Activation of MHD reconnection on ideal timescales

Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number $S$, up to $10^7$. Results confirm that when the critical aspect ratio of $S^{1/3}$ is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfv\'enic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number $P=1$ in the viscous regime.Comment: Accepted for publication in Plasma Physics and Controlled Fusio

An experimental study of dynamic stall on advanced airfoil sections. Volume 1: Summary of the experiment

The static and dynamic characteristics of seven helicopter sections and a fixed-wing supercritical airfoil were investigated over a wide range of nominally two dimensional flow conditions, at Mach numbers up to 0.30 and Reynolds numbers up to 4 x 10 to the 6th power. Details of the experiment, estimates of measurement accuracy, and test conditions are described in this volume (the first of three volumes). Representative results are also presented and comparisons are made with data from other sources. The complete results for pressure distributions, forces, pitching moments, and boundary-layer separation and reattachment characteristics are available in graphical form in volumes 2 and 3. The results of the experiment show important differences between airfoils, which would otherwise tend to be masked by differences in wind tunnels, particularly in steady cases. All of the airfoils tested provide significant advantages over the conventional NACA 0012 profile. In general, however, the parameters of the unsteady motion appear to be more important than airfoil shape in determining the dynamic-stall airloads

An experimental study of dynamic stall on advanced airfoil section. Volume 2: Pressure and force data

Experimentally derived force and moment data are presented for eight airfoil sections that were tested at fixed and varying incidence in a subsonic two dimensional stream. Airfoil incidence was varied through sinusoidal oscillations in pitch over a wide range of amplitude and frequency. The surface pressure distribution, as well as the lift, drag, and pitching moment derived therefrom, are displayed in a uniform fashion to delineate the static and dynamic characteristics of each airfoil both in and out of stall

The structure of trailing vortices generated by model rotor blades

Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described

Astrocytes and Microglia and Their Potential Link with Autism Spectrum Disorders.

The cellular mechanism(s) underlying autism spectrum disorders (ASDs) are not fully understood although it has been shown that various genetic and environmental factors contribute to their etiology. As increasing evidence indicates that astrocytes and microglial cells play a major role in synapse maturation and function, and there is evidence of deficits in glial cell functions in ASDs, one current hypothesis is that glial dysfunctions directly contribute to their pathophysiology. The aim of this review is to summarize microglia and astrocyte functions in synapse development and their contributions to ASDs

From growth goals to proactive organizational resilience: first evidence in women-led and non-women-led Italian wineries

In a fast-changing world, characterized by evenly unexpected challenges and shocks, being resilient is a crucial aspect for every organization. Drawing from the goal setting theory and the double standards of competence perspective, this study aims at understanding the antecedents of organizational proactive resilience. More precisely, it looks at the impact of quantitative and qualitative organizational growth goals on proactive resilience, distinguishing between women-led and non-women-led firms. Based on a unique sample of 167 Italian wineries (67 women-led and 100 non-women-led), this paper tests this theoretical model using path analysis techniques. The wine sector is a particularly interesting context to study the phenomenon due to its exposure to natural disasters, new consumers' behaviours that are requiring firms to continuously innovate and differentiate in a traditionally low-tech sector, but also changes happening at wineries' management level. In fact, the sector has been traditionally male dominated, but women are increasingly taking the lead. The findings indicate that growth goals differently contribute to proactive organizational resilience, but their effects vary in women- and non-women-led businesses. Specifically, these results suggest that in women-led wineries, proactive organizational resilience depends on quantitative growth goals while in non-women-led wineries businesses this depends on qualitative growth goals