A new lens imaging technique based on geometrical optics imaging of lens for measuring nonlinear absorption coefficients of nonlinear materials is developed and demonstrated with ZnSe at 532 nm with picosecond (ps) laser pulse.
Sub-synchronous oscillation may occur when the wind-thermal-bundled system sent out via AC/DC transmission (WTBH) is integrated in power grid. Causing large-scale wind-turbine tripping, even lead the system to collapse. First, in this study the mechanism of sub-synchronous oscillation of this system is analysed. Second, the influencing factors such as the ratio of the wind-thermal-bundled installed capacity, the series compensation parameters of AC transmission line, the different operating conditions of wind power etc., are analysed, which can cause different degree impact on the sub-synchronous oscillation. Finally, the system is simulated under the Power Systems Computer Aided Design (PSCAD) environment. The results show that under the same conditions, the higher series compensation, the greater transmission capacity of the AC line, the greater risk of the sub-synchronous oscillation. Under the condition of full load, the greater proportion of installed capacity of Doubly fed Induction Generator (DFIG) is, the less risk of sub-synchronous oscillation; Under the lower wind speed condition, reducing the number of wind turbine can eliminate the risk of sub-synchronous oscillation, and the oscillation frequency vary with the number of wind turbine.
Human visual perception and visual preferences affect how people perceive and experience the urban environment. Constrained by their methodologies and data availability, the previous studies have struggled to precisely quantify the subjects and objects in urban perception. This research employs visual saliency detection and fractal dimension measurement to quantify the characteristics of urban building façades and visual perception. Through this study, we determine the differences between human visual perception and computer vision. The study shows that (1) human vision exhibits selective preferences, processing building façades with varying complexity levels to form a critical complexity threshold, which is a feature that is not captured by computer vision processing; (2) taking Nanshan District, Shenzhen, as a case study, the value of this threshold is 1.2383; (3) building façades with complexity greater than this threshold are seen as “complex” building façades and vice versa; (4) when perceiving “simple” buildings, human eyes tend to focus on their more complex local areas, whereas for “complex” buildings, they pay more attention to simpler parts. This study provides a reference for conducting quantitative research on urban perception and visual perception.
Particulate matter (PM) and airborne viruses bring adverse influence on human health. As the most feasible way to prevent inhalation of these pollutants, face masks with excellent filtration efficiency and low press drop are in urgent demand. In this study, we report a novel methodology for producing high performance air filter by combining melt blown technique with corona charging treatment. Changing the crystal structure of polypropylene by adding magnesium stearate can avoid charge escape and ensure the stability of filtration performances. Particularly, the influence of fiber diameter, pore size, porosity, and charge storage on the filtration performances of the filter are thoroughly investigated. The filtration performances of the materials, including the loading test performance are also studied. The melt blown materials formed by four layers presented a significant filtration efficiency of 97.96%, a low pressure drop of 84.28 Pa, and a high quality factor (QF) of 0.046 Pa
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