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Search Results: 1 - 10 of 53165 matches for " David Paterson "
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Banishing divergence Part 2: Limits of oscillatory sequences, and applications
David Alan Paterson
Mathematics , 2011,
Abstract: Sequences diverge either because they head off to infinity or because they oscillate. Part 1 \cite{Part1} of this paper laid the pure mathematics groundwork by defining Archimedean classes of infinite numbers as limits of smooth sequences. Part 2 follows that with applied mathematics, showing that general sequences can usually be converted into smooth sequences, and thus have a well-defined limit. Each general sequence is split into the sum of smooth, periodic (including Lebesgue integrable), chaotic and random components. The mean of each of these components divided by a smooth sequence, or the mean of the mean, will usually be a smooth sequence, and so the oscillatory sequence will have at least a leading term limit. Examples of limits of oscillatory sequences with well-defined limits are given. Methodologies are included for a way to calculate limits on the reals and on complex numbers, a way to evaluate improper integrals by limit of a Riemann sum, and a way to square the Dirac delta function.
Banishing divergence Part 1: Infinite numbers as the limit of sequences of real numbers
David Alan Paterson
Mathematics , 2011,
Abstract: Sequences diverge either because they head off to infinity or because they oscillate. Part 1 constructs a non-Archimedean framework of infinite numbers that is large enough to contain asymptotic limit points for non-oscillating sequences that head off to infinity. It begins by defining Archimedean classes of infinite numbers. Each class is denoted by a prototype sequence. These prototypes are used as asymptotes for determining leading term limits of sequences. By subtracting off leading term limits and repeating, limits are obtained for a subset of sequences called here ``smooth sequences". $\mathbb{I}_n$ is defined as the set of ratios of limits of smooth sequences. It is shown that $\mathbb{I}_n$ is an ordered field that includes real, infinite and infinitesimal numbers.
A gastrointestinal stromal tumour presenting incidentally with haemorrhage and perforation associated with a Meckel's diverticulum: a case report
Richard Woolf, Natalie Blencowe, Karim Muhammad, David Paterson, Geoff Pye
Journal of Medical Case Reports , 2009, DOI: 10.4076/1752-1947-3-7423
Abstract: A 59-year-old Caucasian man presented with acute right iliac fossa pain with localized peritonism. At surgery, he was found to have a perforated and haemorrhagic Meckel's diverticulum, associated with a gastrointestinal stromal tumour within the apex of the diverticulum. The absence of necrosis and a low mitotic rate indicated primary resection with subsequent computed tomography surveillance to be the most appropriate management strategy.We report a unique triad of complications associated with the presentation of a Meckel's diverticulum. This article reviews this common congenital abnormality and discusses the management of a gastrointestinal tumour. Meckel's diverticulum will mimic other intra-abdominal pathologies in presentation and should therefore often be considered as a differential diagnosis.This is the first reported case of perforation and haemorrhage of a Meckel's diverticulum leading to the incidental finding of a gastrointestinal stromal tumour within the diverticulum. Meckel's diverticulum is the most common congenital abnormality of the gastrointestinal tract, however, when symptomatic, it is often misdiagnosed at presentation. Common complications presenting in adults include bleeding, obstruction, diverticulitis and perforation. Tumours within a Meckel's diverticulum are a rare but recognised complication.A 59-year-old Caucasian man presented with peri-umbilical pain that had localized to the right iliac fossa. On examination, he was tender in the right iliac fossa, with localized peritonism. His white cell count was 10.2 × 109 (neutrophils 8.1 × 109) and with C-reactive protein (CRP) <5. Acute appendicitis was diagnosed clinically and a diagnostic laparoscopy performed.A perforated Meckel's diverticulum was found, associated with free intra-abdominal fluid and haemorrhage. At subsequent laparotomy, 75 mm of small bowel was resected and primary anastamosis was performed. Histology confirmed a Meckel's diverticulum and with a 25 mm area of perforat
A novel joint location-scale testing framework for improved detection of variants with main or interaction effects
David Soave,Andrew Paterson,Lisa Strug,Lei Sun
Statistics , 2014,
Abstract: We propose a novel and easy-to-implement joint location-scale association testing procedure that can account for complex genetic architecture without explicitly modeling interaction effects, and is suitable for large-scale whole-genome scans and meta-analyses. We focus on Fisher's method and use it to combine evidence from the standard location test and the more recent scale test, and we describe its use for single-variant, gene-set and pathway association analyses.
