3,113 research outputs found
New analytic solutions of the collective Bohr hamiltonian for a beta-soft, gamma-soft axial rotor
New analytic solutions of the quadrupole collective Bohr hamiltonian are
proposed, exploiting an approximate separation of the beta and gamma variables
to describe gamma-soft prolate axial rotors. The model potential is a sum of
two terms: a beta-dependent term taken either with a Coulomb-like or a
Kratzer-like form, and a gamma-dependent term taken as an harmonic oscillator.
In particular it is possible to give a one parameter paradigm for a beta-soft,
gamma-soft axial rotor that can be applied, with a considerable agreement, to
the spectrum of 234U.Comment: (Dipartimento di Fisica ``G.Galilei'' and INFN, via Marzolo 8,
I-35131 Padova, Italy) 10 pages, 3 figure
From bridewealth to dowry? A Bayesian estimation of ancestral states of marriage transfers in Indo-European groups
Significant amounts of wealth have been exchanged as part of marriage settlements throughout history. Although various models have been proposed for interpreting these practices, their development over time has not been investigated systematically. In this paper we use a Bayesian MCMC phylogenetic comparative approach to reconstruct the evolution of two forms of wealth transfers at marriage, dowry and bridewealth, for 51 Indo-European cultural groups. Results indicate that dowry is more likely to have been the ancestral practice, and that a minimum of four changes to bridewealth is necessary to explain the observed distribution of the two states across the cultural groups
Electromagnetic selection rules in the triangular alpha-cluster model of 12C
After recapitulating the procedure to find the bands and the states occurring
in the alpha-cluster model of C in which the clusters
are placed at the vertexes of an equilateral triangle, we obtain the selection
rules for electromagnetic transitions. While the alpha cluster structure leads
to the cancellation of E1 transitions, the approximations carried out in
deriving the roto-vibrational hamiltonian lead to the disappearance of M1
transitions. Furthermore, although in general the lowest active modes are E2,
E3, and M2, M3, , the cancellation of M2, M3 and M5
transitions between certain bands also occurs, as a result of the application
of group theoretical techniques drawn from molecular physics. These
implications can be very relevant for the spectroscopic analysis of
-ray spectra of C
Pairing in the continuum: the quadrupole response of the Borromean nucleus 6He
The ground state and low-lying continuum states of 6He are found within a
shell model scheme, in a basis of two-particle states built out of continuum
p-states of the unbound 5He nucleus, using a simple pairing contact-delta
interaction. This accounts for the Borromean character of the bound ground
state, revealing its composition. We investigate the quadrupole response of the
system and we put our calculations into perspective with the latest
experimental results. The calculated quadrupole strength distribution
reproduces the narrow 2+ resonance, while a second wider peak is found at about
3.9 MeV above the g.s. energy.Comment: 5 pages, 5 figure
Electric multipole response of the halo nucleus He
The role of different continuum components in the weakly-bound nucleus He
is studied by coupling unbound spd-waves of He by means of simple pairing
contact-delta interaction. The results of our previous investigations in a
model space containing only p-waves, showed the collective nature of the ground
state and allowed the calculation of the electric quadrupole transitions. We
extend this simple model by including also sd-continuum neutron states and we
investigate the electric monopole, dipole and octupole response of the system
for transitions to the continuum, discussing the contribution of different
configurations.Comment: 22 pages, 10 figure
Electric and magnetic response to the continuum for A=7 isobars in a dicluster model
Mirror isobars Li and Be are investigated in a dicluster model. The
magnetic dipole moments and the magnetic dipole response to the continuum are
calculated in this framework. The magnetic contribution is found to be small
with respect to electric dipole and quadrupole excitations even at
astrophysical energies, at a variance with the case of deuteron. Energy
weighted molecular sum rules are evaluated and a formula for the molecular
magnetic dipole sum rule is found which matches the numerical calculations.
Cross-sections for photo-dissociation and radiative capture as well as the
S-factor for reactions of astrophysical significance are calculated with good
agreement with known experimental data.Comment: Accepted in EPJ
Do extremists impose the structure of social networks?
The structure and the properties of complex networks essentially depend on
the way how nodes get connected to each other. We assume here that each node
has a feature which attracts the others. We model the situation by assigning
two numbers to each node, \omega and \alpha, where \omega indicates some
property of the node and \alpha the affinity towards that property. A node A is
more likely to establish a connection with a node B if B has a high value of
\omega and A has a high value of \alpha. Simple computer simulations show that
networks built according to this principle have a degree distribution with a
power law tail, whose exponent is determined only by the nodes with the largest
value of the affinity \alpha (the "extremists"). This means that the extremists
lead the formation process of the network and manage to shape the final
topology of the system. The latter phenomenon may have implications in the
study of social networks and in epidemiology.Comment: 4 pages, 3 figure
The electron screening puzzle and nuclear clustering
Accurate measurements of nuclear reactions of astrophysical interest within,
or close to, the Gamow peak, show evidence of an unexpected effect attributed
to the presence of atomic electrons in the target. The experiments need to
include an effective "screening" potential to explain the enhancement of the
cross sections at the lowest measurable energies. Despite various theoretical
studies conducted over the past 20 years and numerous experimental
measurements, a theory has not yet been found that can explain the cause of the
exceedingly high values of the screening potential needed to explain the data.
In this letter we show that instead of an atomic physics solution of the
"electron screening puzzle", the reason for the large screening potential
values is in fact due to clusterization effects in nuclear reactions, in
particular for reaction involving light nuclei.Comment: 6 pages, 2 figures, accepted for publication in Physics Letters
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