1,551 research outputs found
Time-dependent analysis of the nuclear and Coulomb dissociation of 11Be
The breakup of 11Be on carbon and lead targets around 70 MeV/nucleon is
investigated within a semiclassical framework. The role of the 5/2+ resonance
is analyzed in both cases. It induces a narrow peak in the nuclear-induced
breakup cross section, while its effect on Coulomb breakup is small. The
nuclear interactions between the projectile and the target is responsible for
the transition toward this resonant state. The influence of the parametrization
of the 10Be-n potential that simulates 11Be is also addressed. The breakup
calculation is found to be dependent on the potential choice. This leads us to
question the reliability of this technique to extract spectroscopic factors.Comment: 9 pages, 6 figures, to be published in the Proceedings of the Second
Argonne/MSU/JINA/INT RIA Workshop on Reaction Mechanisms for rare Isotope
Beams (2005
Simulating core excitation in breakup reactions of halo nuclei using an effective three-body force
We extend our previous calculation of the breakup of 11Be using Halo
Effective Field Theory and the Dynamical Eikonal Approximation to include an
effective 10Be-n-target force. The force is constructed to account for the
virtual excitation of 10Be to its low-lying 2+ excited state. In the case of
breakup on a 12C target this improves the description of the neutron-energy and
angular spectra, especially in the vicinity of the 11Be 5/2+ state. By
fine-tuning the range parameters of the three-body force, a reasonable
description of data in the region of the 3/2+ 11Be state can also be obtained.
This sensitivity to its range results from the structure of the overlap
integral that governs the 11Be s-to-d-state transitions induced by the
three-body force.Comment: 8 pages, 4 figure
Switching dynamics between metastable ordered magnetic state and nonmagnetic ground state - A possible mechanism for photoinduced ferromagnetism -
By studying the dynamics of the metastable magnetization of a statistical
mechanical model we propose a switching mechanism of photoinduced
magnetization. The equilibrium and nonequilibrium properties of the Blume-Capel
(BC) model, which is a typical model exhibiting metastability, are studied by
mean field theory and Monte Carlo simulation. We demonstrate reversible changes
of magnetization in a sequence of changes of system parameters, which would
model the reversible photoinduced magnetization. Implications of the calculated
results are discussed in relation to the recent experimental results for
prussian blue analogs.Comment: 12 pages, 13 figure
Influence of low energy scattering on loosely bound states
Compact algebraic equations are derived, which connect the binding energy and
the asymptotic normalization constant (ANC) of a subthreshold bound state with
the effective-range expansion of the corresponding partial wave. These
relations are established for positively-charged and neutral particles, using
the analytic continuation of the scattering (S) matrix in the complex
wave-number plane. Their accuracy is checked on simple local potential models
for the 16O+n, 16O+p and 12C+alpha nuclear systems, with exotic nuclei and
nuclear astrophysics applications in mind
Coulomb corrected eikonal description of the breakup of halo nuclei
The eikonal description of breakup reactions diverges because of the Coulomb
interaction between the projectile and the target. This divergence is due to
the adiabatic, or sudden, approximation usually made, which is incompatible
with the infinite range of the Coulomb interaction. A correction for this
divergence is analysed by comparison with the Dynamical Eikonal Approximation,
which is derived without the adiabatic approximation. The correction consists
in replacing the first-order term of the eikonal Coulomb phase by the
first-order of the perturbation theory. This allows taking into account both
nuclear and Coulomb interactions on the same footing within the computationally
efficient eikonal model. Excellent results are found for the dissociation of
11Be on lead at 69 MeV/nucleon. This Coulomb Corrected Eikonal approximation
provides a competitive alternative to more elaborate reaction models for
investigating breakup of three-body projectiles at intermediate and high
energies.Comment: 19 pages, 9 figures, accepted for publication in Phys. Rev.
Global persistence exponent of the two-dimensional Blume-Capel model
The global persistence exponent is calculated for the
two-dimensional Blume-Capel model following a quench to the critical point from
both disordered states and such with small initial magnetizations.
Estimates are obtained for the nonequilibrium critical dynamics on the
critical line and at the tricritical point.
Ising-like universality is observed along the critical line and a different
value is found at the tricritical point.Comment: 7 pages with 3 figure
Influence of the halo upon angular distributions for elastic scattering and breakup
The angular distributions for elastic scattering and breakup of halo nuclei
are analysed using a near-side/far-side decomposition within the framework of
the dynamical eikonal approximation. This analysis is performed for 11Be
impinging on Pb at 69 MeV/nucleon. These distributions exhibit very similar
features. In particular they are both near-side dominated, as expected from
Coulomb-dominated reactions. The general shape of these distributions is
sensitive mostly to the projectile-target interactions, but is also affected by
the extension of the halo. This suggests the elastic scattering not to be
affected by a loss of flux towards the breakup channel.Comment: 11 pages, 3 figures, accepted for publication in Phys. Lett.
Parallel dynamics of the fully connected Blume-Emery-Griffiths neural network
The parallel dynamics of the fully connected Blume-Emery-Griffiths neural
network model is studied at zero temperature for arbitrary using a
probabilistic approach. A recursive scheme is found determining the complete
time evolution of the order parameters, taking into account all feedback
correlations. It is based upon the evolution of the distribution of the local
field, the structure of which is determined in detail. As an illustrative
example, explicit analytic formula are given for the first few time steps of
the dynamics. Furthermore, equilibrium fixed-point equations are derived and
compared with the thermodynamic approach. The analytic results find excellent
confirmation in extensive numerical simulations.Comment: 22 pages, 12 figure
Interaction and thermodynamics of spinons in the XX chain
The mapping between the fermion and spinon compositions of eigenstates in the
one-dimensional spin-1/2 XX model on a lattice with N sites is used to describe
the spinon interaction from two different perspectives: (i) For finite N the
energy of all eigenstates is expressed as a function of spinon momenta and
spinon spins, which, in turn, are solutions of a set of Bethe ansatz equations.
The latter are the basis of an exact thermodynamic analysis in the spinon
representation of the XX model. (ii) For N -> infinity the energy per site of
spinon configurations involving any number of spinon orbitals is expressed as a
function of reduced variables representing momentum, filling, and magnetization
of each orbital. The spins of spinons in a single orbital are found to be
coupled in a manner well described by an Ising-like equivalent-neighbor
interaction, switching from ferromagnetic to antiferromagnetic as the filling
exceeds a critical level. Comparisons are made with results for the
Haldane-Shastry model.Comment: 16 pages, 3 figure
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