809 research outputs found
Bonding, structure and mechanical behavior of vanadium carbide single crystals
Bonding, structure, and mechanical behavior of vanadium carbide single crystal
Minimally-destructive detection of magnetically-trapped atoms using frequency-synthesised light
We present a technique for atomic density measurements by the off-resonant
phase-shift induced on a two-frequency, coherently-synthesised light beam. We
have used this scheme to measure the column density of a magnetically trapped
atom cloud and to monitor oscillations of the cloud in real time by making over
a hundred non-destructive local density measurments. For measurements using
pulses of 10,000-100,000 photons lasting ~10 microsecond, the precision is
limited by statistics of the photons and the photodiode avalanche. We explore
the relationship between measurement precision and the unwanted loss of atoms
from the trap and introduce a figure of merit that characterises it. This
method can be used to probe the density of a BEC with minimal disturbance of
its phase.Comment: Submitted to New Journal of Physic
A Bose-Einstein condensate in a random potential
An optical speckle potential is used to investigate the static and dynamic
properties of a Bose-Einstein condensate in the presence of disorder. For
strong disorder the condensate is localized in the deep wells of the potential.
With smaller levels of disorder, stripes are observed in the expanded density
profile and strong damping of dipole and quadrupole oscillations is seen.
Uncorrelated frequency shifts of the two modes are measured for a weak disorder
and are explained using a sum-rules approach and by the numerical solution of
the Gross-Pitaevskii equation
Classical noise and flux: the limits of multi-state atom lasers
By direct comparison between experiment and theory, we show how the classical
noise on a multi-state atom laser beam increases with increasing flux. The
trade off between classical noise and flux is an important consideration in
precision interferometric measurement. We use periodic 10 microsecond
radio-frequency pulses to couple atoms out of an F=2 87Rb Bose-Einstein
condensate. The resulting atom laser beam has suprising structure which is
explained using three dimensional simulations of the five state
Gross-Pitaevskii equations.Comment: 4 pages, 3 figure
Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide
We investigate the one-dimensional expansion of a Bose-Einstein condensate in
an optical guide in the presence of a random potential created with optical
speckles. With the speckle the expansion of the condensate is strongly
inhibited. A detailed investigation has been carried out varying the
experimental conditions and checking the expansion when a single optical defect
is present. The experimental results are in good agreement with numerical
calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure
Palmitic acid induces inflammation in placental trophoblasts and impairs their migration toward smooth muscle cells through plasminogen activator inhibitor-1
A critical component of early human placental development includes migration of extravillous trophoblasts (EVTs) into the decidua. EVTs migrate toward and displace vascular smooth muscle cells (SMCs) surrounding several uterine structures, including spiral arteries. Shallow trophoblast invasion features in several pregnancy complications including preeclampsia. Maternal obesity is a risk factor for placental dysfunction, suggesting that factors within an obese environment may impair early placental development. Herein, we tested the hypothesis that palmitic acid, a saturated fatty acid circulating at high levels in obese women, induces an inflammatory response in EVTs that hinders their capacity to migrate toward SMCs. We found that SMCs and SMC-conditioned media stimulated migration and invasion of an EVT-like cell line, HTR8/SVneo. Palmitic acid impaired EVT migration and invasion toward SMCs, and induced expression of several vasoactive and inflammatory mediators in EVTs, including endothelin, interleukin (IL)-6, IL-8 and PAI1. PAI1 was increased in plasma of women with early-onset preeclampsia, and PAI1-deficient EVTs were protected from the anti-migratory effects of palmitic acid. Using first trimester placental explants, palmitic acid exposure decreased EVT invasion through Matrigel. Our findings reveal that palmitic acid induces an inflammatory response in EVTs and attenuates their migration through a mechanism involving PAI1. High levels of palmitic acid in pathophysiological situations like obesity may impair early placental development and predispose to placental dysfunction
Unstable regimes for a Bose-Einstein condensate in an optical lattice
We report on the experimental characterization of energetic and dynamical
instability, two mechanisms responsible for the breakdown of Bloch waves in a
Bose-Einstein condensate interacting with a 1D optical lattice. A clear
separation of these two regimes is obtained performing measurements at
different temperatures of the atomic sample. The timescales of the two
processes have been determined by measuring the losses induced in the
condensate. A simple phenomenological model is introduced for energetic
instability while a full comparison is made between the experiment and the 3D
Gross-Pitaevskii theory that accounts for dynamical instability
Test of the quantumness of atom-atom correlations in a bosonic gas
It is shown how the quantumness of atom-atom correlations in a trapped
bosonic gas can be made observable. Application of continuous feedback control
of the center of mass of the atomic cloud is shown to generate oscillations of
the spatial extension of the cloud, whose amplitude can be directly used as a
characterization of atom-atom correlations. Feedback parameters can be chosen
such that the violation of a Schwarz inequality for atom-atom correlations can
be tested at noise levels much higher than the standard quantum limit
Observation of dynamical instability for a Bose-Einstein condensate in a moving 1D optical lattice
We have experimentally studied the unstable dynamics of a harmonically
trapped Bose-Einstein condensate loaded into a 1D moving optical lattice. The
lifetime of the condensate in such a potential exhibits a dramatic dependence
on the quasimomentum state. This is unambiguously attributed to the onset of
dynamical instability, after a comparison with the predictions of the
Gross-Pitaevskii theory. Deeply in the unstable region we observe the rapid
appearance of complex structures in the atomic density profile, as a
consequence of the condensate phase uniformity breakdown
Disorder-enhanced phase coherence in trapped bosons on optical lattices
The consequences of disorder on interacting bosons trapped in optical
lattices are investigated by quantum Monte Carlo simulations. At small to
moderate strengths of potential disorder a unique effect is observed: if there
is a Mott plateau at the center of the trap in the clean limit, phase coherence
{\it increases} as a result of disorder. The localization effects due to
correlation and disorder compete against each other, resulting in a partial
delocalization of the particles in the Mott region, which in turn leads to
increased phase coherence. In the absence of a Mott plateau, this effect is
absent. A detailed analysis of the uniform system without a trap shows that the
disordered states participate in a Bose glass phase.Comment: 4 pages, 4 figure
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