A new wideband spread target maximum likelihood estimator for blood velocity estimation. I. Theory

The derivation and theoretical evaluation of new wideband maximum-likelihood strategies for the estimation of blood velocity using acoustic signals are presented. A model for the received signal from blood scatterers, using a train of short wideband pulses, is described. Evaluation of the autocorrelation of the signal based on this model shows that the magnitude, periodicity, and phase of the autocorrelation are affected by the mean scatterer velocity and the presence of a velocity spread target. New velocity estimators are then derived that exploit the effect of the scatterer velocity on both the signal delay and the shift in frequency. The wideband range spread estimator is derived using a statistical model of the target. Based on the point target assumption, a simpler wideband maximum-likelihood estimator is also obtained. These new estimation strategies are analyzed for their local and global performance. Evaluation of the Cramer-Rao bound shows that the bound on the estimator variance is reduced using these estimators, in comparison with narrowband strategies. In order to study global accuracy, the expected estimator output is evaluated, and it is determined that the width of the mainlobe is reduced. In addition, it is shown that the height of subsidiary velocity peaks is reduced through the use of these new estimators.     

Direction-of-arrival estimation in radar systems: moving window against approximate maximum likelihood estimator

In this study, we compare two radar target direction-of-arrival (DOA) estimation algorithms: the classical moving window (MW) estimator, implemented in many real radar systems and the approximate maximum likelihood (AML) estimator. The first technique exploits multiple detections in the same time-on-target and the second one exploits the fact that the radar antenna mechanical scanning impresses an amplitude modulation on the signals backscattered by the target. Performances of the two estimators are numerically investigated through Monte Carlo simulation and compared in terms of root-mean-square-error (RMSE), probability of detection and probability of target splitting, the latter being defined as the probability of detecting more than one target when instead only one is present in the cell under test. Numerical results show that the AML estimator generally outperforms the classical MW estimator, also in terms of robustness to target splitting.     

A new wideband spread target maximum likelihood estimator for blood velocity estimation. II. Evaluation of estimator with experimental data

For pt.I see ibid., vol.38, p.1-16, Jan. 1991. The signal models and performance of the estimation strategies described in pt.I are tested with experimental ultrasonic data. The ultrasonic data analyzed verify the theoretical model and predicted performance. The averaged correlation, verified experimentally, confirms that the correlation envelope can be used to estimate the velocity of scatterers and that the shape of the correlation function conveys information regarding the velocity profile within the sample volume. For both the wideband point and range spread estimators, the predicted improvement in velocity resolution and the reduction in height of subsidiary velocity peaks are demonstrated. Through the use of these estimation strategies, information regarding the mean velocity and velocity variation are available for each spatial location within the vessel. This information is presented using a three-dimensional spatial velocity profile display, which appears to offer a number of advantages in the rapid identification of pathology.     

基于极大似然估计的惯性测量组合标定方法

针对测试设备或平台框架转角误差( ASE)较大的情况,提出了一种用于惯性测量组合(IMU)标定的新方法.该方法采用相互正交的惯性器件输出的平方和作为观测信息,并以重力加速度ga和地速ωie的幅值平方作为参考基准来标定工具误差系数,这样能够消除ASE对标定结果的影响.同时针对误差项系数也较大的情况,给出了一种基于极大似然...     

极大似然高分辨波达估计新方法

极大似然估计器是波达方向估计中公认的最佳估计器,但是计算量很大。为了解决极大似然估计器由于进行多维格形搜索而带来的计算量大的不足,将粒子滤波方法与极大似然估计相结合,提出了一种基于粒子滤波的极大似然波达方向估计器(Maximum Likelihood DOA Estimator Based on Particle Filtering,简称MLE-PF)。研究结果表明,MLE-PF不但保持了原极大似然估计方法的优良性能,大大减小了计算量,计算复杂度由O(LK)降至O(K×Ns),而且在低信噪比时也具有比MUSIC以及MiniNorm方法更加优越的估计性能。     

A non-parametric monotone maximum likelihood estimator of time trend for repairable system data

The trend-renewal process (TRP) is defined to be a time-transformed renewal process, where the time transformation is given by a trend function λ(·) which is similar to the intensity of a non-homogeneous Poisson process (NHPP). A non-parametric maximum likelihood estimator of the trend function of a TRP is obtained under the often natural condition that λ(·) is monotone. An algorithm for computing the estimate is suggested and examined in detail in the case where the renewal distribution of the TRP is a Weibull distribution. The case where one has data from several systems is also briefly studied.     

