The Multi-Scale Dynamics Organizing a Favorable Environment for Convective Density Currents That Redirected the Yarnell Hill Fire

The deadly shift of the Yarnell Hill, Arizona wildfire was associated with an environment exhibiting gusty wind patterns in response to organized convectively driven circulations. The observed synoptic (>2500 km) through meso-β (approximately 100 km) scale precursor environment that organized a mid-upper tropospheric cross-mountain mesoscale jet streak circulation and upslope thermally direct flow was examined. Numerical simulations and observations indicated that both circulations played a key role in focusing the upper-level divergence, ascent, downdraft potential, vertical wind shear favoring mobile convective gust fronts, and a microburst. This sequence was initiated at the synoptic scale by a cyclonic Rossby Wave Break (RWB) 72 h prior, followed by an anticyclonic RWB. These RWBs combined to produce a mid-continent baroclinic trough with two short waves ushering in cooler air with the amplifying polar jet. Cool air advection with the second trough and surface heating across the Intermountain West (IW) combined to increase the mesoscale pressure gradient, forcing a mid-upper tropospheric subsynoptic jet around the periphery of the upstream ridge over Southern Utah and Northern New Mexico. Convection was triggered by an unbalanced secondary jetlet circulation within the subsynoptic jet in association with a low-level upslope flow accompanying a mountain plains solenoidal circulation above the Mogollon Rim (MR) and downstream mountains.

Pulsed low-energy stimulation initiates electric turbulence in cardiac tissue

Interruptions in nonlinear wave propagation, commonly referred to as wave breaks, are typical of many complex excitable systems. In the heart they lead to lethal rhythm disorders, the so-called arrhythmias, which are one of the main causes of sudden death in the industrialized world. Progress in the treatment and therapy of cardiac arrhythmias requires a detailed understanding of the triggers and dynamics of these wave breaks. In particular, two very important questions are: 1) What determines the potential of a wave break to initiate re-entry? and 2) How do these breaks evolve such that the system is able to maintain spatiotemporally chaotic electrical activity? Here we approach these questions numerically using optogenetics in an in silico model of human atrial tissue that has undergone chronic atrial fibrillation (cAF) remodelling. In the lesser studied sub-threshold illumination régime, we discover a new mechanism of wave break initiation in cardiac tissue that occurs for gentle slopes of the restitution characteristics. This mechanism involves the creation of conduction blocks through a combination of wavefront-waveback interaction, reshaping of the wave profile and heterogeneous recovery from the excitation of the spatially extended medium, leading to the creation of re-excitable windows for sustained re-entry. This finding is an important contribution to cardiac arrhythmia research as it identifies scenarios in which low-energy perturbations to cardiac rhythm can be potentially life-threatening.

Wave-attenuation characteristics of combined-vegetation wave break forests for big rivers with large flood water level changes

For large rivers with a compound cross section, the downstream channel has a very wide water surface during the flood season. A wide water surface, high water level, and larger wind speed will cause higher waves, increasing the threat of flooding to the dike. The design of a combined-vegetation wave break forest was put forward to achieve better wave attenuation effect. The main idea of this concept is to plant different types of vegetation at different locations in front of the dike. Three single-vegetation and four combined-vegetation forest schemes were tested under seven different water depth conditions. Both physical experiments and wave numerical simulations were carried out for each scheme to study the wave attenuation effect. The results showed that the wave attenuation effect of the single-vegetation wave break forest was significantly different under different water depth conditions, and the overall effect of the combined-vegetation of wave forest was better. Combined-vegetation wave break forests combine the advantages of different types of vegetation in different water levels, which makes it more economical and reasonable to plant by rivers with large water level variation. The proposed design ideas and methods could provide theoretical support for ecological revetment engineering of large rivers and insights for practical applications.

