447 research outputs found
Statistical comparison of ensemble implementations of Grover's search algorithm to classical sequential searches
We compare pseudopure state ensemble implementations, quantified by their
initial polarization and ensemble size, of Grover's search algorithm to
probabilistic classical sequential search algorithms in terms of their success
and failure probabilities. We propose a criterion for quantifying the resources
used by the ensemble implementation via the aggregate number of oracle
invocations across the entire ensemble and use this as a basis for comparison
with classical search algorithms. We determine bounds for a critical
polarization such that the ensemble algorithm succeeds with a greater
probability than the probabilistic classical sequential search. Our results
indicate that the critical polarization scales as N^(-1/4) where N is the
database size and that for typical room temperature solution state NMR, the
polarization is such that the ensemble implementation of Grover's algorithm
would be advantageous for N > 10^2
The eclipsing X-ray pulsar X-7 in M33
Using our extensive ROSAT X-ray observations of M33, we confirm a 3.45 day
eclipse period for the Einstein source X-7 (Larson & Schulman, 1997) and
discover evidence for a 0.31-s pulse period. The orbital period, pulse period
and observed X-ray luminosity are remarkably similar to SMC X-1. We therefore
suggest M33 X-7 is a neutron star high mass X-ray binary with a 15-40 Msol O/B
companion and a binary separation of 25-33 Rsol if the companion is almost
filling its Roche lobe.Comment: accepted for publication in MNRA
Polarization Requirements for Ensemble Implementations of Quantum Algorithms with a Single Bit Output
We compare the failure probabilities of ensemble implementations of quantum
algorithms which use pseudo-pure initial states, quantified by their
polarization, to those of competing classical probabilistic algorithms.
Specifically we consider a class algorithms which require only one bit to
output the solution to problems. For large ensemble sizes, we present a general
scheme to determine a critical polarization beneath which the quantum algorithm
fails with greater probability than its classical competitor. We apply this to
the Deutsch-Jozsa algorithm and show that the critical polarization is 86.6%.Comment: 11 pages, 3 figure
Simple computer model for the quantum Zeno effect
This paper presents a simple model for repeated measurement of a quantum
system: the evolution of a free particle, simulated by discretising the
particle's position. This model is easily simulated by computer and provides a
useful arena to investigate the effects of measurement upon dynamics, in
particular the slowing of evolution due to measurement (the `quantum Zeno
effect'). The results of this simulation are discussed for two rather different
sorts of measurement process, both of which are (simplified forms of)
measurements used in previous simulations of position measurement. A number of
interesting results due to measurement are found, and the investigation casts
some light on previous disagreements about the presence or absence of the Zeno
effect.Comment: REVTeX; 12 pages including 11 figures; figures reformatted to be more
readable; some small changes made to the description of the mode
New tunnel diode for zero-bias direct detection for millimeter-wave imagers
High-resolution passive millimeter wave imaging cameras require per pixel detector circuitry that is simple, has high sensitivity, low noise, and low power. Detector diodes that do not require bias or local oscillator input, and have high cutoff frequencies are strongly preferred. In addition, they must be manufacturable in large quantities with reasonable uniformity and reproducibility. Such diodes have not been obtainable for W-band and above. We are developing zero-bias square-law detector diodes based on InAs/Alsb/GaAlSb heterostructures which for the first time offer a cost-effective solution for large array formats. The diodes have a high frequency response and are relatively insensitive to growth and process variables. The large zero- bias non-linearity in current floor necessary for detection arises from interband tunneling between the InAs and the GaAlSb layers. Video resistance can be controlled by varying an Alsb tunnel barrier layer thickness. Our analysis shows that capacitance can be further decreased and sensitivity increased by shrinking the diode area, as the diode can have very high current density. DC and RF characterization of these devices and an estimate of their ultimate frequency performance in comparison with commercially available diodes are presented
Departures From Axisymmetric Morphology and Dynamics in Spiral Galaxies
New HI synthesis data have been obtained for six face-on galaxies with the
Very Large Array. These data and reanalyses of three additional data sets make
up a sample of nine face-on galaxies analyzed for deviations from axisymmetry
in morphology and dynamics. This sample represents a subsample of galaxies
already analyzed for morphological symmetry properties in the R-band. Four
quantitative measures of dynamical nonaxisymmetry are compared to one another
and to the quantitative measures of morphological asymmetry in HI and R-band to
investigate the relationships between nonaxisymmetric morphology and dynamics.
