基于概率迭代的NDP反演方法

针对中子深度分析(NDP)技术,基于概率迭代思想,推导一种迭代反演方法,对其和线性正则化方法在NDP反演问题中的应用进行比较.未引入计数随机误差时,两者都能得到较好的反演结果,迭代法的结果是非负的,线性正则化方法在源强度发生阶跃处得到的结果更好.在考虑随机误差存在的情况下,迭代法的效果更佳.同时,研究了迭代矩阵对结果的影响,矩阵元的指数放大可以实现迭代过程的加速.     

基于相息图迭代的随机相位加密

提出了一种将随机相位加密和相位恢复算法中的求解附加相位分布分二步实施的加密方法. 由于该方法的实质是通过在随机谱和相息图之间进行相位恢复迭代以确定相息图和密钥的相 位分布，因而能够减小图像的解密误差.在相息图相位离散化的迭代过程中，采用增大设计 冗余度的方法，降低了由相位离散化所带来的解密误差.最后，通过计算机模拟实验验证了 该方法在减小图像解密误差方面的有效性. 关键词： 随机相位 光学图像加密 相息图 二元光学 离散化误差 相位恢复算法     

Damage detection of cracked thick rotating blades by a spatial wavelet based approach

This paper presents a technique for blade damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze spatially distributed signals (e.g. mode shape) of cracked thick rotating blades. First, a finite element model is applied to the vibration of a thick rotating blade with a single edge crack. The effects of transverse shear deformation and rotatory inertia are taken into account. Then the mode shapes of the cracked rotating blade are analyzed by wavelet transformation. The effects of crack locations and sizes on the wavelet coefficients are studied. It is found that the distributions of the wavelet coefficients can identify the crack position of the rotating blades by showing a peak at the position of the crack. Then the signals are analyzed by wavelet transform. It is found that the distributions of the wavelet coefficients can identify the crack position. Assumed measurement errors are added to nth mode shape for evaluating the effect of measurement errors on the capability of detecting crack position. The moving average method is used to process the data with assumed measurement errors. The crack positions can also be identified when there exist assumed measurement errors.     

Vibration damage detection of a Timoshenko beam by spatial wavelet based approach

This paper presents a technique for structure damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze the mode shape of a Timoshenko beam. First, the mode shapes of the Timoshenko beam containing a transverse crack are obtained. The crack is represented as a rotational spring. Then these spatially distributed signals are analyzed by wavelet transformation. It is observed that distributions of the wavelet coefficients can identify the crack position of Timoshenko beam by showing a peak at the position of the crack. It is also demonstrated that the crack position can be detected by this method even though the crack is very small. Assumed measurement errors are added to the mode shape for evaluating the effect of measurement errors on the capability of detecting crack position. The moving average method is used to process the data with assumed measurement errors. The crack positions can also be identified when there exist assumed measurement errors.     

Uncertainties of predictions from parton distributions I: Experimental errors

We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the cross-sections for W production and for Higgs boson production via gluon-gluon fusion at the Tevatron and the LHC, on the ratio of W^- to W⁺ production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertainties on the parton distributions in the relevant x,Q² domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using , and extractions of as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002. Received: 13 November 2002 / Published online: 5 May 2003 RID="a" ID="a" Royal Society University Research Fellow     

Solution of the inverse radiative load problem in a two-dimensional system

An inverse radiation analysis is presented for estimating the temperature and the heat load distributions of the heating surface from the temperature and the heat flux measurements of the heated object. The Monte Carlo method is employed to solve the direct radiation problem. The inverse radiation problem is solved using the conjugate gradient and singular value decomposition methods. The measured data are simulated by adding random errors to the exact solution of the direct problem. The effects of the measurement errors on the accuracy of the inverse analysis are investigated. The study shows that the heat load distribution of the heating surface can be estimated accurately for the exact and noisy data. And the conjugate gradient method is better than the singular value decomposition method since the former can obtain more accurate results if the measurement errors are the same.     

原级X射线谱强度分布的定量测定

本文提出了衍射或荧光分析用的X射线管原级X射线谱强度分布的定量测定方法。在带有正比、闪烁计数管的衍射仪上用LiF分光晶体进行展谱测定。实验测定强度经校正计算还原为X射线管窗口处的强度。对荧光X射线管还应测定几个射线束方向的原级谱加以平均求得有效原级谱。分析了原级X射线谱数据的误差及其对基本参数法等实际应用的影响。 关键词：     

Exact lattice calculations of dispersion coefficients in the presence of external fields and obstacles

