Single-channel color image encryption using phase retrieve algorithm in fractional Fourier domain

A single-channel color image encryption is proposed based on a phase retrieve algorithm and a two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and then permuted by a sequence of chaotic pairs generated by the two-coupled logistic map. Secondly, the permutation image is decomposed into three new components, where each component is encoded into a phase-only function in the fractional Fourier domain with a phase retrieve algorithm that is proposed based on the iterative fractional Fourier transform. Finally, an interim image is formed by the combination of these phase-only functions and encrypted into the final gray scale ciphertext with stationary white noise distribution by using chaotic diffusion, which has camouflage property to some extent. In the process of encryption and decryption, chaotic permutation and diffusion makes the resultant image nonlinear and disorder both in spatial domain and frequency domain, and the proposed phase iterative algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.     

基于单路定时准确的低复杂度成对载波复用多址信号盲分离算法

该文分析了传统逐幸存路径处理(Per-Survivor Processing, PSP)算法模型,给出了改进的前馈非二元码软输出维特比(Soft Output Viterbi Algorithm, SOVA)PSP算法。针对单路定时准确的情况,提出了针对成对载波复用多址(Paired Carrier Multiple Access, PCMA)信号的SOVA-PSP盲分离算法。该算法相对传统的PSP算法状态数由原来的M2(L-1)减少到M(L-1)(其中M为调制阶数,L为等效信道响应长度),从而大幅度地降低了算法复杂度。仿真结果表明,改进的算法在降低复杂度的同时与传统PSP算法相比性能几乎没有损失。     

改进混合积累的单通道机载SAR高径向速度目标检测方法

高径向速度目标会产生严重的距离走动并伴随方位失配,方位压缩会使其散焦并弥散在SAR图像中,不易被检测。该文针对高径向速度目标的检测问题,提出一种基于单通道机载SAR的检测方法。该方法通过抽取等效双通道,利用相干对消抑制杂波,并去除动目标的频谱分裂,再运用Dechirp处理和Hough变换积累目标在距离单元内和距离单元间的能量,以获得更大的积累增益。与传统的混合积累方法相比,该方法在抑制杂波的基础上,更好地积累高径向速度目标的能量,从而有效提高该类目标的检测性能。仿真数据和实测数据均验证了该方法的有效性和优越性。     

Stochastic nanopore sensors for the detection of terrorist agents: Current status and challenges

Nanopore stochastic sensor works by monitoring the ionic current modulations induced by the passage of analytes of interest through a single pore, which can be obtained from a biological ion channel by self-assembly or artificially fabricated in a solid-state membrane. In this minireview, we overview the use of biological nanopores and artificial nanopores for the detection of terrorist agents including explosives, organophosphorus nerve agents, nitrogen mustards, organoarsenic compounds, toxins, and viruses. We also discuss the current challenge in the development of deployable nanopore sensors for real-world applications.     

面向多路源信号的单通道盲去卷积算法研究

传统的单通道盲去卷积的方法存在仅能从混合信号中分离出2路源信号的局限,考虑到以上问题,该文提出一种基于优化的深度卷积生成对抗网络的单通道盲去卷积算法(SCBDC),能从1路混合信号中分离和解卷积出3路以上的独立源信号和混合矩阵.该文实验在汉字和遮挡图像数据集上进行,随机选择4路信号与混合矩阵进行卷积混合,实验结合峰值信...     

周期性非均匀采样实现星载SAR高分辨宽测绘带成像

针对单通道星载SAR系统高分辨与宽测绘带之间的矛盾,该文提出了一种周期性非均匀采样的解决方法。该方法利用非均匀的方位采样,避开距离盲区的重叠,使得相同距离单元的盲区最多出现在一个采样通道内;然后利用方位采样的周期性,构造出等效的多通道数据,通过多通道解模糊的方法实现方位信号频谱恢复。文中还详细分析了非均匀采样的优化设计方法。最后仿真实验验证了该文方法的有效性。     

单通道SAR无模糊估计快速运动目标速度

该文提出一种利用单通道相位信息无模糊估计地面运动目标径向速度方法。在距离频域做两视处理,并在多普勒域经过两视干涉处理,使得运动目标的干涉相位满足相位连续性假设。利用最小二乘线性拟合估计干涉相位关于多普勒频率的斜率,径向速度可由该斜率计算得到。该文方法具有不受相位缠绕影响的优点。相比于单通道幅度方法,该方法具有更高的估计精度和实时性。该方法在多普勒域能够同时估计多个目标径向速度。通过实测数据处理验证了该文方法的有效性。     

利用纠错编码的同频调制混合信号单通道盲分离

该文建立了同频调制编码混合信号的基本模型,提出了基于M-PSP的利用编码信息的单通道盲分离算法,重点研究了状态格图的构建、分支度量的计算和信道响应的跟踪。仿真结果表明,利用编码的单通道盲分离算法可以获得比不利用编码更好的性能,对于1/2码率的卷积编码BPSK信号,在误码率为10-4时,信噪比改善可达到2dB左右。     

Development of a temperature-variable magnetic resonance imaging system using a 1.0T yokeless permanent magnet

A temperature variable magnetic resonance imaging (MRI) system has been developed using a 1.0 T permanent magnet. A permanent magnet, gradient coils, radiofrequency coil, and shim coil were installed in a temperature variable thermostatic bath. First, the variation in the magnetic field inhomogeneity with temperature was measured. The inhomogeneity has a specific spatial symmetry, which scales linearly with temperature, and a single-channel shim coil was designed to compensate for the inhomogeneity. The inhomogeneity was drastically reduced by shimming over a wide range of temperature from −5 °C to 45 °C. MR images of an okra pod acquired at different temperatures demonstrated the high potential of the system for visualizing thermally sensitive properties.