665 research outputs found
Controlled Generation of Dark Solitons with Phase Imprinting
The generation of dark solitons in Bose-Einstein condensates with phase
imprinting is studied by mapping it into the classic problem of a damped driven
pendulum. We provide simple but powerful schemes of designing the phase imprint
for various desired outcomes. We derive a formula for the number of dark
solitons generated by a given phase step, and also obtain results which explain
experimental observations.Comment: 4pages, 4 figure
Direct extraction of the Eliashberg function for electron-phonon coupling: A case study of Be(1010)
We propose a systematic procedure to directly extract the Eliashberg function
for electron-phonon coupling from high-resolution angle-resolved photoemission
data. The procedure is successfully applied to the Be(1010) surface, providing
new insights to electron-phonon coupling at this surface. The method is shown
to be robust against imperfections in experimental data and suitable for wider
applications.Comment: 4 pages, 4 figures. More details concerning the procedure are
include
Role of Particle Interactions in the Feshbach Conversion of Fermion Atoms to Bosonic Molecules
We investigate the Feshbach conversion of fermion atomic pairs to condensed
boson molecules with a microscopic model that accounts the repulsive
interactions among all the particles involved. We find that the conversion
efficiency is enhanced by the interaction between boson molecules while
suppressed by the interactions between fermion atoms and between atom and
molecule. In certain cases, the combined effect of these interactions leads to
a ceiling of less than 100% on the conversion efficiency even in the adiabatic
limit. Our model predicts a non-monotonic dependence of the efficiency on mean
atomic density. Our theory agrees well with recent experiments on Li and
K.Comment: 5 pages, 4 figure
SO(5) structure of p-wave superconductivity for spin-dipole interaction model
A closed SO(5) algebraic structure in the the mean-field form of the
Hamiltonian the pure p-wave superconductivity is found that can help to
diagonalized by making use of the Bogoliubov rotation instead of the
Balian-Werthamer approach. we point out that the eigenstate is nothing but
SO(5)-coherent state with fermionic realization. By applying the approach to
the Hamiltonian with dipole interaction of Leggett the consistency between the
diagonalization and gap equation is proved through the double-time Green
function. The relationship between the s-wave and p-wave superconductivities
turns out to be recognized through Yangian algebra, a new type of
infinite-dimensional algebra.Comment: 7 pages, no figures. Accepted Journal of Physcis A: Mathematical and
Genera
On a discrete Davey-Stewartson system
We propose a differential difference equation in and study it by
Hirota's bilinear method. This equation has a singular continuum limit into a
system which admits the reduction to the Davey-Stewartson equation. The
solutions of this discrete DS system are characterized by Casorati and Grammian
determinants. Based on the bilinear form of this discrete DS system, we
construct the bilinear B\"{a}cklund transformation which enables us to obtain
its Lax pair.Comment: 12 pages, 2 figure
Superfluidity of Bose-Einstein Condensate in An Optical Lattice: Landau-Zener Tunneling and Dynamical Instability
Superflow of Bose-Einstein condensate in an optical lattice is represented by
a Bloch wave, a plane wave with periodic modulation of the amplitude. We review
the theoretical results on the interaction effects in the energy dispersion of
the Bloch waves and in the linear stability of such waves. For sufficiently
strong repulsion between the atoms, the lowest Bloch band develops a loop at
the edge of the Brillouin zone, with the dramatic consequence of a finite
probability of Landau-Zener tunneling even in the limit of a vanishing external
force. Superfluidity can exist in the central region of the Brillouin zone in
the presence of a repulsive interaction, beyond which Landau instability takes
place where the system can lower its energy by making transition into states
with smaller Bloch wavenumbers. In the outer part of the region of Landau
instability, the Bloch waves are also dynamically unstable in the sense that a
small initial deviation grows exponentially in time. In the inner region of
Landau instability, a Bloch wave is dynamically stable in the absence of
persistent external perturbations. Experimental implications of our findings
will be discussed.Comment: A new section on tight-binding approximation is added with a new
figur
Bragg spectroscopy of a superfluid Bose-Hubbard gas
Bragg spectroscopy is used to measure excitations of a trapped,
quantum-degenerate gas of 87Rb atoms in a 3-dimensional optical lattice. The
measurements are carried out over a range of optical lattice depths in the
superfluid phase of the Bose-Hubbard model. For fixed wavevector, the resonant
frequency of the excitation is found to decrease with increasing lattice depth.
