A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT

Expression and function of atrial myosin light chain 1 in the porcine right ventricle of normal and pulmonary hypertensive animals

We investigated the expression of atrial myosin light chain 1 (ALC-1) and myosin cycling kinetics in the normal and hypertrophied right ventricle of the neonatal porcine heart. Right ventricular hypertrophy was induced by exposing piglets immediately after birth to hypobaric hypoxia for 3 days. Control piglets were kept under normal conditions for the same time. ALC-1 expression in the hypertrophied right ventricle was 16.9%. No ALC-1 expression could be observed in the right ventricle of control pigs. Force-velocity of chemically skinned right ventricular fibers was analyzed in order to examine the functional role of ALC-1 expression on myosin cross-bridge kinetics. Force generation per cross-section at maximal Ca2+ activation (pCa 4.5) was significantly higher in the hypertrophied group. Maximal shortening velocity (Vmax) of skinned fibers increased statistically significant from 0.69 muscle length per second (ML/s) in the control to 1.2 ML/s in the hypertrophied right ventricle. We conclude that the expression of ALC-1 in the hypertrophied ventricle of neonatal pigs increased cross-bridge cycling kinetics and contractility