1,487 research outputs found
Evolution of the vorticity-area density during the formation of coherent structures in two-dimensional flows
It is shown: 1) that in two-dimensional, incompressible, viscous flows the
vorticity-area distribution evolves according to an advection-diffusion
equation with a negative, time dependent diffusion coefficient and 2) how to
use the vorticity-streamfunction relations, i.e., the so-called scatter-plots,
of the quasi-stationary coherent structures in order to quantify the
experimentally observed changes of the vorticity distribution moments leading
to the formation of these structures.Comment: LaTeX, 15 pp., 2 eps figures. Some sections have been rewritten;
referees' Comments have been include
Comparing non-perturbative models of the breakup of neutron-halo nuclei
Breakup reactions of loosely-bound nuclei are often used to extract structure
and/or astrophysical information. Here we compare three non-perturbative
reaction theories often used when analyzing breakup experiments, namely the
continuum discretized coupled channel model, the time-dependent approach
relying on a semiclassical approximation, and the dynamical eikonal
approximation. Our test case consists of the breakup of 15C on Pb at 68
MeV/nucleon and 20 MeV/nucleon.Comment: 8 pages, 6 figures, accepted for publication in Phys. Rev.
Mechanisms of direct reactions with halo nuclei
Halo nuclei are exotic nuclei which exhibit a strongly clusterised structure:
they can be seen as one or two valence nucleons loosely bound to a core. Being
observed at the ridge of the valley of stability, halo nuclei are studied
mostly through reactions. In this contribution the reaction models most
commonly used to analyse experimental data are reviewed and compared to one
another. A reaction observable built on the ratio of two angular distributions
is then presented. This ratio enables removing most of the sensitivity to the
reaction mechanism, which emphasises the effects of nuclear structure on the
reaction.Comment: Invited talk given by Pierre Capel at the "10th International
Conference on Clustering Aspects of Nuclear Structure and Dynamics"
(Cluster12), Debrecen, Hungary, 24-28 September 2012. To appear in the
Cluster12 Proceedings in the Open Access Journal of Physics: Conference
Series (JPCS). (5 pages, 3 figures
Recent developments in the eikonal description of the breakup of exotic nuclei
The study of exotic nuclear structures, such as halo nuclei, is usually
performed through nuclear reactions. An accurate reaction model coupled to a
realistic description of the projectile is needed to correctly interpret
experimental data. In this contribution, we briefly summarise the assumptions
made within the modelling of reactions involving halo nuclei. We describe
briefly the Continuum-Discretised Coupled Channel method (CDCC) and the
Dynamical Eikonal Approximation (DEA) in particular and present a comparison
between them for the breakup of 15C on Pb at 68AMeV. We show the problem faced
by the models based on the eikonal approximation at low energy and detail a
correction that enables their extension down to lower beam energies. A new
reaction observable is also presented. It consists of the ratio between angular
distributions for two different processes, such as elastic scattering and
breakup. This ratio is completely independent of the reaction mechanism and
hence is more sensitive to the projectile structure than usual reaction
observables, which makes it a very powerful tool to study exotic structures far
from stability.Comment: Contribution to the proceedings of the XXI International School on
Nuclear Physics and Applications & the International Symposium on Exotic
Nuclei, dedicated to the 60th Anniversary of the JINR (Dubna) (Varna,
Bulgaria, 6-12 September 2015), 7 pages, 4 figure
Spin Chains as Perfect Quantum State Mirrors
Quantum information transfer is an important part of quantum information
processing. Several proposals for quantum information transfer along linear
arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect
transfer was shown to exist in two models with specifically designed strongly
inhomogeneous couplings. We show that perfect transfer occurs in an entire
class of chains, including systems whose nearest-neighbor couplings vary only
weakly along the chain. The key to these observations is the Jordan-Wigner
mapping of spins to noninteracting lattice fermions which display perfectly
periodic dynamics if the single-particle energy spectrum is appropriate. After
a half-period of that dynamics any state is transformed into its mirror image
with respect to the center of the chain. The absence of fermion interactions
preserves these features at arbitrary temperature and allows for the transfer
of nontrivially entangled states of several spins or qubits.Comment: Abstract extended, introduction shortened, some clarifications in the
text, one new reference. Accepted by Phys. Rev. A (Rapid Communications
Managing hyponatraemia in a patient with malignant melanoma: a case report
We report the case of a 46-year-old male with a known diagnosis of metastatic malignant melanoma who presented with hyponatraemia. The report details the challenges we faced in identifying the cause of his hyponatraemia and in attempting to reverse his electrolyte disturbance
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
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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