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91.
热电器件能把废热转化为电能,减少二氧化碳排放,符合国家节能减排、逐步实现碳中和的发展需求. 该文通过建立多孔热电器件的热、电传导分析模型,解释了多孔热电泡沫高输出功率的内在机制,并揭示了几何结构及孔隙率对断裂破坏的影响机理. 在此基础上,阐明了断裂破坏对器件转化性能的影响规律. 研究发现,随着孔隙率的增加,热电泡沫与金属层之间的界面剪切应力减小. 同时,只要多孔热电泡沫的内部裂纹开始扩展就不会停止,直至器件完全破坏. 此外,随着裂纹扩展,输出功率呈现先增加后减小的趋势. 这是因为裂纹的形成间接增大了热电泡沫的孔隙率,导致器件与废热的接触面积增大,进而提高热电器件的输出功率;随着裂纹进一步扩展,其必然减弱热电器件的导热和导电性能,进而减小热电器件的输出功率. 相似文献
92.
为研究椭圆截面战斗部在不同起爆方式下破片速度的分布特性,建立了5种具有不同短长轴比的椭圆截面战斗部数值模拟模型。开展了端面中心单点、短(长)轴中点双点、短长轴中点4点以及端面面起爆5种起爆方式数值模拟研究,分析了不同起爆方式下椭圆截面战斗部破片的速度分布及能量输出特性。研究结果表明：在径向方向,战斗部在不同起爆方式下破片最大径向速度变化规律基本一致,均呈现由长轴至短轴方向对数增长,且随着短长轴比的增大,短长轴方向破片速度差值逐渐减小。然而,不同起爆方式下椭圆截面战斗部最大速度截面上破片速度平均值存在明显差异,具体表现为端面起爆时的破片径向平均速度最高,单点起爆最低,且随着起爆点数量的增加,最大速度截面上的破片的整体平均速度逐渐增大。在轴向方向,受端面稀疏波的影响,不同方位角最大破片速度均出现在靠近非起爆端1/4处,且起爆点在短轴轴线上相较于在长轴轴线上会提高靠近起爆端长轴方向的破片速度,但短轴方向沿轴向的破片速度分布无明显差异。此外,不同起爆方式对椭圆截面装药爆炸能量输出特性无明显影响,其中27%的装药能量转化为壳体动能,有50%的能量被壳体断裂变形以及空气冲击波消耗。
相似文献93.
94.
《Mathematical Methods in the Applied Sciences》2018,41(9):3282-3293
This paper investigates the problem of exponential H∞ synchronization of discrete‐time chaotic neural networks with time delays and stochastic perturbations. First, by using the Lyapunov‐Krasovskii (Lyapunov) functional and output feedback controller, we establish the H∞ performance of exponential synchronization in the mean square of master‐slave systems, which is analyzed using a matrix inequality approach. Second, the parameters of a desired output feedback controller can be achieved by solving a linear matrix inequality. Finally, 2 simulated examples are presented to show the effectiveness of the theoretical results. 相似文献
95.
为选择合适的激光参量与光伏电池参量,以提高激光无线能量传输(LWPT)系统的能量转换效率,通过实验研究了LWPT系统中能量接收单元,也即光伏电池在半导体激光照射下的输出特性。通过波长为808 nm和915 nm的激光辐照GaAs和Si光伏电池,研究了不同激光功率密度、光伏电池温度、电池类型以及激光入射角度对光伏电池输出特性与能量转换效率的影响。实验中,在波长为808 nm的激光功率密度从0.06 W/cm2上升至0.37 W/cm2的过程中,Si电池的最大输出功率从0.12 W上升至0.32 W,能量转换效率从50.9%下降至21.2%;GaAs电池的最大输出功率从0.40 W上升到1.07 W,能量转换效率从57.9%下降至23.8%。随着激光功率密度的增加,光伏电池的输出功率先增加而后趋于饱和,但是高功率密度激光引起的电池温升会导致其光电转换效率的下降,所以激光功率密度的选择与光伏电池温度的控制是提高LWPT系统能量转换效率的关键因素。 相似文献
96.
The resilient dissipative dynamic output feedback control problem for a class of uncertain Markov jump Lur’e systems with piecewise homogeneous transition probabilities and time-varying delays in the discrete-time domain are examined in this study. The designed controller can tolerate additive uncertainties in the controller gain matrix, which result from controller implementations. The time-varying delays are also supposed to be mode-dependent with lower and upper bounds known a priori. By constructing a Lyapunov–Krasovskii functional candidate, the sufficient conditions regarding the existence of desired resilient dissipative controllers are obtained in terms of linear matrix inequalities, thereby ensuring that the resulting closed-loop system is stochastically stable and strictly dissipative. Two numerical examples were established to illustrate the effectiveness of the proposed theoretical results. 相似文献
97.