We present a study of the field-dependent dispersion coefficient of point-like particles in various 2D overdamped systems with obstructions (periodic, percolating, and trapping distributions of obstacles). These calculations profit from the synthesis of a newly proposed Monte Carlo algorithm --the first such algorithm that correctly reproduces the free dispersion coefficient in the presence of finite external fields-- and an asymptotically exact calculation technique. The resulting method efficiently produces algebraic and numerical results without the need to actually perform Monte Carlo simulations. When compared to such simulations, our exact method features a negligible computational cost and exponentially small errors. Utilizing the power of this numerical method, we engage in comprehensive parametric analysis of several model systems, revealing very subtle effects that would otherwise be swamped by statistical errors or incur prohibitive computational costs. The unified framework presented here serves as a template for further applications of lattice random-walk models of biased diffusion.Received: 27 July 2004, Published online: 1 October 2004PACS: 87.15.Vv Diffusion - 82.20.Wt Computational modeling; simulation - 05.10.Ln Monte Carlo methods     

Reconciling open-charm production at the Fermilab Tevatron with QCD

We study the inclusive hadroproduction of D0, D+, D*+, and D(s)+ mesons at next-to-leading order in the parton model of quantum chromodynamics endowed with universal nonperturbative fragmentation functions fitted to e+e- annihilation data from CERN LEP1. Working in the general-mass variable-flavor-number scheme, we resum the large logarithms through the evolution of the fragmentation functions and, at the same time, retain the full dependence on the charm-quark mass without additional theoretical assumptions. In this way, the cross section distributions in transverse momentum recently measured by the CDF Collaboration in run II at the Fermilab Tevatron are described within errors.     

两步相移数字全息物光重建误差分析与校正

系统研究了两步相移数字全息干涉术中相移误差引起的波前再现误差的计算和校正方法. 基于衍射物光相位分布的随机性和振幅相位的相互独立性原理,介绍了相移数字全息中物光波前再现误差的表达形式,推导出步长为π/2的两步算法中物光重建误差的表达式. 通过进一步分析这一重建误差的结构和特点,结合物光表达式,给出了自动校正相移误差引起的波前重建误差的校正方法. 该方法无需增加测量,在未知相移误差大小的情况下,只对标准两步相移算法恢复的物光复振幅进行处理就可以实现对物光振幅和相位的同时校正. 计算机模拟结果表明,校正后可将 关键词： 相移干涉术 数字全息 物光重建 误差校正     

Visualization of three-dimensional temperature distributions in a large-scale furnace via regularized reconstruction from radiative energy images: numerical studies

In this paper, the possibility of visualization of three-dimensional (3-D) temperature distributions in large-scale boiler furnaces from radiative energy images captured by multiple charge-coupled device (CCD) cameras mounted around the furnace is studied numerically. For the calculation of the radiative energy image formation, a fast algorithm proposed by the authors for pinhole imaging is used in this paper, which is based on the Monte Carlo method and combined with a concept of angular factor effective for image formation. This algorithm is applicable for the emitting, absorbing, and isotropic scattering medium. For the inversion of the 3-D temperature distributions which is an ill-posed problem, a modified Tikhonov regularization method is improved, where the finite difference regularizer is defined and can be used in 3-D cases, and the optimal regularization parameter is suggested to be selected by using a post-treatment method. For a 3-D unimodal temperature distribution, the numerical simulation results show that the reconstruction errors for the 3-D temperature distribution can be maintained at levels similar to the measurement error and the visualization quality of the temperature distribution is satisfactory. For a kind of bimodal temperature distribution, the reconstruction errors are higher than those for the unimodal distribution, but the bimodal feature of the temperature distribution can also be reproduced clearly.     

A QCD analysis of HERA and fixed target structure function data

The parton momentum density distributions of the proton are determined from a next-to-leading order QCD analysis of structure functions measured at HERA and by fixed target experiments. Also included are data on the difference of the up and down anti-quark distributions. The uncertainties in the parton densities, structure functions and related cross sections are estimated from the experimental errors and those on the input parameters of the fit. Several QCD predictions based on the parton densities obtained from this analysis are calculated and compared to data. Received: 21 December 1999 / Published online: 6 April 2000     

QCD analysis of DIS and SIDIS data with two alternative methods

The global fit analysis of all published data on DIS and semi-inclusive DIS (SIDIS) asymmetries is performed in the next to leading (NLO) QCD order. The respective parameterization on polarized PDFs is constructed. The especial attention is paid to the impact of novel SIDIS data on the polarized distributions of light sea and strange quarks as well as on the polarized gluon distributions. The first moments of these distributions entering the nucleon spin are found to be surprisingly small quantities. The alternative direct (free of any fitting procedure) method of NLO QCD analysis is elaborated. Method is especially important for analysis of SIDIS data because it allows to avoid the problems arising in the conventional fitting procedure: functional arbitrariness at initial scale and ambiguities in the error band calculation. Within the alternative method the central values and uncertainties of the measured asymmetries directly propagate to the central values and uncertainties of the polarized PDFs we are interested in. The method is applied to all existing SIDIS data on pion production for an estimation in NLO QCD of the valence and sea quark contributions to the proton spin. As a result one arrives at the conclusion that, contrary to the valence contributions, the sea contributions to the proton spin are compatible with zero within the errors.     

