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排序方式: 共有2245条查询结果,搜索用时 15 毫秒
1.
Nonlinear Dynamics - The delayed Duffing equation $${\ddot{x}}(t)+x(t-T)+x^3(t)=0$$ is shown to possess an infinite and unbounded sequence of rapidly oscillating, asymptotically stable periodic... 相似文献
2.
Nonlinear Dynamics - Intelligent fault diagnosis provides great convenience for the prognostic and health management of the rotating machinery. Recently, the multiscale diversity entropy has been... 相似文献
4.
Let n>1 and B be the unit ball in n dimensions complex space Cn.Suppose thatφis a holomorphic self-map of B andψ∈H(B)withψ(0)=0.A kind of integral operator,composition Cesàro operator,is defined by Tφψ(f)(z)=∫10f[φ(tz)]Rψ(tz)dt/t,f∈(B)z∈B.In this paper,the authors characterize the conditions that the composition Cesàro operator T_φ,ψis bounded or compact on the normal weight Zygmund space Z_μ(B).At the same time,the sufficient and necessary conditions for all cases are given. 相似文献
5.
Nonlinear Dynamics - Linearizing the equations of motion of a constrained multibody system is a common need in, for example, stability analyses. While the theory of modelling multibody systems is... 相似文献
6.
高端芯片制造所需要的极紫外光刻技术位于我国当前面临35项"卡脖子"关键核心技术之首.高转换效率的极紫外光源是极紫外光刻系统的重要组成部分.本文通过采用双激光脉冲打靶技术实现较强的6.7 nm极紫外光输出.首先,理论计算Gd18+—Gd27+离子最外层4d壳层的4p-4d和4d-4f能级之间跃迁、以及Gd14+—Gd17+离子最外层4f壳层的4d-4f能级之间跃迁对波长为6.7 nm附近极紫外光的贡献.其后开展实验研究,结果表明,随着双脉冲之间延时的逐渐增加,波长为6.7 nm附近的极紫外光辐射强度呈现先减弱、后增加、之后再减弱的变化趋势,在双脉冲延时为100 ns处产生的极紫外光辐射最强.并且,在延时为100 ns处产生的光谱效率最高,相比于单脉冲激光产生的光谱效率提升了33%.此外,发现双激光脉冲打靶技术可以有效地减弱等离子体的自吸收效应,获得的6.7 nm附近极紫外光谱宽度均小于单激光脉冲打靶的情形,且在脉冲延时为30 ns时刻所产生的光谱宽度最窄,约为单独主脉冲产生极紫外光谱宽度的1/3.同时... 相似文献
7.
Catalytic decomposition of NH_3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts. Here, we report the facile preparation of ultra-fine ruthenium(Ru) species dispersed on Mg O, which show excellent activity and high temperature stability for NH_3 decomposition reaction. The hydrogen yield of the prepared Ru/Mg O catalysts reaches ca. 2,092 mmol H_2 g~(–1) Ru min~(–1) at450 °C, far exceeding that of the previously reported most reactive Ru-based catalysts and the same chemical composition samples prepared by other approaches. Various characterization techniques containing X-ray absorption fine structure(XAFS),in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRTFTS) and temperature-programmed reduction/desorption(TPR/TPD) were carried out to explore the structure-function relation of the prepared Ru/Mg O catalysts. We found that the Ru species interact strongly with the Mg O support, which can efficiently protect the Ru species and Mg O support from agglomerating during NH_3 decomposition test, maintaining the stability of the catalysts. 相似文献
8.
Xiaodong Si Yuanyuan Jia Xinqi Luan Luo Yang Yong Pei Wang Zhou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(9):2686-2690
A variety of benzofuranone‐based spiroisochromenes were originally designed and synthesized to gain insight into the oxa‐6π electrocyclic reaction of cis,cis‐1,8‐dioxatetraene for the first time. The stability of the 1,8‐dioxatetraene intermediate is governed by its steric congestion and can be fine‐tuned through modification of the backbone structure, leading to the reactivity differences in the 6π electrocyclic reaction and the emergence of photochromic properties. 相似文献
9.
Yuxiang Chen Ke Gong Feng Jiao Xiulian Pan Guangjin Hou Rui Si Xinhe Bao 《Angewandte Chemie (International ed. in English)》2020,59(16):6529-6534
Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn2+‐ion exchanged ZSM‐5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO2) at 20 % CO conversion. NMR spectroscopy, X‐ray absorption spectroscopy, and X‐ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM‐5. Quasi‐in‐situ solid‐state NMR, obtained by quenching the reaction in liquid N2, detects C2 species such as acetyl (‐COCH3) bonding with an oxygen, ethyl (‐CH2CH3) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C?C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn2+‐ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ‐13, MCM‐22, and ZSM‐12) all give ethane predominantly. By contrast, a physical mixture of ZnO‐ZSM‐5 favors formation of hydrocarbons beyond C3+. These results provide an important guide for tuning the product selectivity in syngas conversion. 相似文献
10.
以3-异丙基苯乙酮(1)为原料,经3步反应合成了花青醛[3-(3-异丙基苯基)丁醛(4)],并优化了反应条件。确定合成3-(3-异丙基苯基)-2-丁烯酸乙酯(2)的最优条件为:n(1)/n(磷酰基乙酸三乙酯)/n(氢化钠)=5/6/6,于室温反应12 h,收率84.5%;合成3-(3-异丙基苯基)-1-丁醇(3)的最佳条件为:n(2)/n(硼氢化钠)/n(六水合二氯化钴)/n(二异丙基胺)=10/20/1/2,于55 ℃反应24 h,收率87.8%;合成4的最优条件为: n(3)/n(乙酸酐)/n(亚硝酸钠)=5/4/15,投料顺序为:乙酸酐、3、亚硝酸钠,反应时间为2 min,收率91.0%。产物结构经1H NMR, 13C NMR和MS(ESI)确证。 相似文献