结构在水平与竖向随机地震同时作用下的相关函数和谱密度

对单自由度结构在水平与竖向地震同时作用下的随机稳定性、响应及其相关函数和谱密度函数进行系统研究。首先利用Stratonovich和It随机微分方程与响应矩微分方程的互相关转化关系,建立了结构响应矩方程;然后根据Hurwitz随机稳定准则,获得了结构一阶和二阶响应矩渐近稳定的解析判别式;继而,利用复模态法获得了结构响应二阶矩的解析瞬态解和平稳解;最后利用It随机微分方程解具有的非可料函数性质,获得了结构位移、速度响应的自相关函数、互相关函数以及谱密度函数、互谱密度函数的解析解,给出了算例,并综合分析了各种参数对结构响应、稳定性以及相关函数和谱密度函数的影响。     

Revisiting the method of cumulants for the analysis of dynamic light-scattering data

The method of cumulants is a standard technique used to analyze dynamic light-scattering data measured for polydisperse samples. These data, from an intensity-intensity autocorrelation function of the scattered light, can be described in terms of a distribution of decay rates. The method of cumulants provides information about the cumulants and the moments of this distribution. However, the method does not permit independent determination of the long-time baseline of the intensity correlation function and can lead to inconsistent results when different numbers of data points are included in the fit. The method is reformulated in terms of the moments about the mean to permit more robust and satisfactory fits. The different versions of the method are compared by analysis of the data for polydisperse-vesicle samples.     

The Measurement of the First-order Factorial Moment of Double-triggered Photocount Distribution as an Alternative to Triple Correlation

The expression corresponding to the normalized first-order factorial moment (NFOFM) of a double triggered photocount distribution (DTPCD) has been developed. It is found that the NFOFM of a DTCPD has the spectral information of incident light corresponding to the third-order autocorrelation function. A theoretical error model was developed and checked by using a computer simulation method. We also compare the results obtained from the measurement of the NFOFM of a DTPCD with those obtained from the second- and third-order correlation functions.     

基于Tchebichef矩的抗几何攻击图像水印

针对几何攻击容易使常规水印算法检测失败的问题,利用Tchebichef矩出色的重构性能,结合图像归一化,提出一种基于Tchebichef矩的抗几何攻击图像水印算法GWTM.该算法在水印嵌入和提取之前对图像进行几何失真的归一化,根据Tchebichef矩系数的特点,进行矩幅度修改量测试,筛选出最优矩集合.根据水印比特自适应地修改集合中的矩,并对修改后的矩进行Tchebichef重构,实现水印的嵌入.水印提取时,以最优矩集合为密钥,通过与原始图像的Tchebichef矩幅度比较提取水印.实验证明,GWTM算法能够抵抗任意角度的旋转攻击、缩放攻击及常规的信号处理攻击.     

商用车驾驶室质心与转动惯量测量方法

分析了基于杠杆原理和刚体转动惯量平行轴原理,在用于商用车驾驶室质心和转动惯量计算的分离算法的基础上,利用K&C试验台的质心位置和转动惯量测试功能,提出了一种可进行K&C坐标系与整车坐标系转换,并能修正测量时安装位置与设计位置错位的改进算法。通过验证测试,证明了改进算法可弥补已有分离方法存在的不足,其结果更加符合商用车驾驶室隔振分析的工程需要。     

Some statistical properties of surface slopes via remote sensing considering a non-Gaussian probability density function

Abstract

Theoretical relationships of statistical properties of surface slope from statistical properties of the image intensity in remotely sensed images, considering a non-Gaussian probability density function of the surface slope, are shown. Considering a variable detector line of sight angle and considering ocean waves moving along a single direction and that the observer and the sun are both in the vertical plane containing this direction, new expressions, using two different glitter functions, between the variance of the intensity of the image and the variance of the surface slopes are derived. In this case, skewness and kurtosis moments are taken into account. However, new expressions between correlation functions of the intensities in the image and surface slopes are numerically analyzed; for this case, the skewness moments were considered only. It is possible to observe more changes in these statistical relationships when the Rect function is used. The skewness and kurtosis values are in direct relation with the wind velocity on the sea surface.     

