7,127 research outputs found
Finite range corrections near a Feshbach resonance and their role in the Efimov effect
We have measured the binding energy of Li Feshbach molecules deep into
the non-universal regime by associating free atoms in a Bose-Einstein
condensate by modulating the magnetic field. We extract the scattering length
from these measurements, correcting for non-universal short-range effects using
several different methods. We find that field-dependent effective range
corrections agree well with the data.
With this more precise determination of the scattering length vs. field we
reanalyze our previous data on the location of atom loss features produced by
the Efimov effect \cite{PollackSci09} and investigate effective range
corrections to universal theory.Comment: Accepted for publication in Phys. Rev.
Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed Interferometer
The Laser Interferometer Space Antenna (LISA) is being designed to detect and
study in detail gravitational waves from sources throughout the Universe such
as massive black hole binaries. The conceptual formulation of the LISA
space-borne gravitational wave detector is now well developed. The
interferometric measurements between the sciencecraft remain one of the most
important technological and scientific design areas for the mission.
Our work has concentrated on developing the interferometric technologies to
create a LISA-like optical signal and to measure the phase of that signal using
commercially available instruments. One of the most important goals of this
research is to demonstrate the LISA phase timing and phase reconstruction for a
LISA-like fringe signal, in the case of a high fringe rate and a low signal
level. We present current results of a test-bed interferometer designed to
produce an optical LISA-like fringe signal previously discussed in the
literature.Comment: find minor corrections in the CQG versio
Towards a Principled Representation of Discourse Plans
We argue that discourse plans must capture the intended causal and
decompositional relations between communicative actions. We present a planning
algorithm, DPOCL, that builds plan structures that properly capture these
relations, and show how these structures are used to solve the problems that
plagued previous discourse planners, and allow a system to participate
effectively and flexibly in an ongoing dialogue.Comment: requires cogsci94.sty, psfig.st
A Demonstration of LISA Laser Communication
Over the past few years questions have been raised concerning the use of
laser communications links between sciencecraft to transmit phase information
crucial to the reduction of laser frequency noise in the LISA science
measurement. The concern is that applying medium frequency phase modulations to
the laser carrier could compromise the phase stability of the LISA fringe
signal. We have modified the table-top interferometer presented in a previous
article by applying phase modulations to the laser beams in order to evaluate
the effects of such modulations on the LISA science fringe signal. We have
demonstrated that the phase resolution of the science signal is not degraded by
the presence of medium frequency phase modulations.Comment: minor corrections found in the CQG versio
Universality in Three- and Four-Body Bound States of Ultracold Atoms
Under certain circumstances, three or more interacting particles may form
bound states. While the general few-body problem is not analytically solvable,
the so-called Efimov trimers appear for a system of three particles with
resonant two-body interactions. The binding energies of these trimers are
predicted to be universally connected to each other, independent of the
microscopic details of the interaction. By exploiting a Feshbach resonance to
widely tune the interactions between trapped ultracold lithium atoms, we find
evidence for two universally connected Efimov trimers and their associated
four-body bound states. A total of eleven precisely determined three- and
four-body features are found in the inelastic loss spectrum. Their relative
locations on either side of the resonance agree well with universal theory,
while a systematic deviation from universality is found when comparing features
across the resonance.Comment: 16 pages including figures and Supplementary Online Materia
Extreme tunability of interactions in a Li Bose-Einstein condensate
We use a Feshbach resonance to tune the scattering length a of a
Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the
spatial extent of the trapped condensate we extract a over a range spanning 7
decades from small attractive interactions to extremely strong repulsive
interactions. The shallow zero-crossing in the wing of the Feshbach resonance
enables the determination of a as small as 0.01 Bohr radii. In this regime,
evidence of the weak anisotropic magnetic dipole interaction is obtained by
comparison with different trap geometries
Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length
We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by
modulating the atomic scattering length via a Feshbach resonance. Excitation
occurs at various modulation frequencies, and resonances located at the natural
quadrupole frequency of the condensate and at the first harmonic are observed.
We also investigate the amplitude of the excited mode as a function of
modulation depth. Numerical simulations based on a variational calculation
agree with our experimental results and provide insight into the observed
behavior.Comment: Submitted to PR
Charge Management for Gravitational Wave Observatories using UV LEDs
Accumulation of electrical charge on the end mirrors of gravitational wave
observatories, such as the space-based LISA mission and ground-based LIGO
detectors, can become a source of noise limiting the sensitivity of such
detectors through electronic couplings to nearby surfaces. Torsion balances
provide an ideal means for testing gravitational wave technologies due to their
high sensitivity to small forces. Our torsion pendulum apparatus consists of a
movable Au-coated Cu plate brought near a Au-coated Si plate pendulum suspended
from a non-conducting quartz fiber. A UV LED located near the pendulum
photoejects electrons from the surface, and a UV LED driven electron gun
directs photoelectrons towards the pendulum surface. We have demonstrated both
charging and discharging of the pendulum with equivalent charging rates of
, as well as spectral measurements of the pendulum
charge resulting in a white noise level equivalent to .Comment: 5 pages, submitted to PR
Optical constants of solid methane
Methane is the most abundant simple organic molecule in the outer solar system bodies. In addition to being a gaseous constituent of the atmospheres of the Jovian planets and Titan, it is present in the solid form as a constituent of icy surfaces such as those of Triton and Pluto, and as cloud condensate in the atmospheres of Titan, Uranus, and Neptune. It is expected in the liquid form as a constituent of the ocean of Titan. Cometary ices also contain solid methane. The optical constants for both solid and liquid phases of CH4 for a wide temperature range are needed for radiative transfer calculations, for studies of reflection from surfaces, and for modeling of emission in the far infrared and microwave regions. The astronomically important visual to near infrared measurements of solid methane optical constants are conspicuously absent from the literature. Preliminary results are presented on the optical constants of solid methane for the 0.4 to 2.6 micrometer region. Deposition onto a substrate at 10 K produces glassy (semi-amorphous) material. Annealing this material at approximately 33 K for approximately 1 hour results in a crystalline material as seen by sharper, more structured bands and negligible background extinction due to scattering. The constant k is reported for both the amorphous and the crystalline (annealed) states. Typical values (at absorption maxima) are in the .001 to .0001 range. Below lambda = 1.1 micrometers the bands are too weak to be detected by transmission through the films less than or equal to 215 micrometers in thickness, employed in the studies to date. Using previously measured values of the real part of the refractive index, n, of liquid methane at 110 K, n is computed for solid methane using the Lorentz-Lorenz relationship. Work is in progress to extend the measurements of optical constants n and k for liquid and solid to both shorter and longer wavelengths, eventually providing a complete optical constants database for condensed CH4
Pre-crisis mouse cells show strain-specific covariation in the amount of 54-kilodalton phosphoprotein and in susceptibility to transformation by simian virus 40.
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