High-performance optical modulators bias control system without dither

A software-based bias control system of push–pull Mach–Zehnder modulators (MZMs) without dither tone is described in this paper. The slope of the average optical output power respect to the bias voltage is used to control the operating bias points in the automatic control system. The paper analyses the theory of automatic bias control intensively and verifies the effectiveness of the proposed technique which is a modulation-format-free method under the RF signal through testing and contrasting the BER (bit error rate) between the new technique and manual measure on the experimental platform. Based on this, an automatic bias control system set up by an optical QPSK composed by double MZMS on the LabVIEW platform is described.     

Technique for gray-scale visual light and infrared image fusion based on non-subsampled shearlet transform

A novel image fusion technique based on NSST (non-subsampled shearlet transform) is presented, aiming at resolving the fusion problem of spatially gray-scale visual light and infrared images. NSST, as a new member of MGA (multi-scale geometric analysis) tools, possesses not only flexible direction features and optimal shift-invariance, but much better fusion performance and lower computational costs compared with several current popular MGA tools such as NSCT (non-subsampled contourlet transform). We specifically propose new rules for the fusion of low and high frequency sub-band coefficients of source images in the second step of the NSST-based image fusion algorithm. First, the source images are decomposed into different scales and directions using NSST. Then, the model of region average energy (RAE) is proposed and adopted to fuse the low frequency sub-band coefficients of the gray-scale visual light and infrared images. Third, the model of local directional contrast (LDC) is given and utilized to fuse the corresponding high frequency sub-band coefficients. Finally, the final fused image is obtained by using inverse NSST to all fused sub-images. In order to verify the effectiveness of the proposed technique, several current popular ones are compared over three different publicly available image sets using four evaluation metrics, and the experimental results demonstrate that the proposed technique performs better in both subjective and objective qualities.     

结合内时理论研究岩石衰减与应变振幅的关系

本文将解决复杂弹塑性问题的有效工具内时理论,引入到岩石衰减的研究中来。根据内时理论,简要推导了在中等应变条件下,岩石衰减与应变振幅的用非弹性参数α表示的具体关系式。在MTS压机上,对砂岩、花岗岩等多种岩石样品进行了一系列的循环加卸载实验。利用应力应变滞回曲线的面积,根据衰减的能量损耗的定义,计算了各种实验条件下的岩石样品的衰减值。实验数据表明,在各次循环平均应力相等的条件下,岩石样品的衰减随应变振幅的增加而增加,与内时理论的推导结果相一致。最后,对表示岩石非弹性的参数α进行了简要的讨论。砂岩的α值较为稳定,在0.5左右;而花岗岩的α值变化较大,但二者都随着应力的增加而增加。该实验结果对地震波在地球介质中的衰减研究有一定的参考意义。     

区域密度滤波及其在数字散斑条纹处理中的应用

利用统计学原理对数字错位散斑条纹的形成进行了系统分析，并针对散斑条纹图所特有颗粒性强的特点，提出一种新的空域滤波方法－区域密度滤波。该方法能更有效地抑制散斑图中的高频噪声，也使条纹图更平滑，并且细节得到了最大程度的保存，避免了有些空域滤波法因误差积累而导致条纹移动的问题，进一步保证了相移技术和神经网络系统的计算精度。     

双稳系统中随机共振与相同步时间的相关性

研究了双稳系统的随机共振(SR)与输入输出之间的相同步相关性. 首先得到系统的输出信噪比(SNR)与输入输出之间的平均相同步时间的表达式,然后讨论了随机共振与输入输出之间的平均相同步时间之间的关系. 结果表明:(1)系统出现了随机共振现象,且平均相同步时间对噪声是敏感的;由于加性与乘性噪声的相互影响,随加性噪声强度的增加,输出信噪比及平均相同步时间曲线上首先出现抑制现象,然后出现峰值,并且, 减小乘性与加性噪声强度比率,可提高输出信噪比和增长平均相同步时间. (2)系统的随机共振与平均相同步时间达到最大值不同步出现,但平均相同步时间对输出信噪比是敏感的. 该结论为信号传输中利用随机共振原则改变系统工作环境提供了依据.      

