Ion Heating and Flow Driven by an Instability Found in Plasma Couette Flow.

We present the first observation of instability in weakly magnetized, pressure dominated plasma Couette flow firmly in the Hall regime. Strong Hall currents couple to a low frequency electromagnetic mode that is driven by high-ß (>1) pressure profiles. Spectroscopic measurements show heating (factor of 3) of the cold, unmagnetized ions via a resonant Landau damping process. A linear theory of this instability is derived that predicts positive growth rates at finite ß and shows the stabilizing effect of very large ß, in line with observations.

Laboratory Resolved Structure of Supercritical Perpendicular Shocks.

Supermagnetosonic perpendicular flows are magnetically driven by a large radius theta-pinch experiment. Fine spatial resolution and macroscopic coverage allow the full structure of the plasma-piston coupling to be resolved in laboratory experiment for the first time. A moving ambipolar potential is observed to reflect unmagnetized ions to twice the piston speed. Magnetized electrons balance the radial potential via Hall currents and generate signature quadrupolar magnetic fields. Electron heating in the reflected ion foot is adiabatic.

Weakly Magnetized, Hall Dominated Plasma Couette Flow.

A novel plasma equilibrium in the high-ß, Hall regime that produces centrally peaked, high Mach number Couette flow is described. Flow is driven using a weak, uniform magnetic field and large, cross field currents. Large magnetic field amplification (factor 20) due to the Hall effect is observed when electrons are flowing radially inward, and near perfect field expulsion is observed when the flow is reversed. A dynamic equilibrium is reached between the amplified (removed) field and extended density gradients.

Representation and complementarity of the long-term coral monitoring on the Great Barrier Reef.

Effective environmental management hinges on efficient and targeted monitoring, which in turn should adapt to increasing disturbance regimes that now characterize most ecosystems. Habitats and biodiversity of Australia's Great Barrier Reef (GBR), the world's largest coral reef ecosystem, are in declining condition, prompting a review of the effectiveness of existing coral monitoring programs. Applying a regional model of coral cover (i.e., the most widely used proxy for coral reef condition globally) within major benthic communities, we assess the representation and complementarity of existing long-term coral reef monitoring programs on the GBR. We show that existing monitoring has captured up to 45% of the environmental diversity on the GBR, while some geographic areas (including major hotspots of cyclone activity over the last 30 yr) have remained unmonitored. Further, we identified complementary groups of reefs characterized by similar benthic community composition and similar coral cover trajectories since 1996. The mosaic of their distribution across the GBR reflects spatial variation in the cumulative impact of multiple acute disturbances, as well as spatial gradients in coral recovery potential. Representation and complementarity, in combination with other performance assessment criteria, can inform the cost-effective design and stratification of future surveys. Based on these results, we formulate recommendations to assist with the design of future long-term coral reef monitoring programs.

Validation and comparison of geostatistical and spline models for spatial stream networks.

Scientists need appropriate spatial-statistical models to account for the unique features of stream network data. Recent advances provide a growing methodological toolbox for modelling these data, but general-purpose statistical software has only recently emerged, with little information about when to use different approaches. We implemented a simulation study to evaluate and validate geostatistical models that use continuous distances, and penalised spline models that use a finite discrete approximation for stream networks. Data were simulated from the geostatistical model, with performance measured by empirical prediction and fixed effects estimation. We found that both models were comparable in terms of squared error, with a slight advantage for the geostatistical models. Generally, both methods were unbiased and had valid confidence intervals. The most marked differences were found for confidence intervals on fixed-effect parameter estimates, where, for small sample sizes, the spline models underestimated variance. However, the penalised spline models were always more computationally efficient, which may be important for real-time prediction and estimation. Thus, decisions about which method to use must be influenced by the size and format of the data set, in addition to the characteristics of the environmental process and the modelling goals. ©2015 The Authors. Environmetrics published by John Wiley & Sons, Ltd.

An experiment on the dynamics of ion implantation and sputtering of surfaces.

A major impediment towards a better understanding of the complex plasma-surface interaction is the limited diagnostic access to the material surface while it is undergoing plasma exposure. The Dynamics of ION Implantation and Sputtering Of Surfaces (DIONISOS) experiment overcomes this limitation by uniquely combining powerful, non-perturbing ion beam analysis techniques with a steady-state helicon plasma exposure chamber, allowing for real-time, depth-resolved in situ measurements of material compositions during plasma exposure. Design solutions are described that provide compatibility between the ion beam analysis requirements in the presence of a high-intensity helicon plasma. The three primary ion beam analysis techniques, Rutherford backscattering spectroscopy, elastic recoil detection, and nuclear reaction analysis, are successfully implemented on targets during plasma exposure in DIONISOS. These techniques measure parameters of interest for plasma-material interactions such as erosion/deposition rates of materials and the concentration of plasma fuel species in the material surface.

Prevalence of hypertrophic cardiomyopathy in an outpatient population referred for echocardiographic study.

Although hypertrophic cardiomyopathy (HC) is believed to be a relatively uncommon cardiac disease, the frequency with which it occurs in the general or cardiac population has not been defined. To address this issue, the patient population of a community-based echocardiography laboratory was used to assess the prevalence of HC in 714 consecutively studied outpatients with (or suspected of having) heart disease. The most common cardiac disease identified was mitral valve prolapse (73 patients [10%]), and HC was present in 4 patients (0.5%). Ages were 50 to 69 years. Maximal left ventricular wall thicknessess were 15 to 22 mm (mean 19); only 1 had evidence of obstruction to left ventricular outflow by virtue of marked mitral valve systolic anterior motion. Before echocardiographic study, each of the 4 patients with HC had signs or symptoms of cardiac disease, but the correct diagnosis had not been suspected. Of 11 other patients who were referred for echocardiographic study because of a clinical suspicion of HC, none proved to have this disease. The present study demonstrates that HC is a particularly uncommon disease entity occurring in about 0.5% of an unselected outpatient population referred for echocardiographic study.

Coexistence of mitral valve prolapse in a consecutive group of 528 patients with hypertrophic cardiomyopathy assessed with echocardiography.

Hypertrophic cardiomyopathy and mitral valve prolapse are both conditions that may be genetically transmitted and incur a risk for sudden cardiac death. Although the small left ventricular cavity and distorted geometry characteristic of hypertrophic cardiomyopathy might suggest a predisposition to mitral valve prolapse, the frequency with which these two entities coexist and the potential clinical significance of such an association are not known. To further define the relation of hypertrophic cardiomyopathy and mitral valve prolapse, 528 consecutive patients with hypertrophic cardiomyopathy were studied by echocardiography. Patients ranged in age from 1 to 86 years (mean 45); 335 (63%) were male. Unequivocal echocardiographic evidence of systolic mitral valve prolapse into the left atrium was identified in only 16 (3%) of the 528 patients. The mitral valve excised at operation from three of the patients had morphologic characteristics of a floppy mitral valve, which was judged to be responsible for the echocardiographic findings. Occurrence of clinically evident atrial fibrillation was common in patients with hypertrophic cardiomyopathy and mitral valve prolapse (9 [56%] of 16). Hence, in a large group of patients with hypertrophic cardiomyopathy, the association of echocardiographically documented mitral valve prolapse was uncommon. The coexistence of mitral valve prolapse in patients with hypertrophic cardiomyopathy appears to predispose such patients to atrial fibrillation.