510 research outputs found
Isovector splitting of nucleon effective masses, ab-initio benchmarks and extended stability criteria for Skyrme energy functionals
We study the effect of the splitting of neutron and proton effective masses
with isospin asymmetry on the properties of the Skyrme energy density
functional. We discuss the ability of the latter to predict observable of
infinite matter and finite nuclei, paying particular attention to controlling
the agreement with ab-initio predictions of the spin-isospin content of the
nuclear equation of state, as well as diagnosing the onset of finite size
instabilities, which we find to be of critical importance. We show that these
various constraints cannot be simultaneously fulfilled by the standard Skyrme
force, calling at least for an extension of its P-wave part.Comment: 17 pages, 9 figures; Minor changes, references added; Accepted for
publication in Phys.Rev.
Odd-even mass differences from self-consistent mean-field theory
We survey odd-even nuclear binding energy staggering using density functional
theory with several treatments of the pairing interaction including the BCS,
Hartree-Fock-Bogoliubov, and the Hartree-Fock-Bogoliubov with the Lipkin-Nogami
approximation. We calculate the second difference of binding energies and
compare with 443 measured neutron energy differences in isotope chains and 418
measured proton energy differences in isotone chains. The particle-hole part of
the energy functional is taken as the SLy4 Skyrme parametrization and the
pairing part of the functional is based on a contact interaction with possible
density dependence. An important feature of the data, reproduced by the theory,
is the sharp gap quenching at magic numbers. With the strength of the
interaction as a free parameter, the theory can reproduce the data to an rms
accuracy of about 0.25 MeV. This is slightly better than a single-parameter
phenomenological description but slightly poorer than the usual two-parameter
phenomenological form C/A^alpha . The following conclusions can be made about
the performance of common parametrization of the pairing interaction: (i) there
is a weak preference for a surface-peaked neutron-neutron pairing, which might
be attributable to many-body effects; (ii) a larger strength is required in the
proton pairing channel than in the neutron pairing channel; (iii) pairing
strengths adjusted to the well-known spherical isotope chains are too weak to
give a good overall fit to the mass differences.Comment: 13 pages, 9 figure
Pandemic influenza control in Europe and the constraints resulting from incoherent public health laws
© 2010 Martin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: With the emergence of influenza H1N1v the world is facing its first 21st century global pandemic. Severe Acute Respiratory Syndrome (SARS) and avian influenza H5N1 prompted development of pandemic preparedness plans. National systems of public health law are essential for public health stewardship and for the implementation of public health policy[1]. International coherence will contribute to effective regional and global responses. However little research has been undertaken on how law works as a tool for disease control in Europe. With co-funding from the European Union, we investigated the extent to which laws across Europe support or constrain pandemic preparedness planning, and whether national differences are likely to constrain control efforts. Methods: We undertook a survey of national public health laws across 32 European states using a questionnaire designed around a disease scenario based on pandemic influenza. Questionnaire results were reviewed in workshops, analysing how differences between national laws might support or hinder regional responses to pandemic influenza. Respondents examined the impact of national laws on the movements of information, goods, services and people across borders in a time of pandemic, the capacity for surveillance, case detection, case management and community control, the deployment of strategies of prevention, containment, mitigation and recovery and the identification of commonalities and disconnects across states. Results: Results of this study show differences across Europe in the extent to which national pandemic policy and pandemic plans have been integrated with public health laws. We found significant differences in legislation and in the legitimacy of strategic plans. States differ in the range and the nature of intervention measures authorized by law, the extent to which borders could be closed to movement of persons and goods during a pandemic, and access to healthcare of non-resident persons. Some states propose use of emergency powers that might potentially override human rights protections while other states propose to limit interventions to those authorized by public health laws. Conclusion: These differences could create problems for European strategies if an evolving influenza pandemic results in more serious public health challenges or, indeed, if a novel disease other than influenza emerges with pandemic potential. There is insufficient understanding across Europe of the role and importance of law in pandemic planning. States need to build capacity in public health law to support disease prevention and control policies. Our research suggests that states would welcome further guidance from the EU on management of a pandemic, and guidance to assist in greater commonality of legal approaches across states.Peer reviewe
Instabilities in the Nuclear Energy Density Functional
In the field of Energy Density Functionals (EDF) used in nuclear structure
and dynamics, one of the unsolved issues is the stability of the functional.
