234 research outputs found
Linear response in infinite nuclear matter as a tool to reveal finite size instabilities
Nuclear effective interactions are often modelled by simple analytical
expressions such as the Skyrme zero-range force. This effective interaction
depends on a limited number of parameters that are usually fitted using
experimental data obtained from doubly magic nuclei. It was recently shown that
many Skyrme functionals lead to the appearance of instabilities, in particular
when symmetries are broken, for example unphysical polarization of odd-even or
rotating nuclei. In this article, we show how the formalism of the linear
response in infinite nuclear matter can be used to predict and avoid the
regions of parameters that are responsible for these unphysical instabilities.Comment: Based on talk presented at 18th Nuclear Physics Workshop "Maria and
Pierre Curie", 2011, Kazimierz, Polan
Fitting Skyrme functionals using linear response theory
Recently, it has been recently shown that the linear response theory in
symmetric nuclear matter can be used as a tool to detect finite size
instabilities for different Skyrme functionals. In particular it has been shown
that there is a correlation between the density at which instabilities occur in
infinite matter and the instabilities in finite nuclei. In this article we
present a new fitting protocol that uses this correlation to add new additional
constraint in Symmetric Infinite Nuclear Matter in order to ensure the
stability of finite nuclei against matter fluctuation in all spin and isospin
channels. As an application, we give the parameters set for a new Skyrme
functional which includes central and spin-orbit parts and which is free from
instabilities by construction.Comment: Proceeding of 19th Nuclear Physics Workshop "Marie & Pierre Curie"
Kazimierz 201
The Many Facets of Mediation: A Requirements-driven Approach for Trading-off Mediation Solutions
Mediation aims at enabling dynamic composition of multi- ple components by making them interact successfully in order to satisfy given requirements. Through dynamic composition, software systems can adapt their structure and behaviour in dynamic and heterogeneous envi- ronments such as ubiquitous computing environments. This paper pro- vides a review of existing mediation approaches and their key character- istics and limitations. We claim that only a multifaceted approach that brings together and enhances the solutions of mediation from different perspectives is viable in the long term. We discuss how requirements can help identify synergies and trade-offs between these approaches and drive the selection of the appropriate mediation solution. We also highlight the open issues and future research directions in the area
Nuclear response for the Skyrme effective interaction with zero-range tensor terms. III. Neutron matter and neutrino propagation
The formalism of the linear response for the Skyrme energy density functional
including tensor terms derived in articles [1,2] for nuclear matter is applied
here to the case of pure neutron matter. As in article [2] we present
analytical results for the response function in all channels, the Landau
parameters and the odd-power sum rules. Special emphasis is given to the
inverse energy weighted sum rule because it can be used to detect non physical
instabilities. Typical examples are discussed and numerical results shown.
Moreover, as a direct application, neutrino propagation in neutron matter is
investigated through its neutrino mean free path at zero temperature. This
quantity turns out to be very sensitive to the tensor terms of the Skyrme
energy density functional
Gamow Shell Model Description of Neutron-Rich Nuclei
This work presents the first continuum shell-model study of weakly bound
neutron-rich nuclei involving multiconfiguration mixing. For the
single-particle basis, the complex-energy Berggren ensemble representing the
bound single-particle states, narrow resonances, and the non-resonant continuum
background is taken. Our shell-model Hamiltonian consists of a one-body finite
potential and a zero-range residual two-body interaction. The systems with two
valence neutrons are considered. The Gamow shell model, which is a
straightforward extension of the traditional shell model, is shown to be an
excellent tool for the microscopic description of weakly bound systems. It is
demonstrated that the residual interaction coupling to the particle continuum
is important; in some cases, it can give rise to the binding of a nucleus.Comment: 4 pages, More realistic s.p. energies used than in the precedent
versio
Enhancing the SVDD accuracy in Intrusion Detection Systems by removing external voids
This work aims to improve the accuracy of the SVDD-based Intrusion Detection Systems. In this study we are interested by approaches using only one-class classification, namely the class of normal user sessions. Sessions are modeled by vectors of points in a finite features space. The goal of using the SVDD in anomaly detection is to find the hypersphere with a minimal volume that encloses the entire scatter of points (i.e. the normal sessions). This paper discusses the general case where the shape of the scatter is arbitrary. In this case some voids can occur between the scatter and the boundary of the hypersphere, and mainly cause a distortion of the data description that reduces the accuracy of the detection. The objective of this work is to study and highlight the best techniques that help removing voids and thus improving the accuracy of the SVDD. Experimental results show that choosing the appropriate techniques and parameters can significantly improve the accuracy of the SVDD
Nuclear response for the Skyrme effective interaction with zero-range tensor terms. II. Sum rules and instabilities
The formalism of linear response theory for Skyrme forces including tensor
terms presented in article [1] is generalized for the case of a Skyrme energy
density functional in infinite matter. We also present analytical results for
the odd-power sum rules, with particular attention to the inverse energy
weighted sum rule, , as a tool to detect instabilities in Skyrme
functionals.Comment: Submitted to Phys. Rev.
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.
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