Ensemble phase averaged equations for multiphase flows in porous media. Part 2: A general theory

Most models for multiphase flows in a porous medium are based on a straightforward extension of Darcy’s law, in which each fluid phase is driven by its own pressure gradient. The pressure difference between the phases is thought to be an effect of surface tension and is called capillary pressure. Independent of Darcy’s law, for liquid imbibition processes in a porous material, diffusion models are sometime used. In this paper, an ensemble phase averaging technique for continuous multiphase flows is applied to derive averaged equations and to examine the validity of the commonly used models. Closure for the averaged equations is quite complicated for general multiphase flows in a porous material. For flows with a small ratio of the characteristic length of the phase interfaces to the macroscopic length, the closure relations can be simplified significantly by an approximation with a second order error in this length ratio. This approximation reveals the information of the length scale separation obscured during an averaging process and leads to an equation system similar to Darcy’s law, but with additional terms. Based on interactions on phase interfaces, relations among closure quantities are studied.     

连拱式大跨悬挑屋盖抗风气动措施研究

本文对连拱式大跨度悬挑屋盖进行了数值风洞试验,分别探讨了在屋盖悬挑前缘增设通风孔、导流板以及同时布设导流板与通风孔这三种气动措施对悬挑屋盖表面风荷载的影响及其作用机理．研究结果表明,同时布设导流板与通风孔的综合气动措施,能显著影响屋盖结构前缘气流的分离,从而减小屋盖的表面风压,并可减弱屋盖的风致振动．在此类屋盖结构设计中,运用综合气动措施可有效降低屋盖整体的升力系数与弯矩系数,对该类屋盖抗风设计较为有利．     

具有幂率度分布的因特网平均最短路径长度估计

针对具有幂律度分布的复杂网络的平均最短路径长度进行了研究.给出了一个计算因特网平 均最短路径长度的公式.提出因特网的整体构造实质是以最小代价换取最大收益，从此出 发通过对因特网这类复杂网络平均最短路径长度影响因素分析，推断出网络最短路径长度分 布P(l)的基本性质，进而构造了一个只含参数α的P(l)的简洁形式，直接打通了拓扑具有幂 律度分布的因特网的度分布P(k)与网络最短路径长度分布P(l)之间的关系.然后说明了导出 的公式的物理意义，即参数α代表网络节点连接方式和网络的总边数对平均最短路径长 度的影响.此公式意味着只要掌握幂律P(k)～k-α中α值，就可以直接计算相应网 络的平均最短路径长度.通过对已知数据的计算，验证了公式的有效性.阐明了参数 α对网络设计的重要性和对网络功能的影响. 关键词： 复杂网络 幂律 度分布 平均最短路径长度     

Two-Qubit Steerability,Nonlocality, and Average Steered Coherence under Classical Dephasing Channels

When two qubits are prepared in a mixture of two Bell states and exposed to local transmission channels, the dynamics of steerability, Bell nonlocality, and average steered coherence are investigated. Disorders are assumed to influence the channels, resulting in either Markovian Ornstein–Uhlenbeck noise or non-Markovian static noise in two models: a single noisy channel or two local noisy channels. Their findings show that the type and number of classical channels, noise, and initial state must be in an optimal setting in order to preserve quantum correlations.     

An optimization of a continuous time risk process

A continuous time risk process is considered, where the premium rate is constant and the claims form a compound Poisson process. We assume that an action is taken, either an investment to other business when the level of surplus reaches V>0$V>0$ or an injection of capital when the surplus goes below τ(0<τ<V)$\tau (0<\tau <V)$. After assigning several costs related to managing the surplus, we obtain the long-run average cost per unit time. A numerical example is studied.