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71.
Considering the random impulses of mechanical noise and the limitations involved while identifying mechanical fault impulse signals via traditional measurement indices of signal-to-noise ratio, which require the characteristic frequency to be known in advance, this study proposes an adaptive unsaturated stochastic resonance method employing maximum cross-correlated kurtosis as the signal detection index. The proposed method combines the features of a cross-correlated coefficient to indicate periodic fault transients and those of spectrum kurtosis to locate these transients in the frequency domain. Actual vibration signals collected from motor and gear bearings subjected to heavy noise are used to demonstrate the effectiveness of the proposed method. Through a coarse tree-based machine learning method, the proposed method is verified to be more suitable for explaining the periodic impulse components of bearing signals, as compared to the ensemble empirical mode decomposition denoising method and unsaturated stochastic resonance using the kurtosis-intercorrelation index. 相似文献
72.
Effect of thickness variations of lithium niobate on insulator waveguide on the frequency spectrum of spontaneous parametric down-conversion 下载免费PDF全文
Guang-Tai Xue 《中国物理 B》2021,30(11):110313-110313
We study the effect of waveguide thickness variations on the frequency spectrum of spontaneous parametric down-conversion in the periodically-poled lithium niobate on insulator (LNOI) waveguide. We analyze several variation models and our simulation results show that thickness variations in several nanometers can induce distinct effects on the central peak of the spectrum, such as narrowing, broadening, and splitting. We also prove that the effects of positive and negative variations can be canceled and thus lead to a variation-robust feature and an ultra-broad bandwidth. Our study may promote the development of on-chip photon sources in the LNOI platform, as well as opens up a way to engineer photon frequency state. 相似文献
74.
Guo Yan Li Zhuang Wei Yuxi Zhang Xinxu Shi Kexin 《Journal of Solid State Electrochemistry》2022,26(4):1051-1065
Journal of Solid State Electrochemistry - Polyvinylpyrrolidone (PVP) and graphene (G)-modified iron oxides (Fe2O3-PVP-G) are prepared by a simple hydrothermal reaction. Their morphology and... 相似文献
75.
Yong Gao Dani Zhang Dr. Jingjing Li Prof. Hao Gong Dr. Cheng Jiang Dr. Hairong Xue Prof. Xianli Huang Prof. Tao Wang Prof. Jianping He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202410
Electrocatalysis is the most promising strategy to generate clean energy H2, and the development of catalysts with excellent hydrogen evolution reaction (HER) performance at high current density that can resist strong alkaline and acidic electrolyte environment is of great significance for practical industrial application. Therefore, a P doped MoS2@Ni3S2 nanorods array (named P-NiMoS) was successfully synthesized through successive sulfuration and phosphorization. P-NiMoS presents a core/shell structure with a heterojunction between MoS2 (shell) and Ni3S2 (core). Furthermore, the doping of P modulates the electronic structure of the P-NiMoS; the electrons transfer from the t2g orbital of Ni element to the eg empty orbital of Mo element through the Ni−S−Mo bond at the Ni3S2 and MoS2 heterojunction, facilitating the hydrogen evolution reaction. As a result, P-NiMoS exhibits excellent HER activity; the overpotential is 290 mV at high current density of 250 mA cm−2 in alkaline electrolyte, which is close to Pt/C (282 mV@250 mA cm−2), and P-NiMoS can stably evolve hydrogen for 48 h. 相似文献
76.
Wenqing Wang Dr. Kun Rui Kaili Wu Yisha Wang Longwei Ke Xin Wang Feng Xu Prof. Yan Lu Prof. Jixin Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(40):e202200789
Realizing the synergy between active site regulation and rational structural engineering is essential in the electrocatalysis community but still challenging. Here, a matrix-confined co-pyrolysis strategy based on molecular bridging is demonstrated to realize highly dispersed Fe atoms on stereoassembled carbon framework. Both polyacrylonitrile matrix and organic linker from metal–organic frameworks (MOFs) provide sufficient N-anchoring sites for the generation of Fe−N4 moieties. A high Fe loading of 2.9 wt.% is readily achieved based on the scalable approach without post-treatment. Owing to the presence of highly exposed Fe−N−C sites and well-tuned pore structures, isolated Fe atoms on porous carbon nanofiber framework (Fe−SA/NCF) exhibits decent oxygen reduction activity and stability in alkaline conditions via a near four-electron path, demonstrating superior performance as air cathode for zinc-air batteries (ZABs) to commercial Pt/C catalyst. 相似文献
77.
