悬丝耦合弯曲共振法测定金属材料杨氏模量

简要介绍了用悬丝耦合弯曲拱振法测定金属材料杨氏模量实验的意义、实验原理、实验装置以及实验中的若干问题,并提出了一组实验数据供参考。     

电子闪光灯光路变换的研究

本文主要论述了直接利用电子闪光灯为光源，产生垂直反射偏振光的原理、方法及在刑事摄影中的应用。通过理论研究和试验，设计出了电子闪光灯光路变换系统，解决了直接利用电子闪光灯为光源的拍摄案件现场某些光滑非金属物体时，物体表面产生强烈反射光线或反射光带和对人犯摄影、物证摄影时的强烈阴影干扰，以及无法直接用以电子闪光灯为光源，对遗留在案件现场上的痕迹进行垂直反射摄影的困难。     

甲苯酚第一激发态的共振多光子电离谱

测量了间位甲苯酚和甲酚异构体混合物能量在３５１８０－３６００２ｃｍ＾－１范围的双光子共振四光子电离谱。对第一电子激发态振动带做了分析和归属，并对苯分子的不同取代对振动模的影响做了比较和分析。     

类锂离子O%5＋的电子碰撞电离

此文采用扭曲库仑波函数描述碰撞电子，用Ｒ─矩阵密耦波函数处理被电离电子与剩余离子构成的系统初末态，在库仑玻恩各级近似下计算了类锂离子Ｏ５＋的电子碰撞电离截面及相应速率系数，这是文献中首次使用密耦方法，在考虑通道相互作用情形下得到的结果。     

两层耦合可激发介质中螺旋波转变为平面波

采用Br-Eiswirth模型研究了两层耦合可激发介质中螺旋波的动力学,两层介质通过网络连接,即在每一层介质上,每一列选一个可激发单元作为中心点,在一层介质上同一列的可激发单元只与另一层介质上对应的中心点及其8个邻居有耦合.数值模拟结果表明:通过这种局部耦合,在适当小的耦合强度下两耦合螺旋波可实现同步,增大耦合强度会导致螺旋波漫游和漂移,造成螺旋波不同步,观察到螺旋波与静息态、低频平面波和不规则斑图共存现象.在适当强的耦合强度下,还观察到两螺旋波转变成同步的平面波消失现象.对产生这些现象的物理机理做了讨论.     

Assessing the relationship between the inter-rod coupling and the efficiency of piezocomposite high-intensity focused ultrasound transducers

The electroacoustic conversion efficiency of the ultrasonic transducer is a critical performance index for high-power applications. The material properties, volume fraction (VF) and aspect ratio (AR) are typically regarded as the design parameters of the piezocomposite transducer. We hypothesized that the spacing between piezoelectric rods was also a dominant factor. Therefore, the inter-rod coupling effects on the efficiency of 1–3 piezocomposite ultrasonic transducers were investigated in this study. The efficiencies of six flat and three curved 1.0 MHz PZT4 epoxy composite transducers with different geometric parameters were measured. Finite element transient analyses of the inter-rod electrical-mechanical coupling in the composites were carried out to explain the measured results. The experimental results showed that for 0.47 AR, the 79% VF transducers had lower efficiency than the 64% VF and 53% VF transducers. For 0.19 AR, the efficiency of the 59% VF transducer was not greater than the efficiency of the 39% VF transducer. Numerical analyses demonstrated that the positive peak voltage induced by the coupling of the side rods was more than twice the level induced by the coupling of the diagonal rods for any spacing. The diagonal coupling voltage peak did not change for spacings larger than 0.2 mm. Moreover, for spacings of 0.05 and 0.1 mm, the inter-rod coupling caused 24% and 20% waveform shifts of the driving voltage, respectively, while the 0.2 mm spacing coupling caused a 14% reduction in the amplitude of the driving voltage. As a result, the asymmetry of the driving voltage degraded the efficiency of the composite transducers and became more severe when the spacing was decreased. We concluded that the efficiency loss induced by inter-rod coupling as a function of spacing should be considered when designing piezocomposite transducers.     

High-contrast imaging for weakly diffracting specimens in coherent diffraction imaging

Coherent diffraction imaging (CDI) and ptychography techniques bypass the difficulty of having high-quality optics in X-ray microscopy by using a numerical reconstruction of the image that is obtained by inverting the diffracted intensity recorded by a charge-coupled device array. However, the reconstruction of the image from the intensity data obtained from a weakly diffracting specimen is known to be difficult because of the obvious reduction in signal-to-noise ratio (SNR). In this case, the specimen only slightly modifies the probe diffraction pattern, resulting in difficulty in the identification of the detailed structure of the specimen from the reconstructed image because of the poor contrast and sharpness of the image. To address this situation, a modification in the image retrieval algorithms used in the iterative reconstruction of the image is suggested. This modification should double the presence of high spatial frequencies in the diffraction pattern to enhance the contrast and edge detection in existing imaging techniques.     

Non‐Isothermal Crystallization Kinetics of PA6/Attapulgite Composites Prepared by Melt Compounding

The non‐isothermal crystallization behaviors of neat polyamide 6 (PA6) and PA6/attapulgite (ATB) composites were examined using differential scanning calorimetry. The results show that ATB acts as a nucleator for PA6 matrix, accelerating the crystallization, and simultaneously obstructs the crystallization especially for the composites with higher ATB content. The analysis results using the Jeziorny and Liu equations verify the dual actions of the nucleation and the obstruction of crystallization of the ATB in the PA6 matrix. Kissinger's method is employed to obtain the activation energy of the crystallization processes; the results further indicate that the addition of ATB may also cause the above actions. It is speculated that there is a very complicated crystallization mechanism in the PA6/ATB composites based on the analysis of Avrami exponents obtained by the Jeziorny model.     

用于木材水分检测的单边核磁共振传感器设计

为了实现对木材水分的无损检测,设计了一种单边核磁共振（unilateral nuclear magnetic resonance,UMR）传感器,该传感器由单边磁体、抗涡流板、射频线圈、阻抗匹配和调谐电路构成．在距离传感器表面上方75 mm处的50 mm×50 mm的平面内,建立了71.1 mT（共振频率为3.027 MHz）的静态磁场．本文详细介绍了该传感器的设计思路和实现方法,并开展了初步的木材水分无损测量实验．对圆柱形树桩的径向水分分布进行了一维扫描测量,观察了水分由树皮向树芯逐步深入过程中横向弛豫时间（T₂）的变化规律,还使用UMR仪对木材干燥过程中水分的挥发进行了测量.实验结果表明,随着干燥的加剧,被测样品T₂谱的长T₂波峰明显左移、积分面积渐减,而且积分面积与木材样品含水率呈正比．本文为木材研究提供了一种便携的NMR测量设备设计方案,且可以实现野外活体树木的无损测量．     

基于SERS与PCA-SLR实现乙基对氧磷定量检测

利用表面增强拉曼光谱(SERS),结合主成分分析(PCA)与分段线性回归(SLR)算法实现乙基对氧磷的定量检测。首先采集820～1 630 cm-1乙基对氧磷溶液SERS,并对820～1 630 cm-1(全范围)与845～875 cm-1(特征范围)光谱分别进行标准正态变换(SNV)、多元散射校正(MSC)、一阶导数绝对值、二阶导数等预处理;然后经PCA降维后利用SLR建立乙基对氧磷溶液浓度预测模型。通过对比不同模型的预测准确度,发现特征范围光谱采用MSC预处理后所建立的模型为最优,总体预测均方误差值(RMSEP)为0.33,满足乙基对氧磷定量检测的需要。