4,849 research outputs found
Description of nuclear systems with a self-consistent configuration-mixing approach. I: Theory, algorithm, and application to the C test nucleus
Although self-consistent multi-configuration methods have been used for
decades to address the description of atomic and molecular many-body systems,
only a few trials have been made in the context of nuclear structure. This work
aims at the development of such an approach to describe in a unified way
various types of correlations in nuclei, in a self-consistent manner where the
mean-field is improved as correlations are introduced. The goal is to reconcile
the usually set apart Shell-Model and Self-Consistent Mean-Field methods. This
approach is referred as "variational multiparticle-multihole configuration
mixing method". It is based on a double variational principle which yields a
set of two coupled equations that determine at the same time the expansion
coefficients of the many-body wave function and the single particle states. The
formalism is derived and discussed in a general context, starting from a
three-body Hamiltonian. Links to existing many-body techniques such as the
formalism of Green's functions are established. First applications are done
using the two-body D1S Gogny effective force. The numerical procedure is tested
on the C nucleus in order to study the convergence features of the
algorithm in different contexts. Ground state properties as well as
single-particle quantities are analyzed, and the description of the first
state is examined. This study allows to validate our numerical algorithm and
leads to encouraging results. In order to test the method further, we will
realize in the second article of this series, a systematic description of more
nuclei and observables obtained by applying the newly-developed numerical
procedure with the same Gogny force. As raised in the present work,
applications of the variational multiparticle-multihole configuration mixing
method will however ultimately require the use of an extended and more
constrained Gogny force.Comment: 22 pages, 18 figures, accepted for publication in Phys. Rev. C. v2:
minor corrections and references adde
A formula for charmonium suppression
In this work a formula for charmonium suppression obtained by Matsui in 1989
is analytically generalized for the case of complex c-cbar potential described
by a 3-dimensional and isotropic time-dependent harmonic oscillator (THO). It
is suggested that under certain conditions the formula can be applied to
describe J/\psi suppression in heavy-ion collisions at CERN-SPS, RHIC, and LHC
with the advantage of analytical tractability.Comment: 4 pages, no figures, to appear in Phys. At. Nucl., vol. 7
High-performance functional renormalization group calculations for interacting fermions
We derive a novel computational scheme for functional Renormalization Group
(fRG) calculations for interacting fermions on 2D lattices. The scheme is based
on the exchange parametrization fRG for the two-fermion interaction, with
additional insertions of truncated partitions of unity. These insertions
decouple the fermionic propagators from the exchange propagators and lead to a
separation of the underlying equations. We demonstrate that this separation is
numerically advantageous and may pave the way for refined, large-scale
computational investigations even in the case of complex multiband systems.
Furthermore, on the basis of speedup data gained from our implementation, it is
shown that this new variant facilitates efficient calculations on a large
number of multi-core CPUs. We apply the scheme to the , Hubbard model on
a square lattice to analyze the convergence of the results with the bond length
of the truncation of the partition of unity. In most parameter areas, a fast
convergence can be observed. Finally, we compare to previous results in order
to relate our approach to other fRG studies.Comment: 26 pages, 9 figure
On the puzzle of Bremsstrahlung as described by coaccelerated observers
We consider anew some puzzling aspects of the equivalence of the quantum
field theoretical description of Bremsstrahlung from the inertial and
accelerated observer's perspectives. More concretely, we focus on the seemingly
paradoxical situation that arises when noting that the radiating source is in
thermal equilibrium with the thermal state of the quantum field in the wedge in
which it is located, and thus its presence does not change there the state of
the field, while it clearly does not affect the state of the field on the
opposite wedge. How then is the state of the quantum field on the future wedge
changed, as it must in order to account for the changed energy momentum tensor
there? This and related issues are carefully discussed.Comment: 29 pages, 1 figure; Revtex, minor changes, PACS correcte
On the quality of climate proxies derived from newspaper reports ? a case study
International audienceOne of the main problems in climate reconstruction from documentary sources is the evaluation of the quality of non instrumental meteorological records in absence of instrumental observations to perform a calibration. In these cases it is mandatory to envision different approaches to assess the climatic signal in a reconstruction. This work is aimed to test the consistency of a snow frequency reconstruction in the central Argentinean Andes by studying the synoptic patterns related to the occurrence of precipitation in this area. While the original reconstruction covers the period between 1885 and 1996, the insufficiency of overlapping instrumental data limited the calibration to a short 15-year interval. In this paper we evaluate the performance of the reconstructed series for the entire 45-year period between 1958 and 1996 by analyzing the displacement in the jet stream and the patterns of geopotential height related to anomalies in the reconstructed snow frequency series. Previous works have linked the precipitation in the central Andes to the ENSO through the Pacific South American mode. We also have found this connection between ENSO and the reconstructed precipitation. Finally, it is shown that the ENSO relationship is the cause of a significant link between the precipitation anomalies in the central Argentinean Andes and the ice extent around the Antarctic Peninsula
Nueva sonda TDR para la medida de la conductividad eléctrica de la solución del suelo
Esta comunicación presenta una sonda TDR
(WECP) para la medida de la conductividad eléctrica de
la solución del suelo (σw), que consiste en una sonda
TDR trifilar (10 cm longitud) insertadas en 14 discos
cerámicos. La σw se estima a partir de la humedad y la
conductividad eléctrica del conjunto de discos cerámicos.
La WECP fue calibrada y testada en laboratorio con suelo
franco y en condiciones de campo con diferentes
soluciones de KCl. La σw estimada con WECP en
laboratorio fue comparada con las obtenidas a partir de la
solución de drenaje. El experimento de campo comparó
σw estimados con WECP con los medidos con lisímetros
de tensión. En ambos experimentos se observó una buena
y significativa correlación (R2 ≥ 0,97; P < 0,001;
Coeficiente de eficeincia Nash-Sutdiffe > 0,96) entre los
valores de σw estimados con WECP y los obtenidos en
laboratorio y campo a partir de la solución de drenajeEsta comunicación presenta una sonda TDR
(WECP) para la medida de la conductividad eléctrica de
la solución del suelo (σw), que consiste en una sonda
TDR trifilar (10 cm longitud) insertadas en 14 discos
cerámicos. La σw se estima a partir de la humedad y la
conductividad eléctrica del conjunto de discos cerámicos.
La WECP fue calibrada y testada en laboratorio con suelo
franco y en condiciones de campo con diferentes
soluciones de KCl. La σw estimada con WECP en
laboratorio fue comparada con las obtenidas a partir de la
solución de drenaje. El experimento de campo comparó
σw estimados con WECP con los medidos con lisímetros
de tensión. En ambos experimentos se observó una buena
y significativa correlación (R2 ≥ 0,97; P < 0,001;
Coeficiente de eficeincia Nash-Sutdiffe > 0,96) entre los
valores de σw estimados con WECP y los obtenidos en
laboratorio y campo a partir de la solución de drenajePublishe
Applicability of the photogrammetry technique to determine the volume and the bulk density of small soil aggregates
Aggregate density (¿) is defined as the relationship between the mass and the volume occupied by an aggregate. Previous studies have characterised ¿ on large to medium-sized soil aggregates (>4mm diameter); however, little information is available for smaller aggregates (0.99, P<0.0001) between the volumes estimated on rough stones with the PHM and Archimedes methods demonstrates that this technique can be satisfactorily used to estimate the volume and, consequently, the ¿ of small soil aggregates. The results showed an increase in ¿ with decreasing aggregate size. A general trend of increasing ¿ with the degree of soil disturbance by tillage was also observed
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