A note on leapfrogging vortex rings

In this paper we provide examples, by numerical simulation using the Navier-Stokes equations for axisymmetric laminar flow, of the 'leapfrogging' motion of two, initially identical, vortex rings which share a common axis of symmetry. We show that the number of clear passes that each ring makes through the other increases with Reynolds number, and that as long as the configuration remains stable the two rings ultimately merge to form a single vortex ring

On the segmentation and classification of hand radiographs

This research is part of a wider project to build predictive models of bone age using hand radiograph images. We examine ways of finding the outline of a hand from an X-ray as the first stage in segmenting the image into constituent bones. We assess a variety of algorithms including contouring, which has not previously been used in this context. We introduce a novel ensemble algorithm for combining outlines using two voting schemes, a likelihood ratio test and dynamic time warping (DTW). Our goal is to minimize the human intervention required, hence we investigate alternative ways of training a classifier to determine whether an outline is in fact correct or not. We evaluate outlining and classification on a set of 1370 images. We conclude that ensembling with DTW improves performance of all outlining algorithms, that the contouring algorithm used with the DTW ensemble performs the best of those assessed, and that the most effective classifier of hand outlines assessed is a random forest applied to outlines transformed into principal components

Defining Meyer's loop-temporal lobe resections, visual field deficits and diffusion tensor tractography

Anterior temporal lobe resection is often complicated by superior quadrantic visual field deficits (VFDs). In some cases this can be severe enough to prohibit driving, even if a patient is free of seizures. These deficits are caused by damage to Meyer's loop of the optic radiation, which shows considerable heterogeneity in its anterior extent. This structure cannot be distinguished using clinical magnetic resonance imaging sequences. Diffusion tensor tractography is an advanced magnetic resonance imaging technique that enables the parcellation of white matter. Using seed voxels antero-lateral to the lateral geniculate nucleus, we applied this technique to 20 control subjects, and 21 postoperative patients. All patients had visual fields assessed with Goldmann perimetry at least three months after surgery. We measured the distance from the tip of Meyer's loop to the temporal pole and horn in all subjects. In addition, we measured the size of temporal lobe resection using postoperative T1-weighted images, and quantified VFDs. Nine patients suffered VFDs ranging from 22% to 87% of the contralateral superior quadrant. In patients, the range of distance from the tip of Meyer's loop to the temporal pole was 24–43 mm (mean 34 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was –15 to +9 mm (mean 0 mm). In controls the range of distance from the tip of Meyer's loop to the temporal pole was 24–47 mm (mean 35 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was –11 to +9 mm (mean 0 mm). Both quantitative and qualitative results were in accord with recent dissections of cadaveric brains, and analysis of postoperative VFDs and resection volumes. By applying a linear regression analysis we showed that both distance from the tip of Meyer's loop to the temporal pole and the size of resection were significant predictors of the postoperative VFDs. We conclude that there is considerable variation in the anterior extent of Meyer's loop. In view of this, diffusion tensor tractography of the optic radiation is a potentially useful method to assess an individual patient's risk of postoperative VFDs following anterior temporal lobe resection

Fractal Stability Border in Plane Couette Flow

We study the dynamics of localised perturbations in plane Couette flow with periodic lateral boundary conditions. For small Reynolds number and small amplitude of the initial state the perturbation decays on a viscous time scale $t \propto Re$. For Reynolds number larger than about 200, chaotic transients appear with life times longer than the viscous one. Depending on the type of the perturbation isolated initial conditions with infinite life time appear for Reynolds numbers larger than about 270--320. In this third regime, the life time as a function of Reynolds number and amplitude is fractal. These results suggest that in the transition region the turbulent dynamics is characterised by a chaotic repeller rather than an attractor.Comment: 4 pages, Latex, 4 eps-figures, submitted to Phys. Rev. Le

Obesity: A Biobehavioral Point of View

Excerpt: If you ask an overweight person, “Why are you fat?’, you will, almost invariably, get the answer, “Because 1 eat too much.” You will get this answer in spite of the fact that of thirteen studies, six find no significant differences in the caloric intake of obese versus nonobese subjects, five report that the obese eat significantly less than the nonobese, and only two report that they eat significantly more

The role of oral antibiotic preparation in elective colorectal surgery: a meta-analysis

