1,837 research outputs found
A Uniform Method for Proving Lower Bounds of the Computational Complexity of Logical Theories
https://deepblue.lib.umich.edu/bitstream/2027.42/154178/1/39015100081655.pd
Nonconvergence, Undecidability, and Intractability in Asymptotic Problems
https://deepblue.lib.umich.edu/bitstream/2027.42/154144/1/39015099114582.pd
Integration of Attributes from Non-Linear Characterization of Cardiovascular Time-Series for Prediction of Defibrillation Outcomes
Objective
The timing of defibrillation is mostly at arbitrary intervals during cardio-pulmonary resuscitation (CPR), rather than during intervals when the out-of-hospital cardiac arrest (OOH-CA) patient is physiologically primed for successful countershock. Interruptions to CPR may negatively impact defibrillation success. Multiple defibrillations can be associated with decreased post-resuscitation myocardial function. We hypothesize that a more complete picture of the cardiovascular system can be gained through non-linear dynamics and integration of multiple physiologic measures from biomedical signals. Materials and Methods
Retrospective analysis of 153 anonymized OOH-CA patients who received at least one defibrillation for ventricular fibrillation (VF) was undertaken. A machine learning model, termed Multiple Domain Integrative (MDI) model, was developed to predict defibrillation success. We explore the rationale for non-linear dynamics and statistically validate heuristics involved in feature extraction for model development. Performance of MDI is then compared to the amplitude spectrum area (AMSA) technique. Results
358 defibrillations were evaluated (218 unsuccessful and 140 successful). Non-linear properties (Lyapunov exponent \u3e 0) of the ECG signals indicate a chaotic nature and validate the use of novel non-linear dynamic methods for feature extraction. Classification using MDI yielded ROC-AUC of 83.2% and accuracy of 78.8%, for the model built with ECG data only. Utilizing 10-fold cross-validation, at 80% specificity level, MDI (74% sensitivity) outperformed AMSA (53.6% sensitivity). At 90% specificity level, MDI had 68.4% sensitivity while AMSA had 43.3% sensitivity. Integrating available end-tidal carbon dioxide features into MDI, for the available 48 defibrillations, boosted ROC-AUC to 93.8% and accuracy to 83.3% at 80% sensitivity. Conclusion
At clinically relevant sensitivity thresholds, the MDI provides improved performance as compared to AMSA, yielding fewer unsuccessful defibrillations. Addition of partial end-tidal carbon dioxide (PetCO2) signal improves accuracy and sensitivity of the MDI prediction model
On the physical origins of the negative index of refraction
The physical origins of negative refractive index are derived from a dilute
microscopic model, producing a result that is generalized to the dense
condensed phase limit. In particular, scattering from a thin sheet of electric
and magnetic dipoles driven above resonance is used to form a fundamental
description for negative refraction. Of practical significance, loss and
dispersion are implicit in the microscopic model. While naturally occurring
negative index materials are unavailable, ferromagnetic and ferroelectric
materials provide device design opportunities.Comment: 4 pages, 1 figur
Identification of individuals with gonorrhoea within sexual networks: a population-based study.
BACKGROUND: Molecular typing of Neisseria gonorrhoeae and contact tracing provide a combined approach for analysis of sexual networks in metropolitan areas, although there are some difficulties in application. Our aim was to examine the application of high-throughput molecular approaches that can identify individuals in linked sexual networks. METHODS: We characterised 2045 isolates of N gonorrhoeae from patients presenting at 13 major sexually transmitted infection clinics in London, UK, between June 1 and Nov 30, 2004. All isolates were assigned a sequence type (strain) on the basis of the sequences of internal fragments of two highly polymorphic loci, por and tbpB. These types were matched to demographic and behavioural data obtained at the clinic for each patient. We assessed the congruence in the demographic and behavioural characteristics of individuals infected with the same strain. FINDINGS: We identified 21 prevalent strains in this diverse gonococcal population, each infecting between 20 and 124 individuals. Seven of these strains were predominantly from men who have sex with men; the remaining 14 were predominantly from heterosexual people. No differences were recorded between the strains associated with men who have sex with men in the demographic or behavioural characteristics of infected individuals. By contrast, significant differences in age (p<0.0001), ethnicity (p=0.001), proportion of women (p=0.01), and HIV status (p=0.03) were noted between the 14 prevalent heterosexual-associated strains. Heterosexuals with strains not shared by others in the sample were significantly older (p=0.0005) and more likely to have had sex outside the UK (p<0.0001) than those sharing a strain with at least one other. INTERPRETATION: The discriminatory high throughput strain characterisation method applied here identified localised transmission networks and suggests little bridging between networks of men who have sex with men and heterosexual networks
Hydrogen peroxide filled poly(methyl methacrylate) microcapsules: potential oxygen delivery materials
