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51.
In this paper, a novel adaptive fractional-order feedback controller is first developed by extending an adaptive integer-order feedback controller. Then a simple but practical method to synchronize almost all familiar fractional-order chaotic systems has been put forward. Through rigorous theoretical proof by means of the Lyapunov stability theorem and Barbalat lemma, sufficient conditions are derived to guarantee chaos synchronization. A wide range of fractional-order chaotic systems, including the commensurate system and incommensurate case, autonomous system, and nonautonomous case, is just the novelty of this technique. The feasibility and validity of presented scheme have been illustrated by numerical simulations of the fractional-order Chen system, fractional-order hyperchaotic Lü system, and fractional-order Duffing system. 相似文献
52.
针对当前遥感目标检测方法只能识别出遥感目标的类别及位置,无法生成与遥感图像内容相关文本描述的问题,提出了一种基于注意力和强化学习的遥感图像描述方法.首先,采用卷积神经网络构建编码器,提取遥感图像的特征.其次,利用长短期记忆网络搭建解码器,学习图像特征与文本语义特征间的映射关系.然后,引入注意力机制,增强模型对显著性特征的关注,减少无关背景特征的干扰.最后,采用强化学习策略,根据离散且不可微的评价指标直接对模型进行优化,消除暴露偏差及优化方向不一致的缺陷.在公开遥感图像描述数据集中的实验结果表明,本方法的检测精度较高,对密集小目标、雾气积聚、背景特征与目标特征相似等复杂环境下的遥感图像具有良好的描述性能. 相似文献
53.
Wang R Xie Y Shi K Wang J Tian C Shen P Fu H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(24):7443-7451
The synergistic effect between Pt and WC is beneficial for methanol electro-oxidation, and makes Pt-WC catalyst a promising anode candidate for the direct methanol fuel cell. This paper reports on the design and synthesis of small-sized and contacting Pt-WC nanostructures on graphene that bring the synergistic effect into full play. Firstly, DFT calculations show the existence of a strong covalent interaction between WC and graphene, which suggests great potential for anchoring WC on graphene with formation of small-sized, well-dispersed WC particles. The calculations also reveal that, when Pt attaches to the pre-existing WC/graphene hybrid, Pt particles preferentially grow on WC rather than graphene. Our experiments confirmed that highly disperse WC nanoparticles (ca. 5?nm) can indeed be anchored on graphene. Also, Pt particles 2-3?nm in size are well dispersed on WC/graphene hybrid and preferentially grow on WC grains, forming contacting Pt-WC nanostructures. These results are consistent with the theoretical findings. X-ray absorption fine structure spectroscopy further confirms the intimate contact between Pt and WC, and demonstrates that the presence of WC can facilitate the crystallinity of Pt particles. This new Pt-WC/graphene catalyst exhibits a high catalytic efficiency toward methanol oxidation, with a mass activity 1.98 and 4.52 times those of commercial PtRu/C and Pt/C catalysts, respectively. 相似文献
54.
Zhi-Sheng Nong Jing-Chuan Zhu Xia-Wei Yang Yong Cao Zhong-Hong Lai Yong Liu 《Physica B: Condensed Matter》2012,407(24):4706-4711
The structural, elastic and electronic properties of Al2La, AlLa3 and Al3La binary intermetallics in the Al–La alloy system were investigated using the first-principles method. The calculated lattice constants were consistent with the experimental values. Formation enthalpy and cohesive energy showed that the studied Al2La, AlLa3 and Al3La all have a higher structural stability, and the alloying ability of Al2La and Al3La is stronger than that of AlLa3. The single-crystal elastic constants (Cij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated by the Voigt–Reuss–Hill (V–R–H) approximations, and the relationship of these elastic parameters between Al2La, AlLa3 and Al3La phases were discussed in detail. The results showed that Al2La and Al3La which are anisotropic materials are absolutely brittle, while the isotropic AlLa3 is slightly ductile. Finally, the electronic density of states (DOS) was also calculated to reveal the underlying mechanism of structural stability. 相似文献
55.
We present an instance-based attention model to predict where humans could look first when searching for an object instance, and we show its application in image synthesis. The proposed model learns configurational rules from vast scene images described by global scene representations. The rules are then used to predict the focus of attention for the purpose of searching for a given object instance with special scale and pose. Finally, the image synthesis results are obtained by putting the object instance into the scene at the position that attracts most attention. Promising experimental results demonstrate the effectiveness of the proposed model. 相似文献
56.
57.
58.
The dynamical behavior of the Φ6-Van der Pol system subjected to both external and parametric excitation is investigated. The effect of parametric excitation
amplitude on the routes to chaos is studied by numerical analysis. It is found that the probability of chaos happening increases
along with the parametric excitation amplitude increases while the external excitation amplitude fixed. Based on the invariance
principle of differential equations, the system is lead to desirable periodic orbit or chaotic state (synchronization) with
different control techniques. Numerical simulations are provided to validate the proposed method. 相似文献
59.
With a variation in reaction conditions, 1, 4‐bis (2‐(2‐chloroethoxy)ethoxy)‐calix[6]arene (3) and l,3,5‐tris(2‐(2‐chloroethoxy) ethoxy)‐calix [6] arene (4) or 4 and 4‐chloroethoxyethoxy‐calix[6]crown‐3 (5) were selectively synthesized from p‐tert‐butyl‐calix [6] arene and 2‐(2‐chloroethoxy)ethyltosylate. l,3–4,6‐p‐tert‐butylcalix[6]‐bis‐crown‐3 (6) with (u,u,u,d,d,d) conformation and 1,3–4,5‐p‐tert‐butylcalix[6]‐biscrown‐3 (7) with self‐anchored (u,u, u, u, u, d) conformation were synthesized through an intramolecularly ring‐closing condensation of 1, 4‐bis (2‐(2‐chloroethoxy)ethoxy)‐p‐tert‐butyl‐calix[6]arene (3) in 25% and 15% yield, respectively. Using 5 instead of 3, only 7 was obtained in 65% high yield. 6 and 7 show different complexation properties toward alkali metal and ammonium ions. 相似文献
60.
A linear time-of-flight mass spectrometer (TOF-MS) has been constructed to measure mass distribution of negatively-charged clusters formed in the hot filament diamond chemical vapor deposition (CVD) process and in the metal evaporation. A conversion dynode made of CsI was employed to enhance detection efficiency of the large clusters greater than 10 000 amu. An atomic peak from the tungsten evaporation was used for the mass calibration of the carbon clusters. The carbon clusters produced in the CVD diamond process was loosely bound so that they were easily fragmented during passage through accelerating electric fields. The mass distribution measured with the TOF-MS system showed much less abundance of large clusters than those measured previously with the energy analyzer and Wien filter. 相似文献