107,190 research outputs found
Center motions of nonoverlapping condensates coupled by long-range dipolar interaction in bilayer and multilayer stacks
We investigate the effect of anisotropic and long-range dipole-dipole
interaction (DDI) on the center motions of nonoverlapping Bose-Einstein
condensates (BEC) in bilayer and multilayer stacks. In the bilayer, it is shown
analytically that while DDI plays no role in the in-phase modes of center
motions of condensates, out-of-phase mode frequency () depends
crucially on the strength of DDI (). At the small- limit,
. In the multilayer stack, transverse
modes associated with center motions of coupled condensates are found to be
optical phonon like. At the long-wavelength limit, phonon velocity is
proportional to .Comment: 7 pages, 5 figure
Using modified Gaussian distribution to study the physical properties of one and two-component ultracold atoms
Gaussian distribution is commonly used as a good approximation to study the
trapped one-component Bose-condensed atoms with relatively small nonlinear
effect. It is not adequate in dealing with the one-component system of large
nonlinear effect, nor the two-component system where phase separation exists.
We propose a modified Gaussian distribution which is more effective when
dealing with the one-component system with relatively large nonlinear terms as
well as the two-component system. The modified Gaussian is also used to study
the breathing modes of the two-component system, which shows a drastic change
in the mode dispersion at the occurrence of the phase separation. The results
obtained are in agreement with other numerical results.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Oscillations of Bose condensates in a one-dimensional optical superlattice
Oscillations of atomic Bose-Einstein condensates in a 1D optical lattice with
a two-point basis is investigated. In the low-frequency regime, four branches
of modes are resolved, that correspond to the transverse in-phase and
out-of-phase breathing modes, and the longitudinal acoustic and optical phonon
modes of the condensates. Dispersions of these modes depend intimately on the
values of two intersite Josephson tunneling strengths, and , and the
on-site repulsion between the atoms. Observation of these mode dispersions
is thus a direct way to access them.Comment: 5 pages,2 figure
Dispelling the Anthropic Principle from the Dimensionality Arguments
It is shown that in d=11 supergravity, under a very reasonable ansatz, the
nearly flat spacetime in which we are living must be 4-dimensional without
appealing to the Anthropic Principle. Can we dispel the Anthropic Principle
completely from cosmology?Comment: 7 pages, Essa
Surface Contribution to Raman Scattering from Layered Superconductors
Generalizing recent work, the Raman scattering intensity from a semi-infinite
superconducting superlattice is calculated taking into account the surface
contribution to the density response functions. Our work makes use of the
formalism of Jain and Allen developed for normal superlattices. The surface
contributions are shown to strongly modify the bulk contribution to the
Raman-spectrum line shape below , and also may give rise to additional
surface plasmon modes above . The interplay between the bulk and
surface contribution is strongly dependent on the momentum transfer
parallel to layers. However, we argue that the scattering
cross-section for the out-of-phase phase modes (which arise from interlayer
Cooper pair tunneling) will not be affected and thus should be the only
structure exhibited in the Raman spectrum below for relatively large
. The intensity is small but perhaps observable.Comment: 14 pages, RevTex, 6 figure
On the rooted Tutte polynomial
The Tutte polynomial is a generalization of the chromatic polynomial of graph
colorings. Here we present an extension called the rooted Tutte polynomial,
which is defined on a graph where one or more vertices are colored with
prescribed colors. We establish a number of results pertaining to the rooted
Tutte polynomial, including a duality relation in the case that all roots
reside around a single face of a planar graph. The connection with the Potts
model is also reviewed.Comment: plain latex, 14 pages, 2 figs., to appear in Annales de l'Institut
Fourier (1999
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