自由端盖Ⅲ型宽带弯张换能器的设计

提出了一种利用多模耦合实现低频、宽带、大功率特性的新结构Ⅲ型弯张换能器。通过在压电陶瓷堆内部嵌入与凹型弯张壳体相连的弹性辅助弯曲梁结构,并用弯曲圆盘作为顶部自由端盖,增加有效工作模态。利用有限元方法对换能器进行了设计优化,分析结果显示换能器在低频段存在4个主要工作模态。根据优化结果,加工制作了换能器样机,水池实验的测试结果表明:在1.5～5.5 kHz范围内,换能器样机的发送电压响应均大于135 dB;1.5～4 kHz内的最大发送电压响应大于142 dB,响应起伏小于6 dB。研究结果表明自由端盖Ⅲ型弯张换能器不仅能够在小尺寸设计下实现大功率工作,还能获得低频宽带发射性能。     

解耦法:一个构建简化或骨架机理的有效方法

高保真的简化或骨架反应机理对多维计算流体力学（CFD）燃烧模拟极其重要。首先,针对不同简化目标,使用包含误差传播和敏感性分析的直接关系图方法（DRGEPSA）通过简化主要参比燃料（PRF）详细机理,获得了一系列简化机理,发现简化机理的结构随简化目标的改变而显著不同;其次,基于不确定性定量化方法评估简化机理的性能,结果表明为避免简化机理的预测结果失真,需要在简化方法中使用较小的相对误差;最后,提出了解耦法的理论依据,并使用该方法构建PRF燃料的骨架机理。结果发现通过耦合详细H₂/CO/C₁子机理和骨架C₄-C_n子机理,最终的骨架机理能够满意地预测滞燃期和火焰传播速度。     

Use of a Lanthanide Shift Reagent for Simplified NMR Analysis of Borneol—Isoborneol Mixtures. Apparent Catalysis of OH Proton Exchange by LSR

The use of ¹H NMR at low field (60 MHz spectrometer frequency) for direct analysis of mixtures of borneol, 1, and isoborneol, 2, is considerably simplified by addition of the lanthanide shift reagent (LSR), tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), 3. The effect of added 3 is twofold. Firstly, the analytical marker signals of the methine proton CHOH in 1 and 2, which are partly overlapped at 60 MHz in CDCl₃ (28°), are separated and rendered baseline-resolved due to preferential LSR binding to the less hindered endo OH of 1. Secondly, the absorption signals of the CHOH methines actually sharpen in the presence of 3, and display clearly defined multiplet structure, attributed to full exchange decoupling of the vicinal OH as a result of enhanced OH exchange rates when LSR is present.     

Noncommutative stochastic integration through decoupling

We present an abstract approach to noncommutative stochastic integration in the context of a finite von Neumann algebra equipped with a normal, faithful, tracial state, with respect to processes with tensor or freely independent increments satisfying a stationarity condition, using a decoupling technique. We obtain necessary and sufficient conditions for stochastic integrability of Lp-processes with respect to such integrators. We apply the theory to stochastic integration with respect to Boson and free Brownian motion.     

A new decoupling method for accurate quantification of polyethylene copolymer composition and triad sequence distribution with 13C NMR

(13)C NMR is a powerful analytical tool for characterizing polyethylene copolymer composition and sequence distribution. Accurate characterization of the composition and sequence distribution is critical for researchers in industry and academia. Some common composite pulse decoupling (CPD) sequences used in polyethylene copolymer (13)C NMR can lead to artifacts such as modulations of the decoupled (13)C NMR signals (decoupling sidebands) resulting in systematic errors in quantitative analysis. A new CPD method was developed, which suppresses decoupling sidebands below the limit of detection (less than 1:40,000 compared to the intensity of the decoupled signal). This new CPD sequence consists of an improved Waltz-16 CPD, implemented as a bilevel method. Compared with other conventional CPD programs this new decoupling method produced the cleanest (13)C NMR spectra for polyethylene copolymer composition and triad sequence distribution analyses.     

Investigation of structure factors in dense colloidal suspensions using frequency domain photon migration: polydisperse systems

Frequency domain photon migration (FDPM) technique was employed to investigate the structure factors of dense, polydisperse colloidal suspensions. The angle-integrated structure factors, [S(q)], extracted from FDPM measurements of scattering properties at volume fractions ranging from 0.05 to 0.4, were compared with the values predicted from the polydisperse hard sphere Percus-Yevick (HSPY) model, as well as decoupling approximation (DA) and local monodisperse approximation (LMA) models that incorporated independently measured particle size information. Results show that the polydisperse HSPY model is the most suitable for accounting for particle interactions which predominantly arise from volume exclusion effects. Furthermore, the influence of size polydispersity upon [S(q)] is most significant at high volume fractions. The static structure factors at small wave vector q, S(0), were also assessed from dual wavelength FDPM measurements by using the small wave number approximation as well as the local monodisperse approximation. The measured S(0) agrees well with the values predicted by the polydisperse HSPY model.     

Invariant Foliations and Decoupling of Non-autonomous Difference Equations

In this paper, we continue a previous study of the geometric properties of a certain prototype system of nonautonomous difference equations. In fact, we show that by means of the fundamental theorem on the existence of invariant fiber bundles two foliations of the extended state space can be found. This detailed information about the geometric structure of the underlying system is then used to construct transformations establishing the topological equivalence between a given coupled and a completely uncoupled system.     

Interference of homonuclear decoupling and exchange in the solid-state NMR of perfluorocyclohexane

We observe an interference between RF irradiation used for homonuclear decoupling of 19F and conformational exchange in the 13C spectrum of perfluorocyclohexane. We show that these effects can be readily reproduced in simulation, and characterise their dependence on the various NMR and experimental parameters. Their application to observing exchange rates on the kHz timescale is evaluated with respect to T(1rho) measurements and the connections between the two approaches established. The implications for experiments that use homonuclear decoupling of 1H to resolve 1J(CH)couplings in the solid-state are also evaluated in detail.     

三点式氧碘化学激光器光腔准直技术

 提出三点式动态准直法,并以此设计具有自动校准功能的光腔自准直系统,提高了氧碘化学激光器的光束质量。该系统采用位置传感器作为光束位置检测元件,压电陶瓷作为动态调整元件,建立三输入三输出的耦合模型,利用多变量自适应闭环解耦控制法,实现准直系统的高速动态调整,实现了光腔准直,提高了光束质量。经初步实验验证,该系统准直范围可达4 mrad,精度为5 mrad,响应频率达20 Hz,满足氧碘化学激光器对光腔准直系统的要求。