Theory and verification of moiréfringes for x-ray three-phase grating interferometer

Dual-phase and three-phase grating x-ray interference is a promising new technique for grating-based x-ray differential phase contrast imaging.Dual-phase grating interferometers have been relatively completely studied and discussed.In this paper,the corresponding imaging fringe formula of the three-phase grating interferometer is provided.At the same time,the similarities and differences between the three-phase grating interferometer and the dual-phase grating interferometer are investigated and verified,and that the three-phase grating interferometer can produce large-period moiréfringes without using the analyzing grating is demonstrated experimentally.Finally,a simple method of designing three-phase grating and multi-grating imaging systems from geometric optics based on the thin-lens theory of gratings is presented.These theoretical formulas and experimental results provide optimization tools for designing three-phase grating interferometer systems.

Wavelength Dependent Nonlinear Spectroscopic Study of Third Harmonic Generation Probed by Rotational Maker Fringes Method

Efficient third-order nonlinearities of the Zinc Oxide and Al-doped Zinc Oxide were studied by Third Harmonic Generation (Third Harmonic Generation) Maker fringes to establish the effect Aluminum of Aluminum doping (Al-doping) on the cubic nonlinearities. Adding the Al-dopant to the Zinc Oxide crystal structure results in changes that affect the optical and nonlinear characteristics. Presented results indicate that the magnitude of X(3) was enhanced at single experimental wavelengths;however, across the broadband experimental spectrum, the effect of Al-doping remained relatively constant. The observed enhancement of third-order nonlinearity was purely from the bound electronic response. The observation is attributed to increased charge carriers and spontaneous polarization in the Zinc Oxide and Al-doped Zinc Oxide crystal structure.

Modeling of multi-depth slanted airgun source for deghosting

To obtain high-resolution of the subsurface structure, we modeled multidepth slanted airgun sources to attenuate the source ghost. By firing the guns in sequence according to their relative depths, such a source can build constructive primaries and destructive ghosts. To evaluate the attenuation of ghosts, the normalized squared error of the spectrum of the actual vs the expected signature is computed. We used a typical 680 cu.in airgun string and found via simulations that a depth interval of 1 or 1.5 m between airguns is optimum when considering deghosting performance and operational feasibility. When more subarrays are combined, preliminary simulations are necessary to determine the optimum depth combination. The frequency notches introduced by the excess use of subarrays may negatively affect the deghosting performance. Two or three slanted subarrays can be combined to remove the ghost effect. The sequence combination may partly affect deghosting but this can be eliminated by matched filtering. Directivity comparison shows that a multi-depth slanted source can significantly attenuate the notches and widen the energy transmission stability area.

Concept Planning of Ecological Landscapes on Urban Fringes——A Case Study of Landscape Concept Planning of Shiling Area in the Eastern New District of Chengdu City, Sichuan Province of China

With Shiling Area of Eastern New District in Chengdu City as a background, concept design scheme was put forward from the perspective of ecological landscape through analyzing present development and ecological landscapes of the study area, applying philosophic thinking and Abstract concepts, and also combining with actual conditions of Chengdu, and meanwhile, concepts, orientation and functional structure of the eco-landscape concept planning were proposed. Key points of the planning were elaborated from 4 perspectives of spatial structure, traffic organization, spatial sequence and plant configuration to discuss spatial configuration of ecological landscapes on the fringes of Chengdu City, then further improve functions of ecological landscapes and quality of ecological environment, and put the concept planning into the construction practice of urban fringes.

Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence

On the basis of the extended Huygens-Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector,the characteristics of the partially coherent Gaussian Schell-model（GSM） beams propagating in slanted atmospheric turbulence are studied.Using the cross-spectral density function（CSDF）,we derive the expressions for the effective beam radius,the spreading angle,and the average intensity.The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically.The influences of the coherence degree,the propagation distance,the propagation height,and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.

An efficient algorithm to compute transient pressure responses of slanted wells with arbitrary inclination in reservoirs

Compared with vertical and horizontal wells, the solution and computation of transient pressure responses of slanted wells are more complex. Vertical and horizontal wells are both simplified cases of slanted wells at particular inclination, so the model for slanted wells is more general and more complex than other models for vertical and horizontal wells. Many authors have studied unsteady-state flow of fluids in slanted wells and various solutions have been proposed. However, until now, few of the published results pertain to the computational efficiency. Whether in the time domain or in the Laplace domain, the computation of integration of complex functions is necessary in obtaining pressure responses of slanted wells, while the computation of the integration is complex and time-consuming. To obtain a perfect type curve the computation time is unacceptable even with an aid of high-speed computers. The purpose of this paper is to present an efficient algorithm to compute transient pressure distributions caused by slanted wells in reservoirs. Based on rigorous derivation, the transient pressure solution for slanted wells of any inclination angle is presented. Assuming an infinite-conductivity wellbore, the location of the equivalent-pressure point is determined. More importantly, according to the characteristics of the integrand in a transient pressure solution for slanted wells, the whole integral interval is partitioned into several small integral intervals, and then the method of variable substitution and the variable step-size piecewise numerical integration are employed. The amount of computation is significantly reduced and the computational efficiency is greatly improved. The algorithm proposed in this paper thoroughly solved the difficulty in the efficient and high-speed computation of transient pressure distribution of slanted wells with any inclination angle.

