153 research outputs found
Long term continuous radon monitoring in a seismically active area
We present the results of a long term, continuous radon monitoring experiment started in April 2010 in a seismically active area, affected during the 2010-2013 data acquisition time window by an intense micro seismic activity and by several small seismic events. We employed both correlation and cross-correlation analyses in order to investigate possible relationship existing between the collected radon data, seismic events and meteorological parameters. Our results do not support the feasibility of a robust one-to-one association between the small magnitude earthquakes characterizing the local seismic activity and single radon measurement anomalies, but evidence significant correlation patterns between the spatio-temporal variations of seismic moment release and soil radon emanations, the latter being anyway dominantly modulated by meteorological parameters variations
Application of the Post-Widder Laplace inversion algorithm to postseismic rebound models
The postseismic response of a viscoelastic Earth can be computed analytically with a normal-mode approach, based on the application of propagator methods. This framework suffers from many limitations, mostly connected with the
solution of the secular equation, whose degree scales with the number of viscoelastic layers so that only low-resolution models can be practically solved. Recently, a
viable alternative to the normal-mode approach has been proposed, based on the Post-Widder inversion formula. This method allows to overcome some of the intrinsic limitations of the normal-mode approach, so that Earth models with arbitrary radial resolution can be employed and general linear non-Maxwell rheologies can be implemented. In this work, we test the robustness of the method against a standard normal-mode approach in order to optimize computation performance while ensuring the solution stability. As an application, we address the issue of finding the minimum number of layers with distinct elastic properties needed to accurately describe the postseismic relaxation of a realistic Earth model
Long term continuous radon monitoring in a seismically active area
We present the results of a long term, continuous radon monitoring experiment started in April 2010 in a seismically active area, affected during the 2010-2013 data acquisition time window by an intense micro seismic activity and by several small seismic events. We employed both correlation and cross-correlation analyses in order to investigate possible relationship existing between the collected radon data, seismic events and meteorological parameters. Our results do not support the feasibility of a robust one-to-one association between the small magnitude earthquakes characterizing the local seismic activity and single radon measurement anomalies, but evidence significant correlation patterns between the spatio-temporal variations of seismic moment release and soil radon emanations, the latter being anyway dominantly modulated by meteorological parameters variations
X-ray Absorption Linear Dichroism at the Ti K-edge of TiO2 anatase single crystal
Anatase TiO2 (a-TiO2) exhibits a strong X-ray absorption linear dichroism
with the X-ray incidence angle in the pre-edge, the XANES and the EXAFS at the
titanium K-edge. In the pre-edge region the behaviour of the A1-A3 and B peaks,
originating from the 1s-3d transitions, is due to the strong -orbital
polarization and strong orbital mixing. An unambiguous assignment of the
pre-edge peak transitions is made in the monoelectronic approximation with the
support of ab initio finite difference method calculations and spherical tensor
analysis in quantitative agreement with the experiment. It is found that A1 is
mostly an on-site 3d-4p hybridized transition, while peaks A3 and B are
non-local transitions, with A3 being mostly dipolar and influence by the 3d-4p
intersite hybridization, while B is due to interactions at longer range.
Finally, peak A2 which was previously assigned to a transition involving
pentacoordinated titanium atoms exhibits a quadrupolar angular evolution with
incidence angle. These results pave the way to the use of the pre-edge peaks at
the K-edge of a-TiO2 to characterize the electronic structure of related
materials and in the field of ultrafast XAS where the linear dichroism can be
used to compare the photophysics along different axes.Comment: 43 pages, 19 figure
Creep, Relaxation and Viscosity Properties for Basic Fractional Models in Rheology
The purpose of this paper is twofold: from one side we provide a general
survey to the viscoelastic models constructed via fractional calculus and from
the other side we intend to analyze the basic fractional models as far as their
creep, relaxation and viscosity properties are considered. The basic models are
those that generalize via derivatives of fractional order the classical
mechanical models characterized by two, three and four parameters, that we
refer to as Kelvin-Voigt, Maxwell, Zener, anti-Zener and Burgers. For each
fractional model we provide plots of the creep compliance, relaxation modulus
and effective viscosity in non dimensional form in terms of a suitable time
scale for different values of the order of fractional derivative. We also
discuss the role of the order of fractional derivative in modifying the
properties of the classical models.Comment: 41 pages, 8 figure
Testing Different Tectonic Models for the Source of the M w 6.5, 30 October 2016, Norcia Earthquake (Central Italy): A Youthful Normal Fault, or Negative Inversion of an Old Thrust?
