Duration of heart failure and the risk of atrial fibrillation: different mechanisms at different times?

Chronic heart failure increases the risk of atrial fibrillation (AF), with the prevalence of AF paralleling the severity of heart failure.1 Factors that underlie this increased susceptibility to AF may include electrical, structural, and neurohumoral changes.2 In AF, it is recognized that atrial electrophysiological remodelling occurs and contributes to the perpetuation of the arrhythmia, most notably the decrease of effective refractory period (ERP) which predisposes to re-entry by shortening the wavelength. Does heart failure cause similar changes in atrial electrophysiology that predispose to the arrhythmia

Toward the Integration of Economics and Outdoor Recreation Management

The general theme of this bulletin is that improved management of public-sector recreational resources is a multidisciplinary task. To this end, we attempt to integrate elements of outdoor recreation management theory and economics. The bulletin is written for both resource managers and researchers. For the former, our intent is to emphasize the importance of being aware of economic implications-at least conceptually-of management actions that influence the character and availability of recreational opportunities. To researchers involved in developing recreation management theory, we draw attention to the parallel between recreation management theory and the traditional managerial economic model of the firm. To economists, particularly those involved in developing and applying nonmarket valuation techniques, we draw attention to the types of decisions faced by resource managers. We argue that the most important resource allocation issues are of the incremental variety, so nonmarket valuation should also yield incremental values. These values alone, however, are not sufficient economic input into rational public choice analysis. The missing link , or nexus, between outdoor recreation management theory and economic analysis is the integration of supply and demand, as called for by traditional managerial economics. Collaborative research to develop recreation supply response functions akin to agricultural production functions is an essential step that is missing from both literatures. Theoretical and applied work assume greater practical importance if they feed information into this broadened framework. It is our hope that this bulletin will bring the disciplines closer to that realization

Anti-adrenergic effects of endothelin on human atrial action potentials are potentially anti-arrhythmic

Endothelin-1 (ET-1) is elevated in patients with atrial fibrillation (AF) and heart failure. We investigated effects of ET-1 on human atrial cellular electrophysiological measurements expected to influence the genesis and maintenance of AF. Action potential characteristics and L-type Ca<sup>2+</sup> current (I<sub>CaL</sub>) were recorded by whole cell patch clamp, in atrial isolated myocytes obtained from patients in sinus rhythm. Isoproterenol (ISO) at 0.05 μM prolonged the action potential duration at 50% repolarisation (APD<sub>50</sub>: 54 ± 10 vs. 28 ± 5 ms; <i>P</i> < 0.05, <i>N</i> = 15 cells, 10 patients), but neither late repolarisation nor cellular effective refractory period (ERP) were affected. ET-1 (10 nM) reversed the effect of ISO on APD<sub>50</sub>, and had no basal effect (in the absence of ISO) on repolarisation or ERP. During repetitive stimulation, ISO (0.05 μM) produced arrhythmic depolarisations (<i>P</i> < 0.05). Each was abolished by ET-1 at 10 nM (<i>P</i> < 0.05). ISO (0.05 μM) increased peak I<sub>CaL</sub> from –5.5 ± 0.4 to –14.6 ± 0.9 pA/pF (P < 0.05; N = 79 cells, 34 patients). ET-1 (10 nM) reversed this effect by 98 ± 10% (P < 0.05), with no effect on basal I<sub>CaL</sub>. Chronic treatment of patients with a β-blocker did not significantly alter basal APD50 or I<sub>CaL</sub>, the increase in APD50 or I<sub>CaL</sub> by 0.05 μM ISO, nor the subsequent reversal of this effect on APD50 by 10 nM ET-1. The marked anti-adrenergic effects of ET-1 on human atrial cellular action potential plateau, arrhythmic depolarisations and I<sub>CaL</sub>, without affecting ERP and independently of β-blocker treatment, may be expected to contribute a potentially anti-arrhythmic influence in the atria of patients with AF and heart failure

Eddy current inspection of graphite fiber components

The recognition of defects in materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques. The unique capabilities of E-probes and horseshoe probes for inspecting probes for inspecting graphite fiber materials were evaluated and appear to hold great promise once the technology development matures. The initial results are described of modeling eddy current interactions with certain flaws in graphite fiber samples

