基于加窗傅立叶变换的SR-CT滤波反投影重建

SR-CT(Synchrotron Radiation Computed Tomography同步辐射X射线计算机断层扫描)实验中,原始投影图像存在噪声,从而影响了滤波反投影重建图像的质量.为提高重建图像质量,提出了一种基于加窗傅立叶变换滤波改进重建图像质量的方法.通过对原始投影图像噪声和滤波反投影算法的讨论,对利用该方法提高重建图像质量的可行性进行了分析.利用加窗傅立叶滤波方法对两组SR-CT实验得到的投影图像分别进行了处理,抑制了原始投影图像的噪声,提高了重建图像的质量.实验的结果验证了该方法的有效性.     

TC材料的低压Hugoniot参数实验测量研究

采用高阻值锰铜压阻传感器,并通过一级轻气炮实验对TC材料的低压Hugoniot参数C0,λ进行了测量,实验得到的压力曲线与理论分析基本一致,并对压力曲线与密实材料的理论波形进行了比较和分析。通过对实验结果进行最小二乘法拟合,得到了该材料低压冲击时的Hugoniot压缩线以及低压Hugoniot参数C0,λ。拟合结果表明:该多孔材料的低压D-u线具有较大的分散性。     

基于多种搜索策略的人工蜂群算法的结构损伤识别

人工蜂群算法是一种元启发式算法,具有构架简单,易于操作和鲁棒性较好的特点。本文对原始蜂群算法进行了改进,为蜜蜂们提供了更丰富的搜索策略。基于轮盘赌原则选择更优的迭代方式,进而使算法的收敛速度和精度有了显著的提高。基于频率残差和模态置信准则(MAC)建立结构损伤识别问题的目标函数,然后利用ABC算法,QABC算法和本文方法求解该目标函数,得到损伤识别的结果。利用一桁架结构做数值模拟,用简支梁结构进行实验验证。算例表明,改进的算法更能有效地检测出结构的局部损伤,具有对测量噪声不敏感、高效率以及高精度等优点。     

一种新的红外脉冲热成像后处理方法

脉冲热成像技术作为一种新兴的无损检测技术已被广泛应用于红外领域,然而由于试样表面加热不均匀及表面发射率低导致的红外图像对比度低、噪声大等问题给缺陷的检测带来困难。本文基于长脉冲热成像技术对碳纤维增强塑料(carbon fiber reinforced polymer,CFRP)板和304不锈钢进行了无损检测研究,提出了比温度的图像后处理方法。该方法对温度序列图像的每一帧图像与前一帧图像进行作商的后处理操作,得到比温度的图像序列。从比温度序列中获取信噪比最大的图像,以进行缺陷识别和缺陷定量。结果表明,与此前的方法相比,该方法显著提高了图像的信噪比,更有利于检测更深、更小的缺陷,相比原始图像,信噪比提高了近98.46%。将该方法与半高全宽法相结合,对试样的尺寸进行定量检测。通过仿真和实验验证,该方法具有良好的鲁棒性,显著降低了缺陷尺寸定量的误差,该方法可作为一种有效的红外图像后处理及缺陷尺寸定量方法。     

干涉条纹图处理的等值线窗口滤波和摄像测量在国防试验的应用

对图像进行滤波或称平滑是干涉条纹图像处理中的一项重要工作。一幅未经处理的原始图像或多或少存在着不同程度的噪声干扰,特别是散斑和Insar干涉条纹图,信噪比很低,难以处理。本文针对光测力学中光学干涉方法得到的条纹图,提出了一种新的滤波方法条纹等值线窗口滤波,并对这种滤波方法进行了研究讨论,提出了几种确定等值线窗口的不同方法。这种滤波方法根据干涉条纹图不同断面上灰度分布的不同特点,选择沿条纹走向的条纹等值线窗口进行滤波,在最大消除条纹图噪声的同时,也能保证对条纹损伤最小。摄像测量技术正在迅速发展和得到广泛应用,在国防试验和航天飞行任务中发挥着不可替代的作用。本文也介绍了作者近年来在该领域所做的应用研究,包括在火箭、导弹发射试验,冲击、碰撞等过程中的动态目标运动测量;针对航天航空和力学工程领域的视频图像实时分析;飞行器三维运动测量;基于投影条纹的物体三维形貌精密测量方法研究;以及对接航天器位置和姿态的实时测量。在这些应用中都实现了高精度测量。     