A weighted total least squares estimator for multivariable systemswith nearly maximum likelihood properties

The aim of the present paper is to develop a parametric estimator for linear time-invariant multivariable systems with nearly maximum likelihood properties. The estimator is based on the total least squares (TLS) method. It can be seen as an “optimally” weighted iterative generalized TLS (GTLS) estimator, combining the nice asymptotic properties of the maximum likelihood (ML) method with the global minimization property of the GTLS estimator     

A good property of the maximum likelihood estimator in a restricted normal model

Summary We consider a normal model with known diagonal covariance matrix and a vector of means constrained to belong to a polyhedral cone. The standard estimatorsX (unrestricted MLE) andX ^* (restricted MLE) are compared for estimation of several components of the parameter simultaneously. We show thatX ^* is preferred toX under several conditions.     

Maximum likelihood estimation techniques for concurrent flaw subpopulations

Failure of structural materials is often caused by the presence of two or more types of defect subpopulations. The maximum likelihood estimation technique for evaluating the Weibull parameters of these underlying subpopulations in the case of known fracture origin is presented. The maximum likelihood estimation equations are derived, and solved by means of nonlinear programming. The estimators obtained therefrom are tested for both accuracy and consistency against a series of simulation runs. For data sets containing a relatively small sample size, the advantage of the method of maximum likelihood over two established nonparametric techniques is demonstrated.     

An experimental comparison of the maximum likelihood estimation and nonlinear least-squares fluorescence lifetime analysis of single molecules

Two procedures based on the weighted least-squares (LS) and the maximum likelihood estimation (MLE) method to confidently analyze single-molecule (SM) fluorescence decays with a total number (N) of 2,500-60,000 counts have been elucidated and experimentally compared by analyzing measured bulk and SM decays. The key observation of this comparison is that the LS systematically underestimates the fluorescence lifetimes by approximately 5%, for the range of 1,000-20,000 events, whereas the MLE method gives stable results over the whole intensity range, even at counts N less than 1,000, where the LS analysis delivers unreasonable values. This difference can be attributed to the different statistics approaches and results from improper weighting of the LS method. As expected from theory, the results of both methods become equivalent above a certain threshold of N detected photons per decay, which is here experimentally determined to be approximately 20,000. In contrast to the bulk lifetime distributions, the SM fluorescence lifetime distributions exhibit standard deviations that are sizably larger than the statistically expected values. This comparison proves the strong influence of the inhomogenuous microenvironment on the photophysical behavior of single molecules embedded in a 10-30-nm thin polymer layer.     

分布源目标方位估计的降维最大似然估计

介绍了已有的分布源目标方位估计中的最大似然估计(MLE)算法,它是四维非线性最优化问题,文中称之为四维MLE算法,因计算量庞大,同时提出了一种降为三维的MLE算法,简化为三维非线性最优化,称之为三维MLE算法。两种算法均采用牛顿型搜索算法,来搜索未知参数的全局最优点。在单次迭代过程中,三维MLE算法比四维MLE算法减少了51次协方差矩阵求逆和87次矩阵乘法,搜索效率得到提高,并且节省了存储空间。得出了新算法克拉美-罗界的计算公式,其计算量也有所降低。计算机仿真验证,三维MLE算法和四维MLE算法的估计精度相当,新算法在减少计算量的同时并无损失性能,所以实用性和实时性都得到显著提高。     

New bounding techniques for goal‐oriented error estimation applied to linear problems

The paper deals with the accuracy of guaranteed error bounds on outputs of interest computed from approximate methods such as the finite element method. A considerable improvement is introduced for linear problems, thanks to new bounding techniques based on Saint‐Venant's principle. The main breakthrough of these optimized bounding techniques is the use of properties of homothetic domains that enables to cleverly derive guaranteed and accurate bounding of contributions to the global error estimate over a local region of the domain. Performances of these techniques are illustrated through several numerical experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