Particle-in-cell simulations of particle energization from low Mach number fast mode shocks

Astrophysical shocks are often studied in the high Mach number limit but weakly compressive fast shocks can occur in magnetic reconnection outflows and are considered to be a site of particle energization in solar flares. Here we study the microphysics of such perpendicular, low Mach number collisionless shocks using two-dimensional particle-in-cell (PIC) simulations with a reduced ion/electron mass ratio and employ a moving wall boundary method for initial generation of the shock. This moving wall method allows for more control of the shock speed, smaller simulation box sizes, and longer simulation times than the commonly used fixed wall, reflection method of shock formation. Our results, which are independent of the shock formation method, reveal the prevalence shock drift acceleration (SDA) of both electron and ions in a purely perpendicular shock with Alfv\'en Mach number $M_A=6.8$ and ratio of thermal to magnetic pressure $\beta=8$. We determine the respective minimum energies required for electrons and ions to incur SDA. We derive a theoretical electron distribution via SDA that compares to the simulation results. We also show that a modified two-stream instability due to the incoming and reflecting ions in the shock transition region acts as the mechanism to generate collisionless plasma turbulence that sustains the shock

Participation, Preferences, and Characteristics of Outlying-Cabin Users in Alaska National Forests

The development and management of public-use cabins have been planned, or at least considered, by several federal and state agencies in Alaska. This bulletin reports the results of a pilot study of the cabin program of the U.S. Forest Service. There are problems of aggregated data which did not allow for detailed analysis; however, the report does provide an overview of the Forest Service outlying cabin program-who uses it, how they use it, and how they feel about it. The manager should be careful in applying the results without consideration of the total recreational spectrum, i.e., where the cabin program fits within this spectrum, and its cost in terms of other recreation opportunities that may be specified. It is the opinion of the authors that it would be unwise to simply mass reproduce the outlying cabin program in all areas having periods of inclement weather. The study sampled only cabin users-not all users or potential users of the particular landscape setting. To over-emphasize an expanded cabin program would reduce the continuum of opportunities. While subsequent studies of the cabin user population would likely find this group to prefer the new program, the users who did not prefer it or who were unwilling to adopt to new conditions would have been displaced. Thus, while the results have some direct applicability, it is also important to consider the maintenance of the continuum of recreational opportunities, only one portion of which is covered by outlying cabins

Fast Shocks From Magnetic Reconnection Outflows

Magnetic reconnection is commonly perceived to drive flow and particle acceleration in flares of solar, stellar, and astrophysical disk coronae but the relative roles of different acceleration mecha- nisms in a given reconnection environment are not well understood. We show via direct numerical simulations that reconnection outflows produce weak fast shocks, when conditions for fast recon- nection are met and the outflows encounter an obstacle. The associated compression ratios lead to a Fermi acceleration particle spectrum that is significantly steeper than the strong fast shocks commonly studied, but consistent with the demands of solar flares. While this is not the only acceleration mechanism operating in a reconnection environment, it is plausibly a ubiquitous one

Modeling the afterglow of the possible Fermi-GBM event associated with GW150914

We model the possible afterglow of the Fermi GBM event associated with LIGO detection GW150914, under the assumption that the gamma-ray are produced by a short GRB-like relativistic outflow. We model GW150914-GBM as both a weak, on-axis short GRB and normal short GRB seen far off axis. Given the large uncertainty in the position of GW150914, we determine that the best chance of finding the afterglow is with ASKAP or possibly the MWA, with the flux from an off-axis short GRB reaching 0.2 - 4 mJy (0.12 - 16 mJy) at 150 MHz (863.5 MHz) by 1 - 12 months after the initial event. At low frequencies, the source would evolve from a hard to soft spectrum over several months. The radio afterglow would be detectable for several months to years after it peaks, meaning the afterglow may still be detectable and increasing in brightness NOW (mid-July 2016). With a localization from the MWA or ASKAP, the afterglow would be detectable at higher radio frequencies with the ATCA and in X-rays with Chandra or XMM.Comment: 7 pages, 4 figures, 1 table. Accepted by ApJ