195 research outputs found
Risks and benefits of adding anti-platelet therapy to warfarin among patients with prosthetic heart valves: a meta-analysis
AbstractOBJECTIVESThe objective of this study was to compare the effectiveness and safety of adding dipyridamole or aspirin to warfarin among patients with prosthetic heart valves using meta-analytic techniques.BACKGROUNDPatients with prosthetic heart valves are at increased risk for valve thrombosis and arterial thromboembolism. Oral anticoagulation alone, or the addition of antiplatelet drugs, has been used to minimize this risk. An important issue is the effectiveness and safety of the latter strategy.METHODSA combined MEDLINE and manual search was made for relevant articles from 1966 to November 1999. Standard meta-analysis techniques were used.RESULTSTen studies involving 2,199 subjects met the inclusion criteria. Compared with anticoagulation alone, the addition of an antiplatelet agent reduced the risk of thromboembolic events (odds ratio [OR]: 0.41, p < 0.001) and total mortality (OR: 0.49, p < 0.001). The risk of major bleeding was increased when antiplatelet agents were added (OR: 1.50, p = 0.033). For major bleeding, the comparison of trials performed before and after 1990 (OR: 2.23 and 0.88, respectively) showed that the chi-square test for heterogeneity was significant (p = 0.025). The latter trials used low-dose aspirin, suggesting that the risk of bleeding may be lower with contemporary low-dose (100 mg daily) aspirin.CONCLUSIONSAdding antiplatelet therapy, especially low-dose aspirin, to warfarin decreases the risk of systemic embolism or death among patients with prosthetic heart valves. The risk of major bleeding is slightly increased with antiplatelet therapy. Nonetheless, the risk of bleeding appears to have diminished with the lower doses of aspirin used in the more recent trials, resulting in a favorable risk-to-benefit profile
Expansion dynamics in the one-dimensional Fermi-Hubbard model
Expansion dynamics of interacting fermions in a lattice are simulated within
the one-dimensional (1D) Hubbard model, using the essentially exact
time-evolving block decimation (TEBD) method. In particular, the expansion of
an initial band-insulator state is considered. We analyze the simulation
results based on the dynamics of a two-site two-particle system, the so-called
Hubbard dimer. Our findings describe essential features of a recent experiment
on the expansion of a Fermi gas in a two-dimensional lattice. We show that the
Hubbard-dimer dynamics, combined with a two-fluid model for the paired and
non-paired components of the gas, gives an efficient description of the full
dynamics. This should be useful for describing dynamical phenomena of strongly
interacting Fermions in a lattice in general.Comment: Fig. 9 changed, text + supplementary material revise
Hopping modulation in a one-dimensional Fermi-Hubbard Hamiltonian
We consider a strongly repulsive two-component Fermi gas in a one-dimensional
(1D) optical lattice described in terms of a Hubbard Hamiltonian. We analyze
the response of the system to a periodic modulation of the hopping amplitude in
presence of large two body interaction. By (essentially) exact simulations of
the time evolution, we find a non-trivial double occupancy frequency
dependence. We show how the dependence relates to the spectral features of the
system given by the Bethe ansatz. The discrete nature of the spectrum is
clearly reflected in the double occupancy after long enough modulation time. We
also discuss the implications of the 1D results to experiments in higher
dimensional systems.Comment: 4 pages, 5 figures; minor changes in the text, updated references
Spectral up- and downshifting of Akhmediev breathers under wind forcing
We experimentally and numerically investigate the effect of wind forcing on
the spectral dynamics of Akhmediev breathers, a wave-type known to model the
modulation instability. We develop the wind model to the same order in
steepness as the higher order modifcation of the nonlinear Schroedinger
equation, also referred to as the Dysthe equation. This results in an
asymmetric wind term in the higher order, in addition to the leading order wind
forcing term. The derived model is in good agreement with laboratory
experiments within the range of the facility's length. We show that the leading
order forcing term amplifies all frequencies equally and therefore induces only
a broadening of the spectrum while the asymmetric higher order term in the
model enhances higher frequencies more than lower ones. Thus, the latter term
induces a permanent upshift of the spectral mean. On the other hand, in
contrast to the direct effect of wind forcing, wind can indirectly lead to
frequency downshifts, due to dissipative effects such as wave breaking, or
through amplification of the intrinsic spectral asymmetry of the Dysthe
equation. Furthermore, the definitions of the up- and downshift in terms of
peak- and mean frequencies, that are critical to relate our work to previous
results, are highlighted and discussed.Comment: 30 pages, 11 figure
Assessing Readability of Online Patient Education Materials for Spine Surgery Procedures
