57 research outputs found
Convergence properties of the effective interaction
The convergence properties of two perturbative schemes to sum the so-called
folded diagrams are critically reviewed, with an emphasis on the intruder state
problem. The methods we study are the approaches of Kuo and co-workers and Lee
and Suzuki. The suitability of the two schemes for shell-model calculations are
discussed.Comment: 10 pages in revtex ver. 3.0. 3 figs can be obtained upon request.
Univerisity of Oslo report UiO/PHYS/93-2
Comparison of the Effective Interaction to Various Orders in Different Mass Regions
The convergence of the perturbation expansion for the effective interaction
to be used in shell-model calculations is investigated as function of the mass
number , from to . As the mass number increases, there are more
intermediate states to sum over in each higher-order diagram which contributes
to the effective interaction. Together with the fact that the energy
denominators in each diagram are smaller for larger mass numbers, these two
effects could largely enhance higher-order contributions to the effective
interaction, thereby deteriorating the order-by-order convergence of the
effective interaction. This effect is counterbalanced by the short range of the
nucleon-nucleon interaction, which implies that its matrix elements are weaker
for valence single-particle states in ``large'' nuclei with large mass number
as compared to those in light nuclei. These effects are examined by comparing
various mean values of the matrix elements. It turns out that the contributions
from higher-order terms remain fairly stable as the mass number increases from
to . The implications for nuclear structure calculations are
discussed.Comment: Revtex, 20 pages, 1 figure not include
Renormalisation and fixed points in Hilbert Space
The energies of low-lying bound states of a microscopic quantum many-body
system of particles can be worked out in a reduced Hilbert space. We present
here and test a specific non-perturbative truncation procedure. We also show
that real exceptional points which may be present in the spectrum can be
identified as fixed points of coupling constants in the truncation procedure.Comment: 4 pages, 1 tabl
Comparison of techniques for computing shell-model effective operators
Different techniques for calculating effective operators within the framework
of the shell model using the same effective interaction and the same excitation
spaces are presented. Starting with the large-basis no-core approach, we
compare the time-honored perturbation-expansion approach and a model-space
truncation approach. Results for the electric quadrupole and magnetic dipole
operators are presented for Li. The convergence trends and dependence of
the effective operators on differing excitation spaces and Pauli Q-operators is
studied. In addition, the dependence of the electric-quadrupole effective
charge on the harmonic-oscillator frequency and the mass number, for A=5,6, is
investigated in the model-space truncation approach.Comment: 18 pages. REVTEX. 4 PostScript figure
Moyal products -- a new perspective on quasi-hermitian quantum mechanics
The rationale for introducing non-hermitian Hamiltonians and other
observables is reviewed and open issues identified. We present a new approach
based on Moyal products to compute the metric for quasi-hermitian systems. This
approach is not only an efficient method of computation, but also suggests a
new perspective on quasi-hermitian quantum mechanics which invites further
exploration. In particular, we present some first results which link the Berry
connection and curvature to non-perturbative properties and the metric.Comment: 14 pages. Submitted to J Phys A special issue on The Physics of
Non-Hermitian Operator
Effective theory for the two-nucleon system
We apply the method of unitary transformations to a model two-nucleon
potential and construct from it an effective potential in a subspace of momenta
below a given cut-off . The S-matrices in the full space and in the
subspace are shown to be identical. We solve numerically the Schr\"odinger
equation in the small momentum space and recover exactly the bound and
scattering states of the full theory. We then expand the heavy repulsive meson
exchange of the effective potential in a series of local contact terms and
discuss the question of naturalness of the corresponding coupling constants.
Using our exact effective theory we address further issues related to the
chiral perturbation theory approach of the two-nucleon system. The coordinate
space representation of the effective potential is also considered.Comment: 24 pp, LaTeX2e, 11 figures, small additions in sections 2 and 3, to
appear in Nuclear Physics
Shell-model calculations and realistic effective interactions
A review is presented of the development and current status of nuclear
shell-model calculations in which the two-body effective interaction is derived
from the free nucleon-nucleon potential. The significant progress made in this
field within the last decade is emphasized, in particular as regards the
so-called V-low-k approach to the renormalization of the bare nucleon-nucleon
interaction. In the last part of the review we first give a survey of realistic
shell-model calculations from early to present days. Then, we report recent
results for neutron-rich nuclei near doubly magic 132Sn and for the whole
even-mass N=82 isotonic chain. These illustrate how shell-model effective
interactions derived from modern nucleon-nucleon potentials are able to provide
an accurate description of nuclear structure properties.Comment: 71 pages, to be published in Progress in Particle and Nuclear Physic
Angiostrongylosis-related restrictive pneumopathy assessed by arterial blood gas analysis in a dog
Pulmonary angiostrongylosis was diagnosed by the Baermann method and larval identification from faecal and bronchoalveolar lavage samples in a five-month- old male mongrel dog with dyspnoea and cough. Arterial blood gas analysis indicated arterial hypoxaemia and restrictive pneumopathy. In addition to the palliative treatment, fenbendazole was administered (50 mg/kg/24 h per os) for 14 days. The respiratory signs subsided within a short time clinically, but serial arterial blood gas analysis demonstrated an ongoing ventilation disorder. Repeated haematology, thoracic radiography, bronchoscopy and blood gas analysis were performed to follow the course of the disease. The most severe eosinophilia was detected after the beginning of the anthelmintic therapy, and the arterial pO2 level was permanently low. Arterial blood gas analysis provided the most adequate information about the course of the pneumopathy and it greatly facilitated the patientâs medical management
Technical and vocational education and training (TVET) for young people in low- and middle-income countries: a systematic review and meta-analysis
The world is facing a worsening youth employment crisis. In response, technical and vocational education and training (TVET) is back on the development agenda after years of neglect. This systematic review examined the evidence from studies evaluating the impacts of TVET interventions for young people in low- and middle-income countries (LMICs). The 26 included studies evaluated 20 different interventions, predominantly from Latin America. Meta-analyses of the effectiveness of TVET on five outcome measure categories were conducted. The overall mean effects on overall paid employment, formal employment, and monthly earnings were small, positive, and significant; however, significant heterogeneity was observed. Moderator analysis was performed in an attempt to explain between-study differences in effects. The overall paucity of research in this area, together with specific gaps and methodological limitations, affirm the need for strengthening the evidence base. Implications for policy, practice and research are discussed
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