To accommodate surrounding rock structure stability control problem in underground mining, we study the coupling effect principle between hydraulic support and surrounding rock, and develop a series of longwall mining...To accommodate surrounding rock structure stability control problem in underground mining, we study the coupling effect principle between hydraulic support and surrounding rock, and develop a series of longwall mining technology and equipment, which solves four common technical problems that significantly undermine coal mining safety, efficiency, and high recovery and extraction rates. Based on the coupling characteristic between mining-induced stress field and supporting stress field of hydraulic support, we identify six controllable factors in the application of hydraulic support to surrounding rock, and further reveal the relationship between hydraulic support and surrounding rock in terms of the strength, the stiffness, and the stability coupling. Our findings provide a plausible solution to the longwall mining technical problem with 6-8 m mining height. By analyzing the dynamic disequilibrium characteristics between hydraulic support and surrounding rock, we propose the intelligent top coal caving control method and the high-coal-recovery-rate tech- nology for fully mechanized caving faces. With the invention of this technology, China is likely to lead the world in terms of the fully mechanized top coal caving mining technology. We are also the first to employ the intelligent coupling technology between hydraulic support and surrounding rock, and automated mining mode, and supporting system coop- erative control with automatic organization. We develop the comprehensive multi-index intelligence adjusting height decision-making mechanism and three-dimensional navigation automatic adjusting straightness technology based on shearer cutting height memory association, cutting power parameters, vibration, and video information, leading to the first set of intelligent longwall mining technology and equipment for thin seam. Our innovation makes a solid contribution to the revolution of intelligence mining technology. With the innovative use of three-dimensional coupling control principle for surrounding rock, we succ展开更多
Background The nocturnal nondipping and elevated morning blood pressure （BP） in patients with obstructive sleep apnea syndrome （OSAS） have not yet been well investigated in Chinese patients. This study aimed to de...Background The nocturnal nondipping and elevated morning blood pressure （BP） in patients with obstructive sleep apnea syndrome （OSAS） have not yet been well investigated in Chinese patients. This study aimed to describe the BP profile, and to elucidate the relationships between daytime BP and nighttime BP, and between evening BP and morning BP in patients with OSAS. Methods Twenty teaching hospital sleep centers in China were organized by the Chinese Medical Association to participate in this study and 2297 patients were recruited between January 2004 and April 2006. BP assessments were made at four time points （daytime, evening, nighttime and morning） and polysomnography （PSG） was performed and subjects were classified into four groups by their apnea-hypopnea index （AHI）： control, n=213 with AHI 〈5; mild, n=420 with AHI -〉5 and 〈15; moderate, n=460 with AHI -〉15 and 〈30; and severe, n=1204 with AHI -〉30. SPSS 11.5 software package was used for statistical analysis and figure drawing. Results All the average daytime, nighttime, evening and morning BPs were positively correlated with AHI and negatively correlated with nadir nocturnal oxygen saturation. The ratios of nighttime/daytime and morning/evening average BP were positively correlated with AHI. The ratio of nighttime/daytime systolic BP became a ＂reversed BP dipping＂ pattern until the classification reached severe, while the ratio of nighttime/daytime diastolic BP became reversed at moderate. Similarly, the ratio of morning/evening diastolic BP becomes reversed even at mild. Conclusions OSAS may result in higher BP levels at all four time points. The ratios of nighttime/daytime and morning/evening BP increase with increased AHI. The increasing of diastolic BP, which is inclined to rise more quickly, is not parallel with increasing systolic BP.展开更多
Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dyna...Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.展开更多
A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from ...A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from being oxidized for 160 h at 1773 K with a weight loss of 6.9 mg/cm^2. The flexural strength retention ratio of the ZrB_2/SiO_2 coated composites is 87% after oxidation for 160 h at1773 K. The continuous SiO_2 glass layer embedded with the submicron ZrSiO_4 particles was formed during oxidation. This was helpful to lower the diffusion rate of oxygen and improve the stability of SiO_2 glass film, thus improving the oxidation resistance of the coated samples. After thermal cycles between 1773 K and room temperature for 15 times, penetrated cracks formed in the coating. The weight loss of the ZrB_2/SiO_2 coated sample presented linear relationship, and the final weight loss per unit area was 6.35 mg/cm^2. The generation of the penetrative cracks and the debonded coating interface resulted in the failure of the ZrB_2/SiO_2 coating.展开更多
The upper mantle structures of Himalayas-Tibet have been obtained from the mi-gration of receiver functions of the teleseismic events recorded by INDEPTH-III. The result of migration imaging shows a dipping interface ...The upper mantle structures of Himalayas-Tibet have been obtained from the mi-gration of receiver functions of the teleseismic events recorded by INDEPTH-III. The result of migration imaging shows a dipping interface subducting northward from the depth of 100 km to the 410-km discontinuity underneath southern Tibet. It indicates that the lithospheric mantle of the Indian continent had been detached from the crust and deeply subducted to the upper mantle of Eurasia during the Indo-Eurasian collision. This kind of continent-continent collision process is fundamentally different from the oceanic collision.展开更多
文摘To accommodate surrounding rock structure stability control problem in underground mining, we study the coupling effect principle between hydraulic support and surrounding rock, and develop a series of longwall mining technology and equipment, which solves four common technical problems that significantly undermine coal mining safety, efficiency, and high recovery and extraction rates. Based on the coupling characteristic between mining-induced stress field and supporting stress field of hydraulic support, we identify six controllable factors in the application of hydraulic support to surrounding rock, and further reveal the relationship between hydraulic support and surrounding rock in terms of the strength, the stiffness, and the stability coupling. Our findings provide a plausible solution to the longwall mining technical problem with 6-8 m mining height. By analyzing the dynamic disequilibrium characteristics between hydraulic support and surrounding rock, we propose the intelligent top coal caving control method and the high-coal-recovery-rate tech- nology for fully mechanized caving faces. With the invention of this technology, China is likely to lead the world in terms of the fully mechanized top coal caving mining technology. We are also the first to employ the intelligent coupling technology between hydraulic support and surrounding rock, and automated mining mode, and supporting system coop- erative control with automatic organization. We develop the comprehensive multi-index intelligence adjusting height decision-making mechanism and three-dimensional navigation automatic adjusting straightness technology based on shearer cutting height memory association, cutting power parameters, vibration, and video information, leading to the first set of intelligent longwall mining technology and equipment for thin seam. Our innovation makes a solid contribution to the revolution of intelligence mining technology. With the innovative use of three-dimensional coupling control principle for surrounding rock, we succ
基金This study was supported by the grants from the National Natural Science Foundation of China （No. 30800507, No. 30770934）. All the coauthors from different centers in the name list have made equal contributions to this article. There is no ordering difference. None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.
