riardo Plain, southern Italy)
The successful management of carbon in the Earth's crust is critical for mitigating the increase of anthropogenic CO2 in the atmosphere. Carbon Capture and Storage (CCS) requires an understanding of the behavior of carbon in the crust and the development of robust monitoring techniques to constrain the movement, mechanisms, and pathways for any potential CO2 leakage. Here, we examine an aquifer from the Riardo Plain (Campania Region, southern Italy), which serves as a suitable natural analogue for CO2 migration to the critical zone (i.e., shallow crust and aquifers) and as a case study to evaluate the geochemical processes that occur when CO2-saturated fluids mix with freshwater in shallow aquifers. We investigate the behavior of various geochemical constituents (major and trace elements, δ18O–H2O, δ13C-DIC, and Rn content). Water from this area has a high degree of mineralization (EC 2500–3000 μS/cm), high HCO3- (~2.5 g/L), is saturated with respect to CaCO3, and is enriched in alkali ions (e.g., Na+ + K+). The high degree of mineralization occurs in groundwater that discharges from the basal aquifer of the Roccamonfina volcanic edifice (~6 km NW), with vast CO2 inputs that promote host rock leaching. Superficial volcanic aquifers are recharged by fresh meteoric precipitation when groundwater flows from carbonates at the edge of the plain to aquifers hosted in the southeastern slope of the Roccamonfina volcano. The presence of normal faults in this area permits natural upwelling of CO2-rich groundwater, which locally mixes with shallow freshwater present within the upper volcanic succession. Significant (R > 0.8) linear correlations between conservative elements suggest that groundwater geochemistry is dominated by a mixture of two main endmembers: (i) deep/mineralized waters and (ii) shallow/diluted waters. The intrusion of freshwater to volcanic aquifers induces oxidation, leading to adsorption of select elements (e.g., As and Ba) onto Fe-oxyhydroxide precipitates within these aquifers. Geochemical modeling suggests that CO2 saturation approaches 3 g/L, which agrees with direct measurements of CO2 flux. We conclude that our conceptual geochemical model helps to constrain mixing of CO2 with freshwater and to diagnose the secondary geochemical processes that influence aqueous geochemistry within CO2-influenced groundwater
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