Spherical single-roll dynamos at large magnetic Reynolds numbers

This paper concerns kinematic helical dynamos in a spherical fluid body surrounded by an insulator. In particular, we examine their behaviour in the regime of large magnetic Reynolds number \Rm, for which dynamo action is usually concentrated upon a simple resonant stream-surface. The dynamo eigensolutions are computed numerically for two representative single-roll flows using a compact spherical harmonic decomposition and fourth-order finite-differences in radius. These solutions are then compared with the growth rates and eigenfunctions of the Gilbert and Ponty (2000) large \Rm asymptotic theory. We find good agreement between the growth rates when \Rm>10^4, and between the eigenfunctions when \Rm>10^5.Comment: 36 pages, 8 figures. V2: incorrect labels in Fig3 corrected. The article appears in Physics of Fluids, 22, 066601, and may be found at http://pof.aip.org/phfle6/v22/i6/p066601_s1 . (Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics

Kinematic roll dynamo computations at large magnetic Reynolds number

The behaviour of the magnetic field produced by spherical kinematic dynamos at large magnetic Reynolds number for two stationary axisymmetric roll flows is examined. Five numerical techniques to solve the large banded eigenvalue problems, which arise for the growth rate of the magnetic field, are compared, particularly their performance when eigenvalues are closely clustered. The five eigenvalue methods are inverse iteration, orthogonal iteration, lop-sided iteration, the implicitly restarted Arnoldi method and the non-symmetric Lanczos method. A shift and invert strategy was employed to obtain the growth rates of largest real part

Magnetohydrodynamic activity inside a sphere

We present a computational method to solve the magnetohydrodynamic equations in spherical geometry. The technique is fully nonlinear and wholly spectral, and uses an expansion basis that is adapted to the geometry: Chandrasekhar-Kendall vector eigenfunctions of the curl. The resulting lower spatial resolution is somewhat offset by being able to build all the boundary conditions into each of the orthogonal expansion functions and by the disappearance of any difficulties caused by singularities at the center of the sphere. The results reported here are for mechanically and magnetically isolated spheres, although different boundary conditions could be studied by adapting the same method. The intent is to be able to study the nonlinear dynamical evolution of those aspects that are peculiar to the spherical geometry at only moderate Reynolds numbers. The code is parallelized, and will preserve to high accuracy the ideal magnetohydrodynamic (MHD) invariants of the system (global energy, magnetic helicity, cross helicity). Examples of results for selective decay and mechanically-driven dynamo simulations are discussed. In the dynamo cases, spontaneous flips of the dipole orientation are observed.Comment: 15 pages, 19 figures. Improved figures, in press in Physics of Fluid

Supporting Aboriginal Community Controlled Health Services to deliver alcohol care : Protocol for a cluster randomised controlled trial

Introduction Indigenous peoples who have experienced colonisation or oppression can have a higher prevalence of alcohol-related harms. In Australia, Aboriginal Community Controlled Health Services (ACCHSs) offer culturally accessible care to Aboriginal and Torres Strait Islander (Indigenous) peoples. However there are many competing health, socioeconomic and cultural client needs. Methods and analysis A randomised cluster wait-control trial will test the effectiveness of a model of tailored and collaborative support for ACCHSs in increasing use of alcohol screening (with Alcohol Use Disorders Identification Test-Consumption (AUDIT-C)) and of treatment provision (brief intervention, counselling or relapse prevention medicines). Setting Twenty-two ACCHSs across Australia. Randomisation Services will be stratified by remoteness, then randomised into two groups. Half receive support soon after the trial starts (intervention or ‘early support’); half receive support 2 years later (wait-control or ‘late support’). The support Core support elements will be tailored to local needs and include: support to nominate two staff as champions for increasing alcohol care; a national training workshop and bimonthly teleconferences for service champions to share knowledge; onsite training, and bimonthly feedback on routinely collected data on screening and treatment provision. Outcomes and analysis Primary outcome is use of screening using AUDIT-C as routinely recorded on practice software. Secondary outcomes are recording of brief intervention, counselling, relapse prevention medicines; and blood pressure, gamma glutamyltransferase and HbA1c. Multi-level logistic regression will be used to test the effectiveness of support. Ethics and dissemination Ethical approval has been obtained from eight ethics committees: the Aboriginal Health and Medical Research Council of New South Wales (1217/16); Central Australian Human Research Ethics Committee (CA-17-2842); Northern Territory Department of Health and Menzies School of Health Research (2017-2737); Central Queensland Hospital and Health Service (17/QCQ/9); Far North Queensland (17/QCH/45-1143); Aboriginal Health Research Ethics Committee, South Australia (04-16-694); St Vincent’s Hospital (Melbourne) Human Research Ethics Committee (LRR 036/17); and Western Australian Aboriginal Health Ethics Committee (779). Trial registration number ACTRN12618001892202; Pre-results

Sample size calculations for the design of cluster randomized trials: A summary of methodology.

