880 research outputs found
Out-of-phase oscillation between superfluid and thermal components for a trapped Bose condensate under oscillatory excitation
The vortex nucleation and the emergence of quantum turbulence induced by
oscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev.
A 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left
a few open questions concerning the basic mechanisms causing those interesting
phenomena. Here, we report the experimental observation of the slosh dynamics
of a magnetically trapped Rb Bose-Einstein condensate (BEC) under the
influence of a time-varying magnetic field. We observed a clear relative
displacement in between the condensed and the thermal fraction center-of-mass.
We have identified this relative counter move as an out-of-phase oscillation
mode, which is able to produce ripples on the condensed/thermal fractions
interface. The out-of-phase mode can be included as a possible mechanism
involved in the vortex nucleation and further evolution when excited by time
dependent magnetic fields.Comment: 5 pages, 5 figures, 25 reference
Photoassociative ionization of Na inside a storage ring
Motivated by recent interest in low dimensional arrays of atoms, we
experimentally investigated the way cold collisional processes are affected by
the geometry of the considered atomic sample. More specifically, we studied the
case of photoassociative ionization (PAI) both in a storage ring where
collision is more unidirectional in character and in a trap with clear
undefinition of collision axis. First, creating a ring shaped trap (atomotron)
we investigated two-color PAI dependence with intensity and polarization of a
probing laser. The intensity dependence of the PAI rate was also measured in a
magneto-optical trap presenting equivalent temperature and density conditions.
Indeed, the results show that in the ring trap, the value of the PAI rate
constant is much lower and does not show evidences of saturation, unlike in the
case of the 3D-MOT. Cold atomic collisions in storage ring may represent new
possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio
Injection locking of a low cost high power laser diode at 461 nm
Stable laser sources at 461 nm are important for optical cooling of strontium
atoms. In most existing experiments this wavelength is obtained by frequency
doubling infrared lasers, since blue laser diodes either have low power or
large emission bandwidths. Here, we show that injecting less than 10 mW of
monomode laser radiation into a blue multimode 500 mW high power laser diode is
capable of slaving at least 50% of the power to the desired frequency. We
verify the emission bandwidth reduction by saturation spectroscopy on a
strontium gas cell and by direct beating of the slave with the master laser. We
also demonstrate that the laser can efficiently be used within the Zeeman
slower for optical cooling of a strontium atomic beam.Comment: 2nd corrected version (minor revisions); Manuscript accepted for
publication in Review of Scientific Instruments; 5 pages, 6 figure
Route to turbulence in a trapped Bose-Einstein condensate
We have studied a Bose-Einstein condensate of atoms under an
oscillatory excitation. For a fixed frequency of excitation, we have explored
how the values of amplitude and time of excitation must be combined in order to
produce quantum turbulence in the condensate. Depending on the combination of
these parameters different behaviors are observed in the sample. For the lowest
values of time and amplitude of excitation, we observe a bending of the main
axis of the cloud. Increasing the amplitude of excitation we observe an
increasing number of vortices. The vortex state can evolve into the turbulent
regime if the parameters of excitation are driven up to a certain set of
combinations. If the value of the parameters of these combinations is exceeded,
all vorticity disappears and the condensate enters into a different regime
which we have identified as the granular phase. Our results are summarized in a
diagram of amplitude versus time of excitation in which the different
structures can be identified. We also present numerical simulations of the
Gross-Pitaevskii equation which support our observations.Comment: 6 pages, 3 figure
Multidomain switching in the ferroelectric nanodots
Controlling the polarization switching in the ferroelectric nanocrystals,
nanowires and nanodots has an inherent specificity related to the emergence of
depolarization field that is associated with the spontaneous polarization. This
field splits the finite-size ferroelectric sample into polarization domains.
Here, based on 3D numerical simulations, we study the formation of 180 polarization domains in a nanoplatelet, made of uniaxial ferroelectric
material, and show that in addition to the polarized monodomain state, the
multidomain structures, notably of stripe and cylindrical shapes, can arise and
compete during the switching process. The multibit switching protocol between
these configurations may be realized by temperature and field variations
Three-vortex configurations in trapped Bose-Einstein condensates
We report on the creation of three-vortex clusters in a
Bose-Einstein condensate by oscillatory excitation of the condensate. This
procedure can create vortices of both circulation, so that we are able to
create several types of vortex clusters using the same mechanism. The
three-vortex configurations are dominated by two types, namely, an
equilateral-triangle arrangement and a linear arrangement. We interpret these
most stable configurations respectively as three vortices with the same
circulation, and as a vortex-antivortex-vortex cluster. The linear
configurations are very likely the first experimental signatures of predicted
stationary vortex clusters.Comment: 4 pages, 4 figure
Analysis of the eukaryotic topoisomerase II DNA gate: a single-molecule FRET and structural perspective
Type II DNA topoisomerases (topos) are essential and ubiquitous enzymes that perform important intracellular roles in chromosome condensation and segregation, and in regulating DNA supercoiling. Eukaryotic topo II, a type II topoisomerase, is a homodimeric enzyme that solves topological entanglement problems by using the energy from ATP hydrolysis to pass one segment of DNA through another by way of a reversible, enzyme-bridged double-stranded break. This DNA break is linked to the protein by a phosphodiester bond between the active site tyrosine of each subunit and backbone phosphate of DNA. The opening and closing of the DNA gate, a critical step for strand passage during the catalytic cycle, is coupled to this enzymatic cleavage/religation of the backbone. This reversible DNA cleavage reaction is the target of a number of anticancer drugs, which can elicit DNA damage by affecting the cleavage/religation equilibrium. Because of its clinical importance, many studies have sought to determine the manner in which topo II interacts with DNA. Here we highlight recent single-molecule fluorescence resonance energy transfer and crystallographic studies that have provided new insight into the dynamics and structure of the topo II DNA gate
Search for H hypernucleus by the Li reaction at = 1.2 GeV/
We have carried out an experiment to search for a neutron-rich hypernucleus,
H, by the Li() reaction at =1.2
GeV/. The obtained missing mass spectrum with an estimated energy resolution
of 3.2 MeV (FWHM) showed no peak structure corresponding to the H
hypernucleus neither below nor above the H particle decay
threshold. An upper limit of the production cross section for the bound
H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence
level.Comment: 6 pages, 5 figures, published versio
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