Cost-Effectiveness of a Central Venous Catheter Care Bundle
Kate A. Halton,David Cook,David L. Paterson,Nasia Safdar,Nicholas Graves
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012815
Abstract: A bundled approach to central venous catheter care is currently being promoted as an effective way of preventing catheter-related bloodstream infection (CR-BSI). Consumables used in the bundled approach are relatively inexpensive which may lead to the conclusion that the bundle is cost-effective. However, this fails to consider the nontrivial costs of the monitoring and education activities required to implement the bundle, or that alternative strategies are available to prevent CR-BSI. We evaluated the cost-effectiveness of a bundle to prevent CR-BSI in Australian intensive care patients.
Cost effectiveness of antimicrobial catheters in the intensive care unit: addressing uncertainty in the decision
Kate A Halton, David A Cook, Michael Whitby, David L Paterson, Nicholas Graves
Critical Care , 2009, DOI: 10.1186/cc7744
Abstract: We used a Markov decision model to compare the cost effectiveness of A-CVCs relative to uncoated catheters. Four catheter types were evaluated: minocycline and rifampicin (MR)-coated catheters, silver, platinum and carbon (SPC)-impregnated catheters, and two chlorhexidine and silver sulfadiazine-coated catheters; one coated on the external surface (CH/SSD (ext)) and the other coated on both surfaces (CH/SSD (int/ext)). The incremental cost per quality-adjusted life year gained and the expected net monetary benefits were estimated for each. Uncertainty arising from data estimates, data quality and heterogeneity was explored in sensitivity analyses.The baseline analysis, with no consideration of uncertainty, indicated all four types of A-CVC were cost-saving relative to uncoated catheters. MR-coated catheters prevented 15 infections per 1,000 catheters and generated the greatest health benefits, 1.6 quality-adjusted life years, and cost savings (AUD $130,289). After considering uncertainty in the current evidence, the MR-coated catheters returned the highest incremental monetary net benefits of AUD $948 per catheter; however there was a 62% probability of error in this conclusion. Although the MR-coated catheters had the highest monetary net benefits across multiple scenarios, the decision was always associated with high uncertainty.Current evidence suggests that the cost effectiveness of using A-CVCs within the ICU is highly uncertain. Policies to prevent CR-BSI amongst ICU patients should consider the cost effectiveness of competing interventions in the light of this uncertainty. Decision makers would do well to consider the current gaps in knowledge and the complexity of producing good quality evidence in this area.Catheter-related bloodstream infections (CR-BSIs) increase health costs and patient morbidity [1], and their prevention has been the target of national initiatives to create safer and more efficient healthcare systems [2,3]. These healthcare-acquired inf
Vancomycin Heteroresistance Is Associated with Reduced Mortality in ST239 Methicillin-Resistant Staphylococcus aureus Blood Stream Infections
Sebastiaan J. van Hal, Mark Jones, Iain B. Gosbell, David L. Paterson
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021217
Abstract: Background Despite hVISA infections being associated with vancomycin treatment failure, no previous study has been able to detect a mortality difference between heteroresistant vancomycin intermediate Staphylococcus aureus (hVISA) and vancomycin susceptible Staphylococcus aureus (VSSA) bloodstream infections (BSI). Methodology Consecutive methicillin-resistant S. aureus (MRSA) BSI episodes between 1996 and 2008 were reviewed. Patient demographics, clinical presentation, treatment and overall mortality at 30 days were extracted from the medical records. All isolates underwent vancomycin minimum inhibitory concentration (VMIC) testing by broth microdilution and Etest. hVISA was confirmed by population analysis profiling using the area under the curve method (PAP-AUC). Principal Findings 401 evaluable MRSA BSI episodes were identified over the 12 years. Of these, 46 (11.5%) and 2 (0.5%) were confirmed as hVISA and VISA by PAP-AUC respectively. hVISA predominantly occurred in ST239-like MRSA isolates with high VMIC (2 mg/L). Compared to VSSA, hVISA was associated with chronic renal failure (p<0.001), device related infections (haemodialysis access) (p<0.001) and previous vancomycin usage (p = 0.004). On multivariate analysis, independent predictors of mortality included age, presence of multiple co-morbidities, principal diagnosis, transit to ICU and severity of illness while infection related surgery and hVISA phenotype were associated with increased survival. Conclusions/Significance The presence of hVISA is dependent on the appropriate interplay between host and pathogen factors. hVISA in ST239 MRSA is an independent predictor of survival. Whether these findings would be replicated across all MRSA clones is unknown and warrants further study.
