46,179 research outputs found
Spin-orbit coupling induced fractionalized Skyrmion excitations in rotating and rapidly quenched spin-1 Bose-Einstein condensates
We investigate the fractionalized Skyrmion excitations induced by spin-orbit
coupling in rotating and rapidly quenched spin-1 Bose-Einstein condensates. Our
results show that the fractionalized Skyrmion excitation depends on the
combination of spin-orbit coupling and rotation, and it originates from a
dipole structure of spin which is always embedded in three vortices constructed
by each condensate component respectively. When spin-orbit coupling is larger
than a critical value, the fractionalized Skyrmions encircle the center with
one or several circles to form a radial lattice, which occurs even in the
strong ferromagnetic/antiferromagnetic condensates. We can use both the
spin-orbit coupling and the rotation to adjust the radial lattice. The
realization and the detection of the fractionalized Skyrmions are compatible
with current experimental technology.Comment: 5 pages, 4 figure
On Linearly Constrained Minimum Variance Beamforming
Beamforming is a widely used technique for source localization in signal processing and neuroimaging. A number of vector-beamformers have been introduced to localize neuronal activity by using
magnetoencephalography (MEG) data in the literature. However, the existing theoretical analyses
on these beamformers have been limited to simple cases, where no more than two sources are allowed in the associated model and the theoretical sensor covariance
is also assumed known. The information about the effects of the MEG spatial and temporal dimensions on the consistency of vector-beamforming is incomplete.
In the present study, we consider a class of vector-beamformers defined by thresholding the sensor covariance matrix, which include the standard vector-beamformer as a special case.
A general asymptotic theory is developed for
these vector-beamformers, which shows the extent of effects to which the MEG spatial and temporal dimensions on estimating the neuronal activity index. The performances of the proposed beamformers are assessed by simulation studies. Superior performances of the proposed beamformers are obtained
when the signal-to-noise ratio is low.
We apply the proposed procedure to real MEG datasets derived from five sessions of a human face-perception experiment, finding several highly active areas in the brain. A good agreement between these findings and the known neurophysiology of the MEG response to human face perception is shown
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