641 research outputs found
Connecting the X(5)-, X(5)-, and X(3) models to the shape/phase transition region of the interacting boson model
The parameter independent (up to overall scale factors) predictions of the
X(5)-, X(5)-, and X(3) models, which are variants of the X(5)
critical point symmetry developed within the framework of the geometric
collective model, are compared to two-parameter calculations in the framework
of the interacting boson approximation (IBA) model. The results show that these
geometric models coincide with IBA parameters consistent with the phase/shape
transition region of the IBA for boson numbers of physical interest (close to
10). Nuclei within the rare-earth region and select Os and Pt isotopes are
identified as good examples of X(3), X(5)-, and X(5)-
behavior
Balmer line shifts in quasars
We offer a broad review of Balmer line phenomenology in type 1 active
galactic nuclei, briefly sum- marising luminosity and radio loudness effects,
and discussing interpretation in terms of nebular physics along the 4D
eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar
Balmer line profiles (i.e., with large shifts with respect to the rest frame or
double and multiple peaked) that start attracted attentions since the 1970s are
still passable of multiple dynamical interpretation. More mainstream objects
are still not fully understood as well, since competing dynamical models and
geometries are possible. Further progress may come from inter-line comparison
across the 4D Eigenvector 1 sequence.Comment: Accepted for publication in Astrophysics and Space Science, Special
Issue on Line Shifts in Astrophysics and Laboratory Plasm
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
Transition from the Seniority to the Anharmonic Vibrator Regime in Nuclei
A recent analysis of experimental energy systematics suggests that all
collective nuclei fall into one of three classes -- seniority, anharmonic
vibrational, or rotational -- with sharp phase transitions between them. We
investigate the transition from the seniority to the anharmonic vibrator regime
within a shell model framework involving a single large j-orbit. The
calculations qualitatively reproduce the observed transitional behavior, both
for U(5) like and O(6) like nuclei. They also confirm the preeminent role
played by the neutron-proton interaction in producing the phase transition.Comment: 9 pages with 2 tables, submitted to Physical Review C, November 199
Molecular Polarizability in Open Ensemble Simulations of Aqueous Nanoconfinements under Electric Field
Molecular polarization at aqueous interfaces involves fast degrees of freedom that are often averaged-out in atomistic-modeling approaches. The resulting effective interactions depend on a specific environment, making explicit account of molecular polarizability particularly important in solutions with pronounced anisotropic perturbations, including solid/liquid interfaces and external fields. Our work concerns polarizability effects in nanoscale confinements under electric field, open to an unperturbed bulk environment. We model aqueous molecules and ions in hydrophobic pores using the Gaussian-charge-on-spring BK3-AH representation. This involves nontrivial methodology devel- opments in expanded ensemble Monte Carlo simulations for open systems with long-ranged multibody interactions and necessitates further improvements for efficient modeling of polarizable ions. Structural differences between fixed-charge and polarizable models were captured in molecular dynamics simulations for a set of closed systems. Our open ensemble results with the BK3 model in neat-aqueous systems capture the ∼10% reduction of molecular dipoles within the surface layer near the hydrophobic pore walls in analogy to reported quantum mechanical calculations at water/vapor interfaces. The polarizability affects the interfacial dielectric behavior and weakens the electric-field dependence of water absorption at pragmatically relevant porosities. We observe moderate changes in thermodynamic properties and atom and charged-site spatial distributions; the Gaussian distribution of mobile charges on water and ions in the polarizable model shifts the density amplitudes and blurs the charge-layering effects associated with increased ion absorption. The use of polarizable force field indicates an enhanced response of interfacial ion distributions to applied electric field, a feature potentially important for in silico modeling of electric double layer capacitors
Band structure from random interactions
The anharmonic vibrator and rotor regions in nuclei are investigated in the
framework of the interacting boson model using an ensemble of random one- and
two-body interactions. We find a predominance of L(P)=0(+) ground states, as
well as strong evidence for the occurrence of both vibrational and rotational
band structures. This remarkable result suggests that such band structures
represent a far more general (robust) property of the collective model space
than is generally thought.Comment: 5 pages, 4 figures, Phys. Rev. Lett., in pres
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
3C 57 as an Atypical Radio-Loud Quasar: Implications for the Radio-Loud/Radio-Quiet Dichotomy
Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the
4D Eigenvector 1 (4DE1) parameter space which implies restricted
geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ)
majority of quasars. We discuss how this restricted domain for the LD RL parent
population supports the notion for a RQ-RL dichotomy among Type 1 sources. 3C
57 is an atypical RL quasar that shows both uncertain radio morphology and
falls in a region of 4DE1 space where RL quasars are rare.
We present new radio flux and optical spectroscopic measures designed to
verify its atypical optical/UV spectroscopic behaviour and clarify its radio
structure. The former data confirms that 3C 57 falls off the 4DE1 quasar "main
sequence" with both extreme optical FeII emission (R_{FeII} ~ 1) and a large
CIV 1549 profile blueshift (~ -1500 km/s). These parameter values are typical
of extreme Population A sources which are almost always RQ. New radio measures
show no evidence for flux change over a 50+ year timescale consistent with
compact steep-spectrum (CSS or young LD) over core-dominated morphology. In the
4DE1 context where LD RL are usually low L/L_{Edd} quasars we suggest that 3C
57 is an evolved RL quasar (i.e. large Black Hole mass) undergoing a major
accretion event leading to a rejuvenation reflected by strong FeII emission,
perhaps indicating significant heavy metal enrichment, high bolometric
luminosity for a low redshift source and resultant unusually high Eddington
ratio giving rise to the atypical CIV 1549.Comment: Accepted for publication in MNRAS; 10 pages, 6 figures, 4 table
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