基于压缩感知与扩展小波树的自适应压缩成像

为了在现有的采样条件下,通过新的压缩采样方式获得计算量小且质量更好的图像,提出了基于压缩感知与扩展小波树的自适应压缩成像方法。首先将图像投影到分区控制的DMD上,获得图像在低分辨率下的测量值,并通过压缩感知重构算法重构出低分辨图像,接着利用扩展小波树预测重要小波位置,通过DMD在小波域采样获取图像的细节信息,最后由小波逆变换恢复高分辨率图像。将该方法与最小化全变分算法（TVAL3）和近来提出的基于扩展小波树的自适应成像算法（EWT-ACS）效果进行对比,实验结果表明,以boat图像为例,在压缩感知采样率为0.75,整体采样率为10%的无噪声条件下,该方法相较于TVAL3、EWT-ACS算法信噪比提高了4.63 dB和2.87 dB,在附加噪声条件下成像效果也较好。该方法能极大地降低压缩感知重建算法的运行时间,同时减少采样次数,具有较好的抗噪性。     

光子集成干涉成像系统微透镜排布设计与图像复原

光子集成干涉成像系统体积小、重量轻、功耗小,且系统分辨率不受单个透镜口径尺寸的限制,是一种新兴的成像技术.针对光子集成干涉成像系统图像复原问题,开展了图像复原技术和微透镜阵列最优排布研究,提出了基于压缩感知的光子集成干涉成像图像恢复技术,以及基于图像残差的最优微透镜阵列排布设计评估方法;通过计算仿真,可实现在有限空间体...     

压缩感知理论在图像处理领域的应用

针对传统的采样方法得到的图像数据量巨大,给图像信息的后续处理造成极大压力的问题,对压缩感知理论（Compressed Sensing,CS）进行了研究。压缩感知理论使采集很少一部分数据并且从这些少量数据中重构出更大量信息的想法变成可能,突破了奈奎-斯特采样定理的限制。综述了CS理论及关键技术问题,并着重介绍了CS理论在成像系统、图像融合、图像目标识别与跟踪等方面的应用与发展状况。文章指出CS理论开拓了信息处理的新思路,随着该理论的进一步完善,会有更广泛的应用领域。     

用于随机解调器压缩采样的重构判定方法

提出了一种随机解调器压缩采样重构成败的判定方法. 该方法利用两次连续重构所得稀疏信号支撑之间的相关性来判断重构是否成功,其计算复杂度低,易于实现. 仿真结果表明,该方法能准确判断随机解调器压缩采样重构成败,用于宽带频谱感知中能够显著降低信号不稀疏时对主用户的干扰概率. 关键词： 认知无线电 频谱感知 随机解调器 压缩采样     

压缩感知理论在图像处理领域的应用

针对传统的采样方法得到的图像数据量巨大,给图像信息的后续处理造成极大压力的问题,对压缩感知理论(Compressed Sensing,CS)进行了研究。压缩感知理论使采集很少一部分数据并且从这些少量数据中重构出更大量信息的想法变成可能,突破了奈奎-斯特采样定理的限制。综述了CS理论及关键技术问题,并着重介绍了CS理论在成像系统、图像融合、图像目标识别与跟踪等方面的应用与发展状况。文章指出CS理论开拓了信息处理的新思路,随着该理论的进一步完善,会有更广泛的应用领域。     

窄带高光谱干涉成像的压缩采样复原方法

利用干涉成像光谱仪对目标进行窄带高光谱成像探测具有高光通量、高光谱分辨率和高目标分辨率等优点。按照尼奎斯特定理对窄带光谱干涉信息进行采样存在较大的数据冗余,增加了后期傅里叶变换的数据处理量,影响光谱的复原效率。在分析窄带光谱傅里叶变换特性的基础上,提出了基于滤光片光谱透射率函数的窄带光谱压缩采样方法。引入滤光片参数和混叠参数,可以复原不同精度的窄带光谱信息。配以符合要求的多带通窄带滤光片,可对目标进行压缩采样获取多个谱段的窄带光谱信息,从而避免了逐个谱段探测,提高了探测效率。对该方法进行了仿真分析和实验验证,得到了与目标光谱相吻合的复原窄带光谱。     

基于离散余弦变换的语音压缩采样和编码算法

针对语音无线通信中带宽资源受限的问题,提出基于压缩采样的低速率语音编码算法。以基尼系数为指标,比较不同稀疏变换域下语音信号的稀疏性,分析常见重构算法对语音信号压缩采样观测信号的重构特性。对标准耳蜗滤波器——伽马啁啾滤波器组的参数进行研究,并以梯度投影稀疏重建(GPSR)算法重构语音信号。利用语音质量感知评估(PESQ)、信噪比和主观听觉测试,对编解码后的合成语音信号进行了质量评估。实验表明,基于压缩感知的语音编码器以4 kbps的低速率对语音进行编码时,PESQ得分可达到3.16,计算复杂度相对较低,可以用于实际的语音编码环境。     