Increased patient reliance on Internet-based health information has amplified the need for comprehensible online patient education articles. As suggested by the AMA and NIH, spine fusion articles should be between a 4th and 6th grade readability level to increase patient comprehension, which may contribute to improved postoperative outcomes. Objective: To determine the average readability level of online healthcare education information relating to anterior cervical discectomy and fusion (ACDF) and lumbar fusion procedures. Design: Online Health-Education Resource Qualitative Analysis. Setting: Rush University Medical Center - Department of Orthopaedic Surgery. Methods: Three popular search engines were utilized to access patient education articles for common cervical and lumbar spine procedures. Relevant articles were analyzed for readability using Readability Studio Professional Edition software (Oleander Software, Ltd). Articles were stratified by organization type as follows: General Medical Websites (GMW), Healthcare Network/Academic Institutions (HNAI), and Private Practices (PP). Thirteen common readability tests were performed with the mean grade level for each readability test compared between subgroups using ANOVA analysis. Results: 79 ACDF and 231 lumbar fusion articles were determined to have a mean readability level of 10.7 ± 1.5 and 11.3 ± 1.6, respectively. GMW, HNAI, and PP subgroups had mean readability levels of 10.9 ± 2.9, 10.7 ± 2.8, and 10.7 ± 2.5 for ACDF and 10.9 ± 3.0, 10.8 ± 2.9, and 11.6 ± 2.7 for lumbar fusion articles. Of 310 total articles, only 6 (3 ACDF and 3 lumbar fusion) were written below the 7th grade reading level. Conclusions: Current online literature from medical websites containing information regarding ACDF and lumbar fusion procedures are written at a grade level higher than the suggested guidelines. Therefore, current patient education articles should be revised to accommodate the average readability level in the United States and may result in improved patient comprehension and postoperative outcomes
Evolution of surface gravity waves over a submarine canyon
The effects of a submarine canyon on the propagation of ocean surface waves
are examined with a three-dimensional coupled-mode model for wave propagation
over steep topography. Whereas the classical geometrical optics approximation
predicts an abrupt transition from complete transmission at small incidence
angles to no transmission at large angles, the full model predicts a more
gradual transition with partial reflection/transmission that is sensitive to
the canyon geometry and controlled by evanescent modes for small incidence
angles and relatively short waves. Model results for large incidence angles are
compared with data from directional wave buoys deployed around the rim and over
Scripps Canyon, near San Diego, California, during the Nearshore Canyon
Experiment (NCEX). Wave heights are observed to decay across the canyon by
about a factor 5 over a distance shorter than a wavelength. Yet, a spectral
refraction model predicts an even larger reduction by about a factor 10,
because low frequency components cannot cross the canyon in the geometrical
optics approximation. The coupled-mode model yields accurate results over and
behind the canyon. These results show that although most of the wave energy is
refractively trapped on the offshore rim of the canyon, a small fraction of the
wave energy 'tunnels' across the canyon. Simplifications of the model that
reduce it to the standard and modified mild slope equations also yield good
results, indicating that evanescent modes and high order bottom slope effects
are of minor importance for the energy transformation of waves propagating
across depth contours at large oblique angles
Generalized Hartree-Fock Theory for Interacting Fermions in Lattices: Numerical Methods
We present numerical methods to solve the Generalized Hartree-Fock theory for
fermionic systems in lattices, both in thermal equilibrium and out of
equilibrium. Specifically, we show how to determine the covariance matrix
corresponding to the Fermionic Gaussian state that optimally approximates the
quantum state of the fermions. The methods apply to relatively large systems,
since their complexity only scales quadratically with the number of lattice
sites. Moreover, they are specially suited to describe inhomogenous systems, as
those typically found in recent experiments with atoms in optical lattices, at
least in the weak interaction regime. As a benchmark, we have applied them to
the two-dimensional Hubbard model on a 10x10 lattice with and without an
external confinement.Comment: 16 pages, 22 figure
Slot-mode-coupled optomechanical crystals
We present a design methodology and analysis of a cavity optomechanical
system in which a localized GHz frequency mechanical mode of a nanobeam
resonator is evanescently coupled to a high quality factor (Q>10^6) optical
mode of a separate nanobeam optical cavity. Using separate nanobeams provides
flexibility, enabling the independent design and optimization of the optics and
mechanics of the system. In addition, the small gap (approx. 25 nm) between the
two resonators gives rise to a slot mode effect that enables a large zero-point
optomechanical coupling strength to be achieved, with g/2pi > 300 kHz in a
Si3N4 system at 980 nm and g/2pi approx. 900 kHz in a Si system at 1550 nm. The
fact that large coupling strengths to GHz mechanical oscillators can be
achieved in SiN is important, as this material has a broad optical transparency
window, which allows operation throughout the visible and near-infrared. As an
application of this platform, we consider wide-band optical frequency
conversion between 1300 nm and 980 nm, using two optical nanobeam cavities
coupled on either side to the breathing mode of a mechanical nanobeam
resonator
The fidelity approach to the Hubbard model
We use the fidelity approach to quantum critical points to study the zero
temperature phase diagram of the one-dimensional Hubbard model. Using a variety
of analytical and numerical techniques, we analyze the fidelity metric in
various regions of the phase diagram, with particular care to the critical
points. Specifically we show that close to the Mott transition, taking place at
on-site repulsion U=0 and electron density n=1, the fidelity metric satisfies
an hyper-scaling form which we calculate. This implies that in general, as one
approaches the critical point U=0, n=1, the fidelity metric tends to a limit
which depends on the path of approach. At half filling, the fidelity metric is
expected to diverge as U^{-4} when U is sent to zero.Comment: 8 pages, 4 figures, added results on the hyper-scaling form of the
fidelity metri
- …