A microscopic study of the proton-neutron symmetry and phonon structure of the low-lying states in 92Zr

We studied in a microscopic multiphonon approach the proton-neutron symmetry and phonon structure of some low-lying states recently discovered in 92Zr. We confirm the breaking of F-spin symmetry, but argue that the breaking mechanism is more complex than the one suggested in the original shell model analysis of the data. We found other new intriguing features of the spectrum, like a pronounced multiphonon fragmentation of the states and a tentative evidence of a three-phonon mixed symmetry state.Comment: 13 pages, to appear in Phys. Rev.

Fine structure of proton-neutron mixed symmetry states in some N=80 isotones

A microscopic multiphonon approach is adopted to investigate the structure of some low-lying states observed experimentally in the N = 80 isotones 134Xe, 136Ba, and 138Ce. The calculation yields levels and electromagnetic transition strengths in good agreement with experiments and relates the observed selection rules to the neutron proton symmetry and phonon content of the observed states. Moreover, it ascribes the splitting of theM1 strength in 138Ce to the proton subshell closure which magnifies the role of pairing in the excitation mechanism

Self-consistency in the Projected Shell Model

The Projected Shell Model is a shell model theory built up over a deformed BCS mean field. Ground state and excited bands in even-even nuclei are obtained through diagonalization of a pairing plus quadrupole Hamiltonian in an angular momentum projected 0-, 2-, and 4-quasiparticle basis. The residual quadrupole-quadrupole interaction strength is fixed self-consistently with the deformed mean field and the pairing constants are the same used in constructing the quasiparticle basis. Taking $^{160}Dy$ as an example, we calculate low-lying states and compare them with experimental data. We exhibit the effect of changing the residual interaction strengths on the spectra. It is clearly seen that there are many $J^\pi = 0^+, 1^+, 4^+$ bandheads whose energies can only be reproduced using the self-consistent strengths. It is thus concluded that the Projected Shell Model is a model essentially with no free parameters.Comment: 13 pages, 10 figures, submitted to Nuclear Physics

Wealth distribution across communities of adaptive financial agents

This paper studies the trading volumes and wealth distribution of a novel agent-based model of an artificial financial market. In this model, heterogeneous agents, behaving according to the Von Neumann and Morgenstern utility theory, may mutually interact. A Tobin-like tax (TT) on successful investments and a flat tax are compared to assess the effects on the agents' wealth distribution. We carry out extensive numerical simulations in two alternative scenarios: i) a reference scenario, where the agents keep their utility function fixed, and ii) a focal scenario, where the agents are adaptive and self-organize in communities, emulating their neighbours by updating their own utility function. Specifically, the interactions among the agents are modelled through a directed scale-free network to account for the presence of community leaders, and the herding-like effect is tested against the reference scenario. We observe that our model is capable of replicating the benefits and drawbacks of the two taxation systems and that the interactions among the agents strongly affect the wealth distribution across the communities. Remarkably, the communities benefit from the presence of leaders with successful trading strategies, and are more likely to increase their average wealth. Moreover, this emulation mechanism mitigates the decrease in trading volumes, which is a typical drawback of TTs.Comment: 18 pages, 7 figures, published in New Journal of Physic

Partial containment control over signed graphs

In this paper, we deal with the containment control problem in presence of antagonistic interactions. In particular, we focus on the cases in which it is not possible to contain the entire network due to a constrained number of control signals. In this scenario, we study the problem of selecting the nodes where control signals have to be injected to maximize the number of contained nodes. Leveraging graph condensations, we find a suboptimal and computationally efficient solution to this problem, which can be implemented by solving an integer linear problem. The effectiveness of the selection strategy is illustrated through representative simulations.Comment: 6 pages, 3 figures, accepted for presentation at the 2019 European Control Conference (ECC19), Naples, Ital

An application of the 3-dimensional q-deformed harmonic oscillator to the nuclear shell model

An analysis of the construction of a q-deformed version of the 3-dimensional harmonic oscillator, which is based on the application of q-deformed algebras, is presented. The results together with their applicability to the shell model are compared with the predictions of the modified harmonic oscillator.Comment: 12 pages, LaTe

Non-Scissors-Mode Behaviour of Isovector Magnetic Dipole Orbital Transitions Involving Isospin Transfer

We study the response of isovector orbital magnetic dipole (IOMD) transitions to the quadrupole-quadrupole ($Q \cdot Q$) interaction, to the isospin-conserving pairing interaction (ICP) and to combinations of both. We find qualitatively different behaviours for transitions in which the final isospin differs from the initial isospin versus cases where the two isospins are the same. For $N=Z$ even-even nuclei with $J^{\pi}=0^+, T=0$ ground states such as $^8Be$ and $^{20}Ne$, the summed $T=0 \to T=1$ IOMD from the ground state to all the $J=1, T=1$ states in the $0 \hbar \omega$ space does not vanish when the $Q \cdot Q$ interaction is turned off. The pairing interaction (ICP) alone leads to a finite transition rate. For nuclei with $J=0^+, T=1$ ground states such as $^{10}Be$ and $^{22}Ne$, the summed $T=1 \to T=1$ IOMD $does$ vanish when the $Q \cdot Q$ interaction is turned off, as is expected in a good scissors-mode behaviour. However this is not the case for the corresponding sum of the $T=1 \to T=2$ IOMD transitions. In $^{22}Ne$ (but not in $^{10}Be$) the sum of the $T=1 \to T=2$ IOMD transitions is remarkably insensitive to the strengths of both the $Q \cdot Q$ and the ICP interactions. In $^{22}Ne$ an energy weighted-sum is similarly insensitive. All our calculations were carried out in the $0 \hbar \omega$ space.Comment: 19 pages (including 5 figures). submitted to Nucl. Phys.

Orbital Magnetic Dipole Mode in Deformed Clusters: A Fully Microscopic Analysis

The orbital M1 collective mode predicted for deformed clusters in a schematic model is studied in a self-consistent random-phase-approximation approach which fully exploits the shell structure of the clusters. The microscopic mechanism of the excitation is clarified and the close correlation with E2 mode established. The study shows that the M1 strength of the mode is fragmented over a large energy interval. In spite of that, the fraction remaining at low energy, well below the overwhelming dipole plasmon resonance, is comparable to the strength predicted in the schematic model. The importance of this result in view of future experiments is stressed.Comment: 10 pages, 3 Postscript figures, uses revte