光纤通信系统中基于光学相位共轭和预啁啾的色散及非线性补偿研究

采用光学相位共轭补偿光纤通信系统的色散及非线性必须满足一个前提条件,即相位共轭器两边线路上的色散和非线性分布(或传输功率分布)必须严格对称,这在现有的一般传输线路（标准单模光纤加集总掺铒光纤放大器）难以实现。提出了预啁啾结合中距相位共轭的补偿方案,并进行了数值计算。结果表明,通过在发送端对输入脉冲进行预啁啾展宽,可有效地减轻非线性效应与色散的相互作用,获得理想的补偿效果;对于皮秒超短光脉冲传输,脉冲内拉曼散射相对于三阶色散对补偿结果的影响很小,因此,频域相位共轭相对于时域相位共轭具有更好的综合补偿性能。该方案简单易行,无需对已敷设好的线路作较大改动。     

摄影测量图像处理的高精度误差补偿法

在高精度的摄影测量中,图像处理精度对整体测量精度起着至关重要的作用,但成像过程中摄像机对特征点图像的离散化采样,会造成图像与原始信号的失真,从而带来图像处理环节的误差。通过对图像处理过程中特征点总能量、能量分布弥散半径和图像处理窗口的特性分析,并以特征点中心位置、提取误差大小和能量密度函数的标准差之间关系为基础,提出一种针对离散化采样的误差补偿法。该方法仅需标定一次补偿参数,适用于所有摄像机和算法,可显著提升原有图像处理精度。实验证明,对于质心法和高斯拟合法,该补偿法可将图像提取精度提高到0.03pixel。     

pr3+ 激活的CaMoO4红色荧光粉的发光性质

采用高温固相法制备了稀土pr3+激活的Ca1-xPrxMoO4(0.005≤x≤0.02)系列红色荧光粉.荧光光谱表明:在453 nm激发下,样品产生了红光发射,其中对应于pr3+的特征跃迁3 P0→3F2位于654 nm的红色发射峰最强.分析了pr3的掺杂摩尔分数x对样品发光强度的影响,确定pr3+的最佳掺杂摩尔分数...     

温度和振动对光纤马赫-曾德干涉仪的影响与动态补偿研究

环境温度变化和振动会引起光纤马赫-曾德干涉仪两臂相差随机性变化,致使干涉仪输出不稳定.本文研究了自然条件下外界温度和振动对基于3×3耦合器干涉仪的影响,分析结果表明,温度和振动所引起的干扰主要集中于100Hz以下的低频成分中.为了消除这些干扰,设计了单臂补偿的反馈回路以稳定输出信号,并提出了一种利用象限判决方法来区分反馈正负性的动态补偿方法.实验中利用3×3耦合器3个输出端中其中2个进行光电变换、差分放大等反馈电路后驱动管状压电陶瓷,使缠绕在其上的光纤伸缩,动态补偿干涉仪相差的漂移,稳定干涉仪输出即3×3耦合器第三输出端口的信号.针对自然环境下温度和振动引起的干扰,本文研制了一种稳定的动态补偿装置,能有效抑制160Hz以下的低频干扰,实时补偿干涉仪两臂的相差漂移,干涉仪输出稳定的干涉信号,波动幅度小于5.64%.     

Suppression of Anderson localization in a graphene sheet applied by a random voltage pattern

We theoretically study the transport of electronic waves through a graphene sheet applied by a random voltage pattern in which the magnitudes and/or the widths of the voltages are random. When the magnitudes of the voltages exceed the electronic energy, the applied region can be considered as left-handed (LH) layers. Compared to the disordered structures with right-handed (RH) layers only, the spectra of the (average) density of states and the localization lengths in mixed random structures with RH and LH layers all show the suppression of Anderson localization, owing to the phase compensation effect of LH layers that reduces the long-range interference in the random system.     

