322 research outputs found
The neutron polaron as a constraint on nuclear density functionals
We study the energy of an impurity (polaron) that interacts strongly in a sea
of fermions when the effective range of the impurity-fermion interaction
becomes important, thereby mapping the Fermi polaron of condensed matter
physics and ultracold atoms to strongly interacting neutrons. We present
Quantum Monte Carlo results for this neutron polaron, and compare these with
effective field theory calculations that also include contributions beyond the
effective range. We show that state-of-the-art nuclear density functionals vary
substantially and generally underestimate the neutron polaron energy. Our
results thus provide constraints for adjusting the time-odd components of
nuclear density functionals to better characterize polarized systems.Comment: 5 pages, 3 figures; v2 corresponds to the published versio
Particle-Number Restoration within the Energy Density Functional formalism: Nonviability of terms depending on noninteger powers of the density matrices
We discuss the origin of pathological behaviors that have been recently
identified in particle-number-restoration calculations performed within the
nuclear energy density functional framework. A regularization method that
removes the problematic terms from the multi-reference energy density
functional and which applies (i) to any symmetry restoration- and/or
generator-coordinate-method-based configuration mixing calculation and (ii) to
energy density functionals depending only on integer powers of the density
matrices, was proposed in [D. Lacroix, T. Duguet, M. Bender, arXiv:0809.2041]
and implemented for particle-number restoration calculations in [M. Bender, T.
Duguet, D. Lacroix, arXiv:0809.2045]. In the present paper, we address the
viability of non-integer powers of the density matrices in the nuclear energy
density functional. Our discussion builds upon the analysis already carried out
in [J. Dobaczewski \emph{et al.}, Phys. Rev. C \textbf{76}, 054315 (2007)].
First, we propose to reduce the pathological nature of terms depending on a
non-integer power of the density matrices by regularizing the fraction that
relates to the integer part of the exponent using the method proposed in [D.
Lacroix, T. Duguet, M. Bender, arXiv:0809.2041]. Then, we discuss the spurious
features brought about by the remaining fractional power. Finally, we conclude
that non-integer powers of the density matrices are not viable and should be
avoided in the first place when constructing nuclear energy density functionals
that are eventually meant to be used in multi-reference calculations.Comment: 17 pages, 12 figures, accepted for publication in PR
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.
Giant hiatal hernias
Dyspnoea is most often caused by disorders of the respiratory and/or cardiovascular systems. Much less often it is brought aboutby the displacement of abdominal organs into the thoracic cage. Hiatal hernias may give rise to diagnostic difficulties, as bothclinical and radiological symptoms suggest different disorders. Computed tomography is the method of choice when makinga diagnosis.We have presented a series of 7 cases of giant hiatal hernias, each with a varying course of the disease, clinical symptoms,radiological features and prognoses.In two of the cases, the hernias were of a post-traumatic nature. Four cases of large diaphragmatic hernias were found in elderlypatients (over 90 years old). An advanced age and numerous coexisting chronic diseases disqualified most of the patients fromsurgical treatment despite the hernias’ large sizes. In only one case was fundoplication performed with a good end result. Twopatients died, and an extensive hernia was the cause of one of the deaths. Upper gastrointestinal symptoms were present onlyin a few of the patients.An early diagnosis of giant hiatal hernia is crucial for the patients to undergo prompt corrective surgeries
The tensor part of the Skyrme energy density functional. I. Spherical nuclei
We perform a systematic study of the impact of the J^2 tensor term in the
Skyrme energy functional on properties of spherical nuclei. In the Skyrme
energy functional, the tensor terms originate both from zero-range central and
tensor forces. We build a set of 36 parameterizations, which covers a wide
range of the parameter space of the isoscalar and isovector tensor term
coupling constants, with a fit protocol very similar to that of the successful
SLy parameterizations. We analyze the impact of the tensor terms on a large
variety of observables in spherical mean-field calculations, such as the
spin-orbit splittings and single-particle spectra of doubly-magic nuclei, the
evolution of spin-orbit splittings along chains of semi-magic nuclei, mass
residuals of spherical nuclei, and known anomalies of charge radii. Our main
