Fine particulate matter (PM 2.5 ) has received worldwide attention due to its threat to public health. In the Sichuan Basin (SCB), PM 2.5 is causing heavy health burdens due to its high concentrations and population density. Compared with other heavily polluted areas, less effort has been made to generate a full-coverage PM 2.5 dataset of the SCB, in which the detailed PM 2.5 spatiotemporal characteristics remain unclear. Considering commonly existing spatiotemporal autocorrelations, the top-of-atmosphere reflectance (TOAR) with a high coverage rate and other auxiliary data were employed to build commonly used random forest (RF) models to generate accurate hourly PM 2.5 concentration predictions with a 0.05°×0.05° spatial resolution in the SCB in 2016. Specifically, with historical concentrations predicted from a spatial RF (S-RF) and observed at stations, an alternative spatiotemporal RF (AST-RF) and spatiotemporal RF (ST-RF) were built in grids with stations (type 1). The predictions from the AST-RF in grids without stations (type 2) and observations in type 1 formed the PM 2.5 dataset. The LOOCV R 2 , RMSE and MAE were 0.9356/0.9367, 8.7135/8.6244 [[EQUATION]] and 5.5841/5.5721 [[EQUATION]] in the AST-RF/ST-RF, respectively. Using the produced dataset, spatiotemporal analysis was conducted for a detailed understanding of the spatiotemporal characteristics of PM 2.5 in the SCB. The PM 2.5 concentrations gradually increased from the edge to the center of the SCB in spatial distribution. Two high-concentration areas centered on Chengdu and Zigong were observed throughout the year, while another high-concentration area centered on Dazhou was only observed in winter. The diurnal variation had double peaks and double valleys in the SCB. The concentrations were high at night and low in daytime, which suggests that characterizing the relationship between PM 2.5 and adverse health outcomes by daily means might be inaccurate with most human activities conducted in daytime.
Composite insulators have been widely used for its excellent flashover endurance capability, but the umbrella of standard composite insulators are easily been bridged in icing condition. Flashover problems caused by icing insulator have a serious threat to the safe operation of transmission lines,. It is the key technologies for the safe operation of power system which should be solved as soon as possible. The influence of two types of composite insulator umbrella structure (common type and anti-ice type) on iced AC flashover voltage characteristics in the same structure length, as well as same artificial pollution and artificial icing test conditions, but also the method of artificial iced flashover test on composite insulator were introduced. Iced flashover test results showed that the ice bridge formation could be prevented or extended if the umbrella structure design of anti-ice-type composite insulators was more reasonable. For the 750kV composite insulator under the same conditions of artificial pollution test (SDD/NSDD=0.08/0.48mg/cm 2 ) and artificial icing test (when icing water converted to 20 °C, the conductivity is 100μS/cm and the iced thickness from 15mm), it is shown that AC iced flashover voltage of Anti-ice type increased 12%~28% than common type. Upon the existent theoretical and experimental results and based on a great of laboratory investigations carried out in environment laboratory of China UHV AC test base, for the first time this paper studies systematically the insulators shed optimization which will contribute to the designation for Ultra-UHV anti-icing composite insulators.
Spark plasma sintering (SPS) is a highly efficient method for the preparation of α/β-SiAlON ceramics. However, the rapid preparation of large-scale α/β-SiAlON ceramic components with reliable mechanical properties is difficult via SPS due to their near-insulating properties. In this study, high-performance α/β-SiAlON ceramic end mill rods with large aspect ratios were successfully prepared via SPS. Two different types of sintering processes (namely vertical-round-rod (VRR) and horizontal-square-rod (HSR) processes) were developed, and their effects on the phase composition, microstructure, mechanical properties, and machining performance of the α/β-SiAlON ceramic end mill rods were studied. The electric and temperature field distributions during sintering were studied through an electro-thermal simulation. The simulated and experimental temperature distributions are in good agreement. In contrast to the VRR samples, the HSR samples with a small axial size show a uniform temperature distribution and satisfactory microstructures within a certain range of dimensions, and the expected phase composition; furthermore, the elongated β-SiAlON grains are preferentially oriented in the direction perpendicular to the sintering pressure direction. As a result, the HSR samples exhibit better mechanical properties and machining performance than the VRR samples.
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