A numerical calculation of the resonant frequencies based on Bogoliubov theory
shows a less steep rate of decrease than the measurements.Comment: 11 pages, 4 figure
Evaluating the accuracy of gridded water resources reanalysis and evapotranspiration products for assessing water security in poorly gauged basins
Achieving water security in poorly gauged basins is critically hindered by a lack of in situ river discharge data to assess past, current, and future evolution of water resources. To overcome this challenge, there has been a shift toward the use of freely available satellite and reanalysis data products. However, due to inherent bias and uncertainty, these secondary sources require careful evaluation to ascertain their performance before being applied in poorly gauged basins. The objectives of this study were to evaluate river discharge and evapotranspiration estimates from eight gridded water resources reanalysis (WRR), six satellite-based evapotranspiration (ET) products, and ET estimates derived from complimentary relationship (CR–ET) across eight river basins located in Central–West Africa. Results highlight strengths and weaknesses of the different WRR in simulating discharge dynamics and ET across the basins. Likewise, satellite-based products also show some strength and weaknesses in simulating monthly ET. Our results further revealed that the performance of the different models in simulating river discharge and evapotranspiration is strongly influenced by model structure, input data, and spatial resolution. Considering all hydrological model evaluation criteria, FLDAS-Noah, Lisflood, AWRAL, and Terra were among the best performing WRR products while for ET estimates, FLDAS-Noah, Terra, GLEAM3.5a and 3.5b, and PMLV2 outperformed the rest of the products. Given the plethora of WRR and ET products available, it is imperative to evaluate their performance in representative gauged basins to identify products that can be applied in each region. However, the choice of a particular product will depend on the application and user requirements. Taking this together, results from this study suggest that gridded WRR and ET products are a useful source of data for assessing water security in poorly gauged basins
Experimental properties of Bose-Einstein condensates in 1D optical lattices: Bloch oscillations, Landau-Zener tunneling and mean-field effects
We report experimental results on the properties of Bose-Einstein condensates
in 1D optical lattices. By accelerating the lattice, we observed Bloch
oscillations of the condensate in the lowest band, as well as Landau-Zener
(L-Z) tunneling into higher bands when the lattice depth was reduced and/or the
acceleration of the lattice was increased. The dependence of the L-Z tunneling
rate on the condensate density was then related to mean-field effects modifying
the effective potential acting on the condensate, yielding good agreement with
recent theoretical work. We also present several methods for measuring the
lattice depth and discuss the effects of the micromotion in the TOP-trap on our
experimental results.Comment: 11 pages, 14 figure
Twisted and Nontwisted Bifurcations Induced by Diffusion
We discuss a diffusively perturbed predator-prey system. Freedman and
Wolkowicz showed that the corresponding ODE can have a periodic solution that
bifurcates from a homoclinic loop. When the diffusion coefficients are large,
this solution represents a stable, spatially homogeneous time-periodic solution
of the PDE. We show that when the diffusion coefficients become small, the
spatially homogeneous periodic solution becomes unstable and bifurcates into
spatially nonhomogeneous periodic solutions.
The nature of the bifurcation is determined by the twistedness of an
equilibrium/homoclinic bifurcation that occurs as the diffusion coefficients
decrease. In the nontwisted case two spatially nonhomogeneous simple periodic
solutions of equal period are generated, while in the twisted case a unique
spatially nonhomogeneous double periodic solution is generated through
period-doubling.
Key Words: Reaction-diffusion equations; predator-prey systems; homoclinic
bifurcations; periodic solutions.Comment: 42 pages in a tar.gz file. Use ``latex2e twisted.tex'' on the tex
files. Hard copy of figures available on request from
[email protected]
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