conclusion is that the currently used central and spin-orbit parts of the
Skyrme energy density functional are not flexible enough to allow for the
presence of large tensor terms.Comment: 38 pages, 36 figures; Minor correction
Tensor part of the Skyrme energy density functional. II: Deformation properties of magic and semi-magic nuclei
We study systematically the impact of the time-even tensor terms of the
Skyrme energy density functional, i.e. terms bilinear in the spin-current
tensor density, on deformation properties of closed shell nuclei corresponding
to 20, 28, 40, 50, 82, and 126 neutron or proton shell closures. We compare
results obtained with three different families of Skyrme parameterizations
whose tensor terms have been adjusted on properties of spherical nuclei: (i)
TIJ interactions proposed in the first paper of this series [T. Lesinski et
al., Phys. Rev. C 76, 014312 (2007)] which were constructed through a complete
readjustment of the rest of the functional (ii) parameterizations whose tensor
terms have been added perturbatively to existing Skyrme interactions, with or
without readjusting the spin-orbit coupling constant. We analyse in detail the
mechanisms at play behind the impact of tensor terms on deformation properties
and how studying the latter can help screen out unrealistic parameterizations.
It is expected that findings of the present paper are to a large extent
independent of remaining deficiencies of the central and spin-orbit
interactions, and will be of great value for the construction of future,
improved energy functionals.Comment: 32 pages revte
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.
Energy density functional on a microscopic basis
In recent years impressive progress has been made in the development of
highly accurate energy density functionals, which allow to treat medium-heavy
nuclei. In this approach one tries to describe not only the ground state but
also the first relevant excited states. In general, higher accuracy requires a
larger set of parameters, which must be carefully chosen to avoid redundancy.
Following this line of development, it is unavoidable that the connection of
the functional with the bare nucleon-nucleon interaction becomes more and more
elusive. In principle, the construction of a density functional from a density
matrix expansion based on the effective nucleon-nucleon interaction is
possible, and indeed the approach has been followed by few authors. However, to
what extent a density functional based on such a microscopic approach can reach
the accuracy of the fully phenomenological ones remains an open question. A
related question is to establish which part of a functional can be actually
derived by a microscopic approach and which part, on the contrary, must be left
as purely phenomenological. In this paper we discuss the main problems that are
encountered when the microscopic approach is followed. To this purpose we will
use the method we have recently introduced to illustrate the different aspects
of these problems. In particular we will discuss the possible connection of the
density functional with the nuclear matter Equation of State and the distinct
features of finite size effects proper of nuclei.Comment: 20 pages, 6 figures,Contribution to J. Phys G, Special Issue, Focus
Section: Open Problems in Nuclear Structur
Pan-European sustainable forest management indicators for assessing Climate-Smart Forestry in Europe
The increasing demand for innovative forest management strategies to adapt to and mitigate climate change and benefit forest production, the so-called Climate-Smart Forestry, calls for a tool to monitor and evaluate their implementation and their effects on forest development over time. The pan-European set of criteria and indicators for sustainable forest management is considered one of the most important tools for assessing many aspects of forest management and sustainability. This study offers an analytical approach to selecting a subset of indicators to support the implementation of Climate-Smart Forestry. Based on a literature review and the analytical hierarchical approach, 10 indicators were selected to assess, in particular, mitigation and adaptation. These indicators were used to assess the state of the Climate-Smart Forestry trend in Europe from 1990 to 2015 using data from the reports on the State of Europe's Forests. Forest damage, tree species composition, and carbon stock were the most important indicators. Though the trend was overall positive with regard to adaptation and mitigation, its evaluation was partly hindered by the lack of data. We advocate for increased efforts to harmonize international reporting and for further integrating the goals of Climate-Smart Forestry into national-and European-level forest policy making
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