Automatic abstraction of interference fringes with image technique

ion technique of interference fringes used in phase modulation and phase scanning modulation interferometer is presented. For the measurement of amplitudes of interference fringes, fringes are fitted and their central points are determined automatically according to their distribution rules. However, for the measurement of their phases, fringes should be recognized and processed with different calculating algorithms and least square optimization methods depending on the scanning modulation mode. When this technique is used for measurement of surface roughness, the measurement uncertainty is better than 5nm and the repeatability is less than 5%.

Workover String Mechanical Model and Calculation of Slanted and Horizontal Well

Force analysis and calculation of workover string in the slanted and horizontal well are the basis of designing and checking string strength, selecting tools and determining operation parameters, which determine the operation safety and success of engineering accidence treatment. In this paper, by comprehensive consideration of wellbore structure, string assembly, string load and workover operation conditions, the workover string mechanical model has been built under three kinds of working states of lifting, lowering and rotating. The downhole string mechanics has been analyzed and calculated. By field verification, the string assembly, tool selection and operation parameter optimization can be achieved, which can improve the safety and success rates of workover engineering accident treatment.

The Formation of Fringes of Equal Chromatic Order across Double Clad Fiber in the Presence of High Power Lasers

Multiple-beam fringes of equal chromatic order interferometry is a powerful technique to extract optical properties over a continuous range of spectrum. In this paper we develop a theory for the spectral shape of the fringes of equal chromatic order (FECO) that are formed across a double-clad fiber. The modified single term Sellmeier dispersion formula is used to construct the refractive index dispersion curves for the liquid, claddings, and core. Expressions for the paraxial optical path length for several rays passing through the fiber and the liquid are developed. The condition of bright fringe is applied to get an analytical expression for the spectral shape of the FECO across a double-clad fiber with an elliptical/circular inner cladding. A potential application of this theory is to determine the dispersion of Kerr constant of the claddings and the core of the fiber. To illustrate the theory and its application, simulation examples are provided and discussed.

Projecting Distortion Calibration and Evaluation of Coding Fringes in Structured Light System

Coded structured light is an accurate, fast 3D measurement approach with high sampling density, of which the encoded fringes are distorted when projected to curved surface. Focused on the demand of encoding, decoding, multiview registration and system calibration, we expect to obtain undistorted fringes from camera image. Therefore, in this paper, we analyze the accuracy and sampling density of projecting distortion calibration approach based on control point and fitting surface. Moreover, combining the characteristic of coded structured light system, we design encoded fringe projecting distortion calibration scheme based on simplified encoded structured light model. Primarily, we neglect the minor parameters that affect the calibration in structured light model to reduce complexity. Then, we build the correspondence between camera image points and projector image points and achieve the calibration. Finally, we design evaluation scheme of projecting distortion calibration with parallelism and equal interval, and verify the effectiveness and accuracy of the approach through visual effect and experimental data.

“城—产—人”关联视角下城市边缘乡村转型的多尺度路径——以江苏溧阳北拓区为例

文章从空间、要素和时间维度,辨析城边村与“城”“产”“人”三重外部动力的多重关联性,构建“城—产—人”关联视角下的城边村转型研究框架。在此视角下,基于城边村演化发展的核心特征总结,从城区、园区、社区3个层面探讨城边村转型的多尺度空间路径,分别为:以城乡融合推动空间结构重组、以产业转型支撑空间布局融合、以人群需求引领品质生活营造。最后以溧阳北拓区乡村为例,以“融入城区—联动园区—激活社区”为脉络,提出城边村多尺度协同的规划策略,以期为我国乡村转型与新型城镇化提供可能的借鉴。

