EXACT LINEARIZATION BASED MULTIPLE-SUBSPACE ITERATIVE RESOLUTION TO AFFINE NONLINEAR CONTROL SYSTEM

To the optimal control problem of affine nonlinear system, based on differential geometry theory, feedback precise linearization was used. Then starting from the simulative relationship between computational structural mechanics and optimal control, multiple-substructure method was inducted to solve the optimal control problem which was linearized. And finally the solution to the original nonlinear system was found. Compared with the classical linearizational method of Taylor expansion, this one diminishes the abuse of error expansion with the enlargement of used region.     

Mixed-mode I/II fields around a crack with a cohesive zone ahead of the crack tip

Considering a cohesive zone ahead of the crack tip, the linear elastic crack problem under Mode I, Mode II or mixed-mode conditions is formulated in an elliptic coordinate system, so that the cohesive surfaces are conveniently represented by straight line segments. It is shown that the displacement and stress fields around the crack tip and the cohesive zone, expressed in terms of elliptic coordinates, have a simple mathematical form, which does not contain a stress singularity at the crack tip due to the existence of the cohesive zone.     

EXPONENTIAL STABILITY OF INTERVAL DYNAMICAL SYSTEM WITH MULTIDELAY

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｓｔａｂｉｌｉｔｙｏｆｔｈｅｉｎｔｅｒｖａｌｍａｔｒｉｘａｎｄｕｎｃｅｒｔａｉｎｓｙｓｔｅｍｗｉｔｈｔｉｍｅｄｅｌａｙｈａｖｅｂｅｅｎｃｏｎｓｉｄｅｒｅｄｂｙｒｅｓｅａｒｃｈｅｒｓｉｎｔｈｅｐａｐｅｒｓ [1 -1 3 ] .Ｔｈｅｓｔａｂｉｌｉｔｙａｎｄαｅｘｐｏｎｅｎｔｉａｌｓｔａｂｉｌｉｔｙｏｆｔｈｅｆｏｌｌｏｗｉｎｇｉｎｔｅｒｖａｌｄｙｎａｍｉｃａｌｓｙｓｔｅｍｗｉｔｈｓｉｎｇｌｅｔｉｍｅｄｅｌａｙ ｘ(ｔ) =Ｎ[Ｐ ,Ｑ]ｘ(ｔ) +Ｎ[Ｃ ,Ｄ]ｘ(ｔ-τ)ｈａｖｅｂｅｅｎｃｏｎｓｉ…     

Fatigue crack growth rate in ferrite-martensite dual-phase steel

An empirical study is made on the fatigue crack growth rate in ferrite-martensite dual-phase (FMDP) steel. Particular attention is given to the effect of ferrite content in the range of 24.2% to 41.5% where good fatigue resistance was found at 33.8%. Variations in ferrite content did not affect the crack growth rate da/dN when plotted against the effective stress intensity factor range ΔK_eff which was assumed to follow a linear relation with the crack tip stress intensity factor range ΔK. A high ΔK_eff corresponds to uniformly distributed small size ferrite and martensite. No other appreciable correlation could be ralated to the microstructure morphology of the FMDP steel. The closure stress intensity factor K_cl, however, is affected by the ferrite content with K_cl/Kmax reaching a maximum value of 0.7. In general, crack growth followed the interphase between the martensite and ferrite.Dividing the fatigue crack growth process into Stage I and II where the former would be highly sensitive to changes in ΔK and the latter would increase with ΔK depending on the R = σ_min/σ_max ratio. The same data when correlated with the strain energy density factor range ΔS showed negligible dependence on mean stress or R ratio for Stage I crack growth. A parameter α involving the ratio of ultimate stress to yield stress, percent reduction of area and R is introduced for Stage II crack growth so that the da/dN data for different R would collapse onto a single curve with a narrow scatter band when plotted against αΔS.     

Feedback minimization of first-passage failure of quasi non-integrable Hamiltonian systems

The non-linear stochastic optimal control of quasi non-integrable Hamiltonian systems for minimizing their first-passage failure is investigated. A controlled quasi non-integrable Hamiltonian system is reduced to an one-dimensional controlled diffusion process of averaged Hamiltonian by using the stochastic averaging method for quasi non-integrable Hamiltonian systems. The dynamical programming equations and their associated boundary and final time conditions for the problems of maximization of reliability and of maximization of mean first-passage time are formulated. The optimal control law is derived from the dynamical programming equations and the control constraints. The dynamical programming equations for maximum reliability problem and for maximum mean first-passage time problem are finalized and their relationships to the backward Kolmogorov equation for the reliability function and the Pontryagin equation for mean first-passage time, respectively, are pointed out. The boundary condition at zero Hamiltonian is discussed. Two examples are worked out to illustrate the application and effectiveness of the proposed procedure.     