This paper describes the synthesis of H2O2āH2O filled poly(methyl methacrylate) (PMMA) microcapsules as potential candidates for controlled O2 delivery. The microcapsules are prepared by a water-in-oil solvent emulsion and evaporation method. The results of this study describe the effect of process parameters on the characteristics of the microcapsules and on their in vitro performance. The size of the microcapsules, as determined from scanning electron microscopy, ranges from ā¼5 to 30 Ī¼m and the size distribution is narrow. The microcapsules exhibit an internal morphology with entrapped H2O2āH2O droplets randomly distributed in the PMMA continuous phase. In vitro release studies of 4.5 wt% H2O2-loaded microcapsules show that ā¼70% of the H2O2 releases in 24 h. This corresponds to a total O2 production of ā¼12 cc/gram of dry microcapsules. Shelf-life studies show that the microcapsules retain ā¼84 wt% of the initially loaded H2O2 after nine months storage at 2ā8 Ā°C, which is an attractive feature for clinical applications
Chronic nitrite treatment activates adenosine monophosphate-activated protein kinase-endothelial nitric oxide synthase pathway in human aortic endothelial cells
Endothelial dysfunction, with impaired bioavailability and/or bioactivity of the vasoprotective molecule, nitric oxide, appears to be a vital step in the initiation of atherosclerosis. Several studies have shown that dietary nitrate/nitrite can have significant benefits on human cardiovascular homeostasis. Although serum nitrite concentrations can reach micromolar levels, the physiological significance of nitrate/nitrite in normal tissues has not been fully elucidated. We investigated in vitro the chronic effects of nitrate/nitrite on endothelial nitric oxide synthase (eNOS) to determine the potential vasoprotective effects of nitrate/nitrite and the underlying molecular mechanisms. Our results demonstrate the expression of phosphorylated eNOS at Ser1177 and phosphorylated adenosine monophosphate activated protein kinase (AMPK) at Thr172 in human aortic endothelial cells were increased after nitrite treatment. We suggest that nitrite stimulation may enhance eNOS activation, which is due, in part, to AMPK activation. The AMPKāeNOS activation by nitrite may be a possible molecular mechanism underlying the vascular protective effects of dietary nitrate
Tailoring Capture-Recapture Methods to Estimate Registry-Based Case Counts Based on Error-Prone Diagnostic Signals
Surveillance research is of great importance for effective and efficient
epidemiological monitoring of case counts and disease prevalence. Taking
specific motivation from ongoing efforts to identify recurrent cases based on
the Georgia Cancer Registry, we extend recently proposed "anchor stream"
sampling design and estimation methodology. Our approach offers a more
efficient and defensible alternative to traditional capture-recapture (CRC)
methods by leveraging a relatively small random sample of participants whose
recurrence status is obtained through a principled application of medical
records abstraction. This sample is combined with one or more existing
signaling data streams, which may yield data based on arbitrarily
non-representative subsets of the full registry population. The key extension
developed here accounts for the common problem of false positive or negative
diagnostic signals from the existing data stream(s). In particular, we show
that the design only requires documentation of positive signals in these
non-anchor surveillance streams, and permits valid estimation of the true case
count based on an estimable positive predictive value (PPV) parameter. We
borrow ideas from the multiple imputation paradigm to provide accompanying
standard errors, and develop an adapted Bayesian credible interval approach
that yields favorable frequentist coverage properties. We demonstrate the
benefits of the proposed methods through simulation studies, and provide a data
example targeting estimation of the breast cancer recurrence case count among
Metro Atlanta area patients from the Georgia Cancer Registry-based Cancer
Recurrence Information and Surveillance Program (CRISP) database
Breast Cancer Screening in Patients With Newly Diagnosed Lung and Colorectal Cancer: A Population-Based Study of Utilization
PurposeāTo assess breast cancer screening utilization in Medicare beneficiaries with colorectal and lung cancer versus cancer-free controls.
MethodsāFemale fee-for-service Medicare beneficiaries who were ā„ 67 years old and diagnosed with lung or colorectal cancer between 2000 and 2011 and who reported to a Surveillance, Epidemiology, and End Results (SEER) registry (case group) were followed for 2 years after their diagnoses, unless death, a diagnosis of breast cancer, or the end of 2013 came first. A similar number of cancer-free controls were individually matched to cases by age, race, registry region, and follow-up time. Screening utilization was defined as the percentage of women with ā„1 screening mammogram during follow-up.
ResultsāOverall, 104,164 cases (48% colorectal, 52% lung; 30% advanced cancer) and 104,164 controls were included. Among women with lung or colorectal cancer, 22% underwent ā„ 1 screening mammogram versus 26% of controls (odds ratio [OR] 0.80; 95% confidence interval [CI] 0.78ā0.82). Stratified by cancer type, 28% of colorectal cancer cases versus 29% of controls (OR 0.98; 95% CI 0.95ā1.01) and 17% of lung cancer cases versus 23% of controls (OR 0.63; 95% CI 0.60ā0.65) received ā„ 1 mammogram. When stratified by stage, 8% with advanced cancer versus 18% of controls (OR 0.33; 95% CI 0.31ā0.35) and 30% with early-stage cancer versus 30% of controls (OR 1; 95% CI 0.97ā1.02) underwent ā„ 1 mammogram.
ConclusionāScreening mammography utilization rates are similar between Medicare beneficiaries with early-stage cancer versus controls. Although the majority of patients with advanced-stage cancer appropriately do not pursue screening mammography, a small number (8%) continue with screening
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