2,755 research outputs found
Pygmy dipole resonances in relativistic random phase approximation
The isovector dipole response in Pb is described in the framework of
a fully self-consistent relativistic random phase approximation. The NL3
parameter set for the effective mean-field Lagrangian with nonlinear meson
self-interaction terms, used in the present calculations, reproduces ground
state properties as well as the excitation energies of giant resonances in
nuclei. In addition to the isovector dipole resonance in Pb, the
present analysis predicts the occurrence of low-lying E1 peaks in the energy
region between 7 and 11 MeV. In particular, a collective state has been
identified whose dynamics correspond to that of a dipole pygmy resonance: the
vibration of the excess neutrons against the inert core composed of equal
number of protons and neutrons.Comment: LaTex 7 pages, 4 eps Figs, submitted to Phys. Lett.
Neutrino and antineutrino cross sections in C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. We have
done a thorough study of exclusive (ground state) properties of B and
N within the projected quasiparticle random phase approximation (PQRPA).
Good agreement with experimental data is achieved in this way. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin.Comment: Proceedings of the International Nuclear Physics Conference 2010,
Vancouver, BC - Canada 4-9 Jul 201
Neutron star structure and collective excitations of finite nuclei
We study relationships between properties of collective excitations in finite
nuclei and the phase transition density and pressure at the inner
edge separating the liquid core and the solid crust of a neutron star. A
theoretical framework that includes the thermodynamic method, relativistic
nuclear energy density functionals and the quasiparticle random-phase
approximation is employed in a self-consistent calculation of and
collective excitations in nuclei. The covariance analysis shows that properties
of charge-exchange dipole transitions, isovector giant dipole and quadrupole
resonances and pygmy dipole transitions are correlated with the core-crust
transition density and pressure. A set of relativistic nuclear energy density
functionals, characterized by systematic variation of the density dependence of
the symmetry energy of nuclear matter, is used to constrain possible values for
. By comparing the calculated excitation energies of giant
resonances, energy weighted pygmy dipole strength, and dipole polarizability
with available data, we obtain the weighted average values: fm and MeV fm.Comment: 4 pages, 3 figures, paper submitted for publicatio
Interacting boson-fermion model calculation of the level scheme and electromagnetic properties of 99Zr
A theoretical study of the 99Zr nucleus is presented. Energy levels, wave functions, and electromagnetic rates were calculated in the framework of the interacting boson-fermion model and are compared to the available data for low-lying states. In particular, we discuss the sensitivity of the g factor of the 3/2+1 state to the quenching of the spin gyromagnetic ratio and to the structure of the respective wave function
The design and construction of an electronic D-C analog computer
To make this project realizable with the funds available and in the time allowed, and to set forth some definite goals, the following objectives were adopted: Design, construct, and place in working order a d-c electronic analog computer capable of solving 4th order linear differential equations with constant coefficients. Include in the design provisions for real time computation, and also fast, repetitive operation. Provide for later expansion of the computer installation. Limit expenditures to $700 --Introduction, page 4
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
Two-neutrino double-beta decay matrix elements based on relativistic nuclear energy density functional
Nuclear matrix elements (NMEs) for two-neutrino double-beta decay
() are studied in the framework of relativistic nuclear energy
density functional (REDF). The properties of nuclei involved in the decay are
obtained using the relativistic Hartree-Bardeen-Cooper-Schrieffer theory and
relevant nuclear transitions are described using the relativistic
proton-neutron quasiparticle random phase approximation based on relativistic
energy density functional (REDF-QRPA). Three effective interactions have been
employed, including density-dependent meson-exchange (DD-ME2) and point
coupling interactions (DD-PC1 and DD-PCX), and pairing correlations are
described consistently both in and channels using a separable
pairing interaction. The optimal values of pairing strength parameter
are constrained by the experimental data on -decay half lives.
The matrix elements and half-lives are calculated for several
nuclides experimentally known to undergo this kind of decay: Ca,
Ge, Se, Zr, Mo, Cd, Xe,
Te, Te, Xe and Nd. The model dependence of the
NMEs and their sensitivity on is investigated, and the NMEs obtained
using optimal values of are discussed in comparison to previous
studies. The results of the present work represent an important benchmark for
the future applications of the relativistic framework in studies of
neutrinoless double-beta decay.Comment: 18 pages, 12 figures, accepted for publication in Physical Review
Pygmies, Giants, and Skins
Understanding the equation of state (EOS) of neutron-rich matter is a central
goal of nuclear physics that cuts across a variety of disciplines. Indeed, the
limits of nuclear existence, the collision of energetic heavy ions, the
structure of neutron stars, and the dynamics of core-collapse supernova all
depend critically on the nuclear-matter EOS. In this contribution I focus on
the EOS of cold baryonic matter with special emphasis on its impact on the
structure, dynamics, and composition of neutron stars. In particular, I discuss
how laboratory experiments on neutron skins as well as on Pygmy and Giant
resonances can help us elucidate the structure of these fascinating objects.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Semantic Transformation of Web Services
Web services have become the predominant paradigm for the development of distributed software systems. Web services provide the means to modularize software in a way that functionality can be described, discovered and deployed in a platform independent manner over a network (e.g., intranets, extranets and the Internet). The representation of web services by current industrial practice is predominantly syntactic in nature lacking the fundamental semantic underpinnings required to fulfill the goals of the emerging Semantic Web. This paper proposes a framework aimed at (1) modeling the semantics of syntactically defined web services through a process of interpretation, (2) scop-ing the derived concepts within domain ontologies, and (3) harmonizing the semantic web services with the domain ontologies. The framework was vali-dated through its application to web services developed for a large financial system. The worked example presented in this paper is extracted from the se-mantic modeling of these financial web services
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