It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel...It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter(STF) and impedance change characteristics. The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process. The STF is used to reduce the randomness of the impedance of repeated discharges underwater, and then the universal identification resistance data is obtained. Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown, main, and oscillatory discharge stages, the threshold values for determining the discharge stage are obtained. These include the threshold values for the resistance variation rate(K) and the moment(t).Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination, with a maximum mean square deviation of Scrless than 1.761.展开更多
Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-...Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg17Al12 from the supersaturated α-Mg solid solution. The pre- cipitate exhibited granular and lath-shaped morphologies in Mg matrix and ftocculent precipitation around AlN particles.展开更多
Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstru...Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstructure,thermal diffusivity and thermal expansion of the Mg–Al/Al N composites using different mixing methods were investigated.The results showed that the intergranular and intragranular distributions of Al N particles were obtained,respectively,by controlling the mixing methods.The composite with intragranular particles exhibited lower thermal diffusivity because of the existences of more interfaces,defects and grain boundaries,which acted as scattering centers and reduced the mean free path of electrons and phonons.The existence of Al N particles lowered the coefficient of thermal expansion（CTE）and enhanced the dimensional stability of the composites.And the use of the improved mixing method further reduced the CTE of Mg–Al/Al N composites.展开更多
In this paper,by proving a differential identity,we obtain a necessary and sufficient condition of nonoscillation for a second-order differential equation.We also improve the known results of nonoscillation for a seco...In this paper,by proving a differential identity,we obtain a necessary and sufficient condition of nonoscillation for a second-order differential equation.We also improve the known results of nonoscillation for a second-order differential equation.展开更多
采用固相微萃取-顶空-气质联用技术,对贮藏20年的某酱香型白酒进行香味化合物检测,与该酱香型白酒的新酒的挥发性成分进行比对,结合感官品评结果进行比较分析,再检测贮存前后的游离氨基酸变化情况,探索白酒长期贮存后的风味物质和游离...采用固相微萃取-顶空-气质联用技术,对贮藏20年的某酱香型白酒进行香味化合物检测,与该酱香型白酒的新酒的挥发性成分进行比对,结合感官品评结果进行比较分析,再检测贮存前后的游离氨基酸变化情况,探索白酒长期贮存后的风味物质和游离成分的变化。结果表明,新酒有91种挥发性化合物被检出,其中包含酱香型代表化合物糠醛等。20年陈酒有56种挥发性化合物被检出,除了有酱香型代表化合物糠醛之外还有酱香关键化合物4-甲基吡嗪的前体物质乙偶姻。新酒和陈酒含有的16种游离氨基酸的含量都小于5 mg/100 m L。本研究为酱香型白酒陈化规律的研究提供了有益参考。展开更多
基金provided by the shale gas resource evaluation methods and exploration technology research project of the National Science and Technology Major Project of China(No.2016ZX05034)Graduate Innovative Engineering Funding Project of China University of Petroleum(East China)(No.YCX2021109)。
文摘It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter(STF) and impedance change characteristics. The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process. The STF is used to reduce the randomness of the impedance of repeated discharges underwater, and then the universal identification resistance data is obtained. Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown, main, and oscillatory discharge stages, the threshold values for determining the discharge stage are obtained. These include the threshold values for the resistance variation rate(K) and the moment(t).Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination, with a maximum mean square deviation of Scrless than 1.761.
文摘Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg17Al12 from the supersaturated α-Mg solid solution. The pre- cipitate exhibited granular and lath-shaped morphologies in Mg matrix and ftocculent precipitation around AlN particles.
文摘Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstructure,thermal diffusivity and thermal expansion of the Mg–Al/Al N composites using different mixing methods were investigated.The results showed that the intergranular and intragranular distributions of Al N particles were obtained,respectively,by controlling the mixing methods.The composite with intragranular particles exhibited lower thermal diffusivity because of the existences of more interfaces,defects and grain boundaries,which acted as scattering centers and reduced the mean free path of electrons and phonons.The existence of Al N particles lowered the coefficient of thermal expansion（CTE）and enhanced the dimensional stability of the composites.And the use of the improved mixing method further reduced the CTE of Mg–Al/Al N composites.
基金the Hubei Provincial Department of Education,grant No.2004D003
文摘In this paper,by proving a differential identity,we obtain a necessary and sufficient condition of nonoscillation for a second-order differential equation.We also improve the known results of nonoscillation for a second-order differential equation.
文摘采用固相微萃取-顶空-气质联用技术,对贮藏20年的某酱香型白酒进行香味化合物检测,与该酱香型白酒的新酒的挥发性成分进行比对,结合感官品评结果进行比较分析,再检测贮存前后的游离氨基酸变化情况,探索白酒长期贮存后的风味物质和游离成分的变化。结果表明,新酒有91种挥发性化合物被检出,其中包含酱香型代表化合物糠醛等。20年陈酒有56种挥发性化合物被检出,除了有酱香型代表化合物糠醛之外还有酱香关键化合物4-甲基吡嗪的前体物质乙偶姻。新酒和陈酒含有的16种游离氨基酸的含量都小于5 mg/100 m L。本研究为酱香型白酒陈化规律的研究提供了有益参考。
