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41.
对sol-gel法制备的不同稀土元素(Ce,Nd,Sm)掺杂的纳米TiO2粒子进行研究。X射线衍射(XRD)和X射线光电子能谱(XPS)分析结果表明,稀土离子均以间隙的形式均匀分布在纳米TiO2晶格内。傅里叶变换红外光谱(FTIR)和太赫兹时域光谱(THz-TDS)显示,掺杂TiO2较纯TiO2具有更强的红外活性;在0.2~1.70 THz波段,TiO2的折射率随着频率的增加而减小,并呈现反常色散现象;Ce掺杂引起新的特征吸收,分别为1.35和1.58 THz,且造成太赫兹吸收谱的吸收边发生红移,Nd和Sm掺杂则造成吸收边蓝移。在0.2~1.7 THz范围内,Sm掺杂引起的介电损耗角正切值(taneδ)最小,其平均值为0.05。 相似文献
42.
The early transient responses of multi-span stepped single walled carbon nanotubes (SWCNTs) under impact loadings are studied by the method of reverberation ray matrix (MRRM). The dynamics model of the carbon nanotubes is established in the Fourier phase space on the basis of the nonlocal Timoshenko beam model. The wave solutions of SWCNTs with arbitrary boundary conditions are obtained by the wave method. The reverberation ray matrix of the multi-span stepped SWCNTs is the product of scattering, phase and permutation matrices, which can be determined by the impact loadings, continuous conditions and boundary conditions. The early transient responses can be calculated by the inverse Fourier transform of the sum of initial ray groups. It can be found that the early transient displacement response in the very short time subjected to the impact loading is very small, while the transient transverse shear strain becomes large in the very short time. The influences of nanotubes span number, nanotubes type and boundary conditions on the early transient responses of multi-span stepped SWCNTs are investigated. 相似文献
43.
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45.
Haoying Wang Ziqiang Yang Zheng Liang 《International Journal of Infrared and Millimeter Waves》2003,24(12):2189-2200
The linear dispersion relation of asymmetric electromagnetic modes in the corrugated-wall waveguide is derived and calculated numerically. The numerical analyses indicate that the effects of lower asymmetric modes on the main interaction mode TMm must be considered and mode selection also must be solved in order to realize the single asymmetric mode operation of the oversized structures. 相似文献
46.
Lei Wang Rui-Min Xu Bo Yan 《International Journal of Infrared and Millimeter Waves》2007,28(12):1133-1141
An accurate small-signal modeling approach applied to GaAs-based pHEMT devices is presented. The procedure for extracting
equivalent-circuit model parameters is illustrated in detail. A genetic algorithm (GA) program is developed to optimize the
model parameters in order to improve the modeling accuracy. The validity of modeling approach is verified by comparing the
simulated and measured result of two pHEMTs and a fabricated ka-band power amplifier. The conclusion can be drawn that the
proposed modeling method is rather accurate and efficient. 相似文献
47.
Ion-Channel Laser (ICL) is a new form of laser, which can produce tunable coherent radiation with frequencies ranging from microwaves to soft X-rays. In this paper, the ICL with slab geometry in the low gain is studied. Using the Madey's theorem, the gain formula of the ICL is derived. The result shows that the Madey's theorem is a valuable guide in research with new types of FEL's.This work was supported by the National Science Foundation of China. 相似文献
48.
Wenxiang Wang Guofen Yu Meisheng Xu Yubin Gong 《International Journal of Infrared and Millimeter Waves》2003,24(5):661-668
The design of a 8mm TE
13 mode gyrotron is given in this paper. Discussions about the selection of the dimensions of the RF structure and electron gun are presented. Calculated results of the operating parameters of the gyrotron are also given. At 37.5GHz, pulse power 56kW is obtained for the gyrotron manufactured according to our design. Mode pattern obtained by scorching method shows that the mode of the output millimeter wave is TE
13. 相似文献
49.
Stability of functional differential equations (FDE) is an increasingly important problem in both science and engineering. Delays, whether uniform or non-uniform, play an important role in the dynamics of a system. Since non-uniform delay is more general and less focused than uniform delay, this paper concentrates on the stability of high-order neutral functional differential equations (HNFDE) with non-uniform delay, and proposes a sufficient condition for it. This result may be widely helpful, thanks to the frequent emergence of a HNFDE with non-uniform delay in various fields. Its effectiveness is illustrated by some examples. 相似文献
50.
When the activation function possesses multilevel property, the Hopfield neural network has some novel dynamical behaviors, and it is worthwhile to study. First, some properties about the activation function are obtained, on this foundation, some theoretical analysis about the quasi-equilibrium points has been made. From local and global view, some theorems about the boundedness are presented. Finally, two theorems about the first derivative of trajectory with respect to time are found, the first theorem indicates that the trajectory cannot keep increasing or decreasing for time t > t0, the second theorem is about the complete stability of the trajectory. 相似文献