30,060 research outputs found
Non-adiabatic corrections to elastic scattering of halo nuclei
We derive the formalism for the leading order corrections to the adiabatic
approximation to the scattering of composite projectiles. Assuming a two-body
projectile of core plus loosely-bound valence particle and a model (the core
recoil model) in which the interaction of the valence particle and the target
can be neglected, we derive the non-adiabatic correction terms both exactly,
using a partial wave analysis, and using the eikonal approximation. Along with
the expected energy dependence of the corrections, there is also a strong
dependence on the valence-to-core mass ratio and on the strength of the
imaginary potential for the core-target interaction, which relates to
absorption of the core in its scattering by the target. The strength and
diffuseness of the core-target potential also determine the size of the
corrections. The first order non-adiabatic corrections were found to be smaller
than qualitative estimates would expect. The large absorption associated with
the core-target interaction in such halo nuclei as Be11 kills off most of the
non-adiabatic corrections. We give an improved estimate for the range of
validity of the adiabatic approximation when the valence-target interaction is
neglected, which includes the effect of core absorption. Some consideration was
given to the validity of the eikonal approximation in our calculations.Comment: 14 pages with 10 figures, REVTeX4, AMS-LaTeX v2.13, submitted to
Phys. Rev.
Sharing data from clinical trials: the rationale for a controlled access approach.
The move towards increased transparency around clinical trials is welcome. Much focus has been on under-reporting of trials and access to individual patient data to allow independent verification of findings. There are many other good reasons for data sharing from clinical trials. We describe some key issues in data sharing, including the challenges of open access to data. These include issues in consent and disclosure; risks in identification, including self-identification; risks in distorting data to prevent self-identification; and risks in analysis. These risks have led us to develop a controlled access policy, which safeguards the rights of patients entered in our trials, guards the intellectual property rights of the original researchers who designed the trial and collected the data, provides a barrier against unnecessary duplication, and ensures that researchers have the necessary resources and skills to analyse the data
Effects of an induced three-body force in the incident channel of (d,p) reactions
A widely accepted practice for treating deuteron breakup in
reactions relies on solving a three-body Schr\"odinger equation with
pairwise -, - and - interactions. However, it was shown in
[Phys. Rev. C \textbf{89}, 024605 (2014)] that projection of the many-body
wave function into the three-body channel results in a
complicated three-body operator that cannot be reduced to a sum of pairwise
potentials. It contains explicit contributions from terms that include
interactions between the neutron and proton via excitation of the target .
Such terms are normally neglected. We estimate the first order contribution of
these induced three-body terms and show that applying the adiabatic
approximation to solving the model results in a simple modification of
the two-body nucleon optical potentials. We illustrate the role of these terms
for the case of Ca()Ca transfer reactions at incident
deuteron energies of 11.8, 20 and 56 MeV, using several parameterisations of
nonlocal optical potentials.Comment: 7 pages, 2 figures. Publication due in Phys. Rev.
Discrete Accidental Symmetry for a Particle in a Constant Magnetic Field on a Torus
A classical particle in a constant magnetic field undergoes cyclotron motion
on a circular orbit. At the quantum level, the fact that all classical orbits
are closed gives rise to degeneracies in the spectrum. It is well-known that
the spectrum of a charged particle in a constant magnetic field consists of
infinitely degenerate Landau levels. Just as for the and
potentials, one thus expects some hidden accidental symmetry, in this case with
infinite-dimensional representations. Indeed, the position of the center of the
cyclotron circle plays the role of a Runge-Lenz vector. After identifying the
corresponding accidental symmetry algebra, we re-analyze the system in a finite
periodic volume. Interestingly, similar to the quantum mechanical breaking of
CP invariance due to the -vacuum angle in non-Abelian gauge theories,
quantum effects due to two self-adjoint extension parameters and
explicitly break the continuous translation invariance of the
classical theory. This reduces the symmetry to a discrete magnetic translation
group and leads to finite degeneracy. Similar to a particle moving on a cone, a
particle in a constant magnetic field shows a very peculiar realization of
accidental symmetry in quantum mechanics.Comment: 25 pages, 2 figure
Mother, I Didn\u27t Understand: Ballad
https://digitalcommons.library.umaine.edu/mmb-vp/2145/thumbnail.jp
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