306 research outputs found
Giant Monopole Resonances and nuclear incompressibilities studied for the zero-range and separable pairing interactions
Background: Following the 2007 precise measurements of monopole strengths in
tin isotopes, there has been a continuous theoretical effort to obtain a
precise description of the experimental results. Up to now, there is no
satisfactory explanation of why the tin nuclei appear to be significantly
softer than 208Pb.
Purpose: We determine the influence of finite-range and separable pairing
interactions on monopole strength functions in semi-magic nuclei.
Methods: We employ self-consistently the Quasiparticle Random Phase
Approximation on top of spherical Hartree-Fock-Bogolyubov solutions. We use the
Arnoldi method to solve the linear-response problem with pairing.
Results: We found that the difference between centroids of Giant Monopole
Resonances measured in lead and tin (about 1 MeV) always turns out to be
overestimated by about 100%. We also found that the volume incompressibility,
obtained by adjusting the liquid-drop expression to microscopic results, is
significantly larger than the infinite-matter incompressibility.
Conclusions: The zero-range and separable pairing forces cannot induce
modifications of monopole strength functions in tin to match experimental data.Comment: 11 RevTeX pages, 16 figures, 1 table, extended versio
Fermi motion effects in electroproduction of hypernuclei
In a previous analysis of electroproduction of hypernuclei the cross sections
were calculated in distorted-wave impulse approximation where the momentum of
the initial proton in the nucleus was set to zero (the frozen-proton
approximation). In this paper we go beyond this approximation assuming a non
zero effective proton momentum due to proton Fermi motion inside of the target
nucleus discussing also other kinematical effects. To this end we have derived
a more general form of the two-component elementary electroproduction amplitude
(Chew-Goldberger-Low-Nambu like) which allows its use in a general reference
frame moving with respect to the nucleus-rest frame. The effects of Fermi
motion were found to depend on kinematics and elementary amplitudes. The
largest effects were observed in the contributions from the longitudinal and
interference parts of the cross sections. The extension of the calculations
beyond the frozen-proton approximation improved the agreement of predicted
theoretical cross sections with experimental data and once we assumed the
optimum on-shell approximation, we were able to remove an inconsistency which
was previously present in the calculations.Comment: 20 pages, 7 figures, 5 table
Linear response strength functions with iterative Arnoldi diagonalization
We report on an implementation of a new method to calculate RPA strength
functions with iterative non-hermitian Arnoldi diagonalization method, which
does not explicitly calculate and store the RPA matrix. We discuss the
treatment of spurious modes, numerical stability, and how the method scales as
the used model space is enlarged. We perform the particle-hole RPA benchmark
calculations for double magic nucleus 132Sn and compare the resulting
electromagnetic strength functions against those obtained within the standard
RPA.Comment: 9 RevTeX pages, 11 figures, submitted to Physical Review
Removal of the center of mass in nuclei and its effects on 4He
Abstract The singular value decomposition of rectangular matrices is shown to provide the recipe for removing the center of mass spurious admixtures from the multiphonon basis generated by an equation of motion method for solving the nuclear eigenvalue problem. It works for any single particle basis without any energy restriction on the selection of the configurations. Its effects on 4He are illustrated
A self-consistent many-body approach to the electroproduction of hypernuclei
The electroproduction of selected - and -shell hypernuclei was studied
within a many-body approach using realistic interactions between the
constituent baryons. The cross sections were computed in distorted-wave impulse
approximation using two elementary amplitudes for the electroproduction of the
hyperon. The structure of the hypernuclei was investigated within the
framework of the self-consistent -nucleon Tamm-Dancoff approach and
its extension known as the -nucleon equation of motion phonon method.
Use was made of the NNLOsat chiral potential plus the effective Nijmegen-F YN
interaction. The method was first implemented on light nuclei for studying the
available experimental data and establishing a relation to other approaches.
After this proof test, it was adopted for predicting the electroproduction
cross section of the hypernuclei K and K in
view of the E12-15-008 experiment in preparation at JLab. On the ground of
these predictions, appreciable effects on the spectra are expected to be
induced by the YN interaction.Comment: 11 pages, 9 figure
Electrical resistivity and ultrasonic measurements during sequential fracture test of cementitious composite
Cracks in cover of reinforced and pre-stressed concrete structures significantly influence the ingress of deleterious species causing decrease in durability of these structures. The paper is focused on the effect of fracture process on two selected physical parameters of concrete – the electrical resistivity and the ultrasonic pulse passing time – which might be employed as the quality indicator of concrete cover within (nondestructive) procedure(s) of assessment of the structural durability. The concrete electrical resistivity and ultrasonic passing time were investigated here with respect to two variants of treatment of the test specimens’ surface (the pre-dried surface and the wet surface). Test configuration of three-point bending of notched beam was utilized to control the crack propagation; the fracture process passed through several loading–unloading sequences between which the electrical resistivity and ultrasonic passing time readings over the fractured region were performed. Equivalent elastic crack model was used for estimation of the fracture advance (described via the effective crack length) at the loading stages corresponding to the resistivity and ultrasonic measurements. Relationships between changes of both the concrete resistivity and ultrasonic pulse passing time and the effective crack length is determined and discussed
Parameterized approximation schemes for steiner trees with small number of Steiner vertices
We study the Steiner Tree problem, in which a set of terminal vertices needs to be connected in the cheapest possible way in an edge-weighted graph. This problem has been extensively studied from the viewpoint of approximation and also parametrization. In particular, on one hand Steiner Tree is known to be APX-hard, and W[2]-hard on the other, if parameterized by the number of non-terminals (Steiner vertices) in the optimum solution. In contrast to this we give an efficient parameterized approximation scheme (EPAS), which circumvents both hardness results. Moreover, our methods imply the existence of a polynomial size approximate kernelization scheme (PSAKS) for the considered parameter. We further study the parameterized approximability of other variants of Steiner Tree, such as Directed Steiner Tree and Steiner Forest. For neither of these an EPAS is likely to exist for the studied parameter: For Steiner Forest an easy observation shows that the problem is APX-hard, even if the input graph contains no Steiner vertices. For Directed Steiner Tree we prove that computing a constant approximation for this parameter is W[1]-hard. Nevertheless, we show that an EPAS exists for Unweighted Directed Steiner Tree. Also we prove that there is an EPAS and a PSAKS for Steiner Forest if in addition to the number of Steiner vertices, the number of connected components of an optimal solution is considered to be a parameter
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