We adopted a multidisciplinary approach to investigate the seismotectonic scenario of the 30
October 2016, Mw 6.5, Norcia earthquake, the largest shock of the 2016\u20132017 central Italy earthquake
sequence. First, we used seismological and geodetic data to infer the dip of the main slip patch of the
seismogenic fault that turned out to be rather low\u2010angle (~37\ub0). To evaluate whether this is an acceptable dip
for the main seismogenic source, we modeled earthquake deformation using single\u2010 and multiple\u2010fault
models deduced from aftershock pattern analyses. These models show that the coseismic deformation
generated by the Norcia earthquake is coherent with slip along a rather shallow\u2010dipping plane. To
understand the geological significance of this solution, we reconstructed the subsurface architecture of the
epicentral area. As the available data are not robust enough to converge on a single fault model, we built
three different models encompassing all major geological evidence and the associated uncertainties,
including the tectonic style and the location of major d\ue9collement levels. In all models the structures
derived from the contractional phase play a significant role: from controlling segmentation to partially
reusing inherited faults, to fully reactivating in extension a regional thrust, geometrically compatible
with the source of the Norcia earthquake. Based on our conclusions, some additional seismogenic sources
falling in the eastern, external portions of the Apennines may coincide with inherited structures. This
may be a common occurrence in this region of the chain, where the inception of extension is as recent as
Middle\u2010Upper Pleistocene
The mechanical relaxation study of polycrystalline MgCNi3
The mechanical relaxation spectra of a superconducting and a
non-superconducting MgCNi3 samples were measured from liquid nitrogen
temperature to room temperature at frequency of kilohertz. There are two
internal friction peaks (at 300 K labeled as P1 and 125 K as P2) for the
superconducting sample. For the non-superconducting one, the position of P1
shifts to 250 K, while P2 is almost completely depressed. It is found that the
peak position of P2 shifts towards higher temperature under higher measuring
frequency. The calculated activation energy is 0.13eV. We propose an
explanation relating P2 to the carbon atom jumping among the off-center
positions. And further we expect that the behaviors of carbon atoms maybe
correspond to the normal state crossovers around 150 K and 50 K observed by
many other experiments.Comment: 4 figure
Fast Domain Growth through Density-Dependent Diffusion in a Driven Lattice Gas
We study electromigration in a driven diffusive lattice gas (DDLG) whose
continuous Monte Carlo dynamics generate higher particle mobility in areas with
lower particle density. At low vacancy concentrations and low temperatures,
vacancy domains tend to be faceted: the external driving force causes large
domains to move much more quickly than small ones, producing exponential domain
growth. At higher vacancy concentrations and temperatures, even small domains
have rough boundaries: velocity differences between domains are smaller, and
modest simulation times produce an average domain length scale which roughly
follows , where varies from near .55 at 50% filling
to near .75 at 70% filling. This growth is faster than the behavior
of a standard conserved order parameter Ising model. Some runs may be
approaching a scaling regime. At low fields and early times, fast growth is
delayed until the characteristic domain size reaches a crossover length which
follows . Rough numerical estimates give and simple theoretical arguments give . Our conclusion that
small driving forces can significantly enhance coarsening may be relevant to
the YBCuO electromigration experiments of Moeckly {\it et
al.}(Appl. Phys. Let., {\bf 64}, 1427 (1994)).Comment: 18 pages, RevTex3.
Anomalously large oxygen-ordering contribution to the thermal expansion of untwinned YBa2Cu3O6.95 single crystals: a glass-like transition near room temperature
We present high-resolution capacitance dilatometry studies from 5 - 500 K of
untwinned YBa2Cu3Ox (Y123) single crystals for x ~ 6.95 and x = 7.0. Large
contributions to the thermal expansivities due to O-ordering are found for x ~
6.95, which disappear below a kinetic glass-like transition near room
temperature. The kinetics at this glass transition is governed by an energy
barrier of 0.98 +- 0.07 eV, in very good agreement with other O-ordering
studies. Using thermodynamic arguments, we show that O-ordering in the Y123
system is particularly sensitive to uniaxial pressure (stress) along the chain
axis and that the lack of well-ordered chains in Nd123 and La123 is most likely
a consequence of a chemical-pressure effect.Comment: 4 pages, 3 figures, submitted to PR
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