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1.
Consider an elastic thin three-dimensional body made of a periodic distribution of elastic inclusions. When both the thickness of the beam and the size of the heterogeneities tend simultaneously to zero the authors obtain three different one-dimensional models of beam depending upon the limit of the ratio of these two small parameters. 相似文献
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《Physics letters. A》2020,384(2):126046
Discussed is the dynamics of optical vortices carrying multi-topological charges, which are nested in optical envelopes with non-circular symmetric amplitudes and phases. As a result of the non-circular symmetry either in amplitudes or in phases, the vortices can split in pairs from the centers of the host beams. During the splitting process of every constituent vortex, its carried integer charges evolve into fractional ones. Furthermore, the overall rotations of the host optical envelopes are found to happen in the splitting process. The theoretical results may find potential applications in beam shaping and engineering. 相似文献
4.
在HL-2A装置上完成了一套32通道束发射诊断系统(BES),可对径向r=12~44cm, 极向-7.5~+7.5cm二维空间范围内的长波长()电子密度扰动信息进行测量,其时间分辨率达到0.5ms,空间分辨率1~2cm。系统由内置于真空室的非对称镜头组、传输光纤、高性能探测器模块以及辅助的冷却和真空设备构成。系统的噪声在低频时(f<100kHz)主要由散粒噪声贡献,在较高频率时由散粒噪声和e噪声共同决定。在典型的HL-2A装置放电模式中,对于200kHz以下的扰动,该系统的信噪比(SNR)均大于3。 相似文献
5.
Qing Yao Hui Li Dr. Jiawei Xue Dr. Shenlong Jiang Prof. Qun Zhang Prof. Jun Bao 《Angewandte Chemie (International ed. in English)》2023,62(34):e202308140
Inspired by its great success in the photovoltaic field, methylammonium lead iodide perovskite (MAPbI3) has recently been actively explored as photocatalysts in H2 evolution reactions. However, the practical application of MAPbI3 photocatalysts remains hampered by the intrinsically fast trapping and recombination of photogenerated charges. Herein, we propose a novel strategy of regulating the distribution of defective areas to promote charge-transfer dynamics of MAPbI3 photocatalysts. By deliberately designing and synthesizing the MAPbI3 photocatalysts featuring a unique continuation of defective areas, we demonstrate that such a feature enables retardation of charge trapping and recombination via lengthening the charge-transfer distance. As an outcome, such MAPbI3 photocatalysts turn out to achieve an impressive photocatalytic H2 evolution rate as high as 0.64 mmol ⋅ g−1 ⋅ h−1, one order of magnitude higher than that of the conventional MAPbI3 photocatalysts. This work establishes a new paradigm for controlling charge-transfer dynamics in photocatalysis. 相似文献
6.
Tian-Sheng Chen Hao Long Yuxing Gao Hai-Chao Xu 《Angewandte Chemie (International ed. in English)》2023,62(40):e202310138
The selective oxygenation of ubiquitous C(sp3)−H bonds remains a highly sought-after method in both academia and the chemical industry for constructing functionalized organic molecules. However, it is extremely challenging to selectively oxidize a certain C(sp3)−H bond to afford alcohols due to the presence of multiple C(sp3)−H bonds with similar strength and steric environment in organic molecules, and the alcohol products being prone to further oxidation. Herein, we present a practical and cost-efficient electrochemical method for the highly selective monooxygenation of benzylic C(sp3)−H bonds using continuous flow reactors. The electrochemical reactions produce trifluoroacetate esters that are resistant to further oxidation but undergo facile hydrolysis during aqueous workup to form benzylic alcohols. The method exhibits a broad scope and exceptional site selectivity and requires no catalysts or chemical oxidants. Furthermore, the electrochemical method demonstrates excellent scalability by producing 115 g of one of the alcohol products. The high site selectivity of the electrochemical method originates from its unique mechanism to cleave benzylic C(sp3)−H bonds through sequential electron/proton transfer, rather than the commonly employed hydrogen atom transfer (HAT). 相似文献
7.
The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared(ATR-FTIR) spectroscopy technique and two dimensional(2D) correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm-1,1033 cm-1 and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g-1 after 150 min. 相似文献
8.
Hybrid composites are promising materials due the possibility of combining the properties of different fiber types with those of the polymeric matrix. The higher number of phases involved in this kind of material and the hydrostatic component of polymer behavior make it unfeasible to use classic models for failure prediction, like the Von Mises or Treska models. In this study, a modified Arcan's device was applied for mechanical characterization of a polymeric blend matrix composite reinforced with randomly oriented continuous fibers (a clutch disc) to generate combined loading conditions. Experimental results were applied in the Von Mises and Drucker-Prager theoretical models for failure prediction. Additionally, scanning electron microscopy (SEM) was applied to analyze the fracture surface. The failure envelope provided by the Drucker-Prager model fit the experimental results, making it a promising tool for predicting the behavior of this type of hybrid composite. 相似文献
9.
This paper is concerned with a nonlinear Timoshenko system with a time delay term in the internal feedback together with initial data and Dirichet boundary conditions. Under some suitable assumptions on the weights of feedback, we obtain the existence of a global attractor with finite fractal dimension for the case of equal speed wave propagation. Furthermore, the existence of exponential attractors is also derived. 相似文献
10.