基于数字相干叠加的相干光正交频分复用系统中光纤非线性容忍性研究

光正交频分复用系统中的光纤非线性效应制约着系统进一步的扩容. 针对此问题, 提出一种数字相干叠加的方法, 用于提高相干光正交频分复用系统对光纤非线性的容忍性. 仿真中, 5通道的波分复用下偏振复用相干光正交频分复用系统的每个通道传输四进制正交振幅调制映射的71.53 Gbit/s信号在光纤中传输400 km. 首先, 通道间隔为25 GHz, 与传统相干光正交频分复用系统相比, 色散补偿前后, 使用数字相干叠加的相干光正交频分复用系统的信噪比分别提升了6.02 dB和9.05 dB, 最佳入纤光功率均增大了2 dB; 其次, 通道间隔为50 GHz, 色散补偿前后, 信噪比分别提升了4.9 dB和8.75 dB. 通过理论推导及仿真, 验证了所提方法能有效消除相干光正交频分复用系统的一阶非线性失真, 进而提高系统对光纤非线性的容忍性.     

Confidence intervals and ellipsoids for estimable functions and estimable vectors in models with orthogonal block structure

Sub-models of mixed linear models are considered. The independence of these sub-models leads to sufficient statistics for the parameters relevant for their densities. Using pivot variables, confidence regions are obtained as well hypothesis testing for variance components, estimable functions, and estimable vectors. In addition, to compare the estimators and the models, we present the histograms with the empirical joint densities for positive and negative parts of the estimators. The figures, for the two-dimensional charts, contain the corresponding UMVUE and are all unimodal with the UMVUE near the mode. The nearness of the estimators and the modes validates the presented methodology and allows the safe use of induced densities. A numerical example applied to real data is presented.     

A case of Budd-Chiari syndrome: Gd-EOB-DTPA-enhanced MR findings

Budd-Chiari syndrome (BCS) is a rare disorder caused by the obstruction of hepatic venous outflow, leading to sinusoidal congestion, ischemic injury to liver cells and portal hypertension. Long-term survival largely depends on whether hepatocellular carcinoma occurs. A recently available liver-specific contrast medium, gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA), reportedly has high diagnostic capability for detection of malignant liver tumors. However, there has been no report of the sue of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) for BCS. We present a case of chronic BCS who underwent both gadopentetate dimeglumine (Gd-DTPA) and Gd-EOB-DTPA-enhanced MRI. Hepatic congestion and edema were seen as slightly hypointense areas on Gd-EOB-DTPA-enhanced hepatobiliary-phase images, although these areas were observed as slightly hyperintense on previously obtained Gd-DTPA-enhanced delayed-phase image. Reduced uptake of Gd-EOB-DTPA by hepatocytes in the region of congestion or edema may account for this difference, which should be recognized in image interpretations.     

高功率激光驱动器中小尺度自聚焦和噪声模型

 建立了一套线性的近似分析方法，研究高功率激光驱动器中强激光传输的小尺度自聚焦效应和相位噪声对光束传输和光束质量的影响，给出了系统噪声强度、B积分值与光束近场调制对比度之间的定量关系。研究表明,为保证输出光束质量，即近场调制对比度小于给定值，系统内的噪声强度必须符合一定的谱分布。     

变工况下旋转机械故障跟踪的相空间曲变方法

为实现在工况变化条件下对旋转机械的故障预测, 提出使用相空间曲变和平滑正交分解理论在变工况条件下跟踪旋转机械的故障演化过程. 首先在对目标系统的观测时间序列相空间重构的基础上, 通过量化相空间曲变构建信号损伤演化的跟踪函数, 为弥补累积模型误差和相空间点局部分布概率差异造成的误差, 将时间序列和相空间进行分割, 并以此构建跟踪矩阵; 再利用平滑正交分解方法将跟踪矩阵中分别由实际损伤劣化和工况变化造成的演化趋势进行分离, 根据平滑正交特征值提取出其中能够反映实际故障演化趋势的平滑正交分量; 最后以变转速情况下轴承外环故障退化的仿真信号为例验证算法的有效性. 计算结果表明: 本文提出的算法能够对旋转机械故障的演化趋势实现有效跟踪, 基本排除转速波动造成的工况变化影响. 关键词： 相空间曲变 平滑正交分解 变工况 故障跟踪     

直视型微光夜视系统最小可分辨对比度模型

从信号检测和人眼视觉角度出发,研究了直视微光夜视系统综合性能评估理论,推导出直视型微光成像系统的MRC（最小可分辨对比度）模型。该模型将光学传递特性与系统信噪比结合,建立了系统直视微光夜视MRC与目标特性、直视微光夜视仪以及人眼各部分参数之间的数学关系。验证结果表明,由该模型得到的系统极限分辨率相较于系统实际测出的分辨率相对误差为3.08%。     

一种严格最佳(ν,k,1)光正交码的设计方法

介绍了严格最佳和准最佳(ν,k,1)光正交码的定义，阐述了它们与(ν,k,1)循环差集族的关系。基于Wilson均匀分布差引理和初等数论的基本理论，提出一种最佳(ν,k,1)循环差集族的构造方法，即构造定义在ν阶有限域上满足特定约束条件的k元集合。将该方法用于光正交码的设计中，可以有效地设计一些严格最佳(ν,k,1)光正交码，其中，码长ν为素数，码重k的取值为4、5和6。最后结合具体实例，给出严格最佳(ν,k,1)光正交码的计算机辅助设计方法。同其他设计方法相比，该设计方法既简单又实用，尤其对严格最佳（ν,k,1）光正交码而言，设计效率较高；随着码重k的增加，码的设计效率逐渐降低。     

Interference of circularly polarized light: contrast and application in fabrication of three-dimensional periodic microstructures

The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously.     

基于正弦灰度变换的X光图像增强

介绍了灰度变换法的几种形式 ,提出了一种正弦非线性变换法 ,对三幅数字X光医学图像进行了处理 ,获得了令人满意的对比度增强效果 ,证明该方法有效而实用