某型电动飞机螺旋桨振动特性实验研究

某型电动飞机采用螺旋桨产生拉力,为了防止螺旋桨工作时共振,利用ES-2-150振动实验系统进行了两叶木质螺旋桨和碳纤维螺旋桨的振动特性实验,采用谐振搜索与驻留方法测量出木质螺旋桨的第一阶固有频率为36.07Hz,碳纤维螺旋桨的第一阶固有频率为73.58Hz。螺旋桨爬升状态转频为39Hz,这与木质螺旋桨的第一阶固有频率非常接近,导致木质螺旋桨在爬升状态出现比较严重的振动故障。因此,某型电动飞机最终选择两叶碳纤维螺旋桨作为其拉力产生装置。     

Analytical and numerical studies for Seiches in a closed basin with bottom friction

A standing wave oscillation in a closed basin, known as a seiche, could cause destruction when its period matches the period of another wave generated by external forces such as wind, quakes, or abrupt changes in atmospheric pressure. It is due to the resonance phenomena that allow waves to have higher amplitude and greater energy, resulting in damages around the area. One condition that might restrict the resonance from occurring is when the bottom friction is present. Therefore, a modified mathematical model based on the shallow water equations will be used in this paper to investigate resonance phenomena in closed basins and to analyze the effects of bottom friction on the phenomena. The study will be conducted for several closed basin shapes. The model will be solved analytically and numerically in order to determine the natural resonant period of the basin, which is the period that can generate a resonance. The computational scheme proposed to solve the model is developed using the staggered grid finite volume method. The numerical scheme will be validated by comparing its results with the analytical solutions. As a result of the comparison, a rather excellent compatibility between the two results is achieved. Furthermore, the impacts that the friction coefficient has on the resonance phenomena are evaluated. It is observed that in the prevention of resonances, the bottom friction provides the best performance in the rectangular type while functioning the least efficient in the triangular basin. In addition, non-linearity effect as one of other factors that provide wave restriction is also considered and studied to compare its effect with the bottom friction effect on preventing resonance.     

对史密斯-帕塞尔自由电子激光光栅的研究

为了研究史密斯-帕塞尔自由电子激光的输出频率和光栅槽深、光栅槽长、光栅槽宽的关系,对于基于矩形光栅的史密斯-帕塞尔自由电子激光利用粒子模拟软件进行模拟和理论分析。首先,利用粒子模拟软件模拟对于基于矩形光栅的史密斯-帕塞尔自由电子激光进行了研究,发现史密斯-帕塞尔自由电子激光的输出频率随光栅槽深、光栅槽长、光栅槽宽的增大而减少。接着,对史密斯-帕塞尔自由电子激光的光栅槽进行了理论分析,发现每个光栅槽都可以等效为一个LC谐振电路,并发现在史密斯-帕塞尔自由电子激光中存在两种辐射,一种是史密斯-帕塞尔辐射,另一种是LC振荡辐射。最后,对光栅槽的LC振荡辐射进行了估算,发现史密斯-帕塞尔自由电子激光输出频率的模拟值与光栅槽的LC振荡辐射估算值的数量级均为102 GHz,且变化规律上一致。据此推测决定史密斯-帕塞尔自由电子激光输出频率的应该是光栅槽,而不是谐振腔。     

Apodization‐Assisted Subdiffraction Near‐Field Localization in 2D Phase Diffraction Grating

Conventional phase diffraction gratings can be used to localize the incoming optical radiation in the near‐field region. A new design of the binary phase diffraction grating is proposed with embedded pupil opaque mask inside each stripe. By means of numerical simulations, it is shown that with this masked phase grating the spatial resolution of the near‐field localization can be substantially improved and brought even beyond the solid immersion limit (λ/2n). Moreover, due to anomalous apodization effect, the subdiffraction field localization is accompanied by intensity enhancement as compared to the non‐masked design. The pupil mask rearranges the optical fluxes within the stripes and promotes the Fano resonances excitation in the periodic step lattice. This can be important for advancing the phase grating‐based super‐resolution technologies, including subdiffraction imaging, interferometry, and surface fabrication.     