基于指数再生窗Gabor框架的窄脉冲欠Nyquist采样与重构

基于Gabor框架的窄脉冲信号采样及重构效果已经得到验证, 其解决了有限新息率(finite rate of innovation, FRI)采样方法无法在波形未知的情况下重构出脉冲波形的问题.但是目前的Gabor框架采样系统的窗函数构造复杂且难以物理实现.本文将指数再生窗函数引入Gabor框架, 将窗函数序列调制部分简化为一阶巴特沃斯模拟滤波器, 构造了Gabor系数重构所需要的压缩感知(compressed sensing, CS)测量矩阵.为了使得测量矩阵满足信号精确重构所需的约束等距特性(restricted isometry property, RIP), 根据高阶指数样条函数能量聚集特性, 选择了最优的窗函数支撑宽度, 推导了信号重构所需的约束条件, 还对其鲁棒性进行了分析.本文通过仿真实验对上述分析进行了有效验证, 该系统可应用于测试仪器、状态监测、雷达及通信领域等多种背景下的窄脉冲信号采样与重构.     

基于分块压缩感知理论的太赫兹波宽光束成像技术

提出了一种基于分块压缩感知理论的太赫兹波宽光束成像技术。模拟结果显示,该技术可以实现高分辨率、高质量的快速成像。采用连续太赫兹波CO_2气体激光器光源,基于宽光束矩阵调制采样,对不同物体进行了分块压缩感知成像,并与基于单像素随机采样的分块压缩感知方法进行了对比。结果表明,所提技术具有更高的成像稳定性,且其采样过程对不同成像物体的普适性更好。     

不同采样模式的固体DQ-SQ实验的压缩感知重建比较

为了提高固体二维双量子-单量子(DQ-SQ)谱的采集速度,根据DQ-SQ谱的自稀疏性,该文使用了一种基于压缩感知技术的重建算法.其优化的能量函数是有限差分约束的l1范数,并使用不同的权重对水平和竖直方向的有限差分项进行约束.该文分别对伪随机采样、全随机采样和e指数采样等采样模式进行了比较,发现伪随机采样表现出最佳的重建结果.进一步研究发现伪随机的极限形式,即t1截尾(t1-cutoff)采样模式效果最佳.     

托普利兹-循环块相位掩膜矩阵压缩成像

在托普利兹和循环矩阵的基础上,提出一种新的托普利兹-循环块相位掩膜矩阵可压缩双透镜成像方法.模拟实验结果表明:新的相位掩膜矩阵压缩成像可以在显著减少测量的同时,有效地捕获图像信息来重建原始图像|新相位掩膜矩阵的研究为确定性测量在压缩成像领域的应用提供了更多的支撑,在拥有原托普利兹和循环确定性测量优点的同时,还拥有自身的块结构特点,可以进一步减少物理实现成本,为新的照相机的设计提供若干理论、计算和技术支撑.     

托普利兹-循环块相位掩膜矩阵压缩成像

在托普利兹和循环矩阵的基础上,提出一种新的托普利兹-循环块相位掩膜矩阵可压缩双透镜成像方法,模拟实验结果表明:新的相位掩膜矩阵压缩成像可以在显著减少测量的同时,有效地捕获图像信息来重建原始图像;新相位掩膜矩阵的研究为确定性测量在压缩成像领域的应用提供了更多的支撑,在拥有原托普利兹和循环确定性测量优点的同时,还拥有自身的...     

确定性矩阵可分离压缩成像

针对可分离压缩传感使用的可分离随机正交矩阵在处理大尺度图像等高维信号感知时难度太大或成本过高的问题,引入确定性测量矩阵,提出确定性矩阵可分离压缩传感,可将如托普利兹矩阵及循环矩阵等具有确定性结构的矩阵作为可分离压缩传感的左、右可分离矩阵.该方案可以降低独立元素的数目,从而显著降低前端物理实现的难度与成本.数值模拟实验分别评估了该方法在不同采样率及不同图像尺寸下的压缩重建性能,结果表明该方法在独立元素非常少的情形下得到与原随机正交矩阵相近的重建质量,证明了其可行性.     

