564 research outputs found
Quantum theory of large amplitude collective motion and the Born-Oppenheimer method
We study the quantum foundations of a theory of large amplitude collective
motion for a Hamiltonian expressed in terms of canonical variables. In previous
work the separation into slow and fast (collective and non-collective)
variables was carried out without the explicit intervention of the Born
Oppenheimer approach. The addition of the Born Oppenheimer assumption not only
provides support for the results found previously in leading approximation, but
also facilitates an extension of the theory to include an approximate
description of the fast variables and their interaction with the slow ones.
Among other corrections, one encounters the Berry vector and scalar potential.
The formalism is illustrated with the aid of some simple examples, where the
potentials in question are actually evaluated and where the accuracy of the
Born Oppenheimer approximation is tested. Variational formulations of both
Hamiltonian and Lagrangian type are described for the equations of motion for
the slow variables.Comment: 29 pages, 1 postscript figure, preprint no UPR-0085NT. Latex + epsf
styl
A basis of cranking operators for the pairing-plus-quadrupole model
We investigate the RPA normal-mode coordinates in the pairing-plus-quadrupole
model, with an eye on simplifying the application of large amplitude collective
motion techniques. At the Hartree-Bogoliubov minimum, the RPA modes are exactly
the cranking operators of the collective coordinate approach. We examine the
possibility of representing the self-consistent cranking operator by linear
combinations of a limited number of one-body operators. We study the Sm nuclei
as an example, and find that such representations exist in terms of operators
that are state-dependent in a characteristic manner.Comment: 6 pages, 1 figure, using IOP journal style files, to be published in
J. Phys.
Towards a practical approach for self-consistent large amplitude collective motion
We investigate the use of an operatorial basis in a self-consistent theory of
large amplitude collective motion. For the example of the
pairing-plus-quadrupole model, which has been studied previously at
equilibrium, we show that a small set of carefully chosen state-dependent basis
operators is sufficient to approximate the exact solution of the problem
accuratly. This approximation is used to study the interplay of quadrupole and
pairing degrees of freedom along the collective path for realistic examples of
nuclei. We show how this leads to a viable calculational scheme for studying
nuclear structure, and discuss the surprising role of pairing collapse.Comment: 19 pages, 8 figures Revised version To be published in Phys. Rev.
Occupation probabilities of single particle levels using the microscopic interacting boson model: Application to some nuclei of interest in neutrinoless double- β
We have developed a new method to calculate the occupancies of single particle levels in atomic nuclei.
This method has been developed in the context of the microscopic interacting boson model, in which neutron
and proton degrees of freedom are treated explicitly. The energies of the single particle levels constitute a very
important input for the calculation of the occupancies in this method. In principle these energies can be considered
as input parameters that can be fitted to reproduce the experimental occupancies. Instead of fitting, in this study
we have extracted the single particle energies from experimental data on nuclei with a particle more or one particle
less than a shell closure. We provide the sets of these single particle energies suitable for several major shells and
apply our method to calculate the occupancies of several nuclei of interest in neutrinoless double-β decay using
these sets. Our results are compared with other theoretical calculations and experimental occupancies, when
available.peerReviewe
Functional renormalisation group for few-nucleon systems: SU(4) symmetry and its breaking
We apply the functional renormalisation group to few-nucleon systems. Our
starting point is a local effective action that includes three- and
four-nucleon interactions, expressed in terms of nucleon and two-nucleon boson
fields. The evolution of the coupling constants in this action is described by
a renormalisation group flow. We derive these flow equations both in the limit
of exact Wigner SU(4) symmetry and in the realistic case of broken symmetry. In
the symmetric limit we find that the renormalisation flow equations decouple,
and can be combined into two sets, one of which matches the known results for
bosons, and the other result matches the one for fermions with spin degrees
only. The equations show universal features in the unitary limit, which is
