404 research outputs found
Feshbach resonances with large background scattering length: interplay with open-channel resonances
Feshbach resonances are commonly described by a single-resonance Feshbach
model, and open-channel resonances are not taken into account explicitly.
However, an open-channel resonance near threshold limits the range of validity
of this model. Such a situation exists when the background scattering length is
much larger than the range of the interatomic potential. The open-channel
resonance introduces strong threshold effects not included in the
single-resonance description. We derive an easy-to-use analytical model that
takes into account both the Feshbach resonance and the open-channel resonance.
We apply our model to Rb, which has a large background scattering
length, and show that the agreement with coupled-channels calculations is
excellent. The model can be readily applied to other atomic systems with a
large background scattering length, such as Li and Cs. Our approach
provides full insight into the underlying physics of the interplay between
open-channel (or potential) resonances and Feshbach resonances.Comment: 16 pages, 12 figures, accepted for publication in Phys. Rev. A; v2:
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Predicting scattering properties of ultracold atoms: adiabatic accumulated phase method and mass scaling
Ultracold atoms are increasingly used for high precision experiments that can
be utilized to extract accurate scattering properties. This calls for a
stronger need to improve on the accuracy of interatomic potentials, and in
particular the usually rather inaccurate inner-range potentials. A boundary
condition for this inner range can be conveniently given via the accumulated
phase method. However, in this approach one should satisfy two conditions,
which are in principle conflicting, and the validity of these approximations
comes under stress when higher precision is required. We show that a better
compromise between the two is possible by allowing for an adiabatic change of
the hyperfine mixing of singlet and triplet states for interatomic distances
smaller than the separation radius. A mass scaling approach to relate
accumulated phase parameters in a combined analysis of isotopically related
atom pairs is described in detail and its accuracy is estimated, taking into
account both Born-Oppenheimer and WKB breakdown. We demonstrate how numbers of
singlet and triplet bound states follow from the mass scaling.Comment: 14 pages, 9 figure
Optical excitations in a non-ideal Bose gas
Optical excitations in a Bose gas are demonstrated to be very sensitive to
many-body effects. At low temperature the momentum relaxation is provided by
momentum exchange collisions, rather than by elastic collisions. A collective
excitation mode forms, which in a Boltzmann gas is manifest in a collision
shift and dramatic narrowing of spectral lines.
In the BEC state, each spectral line splits into two components. The doubling
of the optical excitations results from the physics analogous to that of the
second sound. We present a theory of the line doubling, and calculate the
oscillator strengths and linewidth.Comment: 5 pages, 3 eps figure
Metastable neon collisions: anisotropy and scattering length
In this paper we investigate the effective scattering length of
spin-polarized Ne*. Due to its anisotropic electrostatic interaction, its
scattering length is determined by five interaction potentials instead of one,
even in the spin-polarized case, a unique property among the Bose condensed
species and candidates. Because the interaction potentials of Ne* are not known
accurately enough to predict the value of the scattering length, we investigate
the behavior of as a function of the five phase integrals corresponding to
the five interaction potentials. We find that the scattering length has five
resonances instead of only one and cannot be described by a simple gas-kinetic
approach or the DIS approximation. However, the probability for finding a
positive or large value of the scattering length is not enhanced compared to
the single potential case. The complex behavior of is studied by comparing
a quantum mechanical five-channel numerical calculation to simpler two-channel
models. We find that the induced dipole-dipole interaction is responsible for
coupling between the different |\Omega> states, resulting in an inhomogeneous
shift of the resonance positions and widths in the quantum mechanical
calculation as compared to the DIS approach. The dependence of the resonance
positions and widths on the input potentials turns out to be rather
straightforward. The existence of two bosonic isotopes of Ne* enables us to
choose the isotope with the most favorable scattering length for efficient
evaporative cooling towards the Bose-Einstein Condensation transition, greatly
enhancing the feasibility to reach this transition.Comment: 13pages, 8 eps figures, analytical model in section V has been
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Techniques for measuring weight bearing during standing and walking
