3,545 research outputs found
Fast nucleon emission as a probe of the isospin momentum dependence
In this article we investigate the structure of the non-local part of the
symmetry term, that leads to a splitting of the effective masses of protons and
neutrons in asymmetric matter. Based on microscopic transport simulations we
suggest some rather sensitive observables in collisions of neutron-rich
(unstable) ions at intermediate () energies. In particular we focus the
attention on pre-equilibrium nucleon emissions. We discuss interesting
correlations between the N/Z content of the fast emitted particles and their
rapidity or transverse momentum, that show a nice dependence on the
prescription used for the effective mass splitting.Comment: 5 pages, 6 figures, revtex
Isospin Transport at Fermi Energies
In this paper we investigate isospin transport mechanisms in semi-peripheral
collisions at Fermi energies. The effects of the formation of a low density
region (neck) between the two reaction partners and of pre-equilibrium emission
on the dynamics of isospin equilibration are carefully analyzed. We clearly
identify two main contributions to the isospin transport: isospin diffusion due
to the ratio and isospin drift due to the density gradients. Both effects
are sensitive to the symmetry part of the nuclear Equation of State (EOS), in
particular to the value and slope around saturation density.Comment: 6 pages, 6 figures, revtex4-twocolumn
IMF isotopic properties in semi-peripheral collisions at Fermi energies
We study the neutron and proton dynamical behavior along the fragmentation
path in semi-peripheral collisions: 58Fe+58Fe (charge asymmetric, N/Z = 1.23)
and 58Ni+58Ni (charge symmetric, N/Z = 1.07), at 47 AMeV. We observe that
isospin dynamics processes take place also in the charge-symmetric system
58Ni+58Ni, that may produce more asymmetric fragments. A neutron enrichment of
the neck fragments is observed, resulting from the interplay between
pre-equilibrium emission and the phenomenon of "isospin-migration". Both
effects depend on the EoS (Equation of State) symmetry term. This point is
illustrated by comparing the results obtained with two different choices of the
symmetry energy density dependence.
New correlation observables are suggested, to study the reaction mechanism
and the isospin dynamics.Comment: 5 pages, 8 figures, Revtex4 Latex Styl
Phase transitions of hadronic to quark matter at finite T and \mu_B
The phase transition of hadronic to quark matter and the boundaries of the
mixed hadron-quark coexistence phase are studied within the two Equation of
State (EoS) model. The relativistic effective mean field approach with constant
and density dependent meson-nucleon couplings is used to describe hadronic
matter, and the MIT Bag model is adopted to describe quark matter. The
boundaries of the mixed phase for different Bag constants are obtained solving
the Gibbs equations.
We notice that the dependence on the Bag parameter of the critical
temperatures (at zero chemical potential) can be well reproduced by a fermion
ultrarelativistic quark gas model, without contribution from the hadron part.
At variance the critical chemical potentials (at zero temperature) are very
sensitive to the EoS of the hadron sector. Hence the study of the hadronic EoS
is much more relevant for the determination of the transition to the
quark-gluon-plasma at finite baryon density and low-T. Moreover in the low
temperature and finite chemical potential region no solutions of the Gibbs
conditions are existing for small Bag constant values, B < (135 MeV)^4. Isospin
effects in asymmetric matter appear relevant in the high chemical potential
regions at lower temperatures, of interest for the inner core properties of
neutron stars and for heavy ion collisions at intermediate energies.Comment: 24 pages and 16 figures (revtex4
Damping of giant resonances in asymmetric nuclear matter
The giant collective modes in asymmetric nuclear matter are investigated
within a dynamic relaxation time approximation. We derive a coupled dispersion
relation and show that two sources of coupling appear: (i) a coupling of
isoscalar and isovector modes due to different mean-fields acting and (ii) an
explicit new coupling in asymmetric matter due to collisional interaction. We
show that the latter one is responsible for a new mode arising besides
isovector and isoscalar modes.Comment: Varenna conference proceeding
Sarcopenia and vitamin d deficiency in patients with crohnâs disease: Pathological conditions that should be linked together
Sarcopenia is a prevalent condition in patients with Crohnâs disease (CD), representing an independent predictor factor for the development of major postoperative complications. Thus, a proper assessment of the muscle strength, by using different validated tools, should be deemed an important step of the clinical management of these patients. Patients with CD are frequently malnourished, presenting a high prevalence of different macro-and micro-nutrient deficiencies, including that of vitamin D. The available published studies indicate that vitamin D is involved in the regulation of proliferation, differentiation, and regeneration of muscle cells. The relationship between vitamin D deficiency and sarcopenia has been extensively studied in other populations, with interesting evidence in regards to a potential role of vitamin D supplementation as a means to prevent and treat sarcopenia. The aim of this review was to find studies that linked together these pathological conditions