Effects of polarization on radiation absorption in one-dimensional semitransparent slab exposed to collimated irradiation

The internal distribution of radiative absorption in one-dimensional semitransparent slab exposed to collimated irradiation is determined by the ray tracing method, and the detailed computation formulae for the distribution of radiative absorption are deduced. It is found that the ray will be polarized by specular reflection of slab boundaries even if the collimated irradiation is unpolarized, and the extent of polarization increases with the internal reflection times. The effects of polarization on the radiative absorption are analyzed and the radiative absorption distributions are compared with those obtained from the case in which the effects of polarization are omitted. The results show that the large differences between reflectances of perpendicular and parallel polarized components are the main causes resulting in errors of radiative absorption distribution. The polarization of incident beam has significant influences on the radiative absorption. Even for an unpolarized beam irradiated near Brewster's angle, omitting the effects of polarization will result in large errors, and the errors increase with the refractive index.     

A single-mode-fiber-based point diffraction interferometer

Based on the modification of a point diffraction interferometer, a method for measuring the optical fields from remote objects and external sources is developed. In this method, the reference beam is obtained from the studied beam by filtration of its spatial spectrum with a single-mode optical fiber. To eliminate the effect of phase errors caused by the nonideality of elements of the optical scheme on the measurement results, we developed a procedure of interferometer calibration that permits one to determine these errors with the aim of subtracting them from the measured field phase distributions.     

基于倾斜相位的抗振动干涉面形测量

环境振动会在干涉测量过程中产生随机倾斜、移相误差,导致测量精度下降。为了降低环境振动对移相干涉测量的影响,提出了一种基于倾斜相位的抗振动干涉面形测量方法。首先,利用Fourier变换将干涉图变换到频域;然后,利用频域细分操作对峰值坐标进行亚像素精度定位,求解出振动倾斜平面;最后,利用最小二乘法计算出待测面的相位分布。实验结果表明,本方法与同步移相法的复原结果具有高度一致性,波面峰谷值和均方根值的偏差较小;且本方法无需对硬件进行改动,可为振动环境下的移相干涉测量提供一种低成本、高精度的解决方案。     

三层膜管壁结构的颈动脉超生仿真

颈动脉超声仿真 有助于血管壁超声检测及信号处理方法的性能评价。提出三层膜管壁结构的颈动脉超声仿真方法。根据组织散射点分布的形状和密度与超声回声斑点分布的变化规律,对临床图像统计分析,确定对应组织散射点分布、密度及强度等特征参数,利用FIELD II产生超声射频回波信号并得到B超图像。30 例仿真试验结果表明,血管壁内、中、外膜及血流回声的统计分布与临床B超图像的一致;与中心频率为8 MHz的结果相比,12 MHz仿真的内、中、外膜厚度及管腔直径测量均值与预设值相等,最大相对误差分别为4.01%, 1.25%, 0.04%及0.15%,仿真效果更为逼真。      

Freeform lens for off-axis illumination in optical lithography system

A method of designing a freeform lens for off-axis illumination (OAI) in an optical lithography system is proposed in this paper. Based on the Snell's law and conservation law of energy, a series of first-order partial differential equations are deduced. Coordinate relations are established with the energy mapping relations by the characteristics of the incident beam and the predetermined irradiance distribution on the target plane. The contours of the freeform lens are calculated by solving partial differential equations numerically. Moreover, the optical performance for OAI is simulated and analyzed. Simulation results show that the irradiance distributions can be well controlled with a maximum uniformity of 95.71% and a maximum efficiency of 99.04%. Tolerance analysis shows that the angular errors of the freeform lens are more sensitive than the coordinate errors.     

运用余弦变换的三维物体面形轮廓术

首次提出通过对投影到物体表面的变形光栅图进行余弦变换以获得物体表面高度分布的方法，实验证实此方法比传统的傅里叶变换法有更高精度和更快处理速度，且易实现全场的自动处理。     

三维复杂温度场高精度声学测量方法

声学温度场检测技术通过多路径声波传播时间数据,反演被测区域的温度分布。提供了一种高精度的三维复杂温度场的声学测量方法。首先从射线声学角度给出了三维非均匀温度场中声波传播路径的数学模型。在此基础上,将三维温度场的重建问题转化为声波传播路径的求解和温度场的反演问题,建立了基于多项式修正径向基函数(RBF-PR)和改进的Tikhonov正则化三维温度场重建算法。采用两种典型的炉膛三维温度场模型,在信噪比SNR=35 dB下进行了数值模拟,分析了声波传播路径在非均匀温度场中的弯曲特性、算法的重建质量和抗噪性,同时进行了实际炉膛内二维温度场的重建。结果表明了提出的考虑声线弯曲的温度场重建算法具有精度高,抗噪性强、适用性好的特点,为实现高精度的复杂温度场的声学测量提供了有效方法。