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Knowledge of leader corona is the basis for long spark discharge modelling, which is critical to understand the underlying physics of lightning flashes and dielectric breakdown of long air gap widely utilized in power systems. This paper presents an accurate observation of the leader corona. The morphology of the leader corona region during the discharge was obtained using a high-speed camera and an image-enhanced charge-coupled device camera. Statistical results showed that the morphology of the streamer region varied at different discharge sub-phases. The first corona was a conical region with the average apex angle of 118.91°; the leader corona region behaved as a cone with an average vertex angle of 75.87° during the leader propagation process; the streamer area in the final jump was a combination of a cylinder and a cone with the average vertex angle of 82.61°. Noting that the obtained cone apex angle of the leader corona during the leader propagation phase was significantly smaller than that in photographical reports, and the observation results were related to the selected temporal resolution of the optical image apparatus. The discussion on the effect of the single-frame exposure time on observation results found that the average vertex angle of the conical streamer region gradually decreased with the decrease of the single-frame exposure time, and eventually tended to a stable value of about 75.96°. For comparison purposes, discharge experiments under two gap-distances demonstrated that on the premise of stable leader, the statistical distribution characteristics of the leader corona vertex angle were consistent, indicating the universal applicability to the simulation researches. Finally, it is found that the distortion of the electric field caused by the space charge explained the variation of the streamer area during the discharge process.

In order to manufacture excellent CCF300/PEEK composites, a comprehensive study on controlling porosity of CCF300/PEEK composites was investigated by optimizing the impregnation parameters. Four kinds of PEEK with different melting flow rates (MFR) were employed to study on their rheology behavior and reveal the processing characteristics. The results showed that the viscous flow of PEEK has a higher dependence on the processing pressure than temperature. Furthermore, PEEK rheology behavior was employed to assist the optimization of impregnation parameters. PEEK powders were coated on both sides of single layer CCF300 by a preheating process, and then the semi‐impregnated forms were stacked layer by layer to manufacture CCF300/PEEK composites. An optimized impregnation prediction model was established and verified, showing a pretty effective prediction about pressure and holding time at a certain temperature to control the porosity and achieve the full impregnation. Afterwards, the well‐impregnated CCF300/PEEK composites were evaluated by their compressive performance, flexural performance and interlaminar shear performance, showing good interfacial and interlaminar bonding to resist the propagation of cracks. POLYM. COMPOS., 39:3765–3779, 2018. © 2017 Society of Plastics Engineers

This system was able to monitor the toe-walking strides of children with CP in real time and had the potential to enhance rehabilitation training efficiency and correct toe-walking gait in children with CP with dynamic equinus.

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