A meshless method for generalized linear or nonlinear Poisson-type problems

This paper presents a meshless method, based on coupling virtual boundary collocation method (VBCM) with the radial basis functions (RBF) and the analog equation method (AEM), to analyze generalized linear or nonlinear Poisson-type problems. In this method, the AEM is used to construct equivalent equations to the original differential equation so that a simpler fundamental solution of the Laplacian operator, instead of other complicated ones which are needed in conventional BEM, can be employed. While global RBF is used to approximate fictitious body force which appears when the analog equation method is introduced, and VBCM are utilized to solve homogeneous solution based on the superposition principle. As a result, a new meshless method is developed for solving nonlinear Poisson-type problems. Finally, some numerical experiments are implemented to verify the efficiency of the proposed method and numerical results are in good agreement with the analytical ones. It appears that the proposed meshless method is very effective for nonlinear Poisson-type problems.     

Compactness maximum method and complex measurement problems

A methodical approach to solving complex measurement problems is presented with a review of the results of developing and applyinga posteriori prediction systems for the metrological maintenance of test, monitoring, and control hardware and software. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 15–21, July, 1995.     

A new estimator for vector velocity estimation

A new estimator for determining the two-dimensional velocity vector using a pulsed ultrasound field is derived. The estimator uses a transversely modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new estimator automatically compensates for the axial velocity when determining the transverse velocity. The estimation is optimized by using a lag different from one in the estimation process, and noise artifacts are reduced by averaging RF samples. Further, compensation for the axial velocity can be introduced, and the velocity estimation is done at a fixed depth in tissue to reduce the influence of a spatial velocity spread. Examples for different velocity vectors and field conditions are shown using both simple and more complex field simulations. A relative accuracy of 10.1% is obtained for the transverse velocity estimates for a parabolic velocity profile for flow transverse to the ultrasound beam and a SNR of 20 dB using 20 pulse-echo lines. The overall bias in the estimates was -4.3%     

A novel pseudo‐maximum likelihood estimation method for accelerated degradation tests under Wiener process

For reliability assessment based on accelerated degradation tests (ADTs), an appropriate parameter estimation method is very important because it affects the extrapolation and prediction accuracy. The well‐adopted maximum likelihood estimation (MLE) method focuses on interpolation fitting and obtains results via maximizing the likelihood of the observations. However, a best interpolation fitting does not necessarily yield a best extrapolation. In this paper, therefore, a pseudo‐MLE (P‐MLE) method is proposed to improve the prediction accuracy of constant‐stress ADTs by considering the degradation mechanism equivalence under Wiener process. In particular, the degradation mechanism equivalence is characterized by a mechanism equivalence factor which presents the proportional relationship between degradation rate and variation. Then, the mechanism equivalence factor is determined via a two‐step method. The other model parameters can be estimated by the general MLE method. The asymptotic variances of acceleration factors and the p‐quantile of product failure time under normal condition are adopted to compare the statistical properties of the proposed method and the general MLE approach. Numerical examples show that the novel P‐MLE method may not achieve a maximum likelihood but can provide more benefits regarding prediction accuracy enhancement especially when the sample size is limited.     

An application of splines to maximum likelihood radar imaging

Recent results in radar imaging using estimation theoretic techniques are applied to forming images from data from a compact radar range. Nonparametric maximum likelihood methods based on spline approximations are used. The object imaged is a one meter diameter sphere covered with wrinkled aluminum foil. This rough sphere approximately fits the diffuse model and the ideal scattering function for a rough rotating sphere is known. The results shown demonstrate that the proposed algorithm is realizable and that the image are comparable to simulations.©1993 John Wiley & Sons Inc     

基于EMD间隔阈值消噪与极大似然估计的滚动轴承故障诊断方法

针对小波阈值消噪用作滚动轴承故障信号处理存在小波基函数较难选择及传统硬阈值、软阈值消噪效果差等缺点,将EMD间隔阈值消噪与极大似然估计相结合,应用于滚动轴承早期微弱故障诊断。对原始信号进行EMD分解;对各IMF进行基于极大似然估计的间隔阈值消噪,并重构出故障信号;进行包络谱分析得出诊断结果。数字仿真信号与实验信号验证了该方法的有效性。