Magnetic Correlations in Some FeNi/Cu(100) Multilayers

We present a first-principles electronic structure based study of magnetic correlations in the paramagnetic phase of some Fe and Ni multilayers on Cu(100) substrates. We have used the screened Korringa–Kohn–Rostoker method to calculate the electronic structure within the spin-density functional theory and used the disordered local moments model to describe the paramagnetic phase above the Curie temperature. We find that in the Ni/Cu(100) films, there are no local moments formation for any thickness. For the multilayers of Fe and Ni, we find that there is some, although very small, local moment formation in the interior of the Ni film if the Ni layer is more than 6 monolayers thick. However, the Ni layers facilitate the magnetic correlation between the Fe layers. The Curie temperatures of the multilayers also depend upon the Ni layer thickness.     

Wigner distribution moments in fractional Fourier transform systems

It is shown how all global Wigner distribution moments of arbitrary order in the output plane of a (generally anamorphic) two-dimensional fractional Fourier transform system can be expressed in terms of the moments in the input plane. Since Wigner distribution moments are identical to derivatives of the ambiguity function at the origin, a similar relation holds for these derivatives. The general input-output relationship is then broken down into a number of rotation-type input-output relationships between certain combinations of moments. It is shown how the Wigner distribution moments (or ambiguity function derivatives) can be measured as intensity moments in the output planes of a set of appropriate fractional Fourier transform systems and thus be derived from the corresponding fractional power spectra. The minimum number of (anamorphic) fractional power spectra that are needed for the determination of these moments is derived. As an important by-product we get a number of moment combinations that are invariant under (anamorphic) fractional Fourier transformation.     

The method of moments and its optimization

The method of moments is a semidiscrete numerical method for solving partial differential equations. The method approximates the solution of a partial differential equation by a finite sum of products of two functions. One function in the product is an unknown function of a single variable and the other function (moment function) is a prescribed function in the remaining variables. Using variational technique we obtain a finite system of boundary value problems of ordinary differential equations for the unknown functions. The main goal of this paper is the study of the theoretical background and numerical effectiveness of the method of moments for solving linear partial differential equations on rectangular-like domains. The mathematical formulation of the method together with error estimates and the theory of optimal moment functions are given. If for the one-dimensional moment functions piecewise polynomials of degree K are used then finite element type error bounds are obtained for the approximate solution in two dimensions. We also consider the numerical implementation of the method through the factorization method and efficient initial value methods. Several numerical examples showing the efficiency of the method are presented.     

Methods for constructing analytic phase function for small spherical particle polydispersions

Two ways of constructing analytic phase function for a polydispersion of small spherical non-absorbing particles have been investigated. First one is a straightforward procedure emanating from the implementation of single particle scattering input into the defined polydisperse phase function. This results in an analytic phase function in terms of moments of the distribution. The second approach is a new strategy, based on the Lagrange mean value theorem. A clear understanding of the relationship between these two approaches has been developed. The efficacy and accuracy of the scattering phase functions is illustrated by applying it to a power-law size distributed sphere ensemble.     

Enhancement of Signal-to-Noise Ratio of Turbulence Measurements by Cross Correlation

A novel method for the measurement of very low turbulence intensities in fluids, based on a dual heat-transfer transducer and a cross correlator, is described. The minimum measurable turbulence intensity is shown to vary with the square root of the minimum detectable cross-correlation coefficient ?. The effects of finite additive noise correlation and finite lateral separation between the transducer halves are studied. Details are given of an instrument measuring the normalized cross-correlation coefficient between two time-dependent signals in the frequency range 2 Hz-300 kHz with an accuracy of ±0.05? ±0.01. The described correlator is particularly suitable for measurements of quasi-stationary processes. A variation of 10 percent in the level of either input signal results in a correlation error of less than 0.6 percent.     

The scattering of oblique flexural waves of a cracked conducting plate in a uniform magnetic field

Summary Following a classical plate bending theory for magneto-elastic interactions under quasistatic electromagnetic field, we consider the scattering of time harmonic flexural waves by a through crack in a conducting plate under a uniform magnetic field normal to the crack surface. It is assumed that the plate has the finite electric conductivity, and the electric and magnetic permeabilities of the free space. An incident wave giving rise to moments symmetric about the crack plane is applied in an arbitrary direction. Fourier transform method is used to solve the mixed boundary value problem which reduces to a pair of dual integral equations. These dual integral equations are further reduced to a Fredholm integral equation of the second kind. The dynamic moment intensity factor versus frequency for several values of incident angle is computed and the influence of the magnetic field on the normalized values is displayed graphically.     