Impairment of the Bacterial Biofilm Stability by Triclosan
Helen V. Lubarsky, Sabine U. Gerbersdorf, Cédric Hubas, Sebastian Behrens, Francesco Ricciardi, David M. Paterson
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0031183
Abstract: The accumulation of the widely-used antibacterial and antifungal compound triclosan (TCS) in freshwaters raises concerns about the impact of this harmful chemical on the biofilms that are the dominant life style of microorganisms in aquatic systems. However, investigations to-date rarely go beyond effects at the cellular, physiological or morphological level. The present paper focuses on bacterial biofilms addressing the possible chemical impairment of their functionality, while also examining their substratum stabilization potential as one example of an important ecosystem service. The development of a bacterial assemblage of natural composition – isolated from sediments of the Eden Estuary (Scotland, UK) – on non-cohesive glass beads (<63 μm) and exposed to a range of triclosan concentrations (control, 2 – 100 μg L?1) was monitored over time by Magnetic Particle Induction (MagPI). In parallel, bacterial cell numbers, division rate, community composition (DGGE) and EPS (extracellular polymeric substances: carbohydrates and proteins) secretion were determined. While the triclosan exposure did not prevent bacterial settlement, biofilm development was increasingly inhibited by increasing TCS levels. The surface binding capacity (MagPI) of the assemblages was positively correlated to the microbial secreted EPS matrix. The EPS concentrations and composition (quantity and quality) were closely linked to bacterial growth, which was affected by enhanced TCS exposure. Furthermore, TCS induced significant changes in bacterial community composition as well as a significant decrease in bacterial diversity. The impairment of the stabilization potential of bacterial biofilm under even low, environmentally relevant TCS levels is of concern since the resistance of sediments to erosive forces has large implications for the dynamics of sediments and associated pollutant dispersal. In addition, the surface adhesive capacity of the biofilm acts as a sensitive measure of ecosystem effects.
Impact of biodiversity-climate futures on primary production and metabolism in a model benthic estuarine system
Natalie Hicks, Mark T Bulling, Martin Solan, Dave Raffaelli, Piran CL White, David M Paterson
BMC Ecology , 2011, DOI: 10.1186/1472-6785-11-7
Abstract: The effects of elevated CO2 concentration, temperature and invertebrate diversity were not additive, rather they interacted to determine MPB biomass, and overall this effect was negative. Diversity effects were underpinned by strong species composition effects, illustrating the importance of individual species identity.Overall, our findings suggest that in natural systems, the complex interactions between changing environmental conditions and any associated changes in invertebrate assemblage structure are likely to reduce MPB biomass. Furthermore, these effects would be sufficient to affect the net metabolic balance of the coastal ecosystem, with important implications for system ecology and sustainable exploitation.Rising global temperatures and increasing atmospheric CO2 concentrations are causing changes to a wide range of ecosystems [1]. The influence of these changing conditions on ocean chemistry and the distribution of species in marine systems [2-4] is of particular concern. Atmospheric concentrations of CO2 have risen from pre-industrial levels (275 ppmv) to 370 ppmv and continue to increase by ~1.5 ppmv yr-1 [5]. Up to 50% of the global increase in carbon dioxide has been absorbed by the oceans [6] and the pH of the sea is predicted to fall by up to 0.5 pH units by the end of the century [2]. Concerns over the likely consequences are now widespread [7,8]. Studies of elevated carbon dioxide concentrations have demonstrated potential impacts on nutrient availability, primary productivity and decomposition [1,9,10]. This directly influences the functionality of ecosystems [9] across multiple trophic levels [11] and effects are difficult to anticipate.Empirical research to date has concentrated on the responses of a variety of ecosystems to individual anthropogenic drivers of change (terrestrial [12]; marine [13]; terrestrial soil [14]; freshwater [9]), and few studies have considered the combined effects of multiple drivers [15]. This is of particular importa
The SARD variety of multifractality of ventricular epicardial mapping during ischemia
Ying Chen,Martyn P. Nash,Xinbao Ning,Yelin Wang,David J. Paterson,Jun Wang
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-0809-x
Abstract: We have analyzed cardiac ischemia-reperfusion in an animal model using epicardial electropotential mapping. We investigated the relationship between ischemia and variability of multifractality in epicardial electrograms. We present a new parameter called the singularity spectrum area reference dispersion (SARD) that clearly demonstrates the change in multifractility with the extent of myocardiaischemia. By contrasting the 3D ventricular epicardial SARD map with the activation map, we conclude that myocardial ischemia significantly influences the variety of multifractality of ventricular epicardium electrograms and the SARD parameter is useful in correlating multifractality of epicardial electrograms with location of ischemia closely.
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