776 research outputs found
Nanofiber-based optical trapping of cold neutral atoms
We present experimental techniques and results related to the optimization
and characterization of our nanofiber-based atom trap [Vetsch et al., Phys.
Rev. Lett. 104, 203603 (2010)]. The atoms are confined in an optical lattice
which is created using a two-color evanescent field surrounding the optical
nanofiber. For this purpose, the polarization state of the trapping light
fields has to be properly adjusted. We demonstrate that this can be
accomplished by analyzing the light scattered by the nanofiber. Furthermore, we
show that loading the nanofiber trap from a magneto-optical trap leads to
sub-Doppler temperatures of the trapped atomic ensemble and yields a
sub-Poissonian distribution of the number of trapped atoms per trapping site
The KB paradigm and its application to interactive configuration
The knowledge base paradigm aims to express domain knowledge in a rich formal
language, and to use this domain knowledge as a knowledge base to solve various
problems and tasks that arise in the domain by applying multiple forms of
inference. As such, the paradigm applies a strict separation of concerns
between information and problem solving. In this paper, we analyze the
principles and feasibility of the knowledge base paradigm in the context of an
important class of applications: interactive configuration problems. In
interactive configuration problems, a configuration of interrelated objects
under constraints is searched, where the system assists the user in reaching an
intended configuration. It is widely recognized in industry that good software
solutions for these problems are very difficult to develop. We investigate such
problems from the perspective of the KB paradigm. We show that multiple
functionalities in this domain can be achieved by applying different forms of
logical inferences on a formal specification of the configuration domain. We
report on a proof of concept of this approach in a real-life application with a
banking company. To appear in Theory and Practice of Logic Programming (TPLP).Comment: To appear in Theory and Practice of Logic Programming (TPLP
Recommended from our members
Comparative safety of anesthetic type for hip fracture surgery in adults: retrospective cohort study
Objective: To evaluate the effect of anesthesia type on the risk of in-hospital mortality among adults undergoing hip fracture surgery in the United States. Design: Retrospective cohort study. Setting: Premier research database, United States. Participants: 73 284 adults undergoing hip fracture surgery on hospital day 2 or greater between 2007 and 2011. Of those, 61 554 (84.0%) received general anesthesia, 6939 (9.5%) regional anesthesia, and 4791 (6.5%) combined general and regional anesthesia. Main outcome measure In-hospital all cause mortality. Results: In-hospital deaths occurred in 1362 (2.2%) patients receiving general anesthesia, 144 (2.1%) receiving regional anesthesia, and 115 (2.4%) receiving combined anesthesia. In the multivariable adjusted analysis, when compared with general anesthesia the mortality risk did not differ significantly between regional anesthesia (risk ratio 0.93, 95% confidence interval 0.78 to 1.11) or combined anesthesia (1.00, 0.82 to 1.22). A mixed effects analysis accounting for differences between hospitals produced similar results: compared with general anesthesia the risk from regional anesthesia was 0.91 (0.75 to 1.10) and from combined anesthesia was 0.98 (0.79 to 1.21). Findings were also consistent in subgroup analyses. Conclusions: In this large nationwide sample of hospital admissions, mortality risk did not differ significantly by anesthesia type among patients undergoing hip fracture surgery. Our results suggest that if the previously posited beneficial effect of regional anesthesia on short term mortality exists, it is likely to be more modest than previously reported
Scattering and absorption of ultracold atoms by nanotubes
We investigate theoretically how cold atoms, including Bose-Einstein
condensates, are scattered from, or absorbed by nanotubes with a view to
analysing recent experiments. In particular we consider the role of potential
strength, quantum reflection, atomic interactions and tube vibrations on atom
loss rates. Lifshitz theory calculations deliver a significantly stronger
scattering potential than that found in experiment and we discuss possible
reasons for this. We find that the scattering potential for dielectric tubes
can be calculated to a good approximation using a modified pairwise summation
approach, which is efficient and easily extendable to arbitrary geometries.
