950 research outputs found
Non-empirical pairing functional
The present contribution reports the first systematic finite-nucleus
calculations performed using the Energy Density Functional method and a
non-empirical pairing functional derived from low-momentum interactions. As a
first step, the effects of Coulomb and the three-body force are omitted while
only the bare two-nucleon interaction at lowest order is considered. To cope
with the finite-range and non-locality of the bare nuclear interaction, the 1S0
channel of Vlowk is mapped onto a convenient operator form. For the first time,
neutron-neutron and proton-proton pairing correlations generated in finite
nuclei by the direct term of the two-nucleon interaction are characterized in a
systematic manner. Eventually, such predictions are compared to those obtained
from empirical local functionals derived from density-dependent zero range
interactions. The characteristics of the latter are analyzed in view of that
comparison and a specific modification of their isovector density dependence is
suggested to accommodate Coulomb effects and the isovector trend of neutron
gaps at the same time.Comment: To be printed in the Proceedings of the International Les Houches
School on "Exotic Nuclei: New Challenges", May 7-18 2007, Les Houches,
France, 9 pages, 2 figures. Minor modification
Chiral three-nucleon forces and pairing in nuclei
We present the first study of pairing in nuclei including three-nucleon
forces. We perform systematic calculations of the odd-even mass staggering
generated using a microscopic pairing interaction at first order in chiral
low-momentum interactions. Significant repulsive contributions from the leading
chiral three-nucleon forces are found. Two- and three-nucleon interactions
combined account for approximately 70% of the experimental pairing gaps, which
leaves room for self-energy and induced interaction effects that are expected
to be overall attractive in nuclei.Comment: 4 pages, 3 figure
Application of Value Focused Thinking and Fuzzy Systems to Assess System Architecture
AbstractSince a majority of resources are obligated during the design phase of a system lifecycle, critical assessment of candidate functional and system architectures is vital to identify optimal architectures before proceeding to subsequent lifecycle phases. Common challenges associated with generation and evaluation of system functional architectures include search of the expansive design space and assessment of key performance attributes that are particularly “fuzzy” and qualitative in early architecture development. Several assessment approaches have been presented in the literature to address the assessment challenge to include Quality Function Deployment (QFD), Analytical Hierarchy Process (AHP), Value-Focused Thinking (VFT), and fuzzy logic. In this research we combine the use of value functions and fuzzy assessment to assess a functional and system architecture. There are several benefits of a methodology that combines value-focused thinking and fuzzy assessment. A distinct advantage of the methodology presented is the explicit inclusion of the customer in the assessment process through validation of the TPM value functions Involving the customer in TPM value function development and validation ensures the customer has direct input regarding the TPMs and their associated value across the range of discourse The methodology presented is flexible enough to assess architectures early in the process when things are “fuzzy” as well as later when subsystem and component performance are well defined. The methodology can also be used to analyze and assess impacts of interface changes within the system architecture. . The methodology is domain independent and can be coupled with executable models linked to scenarios. The assessment methodology is applied to the architecture for a soldier knowledge acquisition system for which the key performance attributes are affordability, performance, flexibility, updateability, and availability
Non-empirical pairing energy density functional. First order in the nuclear plus Coulomb two-body interaction
We perform systematic calculations of pairing gaps in semi-magic nuclei
across the nuclear chart using the Energy Density Functional method and a {\it
non-empirical} pairing functional derived, without further approximation, at
lowest order in the two-nucleon vacuum interaction, including the Coulomb
force. The correlated single-particle motion is accounted for by the SLy4
semi-empirical functional. Rather unexpectedly, both neutron and proton pairing
gaps thus generated are systematically close to experimental data. Such a
result further suggests that missing effects, i.e. higher partial-waves of the
NN interaction, the NNN interaction and the coupling to collective
fluctuations, provide an overall contribution that is sub-leading as for
generating pairing gaps in nuclei. We find that including the Coulomb
interaction is essential as it reduces proton pairing gaps by up to 40%.Comment: 6 pages, 1 figure, accepted for publication in EPJ
Caring for the Body and the Soul: Small Businesses Post-Hobby Lobby and HHS Contraceptive Rule
The article examines the corporate personhood movement and its impact on closely-held corporations and individuals focusing on the U.S. Department of Health and Human Services rule
Application of computational intelligence to explore and analyze system architecture and design alternatives
Systems Engineering involves the development or improvement of a system or process from effective need to a final value-added solution. Rapid advances in technology have led to development of sophisticated and complex sensor-enabled, remote, and highly networked cyber-technical systems. These complex modern systems present several challenges for systems engineers including: increased complexity associated with integration and emergent behavior, multiple and competing design metrics, and an expansive design parameter solution space. This research extends the existing knowledge base on multi-objective system design through the creation of a framework to explore and analyze system design alternatives employing computational intelligence. The first research contribution is a hybrid fuzzy-EA model that facilitates the exploration and analysis of possible SoS configurations. The second contribution is a hybrid neural network-EA in which the EA explores, analyzes, and evolves the neural network architecture and weights. The third contribution is a multi-objective EA that examines potential installation (i.e. system) infrastructure repair strategies. The final contribution is the introduction of a hierarchical multi-objective evolutionary algorithm (MOEA) framework with a feedback mechanism to evolve and simultaneously evaluate competing subsystem and system level performance objectives. Systems architects and engineers can utilize the frameworks and approaches developed in this research to more efficiently explore and analyze complex system design alternatives --Abstract, page iv
Pairing in the Framework of the Unitary Correlation Operator Method (UCOM): Hartree-Fock-Bogoliubov Calculations
In this first in a series of articles, we apply effective interactions
derived by the Unitary Correlation Operator Method (UCOM) to the description of
open-shell nuclei, using a self-consistent Hartree-Fock-Bogoliubov framework to
account for pairing correlations. To disentangle the particle-hole and
particle-particle channels and assess the pairing properties of \VUCOM, we
consider hybrid calculations using the phenomenological Gogny D1S interaction
to derive the particle-hole mean field. In the main part of this article, we
perform calculations of the tin isotopic chain using \VUCOM in both the
particle-hole and particle-particle channels. We study the interplay of both
channels, and discuss the impact of non-central and non-local terms in
realistic interactions as well as the frequently used restriction of pairing
interactions to the partial wave. The treatment of the center-of-mass
motion and its effect on theoretical pairing gaps is assessed independently of
the used interactions.Comment: 14 pages, 10 figures, to appear in Phys. Rev. C, title modified
accordingl
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
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
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