彩色光栅投影的三维轮廓自动化测量研究

为了测量物体的三维轮廓数据,提出一种基于改进彩色光栅投影三维轮廓测量技术,并利用DLP来投影彩色光栅条纹到被测物体上来测量被测物体的高度,由于DLP的投射范围太大,无法直接投射在微小物体上,因此通过自行改装的方式改变DLP的投射范围,将其投影面积限制在约20×20 mm内,使其能覆盖整个被测物体。但由于改装时所选用的DLP镜头并不是针对DLP而设计的,因此容易产生光场分布不均的情况,可对无光栅图像或有彩色光栅图像进行光场补偿,使光栅图像更为清楚,用于对被测物体进行更准确的三维轮廓测量与重建分析计算,且获取被测物体的三维数据精度可达2μm,速度在0.024 s内。实验结果表明,该方法具有更高的速度、灵敏度及适用性。

基于条纹投影三目系统的舌面完整点云获取方法

传统的舌诊过程存在客观性较差的问题,将计算机视觉技术应用于舌诊可以有效推进舌诊客观化。双目立体视觉结合结构光条纹投影技术是三维测量的常用手段,但对于舌诊的测量场景,由于舌体表面常带有津液和口水等,造成条纹图像出现分布随机性较大的高反光区域,导致相位解算错误和点云缺失。本文提出了一种基于光栅投影的三目测量系统,由3个相机构成1个三目和3个双目子系统。在相位和级次约束基础上引入双极线约束,提高三目立体匹配精度,并利用匹配点补充优化三目匹配点集,重建高反光区域点云。结果显示,对比传统双目系统,本系统的匹配精度和重建精度均得到提升,特别是在真实舌面测量中能够生成纹理清晰、特征完整的点云,对舌面高反光区域进行了有效测量,有助于舌诊的客观化进行。

柔性浅埋物的声-振智能探测

提出一种基于目标检测算法的柔性浅埋物的声-振智能探测方法,将声波激励、激光散斑干涉测振和目标检测算法有机结合,用以柔性浅埋物的大范围快速探测。在论述YOLO系列目标检测算法原理的基础上,选择并优化柔性浅埋物的智能探测网络模型;然后,搭建声-光融合智能探测系统,构建不同柔性浅埋物的激光散斑干涉条纹图数据集;最后,对数据集进行训练和测试,验证该算法用于干涉条纹图识别的可行性。实验结果表明:在给定实验条件下,柔性浅埋物智能探测网络模型的精确率为98.39%,召回率为84.72%,平均识别精度为99.66%。该声-振智能探测方法可以在给定实验环境下对多种柔性浅埋物的激光散斑干涉条纹图进行智能识别,适用于浅层地下柔性掩埋物的大面积快速探测。

多源干扰下侧扫声呐图像复原的综合校正研究

为了减少因海洋环境以及侧扫声呐工作机理等干扰所造成的声呐图像畸变,提出多源干扰下侧扫声呐图像复原的综合校正方法。针对辐射图像明暗区域差异明显、轮廓特征模糊等问题,基于双伽马函数和Retinex理论设计辐射均衡化和轮廓清晰化算子,实现了图像辐射校正;针对环境干扰及工作机理所造成的图像水柱区及图像压缩等问题,设计了海底点检测因子并通过获取实际平距实现斜距校正;针对AUV速度波动造成的图像异常拖拽和压缩等问题,基于经纬度设计航行速度,并通过校正比例系数复原图像块来实现速度校正。实验测试结果表明,相较于其它方法,文中综合校正方法不仅使校正图像具有均衡性好、特征轮廓清晰、水柱区基本消除和两舷图像衔接平滑的优点,而且SNR指标平均提升了6.060%、ENT指标平均降低了16.583%、SD指标平均降低了49.904%、ENL指标平均增加了78.347%,有效实现了侧扫声呐图像的复原。

腰-盆-髋整复手法治疗成人退行性脊柱侧凸30例疗效

目的观察腰-盆-髋整复手法治疗成人退行性脊柱侧凸(adult degenerative scoliosis,ADS)的临床疗效。方法将2022年1月—12月就诊于宁夏医科大学总医院的30例ADS患者随机分为观察组与对照组,每组15例。采用腰-盆-髋整复手法对观察组患者进行治疗,对照组则采用传统推拿手法治疗。治疗1个疗程后测量对比患者治疗前后X线片中脊柱Cobb角及骶骨倾斜角变化,以疼痛视觉模拟评分(visual analogue scale,VAS)及Oswestry功能障碍指数(Oswestry disability index,ODI)评价治疗前后两组患者疼痛变化与功能障碍程度的改变。结果观察组患者治疗后X线片中脊柱Cobb角及骶骨倾斜角较治疗前角度变小,且VAS及ODI评分低于治疗前(P均<0.05);治疗后,对照组患者X线片中脊柱Cobb角及骶骨倾斜角小于治疗前,VAS及ODI评分均低于治疗前(P均<0.05);治疗后,观察组患者X线片中脊柱Cobb角、骶骨倾斜角小于对照组,且VAS与ODI评分均低于对照组(P均<0.05)。结论腰-盆-髋整复手法治疗ADS,能改善患者体征、缓解其疼痛及功能障碍,是一种有效的治疗方法。