基于MARG传感器的自主姿态测量新算法

针对基于三轴陀螺、三轴加速度计以及三轴磁强计组成的传感器组合(MARG传感器)的姿态测量算法存在的不足和限制,以自主姿态测量为前提,提出了一种新的基于四元数的优化递推估计算法。这一算法能够在线估计补偿陀螺漂移误差,不再需要对系统方程进行线性化处理。与基于EKF的方法相比,在同等计算复杂度下,该算法具有更高的精度和更好的稳定性。算法本身内蕴了对四元数单位长度的限制,不再需要任何归一化处理。仿真结果显示出了该算法具有令人满意的效果,利用水上漂浮试验初步验证了该算法的稳定性。     

一种用于重力测量信号畸变校正的盲反卷积算法（英文）

强阻尼和大时间常数是海洋重力仪的共同特性,它们在抑制垂直方向上干扰加速度的同时也造成了重力仪测量信号的幅值衰减和相位滞后。为了校正重力测量信号的畸变,获得高精度的重力异常信号,在分析重力仪和重力测量信号畸变原理的基础上,提出了一种单通道Bussgang算法,并应用于重力测量信号的畸变校正。该方法首先将盲反卷积滤波器近似简化为FIR模型,然后采用常数恒模算法对Bussgang均衡器权系数进行更新,并在此基础上对反卷积滤波器进行了估计,最后基于实测重力信号将该方法与Kalman逆滤波进行了试验对比。理论分析和试验结果表明,该重力信号畸变校正方法能有效地消除重力测量信号的畸变,且校正效果明显优于Kalman逆滤波,其校正后信号相对于原始信号的标准差为0.328×10-5 m/s2,而Kalman逆滤波校正标准差为1.838×10-5 m/s2。     

基于交互多模型距离平滑的UWB/IMU因子图组合导航方法

为了解决全球导航卫星系统（GNSS）拒止条件下车辆定位困难问题,提出了一种基于交互多模型距离平滑的超宽带/惯性测量单元（UWB/IMU）因子图组合导航方法。首先,针对超宽带信号由于反射或折射导致的非视距问题,分别建立视距与非视距情况下超宽带基站与标签间距离的因子图模型,并利用交互式多模型算法进行原始距离的平滑;然后,对惯性导航系统、交互式多模型处理的超宽带距离信息等测量量进行建模,构建基于因子图的信息融合框架,并根据非线性优化理论与增量平滑算法实现变量节点的递推与更新。最后,采用因子图方法对融合数据进行处理,实现车辆多传感器高精度组合导航。实际测试结果表明,相比基于卡尔曼滤波的多传感器融合方法,所提出的基于交互多模型距离平滑的惯性/超宽带的因子图定位方法在非视距情况下位置估计精度（RMS）提高40%以上。     

光纤陀螺基于本征模态函数筛选的阈值滤波算法

为降低光纤陀螺随机噪声,提高其测量精度,利用周期图法辨识光纤陀螺的随机噪声特征参数,针对其噪声特征,提出了基于本征模态函数筛选的微分经验模态分解阈值滤波算法。以本征模态函数和原始信号二者的概率密度函数的空间距离为判别依据,对所有本征模态函数进行筛选,根据已估计的噪声参数计算阈值大小,采用时间序列阈值的方法对筛选出的本征模态函数进行处理。仿真和实验结果表明,该滤波算法能够在跟踪光纤陀螺信号变化的同时,使其零偏不稳定性下降90.35%,角随机游走下降93.75%,对随机噪声有较好的抑制能力。     

