5,901 research outputs found
Integral relations and the adiabatic expansion method for 1+2 reactions above the breakup threshold: Helium trimers with soft-core potentials
The integral relations formalism introduced in \cite{bar09,rom11}, and
designed to describe 1+ reactions, is extended here to collision energies
above the threshold for the target breakup. These two relations are completely
general, and in this work they are used together with the adiabatic expansion
method for the description of 1+2 reactions. The neutron-deuteron breakup, for
which benchmark calculations are available, is taken as a test of the method.
The s-wave collision between the He atom and He dimer above the
breakup threshold and the possibility of using soft-core two-body potentials
plus a short-range three-body force will be investigated. Comparisons to
previous calculations for the three-body recombination and collision
dissociation rates will be shown.Comment: To be published in Physical Review
How many-body correlations and -clustering shape He
The Borromean He nucleus is an exotic system characterized by two `halo'
neutrons orbiting around a compact He (or ) core, in which the
binary subsystems are unbound. The simultaneous reproduction of its small
binding energy and extended matter and point-proton radii has been a challenge
for {\em ab initio} theoretical calculations based on traditional bound-state
methods. Using soft nucleon-nucleon interactions based on chiral effective
field theory potentials, we show that supplementing the model space with
He++ cluster degrees of freedom largely solves this issue. We analyze
the role played by the -clustering and many-body correlations, and
study the dependence of the energy spectrum on the resolution scale of the
interaction.Comment: 5 pages, 4 figure
Advances in the ab initio description of nuclear three-cluster systems
We introduce the extension of the ab initio no-core shell model with
continuum to describe three-body cluster systems. We present results for the
ground state of 6He and show improvements with respect to the description
obtained within the no-core shell model and the no-core shell model/resonating
group methods.Comment: Proceedings of the 21st International Conference on Few-Body Problems
in Physics. May 18-22, 2015. Chicago, Illinois, US
General integral relations for the description of scattering states using the hyperspherical adiabatic basis
In this work we investigate 1+2 reactions within the framework of the
hyperspherical adiabatic expansion method. To this aim two integral relations,
derived from the Kohn variational principle, are used. A detailed derivation of
these relations is shown. The expressions derived are general, not restricted
to relative partial waves, and with applicability in multichannel
reactions. The convergence of the -matrix in terms of the adiabatic
potentials is investigated. Together with a simple model case used as a test
for the method, we show results for the collision of a He atom on a \dimer
dimer (only the elastic channel open), and for collisions involving a Li
and two He atoms (two channels open).Comment: Accepted for publication in Physical Review
Variational description of continuum states in terms of integral relations
Two integral relations derived from the Kohn Variational Principle (KVP) are
used for describing scattering states. In usual applications the KVP requires
the explicit form of the asymptotic behavior of the scattering wave function.
This is not the case when the integral relations are applied since, due to
their short range nature, the only condition for the scattering wave function
is that it be the solution of in the internal region.
Several examples are analyzed for the computation of phase-shifts from bound
state type wave functions or, in the case of the scattering of charged
particles, it is possible to obtain phase-shifts using free asymptotic
conditions. As a final example we discuss the use of the integral relations in
the case of the Hyperspherical Adiabatic method.Comment: 34 pages, 7 figures, accepted in Phys. Rev.
Unified ab initio approaches to nuclear structure and reactions
The description of nuclei starting from the constituent nucleons and the
realistic interactions among them has been a long-standing goal in nuclear
physics. In addition to the complex nature of the nuclear forces, with two-,
three- and possibly higher many-nucleon components, one faces the
quantum-mechanical many-nucleon problem governed by an interplay between bound
and continuum states. In recent years, significant progress has been made in ab
initio nuclear structure and reaction calculations based on input from
QCD-employing Hamiltonians constructed within chiral effective field theory.
After a brief overview of the field, we focus on ab initio many-body approaches
- built upon the No-Core Shell Model - that are capable of simultaneously
describing both bound and scattering nuclear states, and present results for
resonances in light nuclei, reactions important for astrophysics and fusion
research. In particular, we review recent calculations of resonances in the
He halo nucleus, of five- and six-nucleon scattering, and an investigation
of the role of chiral three-nucleon interactions in the structure of Be.
Further, we discuss applications to the BeB radiative
capture. Finally, we highlight our efforts to describe transfer reactions
including the HHe fusion.Comment: Contribution to the Special Physica Scripta Edition - 40 year
anniversary - Nobel Prize '75, 71 pages, 29 figure
No-Core Shell Model Analysis of Light Nuclei
The fundamental description of both structural properties and reactions of
light nuclei in terms of constituent protons and neutrons interacting through
nucleon-nucleon and three-nucleon forces is a long-sought goal of nuclear
theory. I will briefly present a promising technique, built upon the {\em ab
initio} no-core shell model, which emerged recently as a candidate to reach
such a goal: the no-core shell model/resonating-group method. This approach,
capable of describing simultaneously both bound and scattering states in light
nuclei, complements a microscopic cluster technique with the use of two-nucleon
realistic interactions, and a microscopic and consistent description of the
nucleon clusters. I will discuss applications to light nuclei binary scattering
processes and fusion reactions that power stars and Earth based fusion
facilities, such as the deuterium-He fusion, and outline the progress
toward the inclusion of the three-nucleon force into the formalism and the
treatment of three-body clusters.Comment: 8 pages, 6 figures, Proceedings of the 20th International IUPAP
Conference on Few-Body Problems in Physics, 20 - 25 August, 2012, Fukuoka,
Japa
From Iron Lady’s portrait to Mutti Angela’s photography: the iconic treatment of German Chancellor Angela Merkel
La investigación condensada en estas páginas se basa en el poder de denotación de la
fotografÃa y en la utilidad del análisis de contenido para esclarecer cuál es la representación de Angela
Merkel acuñada en 2015 por cinco diarios españoles de referencia. Concretamente, prima la intención
de comprobar si los rasgos caracterÃsticos de una metáfora extemporánea como es el rol de Dama
de Hierro permean la imagen que los diarios generalistas proyectan sobre la canciller alemana, y
si las actitudes que se le atribuyen coexisten con otras propias de la tradicional interpretación de la
naturaleza femÃnea. Al término del artÃculo se propone el empleo de una tabla de identificación que
permite reconocer en una instantánea si ésta responde a la idiosincrasia de los dos roles más comunes
vinculados a Merkel.The research presented in these pages rests on the photography’s denotation power,
as well as on the usefulness of the content analysis technique in order to clarify which is Angela
Merkel’s representation. So as to, five Spanish newspapers are analysed during 2015. Specifically,
the prevalent intention is to check if the characteristic features of an extemporaneous metaphor —as
it is the role of Iron Lady— pervade the image projected by the mainstream press onto the German
Chancellor. In addition, it is investigated whether the attributed attitudes coexist with traditional
female interpretation features. Moreover, at the end of the article, the use of an identification table
is proposed. It would help to recognize if a picture responds to the idiosyncrasies of the two most
common roles linked to Merkel
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