Cluster randomized trial designs are growing in popularity in, for example, cardiovascular medicine research and other clinical areas and parallel statistical developments concerned with the design and analysis of these trials have been stimulated. Nevertheless, reviews suggest that design issues associated with cluster randomized trials are often poorly appreciated and there remain inadequacies in, for example, describing how the trial size is determined and the associated results are presented. In this paper, our aim is to provide pragmatic guidance for researchers on the methods of calculating sample sizes. We focus attention on designs with the primary purpose of comparing two interventions with respect to continuous, binary, ordered categorical, incidence rate and time-to-event outcome variables. Issues of aggregate and non-aggregate cluster trials, adjustment for variation in cluster size and the effect size are detailed. The problem of establishing the anticipated magnitude of between- and within-cluster variation to enable planning values of the intra-cluster correlation coefficient and the coefficient of variation are also described. Illustrative examples of calculations of trial sizes for each endpoint type are included

Using breath carbon monoxide to validate self-reported tobacco smoking in remote Australian Indigenous communities

Background: This paper examines the specificity and sensitivity of a breath carbon monoxide (BCO) test and\ud optimum BCO cutoff level for validating self-reported tobacco smoking in Indigenous Australians in Arnhem Land,\ud Northern Territory (NT).\ud \ud Methods: In a sample of 400 people (≥16 years) interviewed about tobacco use in three communities, both selfreported\ud smoking and BCO data were recorded for 309 study participants. Of these, 249 reported smoking tobacco\ud within the preceding 24 hours, and 60 reported they had never smoked or had not smoked tobacco for ≥6\ud months. The sample was opportunistically recruited using quotas to reflect age and gender balances in the\ud communities where the combined Indigenous populations comprised 1,104 males and 1,215 females (≥16 years).\ud Local Indigenous research workers assisted researchers in interviewing participants and facilitating BCO tests using\ud a portable hand-held analyzer.\ud \ud Results: A BCO cutoff of ≥7 parts per million (ppm) provided good agreement between self-report and BCO\ud (96.0% sensitivity, 93.3% specificity). An alternative cutoff of ≥5 ppm increased sensitivity from 96.0% to 99.6% with no change in specificity (93.3%). With data for two self-reported nonsmokers who also reported that they smoked\ud cannabis removed from the analysis, specificity increased to 96.6%.\ud \ud Conclusion: In these disadvantaged Indigenous populations, where data describing smoking are few, testing for\ud BCO provides a practical, noninvasive, and immediate method to validate self-reported smoking. In further studies\ud of tobacco smoking in these populations, cannabis use should be considered where self-reported nonsmokers\ud show high BCO

The Be Our Ally Beat Smoking (BOABS) study, a randomised controlled trial of an intensive smoking cessation intervention in a remote aboriginal Australian health care setting

Background: Australian Aboriginal and Torres Strait Islander peoples (Indigenous Australians) smoke at much higher rates than non-Indigenous people and smoking is an important contributor to increased disease, hospital admissions and deaths in Indigenous Australian populations. Smoking cessation programs in Australia have not had the same impact on Indigenous smokers as on non-Indigenous smokers. This paper describes the outcome of a study that aimed to test the efficacy of a locally-tailored, intensive, multidimensional smoking cessation program. Methods: A randomised controlled trial of Aboriginal researcher delivered tailored smoking cessation counselling during face-to-face visits, aiming for weekly for the first four weeks, monthly to six months and two monthly to12 months. The control (“usual care”) group received routine care relating to smoking cessation at their local primary health care service. Data collection occurred at enrolment, six and 12 months. The primary outcome was self-reported smoking cessation with urinary cotinine confirmation at final follow-up (median 13 (interquartile range 12–15) months after enrolment).Results: Participants in the intervention (n = 55) and usual care (n = 108) groups were similar in baseline characteristics, except the intervention group was slightly older. At final follow-up the smoking cessation rate for participants assigned to the intervention group (n = 6; 11%), while not statistically significant, was double that of usual care (n = 5; 5%; p = 0.131). A meta-analysis of these findings and a similarly underpowered but comparable study of pregnant Indigenous Australian women showed that Indigenous Australian participants assigned to the intervention groups were 2.4 times (95% CI, 1.01-5.5) as likely to quit as participants assigned to usual care. Conclusions: Culturally appropriate, multi-dimensional Indigenous quit smoking programs can be successfully implemented in remote primary health care. Intensive one-on-one interventions with substantial involvement from Aboriginal and Torres Strait Islander workers are likely to be effective in these settings. Trial registration: Australian New Zealand Clinical Trials Registry (ACTRN12608000604303)