RIG型磁光薄膜的研究进展及应用

随着光通信技术与光子集成电路的发展,非互易性器件作为光通信系统中重要的组成部分得到了越来越广泛的研究与应用。基于磁光效应制成的磁光隔离器和环行器是目前应用最为广泛的非互易性器件,为了将非互易性器件整块集成在硅片上,需制备性能与块状磁光材料相当的磁光薄膜。在近红外通信波段(1 550 nm),以钇铁石榴石(Y₃Fe₅O₁₂,YIG)为代表的稀土铁石榴石(RIG)具备优良的磁光效应,是最具应用前景的磁光材料之一。研究发现,使用稀土离子对YIG薄膜进行掺杂可以有效改善其磁光性能,尤其是Bi³⁺和Ce³⁺掺杂的YIG表现出巨法拉第效应。本文首先介绍了法拉第效应原理,介绍了三种常见磁光薄膜的生长方法,回顾了近年来的主要研究成果,介绍了磁光薄膜在光隔离器和环行器中的应用,最后对磁光薄膜的未来发展趋势进行了展望。     

Ni单原子催化剂表面CO2电还原动力学的电化学谱学解析

针对Ni单原子催化剂表面的CO₂电还原反应(CO₂RR), 提出了以Ni为活性位点的“单中心”机理以及同时借助Ni位点还原和碳氮锚定位水解的“双功能”机理. 依据稳态极化的实验结果, 开展了CO₂RR的动力学解析与模型参数的敏感性分析; 借助暂态模型方程, 分别获取可表达CO₂RR线性与非线性频响特征的电化学阻抗谱(EIS)与总谐波失真(THD)谱. 研究结果表明, CO₂的溶解分压对CO₂RR活性影响最显著. 若CO₂RR遵循“单中心”机理, Ni位点COOH_ads的形成为速率控制步骤; 但若为“双功能”机理, 碳氮锚定位的水解与Ni位点的CO_2,ads还原同为速率控制步骤. EIS理论上可用于区分CO₂RR的“单中心”机理与“双功能”机理; 与之相比, THD谱在CO₂RR的机理识别中并无优势.     

Ammonia Oxidation Enhanced by Photopotential Generated by Plasmonic Excitation of a Bimetallic Electrocatalyst

We study how visible light influences the activity of an electrocatalyst composed of Au and Pt nanoparticles. The bimetallic composition imparts a dual functionality: the Pt component catalyzes the electrochemical oxidation of ammonia to liberate hydrogen and the Au component absorbs visible light by the excitation of localized surface plasmon resonances. Under visible-light excitation, this catalyst exhibits enhanced electrochemical ammonia oxidation kinetics, outperforming previously reported electrochemical schemes. We trace the enhancement to a photochemical potential resulting from electron–hole carriers generated in the electrocatalyst by plasmonic excitation. The photopotential responsible for enhanced kinetics scales linearly with the light intensity—a general design principle for eliciting superlative photoelectrochemical performance from catalysts comprised of plasmonic metals or hybrids. We also determine a photochemical conversion coefficient.     

Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy

The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra.     

Melamine–Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material

In the last two decades, a large number of self-assembled materials were synthesized and they have already found their way into large-scale industry and science. Hydrogen-bond-based supramolecular adducts are found to have unique properties and to be perfect host structures for trapping target molecules or ions. Such chemical systems are believed to resemble living matter and can substitute a living cell in a number of cases. Herein, a report on an organic material based on supramolecular assembly of barbituric acid and melamine is presented. Surprisingly, the structure is found to host and stabilize radicals under mild conditions allowing its use for biological applications. The number of free radicals is found to be easily tuned by changing the pH of the environment and it increases when exposed to light up to a saturation level. We describe a preparation method as well as stability properties of melamine–barbiturate self-assembly, potentiometric titration, and hydrogen ions adsorption data and EPR spectra concerning the composite.