Theoretical investigation of the spatial progression of temporal statistical moments in linear chromatography

Migration and dispersion in chromatography are modeled by analogy to an effective eddy diffusion process. On the basis of this model, the spatial rates of temporal statistical moment change are derived for general chromatography in linear media. In most practical cases, these equations can be simplified so that temporal statistical moments can be calculated by solving a system of ordinary differential equations that depend only on the local HETP, solute velocity, and initial values of the temporal statistical moments. The calculations of temporal centroid, temporal variance, temporal skew, and temporal excess are demonstrated for the case of linear solvent strength gradients. It is shown for the case of temporally invariant separation environments, such as isocratic liquid chromatographic systems and isothermal gas chromatographic systems, that temporal variance contributions are spatially additive and that the temporal third normalized central moment is unaffected by spatial variations in the medium. A refined explanation is given for how peak symmetry is improved in gradient forms of chromatography.     

流线型闭口箱梁断面风荷载空间相关性试验研究

对典型流线型闭口箱梁断面的风荷载效应进行同步测压风洞试验,比较了来流平均风速、湍流度、风攻角、展向间距等不同参数条件下风荷载在空间分布状况,对风速及其荷载效应的空间相关性进行深入研究,从时、频域两个方面来尝试分析现象及原因,探讨影响因素,证实升力、扭矩的展向相关性远大于风速、阻力的相关性,并发现升力与扭矩的相关性规律相似,风速与阻力相关性规律相似;验证了传统随机抖振动气动力理论所存在的不足     

Delay-independent stability of moments of a linear oscillator with delayed state feedback and parametric white noise

The stability of a linear oscillator with delayed state feedback driven by parametric Gaussian white noise is studied in this paper. The first and second order moment equations of the system response are derived by using moment method and Itô differential rule. Based on the moment equations, the delay-independent stable conditions of both moments are proposed: For the first order moment, the sufficient and necessary condition that guarantee delay-independent stability is identified to that of the deterministic system; for the second order moment, the sufficient condition that ensure delay-independent stability depends on noise intensity. The theoretical results are also illustrated with numerical simulations.     

Image description with generalized pseudo-Zernike moments

A new set, to our knowledge, of orthogonal moment functions for describing images is proposed. It is based on the generalized pseudo-Zernike polynomials that are orthogonal on the unit circle. The generalized pseudo-Zernike polynomials are scaled to ensure numerical stability, and some properties are discussed. The performance of the proposed moments is analyzed in terms of image reconstruction capability and invariant character recognition accuracy. Experimental results demonstrate the superiority of generalized pseudo-Zernike moments compared with pseudo-Zernike and Chebyshev-Fourier moments in both noise-free and noisy conditions.     

A general model-based approach to two-dimensional infrared correlation spectroscopy incorporating the global phase angle

We describe a theoretical framework for a model-based approach to two-dimensional correlation spectroscopy that is generally applicable to any arbitrary model function. The method is based on the correlation between spectral data and a set of model waveforms with a varying correlation index, the global phase angle Theta. When experimental spectral intensity variations are expressed as sinusoidal, exponential, Lorentzian, or quadratic functions, the proposed approach allows us to estimate the quantitative values of the target parameters in those expressions. In addition, this method enables us to assess the sequential order in a series of bands undergoing non-identical intensity changes in a dynamic data set. We present both simulated and experimentally obtained data that illustrate that the deviations from linearity of the absorption band intensity waveforms are clearly detected and can be quantitatively estimated using quadratic functions.     

An exact solution for an anisotropic plate with an elliptic hole under arbitrary remote uniform moments

The problem of an anisotropic plate containing an elliptic hole subjected to remote bending or twisting moments is considered. In contrast with the previous works on the problem, the requirement that the deflection be a single-valued function is satisfied by introducing a correction constant. An exact solution for general anisotropic materials under arbitrary uniform loading conditions is derived. Explicit expressions for the deflection and moments on the edge of an elliptic hole in an orthotropic plate subjected to bending or twisting moments are obtained. The moment intensity factors as the elliptic hole degenerates into a crack are given.     

Analog measurement of scattered optical fluctuations

Astatistical model that describes the analog measurement of a fluctuating light intensity that arises from a non-Gaussian scattering process is developed. The higher-order statistical moments are derived for a p-i-n diode receiver model and gamma-distributed intensity fluctuations. Criteria for the accurate measurement of the scattering fluctuations are found, and these are used to analyze data derived from an on-line scatterometer system. Implications for future on-line measurement technology are discussed.