确定性相位掩膜可压缩双透镜成像

压缩成像是压缩传感理论的一个重要应用领域.本文将确定性测量引入压缩成像,提出一种确定性相位掩膜可压缩双透镜成像方法.模拟实验结果表明,新的成像方法可以在显著地降低物理实现成本的同时,有效地捕获图像信息来重建原始图像.此方法改变了经典的模拟-数字转换的光学成像思路,减少模数转换开销,并有利于图像的传输和存储,可以为照相机的设计提供若干理论、计算和技术支撑.     

Changes in ferroelectric properties of lead indium niobate-lead titanate ceramics under compressive stress applied perpendicular to an electric field

The influences of perpendicular compressive stress on the ferroelectric properties of (1−x)Pb(In_1/2Nb_1/2)O₃-xPbTiO₃ (x=0.1-0.4) ceramics were investigated in this study. In general, with increasing compressive stress the coercive field and the dissipation energy of the ceramics were seen to increase. The stress-induced changes in the polarization, however, depended significantly on ceramic compositions. The observations were mainly interpreted in terms of competing influence of the domain switching through non-180° domain walls, clamping of domain walls, and the stress-induced decrease in the switchable part of spontaneous polarization.     

Laser Shock Processing of 6061-T6 Al alloy with 1064 nm and 532 nm wavelengths

Laser Shock Processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surface treatments in underwater laser irradiation at 532 nm and 1064 nm. The purpose of the work is to compare the effect of both wavelengths on the same material. A convergent lens is used to deliver 1.2 J/pulse (1064 nm) and 0.9 J/pulse (532 nm) in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG laser with spots of a 1.5 mm in diameter moving forward along the work piece. A LSP configuration with experimental results using a pulse density of 2500 pulses/cm² and 5000 pulses/cm² in 6061-T6 aluminum samples are presented. High level compressive residual stresses are produced using both wavelengths. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.     

Compressive mechanical behavior of Au nanowires

The structural evolution, deformation mechanism, and failure behavior of Au [001] nanowires with various sizes and slenderness ratios under uniaxial compression have been investigated using molecular dynamics. The results show that the elastic modulus, yield stress, and strain all are dependent on the diameters and slenderness ratios of the nanowires. Buckling behavior is observed in a long nanowire, followed by slips in the {111} planes. Differences are identified in the failure behavior of a short nanowire and a medium nanowire, although the plastic deformation of both types of nanowire originates from the slips in the {111} planes.     

Novel hybrid image compression–encryption algorithm based on compressive sensing

A new hybrid image compression–encryption algorithm based on compressive sensing is proposed, which can accomplish image encryption and compression simultaneously. The partial Hadamard matrix is adopted as measurement matrix, which is controlled by chaos map. The measurement is scrambled. Compared with the methods adopting the Gaussian random matrix as measurement matrix, and those using the whole measurement matrix as key, the proposed algorithm reduces the burden of transferring key and is more practical. The proposed algorithm with sensitive keys and nice image compression ability can resist various attacks. Simulation results verify the validity and reliability of the proposed algorithm.     

Analytical study for investigating the behaviour of Nd-doped Glass, YAG and GGG under the heat capacity mode of operation

In this paper, detailed analytical studies on heat capacity operation in Nd-doped glass, YAG and GGG has been reported. The effect of the rising temperature on gain and hence on the output energy/power has been numerically worked out. The studies predicted that several kilowatts of the useful output power can be extracted out from the laser materials under investigation when operated under the heat capacity mode. The studies also revealed that output power levels can be scaled up by increasing the number of disks and by increasing the disk aperture size. The factors limiting the power enhancement are also discussed. The estimated results are in good agreement with the other reported experimental results.     

Secret shared multiple-image encryption based on row scanning compressive ghost imaging and phase retrieval in the Fresnel domain

A multiple-image encryption method is proposed that is based on row scanning compressive ghost imaging, (t, n) threshold secret sharing, and phase retrieval in the Fresnel domain. In the encryption process, after wavelet transform and Arnold transform of the target image, the ciphertext matrix can be first detected using a bucket detector. Based on a (t, n) threshold secret sharing algorithm, the measurement key used in the row scanning compressive ghost imaging can be decomposed and shared into two pairs of sub-keys, which are then reconstructed using two phase-only mask (POM) keys with fixed pixel values, placed in the input plane and transform plane 2 of the phase retrieval scheme, respectively; and the other POM key in the transform plane 1 can be generated and updated by the iterative encoding of each plaintext image. In each iteration, the target image acts as the input amplitude constraint in the input plane. During decryption, each plaintext image possessing all the correct keys can be successfully decrypted by measurement key regeneration, compression algorithm reconstruction, inverse wavelet transformation, and Fresnel transformation. Theoretical analysis and numerical simulations both verify the feasibility of the proposed method.