星载分离相位中心方位多波束SAR方位向非均匀采样

星载分离相位中心方位多波束合成孔径雷达可同时实现高分辨率、宽测绘带成像.本文进行进一步分析指出,该技术会产生方位向非均匀采样,并最终可导致虚假目标产生.提出了几种消除方位向非均匀采样影响的算法.通过对各种算法进行比较指出,滤波器组法是最为高效的一种算法.     

用数据矩阵的SVD法确定声源频率和方位时的一种误差校正方法

本文利用均匀线阵接收信号构造的数据矩阵的奇异值分解对频率和方位两参数进行分离估计,并针对实际阵列中存在的三种模型误差,提出一种基于辅助源的校准方法。声学实验证实了上述方法的可行性。     

X射线粉末衍射数据的校正

扼要介绍了X射线粉末衍射数据（峰位峰强和峰形）的校正方法和使用的标样。     

卫星影像几何精校正中控制点数据的综合管理

本文介绍了对控制点数据进行综合管理的必要性、思路;应实现的功能及在卫星影像几何精校正的生产过程中应用控制点数据的方法。     

锥腔型电校准辐射计灵敏面黑涂层热阻的校正

本文介绍了黑涂层热阻的测量,进而推及热电型电校准辐射计锥腔型灵敏面黑涂层热阻的校正因子.     

锥腔型电校准辐射计灵敏面黑涂层热阻的校正

本文介绍了黑涂层热阻的测量,进而推及热电型电校准辐射计锥腔型灵敏面黑涂层热阻的校正因子。     

利用极化SAR数据探索同极化相关特征随地表粗糙度变化的研究

利用冲积扇区域SIR-C全极化SAR数据深入研究了同极化相关特征与粗糙度之间的关系,经分析得出:(1)以圆极化右旋.左旋为正交基的同极化相关系数在粗糙度ks(k是入射波的波数,s是表面高度标准离差)＜0.5时,随ks的增大而减小;(2)仅考虑线性正交基,可以从同极化相关系数响应图中提取线性同极化相关系数曲线,该曲线的极值差或者标准差等代表该曲线平滑程度的参数可以在更大的范围内(ks＜1.2)随粗糙度ks的增大而近似线性地减小,因此能够更有效地反映粗糙度的变化;(3)水平-垂直正交基对应的同极化相位差平均值在ks＜1时,随粗糙度的增大而稳步减小.     

一种基于时空瞬时稳定性的方位谱估计方法

针对基于子空间分解的空间方位谱估计方法稳健性问题,提出了一种基于时空瞬时稳定的方位谱估计方法.该方法首先依据空间目标信号时域瞬时稳定性,将协方差矩阵频域求取过程转换为经相参补偿的复域求取,降低空间数据稳定性对协方差矩阵估计的影响;然后依据各子空间输出方位谱峰值索引离散度差异,提取各子空间方位谱加权因子;最后根据加权因子...     

使用合成滤波器组的SAS方位向非均匀采样信号重构

针对多子阵合成孔径声纳(Synthetic Aperture Sonar,SAS)在方位向上非均匀采样对后续成像处理带来的方位向失真的影响,给出了基于滤波器组的方位向非均匀采样信号重构算法.该算法利用SAS方位向周期性非均匀采样信号与经过分析滤波器组的信号之间的相似性,将周期非均匀采样信号通过合成滤波器组进行重构得到均...     

Calculation of the Background Correction Error in Electrothermic Atomic Absorption Spectrometry

A theoretical estimate is presented of the background correction error in electrothermic atomic absorption spectrometry with modulation of the coefficient of atomic absorption in an alternating magnetic field. The experimental results for the background absorption induced by scattering of radiation are in good agreement with theory. Substantial additional distortions in the output signal due to interaction of molecular vapor with the graphite surface arise in the case of a molecular background.     

砝码磁性测量过程中几何形状修正因子的计算与影响

通过一系列实验和数据,讨论用磁化率计法测量砝码磁性时各测量分量对砝码磁化率测量结果的影响,并着重分析了砝码几何形状修正因子的测量与确定,比较不同测量方式的特点,以求减少砝码磁性测量时的误差。     

水下多层均匀材料垂直入射的声特性分析

采用传递矩阵方法研究了材料特性、几何参数对水下多层均匀复合结构声学性能的影响,给出了吸声系数的理论公式并开展了计算仿真。研究表明:不同橡胶材料对复合结构吸声性能有显著影响;增加复合结构层次有利于改善结构吸声特性,特别是改善低频吸声特性。     

阻力矩阵法计算斜波入射下平板的声辐射

利用声辐射阻力矩阵和振动面上的速度矢量预报了结构声辐射的总功率.振动面等效为有限个活塞振动单元.通过计算,得到了嵌在无限大障板中简支板模型在斜波入射作用下的声辐射功率和辐射效率.利用阻力矩阵法,不仅避免了声场的计算,而且能达到经典法所能达到的精度.这样,在辐射计算经典方法所需的辐射声场难以测量的情况下,阻力矩阵法尤为有用.     