文摘Background The nocturnal nondipping and elevated morning blood pressure （BP） in patients with obstructive sleep apnea syndrome （OSAS） have not yet been well investigated in Chinese patients. This study aimed to describe the BP profile, and to elucidate the relationships between daytime BP and nighttime BP, and between evening BP and morning BP in patients with OSAS. Methods Twenty teaching hospital sleep centers in China were organized by the Chinese Medical Association to participate in this study and 2297 patients were recruited between January 2004 and April 2006. BP assessments were made at four time points （daytime, evening, nighttime and morning） and polysomnography （PSG） was performed and subjects were classified into four groups by their apnea-hypopnea index （AHI）： control, n=213 with AHI 〈5; mild, n=420 with AHI -〉5 and 〈15; moderate, n=460 with AHI -〉15 and 〈30; and severe, n=1204 with AHI -〉30. SPSS 11.5 software package was used for statistical analysis and figure drawing. Results All the average daytime, nighttime, evening and morning BPs were positively correlated with AHI and negatively correlated with nadir nocturnal oxygen saturation. The ratios of nighttime/daytime and morning/evening average BP were positively correlated with AHI. The ratio of nighttime/daytime systolic BP became a ＂reversed BP dipping＂ pattern until the classification reached severe, while the ratio of nighttime/daytime diastolic BP became reversed at moderate. Similarly, the ratio of morning/evening diastolic BP becomes reversed even at mild. Conclusions OSAS may result in higher BP levels at all four time points. The ratios of nighttime/daytime and morning/evening BP increase with increased AHI. The increasing of diastolic BP, which is inclined to rise more quickly, is not parallel with increasing systolic BP.
基金financially supported by the Key National Basic Research Program of China (Nos.2014CB260404 and 2015CB251602)the Key National Natural Science Foundation of China (No.U13612030)+1 种基金Shaanxi Innovation Team Program (No.2013KCT-16)the High Technology Development Program of Xin Jiang Municipality (No.201432102)
文摘Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51302160 and 51402177)the Science and Technique Talent Project of Shaanxi Province (Grant No. 2016KJXX-07)+2 种基金Natural Science Foundation of Shaanxi Province (Grant No. 2018JM5038)Natural Science Foundation of Education Department of Shaanxi Province (Grant No. 14JK1103)Research Foundation of Shaanxi University of Science & Technology (Grant No. BJ14-20)
文摘A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from being oxidized for 160 h at 1773 K with a weight loss of 6.9 mg/cm^2. The flexural strength retention ratio of the ZrB_2/SiO_2 coated composites is 87% after oxidation for 160 h at1773 K. The continuous SiO_2 glass layer embedded with the submicron ZrSiO_4 particles was formed during oxidation. This was helpful to lower the diffusion rate of oxygen and improve the stability of SiO_2 glass film, thus improving the oxidation resistance of the coated samples. After thermal cycles between 1773 K and room temperature for 15 times, penetrated cracks formed in the coating. The weight loss of the ZrB_2/SiO_2 coated sample presented linear relationship, and the final weight loss per unit area was 6.35 mg/cm^2. The generation of the penetrative cracks and the debonded coating interface resulted in the failure of the ZrB_2/SiO_2 coating.
基金the National Natual Science Foundation of China(Gant No.4974021).
文摘The upper mantle structures of Himalayas-Tibet have been obtained from the mi-gration of receiver functions of the teleseismic events recorded by INDEPTH-III. The result of migration imaging shows a dipping interface subducting northward from the depth of 100 km to the 410-km discontinuity underneath southern Tibet. It indicates that the lithospheric mantle of the Indian continent had been detached from the crust and deeply subducted to the upper mantle of Eurasia during the Indo-Eurasian collision. This kind of continent-continent collision process is fundamentally different from the oceanic collision.