An anti-attack model based on complex network theory in P2P networks

Complex network theory is a useful way to study many real systems. In this paper, an anti-attack model based on complex network theory is introduced. The mechanism of this model is based on a dynamic compensation process and a reverse percolation process in P2P networks. The main purpose of the paper is: (i) a dynamic compensation process can turn an attacked P2P network into a power-law (PL) network with exponential cutoff; (ii) a local healing process can restore the maximum degree of peers in an attacked P2P network to a normal level; (iii) a restoring process based on reverse percolation theory connects the fragmentary peers of an attacked P2P network together into a giant connected component. In this way, the model based on complex network theory can be effectively utilized for anti-attack and protection purposes in P2P networks.     

Critical properties of mixed spin-1 and spin-5/2 with equal and unequal crystal fields

The effects of assuming equal or unequal crystal fields (CF) on the phase diagrams of a mixed spin-1 and spin-5/2 system are investigated in terms of the recursion relations on the Bethe lattice (BL). The equal CF case was considered for the coordination numbers q=3, 4, and 6, while for q=3 the unequal CF case was also studied. It was found that for the equal CF case, the model exhibits second-order phase transitions and two compensation temperatures for all q, the reentrant behavior for q=4 and first-order phase transitions and tricritical point (TCP) for q=6. In the unequal CF case for q=3, the system yields first- and second-order phase transitions, TCP's, and three compensation temperatures. In addition, the TCP's in a very short range are classified as the stable and unstable ones depending on their free energies.     

Dispersion compensation for an ultrathin metal film using LCD—CCD system

A dispersion compensation method is introduced to correct the distorted image passing through an ultrathin metal film.An LCD-CCD system is modeled by the back propagation network and used to evaluate the transmittance of the ultrathin metal film.Training samples for the network come from 729 images captured by shooting test patches,in which the RGB values are uniformity distributed between 0 and 255.The RGB value of the original image that will be distorted by the dispersion is first transformed by mapping from the LCD to the CCD,multiplied by the inverse matrix of the transmittance matrix,and finally transformed by mapping from the CCD to the LCD,then the corrected image is obtained.In order to verify the effectiveness of the proposed method,ultrathin aluminum films with different thicknesses are evaporated on glass substrates and laid between the CCD and LCD.Experimental results show that the proposed method compensates for the dispersion successfully.     

First‐principles calculations of the stability and electronic properties of the PbTiO3 (110) polar surface

The structural and electronic properties of five terminations of cubic lead titanate (PbTiO₃) (110) polar surface were investigated by first‐principles total‐energy calculations using a periodic slab model. On the PbTiO termination, an anomalous filling of conduction band was observed, whereas on the O₂ termination, two surface oxygen atoms formed a peroxo group, demonstrating that the electronic structures of the two stoichiometric terminations undergo significant changes with respect to bulk materials. However, for the three nonstoichiometric TiO‐, Pb‐, and O‐terminated surfaces, their electronic structures are very similar to bulk. Charge redistribution results for the five terminations confirmed that electronic structure and surface composition changes are responsible for their polarity compensation. However, which mechanism actually dominates the stabilization process depends upon energetic considerations. A thermodynamic stability diagram suggested that the two stoichiometric terminations are unstable; however, the three nonstoichiometric terminations can be stabilized in some given regions. Furthermore, this study indicates that the very different stabilities and surface states filling behaviors of the PbTiO₃ (110) polar surface with respect to SrTiO₃ and BaTiO₃ ones seem to originate from the partially covalent characteristics of Pb O pairs. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

A General Theoretical Model of Enthalpy‐Entropy Compensation

Enthalpy‐entropy compensation remains a mystery in chemistry and biophysics. Recent study suggested that the solvent reorganization might constitute the physical origin of the compensation, which was unfortunately not widely applicable because compensation was also observed in solid phase reactions. In this study, a general theoretical model based upon strict mathematical deduction was presented, which indicated that the redistribution of the distinguishable subspecies might be the physical origin of the enthalpy‐entropy compensation in complex systems. As examples, the enthalpy‐entropy compensations in solvation and surface adsorption were discussed.