Thick and ultra-thick coal seams are main coal seams for high production rate and high efficiency in Chinese coal mines, which accounts for 44 % of the total minable coal reserve. A fully mechanized top-coal caving mining method is a main underground coal extraction method for ultra-thick coal seams. The coal extraction technologies for coal seams less than 14 m thick were extensively used in China. However, for coal seams with thickness greater than 14 m, there have been no reported cases in the world for underground mechanical extraction with safe performance, high efficiency and high coal recovery ratio. To deal with this case, China Coal Technology & Engineering Group, Datong Coal Mine Group, and other 15 organizations in China launched a fundamental and big project to develop coal mining technologies and equipment for coal seams with thicknesses greater than 14 m. After the completion of the project, a coal extraction method was developed for top-coal caving with a large mining height, as well as a ground control theory for ultra-thick coal seams. In addition, the mining technology for top-coal caving with a large mining height, the ground support technology for roadway in coal seams with a large cross-section, and the prevention and control technology for gas and fire hazards were developed and applied. Furthermore, a hydraulic support with a mining height of 5.2 m, a shearer with high reliability, and auxiliary equipment were developed and manufactured. Practical implication on the technologies and equipment developed was successfully completed at the No. 8105 coal face in the Tashan coal mine, Datong, China. The major achievements of the project are summarized as follows: 1. A top-coal caving method for ultra-thick coal seams is proposed with a cutting height of 5 m and a top-coal caving height of 15 m. A structural mechanical model of overlying strata called cantilever beam-articulated rock beam is established. Based on the model, the load resistance of the hydraulic support with a large mining height for top-coal caving method is determined. With the analysis, the movement characteristics of the top coal and above strata are evaluated during top-coal caving operation at the coal face with a large mining height. Furthermore, there is successful development of comprehensive technologies for preventing and controlling spalling of the coal wall, and the top-coal caving technology with high efficiency and high recovery at the top-coal caving face with a large mining height. This means that the technologies developed have overcome the difficulties in strata control, top-coal caving with high efficiency and high coal recovery, and enabled to achieve a production rate of more than 10 Mtpa at a single top-coal caving face with a large mining height in ultra-thick coal seams; 2. A hydraulic support with 5.2 m supporting height and anti-rockburst capacity, a shearer with high reliability, a scraper conveyor with a large power at the back of face, and a large load and long distance headgate belt conveyor ...

HfO2‐based ferroelectric materials are promising candidates for next‐generation nonvolatile memories. Since the first report on Si‐doped HfO2 ferroelectric thin film in 2011, it has been confirmed that various dopants can induce ferroelectricity in HfO2‐based films, and the “wake‐up” effect in HfO2 films with different dopants deposited by different processes has been studied extensively. Recent developments in the wake‐up effect of doped HfO2‐based films are presented. Aside from the differences between the various ferroelectric materials and their deposition methods, the electrodes used in a ferroelectric capacitor, which determine the nature of the interface between the electrode and the ferroelectric layer, can strongly influence the characteristics of the wake‐up effect. The rate of variation of the remanent polarization shows certain trends with different dopants. Based on the wake‐up mechanisms, many methods to optimize and control this effect are presented in this letter. Until now, the reported mechanism explanations of the wake‐up effect all aimed at one type of specific dopant or deposition technique, but can't systematically interpret why the root causes might be different with different dopants and deposition processes. There is also a lack of in‐depth research on the effects of interfacial layer with respect to different electrode material.

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