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61.
62.
《等离子体科学和技术》2020,22(4):45403
In this paper, an efficient boundary condition is applied to solve the photoionization rate, and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure. The results show that the new boundary condition improves the calculation accuracy, but the influence of photoionization on the streamer discharge process is not obvious. The discharge current in the development of streamer discharge is defined, and the corresponding expression of the positive and negative streamer discharge current is given. The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced. In the process of discharge, only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure, and the trend of the other parameters is basically the same as that described in the previous paper. The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure, which has certain significance for the development of aviation and high voltage engineering. 相似文献
63.
《Ceramics International》2021,47(19):27479-27486
Threshold switching (TS) devices have evolved as one of the most promising elements in memory circuit due to their important significance in suppressing crosstalk current in the crisscross array structure. However, the issue of high threshold voltage (Vth) and low stability still restricts their potential applications. Herein, the vanadium oxide (VOx) films deposited by the pulsed laser deposition (PLD) method are adopted as the switching layer to construct the TS devices. The TS devices with Pt/VOx/Pt/PI structure exhibit non-polar, electroforming-free, and volatile TS characteristics with an ultralow Vth (+0.48 V/−0.48 V). Besides that, the TS devices also demonstrates high stability, without obviously performance degradations after 350 cycles of endurance measurements. Additionally, the transition mechanism is mainly attributed to the synergistic effect of metal-insulator transition of VO2 and oxygen vacancies. Furthermore, the nonvolatile bipolar resistance switching behaviors can be obtained by changing oxygen pressure during the deposition process for switching films. This work demonstrates that vanadium oxide film is a good candidate as switching layer for applications in the TS devices and opens an avenue for future electronics. 相似文献
64.
An unsteady stagnation point flow of a Maxwell fluid over a unidirectional linearly stretching sheet is studied under the influence of a magnetic field. The parabolic energy equation, which is based on parabolic Fourier law is replaced with a hyperbolic energy equation incorporating the heat flux model of Cattaneo–Christov. The Buongiorno model is used to characterize the properties of nanofluids using thermophoresis and Brownian diffusion coefficients. The phenomenon of melting heat transfer and slip mechanism is also embodied in the present study. Coupled nonlinear differential equations have appeared when the specified similarity transformations are applied. The mathematical problem is tackled via the homotopy analysis method. The impact of important physical parameters on the velocity, concentration, and temperature are highlighted via graphs. To verify our present results, a comparison is given with a limiting case with an already published article. It is witnessed through the graphs that the higher unsteadiness parameter and melting heat coefficient both are responsible for the reduction in the velocity and temperature of the nanofluid. Also, the velocity slip parameter detracts the velocity profile and affiliated boundary layer thickness of the Maxwell nanofluid. 相似文献
65.
Yaru Zhang Tao Zhang Yu Zhang Zhengzhang Wu Peng Zhang Ruijie Liu Ming Chang Xingguo Wang 《International Journal of Food Science & Technology》2022,57(5):3162-3170
A low-temperature reaction is of considerable importance in avoiding the degradation of phytosterol esters caused by high temperatures. In this study, an efficient method under mild conditions was developed to synthesise phytosterol esters by using microwave-assisted catalyst dodecyl benzene sulphonic acid (DBSA). The phytosterol conversion reached 94.27% under the optimal conditions: oleic acid to phytosterol molar ratio of 2.5:1, catalyst dosage of 20% (mol%) and reaction temperature of 60°C for 60 min. Fourier transform infrared (FTIR) spectroscopy was applied to determine the structure of phytosterol oleates. Moreover, a second-order kinetic model describing phytosterols esterification exhibited an adequate agreement with the experimental data. Microwave irradiation achieved the reduction of energy barrier (Ea = 29.17 kJ mol−1) in comparison with conventional heating (Ea = 49.22 kJ mol−1). This study suggests that microwave-assisted catalyst DBSA is a reliable and efficient method for the production of high-quality phytosterol esters. 相似文献
66.
风力机一般放置在恶劣的环境中,其桨距执行器极易出现故障。文中针对一类含有未知但有界干扰和噪声的风力机系统的桨距执行器故障问题,设计了集员未知输入观测器对桨距的执行器故障进行检测并分离。采用气动机理和现代辨识原理建立风力机系统模型,通过优化未知输入观测器设计对系统中的干扰解耦,基于中心对称多胞体估计不考虑故障时残差的区间包络,并将其作为残差估计的上下动态阈值,实现状态估计。在上述基础上提出了利用一组集员未知输入观测器进行故障诊断的策略。仿真结果表明,在实验过程中,文中所设计的集员未知输入观测器准确地诊断出了风力机桨距执行器的3阶和5阶线性系统在发生突变故障和缓慢时变故障的时间和位置,证明了所提故障诊断策略的有效性。 相似文献
67.
68.
林振华 《探矿工程(岩土钻掘工程)》2006,33(10):42-45
结合工程实例,讨论了在大口径钻孔灌注桩施工中,如何针对具体地质情况选择不同的桩机的问题,从而提高施工效率。 相似文献
69.
三峡库区滑坡稳定性计算中的常用方法 总被引:1,自引:0,他引:1
稳定性计算问题是滑坡及边坡研究中的重要问题之一。对目前在三峡库区滑坡治理过程中常用的计算方法极限平衡法从其原理、应用场合、应用局限等方面进行了总结,结合重庆市巫山县川东淀粉厂滑坡这一具体算例,用常用条分法方法对其在组合工况下的稳定性作了具体的分析。 相似文献
70.