Numerical issues aside, some EDFs are unstable with respect to particular
perturbations of the nuclear ground-state density. The aim of this contribution
is to raise questions about the origin and nature of these instabilities, the
techniques used to diagnose and prevent them, and the domain of density
functions in which one should expect a nuclear EDF to be stable.Comment: Special issue "Open Problems in Nuclear Structure Theory" of
Jour.Phys.G - accepted. 7 pages, 2 figure
Comment on ``Structure of exotic nuclei and superheavy elements in a relativistic shell model''
A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduces the
new parameterization NL-RA1 of the relativistic mean-field model which is
claimed to give a better description of nuclear properties than earlier ones.
Using this model ^{298}114 is predicted to be a doubly-magic nucleus. As will
be shown in this comment these findings are to be doubted as they are obtained
with an unrealistic parameterization of the pairing interaction and neglecting
ground-state deformation.Comment: 2 pages REVTEX, 3 figures, submitted to comment section of Phys. Rev.
C. shortened and revised versio
Particle-Number Restoration within the Energy Density Functional Formalism
We give a detailed analysis of the origin of spurious divergences and finite
steps that have been recently identified in particle-number restoration
calculations within the nuclear energy density functional framework. We isolate
two distinct levels of spurious contributions to the energy. The first one is
encoded in the definition of the basic energy density functional itself whereas
the second one relates to the canonical procedure followed to extend the use of
the energy density functional to multi-reference calculations. The first level
of spuriosity relates to the long-known self-interaction problem and to the
newly discussed self-pairing interaction process which might appear when
describing paired systems with energy functional methods using auxiliary
reference states of Bogoliubov or BCS type. A minimal correction to the second
level of spuriosity to the multi-reference nuclear energy density functional
proposed in [D. Lacroix, T. Duguet, M. Bender, arXiv:0809.2041] is shown to
remove completely the anomalies encountered in particle-number restored
calculations. In particular, it restores sum-rules over (positive) particle
numbers that are to be fulfilled by the particle-number-restored formalism. The
correction is found to be on the order of several hundreds of keVs up to about
1 MeV in realistic calculations, which is small compared to the total binding
energy, but often accounts for a substantial percentage of the energy gain from
particle-number restoration and is on the same energy scale as the excitations
one addresses with multi-reference energy density functional methods.Comment: 37 pages, 14 figures, accepted for publication in PR
Ab-initio self-consistent Gorkov-Green's function calculations of semi-magic nuclei - I. Formalism at second order with a two-nucleon interaction
An ab-initio calculation scheme for finite nuclei based on self-consistent
Green's functions in the Gorkov formalism is developed. It aims at describing
properties of doubly-magic and semi-magic nuclei employing state-of-the-art
microscopic nuclear interactions and explicitly treating pairing correlations
through the breaking of U(1) symmetry associated with particle number
conservation. The present paper introduces the formalism, necessary to
undertake applications at (self-consistent) second-order using two-nucleon
interactions, in a detailed and self-contained fashion. First applications of
such a scheme will be reported soon in a forthcoming publication. Future works
will extend the present scheme to include three-nucleon interactions and
implement more advanced truncation schemes.Comment: 38 page
Microscopic evaluation of the pairing gap
We discuss the relevant progress that has been made in the last few years on
the microscopic theory of the pairing correlation in nuclei and the open
problems that still must be solved in order to reach a satisfactory description
and understanding of the nuclear pairing. The similarities and differences with
the nuclear matter case are emphasized and described by few illustrative
examples. The comparison of calculations of different groups on the same set of
nuclei show, besides agreements, also discrepancies that remain to be
clarified. The role of the many-body correlations, like screening, that go
beyond the BCS scheme, is still uncertain and requires further investigation.Comment: 21 pages,7 figures; minor modification, accepted for publication in
J. Phys.
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