Prompt dipole radiation in fusion reactions
The prompt gamma ray emission was investigated in the 16A MeV energy region
by means of the 36,40Ar+96,92Zr fusion reactions leading to a compound nucleus
in the vicinity of 132Ce. We show that the prompt radiation, which appears to
be still effective at such a high beam energy, has an angular distribution
pattern consistent with a dipole oscillation along the symmetry axis of the
dinuclear system. The data are compared with calculations based on a collective
bremsstrahlung analysis of the reaction dynamics
Frictional melting of peridotite and seismic slip
The evolution of the frictional strength along a fault at seismic slip rates (about 1 m/s) is
a key factor controlling earthquake mechanics. At mantle depths, friction-induced melting
and melt lubrication may influence earthquake slip and seismological data. We report on
laboratory experiments designed to investigate dynamic fault strength and frictional melting
processes in mantle rocks. We performed 20 experiments with Balmuccia peridotite in a
high-velocity rotary shear apparatus and cylindrical samples (21.8 mm in diameter) over a
wide range of normal stresses (5.4â16.1 MPa), slip rates (0.23â1.14 m/s), and displacements
(1.5â71 m). During the experiments, shear stress evolved with cumulative displacement in
five main stages (stages 1â5). In stage 1 (first strengthening), the coefficient of friction m
increased up to 0.4â0.7 (first peak in friction). In stage 2 (abrupt firstweakening), m decreased
to about 0.25â0.40. In stage 3 (gradual second strengthening), shear stress increased toward
a second peak in friction (m = 0.30â0.40). In stage 4 (gradual second weakening), the
shear stress decreased toward a steady state value (stage 5) with m = 0.15. Stages 1 and 2 are
of too short duration to be investigated in detail with the current experimental configuration.
By interrupting the experiments during stages 3, 4, and 5, microstructural (Field Emission
Scanning Electron Microscope) and geochemical (Electron Probe Micro-Analyzer and
Energy Dispersive X-Ray Spectroscopy) analysis of the slipping zone suggest that second
strengthening (stage 3) is associated with the production of a grain-supported melt-poor
layer, while second weakening (stage 4) and steady state (stage 5) are associated with the
formation of a continuous melt-rich layer with an estimated temperature up to 1780 C.
Microstructures formed during the experiments were very similar to those found in natural
ultramafic pseudotachylytes. By performing experiments at different normal stresses
and slip rates, (1) the ââthermalââ (as it includes the thermally activated first and second
weakening) slip distance to achieve steady state from the first peak in strength decreased
with increasing normal stress and slip rate and (2) the steady state shear stress slightly
increased with increasing normal stress and, for a given normal stress, decreased with
increasing slip rate. The ratio of shear stress versus normal stress was about 0.15, well below
the typical friction coefficient of rocks (0.6â0.8). The dependence of steady state shear stress
with normal stress was described by means of a constitutive equation for melt lubrication.
The presence of microstructures similar to those found in natural pseudotachylytes and the
determination of a constitutive equation that describes the experimental data allows
extrapolation of the experimental observations to natural conditions and to the study of
rupture dynamics in mantle rocks
Structural evolution of a crustalâscale seismogenic fault in a magmatic arc: The Bolfin Fault Zone (Atacama Fault System)
How major crustal-scale seismogenic faults nucleate and evolve in crystalline basements represents a long-standing, but poorly understood, issue in structural geology and fault mechanics. Here, we address the spatio-temporal evolution of the Bolfin Fault Zone (BFZ), a >40-km-long exhumed seismogenic splay fault of the 1000-km-long strike-slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile) and formed during the oblique subduction of the Aluk plate beneath the South American plate. Seismic faulting occurred at 5â7 km depth and †300°C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite veining. Ancient (125â118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes. Field geologic surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Seismic faulting exploited the segments of precursory anisotropies that were optimal to favorably oriented with respect to the long-term far-stress field associated with the oblique ancient subduction. The large-scale sinuous geometry of the BFZ resulted from the hard linkage of these anisotropy-pinned segments during fault growth
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