Experiments on initial stages of development of dam-break waves

ABSTRACT The initial stages of instantaneous dam-break waves are here evaluated spatially and temporally through 36 physical experiments. Different conditions were tested for downstream (J) and upstream (M) water depths and their ratios (r) to approach realistic conditions for prototype dams. Two non-dimensional parameters are proposed – effective height (HEF) and effective velocity (VEF) – to evaluate water depths and velocity peaks along the dam-break wave evolution. The maximum wave height is estimated as a function of r, whereas the HEF is inversely related to r. The maximum VEF peak is registered for r between 0.1 and 0.2, considered a critical description for real dams. The presence of downstream water depth also modifies the dam-break wave frontal shape and types of wave break features. Previously published classifications of the moving wave based on those features are now expanded with a first tested r = 0.8 in which no jet was identified (undulated movement).

Multi-objective optimization of wave break forest design through machine learning

Planting trees on a floodplain along a river is a practical and ecological method for embankment protection. Optimization of wave break forest is also a new concept on wave attenuation studies. In this study, we carried out physical experiments to obtain fundamental data and proposed the Cluster Structure Preserving Based on Dictionary Pair for Unsupervised Feature Weighting model (CDUFW) for multi-objective wave break forest design. Physical experiments were designed with considering the effects of different planting configurations on wave attenuation in three scenarios: (1) the equilateral triangle arrangement with different row spacings; (2) different arrangements with the same density; (3) different tree shapes with the same row spacing. The physical experiment condition was typically defined according to the field research of the study area. Then, a multi-objective weighting model for wave break forest design optimization was based on the scheme set of physical experiment outputs using the proposed CDUFW model. Physical experiments showed that different arrangement modes take advantage of the wave attenuation effect of different forest widths. The CDUFW model performed well in finding the effective, economic and reasonable scheme. The proposed model is excellent in data mining and classification, and can be applied to many decision-making and evaluation fields.

Abstract 18637: Recurrence Quantification Analysis to Distinguish Active From Passive Mechanisms of CFAEs During Catheter Ablation of Atrial Fibrillation

Background: Ablation of complex fractionated atrial electrograms (CFAEs) is controversial, primarily because of difficulty in visually distinguishing CFAEs representing an active site of driver activity from a passive site of double potentials, wave break, and/or slow conduction. We hypothesized that CFAEs within rotors in atrial fibrillation (AF) would exhibit highly recurrent behavior compared with CFAEs remote from these driver regions. Methods: Active and passive mechanisms of CFAE formation were simulated in several 2D 7.5 x 7.5 cm modified Luo-Rudy 1 models. CFAEs within areas of rotors were considered active, while those caused by wave break, slow conduction or double potentials remote from rotors were considered passive. Clinical signals were also collected during catheter ablation of paroxysmal AF (n=8 patients). An active driver CFAE site was defined by termination of AF with ablation followed by non-inducibility. A passive site was defined as CFAE occurring remotely. Detection of CFAEs was based on mean cycle length (MCL) calculated from 4 second windows using -dV/dt for detection (40ms refractory period/10ms maximum EGM width for simulations; 45ms/15ms respectively for clinical signals). Recurrence quantification analysis (RQA) was performed on discrete time series of simulated and clinical CFAE activations. Results: RQA was performed on 20 simulated EGMs. MCL was similar in both active and passive CFAEs (74±11ms and 78±6ms respectively, p=NS), but recurrence was significantly higher in active compared to passive sites (%recurrence: 61±22% active, 4±6% passive, p<0.01). In patients with AF, the driver sites were all located within the pulmonary vein antra while passive CFAEs were remote. The MCL of CFAEs at active driver sites was similar to that of passive sites (100±13ms active, 98±17ms passive, p=NS), but recurrence was significantly higher in the active driver sites (%recurrence: 18±15% active, 2±1% passive, p=0.02). Conclusion: CFAEs may occur due to either active or passive mechanisms. Sites within rotors or focal drivers of AF are more likely to exhibit recurrent patterns. RQA may be a powerful tool to differentiate driver from bystander CFAEs enabling more efficient targeting for ablation.