基于ISM和AHP的城乡结合部公众突发公共卫生事件风险感知关键影响因素分析

深入研究城乡结合部公众突发公共卫生事件风险感知关键影响因素,对政府调节公众风险感知、提升应急管理能力具有重要意义。首先构建城乡结合部公众突发公共卫生事件风险感知影响因素指标体系,然后利用解释结构模型(ISM)方法对影响因素进行层次分析,并采用层次分析(AHP)法对各层次影响因素的影响力大小进行分析,确定城乡结合部公众突发公共卫生事件风险感知的关键影响因素。结果表明:城乡结合部公众突发公共卫生事件风险感知的影响因素分为直接因素、间接因素和根本因素三个层次;应急决策指挥和感染死亡情况是关键直接影响因素,医疗救援能力和应急物资保障是关键间接影响因素,文化水平、技能水平和公共设施完善度是关键根本影响因素。针对关键影响因素,提出建立和完善预警系统、普及宣传应急知识和加大对城乡结合部地区医疗机构的投入等措施,为政府应急管理提供决策支持。

人工采砂坑对规则波岸礁水动力特性的影响研究

本文基于非静压单相流模型NHWAVE,系统分析了人工采砂坑对规则波岸礁水动力特性的影响。研究结果表明:人工采砂坑会使局部波高在坑前和坑内分别增大和减小,但是采砂坑对礁缘和礁后岸滩附近局部波高的变化无显著影响;采砂坑对平均水位的变化几乎没有影响。随着入射波高的增大,采砂坑附近局部波高的变化幅度相对减小,但礁坪上波浪增水随之增大。礁坪水深越大,采砂坑附近的局部波高变化幅度越大,但礁坪上的增水效应会随着礁坪水深的增大而减小。当波浪周期增大时,波高在坑前升高、坑内降低这一现象更为显著,小周期的波浪几乎不发生这种现象。人工采砂坑的位置、宽度和深度对规则波的传播变形均有显著影响;采砂坑从礁缘移动至岸线附近过程中,波高在坑前升高和坑内降低现象逐渐不明显,但岸线附近的平均水位逐渐增大;随着采砂坑宽度和深度的增大,岸线附近的平均水位逐渐减小。采砂坑的存在在一定程度上会增加波浪的反射系数;采砂坑的存在显著降低了波浪在岸线附近的爬高。研究结果可进一步为评估珊瑚礁上的采砂活动提供参考依据。

基于深度学习的弱反馈自混合干涉信号滤波方法

采集激光自混合干涉信号的过程中会受到环境和电路噪声的干扰,导致信号失真。为了去掉噪声,最大限度保留原信号特征,提出了基于深度学习的自混合干涉滤波方法,该方法适用于弱反馈条件。使用自编码器作为神经网络,用加入噪声的信号作为输入,未加噪声的信号作为输出来训练网络。仿真结果表明:该方法处理含噪声自混合干涉信号时不仅能提高含噪声信号的信噪比,还能很好地保留干涉条纹的波形特征,即条纹的倾斜方向。实验中,使用深度学习方法滤波,再用条纹计数法进行位移重构,结果表明该方法对弱反馈条件下的自混合干涉信号有较好的滤波效果。

弱风条件下斜程海洋湍流中涡旋光束的传输特性

光束在海洋介质中传输会极大地受到海洋湍流的影响。此外,涡旋光束轨道角动量的复用会极大地提高系统容量,因此研究涡旋光束在海洋湍流中的传输具有重要意义。在水平海洋湍流理论基础上,创新性地构建了斜程路径上海洋湍流相位屏模型,以相位结构函数为依据验证了海洋湍流相位屏的准确性,根据多相位屏法搭建准直高斯涡旋光束在海洋湍流中的上行传输链路模型。数值模拟并分析了不同天顶角、海洋湍流内外尺度及拓扑荷数等其他海洋湍流参数对准直高斯涡旋光束经海洋湍流上行传输的光强及相位分布、光束漂移、轴上闪烁指数和长曝光光斑半径的影响。结果表明:涡旋光束的拓扑荷数越小、天顶角越小,光束受到湍流的影响越大;在海洋湍流上行传输链路中,准直高斯涡旋光束的光束漂移、轴上闪烁指数及长曝光光斑半径随海洋湍流外尺度的增大而增大,且主要受传输距离的影响;理想情况下,取海洋湍流外尺度为无穷大,会高估湍流对光束的影响;由于涡旋光束的本身特性,拓扑荷数对光强及相位分布和长曝光光斑半径的影响也较为显著。