共查询到20条相似文献,搜索用时 46 毫秒
1.
The best simple method for Newtonian molecular dynamics is indisputably the leapfrog Stormer-Verlet method. The appropriate generalization to simple Langevin dynamics is unclear. An analysis is presented comparing an ‘impulse method’ (kick; fluctuate; kick), the 1982 method of van Gunsteren and Berendsen, and the Brünger-Brooks-Karplus (BBK) method. It is shown how the impulse method and the van Gunsteren-Berendsen methods can be implemented as efficiently as the BBK method. Other considerations suggest that the impulse method is the best basic method for simple Langevin dynamics, with the van Gunsteren-Berendsen method a close contender. 相似文献
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An accurate and efficient hybrid numerical method is developed for direct numerical simulation of passive scalar in homogeneous turbulence for the Schmidt number 1 and 50. The hybrid method uses the standard Fourier spectral method for the incompressible Navier–Stokes equation and the combined compact difference scheme for the passive scalar transport equation. Accuracy of the method is carefully examined by comparing with the full spectral method regarding the spectra, probability density function, field structure of the passive scalar, and is found to be very satisfactory. The computational time for the hybrid method is decreased by 26% for the Schmidt number 1 when compared to the full spectral method, and by 77% for the Schmidt number 50 when the number of grid points for the velocity field is reduced under the scale separation. 相似文献
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José Canosa H.R. Penafiel 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(1):21-39
A direct method is given for the solution of the spherical harmonics approximation to the equation of radiative transfer in plane-parallel atmospheres. Although the method is formulated theoretically for non-homogeneous atmospheres with an arbitrary phase function, at present it has only been implemented for homogeneous atmospheres. Test computations performed for Rayleigh and Mie scattering phase functions show that the direct method is unconditionally stable and solves efficiently problems both for optically thin and very thick atmospheres. Timing comparisons with the method of Chandrasekhar for Rayleigh atmospheres and with an integral-equation iterative method for Mie atmospheres are quite favorable to the proposed method. 相似文献
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长周期光纤光栅透射谱的求解方法有多种,本文以耦合模理论为基础,对常用的积分法、公式法、传输矩阵法求解长周期光纤光栅的透射谱进行比较与分析,指出这三种求解方法各自的特点和适用条件.积分法可在较宽波长范围内直接得到多个模式透射谱的精确解,但求解过程繁琐,运算量大;公式法虽然在表述和计算上较为方便,但只能在较小波长范围内直接求解单个模式的透射谱;传输矩阵法求解过程简便、准确度高、计算量相对较小,特别适合计算一些非均匀光纤光栅的透射谱.该研究为选择一种精确度高且理论和计算都较简单的计算长周期光纤光栅透射谱的方法提供理论依据. 相似文献
5.
We propose a new method for recording the wave field. The method is based on that the angular spectrum of the field is modulated
using an amplitude mask. It is shown that the new method ensures high spatial and angular resolutions. An optical scheme for
implementing the method and an algorithm for reconstructing the wave-field phase from the measurement data are developed.
Computer simulation of the experiment for recording the wave field on the basis of the proposed method is performed. 相似文献
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Traditional algorithms for solving the inverse scattering problem for a fiber Bragg grating are described, and a new numerical method for this problem is developed. The method is based on the fast inversion of a matrix using its Toeplitz symmetry and on a special “inner-bordering” procedure. It is shown that the method is equally efficient as the well-known discrete layer peeling method but exceeds the latter in accuracy, especially for high-reflectance gratings. The stability of the proposed method with respect to initial data errors is demonstrated. 相似文献
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通过试炼、试测、分析,确定一种满足技术要求的与GaAlAs半导体匹配的光阴极台屏玻璃配方。对该玻璃表面黑化,采用了离子交换氢还原法、玻璃中掺杂着色离子法、表面涂覆法以及溶胶凝胶法。经过试验分析,得出了玻璃表面涂覆法和溶胶凝胶法是使玻璃表面黑化的可行途径。 相似文献
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针对红外遥感图像非均匀性的定量评价问题,研究了基于场景的红外焦平面阵列响应非均匀性的定量评价方法。利用真实红外遥感图像序列量值分布的特点,针对小序列图像提出了基于序列排序和小波变换的标准图像构建算法;结合非均匀性评价指标,提出了利用构建标准图像的响应非均匀性对红外图像的非均匀性进行定量估计;分别利用黑体定标实验和统计方法对标准图像构建算法进行了验证,同时进行了不同校正算法的剩余非均匀性评价实验。结果表明,128frame序列构建得到的标准图像的非均匀性分别比同温黑体图像小0.92%,比统计标准图像大0.59%。该方法可用于定量估计红外遥感图像的非均匀性。 相似文献
10.
