粘弹性阻尼器的力学特性分析

在正弦输入的假设下,推导了用分数微分Maxwell模型建模粘弹性阻尼器时力和位移的表达式,并用该表达式分析了阻尼器的力学特性。将该算法的理论计算分别与已有的理论计算和试验结果进行比较,结果吻合的都比较好,证明了该算法的正确性。同时根据该表达式给出了粘弹性阻尼器能量耗散的计算方法。     

Copper corrosion inhibition by Azadirachta indica leaves extract in 0.5 M sulphuric acid

Azadirachta indica leaves extract (AI) was investigated as a copper corrosion inhibitor in 0.5 M sulphuric acid. Inhibition efficiency of AI was compared to that of the already proven good inhibitors 2-acetamino-5-mercapto-1,3,4-thiadiazole (AAMTDA) and 1,2,3-benzotriazole (BTAH). The inhibition properties were studied using electrochemical polarization and weight loss techniques. In the region of active copper dissolution, the highest inhibition efficiency was exhibited by AAMTDA (92.7%). AI exhibited somewhat higher efficiency (86.4%) than the widely used BTAH (85.5%), showing that the extract could serve as a effective substitute for currently preferred copper corrosion inhibitors in sulphuric acid. The weight loss results were interpreted by means of the Frumkin isotherm of adsorption on the metal surface. The values of ΔG_ads equal to − 41.96 kJ mol^− 1 for AAMTDA and − 35.22 kJ mol^− 1 for BTAH indicate strong spontaneous adsorption while the surface coverage dependence on the log c following the Frumkin isotherm is suggestive of chemisorption in case of all three tested inhibitors.     

半埋目标低频声波散射反演的一种新算法

半埋目标低频声波散射在数学上归纳为求解带有混合边界的不可穿透的散射体外声场问题,是一个公认的理论难题。本文首次将区域导数法引入边界条件为混合边界不可穿透的散射体的外声场问题中,数值结果证明算法是可行的、正确的,为解决半埋目标低频声波散射物形状识别提供了一种新方法,这在工程实际及军事上均有重要的应用价值。     

激光陀螺温度误差的多因素BP网络模型

分析了激光陀螺刻度因子随温度变化的特点,指出了激光陀螺刻度因子与环境温度、温度增量和温度变化率有关,提出了激光陀螺刻度因子温度误差的三因素三层BP网络新模型,模型结构简单。实测数据的仿真结果表明,模型精度高,均方差优于6.1×10-7("/pulse)。     

镍酸锂派生物LiNi1-yREyO2的制备和性能

首次报道了稀土金属(RE)氧化物添加到锂离子蓄电池正极材料LiNiO2中合成派生物的新方法,为LiNiO2的性能改善开辟了新的领域。采用增加系统氧气压力的方法,研究了派生物合成的工艺条件。对合成的材料进行了X射线衍射和扫描电镜分析,结果表明,铈部分取代镍很好地改善了活性正极材料的层状结构,使晶型结构更加完整有序。派生物LiNi1-xREyO2的放电比容量高达170mAh/g以上,可用于锂离子蓄电池作正极材料。     

常用周期信号的分数阶微分运算

分数计算——分数阶微分与分数阶积分受到众多领域的广泛关注。从信号处理的观点来考察分数阶微分问题。首先，在频域中将微分算子分解为幅度算子和相位算子，导出正弦、余弦和复指数信号的分数阶微分表达式；然后考察矩形、三角形、梯形等常用周期信号的分数阶微分。给出了一些常用周期信号分数阶微分的解析形式，同时也研究了周期序列的分数阶微分运算的数字实现。结果表明分数微分运算确实存在，它同时改变了信号的幅度和相位，可以对之进行非线性分析。     

激光光斑图像增强与二值化

提出了一种基于数字图像二阶方向导数的激光光斑图像增强方法，通过局部光环方向角及二阶方向导数的计算来对光环进行检测，并进行二值化处理．在像素亮度二阶方向导数计算的近似上使用了小平面模型，并对邻域的大小做了定性的描述，以提高近似精度．最后用实际激光光斑图像对提出的方法进行验证表明：无论精度和稳定性都达到设计要求．     

关于平稳随机过程任意阶导数的平稳性

介绍了随机过程在均方极限意义下的可微性概念，并论述了平稳随机过程的任意阶导数(如果存在的话)仍然是平稳随机过程这一结论。     

On linear models for nonlinear systems

Best linear time-invariant (LTI) approximations are analysed for several interesting classes of discrete nonlinear time-invariant systems. These include nonlinear finite impulse response systems and a class of nonsmooth systems called bi-gain systems. The Fréchet derivative of a smooth nonlinear system is studied as a potential good LTI model candidate. The Fréchet derivative is determined for nonlinear finite memory systems and for a class of Wiener systems. Most of the concrete results are derived in an ?_∞ signal setting. Applications to linear controller design, to identification of linear models and to estimation of the size of the unmodelled dynamics are discussed.     

Computing Bessel functions of the second kind in extreme parameter regimes

A useful method of computing the integral order Bessel functions of the second kind Y_n(x+iy) when either, the absolute value of the real part, or the imaginary part of the argument z=x+iy is small, is described. This method is based on computing the Bessel functions for extreme parameter regimes when x∼0 (or y∼0) and is useful because a number existing algorithms and methods fail to give correct results for small x or small y. The approximating equations are derived by expanding the Bessel function in Taylor series, are tested and discussed. The present work is a continuation of the previous one conducted in regard to the Bessel function of the first kind. The results of our formalism are compared to the available existing numerical methods used in Mathematica, IMSL, MATLAB, and the Amos library. Our numerical method is easy to implement, efficient, and produces reliable results. In addition, this method reduces the computation of the Bessel functions of the second complex argument to that of real argument which simplify the computation considerably.