An estimation procedure for the disposition of fitting parts

This article deals with the estimation of the functional parameters of a (normal-)distribution from grouped samples. In contrast to the well-known problem, in the present investigation the data are classified into several noncontiguous and overlapping intervals (i.e., the classes arenot mutually exclusive). Therefore, conventional methods cannot be applied. Of course, this grouping is not done intentionally, but is due to certain “production requirements”. Two methods, based on maximum-likelihood and minimum-X ², are derived in order to handle this awkward situation and to render an estimation possible. Numerical results of a simulation study show that both methods lead to fair results, provided that the sample size is large enough.      

A fast method for direction-of-arrival estimation

In many eigenvalue-eigenvector-based direction-of-arrival estimation algorithms, one finds orthogonal basis vectors for the noise subspace. We propose a circulant basis for the noise space which can be calculated more efficiently than an orthogonal basis. The new method for high signal-to-noise ratio (SNR) has a performance similar to the well-known MUSIC algorithm but can be implemented much more efficiently.     

A surface fitting method for three dimensional scattered data

A method is presented that may be used to empirically establish the type of relationship that is present between a response variable and its influencing factors, by fitting a mathematical model to three dimensional scattered data. The generated response surface is composed of continuous triangular planes that are fitted to the corresponding data in the least squares sense. The method may be easily implemented. It requires some fairly large number of scattered data, two initial boundary conditions and a desired accuracy for the band-wise partitioning of the data. The proposed surface fitting technique has been successfully applied to solar radiation modelling for a number of different data combinations.     

Three-dimensional track and vertex fitting in chambers with stereo wires

A formalism has been developed, and used in the TASSO experiment, for track fitting and geometrical vertex fitting in a uniform magnetic field. A two-dimensional fit, suitable for many detectors, has been extended into three dimensions in the case of cylindrical drift chambers with small-angle stereo measurements. Error matrices are calculated which are suitable for input to subsequent calculations. Multiple scattering is approximated by a model.     

A model for fitting peaks induced by fast neutrons in an HPGe detector

Inelastic neutron scattering in the HPGe detector produces wide, triangular-shaped peaks in the spectrum. We develop an accurate model for the peak shape and show that the inclusion of the model in the gamma spectrum analysis makes it possible to quantify fast neutron scattering in the Ge crystal and improves the estimation of the baseline. This in turn facilitates the detection of fission products present at trace levels in environmental samples. The model, together with simulations, is used to deduce some properties of the underlying neutron energy distribution. The neutron evaporation temperature of 1.1 MeV is obtained from the analysis of environmental monitoring gamma spectra.     

A fast wavelet-multipole method for direct BEM

A fast wavelet-multipole method (WMM) has been developed to achieve further speedup for the boundary element method in solving the direct boundary integral equations. The main idea is to compute the right-hand-side vector by the fast multipole method and to solve the linear system by the wavelet compression method. By using the variable order moments, almost linear complexity can be obtained. The primary advantages of the present WMM lie in that it (1) permits efficient implementation; (2) is universal in handling practical problems with complicated geometries. Numerical examples with around 1 million unknowns, performed on nontrivial geometries, clearly show that the WMM can shorten the total computational time by reducing the time for computing the right-hand-side.     

A fast numerical procedure for steady capillary flow in open channels

The surface evolver (SE) algorithm is a valued numerical tool for computations of complex equilibrium interfacial phenomena. In this work, an iterative procedure is implemented such that SE can be employed to predict steady-state flows along capillary channels of arbitrary cross-section. As a demonstration, a one-dimensional stream filament flow model is solved that approximates the pressure changes inside the channel. Despite its simplicity, the precision, stability, and speed of the method affirm it as an efficient and unique design tool for a variety of capillary flow problems. The procedure is ideally suited for slender column flows such as open wedge channel flows, several of which are validated herein via parabolic flight and drop tower experiments.     

A least squares method for fitting head fields by parametricequations

Models of magnetic recording systems generally require the field of the record head to be calculated. In the interests of speed a simple, but accurate, analytic expression is desirable. In this paper the method of minimization of squared residuals is used to obtain parameters defining a parametric approximation to the head field. As an example parameters are obtained which give best fits to finite pole tip head fields produced by conformal mapping. It is found that a good set of parameters is obtained by separately characterizing the infinite pole length head field and correction terms due to the outer pole edges evaluated at the medium surface. The same method could be used to fit measured data or fields obtained using numerical models     

快速控制反射镜系统中的传递函数辨识

提出一种传递函数辨识方法。该方法使用非线性最小二乘曲线拟合法,结合控制对象的传递函数模型选取参数初始值,针对不同的频率特性分段拟合。使用该方法可以将复杂的控制系统频率特性转化为高精度的传递函数。在系统的中低频段内获得幅频±1dB和相频±1°的传递函数辨识精度。由此设计的数字补偿器有效补偿了机械谐振带来的影响,扩宽了控制系统的闭环带宽。传递函数辨识方法摆脱了数字补偿器设计依赖手工调试的状况,并可以提供复杂的数字补偿器以得到高性能的控制系统。     

A fast wavelet-based moment method for solving thin-wire EFIE

Solving the thin-wire electric field integral equation (EFIE) by the multiresolution wavelet expansion method involves a time-consuming double numerical integration for each nonzero element of the moment matrix which in turn can outweigh the advantages of achieving a sparse matrix. To speed up the matrix fill process in wavelet-based moment method codes, first, the triangular scaling functions of a nonorthogonal piecewise liner wavelet at the finest spatial resolution are appropriately replaced by sinusoidal dipoles for which mutual impedances are available in closed-form analytical expressions. The fast wavelet bases transform is then exploited to effectively transfer the resultant matrix equation to multiresolution wavelet domain. Numerical results obtained by the compactly supported semi-orthogonal linear B-spline wavelet demonstrate dramatic reduction of the overall solution time without any degradation in the accuracy of the final solution.     