We find no significant relationship between asymmetric morphology and most of
the dynamical measures in our sample. A possible relationship is found,
however, between morphology and dynamical position angle differences between
approaching and receding sides of the galaxy.Comment: 24 pages, 19 figures, AASTeX, accepted for publication in AJ,
postscript figures available at
ftp://culebra.tn.cornell.edu/pub/david/figures.tar.g
Introduction of the Tools for Economic Analysis of Patient Management Interventions in Heart Failure Costing Tool: A User-Friendly Spreadsheet Program to Estimate Costs of Providing Patient-Centered Interventions
Background—Patient-centered health care interventions, such as heart failure disease management programs, are under increasing pressure to demonstrate good value. Variability in costing methods and assumptions in economic evaluations of such interventions limit the comparability of cost estimates across studies. Valid cost estimation is critical to conducting economic evaluations and for program budgeting and reimbursement negotiations. Methods and Results—Using sound economic principles, we developed the Tools for Economic Analysis of Patient Management Interventions in Heart Failure (TEAM-HF) Costing Tool, a spreadsheet program that can be used by researchers and health care managers to systematically generate cost estimates for economic evaluations and to inform budgetary decisions. The tool guides users on data collection and cost assignment for associated personnel, facilities, equipment, supplies, patient incentives, miscellaneous items, and start-up activities. The tool generates estimates of total program costs, cost per patient, and cost per week and presents results using both standardized and customized unit costs for side-by-side comparisons. Results from pilot testing indicated that the tool was well-formatted, easy to use, and followed a logical order. Cost estimates of a 12-week exercise training program in patients with heart failure were generated with the costing tool and were found to be consistent with estimates published in a recent study. Conclusions—The TEAM-HF Costing Tool could prove to be a valuable resource for researchers and health care managers to generate comprehensive cost estimates of patient-centered interventions in heart failure or other conditions for conducting high-quality economic evaluations and making well-informed health care management decisions
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Aspiration therapy for the treatment of obesity: 4-year results of a multicenter randomized controlled trial.
BackgroundThe AspireAssist is the first Food and Drug Administration-approved endoluminal device indicated for treatment of class II and III obesity.ObjectivesWe earlier reported 1-year results of the PATHWAY study. Here, we report 4-year outcomes.SettingUnited States-based, 10-center, randomized controlled trial involving 171 participants with the treatment arm receiving Aspiration Therapy (AT) plus Lifestyle Therapy and the control arm receiving Lifestyle Therapy (2:1 randomization).MethodsAT participants were permitted to continue in the study for an additional year up to a maximum of 5 years providing they maintained at least 10% total weight loss (TWL) from baseline at each year end. For AT participants who continued the study, 5 medical monitoring visits were provided at weeks 60, 68, 76, 90, and 104 and thereafter once every 13 weeks up to week 260. Exclusion criteria were a history of eating disorder or evidence of eating disorder on a validated questionnaire. Follow-up weight, quality of life, and co-morbidities were compared with the baseline levels. In addition, rates of serious adverse event, persistent fistula, withdrawal, and A-tube replacement were reported. All analyses were performed using a per-protocol analysis.ResultsOf the 82 AT participants who completed 1 year, 58 continued to this phase of the trial. Mean baseline body mass index of these 58 patients was 41.6 ± 4.5 kg/m2. At the end of first year (at the beginning of the follow-up study), these 58 patients had a body mass index of 34.1 ± 5.4 kg/m2 and had achieved an 18.3 ± 8.0% TWL. On a per protocol basis, patients experienced 14.2%, 15.3%, 16.6%, and 18.7% TWL at 1, 2, 3, and 4 years, respectively (P < .01 for all). Forty of 58 patients (69%) achieved at least 10% TWL at 4 years or at time of study withdrawal. Improvements in quality of life scores and select cardiometabolic parameters were also maintained through 4 years. There were 2 serious adverse events reported in the second through fourth years, both of which resolved with removal or replacement of the A tube. Two persistent fistulas required surgical repair, representing approximately 2% of all tube removals. There were no clinically significant metabolic or electrolytes disorders observed, nor any evidence for development of any eating disorders.ConclusionsThe results of this midterm study have shown that AT is a safe, effective, and durable weight loss alternative for people with class II and III obesity and who are willing to commit to using the therapy and adhere to adjustments in eating behavior
The Bond-Algebraic Approach to Dualities
An algebraic theory of dualities is developed based on the notion of bond
algebras. It deals with classical and quantum dualities in a unified fashion
explaining the precise connection between quantum dualities and the low
temperature (strong-coupling)/high temperature (weak-coupling) dualities of
classical statistical mechanics (or (Euclidean) path integrals). Its range of
applications includes discrete lattice, continuum field, and gauge theories.
