基于随机相位调制的数字全息相移量提取方法

提出了一种在相移数字全息中提取相移角的方法.该方法通过在相移数字全息中引入随机相位板对物光波的相位进行调制,使得物光波在全息面上的相位分布成为近似理想的随机分布,进而根据这种随机分布的统计性质对相移角进行提取.计算机模拟结果表明,该方法提取出的相移角与设定的相移角之间的相对误差小于千分之一.同时,经过对比采用随机相位板和不采用随机相位板的计算结果发现,物体衍射光波在全息面上的相位分布具有一定的相关性.     

A five-point stencil based algorithm used for phase shifting low-coherence interference microscopy

The phase shifting technique is the most widely used approach for detecting the envelope in low coherence interferometry. However, if the phase shifts calibration contains errors, some parasitic fringe structure will propagate into the calculated envelopes and cause imprecision in the envelope peak detection. To tackle these problems, a five-point stencil algorithm is introduced into the phase shifting interference microscopy. Considering the amount of parasitic fringes, envelope peak detection and computational efficiency, the presented approach leads to satisfactory results in performance. In combination with a simple polynomial curve fitting method the proposed algorithm exhibits good performance on envelope peak detection in surface profiling. Both of the simulated results and the experimental results indicated that the presented approach can be taken as an alternative to the currently existing methods used for phase shifting low-coherence interference microscopy.     

Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter

We present a digital holography microscopy technique based on a parallel-quadrature phase-shifting method. Two π/2 phase-shifted holograms are recorded simultaneously using polarization phase-shifting principle, slightly off-axis recording geometry, and two identical CCD sensors. The parallel phase-shifting is realized by combining circularly polarized object beam with a 45° degree polarized reference beam through a polarizing beam splitter. DC term is eliminated by subtracting the two holograms from each other and the object information is reconstructed after selecting the frequency spectrum of the real image. Both amplitude and phase object reconstruction results are presented. Simultaneous recording eliminates phase errors caused by mechanical vibrations and air turbulences. The slightly off-axis recording geometry with phase-shifting allows a much larger dimension of the spatial filter for reconstruction of the object information. This leads to better reconstruction capability than traditional off-axis holography.     

A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging

Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique.By using two-dimensional(2D) gratings,the observable contrast is extended to two refraction directions.Recently,we have developed a novel reverse-projection(RP) method,which is capable of retrieving the object information efficiently with one-dimensional(1D) grating-based phase contrast imaging.In this contribution,we present its extension to the 2D grating-based X-ray phase contrast imaging,named the two-dimensional reverseprojection(2D-RP) method,for information retrieval.The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption,the horizontal and the vertical refraction images.The obtained information can be used for the reconstruction of the three-dimensional phase gradient field,and for an improved phase map retrieval and reconstruction.Numerical experiments are carried out,and the results confirm the validity of the 2D-RP method.     

Comparative analysis of phase extraction methods based on phase-stepping and shifting curve in grating interferometry

Two phase extraction methods which are based separately on phase-stepping and shifting curve are mainly used in phase-sensitive imaging in gating interferometry to determine the x-ray phase shift induced by an object in the beam. In this paper, the authors perform a full comparative analysis and present the main virtues and limitations of these two methods according to the theoretical analysis of the grating interferometry.     

Analysis of Phase Measurement Errors in Electro-Optic Holography

This paper presents the results of an error analysis in electro-optics holography. These errors include phase measurement errors due to the linear phase shifter errors in static electro-optic holography, and phase measurement errors due to the errors in the vibrating bias amplitude and phase in dynamic electro-optic holography. Through the error analysis, we found that the phase shifting errors in static electro-optic holography are twice as large as those in the conventional 4-bucket phase shifting algorithm, and the phase shifting errors in dynamic electro-optic holography are similar to those in the 4-bucket phase shifting algorithm.     

A large closed queueing network with autonomous service and bottleneck

This paper studies the queue-length process in a closed Jackson-type queueing network with the large number N of homogeneous customers by methods of the theory of martingales and by the up- and down-crossing method. The network considered here consists of a central node (hub), being an infinite-server queueing system with exponentially distributed service times, and k single-server satellite stations (nodes) with generally distributed service times with rates depending on the value N. The service mechanism of these k satellite stations is autonomous, i.e., every satellite server j serves the customers only at random instants that form a strictly stationary and ergodic sequence of random variables. Assuming that the first k-1 satellite stations operate in light usage regime the paper considers the cases where the kth satellite station is a bottleneck node. The approach of the paper is based both on development of the method from the paper by Kogan and Liptser [16], where a Markovian version of this model has been studied, and on development of the up- and down-crossing method. This revised version was published online in June 2006 with corrections to the Cover Date.     

大型土木结构多尺度模拟与损伤分析——————从材料多尺度力学到结构多尺度

从阐述重大土木工程结构安全运营面临的挑战性课题------结构多尺度力学问题开始, 对多尺度力学中的材料多尺度模拟和结构多尺度模拟的工程背景、多尺度特征和关键研究内容进行比较性评述;在此基础上, 重点介绍了对研究大型土木结构多尺度力学问题可能有参考价值的材料多尺度模拟和分析方法如周期性异质材料问题的平均化与渐进分析方法、单位分解法和多尺度重构核函数法, 以及大型土木结构多尺度模拟与分析领域的研究现状,由此引出结构多尺度力学研究中亟待解决的关键问题并加以评述;通过认识与比较结构多尺度与材料多尺度问题的共性与个性, 文中综述了在大型土木结构多尺度问题的研究进程中可供参考的理论与方法, 提出了这类结构多尺度力学问题研究的几个关键科学问题为: 结构多尺度模拟中的连接与跨越问题、多尺度模型的修正和验证、结构损伤的时间多尺度模拟与分析、结构强度和损伤失效过程中多尺度分析的跨尺度敏感性与随机性因素, 以及适用于大型土木结构多尺度模拟和计算分析的实施策略与技术.      

原子力显微扫描云纹法的相移技术研究

提出一种原子力显微镜扫描云纹法的相移新技术 ,运用原子力显微镜的压电扫描头作为相移元件 ,对所得云纹图像可进行 0 - 2 π范围内的四步相移。对该方法的测量原理和实验技术进行了详细的阐述。作为典型实验和应用实例 ,分别对由全息光栅和含热变形的电子封装试件栅形成的云纹进行相移分析。成功的实验结果表明 ,该方法是可行的 ,为微米云纹方法的条纹处理提供了一种新途径。该方法可望在微观变形的云纹法测量中发挥积极作用     

Probabilistic asymptotic properties of some combinatorial optimization problems

A class of combinatorial optimization problems with sum- and bottleneck objective function is described, having the following probabilistic asymptotic behaviour: With probability tending to one the ratio between worst and optimal objective function value approaches one as the size of the problem tends to infinity.Problems belonging to this class are among others quadratic assignment problems, as well as certain combinatorial and graph theoretical optimization problems.The obtained results suggest that even very simple heuristic algorithms incline to yield good solutions for high dimensional problems of this class.