M.V. Kirov Author Vitae 《Physica A》2009,388(8):1431-1445
A new method for the combinatorial optimization of quasi-one-dimensional systems is presented. This method is in close analogy with the well-known transfer-matrix method. The method allows for the calculation of the lowest energy levels of the system. However, when finding the ground and some low-lying states of large complex systems, this method is more economical when compared to the standard transfer-matrix method. The method presented here is based on max-plus algebra, which has maximization and addition as its basic arithmetic operations. For the explanation of this method we use cyclic water clusters as simple examples. The efficiency of the max-plus-algebraic method is demonstrated in the course of global combinatorial optimization of hydrogen bond arrangements in large polyhedral water clusters with fixed positions of the oxygen atoms. The energy of the clusters is estimated using approximate discrete models for the intermolecular interactions. 相似文献
11.
对于深穿透问题则一般蒙特卡罗方法存在一定的困难。本文提出了一个新的蒙特卡罗计算深穿透问题的小区域方法。在此基础上给出了两个小区域方法,即平几何小区域方法和球几何小区域方法,通过例子的实际计算表明,小区域方法是比较好的和可行的,克服了一般蒙特卡罗方法解深穿透问题的缺点。 相似文献
12.
Fringe orientation can direct the processing of fringe patterns and provide basic information for understanding the fringe patterns. The gradient method is popularly used for its convenience but it is easily affected by noise. The plane-fit method is capable of obtaining precise local fringe orientation despite the high speckle noise but it is strict with the calculating window size. In this paper, a combined method is proposed. This method uses the plane-fit algorithm to get local gradients and uses the gradient method to get the orientation results from these gradients. It can be seen that this new method can get more accurate orientations for ESPI than both the gradient method and the plane-fit method. 相似文献
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Huiyu Xue 《Journal of sound and vibration》2003,268(5):881-895
A stiffness equation transfer method is proposed for obtaining vibration frequencies of structures. This method is an extension of the finite element-transfer matrix (FE-TM) method. In the present method, the transfer of state vectors from left to right in the ordinary FE-TM method is changed into the transfer of stiffness equations of every section from left to right. This method reduces the propagation of round-off errors produced in the ordinary transfer matrix method. Furthermore, the drawback that the number of degrees of freedom on the left boundary must be the same as that on the right boundary in the ordinary FE-TM method, is now avoided. Besides, this method finds out the values of the frequency by Newton-Raphson iteration method, so no plotting of the value of the determinant versus assumed frequency is necessary. An IFETM—W program based on this method for use on an IBM PC586 microcomputer is developed. Finally, numerical examples are presented to demonstrate the accuracy as well as the potential of the proposed method for free vibration analysis of structures. 相似文献
15.
长周期光纤光栅透射谱的求解方法有多种,本文以耦合模理论为基础,对常用的积分法、公式法、传输矩阵法求解长周期光纤光栅的透射谱进行比较与分析,指出这三种求解方法各自的特点和适用条件.积分法可在较宽波长范围内直接得到多个模式透射谱的精确解,但求解过程繁琐,运算量大;公式法虽然在表述和计算上较为方便,但只能在较小波长范围内直接求解单个模式的透射谱;传输矩阵法求解过程简便、准确度高、计算量相对较小,特别适合计算一些非均匀光纤光栅的透射谱.该研究为选择一种精确度高且理论和计算都较简单的计算长周期光纤光栅透射谱的方法提供理论依据. 相似文献
16.
We propose an explicit multi-symplectic method to solve the two-dimensional Zakharov-Kuznetsov equation. The method combines the multi-symplectic Fourier pseudospectral method for spatial discretization and the Euler method for temporal discretization. It is verified that the proposed method has corresponding discrete multi-symplectic conservation laws. Numerical simulations indicate that the proposed scheme is characterized by excellent conservation. 相似文献
17.
Boundary element-free method for elastodynamics 总被引:3,自引:0,他引:3
CHENG Yumin & PENG Miaojuan . Shanghai Institute of Applied Mathematics Mechanics Shanghai University Shanghai China . Department of Civil Engineering Shanghai University Shanghai China 《中国科学G辑(英文版)》2005,48(6):641-657
1 Introduction In recent years, more and more attention has been paid to researches on the meshless (or meshfree) method, which makes it a hot direction of computational mechanics[1,2]. The meshless method is the approximation based on nodes, then the large deformation and crack growth problems can be simulated with the method without the re-meshing technique. And the meshless method has some advantages over the traditional computa- tional methods, such as finite element method (FEM) and boun… 相似文献
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利用级数展开的Z扫描理论分析 总被引:6,自引:0,他引:6
利用级数展开的方法,对薄介质的Z扫描理论进行了分析,并对于通常所采用的级数展开和菲涅耳衍射分析方法进行了讨论,证明了在分析利用高斯光束对薄介质进行Z扫描测量时,即使对于大的非线性相移,高斯分解方法和菲涅耳衍射积分方法仍具有等效性,澄清了人们认识上的一些误解。同时分析了远场小孔的归一化透射率与积分限的关系,并对采用高斯分解方法时级数求和的振荡原因进行了分析和讨论,给出了消除振荡所需的最小求和数的判据。针对高斯分解方法和菲涅耳衍射积分方法的使用场合,也进行了讨论。根据所得结论,可以在具体的实验和理论分析中,正确地选择更高效的分析方法。 相似文献