Complex dynamics in Duffing–Van der Pol equation

Duffing–Van der Pol equation with fifth nonlinear-restoring force and two external forcing terms is investigated. The threshold values of existence of chaotic motion are obtained under the periodic perturbation. By second-order averaging method and Melnikov method, we prove the criterion of existence of chaos in averaged system under quasi-periodic perturbation for ω₂ = nω₁ + εσ, n = 1, 3, 5, and cannot prove the criterion of existence of chaos in second-order averaged system under quasi-periodic perturbation for ω₂ = nω₁ + εσ, n = 2, 4, 6, 7, 8, 9, 10, where σ is not rational to ω₁, but can show the occurrence of chaos in original system by numerical simulation. Numerical simulations including heteroclinic and homoclinic bifurcation surfaces, bifurcation diagrams, Lyapunov exponent, phase portraits and Poincaré map, not only show the consistence with the theoretical analysis but also exhibit the more new complex dynamical behaviors. We show that cascades of interlocking period-doubling and reverse period-doubling bifurcations from period-2 to -4 and -6 orbits, interleaving occurrence of chaotic behaviors and quasi-periodic orbits, transient chaos with a great abundance of period windows, symmetry-breaking of periodic orbits in chaotic regions, onset of chaos which occurs more than one, chaos suddenly disappearing to period orbits, interior crisis, strange non-chaotic attractor, non-attracting chaotic set and nice chaotic attractors. Our results show many dynamical behaviors and some of them are strictly departure from the behaviors of Duffing–Van der Pol equation with a cubic nonlinear-restoring force and one external forcing.     

基于HMM的机载设备状态健康评估方法研究

针对机载设备的状态健康评估问题,采用隐马尔科夫模型(HMM)对其进行性能退化程度的评估。首先引入状态条件概率矢量对HMM进行不确定性改进,并推导了其表达式;其次以状态条件概率比值为基础,给出了机载设备状态等级量化分值的计算方法,并据此设计了机载设备状态健康评估流程。最后以飞机发动机温控放大器为例进行仿真验证,结果表明上述方法能够给出直观、准确的状态评估结果。     

Consistency of open superstring theories

The infinities and the anomalies in the G≠SO(32) open superstring arise from the same limit of the one-loop Riemann surfaces. The dilaton tadpole infinity is removable by an appropriate choice of background, as in the work of Fischler and Susskind. However, we find that the anomalies arise from the tadpole of an unphysical field, and cannot be removed by any choice of background. Thus, the spacetime anomalies are due to a world-sheet superconformal anomaly of topological origin. We also give a general discussion of the relation between anomalies and surface terms in moduli space, and point out several new applications.     

服役环境下腐蚀坑等效为表面裂纹的有效性分析

对取自退役飞机机翼蒙皮的光滑试件进行了等幅疲劳试验,通过疲劳断口分析得到了服役环境下飞机主体材料LY12CZ 铝合金蚀坑的拓扑特征.基于飞机结构的实际腐蚀尺寸,将蚀坑的宽度和深度作为等效裂纹的长轴和短轴,并应用 Stress Check 软件对蚀坑等效为裂纹的可行性进行了有限元分析.结果表明:实际蚀坑与等效裂纹对结构应力分布的影响十分相似;应力强度因子在蚀坑等效前后数值大小和变化趋势不大.在分析蚀坑对典型试件疲劳寿命影响时将蚀坑等效成半椭圆形裂纹,选取 Walker 公式作为扩展速率模型,并与试验值进行了对比.结果表明:预测值与试验值比较吻合,最大误差为9.23%,满足工程需求.     

Rapid transfer alignment of laser SINS using quaternion based angular measurement

A novel rapid transfer alignment algorithm for laser strapdown inertial navigation system (SINS) is studied. Transfer alignment have typically relied on velocity measurements from the master SINS as the source of alignment information, but lever arm error must be compensated accurately while velocity information is utilized, all most every quaternion based error model is nonlinear, so nonlinear filtering algorithms are need, suffering from computational complex and large error. Aim at these problems, a novel improved rapid transfer alignment algorithm formulation is presented, applying quaternion to built the process and measurement models, the improvement employs a special manipulation of the measurement equation results in a linear pseudo-measurement equation, thus the classical linear Kalman filter is employed to estimate the state, need not lever arm error compensation, results in the reduce of computational burden. Observability analysis of this new transfer alignment algorithm has been done based on the piece-wise constant system (PWCS) method, results show that the presented algorithm can accomplish the initial alignment task perfectly. A transfer alignment simulation system is also developed for the evaluation and analysis of the presented algorithm, simulation results are confirmed with the theoretical conclusion, which can achieve the transfer alignment accuracy about 1 mrad within 10 s.     

基于多项式模型法的低端数码相机的颜色特性化

近年来随着数字技术,以及彩色数字图像输入输出设备的不断发展和广泛使用,颜色在不同的设备之间精确的传递或再现成为该领域的重要课题。本论文以彩色数码相机特性化为研究内容,采用多项式转换方法,研究了多项式回归模型不同系数矩阵、不同训练样本对数码相机特性化精度的影响,得出了系数矩阵为11×3多项式模型时误差较小(2.874ΔE*ab)的结论,达到了实用水平。     

激光对反舰导弹红外探测器干扰分析

针对激光对红外制导的反舰导弹干扰问题,建立了激光对反舰导弹红外探测器的干扰链路模型,推导了激光海上传输的大气透过率,计算了1．06μm激光在海上大气传输时仰角、能见度与大气透过率的关系,估算了对不同距离的反舰导弹红外探测器实现有效干扰所需发射的激光能量。     

基于可用度的复杂结构装备检修时机决策模型

为最大限度地提高装备的可用度水平,检修工作十分必要,而检修时机的确定即成为一个重要的决策问题。对于复杂结构装备,组成部件的数量、寿命分布及对应的维修策略等都是可用度的影响因素。在采取预防性维修和修复性维修相结合策略的基础上,推导出了单装备任务周期内可用度关于检修时机的表达式,以此获得了装备群系统的检修时机决策模型,并充分考虑了部件工作年龄的影响。通过实例分析,验证了模型的合理性和实用性。     

一种香豆素衍生物分子的红外光谱及核磁共振谱的理论研究

用密度泛函理论(Density Functional Theory,DFT)方法,在B3LYP/6-31G(d,p)水平上对一种香豆素衍生物分子进行几何结构优化,得到其最稳定构型、分子能量及HOMO、LUMO轨道能量。在优化结构的基础上用同样的方法,在B3LYP/6-31G基组水平上计算了该分子的红外振动光谱和核磁共振1HNMR谱,并对其红外光谱峰位及1HNMR化学位移进行了归属。     

Trichocitrin,a new fusicoccane diterpene from the marine brown alga-endophytic fungus Trichoderma citrinoviride cf-27

One new diterpene, trichocitrin (1), and four known secondary metabolites, nafuredin (2), 5-hydroxy-2,3-dimethyl-7-methoxychromone (3), 24-methylenecycloartanol (4) and citrostadienol (5), were isolated from the culture of marine brown alga-endophytic Trichoderma citrinoviride cf-27. Trichocitrin (1) represents the first Trichoderma-derived and furan-bearing fusicoccane diterpene, and its structure and relative configuration were identified by analysis of 1D/2D NMR and mass spectroscopic data. Compounds 1 and 2 exhibited 8.0- and 9.5-mm inhibition zones, respectively, against Escherichia coli at 20 μg/disc and 54.1 and 36.7% growth inhibition, respectively, of Prorocentrum donghaiense at 80 μg/mL.