2,996 research outputs found
Rotating binary Bose-Einstein condensates and vortex clusters in quantum droplets
Quantum droplets may form out of a gaseous Bose-Einstein condensate,
stabilized by quantum fluctuations beyond mean field. We show that multiple
singly-quantized vortices may form in these droplets at moderate angular
momenta in two dimensions. Droplets carrying these precursors of an Abrikosov
lattice remain self-bound for certain timescales after switching off an initial
harmonic confinement. Furthermore, we examine how these vortex-carrying
droplets can be formed in a more pertubation-resistant setting, by starting
from a rotating binary Bose-Einstein condensate and inducing a metastable
persistent current via a non-monotonic trapping potential.Comment: 5 page, 4 figure
Phase diagram of a rapidly-rotating two-component Bose gas
We derive analytically the phase diagram of a two-component Bose gas confined
in an anharmonic potential, which becomes exact and universal in the limit of
weak interactions and small anharmonicity of the trapping potential. The
transitions between the different phases, which consist of vortex states of
single and multiple quantization, are all continuous because of the addition of
the second component.Comment: 5 pages, 3 figure
Rotational properties of non-dipolar and dipolar Bose-Einstein condensates confined in annular potentials
We investigate the rotational response of both non-dipolar and dipolar
Bose-Einstein condensates confined in an annular potential. For the non-dipolar
case we identify certain critical rotational frequencies associated with the
formation of vortices. For the dipolar case, assuming that the dipoles are
aligned along some arbitrary and tunable direction, we study the same problem
as a function of the orientation angle of the dipole moment of the atoms.Comment: 5 pages, 4 figure
Finite-size effects in the dynamics of few bosons in a ring potential
We study the temporal evolution of a small number of ultra-cold bosonic
atoms confined in a ring potential. Assuming that initially the system is in a
solitary-wave solution of the corresponding mean-field problem, we identify
significant differences in the time evolution of the density distribution of
the atoms when it instead is evaluated with the many-body Schr\"odinger
equation. Three characteristic timescales are derived: the first is the period
of rotation of the wave around the ring, the second is associated with a
"decay" of the density variation, and the third is associated with periodic
"collapses" and "revivals" of the density variations, with a factor of separating each of them. The last two timescales tend to infinity in the
appropriate limit of large , in agreement with the mean-field approximation.
These findings are based on the assumption of the initial state being a
mean-field state. We confirm this behavior by comparison to the exact solutions
for a few-body system stirred by an external potential. We find that the exact
solutions of the driven system exhibit similar dynamical features.Comment: To appear in Journal of Physics
Spin-orbit-coupled Bose-Einstein-condensed atoms confined in annular potentials
A spin-orbit-coupled Bose-Einstein-condensed cloud of atoms confined in an
annular trapping potential shows a variety of phases that we investigate in the
present study. Starting with the non-interacting problem, the homogeneous phase
that is present in an untrapped system is replaced by a sinusoidal density
variation in the limit of a very narrow annulus. In the case of an untrapped
system there is another phase with a striped-like density distribution, and its
counterpart is also found in the limit of a very narrow annulus. As the width
of the annulus increases, this picture persists qualitatively. Depending on the
relative strength between the inter- and the intra-components, interactions
either favor the striped phase, or suppress it, in which case either a
homogeneous, or a sinusoidal-like phase appears. Interactions also give rise to
novel solutions with a nonzero circulation.Comment: Final, slightly revised versio
Superfluidity in a gas of strongly-interacting bosons
We consider small systems of bosonic atoms rotating in a toroidal trap. Using
the method of exact numerical diagonalization of the many-body Hamiltonian, we
examine the transition from the Bose-Einstein condensed state to the
Tonks-Girardeau state. The system supports persistent currents in a wide range
between the two limits, even in the absence of Bose-Einstein condensation.Comment: 7 pages, 3 figures, revised version, to appear in Europh. Let
Slice Stretching at the Event Horizon when Geodesically Slicing the Schwarzschild Spacetime with Excision
Slice-stretching effects are discussed as they arise at the event horizon
when geodesically slicing the extended Schwarzschild black-hole spacetime while
using singularity excision. In particular, for Novikov and isotropic spatial
coordinates the outward movement of the event horizon (``slice sucking'') and
the unbounded growth there of the radial metric component (``slice wrapping'')
are analyzed. For the overall slice stretching, very similar late time behavior
is found when comparing with maximal slicing. Thus, the intuitive argument that
attributes slice stretching to singularity avoidance is incorrect.Comment: 5 pages, 2 figures, published version including minor amendments
suggested by the refere
Rotating Bose-Einstein condensates: Closing the gap between exact and mean-field solutions
When a Bose-Einstein condensed cloud of atoms is given some angular momentum,
it forms vortices arranged in structures with a discrete rotational symmetry.
For these vortex states, the Hilbert space of the exact solution separates into
a "primary" space related to the mean-field Gross-Pitaevskii solution and a
"complementary" space including the corrections beyond mean-field. Considering
a weakly-interacting Bose-Einstein condensate of harmonically-trapped atoms, we
demonstrate how this separation can be used to close the conceptual gap between
exact solutions for systems with only a few atoms and the thermodynamic limit
for which the mean-field is the correct leading-order approximation. Although
we illustrate this approach for the case of weak interactions, it is expected
to be more generally valid.Comment: 8 pages, 5 figure
Thermal ratchet effects in ferrofluids
Rotational Brownian motion of colloidal magnetic particles in ferrofluids
under the influence of an oscillating external magnetic field is investigated.
It is shown that for a suitable time dependence of the magnetic field, a noise
induced rotation of the ferromagnetic particles due to rectification of thermal
fluctuations takes place. Via viscous coupling, the associated angular momentum
is transferred from the magnetic nano-particles to the carrier liquid and can
then be measured as macroscopic torque on the fluid sample. A thorough
theoretical analysis of the effect in terms of symmetry considerations,
analytical approximations, and numerical solutions is given which is in
accordance with recent experimental findings.Comment: 18 pages, 6 figure
The role of gut endocrine cells in control of metabolism and appetite.
After food is ingested, nutrients pass through the gastrointestinal tract, stimulating the release of a range of peptide hormones. Among their many local, central and peripheral actions, these hormones act to mediate glucose metabolism and satiety. Indeed, it is the modification of gut hormone secretion that is considered partly responsible for the normalization of glycaemic control and the reduction in appetite seen in many patients after certain forms of bariatric surgery. This review describes recent developments in our understanding of the secretion and action of anorexigenic gut hormones, primarily concentrating on glucagon-like peptide-1 (GLP-1).This is the final version. It was first published by Wiley in Experimental Physiology here: http://onlinelibrary.wiley.com/doi/10.1113/expphysiol.2014.079764/abstract
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