斜坡补偿电流模式控制开关变换器的动力学建模与分析

降压型、升压型和升压-降压型DC-DC变换器是应用广泛的基本开关DC-DC变换器.电流模式控制开关DC-DC变换器在较宽的电路参数范围内具有两个边界,基于开关切换前后电感电流的上升和下降斜率,建立了斜坡补偿电流模式控制开关DC-DC变换器的统一模型.该模型进行无量纲归一化处理后只有三个参数,可有效展示开关DC-DC变换器在电感电流连续传导模式(CCM)和电感电流不连续传导模式(DCM)时的动力学特性.利用此模型,导出了轨道状态发生转移时的两个分界线方程,由此确定了开关DC-DC变换器的稳定周期1域、CCM鲁棒混沌域和DCM弱混沌强阵发域三个工作状态区域.开关DC-DC变换器二维参数映射图和电流模式控制降压型DC-DC变换器的电路实验观察验证了由两条分界线划分工作状态域的正确性.     

Adaptive co-evolution of strategies and network leading to optimal cooperation level in spatial prisoner’s dilemma game

We study evolutionary prisoner's dilemma game on adaptive networks where a population of players co-evolves with their interaction networks. During the co-evolution process, interacted players with opposite strategies either rewire the link between them with probability $p$ or update their strategies with probability $1-p$ depending on their payoffs. Numerical simulation shows that the final network is either split into some disconnected communities whose players share the same strategy within each community or forms a single connected network in which all nodes are in the same strategy. Interestingly, the density of cooperators in the final state can be maximised in an intermediate range of $p$ via the competition between time scale of the network dynamics and that of the node dynamics. Finally, the mean-field analysis helps to understand the results of numerical simulation. Our results may provide some insight into understanding the emergence of cooperation in the real situation where the individuals' behaviour and their relationship adaptively co-evolve.     

High precision Zernike modal gray map reconstruction for liquid crystal corrector

This paper proposes a new Zernike modal gray map reconstruction algorithm used in the nematic liquid crystal adaptive optics system. Firstly, the new modal algorithm is described. Secondly, a single loop correction experiment was conducted, and it showed that the modal method has a higher precision in gray map reconstruction than the widely used slope method. Finally, the contrast close-loop correction experiment was conducted to correct static aberration in the laboratory. The experimental results showed that the average peak to valley (PV) and root mean square (RMS) of the wavefront corrected by mode method were reduced from 2.501\lambda (\lambda =633~nm) and 0.610\lambda to 0.0334\lambda and 0.00845\lambda , respectively. The corrected PV and RMS were much smaller than those of 0.173\lambda and 0.048\lambda by slope method. The Strehl ratio and modulation transfer function of the system corrected by mode method were much closer to diffraction limit than with slope method. These results indicate that the mode method can take good advantage of the large number of pixels of the liquid crystal corrector to realize high correction precision.     

An algorithm for computed tomography image reconstruction from limited-view projections

<正>With the development of the compressive sensing theory,the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology.This paper develops an iterative algorithm for image reconstruction,which can fit most cases.This method gives an image reconstruction flow with the difference image vector,which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough.Then the l_2-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles.The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data.Moreover,all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed.     

Willis环状脑动脉瘤系统的自适应模糊控制

针对不确定非线性生物系统—W illis环状脑动脉瘤系统,利用高斯型模糊逻辑系统的逼近能力及新构造的Lyapunov函数,基于模糊建模提出了一种自适应模糊控制器设计的新方案.该方案把逼近误差引入到控制器设计条件中用以改善系统的动态性能.不但设计简单还保证了控制方法的鲁棒性与稳定性.通过反向传播算法调整模糊基函数参数及递归最小二乘法调整参数向量,θ更新控制律,实现了理想跟踪.从理论上研究了脑动脉瘤内血流速度的非线性行为及控制,具有实际意义.仿真结果表明该控制方法的有效性.     

Numerical differentiation from a viewpoint of regularization theory

In this paper, we discuss the classical ill-posed problem of numerical differentiation, assuming that the smoothness of the function to be differentiated is unknown. Using recent results on adaptive regularization of general ill-posed problems, we propose new rules for the choice of the stepsize in the finite-difference methods, and for the regularization parameter choice in numerical differentiation regularized by the iterated Tikhonov method. These methods are shown to be effective for the differentiation of noisy functions, and the order-optimal convergence results for them are proved.

     

曲率波前传感器探测高斯光束时的信号误差

曲率波前传感器已被用于天文自适应光学和光学度量等领域。在这些领域使用时都假设入射波前光强均匀,但这种假设与曲率传感技术的基本原理不一致。利用傅里叶光学理论,给出了光强不均匀情况下曲率波前传感器的曲率信号解析式,并利用光强均匀和不均匀情况下的信号表达式对探测高斯光束时的信号误差进行了数值分析。结果表明：曲率波前传感器探测高斯光束时存在一定误差,相位分布为4阶Zernike多项式时,误差最大,且阶数越高,误差越小;分区平均曲率信号误差较小,一般在10％以下。     

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening

In the terahertz(THz) band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.     

自适应光学系统随机并行梯度下降算法

随机并行梯度下降（SPGD）算法可以对系统性能指标直接优化来校正畸变波前。对基于SPGD算法的61单元自适应光学系统进行仿真模拟,分析了对不同初始静态畸变波前的校正能力,并比较了不同性能指标情况下的算法增益系数、扰动幅度值的选取及校正情况。仿真结果表明:算法收敛速度很大程度上依赖于增益系数和扰动幅度值,对畸变较大的波前,随机扰动幅度在0.50～0.85范围内,性能指标采用焦斑平均半径比采用斯特列尔比取得的校正效果好。     

基于机场货运预测的GM(1,1)建模过程问题分析

运用灰色系统GM(1,1)模型进行预测时,模拟精度和预测精度是关注的焦点.对原始数据构造缓冲算子和进行完整的前期检验,运用等维灰数递补的动态建模方法,针对误差建立残差修正模型,都可以提高预测的可信度.通过归纳建模各阶段可能出现的典型问题以及解决方法,以期对建立优化模型有所帮助.最后建立GM(1,1)模型预测天津滨海机场货邮吞吐量.