7,676 research outputs found
Three-dimensional Gross-Pitaevskii solitary waves in optical lattices: stabilization using the artificial quartic kinetic energy induced by lattice shaking
In this Letter, we show that a three-dimensional Bose-Einstein solitary wave
can become stable if the dispersion law is changed from quadratic to quartic.
We suggest a way to realize the quartic dispersion, using shaken optical
lattices. Estimates show that the resulting solitary waves can occupy as little
as -th of the Brillouin zone in each of the three directions and
contain as many as atoms, thus representing a \textit{fully
mobile} macroscopic three-dimensional object.Comment: 8 pages, 1 figure, accepted in Phys. Lett.
Radiometric force in dusty plasmas
A radiofrequency glow discharge plasma, which is polluted with a certain
number of dusty grains, is studied. In addition to various dusty plasma
phenomena, several specific colloidal effects should be considered. We focus on
radiometric forces, which are caused by inhomogeneous temperature distribution.
Aside from thermophoresis, the role of temperature distribution in dusty
plasmas is an open question. It is shown that inhomogeneous heating of the
grain by ion flows results in a new photophoresis like force, which is specific
for dusty discharges. This radiometric force can be observable under conditions
of recent microgravity experiments.Comment: 4 pages, amsmat
Pair correlations of scattered atoms from two colliding Bose-Einstein Condensates: Perturbative Approach
We apply an analytical model for anisotropic, colliding Bose-Einstein
condensates in a spontaneous four wave mixing geometry to evaluate the second
order correlation function of the field of scattered atoms. Our approach uses
quantized scattering modes and the equivalent of a classical, undepleted pump
approximation. Results to lowest order in perturbation theory are compared with
a recent experiment and with other theoretical approaches.Comment: 9 pages, 3 figure
Rubidium-87 Bose-Einstein condensate in an optically plugged quadrupole trap
We describe an experiment to produce 87Rb Bose-Einstein condensates in an
optically plugged magnetic quadrupole trap, using a blue-detuned laser. Due to
the large detuning of the plug laser with respect to the atomic transition, the
evaporation has to be carefully optimized in order to efficiently overcome the
Majorana losses. We provide a complete theoretical and experimental study of
the trapping potential at low temperatures and show that this simple model
describes well our data. In particular we demonstrate methods to reliably
measure the trap oscillation frequencies and the bottom frequency, based on
periodic excitation of the trapping potential and on radio-frequency
spectroscopy, respectively. We show that this hybrid trap can be operated in a
well controlled regime that allows a reliable production of degenerate gases.Comment: 13 pages, 8 figure
RF spectroscopy in a resonant RF-dressed trap
We study the spectroscopy of atoms dressed by a resonant radiofrequency (RF)
field inside an inhomogeneous magnetic field and confined in the resulting
adiabatic potential. The spectroscopic probe is a second, weak, RF field. The
observed line shape is related to the temperature of the trapped cloud. We
demonstrate evaporative cooling of the RF-dressed atoms by sweeping the
frequency of the second RF field around the Rabi frequency of the dressing
field.Comment: 7 figures, 8 pages; to appear in J. Phys.
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Fast Image-Based Model of Mitral Valve Closure for Surgical Planning
Surgical repair of the mitral valve results in better
outcomes than valve replacement, yet diseased valves
are often replaced due to the technical difficulty of the
repair process. A surgical planning system based on
patient-specific medical images that allows surgeons to
simulate and compare potential repair strategies could
greatly improve surgical outcomes. The system must
simulate valve closure quickly and handle the complex
boundary conditions imposed by the chords that tether
the valve leaflets. We have developed a process for
generating a triangulated mesh of the valve surface
from volumetric image data of the opened valve. The
closed position of the mesh is then computed using a
mass-spring model of dynamics. In the mass-spring
model, triangle sides are treated as linear springs
supporting only tension. Chords are also treated as
linear springs, and self-collisions are detected and
handled inelastically. The equations of motion are
solved using implicit numerical integration. The
simulated closed state is compared with an image of the
same valve taken in the closed state to assess accuracy
of the model. The model exhibits rapid valve closure
and is able to predict the closed state of the valve with
reasonable accuracy.Engineering and Applied Science
Technology challenges for space interferometry: the option of mid-infrared integrated optics
Nulling interferometry is a technique providing high angular resolution which
is the core of the space missions Darwin and the Terrestrail Planet Finder. The
first objective is to reach a deep degree of starlight cancelation in the range
6 -- 20 microns, in order to observe and to characterize the signal from an
Earth-like planet. Among the numerous technological challenges involved in
these missions, the question of the beam combination and wavefront filtering
has an important place. A single-mode integrated optics (IO) beam combiner
could support both the functions of filtering and the interferometric
combination, simplifying the instrumental design. Such a perspective has been
explored in this work within the project Integrated Optics for Darwin (IODA),
which aims at developing a first IO combiner in the mid-infrared. The solutions
reviewed here to manufacture the combiner are based on infrared dielectric
materials on one side, and on metallic conductive waveguides on the other side.
With this work, additional inputs are offered to pursue the investigation on
mid-infrared photonics devices.Comment: Accepted in Adv. in Space Researc
Quantum Logic Gates in Optical Lattices
We propose a new system for implementing quantum logic gates: neutral atoms
trapped in a very far-off-resonance optical lattice. Pairs of atoms are made to
occupy the same well by varying the polarization of the trapping lasers, and
then a near-resonant electric dipole is induced by an auxiliary laser. A
controlled-NOT can be implemented by conditioning the target atomic resonance
on a resolvable level shift induced by the control atom. Atoms interact only
during logical operations, thereby suppressing decoherence.Comment: Revised version, To appear in Phys. Rev. Lett. Three separate
postscript figure
Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling
The recently discovered exoplanet Gl581d is extremely close to the outer edge
of its system's habitable zone, which has led to much speculation on its
possible climate. We have performed a range of simulations to assess whether,
given simple combinations of chemically stable greenhouse gases, the planet
could sustain liquid water on its surface. For best estimates of the surface
gravity, surface albedo and cloud coverage, we find that less than 10 bars of
CO2 is sufficient to maintain a global mean temperature above the melting point
of water. Furthermore, even with the most conservative choices of these
parameters, we calculate temperatures above the water melting point for CO2
partial pressures greater than about 40 bar. However, we note that as Gl581d is
probably in a tidally resonant orbit, further simulations in 3D are required to
test whether such atmospheric conditions are stable against the collapse of CO2
on the surface.Comment: 9 pages, 11 figures. Accepted for publication in Astronomy &
Astrophysic
Almost Linear B\"uchi Automata
We introduce a new fragment of Linear temporal logic (LTL) called LIO and a
new class of Buechi automata (BA) called Almost linear Buechi automata (ALBA).
We provide effective translations between LIO and ALBA showing that the two
formalisms are expressively equivalent. While standard translations of LTL into
BA use some intermediate formalisms, the presented translation of LIO into ALBA
is direct. As we expect applications of ALBA in model checking, we compare the
expressiveness of ALBA with other classes of Buechi automata studied in this
context and we indicate possible applications
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