基于超高速相机的数字图像相关性全场应变分析在SHTB实验中的应用

基于超高速相机和数字图像相关性全场应变分析方法对传统的分离式Hopkinson拉杆(SHTB)实验系统进行改进,获得尼龙和铝合金材料的动态拉伸应力应变曲线,验证了数字图像相关性全场应变分析在SHTB实验中的有效性。实验结果显示:该方法测量的平均应变与应变片测量结果一致性很好, 而传统的SHTB实验原理计算的应变结果则明显偏大,需要对试件原始标距进行修正后才能获得有效的试件应变,并且在试件的材料和几何尺寸不变的条件下标距修正不依赖于应变率。基于数字图像相关性全场应变测量,讨论了应变均匀性问题:脆性的尼龙试件在标距范围内应变均匀性良好,而韧性的铝合金试件表现出比较严重的应变不均匀性,归因于颈缩变形的影响。     

(Q)SAR modelling of nanomaterial toxicity: A critical review

There is increasing recognition that some nanomaterials may pose a risk to human health and the environment. Moreover, the industrial use of the novel engineered nanomaterials (ENMs) increases at a higher rate than data generation for hazard assessment; consequently, many of them remain untested. The large number of nanomaterials and their variants (e.g., different sizes and coatings) requiring testing and the ethical pressure towards nonanimal testing means that in a first instance, expensive animal bioassays are precluded, and the use of (quantitative) structure–activity relationships ((Q)SARs) models as an alternative source of (screening) hazard information should be explored. (Q)SAR modelling can be applied to contribute towards filling important knowledge gaps by making best use of existing data, prioritizing the physicochemical parameters driving toxicity, and providing practical solutions for the risk assessment problems caused by the diversity of ENMs. This paper covers the core components required for successful application of (Q)SAR methods to ENM toxicity prediction, summarizes the published nano-(Q)SAR studies, and outlines the challenges ahead for nano-(Q)SAR modelling. It provides a critical review of (1) the present availability of ENM characterization/toxicity data, (2) the characterization of nanostructures that meet the requirements for (Q)SAR analysis, (3) published nano-(Q)SAR studies and their limitations, (4) in silico tools for (Q)SAR screening of nanotoxicity, and (5) prospective directions for the development of nano-(Q)SAR models.     

A review: Acoustic emission,a tool for composite-materials studies

The technique of acoustic emission has two broad applications areas. The first is nondestructive evaluation. The second is as a tool in studies or research which are not fundamentally directed towards acoustic emission. It is this second application with which we are concerned here. Acoustic emission is a very useful tool in this role because of its high sensitivity, real-time capability, volume-monitoring approach, and sensitivity to any process or mechanism which generates sound waves. This paper presents a comprehensive review of areas where acoustic emission (AE) has been used for materials studies on composite materials. The following fields, among others, will be covered: (1) time-dependent composite properties, (2) impact studies, (3) correlation of AE with stress level, (4) application to matrix cure studies, (5) relationship of AE-detected damage to other measures of damage, (6) studies of the effects of matrix material, (7) application to differences in second phase, (8) interface studies, (9) AE and dimensional stability, (10) AE applied to orientation studies, and (11) environmental effects. This review will emphasize the roles that AE can play as a tool for the materials scientist: (1) discovery of damage mechanisms, (2) characterization of damage progression with increasing time or stress, (3) optimization of fabrication variables, and (4) reduction in the numbers of test specimens required in various studies.     

Real-life experiences with flow-induced vibration

A number of occurrences of flow-induced vibration in the power-generating industry are presented, many in nuclear plant where all incidents/problems have to be reported. Specifically, cases of (i) vortex-induced vibration (VIV), (ii) fluidelastic instability in cylinder arrays, (iii) axial and (iv) annular-flow-induced vibration, (v) leakage-flow instability and (vi) shell-type ovalling are discussed. For items (ii), (v) and (vi), a few words on the mechanisms underlying the vibration are provided.     