Xuan Liu Dr. Chengxi Huang Dr. Bo Ouyang Dr. Yongping Du Boyu Fu Zhengwei Du Qiang Ju Dr. Jingjing Ma Prof. Dr. Ang Li Prof. Dr. Erjun Kan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202201034
The CO2 reduction reaction (CRR) represents a promising route for the clean utilization of renewable resources. But mass-transfer limitations seriously hinder the forward step. Enhancing the surface hydrophobicity by using polymers has been proved to be one of the most efficient strategies. However, as macromolecular organics, polymers on the surface hinder the transfer of charge carriers from catalysts to reactants. Herein, we describe an in-situ surface fluorination strategy to enhance the surface hydrophobicity of TiO2 without a barrier layer of organics, thus facilitating the mass transfer of CO2 to catalysts and charge transfer. With less obstruction to charge transfer, a higher CO2, and lower H+ surface concentration, the photocatalytic CRR generation rate of methanol (CH3OH) is greatly enhanced to up to 247.15 μmol g−1 h−1. Furthermore, we investigated the overall defects; enhancing the surface hydrophobicity of catalysts provides a general and reliable method to improve the competitiveness of CRR. 相似文献
78.
Feng Jundong Wang Weitai Zhao Xida Liu Wenqian Yang Yingqing 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(7):3093-3105
Journal of Radioanalytical and Nuclear Chemistry - In this paper, the effects of three coexisting ion systems (Cs, Sr), (Cr, Sr) and (Cs, Cr, Sr) on the adsorption of Sr(II) by irradiated... 相似文献
79.
《中国化学快报》2023,34(6):107935
A facile and elegant method for synthesis of novel N–aryl phenothiazine derivatives from 2-phenylindolizines and phenothiazines through direct electrochemical oxidation has been developed. This approach was performed smoothly at room temperature without external oxidant and catalyst. Cyclic voltammetry and in situ FTIR techniques were applied to analyze the cross-coupling process of phenothiazines and 2-phenylindolizines, which helped to select the appropriate reaction potential. Under the optimized conditions, a broad range of substrates were well tolerated, affording the desired products in moderate to excellent isolated yields (up to 91%) with high regioselectivity. Meanwhile, a plausible mechanism involving a radical pathway has been proposed. 相似文献
80.
《中国化学快报》2023,34(6):107939
The water promotion effects, where water can provide a solution-mediated reaction pathway in various heterogeneous chemical catalysis, have been presented and attracted wide attention recently, yet, the rational design of catalysts with a certain ability of enhancing water-induced reaction process is full of challenges and difficulties. Here, we show that by incorporating alkali (Na, K) cations as an electronic and/or structural promoter into Pd/rGO-ZnCr2O4 (rGO, reduced graphene oxide), the obtained Pd(Na)/rGO-ZnCr2O4 as a representative example demonstrates an outstanding benzyl alcohol oxidation activity in the Pickering emulsion system in comparison to the alkali-free counterpart. The response experiments of water injection confirm the enhanced activity, and the Na-modified catalyst can further enhance the promotion effects of water on the reaction. The effects of alkali cations for Pd nanoparticles are identified and deciphered by a series of experimental characterizations (XPS, in situ CO-DRIFTS, and CO-TPR coupled with MS), showing that there is abundant −OH on the surface of the catalyst, which is stabilized by the formation of Pd−OHx. The alkali-stabilized Pd−OHx is helpful to enhance the water-induced reaction process. According to the results of in situ Raman as well as UV-vis absorption spectra, the Na-modulated Pd(Na)/rGO-ZnCr2O4 enables the beneficial characteristics for distorting the benzyl alcohol structure and enhancing the adsorption of benzyl alcohol. Further, the mechanism for enhanced water promotion effects is rationally proposed. The strategy of alkali cations-modified catalysts can provide a new direction to effectively enhance the chemical reaction involving small molecule water. 相似文献