50,973 research outputs found
Collision-Dependent Atom Tunnelling Rate in Bose-Einstein Condensates
We show that the interaction (cross-collision) between atoms trapped in
distinct sites of a double-well potential can significantly increase the atom
tunneling rate for special trap configurations leading to an effective linear
Rabi regime of population oscillation between the trap wells. The inclusion of
cross-collisional effects significantly extends the validity of the two-mode
model approach allowing it to be alternatively employed to explain the recently
observed increase of tunneling rates due to nonlinear interactions.Comment: 4 pages, 2 figures. Replaced with improved versio
Noncommutativity and Duality through the Symplectic Embedding Formalism
This work is devoted to review the gauge embedding of either commutative and
noncommutative (NC) theories using the symplectic formalism framework. To sum
up the main features of the method, during the process of embedding, the
infinitesimal gauge generators of the gauge embedded theory are easily and
directly chosen. Among other advantages, this enables a greater control over
the final Lagrangian and brings some light on the so-called "arbitrariness
problem". This alternative embedding formalism also presents a way to obtain a
set of dynamically dual equivalent embedded Lagrangian densities which is
obtained after a finite number of steps in the iterative symplectic process,
oppositely to the result proposed using the BFFT formalism. On the other hand,
we will see precisely that the symplectic embedding formalism can be seen as an
alternative and an efficient procedure to the standard introduction of the
Moyal product in order to produce in a natural way a NC theory. In order to
construct a pedagogical explanation of the method to the nonspecialist we
exemplify the formalism showing that the massive NC U(1) theory is embedded in
a gauge theory using this alternative systematic path based on the symplectic
framework. Further, as other applications of the method, we describe exactly
how to obtain a Lagrangian description for the NC version of some systems
reproducing well known theories. Naming some of them, we use the procedure in
the Proca model, the irrotational fluid model and the noncommutative self-dual
model in order to obtain dual equivalent actions for these theories. To
illustrate the process of noncommutativity introduction we use the chiral
oscillator and the nondegenerate mechanics
Near-infrared study of new embedded clusters in the Carina complex
We analyse the nature of a sample of stellar overdensities that we found
projected on the Carina complex. This study is based on 2MASS photometry and
involves the photometry decontamination of field stars, elaboration of
intrinsic colour-magnitude diagrams J(J-Ks), colour-colour diagrams
(J-H)(H-Ks) and radial density profiles, in order to determine the
structure and the main astrophysical parameters of the best candidates. The
verification of an overdensity as an embedded cluster requires a CMD consistent
with a PMS content and MS stars, if any. From these results, we are able to
verify if they are, in fact, embedded clusters. The results were, in general,
rewarding: in a sample of 101 overdensities, the analysis provided 15
candidates, of which three were previously catalogued as clusters
(CCCP-Cl16, Treasure Chest and FSR1555), and the 12 remaining are
discoveries that provided significant results, with ages not above 4.5Myr
and distances compatible with the studied complex. The resulting values for the
differential reddening of most candidates were relatively high, confirming that
these clusters are still (partially or fully) embedded in the surrounding gas
and dust, as a rule within a shell. Histograms with the distribution of the
masses, ages and distances were also produced, to give an overview of the
results. We conclude that all the 12 newly found embedded clusters are related
to the Carina complex.Comment: 10 pages, 14 figures, accepted for publication in MNRA
- …