Virtual Excitation and Multiple Scattering Correction Terms to the Neutron Index of Refraction for Hydrogen

The neutron index of refraction is generally derived theoretically in the Fermi approximation. However, the Fermi approximation neglects the effects of the binding of the nuclei of a material as well as multiple scattering. Calculations by Nowak introduced correction terms to the neutron index of refraction that are quadratic in the scattering length and of order 10⁻³ fm for hydrogen and deuterium. These correction terms produce a small shift in the final value for the coherent scattering length of H₂ in a recent neutron interferometry experiment.     

Correction to the Crack Extension Direction in Numerical Modelling of Mixed Mode Crack Paths

In order to avoid introduction of an error when a local crack growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction is proposed in connection with crack growth analyzed by the Dual Boundary Element Method (DBEM). The proposed correction procedure and a reference correction procedure already described in the literature are evaluated by solving two different computational crack growth examples. In the two examples it is found that analyses of the crack paths performed with the proposed crack correction procedure using big increments of crack extension are in excellent agreement with analyses of the crack paths performed by using very small increments of crack extension. Furthermore, it is shown that the reference correction procedure has a tendency to overcorrect the crack growth direction if the stop criterion for the iterative correction procedure is not calibrated in each new crack growth analysis.     

Correction of the Spurious Strains and Displacements Caused by Out of Plane Movements in Digital Image Correlation (DIC) with a Single Camera

Digital image correlation (DIC) is a powerful experimental technique capable to measure the displacement field of a wide region through images. Also it’s scalable and can be applied to large structures, calculating the full strain field of a certain region. This potentiality is restricted by the spurious movements that insert noise in the measurements, reducing considerably the accuracy of the method and its applicability. This paper presents an algorithm capable to remove the effect of those spurious movements from a dataset, enhancing the accuracy of the technique. This is essential for the applicability of DIC to large structures where the spurious movement can’t be prevented and the deformations are very small due to the stiffness of the structures.     

一种消除AFM中悬臂梁横向扭转串扰误差的修正技术

串扰效应始终存在于原子力显微镜(AFM)的测量过程中,并影响其测量精度.在对串扰效应的产生机理进行分析,并建立了悬臂梁形变与光斑位置检测器(PSPD)输出信号之间的数学关系的基础上,提出了一种可消除横向扭转串扰影响的修正方法.在该方法中AFM系统可由输出信号直接获得悬臂梁的实际形变量,进而获得原子间作用力的实际值,并通过保持作用力的恒定对样品进行测量.该方法可有效地将悬臂梁扭转导致的纵向信号的变化从系统测得的纵向信号中剔除出去.仿真结果表明,在恒力接触模式下,串扰效应严重影响测量结果,导致测量误差,且针尖.样品夹角导致的串扰效应比摩擦力导致的串扰效应更严重.为验证本文方法消除串扰效应的效果,在应用该修正方法前后分别对标准梯形样品进行测量.实验对比结果表明,在普通恒力接触模式下的样品表面最大测量误差范围为21.2 nm～32.0 nm;对串扰效应进行修正后,最大测量误差范围降低至5.5 nm～10.2 nm.这表明该方法可有效降低AFM中串扰效应导致的测量误差,提高其测量精度.     

超声纵波换能器用于平测时的测距修正方法研究

研究了超声纵波换能器用于平测时的测距修正方法.首先,根据弹性波理论分析了利用平测布置代替对测布置测量波速时的实际物理意义;然后,分析了两种换能器布置方式的真实传播距离并通过设计混凝土试件切割-测量实验进行了两种布置方式的声时对比;最后,根据实验数据在对测回归直线方程的基础上提出了计算换能器平测布置修正测距的最小二乘法....     

Correction for the asphalt overlay thickness of flexible pavements considering pavement conditions

Pavement overlays represent a common technique used for pavement rehabilitation and maintenance and to increase the structural support of the pavements. In the Department of Defense, the methodology for the design of flexible pavement overlays is contained in the Unified Facilities Criteria 03-260-02 criteria and involves the use of an empirically derived formulation. The overlay design of flexible pavements is based on the thicknesses of the existing asphalt, base and subbase layers and the required minimum thickness for the asphalt layer. However, this formulation does not take into account the quality or the structural condition of the existing surface layers. The current formulation considers the materials to have full structural strength and no deterioration. This study proposes an improved methodology for calculating the required flexible overlay thickness of a flexible pavement by taking into account the structural condition of the existing asphalt layer. An asphalt thickness correction factor is introduced to quantify the amount of the existing asphalt layer thickness that can still offer structural support, and therefore influence the overlay thickness. The asphalt correction factor is based on the existing load-related distresses affecting the asphalt surface. The implementation of this new approach showed that an asphalt layer in poor condition requires up to 60% more in thickness than an asphalt layer in good condition. The proposed methodology aims to standardise the design and evaluation of flexible pavements overlaid with asphalt layers and account for existing structural conditions. Moreover, allocation of maintenance funding can be optimised, thus limiting pavement overdesign.