16,613 research outputs found
Optical Weak Link between Two Spatially Separate Bose-Einstein Condensates
Two spatially separate Bose-Einstein condensates were prepared in an optical
double-well potential. A bidirectional coupling between the two condensates was
established by two pairs of Bragg beams which continuously outcoupled atoms in
opposite directions. The atomic currents induced by the optical coupling depend
on the relative phase of the two condensates and on an additional controllable
coupling phase. This was observed through symmetric and antisymmetric
correlations between the two outcoupled atom fluxes. A Josephson optical
coupling of two condensates in a ring geometry is proposed. The continuous
outcoupling method was used to monitor slow relative motions of two elongated
condensates and characterize the trapping potential.Comment: 4 pages, 5 figure
Inferring the eccentricity distribution
Standard maximum-likelihood estimators for binary-star and exoplanet
eccentricities are biased high, in the sense that the estimated eccentricity
tends to be larger than the true eccentricity. As with most non-trivial
observables, a simple histogram of estimated eccentricities is not a good
estimate of the true eccentricity distribution. Here we develop and test a
hierarchical probabilistic method for performing the relevant meta-analysis,
that is, inferring the true eccentricity distribution, taking as input the
likelihood functions for the individual-star eccentricities, or samplings of
the posterior probability distributions for the eccentricities (under a given,
uninformative prior). The method is a simple implementation of a hierarchical
Bayesian model; it can also be seen as a kind of heteroscedastic deconvolution.
It can be applied to any quantity measured with finite precision--other orbital
parameters, or indeed any astronomical measurements of any kind, including
magnitudes, parallaxes, or photometric redshifts--so long as the measurements
have been communicated as a likelihood function or a posterior sampling.Comment: Ap
Observation of inhomogeneous domain nucleation in epitaxial Pb(Zr,Ti)O3 capacitors
We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors
under a modified piezoresponse force microscope. We obtained domain evolution
images during polarization switching process and observed that domain
nucleation occurs at particular sites. This inhomogeneous nucleation process
should play an important role in an early stage of switching and under a high
electric field. We found that the number of nuclei is linearly proportional to
log(switching time), suggesting a broad distribution of activation energies for
nucleation. The nucleation sites for a positive bias differ from those for a
negative bias, indicating that most nucleation sites are located at
ferroelectric/electrode interfaces
Fetal atrial septal aneurysm: A cause of fetal atrial arrhythmias
AbstractAtrial arrhythmias are commonly found during fetal echocardiography performed during pregnancy to evaluate fetal arrhythmias. An association between atrial arrhythmias and an atrial septal aneurysm has been noted in children and adults. In this study, 105 fetuses were evaluated by fetal echocardiography, 39 (37%) referred to evaluate fetal arrhythmia and 66 (63%) to rule out congenital heart disease. An atrial septal aneurysm was found in 42 (40%) of the fetuses and an atrial arrhythmia in 37 (35%). An atrial septal aneurysm was found in 25 (64%) of the 39 fetuses referred to evaluate a fetal arrhythmia compared with only 17 (26%) of the 66 fetuses referred to rule out congenital heart disease. In this study, the association of an atrial septal aneurysm with an atrial arrhythmia was highly significant (p < 0.001)
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
Low velocity quantum reflection of Bose-Einstein condensates
We studied quantum reflection of Bose-Einstein condensates at normal
incidence on a square array of silicon pillars. For incident velocities of
2.5-26 mm/s observations agreed with theoretical predictions that the
Casimir-Polder potential of a reduced density surface would reflect slow atoms
with much higher probability. At low velocities (0.5-2.5 mm/s), we observed
that the reflection probability saturated around 60% rather than increasing
towards unity. We present a simple model which explains this reduced
reflectivity as resulting from the combined effects of the Casimir-Polder plus
mean field potential and predicts the observed saturation. Furthermore, at low
incident velocities, the reflected condensates show collective excitations.Comment: 4 figure
Phase Sensitive Recombination of Two Bose-Einstein Condensates on an Atom Chip
The recombination of two split Bose-Einstein condensates on an atom chip is
shown to result in heating which depends on the relative phase of the two
condensates. This heating reduces the number of condensate atoms between 10 and
40% and provides a robust way to read out the phase of an atom interferometer
without the need for ballistic expansion. The heating may be caused by the
dissipation of dark solitons created during the merging of the condensates.Comment: 5 pages, 4 figure
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