直接调制半导体激光器的脉冲驱动电路研究

研制了一种应用于直接调制半导体激光器的脉冲驱动电路.根据直接数字频率合成原理,利用现场可编程逻辑阵列产生频率可调方波去触发雪崩晶体管,以及雪崩晶体管的雪崩效应产生频率可调脉宽固定在3 ns的主体脉冲.该脉冲经过衰减器衰减得到合时的脉冲幅度.输出脉冲最高频率可到100 kHz,其输出电压幅度为9 V.     

基于SIFT特征区域的抗几何攻击图像水印算法

提出了一种基于局部特征区域的抗几何攻击图像水印算法.首先利用尺度不变特征变换在载体图像的尺度空间上提取特征点并形成特征区域,该区域具有缩放、平移不变性;然后通过主方向归一化,使这些区域具有旋转不变性;最后将水印信息重复嵌入到多个不重叠的局部特征区域的DFT中频系数中.仿真结果表明,该算法在获得较好的不可见性的同时,对几何攻击和常规信号处理均具有良好的鲁棒性.     

Perceptual discrimination of very high frequency components in wide frequency range musical sound

Subjective evaluation tests on perceptual discrimination between musical sounds with and without very high frequency (above 20 kHz) components were conducted. To make a precise evaluation, the test system was designed to exclude any influence from very high frequency components in the audible frequency range. Moreover, a newly developed very wide frequency range microphone was used to record various sound stimuli that contained enough components in the very high frequency range. Tests showed that the subjects could discriminate between musical sounds with and without very high frequency components. This paper describes these subjective evaluations in terms of reproducing such very high frequency components in musical sound.     

用于核磁共振的直接数字合成频率源

直接数字频率源的使用可以简化核磁共振谱仪的设计,降低核磁共振谱仪设计的成本. 文中介绍一种采用Analog Device公司的AD7008芯片设计的基于PC机的直接数字合成频率源,它可实现频率和相位的高速切换,频率分辨率为0.01Hz,相位分辨率为0.09°,最后给出核磁共振实验结果.     

基于图象特征的小波域水印算法

提出一种基于图象特征点的小波变换域第二代水印算法.首先对图象作小波变换,其中最低频成分是图象的粗尺度(低分辨率)逼近,从中提取出图象的特征点;然后在特征点对应的所有高频系数中嵌入水印.水印检验不需要原始图象,但需要原始图象的特征点位置信息,计算特征点对应的所有高频系数与嵌入水印的互相关,利用门限值检验水印是否存在. 实验证明该算法对通常的图象处理有很强的鲁棒性,对有损压缩的鲁棒性尤为突出,而且对几何变换也有一定鲁棒性.     

图象的多尺度边缘相位水印算法

提出一种基于图象多尺度边缘的新相位水印算法.利用常用于边缘检测的二进小波刻画图象的多尺度边缘,在多尺度边缘的相位成分中嵌入数字水印,利用相关检测器进行水印检测.实验证明算法具有不可见性,较好的安全性,对通常的图象处理有很强的鲁棒性.     

The optical measurement station for complex testing of microelements

The paper presents a concept of optical measurement station for complex testing of microelements including MEMS, MOEMS and electronic components and assemblies. The wide selection of examples proves that the specific measurement requirements are fulfilled by alternative usage of combined conventional and grating interferometers CI/GI (reflective surfaces), in-plane and out-of-plane ESPI (scattering surfaces) and digital holographic interferometry DHI (mixed surfaces) supported by thermovision. All these methods are realized by integrated microinterferometer (IWaM) based on a glass waveguide or air cavity waveguide arrangements. The air cavity IWaM allows to form a thermal output for combined thermovision CI/GI or ESPI measurements.IWaM has a compact design insensitive to mechanical vibrations and may be easily rearranged to work with the selected measurement techniques. It is also fully integrated with an optical microscope and it is designed to work both in laboratories and in production environments.     

Initiation and propagation of complex 3D networks of cracks in heterogeneous quasi-brittle materials: Direct comparison between in situ testing-microCT experiments and phase field simulations

We provide the first direct comparisons, to our knowledge, of complex 3D micro cracking initiation and propagation in heterogeneous quasi-brittle materials modelled by the phase field numerical method and observed in X-ray microtomography images recorded during in situ mechanical testing. Some material parameters of the damage model, including the process zone (internal) length, are identified by an inverse approach combining experimental data and 3D simulations. A new technique is developed to study the micro cracking at a finer scale by prescribing the local displacements measured by digital volume correlation over the boundary of a small sub-volume inside the sample during the numerical simulations. The comparisons, performed on several samples of lightweight plaster and concrete, show a remarkable quantitative agreement between the 3D crack morphology obtained by the model and by the experiments, without any a priori knowledge about the location of the initiation of the cracks in the numerical model. The results indicate that the crack paths can be predicted in a fully deterministic way in spite of the highly random geometry of the microstructure and the brittle nature of its constituents.     

Large Deformation of Nitinol Under Shear Dominant Loading

Full-field quantitative strain maps of phase transformation and plasticity in Nitinol under large shear-dominated deformation are presented. To achieve a shear-dominated deformation mode with relatively uniform stresses and strains, a shear compression specimen (SCS) geometry was utilized. Shear deformation appears to impede the development of the strain localization during phase transformation that is seen in uniaxial testing. The shear-dominant deformation of Nitinol in the plastic regime exhibits low hardening and results in the development of significant strain inhomogeneity.     

基于pt100的温度测控实验装置的开发与应用

本文介绍了pt100作为温度传感器件的温度测控实验装置的开发与应用．该装置能够实现在恒温箱中进行的温度测控实验,可用于展示温度测量与控制的全过程．同时包含了信号检测、转换、处理和控制等电路．是一个开发综合性实验的范例．