Effects of surrounding gases on the propagation of room-temperature atmospheric-pressure plasma jets are reported. A highly unusual feather-like plasma plume is observed only when N2 is used as surrounding gas. The He concentration on the axis at the starting point of the feather-like plume is ∼0.85 of the maximum value and is independent on the He flow rates. High-speed optical imaging reveals that dim diffuse plasmas emerge just behind the bright head of the plasma bullet at the starting point of the feather-like plume. These results help tailoring surface exposure in emerging applications of plasma jets in medicine and nanotechnology.
Au/La2 O3 nanomaterials were prepared through calcining Au-modified La(OH)3 precursors. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD) were employed to characterize the as-prepared samples. Benzene, a common volatile organic compound, was selected as a model to investigate the cataluminescence (CTL)-sensing properties of the Au/La2 O3 nanomaterials. Results indicated that the as-prepared Au/La2 O3 exhibited outstanding CTL properties such as stable intensity, high signal-to-noise values, and short response and recovery times. Under optimized conditions, the benzene assay exhibited a broad linear range of 1-4000 ppm, with a limit of detection of 0.7 ppm, which was below the standard permitted concentrations. Furthermore, the gas sensor system showed outstanding selectivity for benzene compared with seven other types of common volatile organic compounds (VOCs). The proposed gas sensor showed good characteristics with high selectivity, fast response time and long lifetime, which suggested the promising application of the Au/La2 O3 nanomaterials as a novel highly efficient CTL-sensing material.
A chiral plasma plume has recently been reported inside a circular quartz tube without the use of an external magnetic field. It is believed that the quartz tube plays an important role in the formation of the chiral plasma plume. In this paper, to better understand how this interesting structure is generated, the effect of the tube geometry on the chiral plasma is investigated. First, the effect of the thickness of the tube wall on the chiral plasma is investigated. It is interesting to find that a too thin or too thick tube wall is not favorable for generating the chiral plasma. The chiral plasma plume can be obtained only at the tube wall thickness of 2 mm. Second, the effect of the diameter of the tube on the chiral plasma is investigated. It is found that, when a tube with an inner diameter of 2 mm is connected with a tube with an inner diameter of 4 mm and the high voltage electrode is placed in the tube with an inner diameter of 2 mm, a diffuse plasma is generated in the tube with an inner diameter of 2 mm, it propagates into the tube with an inner diameter of 4 mm, and a chiral plasma can be obtained at a distance of about 2 cm away from the joint of the two tubes. Third, to further understand how the tube diameter affects the appearance of the chiral plasma, horn shaped tubes with different opening angles are tested. It is found that, when the opening angle is 5 , the chiral plasma formation in the straight part of the tube can maintain the chiral shape and keep propagating in the horn shaped tube but with a much longer pitch. Fourth, to disrupt the axial symmetry, square quartz tubes are used. No chiral plasma can be obtained in the square quartz tubes under all experimental conditions. In addition, when a circular quartz tube is connected with a square tube, the chiral plasma formation in the circular quartz tube changes to a straight plasma plume in the square tube. Finally, the high voltage electrode is placed away from the center of the circular tube to disrupt its symmetry, and it is found that the chiral plasma plume can always be seen even if the high voltage is placed next to the inner wall of the tube.
This paper describes the design of a new type of pantograph-catenary arc simulation test device and simulation of the arc generated by the pantograph during operation under laboratory conditions. The influence of the burning position of the pantograph-catenary arc on the overvoltage of the traction system is studied. Corresponding suppression measures for the arcs are proposed, and the dynamics of the arc processes are carried out by theoretical simulation. The characteristics of the pantograph-catenary arc and the discharge process are analyzed, and the relationship between the characteristics of the pantograph and the arc is explored.
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