obtained when the two-body scattering length tends to infinity. We calculate
the spin-quartet neutron-deuteron scattering length and the deuteron-deuteron
scattering lengths in the spin-singlet and quintet channels
Colour superconductivity in finite systems
In this paper we study the effect of finite size on the two-flavour colour
superconducting state. As well as restricting the quarks to a box, we project
onto states of good baryon number and onto colour singlets, these being
necessary restrictions on any observable ``quark nuggets''. We find that
whereas finite size alone has a significant effect for very small boxes, with
the superconducting state often being destroyed, the effect of projection is to
restore it again. The infinite-volume limit is a good approximation even for
quite small systems.Comment: 14 pages RevTeX4, 12 eps figure
Application of a semi-microscopic core-particle coupling method to the backbending in odd deformed nuclei
In two previous papers, the Kerman-Klein-Donau-Frauendorf (KKDF) model was
used to study rotational bands of odd deformed nuclei. Here we describe
backbending for odd nuclei using the same model. The backbending in the
neighboring even nuclei is described by a phenomenological two band model, and
this core is then coupled to a large single-particle space, as in our previous
work. The results obtained for energies and M1 transition rates are compared
with experimental data for 165Lu and for energies alone to the experimental
data for 179W. For the case of 165Lu comparison is also made with previous
theoretical work.Comment: 16 pages including 8 figure(postscript), submitted to Phys.Rev.
Skyrmions and the Nuclear Force
The derivation of the nucleon-nucleon force from the Skyrme model is
reexamined. Starting from previous results for the potential energy of
quasistatic solutions, we show that a calculation using the Born-Oppenheimer
approximation properly taking into account the mixing of nucleon resonances,
leads to substantial central attraction. We obtain a potential that is in
qualitative agreement with phenomenological potentials. We also study the
non-adiabatic corrections, such as the velocity dependent transition
potentials, and discuss their importance.Comment: 24 pages, UPR-0124M
A 12-week lifestyle intervention: effects on fatigue, fear, and nutritional status in children with a Fontan circulation
INTRODUCTION: Children and adolescents with a Fontan circulation are less physically active compared to healthy peers. In the current study, effects of a 12-week lifestyle intervention on fatigue, fears regarding exercise, caloric intake, rest energy expenditure (REE), and body composition were measured in children with a Fontan circulation.METHODS: This study was a semi-cross-over randomized controlled trial. The lifestyle intervention consisted of a 12-week high-weight resistance training (three supervised training sessions a week) supported by high-protein diet (>2 g/kg) and tailored recommended caloric intake. Fatigue (measured by the validated PedsQol Multidimensional Fatigue Scale), fears regarding exercise (measured on a fear thermometer), REE (measured using indirect calorimetry), caloric intake and body composition using air displacement plethysmography, and four-skinfold method were measured before and after the intervention and control period.RESULTS: Twenty-seven pediatric Fontan patients, median age 12.9 years (IQR: 10.5-16.2), of the included 28 patients successfully completed the program. Before training, both child- and parent-reported levels of fatigue were significantly worse on all domains (general, sleep/rest, and cognitive fatigue) compared to healthy peers. After training, parent-reported fatigue significantly improved on the general and cognitive fatigue domains [effect size +16 points (7-25), p  < 0.001, and +10 points (2-17), p  = 0.015, compared to the control period]. Before training, fear regarding exercise scored on the fear thermometer was low for both children and parents (median score 1 and 2, respectively, on a scale of 0-8). After training, child-reported fear decreased further compared to the control period [effect size -1.4 points (-2.3 to -0.6), p  = 0.001]. At baseline, children had increased REE +12% compared to reference values, which did not change after exercise. Children ate an average of 637 calories below recommended intake based on REE, caloric deficit became smaller after the intervention, and protein intake increased compared to the control period [-388 calories (-674 to -102), p  = 0.008, and +15 g (0.4-30), p  = 0.044]. Body fat percentage did not change significantly. CONCLUSION: A 12-week lifestyle intervention improved parent-reported fatigue symptoms in the children, further decreased child-reported fears, and increased caloric and protein intake.</p
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