排序方式: 共有38条查询结果,搜索用时 46 毫秒
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W. C. A. N. Ceelen M. de Ridder B. Moest A. W. Denier van der Gon H. H. Brongersma 《Surface science》1999,430(1-3):146-153
Spot profile analysis low-energy electron diffraction, low-energy ion scattering and Auger electron spectroscopy were employed to study the morphology and composition of Au films on Si(100). After annealing, two distinct surface reconstructions were observed: a two-domain c(8×2) phase and a four-domain incommensurate (5×3.2)R5.7° phase. During the transition from the c(8×2) to the (5×3.2)R5.7° phase, the subsurface composition changes drastically from Au-rich to Si-rich, whereas the outermost layer composition remains almost constant (about 65 at.% Au). Detailed information concerning the domain structure for the two phases is subtracted from the profiles of the LEED spots. 相似文献
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用ISS镇定方法研究了一类带不确定输入动态受扰非线性系统的干扰抑制问题,利用小增益定理设计了连续的鲁棒反馈控制器对所有可允许的不确定动态实现系统的ISS镇定. 相似文献
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C. Lämmerzahl G. Ahlers N. Ashby M. Barmatz P. L. Biermann H. Dittus V. Dohm R. Duncan K. Gibble J. Lipa N. Lockerbie N. Mulders C. Salomon 《General Relativity and Gravitation》2004,36(3):615-649
This is a review of those experiments in the area of Fundamental Physics that are either approved by ESA and NASA, or are currently under development, which are to be performed in the microgravity environment of the International Space Station. These experiments cover the physics of liquid Helium (SUE, BEST, MISTE, DYNAMX, and EXACT), ultrastable atomic clocks (PHARAO, PARCS, RACE), ultrastable microwave resonators (SUMO), and particle detectors (AMS and EUSO). The scientific goals are to study more precisely the universality properties of liquid Helium under microgravity conditions, to establish better time standards and to test the universality of the gravitational red shift, to make more precise tests of the constancy of the speed of light, and to measure the particle content in space directly without disturbances from the Earth's inner atmosphere. 相似文献
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基于分数阶相关盲图像水印算法 总被引:1,自引:1,他引:0
针对改进的扩频(Improved spread spectrum,ISS)技术局部嵌入失真不可控制的缺点,结合人类视觉系统模型(HVS模型)建立的限失真的数学模型实现水印自适应最优嵌入.嵌入的水印是一个线性调频信号(LFM),也就是说不同的LFM信号的调频率表示不同的水印信息,检测时采用分数阶相关估计提取水印的调频率.实验结果表明,水印图像在JPEG压缩、各种噪声的攻击下尽管最大的BER接近40%,经过分数阶相关后处理仍然能够实现BER为零的水印信息提取,表现较强的鲁棒性. 相似文献
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Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO2, TiO2 and Cu2O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO2, TiO2 and Cu2O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible. 相似文献
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In this paper, we propose a new input-to-state stable (ISS) synchronization method for chaotic behavior in nonlinear Bloch equations with external disturbance. Based on Lyapunov theory and linear matrix inequality (LMI) approach, for the first time, the ISS synchronization controller is presented to not only guarantee the asymptotic synchronization but also achieve the bounded synchronization error for any bounded disturbance. The proposed controller can be obtained by solving a convex optimization problem represented by the LMI. Simulation study is presented to demonstrate the effectiveness of the proposed synchronization scheme. 相似文献
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基于李雅普诺夫函数方法,给出了无激励非线性切换系统一致有界和一致最终有界的充分条件.对具有任意有界输入的非线性切换系统,分析并给出了输入状态稳定性的充分条件,通过一个数值例子说明了研究结果的有效性. 相似文献
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研究了具有输入状态稳定(input-to-state stability,ISS)未建模动态的一类非线性系统的全局实际输出跟踪控制问题.该类非线性系统具有非线性参数化的未知参数不确定性,未知的非线性不确定性及未建模动态不确定性.与现有结果不同,所考察的系统具有未知的控制系数,其人小及符号等信息都假设是完全未知的.通过利... 相似文献