一种扩大8 mm波段综合孔径辐射计成像视场的方法

针对8mm波段综合孔径辐射计射频前端电尺寸较大,采用常规Y形阵列布局系统成像视场范围小的缺点,首先提出了一种星形天线阵列布局,它使可视度函数采样点之间的间隔变为天线单元间隔的一半,从而使系统的成像视场扩大到原来的两倍;然后,针对星形阵列可视度函数采样点缺失的问题,研究了背景对消与凸集投影相结合的图像反演算法,并进行了成像仿真。仿真结果验证了该反演算法的有效性。     

Layer by layer characterisation of the degradation process in PCDTBT:PC71BM based normal architecture polymer solar cells

This work demonstrates the stability and degradation of OSCs based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadiazole)] (PCDTBT): (6,6)-Phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) photoactive blend layers as a function of ageing time in air. Analysis of the stability and degradation process for the OSCs was conducted under ambient air by using current-voltage (I-V) measurements and x-ray photoelectron spectroscopy (XPS). The interface between photoactive layer and HTL (PEDOT:PSS) was also investigated. Device stability was investigated by calculating decay in power conversion efficiency (PCE) as a function of ageing time in the air. The PCE of devices decrease from 5.17 to 3.61% in one week of fabrication, which is attributed to indium and oxygen migration into the PEDOT:PSS and PCDTBT:PC₇₁BM layer. Further, after aging for 1000 h, XPS spectra confirm the significant diffusion of oxygen into the HTL and photoactive layer which increased from 3.0 and 23.3% to 20.4 and 35.7% in photoactive layer and HTL, respectively. Similarly, the indium content reached to 17.9% on PEDOT:PSS surface and 0.4% on PCDTBT:PC₇₁BM surface in 1000 h. Core-level spectra of active layer indicate the oxidation of carbon atoms in the fullerene cage, oxidation of nitrogen present in the polymer matrix and formation of In₂O₃ due to indium diffusion. We also observed a steady fall in the optical absorption of the active layer during ageing in ambient air and it reduced to 76.5% of initial value in 1000 h. On the basis of these experimental results, we discussed key parameters that account for the degradation process and stability of OSCs in order to improve the device performance.     

任意截面的非平行多导体传输线瞬态分析

以分析多导体传输线的时域有限差分(FDTD)法为基础,在考虑任意截面传输线分布参数无法直接计算的情况下,提出MOM-FDTD 混合方法对不平行多导体传输线进行瞬态分析。首先,利用FDTD建立多导体传输线时域差分模型,然后用MOM 法计算任意截面形状的非平行传输线的分布参数,并且与FDTD法混合进行瞬态分析计算。此算法相对于全波算法,在时间与存储空间消耗上具有很大的优势,并且满足精度要求。最后通过同轴传输线与矩形带状线的例子验证这个方法是正确有效的。     

均匀设计法研究PZT铁电薄膜制备工艺的优化

应用射频磁控溅射工艺在Pt/Ti/SiO2/Si衬底上制备具有钙钛矿结构的PZT铁电薄膜。对影响PZT薄膜性能、形貌的工作气压、基片温度、氧/氩 氧之比、溅射功率、退火温度5个主要因素进行分析,在其允许范围和精度内设置5个水平,并根据均匀设计理论对该5因素及5水平进行均匀设计。不同温度下退火之后测定了PZT薄膜的厚度、SEM表面形貌、电容、介电损耗、电滞回线(包括矫顽场强、饱和极化强度、剩余极化强度)等。最后对响应结果进行多元二次线性回归,得出了回归方程。探讨达到最优化薄膜特性所需要的工艺条件。     

Adaptive histogram-based filter for image restoration

A novel filter for image restoration is proposed in this paper. The filter estimates histogram of original image via input image. It gets a membership function through the histogram, and the membership function contains a lot of information of original image. Then a weighted fuzzy mean filter is established based on this membership function; meanwhile, the filter adaptively adopts different filter scale according to the character divergence of image region and intensity of impulsive noise. Experimental result shows that new filter gives superior performance to conventional filters and currently used fuzzy filter.     

多视点视频编码中的视频目标提取与视差匹配

在单通道视频目标分割算法的基础上,首先提出一种多视点视频编码中的视频目标提取方案.然后提出一种基于多级块匹配视差估计算法.应用Moravec算子对视差矢量图进行检测,提取特征视差矢量并对其进行精确度检验.若特征视差矢量不够精确,则其所在块将重新进行小范围的块匹配.若块匹配误差仍太大则将其分裂为四个子块重新匹配.与传统块匹配算法相比,新方法能获得较为精确和平滑的视差场,提高重建后的图像质量.     

MPEG-2压缩域的视频数字水印新算法

视频数字水印技术是当前水印研究中的一个热点.本文提出一种视频数字水印新算法,直接对压缩后的视频数据流进行操作,根据运动矢量的特征值,将水印信息嵌入到运动矢量上,不需要完全解码和再编码过程.所提出的水印算法简单、有效,实现了水印盲检.与嵌入水印前的原视频图像相比,嵌入水印后的视频图像信噪比损失很小.     

综合孔径辐射计二维稀疏天线阵列排列方法

考价值.     

基于三维DCT的彩色图象自适应水印算法

本文提出了一种基于3D-DCT的彩色图象自适应水印算法.证实了RGB彩色图象的3D-DCT比2D-DCT具有更好的能量汇聚性质并因此具有更大的感觉容量,从而允许嵌入更强的水印信号.在此基础上,提出了利用人眼彩色视觉特性来自适应控制水印嵌入强度的方法.实验证明该算法较好地平衡了隐形水印的不可见性和稳健性之间的矛盾,所隐藏的水印对常规性攻击,如JPEG压缩、加性噪声、图象滤波、彩色变化和亮度/对比度变化等,具有很好的抵抗能力.     

A novel batch-based group key management protocol applied to the Internet of Things

Many applications for ad hoc networks are based on a point-to-multipoint (multicast) communication paradigm, where a single source sends common data to many receivers, or, inversely, on a multipoint-to-point communication paradigm, where multiple sources send data to a single receiver. In such scenarios, communication can be secured by adopting a common secret key, denoted as “group key”, shared by multiple communication endpoints. In this work, we propose a novel centralized approach to efficiently distribute and manage a group key in generic ad hoc networks and Internet of Things, while reducing the computational overhead and network traffic due to group membership changes caused by users’ joins and leaves. In particular, the proposed protocol takes advantage of two possible leave strategies: (i) at a pre-determined time selected when the user joins the group or (ii) at an unpredictable time, as in the case of membership revocation. The proposed protocol is applied to two following relevant scenarios: (i) secure data aggregation in Internet of Things (IoT) and (ii) Vehicle-to-Vehicle (V2V) communications in Vehicular Ad hoc Networks (VANETs).