Efficiency Improvement in Polymer Light‐Emitting Diodes by “Far‐Field” Effect of Gold Nanoparticles

The “far‐field” effect of metal nanoparticles (NPs), when chromophores localized nearby metal NPs (typically the distance >λ/10), is an important optical effect to enhance emission in photoluminescence. The far‐field effect originates mainly from the interaction between origin emission and mirror‐reflected emission, resulting in the increased irradiative rate of chromophores on the mirror‐type substrate. Here, the far‐field effect is used to improve emission efficiency of polymer light‐emitting diodes (PLEDs). A universal performance improvement is achieved for the full visible light (red, green, blue) PLEDs, utilizing gold (Au) NPs to modify the indium tin oxide (ITO) substrates; this is shown by experimental and theoretical simulation to mainly come from the far‐field effect. The optimized distance, between the NPs and chromophores with visible light emission ranging from 400 to 700 nm, is 80–120 nm. Thus the scope of the far‐field may overlap the light‐emitting profile very well to enhance the efficiency of optoelectronic devices. The 30–40% enhancement is obtained for different color‐emitting materials through distance optimization. The far‐field effect is demonstrated to enhance device performance for materials in the full‐visible spectral range, which extends the optoelectric applications of Au NPs.     

高温应变下的晶界湮没机理的晶体相场法研究

应用晶体相场方法研究高温应变下的预熔化晶界位错湮没机理. 结果表明, 原预熔化晶界上的位错在应变作用下发生分离运动, 形成新晶界, 即亚晶界. 该过程的实质是生成了亚晶粒; 亚晶界的迁移过程的本质是亚晶粒长大、吞噬旧晶粒的过程; 亚晶界之间的湮没是亚晶粒完全吞噬旧晶粒过程的结束, 体系转变成为单个晶粒结构. 根据原子密度序参数沿x和y方向的投影值随应变量的变化特征, 可以揭示出高温应变作用下, 预熔化亚晶界相遇湮没的本质是两对极性相反的偶极子位错对发生二次湮没, 该湮没的微观过程是通过位错连续二次滑移湮没而实现的, 其湮没的速率较低温时的湮没速率要小许多.     

电光调制对外部光注入垂直腔表面发射激光器的偏振转换及其非线性动力学行为的操控性研究

针对主和副垂直腔表面发射激光器构成的外部注入激光器系统的偏振转换及其非线性动力学行为, 利用周期性极化铌酸锂晶体中准相位匹配线性电光调制, 本文提出了一种新的操控方案并且探索了其控制规律. 研究结果发现, 受到平行光注入或正交光注入的副激光器输出偏振度随外加电场成周期性振荡变化, 其振荡波峰轨迹包络曲线为正弦曲线, 而振荡波谷轨迹包络曲线为余弦曲线; 选取一定的主激光器偏置电流, 通过对来自主激光器的光进行电光调制, 受到两种方式注入的副激光器可以输出任意偏振模, 并且其非线性动力行为经历不同的演变. 另外, 副激光器的偏振度仅依赖于外加电场, 与副激光器的偏置电流无关.     

互注入垂直腔表面发射激光器的多次偏振转换特性研究

基于垂直腔表面发射激光器(VCSELs)的自旋反转模型, 研究了互注入VCSELs系统中参数连续变化所引起的多次偏振转换(PS)特性. 研究结果表明: 连续改变互注入强度ξ、两个互注入VCSELs中一个激光器的激射频率以及同时连续改变两个激光器的激射频率, 均可产生多次的PS. 详细分析了上述三种参数连续变化所引起的多次PS的特性, 并讨论了耦合延时时间对多次PS特性的影响.     

基于背景最佳滤波尺度的红外图像复杂度评价准则

提出一种基于背景最佳滤波尺度的红外图像复杂度评价准则来解决传统方法评价背景效果较差的问题. 同时, 这种方法还可以为红外图像滤波提供最佳高通滤波尺度信息, 从而对红外图像进行性能最佳滤波. 首先, 生成高斯仿真目标并与红外图像进行融合, 获得包含仿真目标及真实红外背景的图像. 然后, 在不同高斯滤波尺度下对图像滤波, 并计算滤波后仿真目标的信噪比. 最后, 取滤波后目标信噪比最大时的滤波尺度作为背景最佳滤波尺度, 使用该尺度可评价红外图像的复杂度. 另外, 本文还使用数学模型推导了红外图像最佳滤波尺度, 得出最佳滤波尺度的数学表达式. 大量实验表明: 1) 本文推导的最佳滤波尺度数学表达式与实验曲线吻合. 2) 这种方法在评价红外图像复杂度方面比传统的基于信息熵的方法效果要好很多. 并且这种方法获取的红外背景复杂度为滤波最佳尺度, 可以直接利用这项指标对图像进行最佳滤波从而更好地检测弱小目标. 3) 仿真目标尺度越大, 最佳滤波尺度也会相应增大. 因此, 在评价图像复杂度时, 应使用相同尺度的仿真目标, 不同图像之间才具备可比性. 同时, 最佳滤波尺度与仿真目标的强度无关. 4) 本文算法使用的滤波器宜用高斯及Butterworth高通滤波器实现. 5) 本文提出的方法不仅可以有效分析红外视频的复杂度, 并且可以通过复杂度的变化分析图像内容的突变.