512 research outputs found
Core-mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake
The deformation at the core-mantle boundary produced by the 2004 Sumatra
earthquake is investigated by means of a semi-analytic theoretical model of
global coseismic and postseismic deformation, predicting a millimetric
coseismic perturbation over a large portion of the core-mantle boundary.
Spectral features of such deformations are analysed and discussed. The
time-dependent postseismic evolution of the elliptical part of the gravity
field (J2) is also computed for different asthenosphere viscosity models. Our
results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the
postseismic J2 variation in the next years is expected to leave a detectable
signal in geodetic observations.Comment: 14 pages, 8 figures, 1 table. It will appear in Geophysical Journal
Internationa
The effects of a revised Be e-capture rate on solar neutrino fluxes
The electron-capture rate on Be is the main production channel for Li
in several astrophysical environments. Theoretical evaluations have to account
for not only the nuclear interaction, but also the processes in the plasma
where Be ions and electrons interact. In the past decades several estimates
were presented, pointing out that the theoretical uncertainty in the rate is in
general of few percents. In the framework of fundamental solar physics, we
consider here a recent evaluation for the Be+e rate, not used up to now
in the estimate of neutrino fluxes. We analysed the effects of the new
assumptions on Standard Solar Models (SSMs) and compared the results obtained
by adopting the revised Be+e rate to those obtained by the one reported
in a widely used compilation of reaction rates (ADE11). We found that new SSMs
yield a maximum difference in the efficiency of the Be channel of about
-4\% with respect to what is obtained with the previously adopted rate. This
fact affects the production of neutrinos from B, increasing the relative
flux up to a maximum of 2.7\%. Negligible variations are found for the physical
and chemical properties of the computed solar models. The agreement with the
SNO measurements of the neutral current component of the B neutrino flux is
improved.Comment: 7 pages, 3 figures, 4 tables. Accepted for the publication on A&
Core-mantle boundary deformations triggered by the Sumatra earthquake
The devastating megathrust earthquake of December 26 2004 off the west coast of northern Sumatra has been probably the largest since the 1960 Chile event. The occurrence of this event revived the debate, among the scientific community, upon several open geophysical problems possibly connected with the energy release of giant earthquakes. One of these problems concerns the origin of geomagnetic jerks and its eventual relationship with large seismic activity. Though a final answer to this question seems not to be at hand presently, this answer (whatever positive or negative) appears to be connected with the possibility that giant seismic events could cause significant changes in the CMB topography. Until now, no attempts have been made to compute the impact of a seismic event on the CMB: the great Sumatra earthquake, for the first time, gave unambiguous instrumental evidence that the deformation field associated with a giant event is detectable at distances up to several thousands of km with a magnitude of the displacements of the order of 1 mm. Since perturbations to the CMB even smaller than this value are likely to be able to produce a geomagnetic jerk, a precise evaluation of the CMB topography perturbation associated with a giant earthquake like Sumatra has become an important scientific question
Review of the ELI-NP-GBS low level rf and synchronization systems
The Gamma Beam System (GBS) of ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module, for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described
Asymptotic Giant Branch models at very low metallicity
In this paper we present the evolution of a low mass model (initial mass
M=1.5 Msun) with a very low metal content (Z=5x10^{-5}, equivalent to
[Fe/H]=-2.44). We find that, at the beginning of the AGB phase, protons are
ingested from the envelope in the underlying convective shell generated by the
first fully developed thermal pulse. This peculiar phase is followed by a deep
third dredge up episode, which carries to the surface the freshly synthesized
13C, 14N and 7Li. A standard TP-AGB evolution, then, follows. During the proton
ingestion phase, a very high neutron density is attained and the s-process is
efficiently activated. We therefore adopt a nuclear network of about 700
isotopes, linked by more than 1200 reactions, and we couple it with the
physical evolution of the model. We discuss in detail the evolution of the
surface chemical composition, starting from the proton ingestion up to the end
of the TP-AGB phase.Comment: Accepted for Publication on PAS
Realization and high power tests of damped C-band accelerating structures for the ELI-NP linac
Modeling cardiac muscle fibers in ventricular and atrial electrophysiology simulations
Since myocardial fibers drive the electric signal propagation throughout the
myocardium, accurately modeling their arrangement is essential for simulating
heart electrophysiology (EP). Rule-Based-Methods (RBMs) represent a commonly
used strategy to include cardiac fibers in computational models. A particular
class of such methods is known as Laplace-Dirichlet-Rule-Based-Methods (LDRBMs)
since they rely on the solution of Laplace problems. In this work we provide a
unified framework, based on LDRBMs, for generating full heart muscle fibers.
First, we review existing ventricular LDRBMs providing a communal mathematical
description and introducing also some modeling improvements with respect to the
existing literature. We then carry out a systematic comparison of LDRBMs based
on meaningful biomarkers produced by numerical EP simulations. Next we propose,
for the first time, a LDRBM to be used for generating atrial fibers. The new
method, tested both on idealized and realistic atrial models, can be applied to
any arbitrary geometries. Finally, we present numerical results obtained in a
realistic whole heart where fibers are included for all the four chambers using
the discussed LDRBMs
Longitudinal phase-space manipulation with beam-driven plasma wakefields
The development of compact accelerator facilities providing high-brightness
beams is one of the most challenging tasks in field of next-generation compact
and cost affordable particle accelerators, to be used in many fields for
industrial, medical and research applications. The ability to shape the beam
longitudinal phase-space, in particular, plays a key role to achieve high-peak
brightness. Here we present a new approach that allows to tune the longitudinal
phase-space of a high-brightness beam by means of a plasma wakefields. The
electron beam passing through the plasma drives large wakefields that are used
to manipulate the time-energy correlation of particles along the beam itself.
We experimentally demonstrate that such solution is highly tunable by simply
adjusting the density of the plasma and can be used to imprint or remove any
correlation onto the beam. This is a fundamental requirement when dealing with
largely time-energy correlated beams coming from future plasma accelerators
Study of the time and space distribution of beta+ emitters from 80 MeV/u carbon ion beam irradiation on PMMA
Proton and carbon ion therapy is an emerging technique used for the treatment
of solid cancers. The monitoring of the dose delivered during such treatments
and the on-line knowledge of the Bragg peak position is still a matter of
research. A possible technique exploits the collinear 511\ \kilo\electronvolt
photons produced by positrons annihilation from emitters created by
the beam. This paper reports rate measurements of the 511\ \kilo\electronvolt
photons emitted after the interactions of a 80\ \mega\electronvolt / u fully
stripped carbon ion beam at the Laboratori Nazionali del Sud (LNS) of INFN,
with a Poly-methyl methacrylate target. The time evolution of the
rate was parametrized and the dominance of emitters over the other
species (, , ) was observed, measuring the fraction of
carbon ions activating emitters . The
average depth in the PMMA of the positron annihilation from emitters
was also measured, D_{\beta^+}=5.3\pm1.1\ \milli\meter, to be compared to the
expected Bragg peak depth D_{Bragg}=11.0\pm 0.5\ \milli\meter obtained from
simulations
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