710 research outputs found
Ground states of trapped spin-1 condensates in magnetic field
We consider a spin-1 Bose-Einstein condensate trapped in a harmonic potential
under the influence of a homogeneous magnetic field. We investigate spatial and
spin structure of the mean-field ground states under constraints on the number
of atoms and the total magnetization. We show that the trapping potential can
make the antiferromagnetic condensate separate into three, and ferromagnetic
condensate into two distinct phases. In the ferromagnetic case, the
magnetization is located in the center of the harmonic trap, while in the
antiferromagnetic case magnetized phases appear in the outer regions. We
describe how the transition from the Thomas-Fermi regime to the single-mode
approximation regime with decreasing number of atoms results in the
disappearance of the domains. We suggest that the ground states can be created
in experiment by adiabatically changing the magnetic field strength
Stability analysis of three-dimensional breather solitons in a Bose-Einstein Condensate
We investigate the stability properties of breather soliton trains in a
three-dimensional Bose-Einstein Condensate with Feshbach Resonance Management
of the scattering length. This is done so as to generate both attractive and
repulsive interaction. The condensate is con ned only by a one dimensional
optical lattice and we consider both strong, moderate, and weak con nement. By
strong con nement we mean a situation in which a quasi two dimensional soliton
is created. Moderate con nement admits a fully three dimensional soliton. Weak
con nement allows individual solitons to interact. Stability properties are
investigated by several theoretical methods such as a variational analysis,
treatment of motion in e ective potential wells, and collapse dynamics. Armed
with all the information forthcoming from these methods, we then undertake a
numerical calculation. Our theoretical predictions are fully con rmed, perhaps
to a higher degree than expected. We compare regions of stability in parameter
space obtained from a fully 3D analysis with those from a quasi two-dimensional
treatment, when the dynamics in one direction are frozen. We nd that in the 3D
case the stability region splits into two parts. However, as we tighten the con
nement, one of the islands of stability moves toward higher frequencies and the
lower frequency region becomes more and more like that for quasi 2D. We
demonstrate these solutions in direct numerical simulations and, importantly,
suggest a way of creating robust 3D solitons in experiments in a Bose Einstein
Condensate in a one-dimensional lattice.Comment: 14 pages, 6 figures; accepted to Proc. Roy. Soc. London
Interactive optomechanical coupling with nonlinear polaritonic systems
We study a system of interacting matter quasiparticles strongly coupled to
photons inside an optomechanical cavity. The resulting normal modes of the
system are represented by hybrid polaritonic quasiparticles, which acquire
effective nonlinearity. Its strength is influenced by the presence of the
mechanical mode and depends on the resonance frequency of the cavity. This
leads to an interactive type of optomechanical coupling, being distinct from
the previously studied dispersive and dissipative couplings in optomechanical
systems. The emergent interactive coupling is shown to generate effective
optical nonlinearity terms of high order, being quartic in the polariton
number. We consider particular systems of exciton-polaritons and dipolaritons,
and show that the induced effective optical nonlinearity due to the interactive
coupling can exceed in magnitude the strength of Kerr nonlinear terms, such as
those arising from polariton-polariton interactions. As applications, we show
that the higher order terms give rise to localized bright flat top solitons,
which may form spontaneously in polariton condensates.Comment: 6 pages, 3 figure
Spontaneous symmetry breaking of gap solitons in double-well traps
We introduce a two dimensional model for the Bose-Einstein condensate with
both attractive and repulsive nonlinearities. We assume a combination of a
double well potential in one direction, and an optical lattice along the
perpendicular coordinate. We look for dual core solitons in this model,
focusing on their symmetry-breaking bifurcations. The analysis employs a
variational approximation, which is verified by numerical results. The
bifurcation which transforms antisymmetric gap solitons into asymmetric ones is
of supercritical type in the case of repulsion; in the attraction model,
increase of the optical latttice strength leads to a gradual transition from
subcritical bifurcation (for symmetric solitons) to a supercritical one.Comment: 6 pages, 5 figure
Statistical region based active contour using a fractional entropy descriptor: Application to nuclei cell segmentation in confocal microscopy images
We propose an unsupervised statistical region based active contour approach integrating an original fractional entropy measure for image segmentation with a particular application to single channel actin tagged fluorescence confocal microscopy image segmentation. Following description of statistical based active contour segmentation and the mathematical definition of the proposed fractional entropy descriptor, we demonstrate comparative segmentation results between the proposed approach and standard Shannon’s entropy on synthetic and natural images. We also show that the proposed unsupervised
statistical based approach, integrating the fractional entropy measure, leads to very satisfactory segmentation of the cell nuclei from which shape characterization can be calculated
Investigating of the Knocking Out Properties of Moulding Sands with New Inorganic Binders Used for Castings of Non-ferrous Metal Alloys in Comparison with the Previously Used
The article presents the results of investigations, which make a fragment of the broad-scale studies carried out as a part of the projectPOIG.01.01.02-00-015/09 “Advanced materials and technologies”.One of the objectives of the introduction of new inorganic binders is to provide a good knocking out properties of moulding sands, whilemaintaining an appropriate level of strength properties.Therefore, a logical continuation of the previous studies were carried out the tests knocking out properties of moulding sands with newinorganic binders, including making moulds, pouring them by the chosen of non-ferrous metal alloys, knoking-out, and determining theknocking out work.The results of the study were related to the research results obtained by applying the moulding sand performed by existing technology
Instability-induced formation and non-equilibrium dynamics of phase defects in polariton condensates
We study, theoretically and numerically, the onset and development of
modulational instability in an incoherently pumped spatially homogeneous
polariton condensate. Within the framework of mean-field theory, we identify
regimes of modulational instability in two cases: 1) Strong feedback between
the condensate and reservoir, which may occur in scalar condensates, and 2)
Parametric scattering in the presence of polarization splitting in spinor
condensates. In both cases we investigate the instability induced textures in
space and time including non-equilibrium dynamics of phase dislocations and
vortices. In particular we discuss the mechanism of vortex destabilization and
formation of spiraling waves. We also identify the presence of topological
defects, which take the form of half-vortex pairs in the spinor case, giving an
"eyelet" structure in intensity and dipole type structure in the spin
polarization. In the modulationally stable parameter domains, we observe
formation of the phase defects in the process of condensate formation from an
initially spatially incoherent low-density state. In analogy to the
Kibble-Zurek type scaling for nonequilibrium phase transitions, we find that
the defect density scales with the pumping rate.Comment: 13 pages, 9 figures, revised manuscript sent to Phys. Rev.
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