On the boundedness and the stability properties of solution of certain fourth order differential equations

This paper investigates equation(1)in two cases:(i)P≡0,(ii)P(≠O)satisfies|P(t,x,y,z,ω)|≤(A |y| |z| |ω|)q(t),where q(t)is a nonnegative function of t.For case(i)the asymptotic stability in the large of the trivial solution x=0 is investigatedand for case(ii)the boundedness result is obtained for solutions of equation(1).Theseresults improve and include several well-known results.     

流变学研究的若干问题

本文综述了1988年8月第10届国际流变学会议部分大会邀请报告及分组报告的下列几个领域内容:①分子动力学;②光学流变测量;⑧血液的动态测量;④数值仿真;⑤钻探油井;⑥强化采油;⑦减阻;⑧聚合物挤压成形加工;⑨食品流变学.     

(Q)SAR modelling of nanomaterial toxicity:A critical review

There is increasing recognition that some nanomaterials may pose a risk to human health and the environment.Moreover,the industrial use of the novel engineered nanomaterials(ENMs) increases at a higher rate than data generation for hazard assessment;consequently,many of them remain untested.The large number of nanomaterials and their variants(e.g.,different sizes and coatings) requiring testing and the ethical pressure towards nonanimal testing means that in a first instance,expensive animal bioassays are precluded,and the use of(quantitative) structure-activity relationships((Q)SARs) models as an alternative source of(screening) hazard information should be explored.(Q)SAR modelling can be applied to contribute towards filling important knowledge gaps by making best use of existing data,prioritizing the physicochemical parameters driving toxicity,and providing practical solutions for the risk assessment problems caused by the diversity of ENMs.This paper covers the core components required for successful application of(Q)SAR methods to ENM toxicity prediction,summarizes the published nano-(Q)SAR studies,and outlines the challenges ahead for nano-(Q)SAR modelling.It provides a critical review of(1) the present availability of ENM characterization/toxicity data,(2) the characterization of nanostructures that meet the requirements for(Q)SAR analysis,(3) published nano-(Q)SAR studies and their limitations,(4)in silico tools for(Q)SAR screening of nanotoxicity,and(5) prospective directions for the development of nano-(Q)SAR models.     

国内非牛顿流体力学进展

非牛顿流体;;本构方程;;流变测量;;流动稳定性;;收缩流动;;聚合物加工;;石油工业;;生物流体力学     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene （PSt） microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate （KPS） as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene （St） with acrylonitrile （AN） was carried out in the presence of poly（ethylene glycol） monomethoxymonomethacrylate （PEGm） macromonomer as reactive stabilizer and 2,2＇-azobisisobutyronitrile （AIBN） as initiator to obtain submicron-sized PEGm graft poly（styrene-coacrylonitrile） （PEGm-g-PSAN） composite particles with unique morphology. Scanning electron microscopy （SEM） indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

粘性土(红土)中游离氧化铁含量对其工程地质性质的影响

通过试验, 本文就游离氧化铁在粘性土尤其是红土中富积含量的变化对土体工程地质性质产生的影响及其规律性做了初步研究。     

Computerized Developments in Design,Generation, Simulation of Meshing,and Stress Analysis of Gear Drives

The paper represents new computerized developments in design, generation, simulation of meshing, and stress analysis of gear drives. The main contents of the paper are: (i) application of a predesigned parabolic function of transmission errors for reduction of noise, (ii) computerized simulation of noise caused by transmission errors, (iii) modification of the basic algorithm of tooth contact analysis, and (iv) application of approaches developed for enhanced design and simulation of meshing of the following gear drives: (a) spiral bevel gear drives, (b) face-gear drives (including an approach for grinding), and (c) modified helical gear drives. The developed theory is illustrated with numerical examples.