46,998 research outputs found
Coherent diffraction of thermal currents in Josephson tunnel junctions
We theoretically investigate heat transport in temperature-biased Josephson
tunnel junctions in the presence of an in-plane magnetic field. In full analogy
with the Josephson critical current, the phase-dependent component of the heat
flux through the junction displays coherent diffraction. Thermal transport is
analyzed in three prototypical junction geometries highlighting their main
differences. Notably, minimization of the Josephson coupling energy requires
the quantum phase difference across the junction to undergo \pi-slips in
suitable intervals of magnetic flux. An experimental setup suited to detect
thermal diffraction is proposed and analyzed.Comment: 6.5 pages, 4 color figures, updated versio
Excited-state quantum phase transitions in a two-fluid Lipkin model
Background: Composed systems have became of great interest in the framework
of the ground state quantum phase transitions (QPTs) and many of their
properties have been studied in detail. However, in these systems the study of
the so called excited-state quantum phase transitions (ESQPTs) have not
received so much attention.
Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is
presented in this work. The study is performed through the Hamiltonian
diagonalization for selected values of the control parameters in order to cover
the most interesting regions of the system phase diagram. [Method:] A
Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting
boson model (IBM) is diagonalized for selected values of the parameters and
properties such as the density of states, the Peres lattices, the
nearest-neighbor spacing distribution, and the participation ratio are
analyzed.
Results: An overview of the spectrum of the two-fluid Lipkin model for
selected positions in the phase diagram has been obtained. The location of the
excited-state quantum phase transition can be easily singled out with the Peres
lattice, with the nearest-neighbor spacing distribution, with Poincar\'e
sections or with the participation ratio.
Conclusions: This study completes the analysis of QPTs for the two-fluid
Lipkin model, extending the previous study to excited states. The ESQPT
signatures in composed systems behave in the same way as in single ones,
although the evidences of their presence can be sometimes blurred. The Peres
lattice turns out to be a convenient tool to look into the position of the
ESQPT and to define the concept of phase in the excited states realm
Hyperonic crystallization in hadronic matter
Published in Hadrons, Nuclei and Applications, World Scientific, Singapore,
Proc.of the Conference Bologna2000. Structure of the Nucleus at the Dawn of the
Century, G. Bonsignori, M. Bruno, A. Ventura, D. Vretenar Editors, pag. 319.Comment: 4 pages, 2figure
Lagrangian dynamical geography of the Gulf of Mexico
We construct a Markov-chain representation of the surface-ocean Lagrangian
dynamics in a region occupied by the Gulf of Mexico (GoM) and adjacent portions
of the Caribbean Sea and North Atlantic using satellite-tracked drifter
trajectory data, the largest collection so far considered. From the analysis of
the eigenvectors of the transition matrix associated with the chain, we
identify almost-invariant attracting sets and their basins of attraction. With
this information we decompose the GoM's geography into weakly dynamically
interacting provinces, which constrain the connectivity between distant
locations within the GoM. Offshore oil exploration, oil spill contingency
planning, and fish larval connectivity assessment are among the many activities
that can benefit from the dynamical information carried in the geography
constructed here.Comment: Submitted to Scientific Report
The Peculiar Balmer Line Profiles of OQ 208
We present spectrophotometric observations of the Broad Line Radio Galaxy OQ
208 (Mrk 668, 1404+286) obtained between 1985 and 1991. We show that the Balmer
line fluxes and profile shapes undergo remarkable changes. The ratio of
intensities between the broad and narrow components of Hbeta increased
monotonically from 15 in 1985 to 40 in 1991. The peak of the broad components
of Hbeta and Halpha were known to be strongly displaced to the red. We have
discovered a correlation between the amplitude of the broad peak displacement
and the luminosity of Hbeta, in the sense that the displacement is larger when
the line luminosity is higher. We suggest that the observations are not
compatible with either a binary Broad Line Region model or one involving
ballistic acceleration of the line emitting gas. Radiative acceleration of a
system of outflowing clouds readily explains the correlation between line shift
and luminosity as well as the peculiar line profiles. Furthermore, it seems
that most or all of the Balmer emission originates from the inward face of the
clouds. Theoretical line profiles suggest that the observed Hbeta profile is
best fit assuming the contribution of an ensemble which might be spherical or
confined in a thick disk in addition to a component emitted in a thin shell
contained in a cone of half opening angle 12 degrees seen along its axis.Comment: 28 pages + tables and figures available upon request, Latex, No
preprint numbe
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