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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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求解定态薛定谔方程常常会涉及到常微分方程的本征值问题.目前解常微分方程本征值用的比较多的方法是以龙格-库塔方法为基础的打靶方法.打靶方法常用,但是计算时间长.当边界条件比较复杂或比较敏感的时候,用松弛法会有更好的效果.本文用松弛法解薛定谔方程,并和理论解进行比较.发现松弛法得到的数值解和理论解符合度很高,而且使用松弛法... 相似文献
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能量色散X射线荧光分析中改进型基本参数法研究 总被引:2,自引:0,他引:2
能量色散X射线荧光分析方法是目前常用的一种多元素分析方法,但该方法检出限和分析精度,受到分析基体的影响。基本参数法是目前一种常用的分析方法,但在使用过程必须获取净峰面积和基体所有成分,而在实际使用时,尤其在分析低含量样品时,净峰面积计算、基体中“暗物质”影响了测量精度,制约了基本参数法的应用。针对基本参数法的不足,将谱线解析方法与基本参数法融合,将重叠峰剥离过程嵌入基本参数法迭代过程中。在含量计算过程中,采用分析样品特征X射线分支比的理论系数,对重叠峰进行剥离,解决能量色散X射线荧光测量中净峰面积计算和定量分析问题;在计算过程中,对“暗物质”进行均一化处理。通过对标准物质测量分析,结果表明对于Ni,Cu,Zn三个元素改进型基本参数法(改进型FP)测量结果准确度高于影响系数法。 相似文献
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FAAS法对三种制备样品方法的研究 总被引:8,自引:0,他引:8
在FAAS法分析中,样品预处理始终占有极为重要的位置。本文比较了三种样品消化方式,即传统酸消化法,灰化法及微波消化法。传统的消化方式过程长、速度慢、效率低、而且被测元素易受到损失及易污染等不足,而微波是一种非常快捷、省时、省试剂和无污染的消化方式。通过对校准物质贻贝中的铜、锌、铁的测定结果证明微波消化方式比传统的消化方式优点多。 相似文献
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基于经验模态分解和小波阈值的冲击信号去噪 总被引:2,自引:0,他引:2
冲击信号是非线性的并且容易受到噪声污染。为研究冲击信号去噪的问题,本文针对经验模态分解(Empirical Mode Decomposition,EMD)去噪和小波阈值去噪方法存在的不足,提出了基于EMD的小波阈值去噪方法。单纯的EMD去噪方法会在去除高频噪声的同时压制高频的有效信息。本文将EMD与小波阈值去噪相结合,利用连续均方误差准则确定含噪较多的高频固有模态函数(Intrinsic Mode Function, IMF),对高频IMF分量进行小波阈值去噪,以分离并保留这些分量中的有效信息,同时保持低频IMF分量不变。对模拟数据和实际冲击信号进行去噪处理,结果表明,基于EMD的小波阈值去噪方法的去噪效果优于单纯的EMD去噪方法和小波阈值去噪方法。 相似文献
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焦距法测试自聚焦透镜折射率分布常数 总被引:1,自引:0,他引:1
本文介绍了一种测量自聚焦透镜折射率分布常数的方法─—焦距法,并进行了原理公式推导,和精度分析,其测量不确定度为±1×10 ̄(-3);其次,简要地介绍了实验方法。实验结果证明了焦距法是测量自聚焦透镜折射率分布常数的简单实用的方法,它具有装置简单、数据处理也不复杂的特点,是一种非破坏性的测试方法。 相似文献
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An improved interpolating element-free Galerkin method with nonsingular weight function for two-dimensional potential problems
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In this paper, an improved interpolating moving least-square (IIMLS) method is presented. The shape function of the IIMLS method satisfies the property of Kronecker δ function. The weight function used in the IIMLS method is nonsingular. Then the IIMLS method can overcome the difficulties caused by the singularity of the weight function in the IMLS method. And the number of unknown coefficients in the trial function of the IIMLS method is less than that of the moving least-square (MLS) approximation. Then by combining the IIMLS method with the Galerkin weak form of the potential problem, the improved interpolating element-free Galerkin (IIEFG) method for two-dimensional potential problems is presented. Compared with the conventional element-free Galerkin (EFG) method, the IIEFG method can directly use the essential boundary conditions. Then the IIEFG method has a higher accuracy. For demonstration, three numerical examples are solved using the IIEFG method. 相似文献
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An improved interpolating element-free Galerkin method with a nonsingular weight function for two-dimensional potential problems
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In this paper, an improved interpolating moving least-square (IIMLS) method is presented. The shape function of the IIMLS method satisfies the property of the Kronecker δ function. The weight function used in the IIMLS method is nonsingular. Then the IIMLS method can overcome the difficulties caused by the singularity of the weight function in the IMLS method. The number of unknown coefficients in the trial function of the IIMLS method is less than that of the moving least-square (MLS) approximation. Then by combining the IIMLS method with the Galerkin weak form of the potential problem, the improved interpolating element-free Galerkin (IIEFG) method for two-dimensional potential problems is presented. Compared with the conventional element-free Galerkin (EFG) method, the IIEFG method can directly use the essential boundary conditions. Then the IIEFG method has higher accuracy. For demonstration, three numerical examples are solved using the IIEFG method. 相似文献
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为了计算微波器件的微放电阈值,提出了一种快速单粒子蒙特卡罗方法.该方法对二次电子出射能量、出射角度和相位等参数进行随机处理,结合四阶龙格库塔法和Furman模型模拟了电子运动和二次电子发射系数,并以多次连续碰撞的二次电子发射系数的算数平均值作为微放电效应发生的判据.以平板传输线横电磁模式为研究对象,分别采用快速单粒子蒙特卡罗方法、统计模型、传统蒙特卡罗方法以及粒子模拟方法计算其微放电阈值和敏感区域.计算结果表明,该方法不仅具有与统计模型和粒子模拟方法相当的计算精度,而且比统计模型方法的适应性更强,比传统蒙特卡罗方法的稳定性更好,比粒子模拟方法的计算效率高几十倍以上. 相似文献
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基线漂移是光谱检测仪器普遍存在的现象,会对光谱信号的特征提取带来十分不利的影响,而基线校正是解决该问题的重要手段,也是拉曼光谱信号预处理的重要组成部分。基线校正的原理一般是通过拟合基线的方法来去除光谱信号中的基线漂移。传统的基线校正方法是利用多项式拟合的方法对拉曼光谱信号的基线进行拟合的,但是该方法容易出现过拟合和欠拟合现象,且拟合阶数难以确定。针对传统方法的缺点进行了改进,利用B样条方法对拉曼光谱信号的基线进行拟合,发挥B样条低阶光滑的优点,能够有效地克服多项式方法的缺陷。在实验中,利用该方法对孔雀石绿、罗丹明B的拉曼光谱信号进行了基线校正,观察并比较该方法和传统方法的校正结果。实验结果表明,该方法能够有效地消除拉曼光谱信号的基线漂移,在基线漂移较小和较大的位置,可以采用相同的拟合阶数,不会出现欠拟合和过拟合的现象,获得了良好的基线校正效果,为进一步分析光谱数据提供准确可靠的信息。 相似文献
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B. S. Ishkhanov A. S. Kurilik D. S. Rudenko K. A. Stopani V. I. Shvedunov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):859-862
A multiple-beam method for scanning large objects is proposed, which is based on the use of multiple bremsstrahlung beams with different upper limits. Mathematical modeling is performed to compare the multiple-beam method with the double-beam method, and an advantage of the proposed technique over the double-beam method method is shown. 相似文献
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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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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
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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