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The determination of the low-temperature plasma propagation of SF6/N2 in gas discharge will accelerate the application of SF6/N2 in advanced electrical equipment. This study investigates the positive streamer propagation characteristics of SF6/N2 by establishing a plasma discharge model and discusses the effects of SF6 ratio on the electron density, electric field, chemical reaction rates, ion concentrations, and streamer thickness and velocity. As the streamer propagates, the shapes of the electron density and electric field become "narrower and taller." Moreover, the ionization and attachment reaction rates increase, and the streamer thickness and velocity decrease with increasing SF6 mixing ratio and propagation time. As the SF6 ratio increases, the electric field distortion degree and particle mobility near the high-voltage electrode decrease due to the increase in the ionization and attachment rates. Consequently, the streamer velocity remains nearly unchanged, but the streamer thickness obviously decreases in the corona discharge process. In the streamer propagation process, the decrease in the streamer thickness and velocity with increasing SF6 ratio is attributed to the reduction in the electric field distortion and particle mobility, which stems from the increase in the DC breakdown voltage with the SF6 mixing ratio. The study results clarify the influence mechanisms of the SF6 mixing ratio on the particles' spatiotemporal evolution during streamer propagation. [ABSTRACT FROM AUTHOR]

Zero index metamaterials have shown the ability to achieve total transmission or reflection by embedding particular defects with various effective parameters. Here, we present that tunable sound transmission can be realized by configuring a subwavelength-sized dopant inside zero index acoustic metamaterials. Despite its small spatial signature, the dopant is able to strongly interact with the acoustic waves inside the whole zero index metamaterials. It is due to the essence of the zero effective index that can homogenize the pressure field within the metamaterials. Sound transmission can thus be fully switched on and off by adjusting the dopant's surface impedance. A simple rectangular cavity with varied lengths is proposed to provide the required impedance boundary. Our model of correlating the dopant design with sound transmission performance is validated theoretically and numerically. We further demonstrate the utilization of the proposed design to effectively modulate the sound focusing effect. Such a dopant-modulated sound transmission scheme, with its simplicity and capability, has potential applications in fields like noise control and ultrasonography. [ABSTRACT FROM AUTHOR]

Sleep quantification and automatic scoring of sleep stages via electroencephalogram (EEG) signals has been a challenge for years. It is crucial to investigate the correlation of brain waves by sleep EEG analysis due to the association between rhythmic oscillations of neuronal activity and neocortical synchronization. Multiscale joint permutation entropy (MJPE) had been proven to be capable of measuring the correlation between time series from the view of multiple time scales and thus can be a promising approach to address the challenge. Instead of simulation, we tested the MJPE method on a widely used open dataset of sleep EEG time series from healthy subjects and found that the correlation index obtained by MJPE had the capability of quantifying the brain wave correlations under different sleep stages, reflecting the typical sleep patterns and indicating the weakened correlation with aging. A higher level of correlation was found as the sleep stage advanced. The findings based on the MJPE results were in accordance with previous studies and existing knowledge in sleep medicine. In the second part of the study, we applied MJPE on sleep EEGs from subjects under pathological conditions (sleep apnea and sleep at high altitude). Likewise, the correlation index also properly revealed their sleep architectures, with consistent trends of the correlation through the nights. The effectiveness and practicability of the MJPE method had been verified on sleep EEGs. Therefore, the MJPE method should be encouraged to be widely used for analyzing large-scale sleep EEGs under various pathological conditions to provide insight into the mechanisms of the sleep process and neuron synchronization. [ABSTRACT FROM AUTHOR]