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Dissolved gas analysis is important for the early warning and diagnosis of transformer faults. Aiming at the problems of numerous types of features for dissolved gas in oil and the insufficient analysis of fault associated features, a new fault diagnosis method for oil-immersed transformers based on feature selection of dissolved gas in oil is proposed. Firstly, the derivation of original features for dissolved gases is completed. The optimal combination of features is selected by calculating the importance of features for fault diagnosis based on random forest (RF). Then, the tree-structured parzen estimator (TPE) is used to realize the parameter optimization of the RF model, and the TPE-RF diagnostic model is obtained. Combined with the various evaluated indicators, the proposed method is proved to be able to diagnosis the transformer faults accurately. Finally, the TreeSHAP model is introduced to analyze the importance of the features corresponding to each fault, and the specialized features for each fault are selected. According to the case of transformer in operation, the applicability of the method in the power system is discussed, and the effectiveness of the method is verified.

The distribution of surface water is highly dynamic both spatially and temporally, and very sensitive to climate change and anthropogenic interference, especially in highly urbanized regions. The abundance of surface water and its spatiotemporal distribution indicate the availability of water resources and the difficulty of water development and utilization. Consequently, it is essential to perform reconstruction and trend prediction of surface water body changes with high accuracy in time and space for scientific research as well as for practical purposes such as flood prevention, sustainable development of water resource systems, and regional ecological management. The Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is highly developed economically and societally and is characterized by a subtropical humid monsoon climate with an extensive distribution of surface water bodies. Under the integrated pressure of continuous natural environmental change and intense human activity, concerns regarding both the water environment and water security in this area is increasing at an unprecedented rate. In this study, we collected water distribution information from 2001 to 2020 at 5-year intervals, as well as annual and monthly water extent dynamics data for the GBA from the Global Land Analysis & Discovery database. Subsequently, the spatial and temporal changes in water extent, frequency, and distribution characteristics in the last two decades were investigated using remote sensing and geographic information system methods. Finally, elastic analysis was conducted to identify the sensitivity of water body changes to changing environmental parameters, including precipitation, temperature, and urbanization. Focusing on the national and regional strategic needs of GBA, the research objectives of this study were to explore the mechanism of temporal and spatial dynamics of the water extent and frequency, trace the volatile areas of regional water changes, clarify the driving factors of water distribution changes, and provide a basis and guidance for comprehensive management of water resources, flood disaster prevention, and control in areas with high human activity. The first result shows that in the last two decades, the water extent and frequency of the GBA are on a decreasing trend, with an average decreasing rate of 50, 31, and 11 km2/a for maximum, annual, and permanent water extent, respectively, while a large proportion of seasonal water bodies changed into permanent and flood-prone bodies during the same period. Second, although the water frequency showed distinct spatial and urban/rural heterogeneity, it was on a decreasing trend in most of the GBA, except in the eastern region. A steeper decline was observed in urban areas, especially the emerging urban regions. Third, the dike-pond system decreased both in water extent and frequency, while the large and medium-sized lakes and reservoirs in the upper catchment increased in extent. Finally, elastic analysis suggests the dominant driving factor of regional water body change is land use change, which contributed more than 80% to the decrease in water extent, and the reservoir increase is mainly due to precipitation change. The results of this research provide scientific guidance for regional water resource guarantee, water environment optimization, and sustainable development promotion. In addition, this research can serve as a decision-making reference for the development of the "One Belt One Road" national strategy and Guangdong-Hong Kong-Macao Greater Bay Area.

In view of problems of low power quality, low cruising power, short service life of battery, separation between battery charging device and locomotive driving system existed in current charging system of mine-used electric locomotive with lead-acid battery, a new integrated on-board charging system was designed. The system is composed of the front-stage PWM rectifier circuit and the back-stage Buck circuit in series. When charging, the motor windings are reconstructed into the boost inductance of the PWM rectifier circuit to form an integrated on-board charging and discharging circuit. The supercapacitor is used to replace the battery as the energy storage element, which can realize quick on-board charging and discharging function. The simulation results show the system has shorter charging time and higher efficiency, and can realize functions such as power factor correction, ripple suppression, efficient and rapid charging and discharging compared with the traditional charging system.

A high performance liquid chromatography (HPLC) method was established by optimizing the mobile phase to determine the mobile phase content of flavonol glycosides in Ginkgo biloba extract. Under the mobile phase conditions of the chromatographic column EC-C18 (4 m, 4.6 mm x 150 mm), the column temperature is 25 °C, the flow rate is 1.0 mL/min, the detection wavelength is 370 nm, the methanol, water and acetonitrile (60 • 35 ! 5 by volume),the content of quercetin, kaempferol and isorhamnetin in the flavonol glycosides were determined. The results show that under the determined optimal conditions, the separation effect of the three substances is great, and there is a good linear relationship in the range of detection concentration. Besides, the average spiked recovery rates of this three compounds are 99.26%, 100.1% and 100.35%. The method is simple and rapid, and can be used for the accurate determination of the contents of three substances in flavonol glycosides. [ABSTRACT FROM AUTHOR]

An experimental study is presented on the static behavior of steel plate-masonry composite ( SPMC) columns consisting of irregular masonry columns with steel plates attached to all sides with a combination of steel bolts and epoxy adhesive. Six composite L-shaped and T-shaped specimens were tested. The influence of the bolt-spacing and restraint effect of the bolts were taken into account. The failure process and mode, load-strain curve and bearing capacity of composite columns were elaborated and analyzed. Test results show that the damage of composite columns always starts from the local buckling of steel plates. Critical buckling loads are different between the plates due to the different boundary conditions. The stress redistribution happens as columns approaches the ultimate load. Rather than the rectangular section, the irregular section is remarkably affected by the restraint of the bolts. Cold formed steel plates contribute to the ductility of the specimens. Design equations are given to calculate the compression bearing capacity of such irregular composite columns. [ABSTRACT FROM AUTHOR]