2,564 research outputs found
Passive seismology in southern Italy: the SAPTEX array
Abstract
In this paper we describe the Southern APennines Tomography EXperiment (SAPTEX) temporary array deployed in southern Italy from June 2001 to
December 2003. Five to twelve three-components seismic stations, all equipped with RefTek 72A07 digitizers in continuous mode recording and Lennartz
3D/5s sensors, were operating in the region during the three-year project. Many local, regional and teleseismic events have been recorded at 26 different
recording sites, providing an invaluable data set for high-resolution seismological studies. Moreover, by the second half of 2002, two stations were
installed in the Aeolian Islands with the main objective to record and better constrain the spatial distribution of the deep seismicity of the southern
Tyrrhenian subduction zone. The preliminary analysis of the waveforms collected in the first two years includes phase identification and body wave
arrival time estimation, local earthquakes (re)location and focal mechanisms computation, P -wave traveltime residuals, and resolution of crustal and upper
mantle structure derived by teleseismic ray sampling
Pair-distribution functions of the two-dimensional electron gas
Based on its known exact properties and a new set of extensive fixed-node
reptation quantum Monte Carlo simulations (both with and without backflow
correlations, which in this case turn out to yield negligible improvements), we
propose a new analytical representation of (i) the spin-summed
pair-distribution function and (ii) the spin-resolved potential energy of the
ideal two-dimensional interacting electron gas for a wide range of electron
densities and spin polarization, plus (iii) the spin-resolved pair-distribution
function of the unpolarized gas. These formulae provide an accurate reference
for quantities previously not available in analytic form, and may be relevant
to semiconductor heterostructures, metal-insulator transitions and quantum dots
both directly, in terms of phase diagram and spin susceptibility, and
indirectly, as key ingredients for the construction of new two-dimensional spin
density functionals, beyond the local approximation.Comment: 12 pages, 10 figures; misprints correcte
Local-spin-density functional for multideterminant density functional theory
Based on exact limits and quantum Monte Carlo simulations, we obtain, at any
density and spin polarization, an accurate estimate for the energy of a
modified homogeneous electron gas where electrons repel each other only with a
long-range coulombic tail. This allows us to construct an analytic
local-spin-density exchange-correlation functional appropriate to new,
multideterminantal versions of the density functional theory, where quantum
chemistry and approximate exchange-correlation functionals are combined to
optimally describe both long- and short-range electron correlations.Comment: revised version, ti appear in PR
The 2013–2018 matese and beneventano seismic sequences (Central–Southern apennines). New constraints on the hypocentral depth determination
The Matese and Beneventano areas coincide with the transition from the central to the southern Apennines and are characterized by both SW-and NE-dipping normal faulting seismogenic structures, responsible for the large historical earthquakes. We studied the Matese and Beneventano seismicity by means of high-precision locations of earthquakes spanning from 29 December 2013 to 4 September 2018. Events were located by using all of the available data from temporary and permanent stations in the area and a 1D computed velocity model, inverting the dataset with the Velest code. For events M > 2.8 we used P-and S-waves arrival times of the strong motion stations located in the study area. A constant value of 1.83 for Vp/Vs was computed with a modified Wadati method. The dataset consists of 2378 earthquakes, 18,715 P-and 12,295 S-wave arrival times. We computed 55 new fault plane solutions. The mechanisms show predominantly normal fault movements, with T-axis trends oriented NE–SW. Only relatively small E–W trending clusters in the eastern peripheral zones of the Apenninic belt show right-lateral strike-slip kinematics similar to that observed in the Potenza (1990–1991) and Molise (2002 and 2018) sequences. These belong to transfer zones associated with differential slab retreat of the Adriatic plate subduction beneath the Apennines. The Matese sequence (December 2013–February 2014; main shock Mw 5.0) is the most relevant part of our dataset. Hypocentral depths along the axis of the Apenninic belt are in agreement with previous seismological studies that place most of the earthquakes in the brittle upper crust. We confirm a general deepening of seismicity moving from west to the east along the Apennines. Seismicity depth is controlled by heat-flow, which is lower in the eastern side, thus causing a deeper brittle–ductile transition
Attractive and repulsive contributions of medium fluctuations to nuclear superfluidity
Oscillations of mainly surface character (S=0 modes) give rise, in atomic
nuclei, to an attractive (induced) pairing interaction, while spin (S=1) modes
of mainly volume character generate a repulsive interaction, the net effect
being an attraction which accounts for a sizeable fraction of the experimental
pairing gap. Suppressing the particle-vibration coupling mediated by the proton
degrees of freedom, i.e., mimicking neutron matter, the total surface plus
spin-induced pairing interaction becomes repulsive
Cortical visuomotor interactions in Freezing of Gait: A TMS approach
