2,287 research outputs found
Exploring Rigidly Rotating Vortex Configurations and their Bifurcations in Atomic Bose-Einstein Condensates
In the present work, we consider the problem of a system of few vortices as it emerges from its experimental realization in the field of atomic
Bose-Einstein condensates. Starting from the corresponding equations of motion,
we use a two-pronged approach in order to reveal the configuration space of the
system's preferred dynamical states. On the one hand, we use a Monte-Carlo
method parametrizing the vortex "particles" by means of hyperspherical
coordinates and identifying the minimal energy ground states thereof for and different vortex particle angular momenta. We then complement this
picture with a dynamical systems analysis of the possible rigidly rotating
states. The latter reveals all the supercritical and subcritical pitchfork, as
well as saddle-center bifurcations that arise exposing the full wealth of the
problem even at such low dimensional cases. By corroborating the results of the
two methods, it becomes fairly transparent which branch the Monte-Carlo
approach selects for different values of the angular momentum which is used as
a bifurcation parameter.Comment: 12 pages, 7 figures. New improved result
Dark solitons and vortices in PT-symmetric nonlinear media: from spontaneous symmetry breaking to nonlinear PT phase transitions
We consider nonlinear analogues of Parity-Time (PT) symmetric linear systems
exhibiting defocusing nonlinearities. We study the ground state and excited
states (dark solitons and vortices) of the system and report the following
remarkable features. For relatively weak values of the parameter
controlling the strength of the PT-symmetric potential, excited states undergo
(analytically tractable) spontaneous symmetry breaking; as is
further increased, the ground state and first excited state, as well as
branches of higher multi-soliton (multi-vortex) states, collide in pairs and
disappear in blue-sky bifurcations, in a way which is strongly reminiscent of
the linear PT-phase transition ---thus termed the nonlinear PT-phase
transition. Past this critical point, initialization of, e.g., the former
ground state leads to spontaneously emerging solitons and vortices.Comment: 8 pages, 8 figure
Bright-Dark Soliton Complexes in Spinor Bose-Einstein Condensates
We present bright-dark vector solitons in quasi-one-dimensional spinor (F=1)
Bose-Einstein condensates. Using a multiscale expansion technique, we reduce
the corresponding nonintegrable system of three coupled Gross-Pitaevskii
equations (GPEs) to a completely integrable Yajima-Oikawa system. In this way,
we obtain approximate solutions for small-amplitude vector solitons of
dark-dark-bright and bright-bright-dark types, in terms of the
spinor components, respectively. By means of numerical simulations of the full
GPE system, we demonstrate that these states indeed feature soliton properties,
i.e., they propagate undistorted and undergo quasi-elastic collisions. It is
also shown that, in the presence of a parabolic trap of strength , the
bright component(s) is (are) guided by the dark one(s), and, as a result, the
small-amplitude vector soliton as a whole performs harmonic oscillations of
frequency in the shallow soliton limit. We investigate
numerically deviations from this prediction, as the depth of the solitons is
increased, as well as when the strength of the spin-dependent interaction is
modified.Comment: 10 pages, 4 figures. Submitted to PRA, May 200
Obesity-induced changes in lipid mediators persist after weight loss.
BackgroundObesity induces significant changes in lipid mediators, however, the extent to which these changes persist after weight loss has not been investigated.Subjects/methodsWe fed C57BL6 mice a high-fat diet to generate obesity and then switched the diet to a lower-fat diet to induce weight loss. We performed a comprehensive metabolic profiling of lipid mediators including oxylipins, endocannabinoids, sphingosines and ceramides in key metabolic tissues (including adipose, liver, muscle and hypothalamus) and plasma.ResultsWe found that changes induced by obesity were largely reversible in most metabolic tissues but the adipose tissue retained a persistent obese metabolic signature. Prostaglandin signaling was perturbed in the obese state and lasting increases in PGD2, and downstream metabolites 15-deoxy PGJ2 and delta-12-PGJ2 were observed after weight loss. Furthermore expression of the enzyme responsible for PGD2 synthesis (hematopoietic prostaglandin D synthase, HPGDS) was increased in obese adipose tissues and remained high after weight loss. We found that inhibition of HPGDS over the course of 5 days resulted in decreased food intake in mice. Increased HPGDS expression was also observed in human adipose tissues obtained from obese compared with lean individuals. We then measured circulating levels of PGD2 in obese patients before and after weight loss and found that while elevated relative to lean subjects, levels of this metabolite did not decrease after significant weight loss.ConclusionsThese results suggest that lasting changes in lipid mediators induced by obesity, still present after weight loss, may play a role in the biological drive to regain weight
Beating dark-dark solitons in Bose-Einstein condensates
Motivated by recent experimental results, we study beating dark-dark solitons
as a prototypical coherent structure that emerges in two-component
Bose-Einstein condensates. We showcase their connection to dark- bright
solitons via SO(2) rotation, and infer from it both their intrinsic beating
frequency and their frequency of oscillation inside a parabolic trap. We
identify them as exact periodic orbits in the Manakov limit of equal inter- and
intra-species nonlinearity strengths with and without the trap and showcase the
persistence of such states upon weak deviations from this limit. We also
consider large deviations from the Manakov limit illustrating that this
breathing state may be broken apart into dark-antidark soliton states. Finally,
we consider the dynamics and interactions of two beating dark-dark solitons in
the absence and in the presence of the trap, inferring their typically
repulsive interaction.Comment: 13 pages, 14 figure
Matter sound waves in two-component Bose-Einstein condensates
The creation and propagation of sound waves in two-component Bose-Einstein
condensates (BEC) are investigated and a new method of wave generation in
binary BEC mixtures is proposed. The method is based on a fast change of the
inter-species interaction constant and is illustrated for two experimental
settings: a drop-like condensate immersed into a second large repulsive
condensate, and a binary mixture of two homogeneous repulsive BEC's. A
mathematical model based on the linearized coupled Gross-Pitaevskii equations
is developed and explicit formulae for the space and time dependence of sound
waves are provided. Comparison of the analytical and numerical results shows
excellent agreement, confirming the validity of the proposed approach.Comment: 16 pages, 9 figure
Mobility of Discrete Solitons in Quadratically Nonlinear Media
We study the mobility of solitons in second-harmonic-generating lattices.
Contrary to what is known for their cubic counterparts, discrete quadratic
solitons are mobile not only in the one-dimensional (1D) setting, but also in
two dimensions (2D). We identify parametric regions where an initial kick
applied to a soliton leads to three possible outcomes, namely, staying put,
persistent motion, or destruction. For the 2D lattice, it is found that, for
the solitary waves, the direction along which they can sustain the largest kick
and can attain the largest speed is the diagonal. Basic dynamical properties of
the discrete solitons are also discussed in the context of an analytical
approximation, in terms of an effective Peierls-Nabarro potential in the
lattice setting.Comment: 4 page
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