© 2018 The Author(s). Published by Wolters Kluwer Health, Inc. Objectives:To compare the impact of the use of oral antibiotics (OAB) with or without mechanical bowel preparation (MBP) on outcome in elective colorectal surgery.Summary Background Data:Meta-analyses have demonstrated that MBP does not impact upon postoperative morbidity or mortality, and as such it should not be prescribed routinely. However, recent evidence from large retrospective cohort and database studies has suggested that there may be a role for combined OAB and MBP, or OAB alone in the prevention of surgical site infection (SSI).Methods:A meta-analysis of randomized controlled trials and cohort studies including adult patients undergoing elective colorectal surgery, receiving OAB with or without MBP was performed. The outcome measures examined were SSI, anastomotic leak, 30-day mortality, overall morbidity, development of ileus, reoperation and Clostridium difficile infection.Results:A total of 40 studies with 69,517 patients (28 randomized controlled trials, n = 6437 and 12 cohort studies, n = 63,080) were included. The combination of MBP+OAB versus MBP alone was associated with a significant reduction in SSI [risk ratio (RR) 0.51, 95% confidence interval (CI) 0.46-0.56, P < 0.00001, I2 = 13%], anastomotic leak (RR 0.62, 95% CI 0.55-0.70, P < 0.00001, I2 = 0%), 30-day mortality (RR 0.58, 95% CI 0.44-0.76, P < 0.0001, I2 = 0%), overall morbidity (RR 0.67, 95% CI 0.63-0.71, P < 0.00001, I2 = 0%), and development of ileus (RR 0.72, 95% CI 0.52-0.98, P = 0.04, I2 = 36%), with no difference in Clostridium difficile infection rates. When a combination of MBP+OAB was compared with OAB alone, no significant difference was seen in SSI or anastomotic leak rates, but there was a significant reduction in 30-day mortality, and incidence of postoperative ileus with the combination. There is minimal literature available on the comparison between combined MBP+OAB versus no preparation, OAB alone versus no preparation, and OAB versus MBP.Conclusions:Current evidence suggests a potentially significant role for OAB preparation, either in combination with MBP or alone, in the prevention of postoperative complications in elective colorectal surgery. Further high-quality evidence is required to differentiate between the benefits of combined MBP+OAB or OAB alone

Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure

The evolution of rotating stars with zero-age main sequence (ZAMS) masses in the range 8 to 25 M_sun is followed through all stages of stable evolution. The initial angular momentum is chosen such that the star's equatorial rotational velocity on the ZAMS ranges from zero to ~ 70 % of break-up. Redistribution of angular momentum and chemical species are then followed as a consequence of rotationally induced circulation and instablities. The effects of the centrifugal force on the stellar structure are included. Uncertain mixing efficiencies are gauged by observations. We find, as noted in previous work, that rotation increases the helium core masses and enriches the stellar envelopes with products of hydrogen burning. We determine, for the first time, the angular momentum distribution in typical presupernova stars along with their detailed chemical structure. Angular momentum loss due to (non-magnetic) stellar winds and the redistribution of angular momentum during core hydrogen burning are of crucial importance for the specific angular momentum of the core. Neglecting magnetic fields, we find angular momentum transport from the core to the envelope to be unimportant after core helium burning. We obtain specific angular momenta for the iron core and overlaying material of 1E16...1E17 erg s. These values are insensitive to the initial angular momentum. They are small enough to avoid triaxial deformations of the iron core before it collapses, but could lead to neutron stars which rotate close to break-up. They are also in the range required for the collapsar model of gamma-ray bursts. The apparent discrepancy with the measured rotation rates of young pulsars is discussed.Comment: 62 pages, including 7 tables and 19 figures. Accepted by Ap

Can screening and brief intervention lead to population-level reductions in alcohol-related harm?

A distinction is made between the clinical and public health justifications for screening and brief intervention (SBI) against hazardous and harmful alcohol consumption. Early claims for a public health benefit of SBI derived from research on general medical practitioners' (GPs') advice on smoking cessation, but these claims have not been realized, mainly because GPs have not incorporated SBI into their routine practice. A recent modeling exercise estimated that, if all GPs in England screened every patient at their next consultation, 96% of the general population would be screened over 10 years, with 70-79% of excessive drinkers receiving brief interventions (BI); assuming a 10% success rate, this would probably amount to a population-level effect of SBI. Thus, a public health benefit for SBI presupposes widespread screening; but recent government policy in England favors targeted versus universal screening, and in Scotland screening is based on new registrations and clinical presentation. A recent proposal for a national screening program was rejected by the UK National Health Service's National Screening Committee because 1) there was no good evidence that SBI led to reductions in mortality or morbidity, and 2) a safe, simple, precise, and validated screening test was not available. Even in countries like Sweden and Finland, where expensive national programs to disseminate SBI have been implemented, only a minority of the population has been asked about drinking during health-care visits, and a minority of excessive drinkers has been advised to cut down. Although there has been research on the relationship between treatment for alcohol problems and population-level effects, there has been no such research for SBI, nor have there been experimental investigations of its relationship with population-level measures of alcohol-related harm. These are strongly recommended. In this article, conditions that would allow a population-level effect of SBI to occur are reviewed, including their political acceptability. It is tentatively concluded that widespread dissemination of SBI, without the implementation of alcohol control measures, might have indirect influences on levels of consumption and harm but would be unlikely on its own to result in public health benefits. However, if and when alcohol control measures were introduced, SBI would still have an important role in the battle against alcohol-related harm