Dualities are revealed to be local, structure-preserving mappings between
model-specific bond algebras that can be implemented as unitary
transformations, or partial isometries if gauge symmetries are involved. This
characterization permits to search systematically for dualities and
self-dualities in quantum models of arbitrary system size, dimensionality and
complexity, and any classical model admitting a transfer matrix representation.
Dualities like exact dimensional reduction, emergent, and gauge-reducing
dualities that solve gauge constraints can be easily understood in terms of
mappings of bond algebras. As a new example, we show that the (\mathbb{Z}_2)
Higgs model is dual to the extended toric code model {\it in any number of
dimensions}. Non-local dual variables and Jordan-Wigner dictionaries are
derived from the local mappings of bond algebras. Our bond-algebraic approach
goes beyond the standard approach to classical dualities, and could help
resolve the long standing problem of obtaining duality transformations for
lattice non-Abelian models. As an illustration, we present new dualities in any
spatial dimension for the quantum Heisenberg model. Finally, we discuss various
applications including location of phase boundaries, spectral behavior and,
notably, we show how bond-algebraic dualities help constrain and realize
fermionization in an arbitrary number of spatial dimensions.Comment: 131 pages, 22 figures. Submitted to Advances in Physics. Second
version including a new section on the eight-vertex model and the correction
of several typo
Perioperative Bridging Anticoagulation in Patients with Atrial Fibrillation
BACKGROUND: It is uncertain whether bridging anticoagulation is necessary for patients with atrial fibrillation who need an interruption in warfarin treatment for an elective operation or other elective invasive procedure. We hypothesized that forgoing bridging anticoagulation would be noninferior to bridging with low-molecular-weight heparin for the prevention of perioperative arterial thromboembolism and would be superior to bridging with respect to major bleeding. METHODS: We performed a randomized, double-blind, placebo-controlled trial in which, after perioperative interruption of warfarin therapy, patients were randomly assigned to receive bridging anticoagulation therapy with low-molecular-weight heparin (100 IU of dalteparin per kilogram of body weight) or matching placebo administered subcutaneously twice daily, from 3 days before the procedure until 24 hours before the procedure and then for 5 to 10 days after the procedure. Warfarin treatment was stopped 5 days before the procedure and was resumed within 24 hours after the procedure. Follow-up of patients continued for 30 days after the procedure. The primary outcomes were arterial thromboembolism (stroke, systemic embolism, or transient ischemic attack) and major bleeding. RESULTS: In total, 1884 patients were enrolled, with 950 assigned to receive no bridging therapy and 934 assigned to receive bridging therapy. The incidence of arterial thromboembolism was 0.4% in the no-bridging group and 0.3% in the bridging group (risk difference, 0.1 percentage points; 95% confidence interval [CI], -0.6 to 0.8; P=0.01 for noninferiority). The incidence of major bleeding was 1.3% in the no-bridging group and 3.2% in the bridging group (relative risk, 0.41; 95% CI, 0.20 to 0.78; P=0.005 for superiority). CONCLUSIONS: In patients with atrial fibrillation who had warfarin treatment interrupted for an elective operation or other elective invasive procedure, forgoing bridging anticoagulation was noninferior to perioperative bridging with low-molecular-weight heparin for the prevention of arterial thromboembolism and decreased the risk of major bleeding. (Funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health; BRIDGE ClinicalTrials.gov number, NCT00786474.)
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