OBJECTIVE: To classify and assess techniques for measuring the amount of weight bearing during standing and walking.BACKGROUND: A large variety of weight bearing measuring techniques exists. This review describes their advantages and limitations to assist clinicians and researchers in selecting a technique for their specific application in measuring weight bearing.METHODS: A literature search was performed in Pubmed-Medline, CINAHL, and EMBASE. Measurement techniques were classified in 'clinical examination', 'scales', 'biofeedback systems', 'ambulatory devices' and 'platforms', and assessed on aspects of methodological quality, application, and feasibility.RESULTS: A total of 68 related articles was evaluated. The clinical examination technique is a crude method to estimate the amount of weight bearing. Scales are useful for static measurements to evaluate symmetry in weight bearing. Biofeedback systems give more reliable, accurate and objective data on weight bearing compared to clinical examination and scales, but the high costs could limit their use in physical therapy departments. The ambulatory devices can measure weight bearing with good accuracy and reliability in the hospital and at home. Platforms have the best methodological quality, but are mostly restricted to a gait laboratory, need trained personnel, and are expensive.CONCLUSIONS: The choice of a technique largely depends upon the criteria discussed in this review; however the clinical utilisation, the research question posed, and the available budget also play a role. The new developments seen in the field of 'ambulatory devices' are aimed at extending measuring time, and improved practicality in data collection and data analysis. For these latter devices, however, mainly preliminary studies have been published about devices that are not (yet) commercially available.</p
Radio-Frequency Spectroscopy of Ultracold Fermions
Radio-frequency techniques were used to study ultracold fermions. We observed
the absence of mean-field "clock" shifts, the dominant source of systematic
error in current atomic clocks based on bosonic atoms. This is a direct
consequence of fermionic antisymmetry. Resonance shifts proportional to
interaction strengths were observed in a three-level system. However, in the
strongly interacting regime, these shifts became very small, reflecting the
quantum unitarity limit and many-body effects. This insight into an interacting
Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure
Functional capacity and actual daily activity do not contribute to patient satisfaction after total knee arthroplasty
<p>Abstract</p> <p>Background</p> <p>After total knee arthroplasty (TKA) only 75-89% of patients are satisfied. Because patient satisfaction is a prime goal of all orthopaedic procedures, optimization of patient satisfaction is of major importance. Factors related to patient satisfaction after TKA have been explored, but no studies have included two potentially relevant factors, i.e. the functional capacity of daily activities and actual daily activity. This present prospective study examines whether functional capacity and actual daily activity (in addition to an extensive set of potential factors) contribute to patient satisfaction six months after TKA.</p> <p>Methods</p> <p>A total of 44 patients were extensively examined preoperatively and six months post surgery. Functional capacity was measured with three capacity tests, focusing on walking, stair climbing, and chair rising. Actual daily activity was measured in the patient's home situation by means of a 48-hour measurement with an Activity Monitor. To establish which factors were related to patient satisfaction six months post surgery, logistic regression analyses were used to calculate odds ratios.</p> <p>Results</p> <p>Preoperative and postoperative functional capacity and actual daily activity had no relation with patient satisfaction. Preoperatively, only self-reported mental functioning was positively related to patient satisfaction. Postoperatively, based on multivariate analysis, only fulfilled expectations regarding pain and experienced pain six months post surgery were related to patient satisfaction.</p> <p>Conclusions</p> <p>Functional capacity and actual daily activity do not contribute to patient satisfaction after TKA. Patients with a better preoperative self-reported mental functioning, and patients who experienced less pain and had fulfilled expectations regarding pain postoperatively, were more often satisfied.</p
Analytic structure and power-series expansion of the Jost function for the two-dimensional problem
For a two-dimensional quantum mechanical problem, we obtain a generalized
power-series expansion of the S-matrix that can be done near an arbitrary point
on the Riemann surface of the energy, similarly to the standard effective range
expansion. In order to do this, we consider the Jost-function and analytically
factorize its momentum dependence that causes the Jost function to be a
multi-valued function. The remaining single-valued function of the energy is
then expanded in the power-series near an arbitrary point in the complex energy
plane. A systematic and accurate procedure has been developed for calculating
the expansion coefficients. This makes it possible to obtain a semi-analytic
expression for the Jost-function (and therefore for the S-matrix) near an
arbitrary point on the Riemann surface and use it, for example, to locate the
spectral points (bound and resonant states) as the S-matrix poles. The method
is applied to a model simlar to those used in the theory of quantum dots.Comment: 42 pages, 9 figures, submitted to J.Phys.
Influence of nearly resonant light on the scattering length in low-temperature atomic gases
We develop the idea of manipulating the scattering length in
low-temperature atomic gases by using nearly resonant light. As found, if the
incident light is close to resonance with one of the bound levels of
electronically excited molecule, then virtual radiative transitions of a pair
of interacting atoms to this level can significantly change the value and even
reverse the sign of . The decay of the gas due to photon recoil, resulting
from the scattering of light by single atoms, and due to photoassociation can
be minimized by selecting the frequency detuning and the Rabi frequency. Our
calculations show the feasibility of optical manipulations of trapped Bose
condensates through a light-induced change in the mean field interaction
between atoms, which is illustrated for Li.Comment: 12 pages, 1 Postscript figur
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