一种快速检测光滑半球表面缺陷的方法

针对具有镜面反射特性的光滑球面,提出了一种利用反光带的镜像变形来对表面缺陷进行快速检测的新方法。这种方法通过漫反射反光带增强图像上的缺陷信息,克服了背景噪声在图像处理中会造成较大误差的缺点,也降低了照明系统的设计难度。根据缺陷引起的反光带镜像变形获取缺陷特征,使图像处理软件的工作量大大减少。通过实验,给出了缺陷尺寸和扫描间隔等因素对检测结果影响的分布曲线,为合理提取缺陷尺寸提供了参考。实验表明,该方法的鲁棒性好、效率高,能识别0.5mm以上的全部缺陷,定位误差在 1之内。     

Equivalent-strain method and crack vertex advance

Summary An approximate approach is proposed for determining the opening of a crack and the size of the plastic zone arising ahead of the crack front for bounded bodies. The basis of the approach is the equivalent loaded-state method. The method has been tested in solving various standard problems and has been found very effective.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 25, No. 2, pp. 16–19, March–April, 1989.     

A new procedure for lifetime determination using the Doppler-shift attenuation method

A new procedure for lifetime determination in singles measurements performed by means of the Doppler-shift attenuation method is proposed. An explicit separation of the shifted and unshifted fractions of the line-shape is achieved employing a summation over recoil histories calculated using a Monte-Carlo simulation. The lifetime is derived according to the Differential decay-curve approach. Tests with simulated data and experimental data analyzed earlier by a different method confirm the applicability of the procedure. Practical aspects of the new approach are investigated and discussed.     

A fast Green's function method for the analysis of IDT's for acousto-optical devices

Surface acoustic wave (SAW) interdigital transducers are key components in X-Y LiNbO₃ acousto-optical (A-O) devices. SAW interdigital transducers (IDT's) on this substrate exhibit a high spurious resonance that may reduce the A-O efficiency. In this paper we present a detailed analysis of X-Y LiNbO₃ IDT's based on a fast Green's function method (GFM). In order to correctly evaluate the spurious effects on IDT's performance, we also considered bulk terms of the Green's function. When the GFM is applied to IDT's with general topology and over a wide frequency range, the required computation time can reach quickly unacceptable values for long IDT structures. We developed a new model order reduction technique based on the singular value decomposition (SVD) for the fast generation of the IDT's frequency response. Numerical results for different configurations of X-Y LiNbO ₃ IDT's are in good agreement with measured data and a correct interpretation of the spurious resonance is reported. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band IDT's for A-O devices     

X射线TICT中射束硬化拟合校正研究

X射线TICT中,由于射线硬化现象使图像重建时出现伪影。文中对X射线硬化现象进行了分析,探讨了在均匀物质中,X射线射束和与透射厚度的关系,并根据Beer定律和X射线与物质作用的特点,通过获取X射线射束和数据,首先拟合出射束和与透射厚度的关系式,然后得出X射线射束和校正为单色射线射束和的等效厚度与透射厚度的关系及其等效方法,最终得出X射线等效单色射线的衰减系数的拟合值,再对此衰减系数拟合值进行卷积反投影重构,即可有效消除X射线射束硬化的影响。     

A practical toolkit for computational steering

Computational steering refers to the real-time interaction of a scientist with their running simulation code. Despite the many benefits associated with computational steering, its uptake to date has been limited. In this paper we discuss the reasons for this and how the computational steering library and associated tools developed as part of the RealityGrid project aim to tackle them. We describe the functionality of the steering library and the use of Grid services in constructing a generic, dynamic architecture for discovering, steering and connecting visualization software to running simulations. The use of on-line visualization for providing feedback to the scientist is described, including the ways in which it may be enhanced through tools such as Chromium and Access Grid. Finally, we illustrate the flexibility of our approach by describing the functionality that has been added to various simulation codes as part of the RealityGrid project.     

Parratt-based and model-independent X-ray reflectivity fitting procedure for nanoscale thin film characterization

A general-purpose fitting procedure is presented for X-ray reflectivity data. The Parratt formula was used to fit the low-angle region of the reflectivity data and the resulting electron density profile (continuous base EDP or cbEDP) was then divided into a series of electron density slabs of width 1 angstroms (discrete base EDP or dbEDP), which is then easily incorporated into the Distorted Wave Born Approximation (DWBA). An additional series of density slabs of resolution-limited width are overlapped to the dbEDP, and the density value of the each additional slab is allowed to vary to further fit the data model-independently using DWBA. Because this procedure combines the Parratt formula and the model-independent DWBA fitting, each fitting method can always be employed depending on the type of thin film. Moreover, it provides a way to overcome the difficulties when both fitting methods do not work well for certain types of thin films. Simulations show that this procedure is suitable for nanoscale thin film characterization.     

A new method for the electro-optical measuring of fast high voltage pulses

This report describes a new method for measuring fast high voltage electric pulses based on one particular application of the Kerr effect. This work was carried out in order to further the development of optical particle detectors. At the present time with our method, the minimum risetime of the measured pulse reaches the nanosecond domain while the maximum voltage is limited only by the physical dimension of the electro-optical transducer.The measuring principle chosen requires a new calibration method in order to reconstruct the observed signal.The use of nitrobenzol as the active liquid allows the continuous modification of the cell sensitivity over a ratio of 1 to 3 without changing the geometry of the cell.