Quantum reflection of atoms from a nanotube may become a significant factor at
low temperatures, especially for non-metallic tubes. Interatomic interactions
are shown to increase the rate at which atoms are lost to the nanotube and lead
to non-trivial dynamics. Thermal nanotube vibrations do not significantly
increase loss rates or reduce condensate fractions, but lower frequency
oscillations can dramatically heat the cloud.Comment: 7 pages, 4 figure
Recommended from our members
Differential risk of death in older residents in nursing homes prescribed specific antipsychotic drugs: population based cohort study
Objective To assess risks of mortality associated with use of individual antipsychotic drugs in elderly residents in nursing homes
State-Insensitive Trapping of Alkaline-Earth Atoms in a Nanofiber-Based Optical Dipole Trap
Neutral atoms trapped in the evanescent optical potentials of nanotapered
optical fibers are a promising platform for developing quantum technologies and
exploring fundamental science, such as quantum networks and quantum
electrodynamics. Building on the successful advancements with trapped alkali
atoms, here we demonstrate a state-insensitive optical dipole trap for
strontium-88, an alkaline-earth atom, using the evanescent fields of a
nanotapered optical fiber. Leveraging the low laser-cooling temperatures of
K readily achievable with strontium, we demonstrate trapping in
record low trap depths corresponding to K. Further, employing a
double magic wavelength trapping scheme, we realize state-insensitive trapping
on the kilohertz-wide 5s^{2}\;^{1}\!S_{0}-5s5p\;^{3}\!P_{1,|m|=1} cooling
transition, which we verify by performing near-surface high-resolution
spectroscopy of the atomic transition. This allows us to experimentally find
and verify the state insensitivity of the trap nearby a theoretically predicted
magic wavelength of 435.827(25) nm. Given the non-magnetic ground state and low
collisional scattering length of strontium-88, this work also lays the
foundation for developing versatile and robust matter-wave atomtronic circuits
over nanophotonic waveguides.Comment: 14 pages, 15 figure
Performance of propensity score calibration - A simulation study
Confounding can be a major source of bias in nonexperimental research. The authors recently introduced propensity score calibration (PSC), which combines propensity scores and regression calibration to address confounding by variables unobserved in the main study by using variables observed in a validation study. Here, the authors assess the performance of PSC using simulations in settings with and without violation of the key assumption of PSC: that the error-prone propensity score estimated in the main study is a surrogate for the gold-standard propensity score (i.e., it contains no additional information on the outcome). The assumption can be assessed if data on the outcome are available in the validation study. If data are simulated allowing for surrogacy to be violated, results depend largely on the extent of violation. If surrogacy holds, PSC leads to bias reduction between 32% and 106% (>100% representing overcorrection). If surrogacy is violated, PSC can lead to an increase in bias. Surrogacy is violated when the direction of confounding of the exposure-disease association caused by the unobserved variable(s) differs from that of the confounding due to observed variables. When surrogacy holds, PSC is a useful approach to adjust for unmeasured confounding using validation data
A Nanofiber-Based Optical Conveyor Belt for Cold Atoms
We demonstrate optical transport of cold cesium atoms over millimeter-scale
distances along an optical nanofiber. The atoms are trapped in a
one-dimensional optical lattice formed by a two-color evanescent field
surrounding the nanofiber, far red- and blue-detuned with respect to the atomic
transition. The blue-detuned field is a propagating nanofiber-guided mode while
the red-detuned field is a standing-wave mode which leads to the periodic axial
confinement of the atoms. Here, this standing wave is used for transporting the
atoms along the nanofiber by mutually detuning the two counter-propagating
fields which form the standing wave. The performance and limitations of the
nanofiber-based transport are evaluated and possible applications are
discussed
Changes in Drug Utilization during a Gap in Insurance Coverage: An Examination of the Medicare Part D Coverage Gap
Jennifer Polinski and colleagues estimated the effect of the "coverage gap" during which US Medicare beneficiaries are fully responsible for drug costs and found that the gap was associated with a doubling in discontinuing essential medications
Analytic strategies to adjust confounding using exposure propensity scores and disease risk scores: Nonsteroidal antiinflammatory drugs and short-term mortality in the elderly
Little is known about optimal application and behavior of exposure propensity scores (EPS) in small studies. In a cohort of 103,133 elderly Medicaid beneficiaries in New Jersey, the effect of nonsteroidal antiinflammatory drug use on 1-year all-cause mortality was assessed (1995-1997) based on the assumption that there is no protective effect and that the preponderance of any observed effect would be confounded. To study the comparative behavior of EPS, disease risk scores, and "conventional" disease models, the authors randomly resampled 1,000 subcohorts of 10,000, 1,000, and 500 persons. The number of variables was limited in disease models, but not EPS and disease risk scores. Estimated EPS were used to adjust for confounding by matching, inverse probability of treatment weighting, stratification, and modeling. The crude rate ratio of death was 0.68 for users of nonsteroidal antiinflammatory drugs. "Conventional" adjustment resulted in a rate ratio of 0.80 (95% confidence interval: 0.77, 0.84). The rate ratio closest to 1 (0.85) was achieved by inverse probability of treatment weighting (95% confidence interval: 0.82, 0.88). With decreasing study size, estimates remained further from the null value, which was most pronounced for inverse probability of treatment weighting (n = 500: rate ratio = 0.72, 95% confidence interval: 0.26, 1.68). In this setting, analytic strategies using EPS or disease risk scores were not generally superior to "conventional" models. Various ways to use EPS and disease risk scores behaved differently with smaller study size
- …