回旋行波管的全固态Marx高压脉冲调制器设计

为回旋行波管设计了全固态近方波Marx高压脉冲调制器,设计参数:输出电压70kV,输出电流15A,工作频率0~2kHz可调,脉宽200μs可调,功率容量可以达到百kW级。设计利用串联IGBT作为控制开关,利用FPGA通过光纤传输的方式对IGBT进行逻辑控制、电路保护和监测,补偿单元利用FPGA控制IGBT自动补偿的方式对顶部压降进行补偿,使得输出电压平顶度达到±1%。对电路各个部分进行仿真及测试。结果验证此设计方案的可行性,可以提高回旋管电源的稳定性和工作频率,减小调制器体积及维护成本,并为高压测试提供了实验基础。     

Characterization of an electrochemical mercury sensor using alternating current,cyclic, square wave and differential pulse voltammetry

Here we report the characterization of an electrochemical mercury (Hg²⁺) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a “signal-off” sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a “signal-off” or “signal-on” sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed “signal-on” behavior at low frequencies and “signal-off” behavior at high frequencies. In DPV, the sensor showed “signal-off” behavior at short pulse widths and “signal-on” behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10 nM, with a linear dynamic range between 10 nM and 500 nM. In addition, the sensor responded to Hg²⁺ rather rapidly; majority of the signal change occurred in <20 min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg²⁺, which has not been previously reported. More importantly, the observed “switching” behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors.     

White and narrow band image compressor based on a new color space for capsule endoscopy

In this paper, we present the design of a low power and hardware efficient image compressor integrated circuit for wireless capsule endoscopy application. The proposed compression algorithm supports dual-band imaging, that is, works on both white-band imaging (WBI) and narrow-band imaging (NBI). The scheme uses a novel color-space and simple predictive coding for optimized performance. Based on the nature of the narrow- and white-band endoscopic images and video sequences, several sub-sampling schemes are introduced. The proposed dual-band compressor is designed in such as way that it can easily be interfaced with any commercial low power image sensor that outputs RGB image pixels in a raster scan fashion, eliminating the need of large buffer memory and temporary storage. Both NBI and WBI reconstructed images have been verified by medical doctors for acceptability. Compared to other designs targeted to video capsule endoscopy, the proposed algorithm performs strongly with a compression ratio of 80.4% (for WBI) and 79.2% (for NBI), and a high reconstruction peak-signal-to-noise-ratio (over 43.7 dB for both bands). The results of the fabricated chip are also presented.     

Adaptive depth truncation filter for MVC based compressed depth image

In multiview video plus depth (MVD) format, virtual views are generated from decoded texture videos with corresponding decoded depth images through depth image based rendering (DIBR). 3DV-ATM is a reference model for the H.264/AVC based multiview video coding (MVC) and aims at achieving high coding efficiency for 3D video in MVD format. Depth images are first downsampled then coded by 3DV-ATM. However, sharp object boundary characteristic of depth images does not well match with the transform coding based nature of H.264/AVC in 3DV-ATM. Depth boundaries are often blurred with ringing artifacts in the decoded depth images that result in noticeable artifacts in synthesized virtual views. This paper presents a low complexity adaptive depth truncation filter to recover the sharp object boundaries of the depth images using adaptive block repositioning and expansion for increasing the depth values refinement accuracy. This new approach is very efficient and can avoid false depth boundary refinement when block boundaries lie around the depth edge regions and ensure sufficient information within the processing block for depth layers classification. Experimental results demonstrate that the sharp depth edges can be recovered using the proposed filter and boundary artifacts in the synthesized views can be removed. The proposed method can provide improvement up to 3.25 dB in the depth map enhancement and bitrate reduction of 3.06% in the synthesized views.     

只收不发--AIS技术在舰船上的应用

在分析和讨论了通导设备AIS的发射技术的基础上,分别就时分多址、时域和频域层面说明信道的有限性和电磁辐射特性。然后针对船舶终端的只收不发的需求,提出三个解决方案。     

基于FPGA+DSP架构视频处理系统设计

实时图像处理技术在工业、医学、军事和商业等领域有广泛的应用。基于FPGA+DSP架构的视频处理系统充分发挥了各自器件的长处,不仅设计周期短,开发费用低,而且设计灵活,更改方便,功耗较低,便于实现系统的小型化。因此对基与FPGA+DSP架构的视频处理系统进行研究和设计具有重要的意义[1]。     

变电站直流系统绝缘低情况分析

本文根据某重要枢纽变电站直流系统中存在的直流系统绝缘低隐患,结合现场实际情况及直流接地故障查找原理,重点阐出现系统直流绝缘偏低时,运行人员应如何分析,如何排除干扰,并利用现有的设备查找故障,确定系统中绝缘低的支路。     

基于动态规划算法的数字图像变位压缩技术探究

在众多数字图像的压缩编码技术中,变位压缩编码技术是基于动态规划算法,它可高效解决许多算法无法解决的问题。在用动态规划算法解决实际问题时,把相互关联的重叠子问题只求解一次,把其状态存入一个二维表中,如果有相同或相似的问题可以直接从二维表中取出结果,减少了重复,提高了效率。     

基于残差偏置和查找表的高光谱图像无损压缩

为了提高高光谱遥感图像的压缩比,提出一种基于残差偏置和查找表的高光谱图像无损压缩方法。在高光谱图像的第一谱段图像采用了无损压缩标准中值预测器方法进行谱段内预测,其它谱段图像采用谱间预测方法。首先,在多级查找表（LAIS-LUT）预测方法的基础上搜索当前预测值,用当前预测值周围特定的5个像素点和当前像素值周围相同位置的5个像素点进行比较,通过比较结果,得出一个偏置值;然后在预测残差上加上偏置值;最后,将最终预测残差进行算术编码,并进行了理论分析和实验验证。结果表明,针对美国航空航天局的高光谱图像,所提出的方法比LAIS-LUT压缩比平均提高0.05;针对国内高光谱图像,该方法比LAIS-LUT压缩比平均提高0.07。这一结果对提高高光谱图像压缩效率是有帮助的。     

光束发散角对紫外LED散射通信接收能量的影响

为了更准确地研究紫外光的通信性能,针对紫外LED散射光通信中光能量传输特征,以及光束发散角对散射链路构成与接收光子能量有一定影响,采用多个LED组成阵列发射的方法,扩大光束与散射体的作用效应,分析了光束发散角对不同散射体作用时光子能量的变化关系,研究了紫外光散射通信脉冲调制方法与提高发射功率措施,提出了脉冲位置调制驱动阵列LED的解决方案,并进行了紫外LED散射通信系统室外传输测试。结果表明,在短距离通信中,大的散射角使得光对散射体的作用区域增大,散射效应明显,到达光接收端的光子数量增加;实际通信应用中,散射光通信具有较高的灵活性和实时性,可适当进行光学处理来优化光路结构。此结果为进一步增加传输距离和传输效果提供了正确的指导。