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Volume diffuse dielectric barrier discharge (DBD) plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra (OES), the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.

Based on a Marx generator and a coaxial pulse forming line, an experimental investigation of surface flashover characteristics in vacuum is conducted by using nanosecond pulses of 10 ns rise time and 30 ns full width at half maximum (FWHM). Insulator dielectrics chosen for this investigation are Teflon, PMMA and Nylon. The tested factors include gas pressure, cone angle of conical frustum, diameter and length of cylindrical insulator, material and shape of electrode, and contact style between insulator and electrodes. The effects of these parameters on the surface flashover characteristics are described and analyzed in this paper. In addition, the character of flashover time lag in the nanosecond range, and surface flashover theory in vacuum charged by nanosecond pulses are also discussed.Index Terms -Surface flashover, vacuum, nanosecond pulse, cathode triple junction, electron emission. Ping Yan

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An all-fiber optical heterodyne detection configuration was proposed based on an all-fiber acousto-optic structure, which acted as both frequency shifter and coupler at the same time. The vibration waveform within a frequency range between 1 Hz to 200 kHz of a piezoelectric mirror was measured using this optical heterodyne detection system. The minimal measurable vibration amplitude and resolution are around 6 pm and 1 pm in the region of tens to hundreds of kilohertz, respectively. The configuration has advantages of compact size, high accuracy and non-contact measurement. Moreover, it is of a dynamically adjustable signal-to-noise ratio to adapt different surface with different reflections in the measurement, which will improve the usage efficiency of the light power.

A flexible polyimide-based single-walled carbon nanotube (SWCNT) thermal film sensor has been developed for wall shear stress measurements in both air and water. To ensure high sensitivity, vacuum thermal annealing and electrical aging are conducted to enhance the electric properties of the sensor with low-resistance and the high temperature coefficient of resistivity (TCR). The TCR of sensors can reach to 8040 ppm/°C to the author's knowledge, which is the highest reported value of thermal sensors used for shear stress measurements. In calibration, the output voltage of the sensor is proportional to the one third power of wall shear stress with the sensitivity on the order of mV Pa −1 in the constant current operation mode. The repeatability error is no more than 1% in both air and water, which confirms the capability of the flexible SWCNT thermal film sensor for fluid wall shear stress measurements with high sensitivity.

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The icing of transmission lines will bring considerable challenges to the safe operation of the power grid. Therefore, a novel method combines machine vision and machine learning algorithms for identifying the ice thickness on high-voltage transmission line (HVTL) as proposed herein. First, noise and background interference in the image are filtered, and the grey image is used as input. Then, the algorithms of improved Canny edge detection, Hough transform, improved K-means clustering, and least-squares fitting are adopted in turn to locate the edges of conductors. Finally, according to the distance mapping model based on monocular vision, the ice thickness of the conductor is determined by calculating the width difference before and after icing. The experimental results show that the proposed method can accurately locate the edge of the conductor in both field and experimental environments. Moreover, it can ensure ideal effects under different illumination and hardly not be affected by distortion in both horizontal and vertical directions. Besides, the distance mapping model can map the pixel distance to the actual distance with high precision, no matter whether the background is simple or complex, and the calculated ice thickness has only a small deviation compared to the actual value. In addition, the proposed method shows high reliability and effectiveness when various interference such as different backgrounds, uneven icing, height difference changes, conductor movement, contrast changes, and conductor sag occur.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.