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131.
Ram C. Tripathi Ramesh C. Gupta John Gurland 《Annals of the Institute of Statistical Mathematics》1994,46(2):317-331
This paper contains some alternative methods for estimating the parameters in the beta binomial and truncated beta binomial models. These methods are compared with maximum likelihood on the basis of Asymptotic Relative Efficiency (ARE). For the beta binomial distribution a simple estimator based on moments or ratios of factorial moments has high ARE for most of the parameter space and it is an attractive and viable alternative to computing the maximum likelihood estimator. It is also simpler to compute than an estimator based on the mean and zeros, proposed by Chatfield and Goodhart (1970,Appl. Statist.,19, 240–250), and has much higher ARE for most part of the parameter space. For the truncated beta binomial, the simple estimator based on two moment relations does not behave quite as well as for the BB distribution, but a simple estimator based on two linear relations involving the first three moments and the frequency of ones has extremely high ARE. Some examples are provided to illustrate the procedure for the two models. 相似文献
132.
QIU WenYuan ZHAI XinDong QIU YuanYuan Department of Chemistry State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou China Faculty of Arts Social Sciences The National University of Singapore SG Singapore 《中国科学B辑(英文版)》2008,51(1):13-18
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic and Archimedean solids by using our method of the ‘three-cross-curve and dou- ble-twist-line covering’. There are five classes of polyhedral links that can be explored: the tetrahedral and truncated tetrahedral links; the hexahedral and truncated hexahedral links; the dodecahedral and truncated dodecahedral links; the truncated octahedral and icosahedral links. Our results show that the tetrahedral and truncated tetrahedral links have T symmetry; the hexahedral and truncated hexahedral links, as well as the truncated octahedral links, O symmetry; the dodecahedral and truncated dodeca- hedral links, as well as the truncated icosahedral links, I symmetry, respectively. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA and protein catenanes. 相似文献
133.
Using the techniques proposed in [3], we prove that two nonconstant meromorphic functions f and g on C must be linked by a quasi-Mbius transformation if they share some pairs of small functions with more precise truncated multiplicities, which improve and extend the results of Duc Quang Si. 相似文献
134.
Josep Batle 《Annalen der Physik》2020,532(6):2000118
Several magnetic compounds owe their properties to the particular nature of the dipole–dipole interaction. Changes induced in their structure will vary the total interaction energy in nontrivial fashions. In the present work, systems of identical particles possessing dipole moments arranged on various types of 2D structures are studied. By continuously varying a structural parameter, the state of minimum energy will favor distinct dipole configurations, giving rise to different phases. The ultimate goal is to quantitatively address the relation existing between the minimum possible energy for different systems of classic dipoles and the concomitant dipole phases that appear. The systems of dipoles considered here are studied in detail for the first time. With the exploration, new light will be shed on the existence of structural phase transitions in classical systems even at zero temperature, changes induced by the variation of a continuous parameter, and not the temperature, that resemble the ones occurring in quantum phase transitions. 相似文献
135.
In this paper, the so‐called ‘continuous adjoint‐direct approach’ is used within the truncated Newton algorithm for the optimization of aerodynamic shapes, using the Euler equations. It is known that the direct differentiation (DD) of the flow equations with respect to the design variables, followed by the adjoint approach, is the best way to compute the exact matrix, for use along with the Newton optimization method. In contrast to this, in this paper, the adjoint approach followed by the DD of both the flow and adjoint equations (i.e. the other way round) is proved to be the most efficient way to compute the product of the Hessian matrix with any vector required by the truncated Newton algorithm, in which the Newton equations are solved iteratively by means of the conjugate gradient (CG) method. Using numerical experiments, it is demonstrated that just a few CG steps per Newton iteration are enough. Considering that the cost of solving either the adjoint or the DD equations is approximately equal to that of solving the flow equations, the cost per Newton iteration scales linearly with the (small) number of CG steps, rather than the (much higher, in large‐scale problems) number of design variables. By doing so, the curse of dimensionality is alleviated, as shown in a number of applications related to the inverse design of ducts or cascade airfoils for inviscid flows. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
136.
截断光束的二阶矩矩阵 总被引:1,自引:0,他引:1
采用复高斯展开法和维格纳分布函数(WDF),推导出了截断光束的二阶矩矩阵通过大气湍流的传输公式。研究表明,将硬边光阑的复高斯展开函数引入z=0平面处的WDF中,能够避免截断光束二阶矩的积分发散问题,得到z=0平面处二阶矩的解析结果,并且保证了精度,从而方便地得到截断光束在大气湍流中传输的二阶矩矩阵。实验所得到的结果具有一般性,即无截断光束的二阶矩矩阵通过大气湍流传输和截断光束的二阶矩矩阵在自由空间的传输都可以分别作为特例给出。 相似文献
137.
高功率激光通常具有振幅调制和相位畸变. 采用统计光学方法推导了截断的有振幅调制和位相畸变光束在大气湍流中传输 的等效曲率半径R的解析公式.研究表明:随着位相畸变参量、振幅调制参量和光 束截断参量的增大,光束在自由空间中的 R增大,但R受湍流的影响也会增大; 并且高斯光束在自由空间中的R最大, 但其受湍流影响也最大. 因此,在大气湍流中传输到足够远时, 截断的有振幅调制和位相畸变光束的R就要比高斯光束的大.特别地, 相对等效曲率半径Rr随传输距离为非单调变化, 存在一个最小值, 即在该位置处R受湍流的影响最大. 此外, 达到 Rr最小值所需传输距离随光束位相畸变和振幅调制的加剧而增大. 相似文献
138.
A connection between the (G′/G)-expansion method and the truncated Painlev 'e expansion method and its application to the mKdV equation 下载免费PDF全文
Recently the (G′/G)-expansion method was proposed to find the traveling wave solutions of nonlinear evolution equations. This paper shows that the (G′/G)-expansion method is a special form of the truncated Painlev'e expansion method by introducing an intermediate expansion method. Then the generalized (G′/G)-(G/G′) expansion method is naturally derived from the standpoint of the nonstandard truncated Painlev'e expansion. The application of the generalized method to the mKdV equation shows that it extends the range of exact solutions obtained by using the ( G′/ G)-expansion method. 相似文献
139.
在传统的CT系统中, 系统的硬件成本和计算量都是非常巨大的. 提出了一种利用偏移放置的面阵探测器的锥束CT系统, 在这种系统中X射线束仅仅覆盖被扫描物体的一半体积, 投影数据在探测器方向上是截断的, 探测器尺寸和投影数据量都减少为传统CT系统的一半. 在这种新型扫描方式下, 现有的CT重建算法都不能处理. 因此, 提出了一种BPF形式的直接反投影重建方法. 该方法不需要对投影数据重排, 直接反投影滤波重建出最终的图像. 因此, 该算法在数学上更简洁, 计算速度更快. 最后, 数值模拟实验和真实CT系统实验结果均验证了该系统和重建算法能够获得高质量的CT图像. 相似文献
140.
G. Fasano F. Lampariello M. Sciandrone 《Computational Optimization and Applications》2006,34(3):343-358
In this paper, a Gauss-Newton method is proposed for the solution of large-scale nonlinear least-squares problems, by introducing
a truncation strategy in the method presented in [9]. First, sufficient conditions are established for ensuring the convergence
of an iterative method employing a truncation scheme for computing the search direction, as approximate solution of a Gauss-Newton
type equation. Then, a specific truncated Gauss-Newton algorithm is described, whose global convergence is ensured under standard
assumptions, together with the superlinear convergence rate in the zero-residual case. The results of a computational experimentation
on a set of standard test problems are reported. 相似文献