OBJECTIVES: Altered cortical visuomotor integration has been involved in the pathophysiology of freezing of gait (FoG) in parkinsonism. The aim of this study was to assess the connections between the primary visual (V1) and motor (M1) areas with a paired-pulse, twin-coil transcranial magnetic stimulation (TMS) technique in patients with FoG. METHODS: Twelve Parkinson's disease (PD) patients suffering from levodopa-responsive-FoG (off-FoG) were compared with 12 PD patients without FoG and 12 healthy subjects of similar age/sex. In the "off" condition, visuomotor connections (VMCs) were assessed bilaterally. A conditioning stimulus over the V1 phosphene hotspot was followed at interstimulus intervals (ISIs) of 18 and 40ms by a test stimulus over M1, to elicit motor evoked potentials (MEPs) in the contralateral first dorsal interosseous muscle. RESULTS: Significant (P<0.01), bilateral effects due to VMCs were detected in all three groups, consisting of a MEP suppression at ISI 18 and 40ms. However, in PD patients with FoG, the MEP suppression was significantly (P<0.05) enhanced, both at ISI 18-40ms, in comparison with the other two groups. The phenomenon was limited to the right hemisphere. CONCLUSIONS: PD patients with FoG showed an excessive inhibitory response of the right M1 to inputs travelling from V1 at given ISIs. Right-sided alterations of the cortical visuomotor integration may contribute to the pathophysiology of FoG
Effective interactions between parallel-spin electrons in two-dimensional jellium approaching the magnetic phase transition
We evaluate the effective interactions in a fluid of electrons moving in a
plane, on the approach to the quantum phase transition from the paramagnetic to
the fully spin-polarized phase that has been reported from Quantum Monte Carlo
runs. We use the approach of Kukkonen and Overhauser to treat exchange and
correlations under close constraints imposed by sum rules. We show that, as the
paramagnetic fluid approaches the phase transition, the effective interactions
at low momenta develop an attractive region between parallel-spin electrons and
a corresponding repulsive region for antiparallel-spin electron pairs. A
connection with the Hubbard model is made and used to estimate the magnetic
energy gap and hence the temperature at which the phase transition may become
observable with varying electron density in a semiconductor quantum well.Comment: 11 pages, 3 figure
Pattern of seismicity in the Lucanian Apennines and foredeep (Southern Italy) from recording by SAPTEX temporary array
The deployment of a temporary seismic network in Southern Italy during 2001-2004 (the SAPTEX array, Southern
APennine Tomography EXperiment) allowed us to relocate the hypocenters of Southern Apennines earthquakes
with low uncertainty among the location parameters. The best array distribution of the SAPTEX network
for the analysis of seismicity in the Lucanian Apennines and foredeep was reached in the first two years of
recording. The SAPTEX data were merged with those of the Italian National Seismic Network (RSNC) operated
by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). For the hypocenters computation of events in
the upper Agri Valley we also included P- and S- waves arrivals from the local Eni-Agip network. The seismicity
for the Lucanian Apennines and foredeep in the analyzed period has magnitudes ranging from 2.0 to 4.1. A
major finding is the identification of two different crustal domains: the westernmost characterizing the chain,
mostly with shallow earthquakes (within about 20 km of depth), and the easternmost one belonging to the outer
margin of the chain and to the foredeep, with deeper seismicity (mostly between 20-40 km of depth). Thirty
fault-plane solutions were computed and used for stress inversion; most of them are related to earthquakes within
the chain sector and indicate a generalized NE-SW extension. Moreover, the dense network allowed us to improve
the location of events relative to two low magnitude sequences which occurred in the study period
Self-consistent Overhauser model for the pair distribution function of an electron gas in dimensionalities D=3 and D=2
We present self-consistent calculations of the spin-averaged pair
distribution function for a homogeneous electron gas in the paramagnetic
state in both three and two dimensions, based on an extension of a model that
was originally proposed by A. W. Overhauser [Can. J. Phys. {\bf 73}, 683
(1995)] and further evaluated by P. Gori-Giorgi and J. P. Perdew [Phys. Rev. B
{\bf 64}, 155102 (2001)]. The model involves the solution of a two-electron
scattering problem via an effective Coulombic potential, that we determine
within a self-consistent Hartree approximation. We find numerical results for
that are in excellent agreement with Quantum Monte Carlo data at low and
intermediate coupling strength , extending up to in
dimensionality D=3. However, the Hartree approximation does not properly
account for the emergence of a first-neighbor peak at stronger coupling, such
as at in D=2, and has limited accuracy in regard to the spin-resolved
components and . We also
report calculations of the electron-electron s-wave scattering length, to test
an analytical expression proposed by Overhauser in D=3 and to present new
results in D=2 at moderate coupling strength. Finally, we indicate how this
approach can be extended to evaluate the pair distribution functions in
inhomogeneous electron systems and hence to obtain improved
exchange-correlation energy functionals.Comment: 14 pages, 7 figuers, to apear in Physical Review
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