98.
ZHANG Zhirong;XIA Hua;SUN Pengshuai;YU Runqing;YANG Xi;LIN Yuqing;WU Bian;PANG Tao;GUO Qiang;LI Zhe;LIU Xu;CAI Yongjun;SIGRIST Markus W;CALSHAW Brain;SHU Chimin 《光子学报》2023,52(3):119-135
Stable isotope technology has been widely used in geochemistry, geophysics, agriculture, biology, clinical medicine and ecological environment science. It is very important for the study of atmosphere, soil, water quality and health to realize the accurate measurement of gas isotope abundance. At present, isotope abundance is measured and analyzed mostly by Isotope Ratio Mass Spectrometers. It is a relatively large, expensive and complex pre-processing, which is not conducive to real-time measurement of isotope abundance in the field. With the development of laser technology, the output wavelength can cover more and more wide bands, and the performance is more better. Many kinds of gases can be detected by laser absorption spectroscopy, and the detection sensitivity is further improved. This makes it possible to measure isotopic gases, which have attracted more and more attention and become one of the hot spots of laser spectroscopy. Compared with the traditional stable isotope analysis instruments, the isotope analysis technology based on laser absorption spectroscopy, as a relatively new isotope abundance measurement method, has the advantages of high selectivity, high accuracy, small volume, real-time online monitoring concentration and abundance, etc. So, the gas isotope analysis system based on laser absorption spectroscopy technology has important application value in environmental monitoring, ecosystem research, pollution tracing and tracing because of its miniaturization, fast response and real-time online measurement. Taking Tunable Diode Laser Absorption Spectroscopy （TDLAS）, Integrated Cavity Absorption Spectroscopy （ICOS） and Cavity Ring-Down Absorption spectroscopy （CRDS） as examples, the basic principle, spectrum line selection, system structure and some test results are described in this paper. Under the control of the PID system of temperature and pressure, the temperature control error is 0.003 ℃, and the pressure control error is 0.03mbar, which can meet the requirements of temperature and pressure control during the measurement of isotope gas. The 13C measurement accuracy of atmospheric CO2 is 0.3‰, the 13CH4 measurement accuracy of coalbed methane is 1.25‰, the 18O, 17O and D measurement accuracy of glacial H2O are 0.3‰, 0.2‰ and 0.5‰, respectively. And also, the “gold standard” for 13CO2 of detecting helicobacter pylori infection is also introduced. The feasibility and reliability of laser absorption spectroscopy in isotope measurement are verified. And it is also fully demonstrated that the measurement method based on laser absorption spectroscopy has a very good technical advantage. TDLAS, ICOS and CRDS have become the best choice for the high-sensitivity detection of trace gases and isotope gases. The three technologies have their characteristics： TDLAS technology has the simplest structure, but its cavity volume is large and requires the largest gas samples. The system structure of ICOS technology is relatively simple, but the technology is based on absorption intensity measurement technology, limited by laser intensity noise and frequency drift, which is also a major problem in applying ICOS technology in high sensitivity detection. Therefore, the signal-to-noise ratio and measurement accuracy of ICOS technology is slightly lower than that of CRDS technology. The structure of CRDS technology is relatively complex, and the conditions are relatively harsh, but it can achieve the absorption optical path that the above two technologies cannot reach, so it has the best sensitivity and measurement limits. Based on the above advantages and practical feasibility, laser absorption spectral isotope analysis system will be more and more applied to various fields. And the related system research still has a long way to go. At the same time, laser absorption spectroscopy is also faced with many shortcomings, such as： in these measurements, it is also necessary to consider the error sources such as the concentration dependence of the instrument and the time drift. A certain correction frequency should be set for periodic correction to eliminate the influence of the instrument drift, and the measurement results with accuracy and accuracy meeting the research needs should be obtained through appropriate correction strategies. 相似文献
99.
100.
This work mainly addresses terminal constrained robust hybrid iterative learning model predictive control against time delay and uncertainties in a class of complex batch processes with input and output constraints. In this work, an equivalently novel extended two-dimensional switched system is first constructed to represent the process model by introducing state difference, output error and new relaxation variable information. Then, a hybrid predictive updating controller is proposed and an optimal performance index function including terminal constraints is designed. Under the condition that the switching signal meets certain conditions, the solvable problem of model predictive control is realized by Lyapunov stability theory. Meanwhile, the design scheme of controller parameters is also given. In addition, the robust constraint set is adopted to overcome the disadvantage that the traditional asymptotic stability cannot converge to the origin when it involves disturbances, such that the system state converges to the constraint set and meets its expected value. Finally, the effectiveness of the proposed algorithm is verified by controlling the speed and pressure parameters of the injection molding process. 相似文献