基于正交化算法的三值互连神经网络模型

提出了以信息损失最少为原则的三值(±1)互连权重编码方法，这种编码方法比以前的三值权重编码方法显著地提高了神经网络的性能。由于互连权重只有三值，恰恰弥补了光互连精度不高的缺点，易于光学实现。     

Feasibility of fat-saturated T2-weighted magnetic resonance imaging with slice encoding for metal artifact correction (SEMAC) at 3T

Background and Purpose

Fluid-sensitive MR imaging in postoperative evaluation is important, however, metallic artifacts is inevitable. The purpose is to investigate the feasibility of fat-saturated slice encoding for metal artifact correction (SEMAC)-corrected T2-weighted magnetic resonance (MR) at 3T in patients with spinal prostheses.

Methods

Following institutional review board approval, 27 SEMAC-encoded spinal MRs between September 2012 and October 2013 in patients with spinal metallic prostheses were analyzed. The MR images were scanned on a 3T MR system including SEMAC-corrected and uncorrected fast spin echo (FSE) T2-weighted MR images with fat-saturation. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images using a five-point scale in terms of artifact reduction around the prosthesis, visualization of the prosthesis and pedicle, and intervertebral neural foramina. Quantitative assessments were performed by calculating the ratio of signal intensity from the fixated vertebra and that from upper level vertebra. For statistical analyses, paired t-test was used.

Results

Fat-saturated SEMAC-corrected T2-weighted MR images enabled significantly improved metallic artifact reduction (P < 0.05). Quantitative evaluation of the signal intensity ratio of screw-fixated vertebra and upper level vertebra showed a significantly lower ratio on fat-saturated SEMAC images (P < 0.05), however, the high signal intensity of signal pile-up could be not completely corrected.

Conclusion

SEMAC correction in fat-suppressed T2-weighted MR images can overcome the signal loss of metallic artifacts and provide improved delineation of the pedicle screw and peri-prosthetic region. Signal pile-up, however, could not be corrected completely, therefore readers should be cautious in the evaluation of marrow around the prosthesis.     

40 Gb/s超短光脉冲序列的四相编解码实验研究

采用3码片的超结构光纤布拉格光栅(SSFBG)作为编/解码器,该编/解码器光栅包含3段子光栅(空间码片),在相邻的空间码片的边界处存在离散的四相相移(0,π/2,π,3π/2)。利用四相编解码所具有的良好自相关和互相关特性,成功实现了单信道速率高达40 Gb/s,码片速率高达240 Gchip/s的全光编解码实验。据我们所知,这是利用光纤布拉格光栅作为编/解码器的全光码分复用(OCDM)系统所达到的最高单信道传输速率。理论计算和实验结果表明了利用超结构光纤布拉格光栅(SSFBG)实现多相高速全光编解码的可行性。这样高速的全光编解码可以应用于光码分复用系统和分组交换网络。     

利用偏振编码实现取零阈值的单通道击中与否运算

基于数学形态学的对偶法则以及数学形态学理论与线性位移不变系统理论间的关系,引入了偏振编码技术,提出使击中与否运算通过单通道取零阈值非相干光学相关器来实现的方案。该方案采用偏振编码,将图像的前景和背景都包含在一个编码图像中,从而使击中与否运算可以用一个腐蚀算子完成(即通过单通道实现),大大简化了实验装置,节约了空间,降低了对光路调节的要求。同时,通过取零阈值,消除了由于入射光强分布不均匀及CCD光电响应的非完全线性所导致的对输出图像取阈值时出现的误差。最后,还对该方案进行了实验验证,结果表明这是一种方便、准确、有效的图像处理方法。     

气象卫星云图压缩编码方法的研究

本文根据对气象卫星云图统计特性的研究结果,提出了一种“差分变换—Huffman编码算法”,并利用该算法对气象卫星云图进行信息保持型压缩编码。文中介绍了在程序中应用本文作者所提出的最小频数顺序合成—逆序分解算法实现这种压缩编码的基本步骤。通过对实际卫星云图磁带数据的压缩编码,结果表明,平均压缩比高达2.4～3.9,最高编码效率达97.9%,并且解码复原图象准确无误。     

An Optical Image Encryption Method Using Hopfield Neural Network

In this paper, aiming to solve the problem of vital information security as well as neural network application in optical encryption system, we propose an optical image encryption method by using the Hopfield neural network. The algorithm uses a fuzzy single neuronal dynamic system and a chaotic Hopfield neural network for chaotic sequence generation and then obtains chaotic random phase masks. Initially, the original images are decomposed into sub-signals through wavelet packet transform, and the sub-signals are divided into two layers by adaptive classification after scrambling. The double random-phase encoding in 4f system and Fresnel domain is implemented on two layers, respectively. The sub-signals are performed with different conversions according to their standard deviation to assure that the local information’s security is guaranteed. Meanwhile, the parameters such as wavelength and diffraction distance are considered as additional keys, which can enhance the overall security. Then, inverse wavelet packet transform is applied to reconstruct the image, and a second scrambling is implemented. In order to handle and manage the parameters used in the scheme, the public key cryptosystem is applied. Finally, experiments and security analysis are presented to demonstrate the feasibility and robustness of the proposed scheme.     

多波段复合密度假彩色编码

本文根据陆地资源卫星遥感图象的多波段特点,首次提出用光学滤波进行多波段图象复合的密度假彩色编码法.先制作一张带有两个不同波段信息的夹层型位相调制图象,然后在白光信息处理系统中解调以获得能反映出不同密度及其复合效果的假彩色图象.文中讨论了编码原理并给出了实验结果.这种新方法估计也能同样有效地应用于“多波段”的X射线及电镜黑白图象.     

光栅调制密度假彩色化及其应用

本文讨论黑白片光栅调制密度假彩色化的基本原理和实验方法。将黑白金相片和X—CT颅脑片进行假彩色处理,分析了假彩色图片与黑白图片相比在判读时的优点。     

基于矢量叠加实现差分编码的光子模数转换方案

提出并验证了一种基于矢量叠加原理对输入射频信号进行差分编码的光子模数转换方案.该方案采用两路不同波长脉冲源通过一个相位调制器对输入射频信号进行调制,调制输出接入延时线干涉仪从而产生两路具有固定相位差的差分调制信号.利用矢量叠加模块对两路差分调制信号的强度进行不同程度的衰减和组合,从而获得系统量化所需的各路传递函数之间的相移量.该方案能够对输入射频信号实现差分编码,有效提高了系统的比特精度.同时该方案结构简单,只需要一个相位调制器,一个延时线干涉仪和一个矢量叠加模块即可构建.另外,各路传递函数之间的相移量是通过衰减两路差分调制信号的强度来实现,避免了传统光子模数转换方案中调制器对温度、环境敏感而引入的相位漂移问题.本文对4比特模数转换系统进行了原理性验证,实验结果证实了基于矢量叠加原理的光子模数转换方案的可行性.     

Encoding entanglement-assisted quantum stabilizer codes

We address the problem of encoding entanglement-assisted (EA) quantum error-correcting codes (QECCs) and of the corresponding complexity. We present an iterative algorithm from which a quantum circuit composed of CNOT, H, and S gates can be derived directly with complexity O(n²) to encode the qubits being sent. Moreover, we derive the number of each gate consumed in our algorithm according to which we can design EA QECCs with low encoding complexity. Another advantage brought by our algorithm is the easiness and efficiency of programming on classical computers.