共查询到20条相似文献，搜索用时 15 毫秒
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为了准确地获得直线加速器的光子能谱,根据测量的百分深度剂量和蒙特卡洛模拟的单能光子百分深度剂量,采用先验约束模型和遗传算法来进行优化求解.首先,将光子能谱建模为一个包含2个参数α和Ep的先验解析函数,采用遗传算法对该模型进行优化求解;然后,将光子能谱建模为一个离散约束优化模型,并利用遗传算法进行优化求解,初始解由第1步获得的解析函数产生.将该方法应用于瓦里安iX直线加速器来计算其6和15 MV光子束的能谱,实验结果表明,采用该方法重建获得的光子能谱以及百分深度剂量与蒙特卡洛模拟计算的结果具有良好的一致性. 相似文献
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This Monte Carlo simulation adds to the growing body of enumeration index performance research in continuous response variable mixture models by addressing the issue of the performance of these indexes in discrete-time survival mixture analysis (DTSMA) models. Results showed that although all enumeration indexes performed very well in identifying a homogeneous DTSMA model (i.e., k = 1 hazard function in the sample data), the findings also showed that the enumeration indexes performed poorly in identifying the correct number of unobserved hazard functions present in a heterogeneous (i.e., k = 3) DTSMA model. More important, the performance of the enumeration indexes for the heterogeneous DTSMA models did not improve as the sample size, the effect of time-invariant covariates, or adjacent hazard function separation distance increased, which is inconsistent with some previous Monte Carlo simulation results. The limitations of this Monte Carlo simulation study and future empirical investigation possibilities are both discussed. 相似文献
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改进粒子滤波在被动目标跟踪中的应用 总被引：3，自引：0，他引：3
As a new method for dealing with any nonlinear or non-Ganssian distributions, based on the Monte Carlo methods and Bayesian filtering, particle filters （PF） are favored by researchers and widely applied in many fields. Based on particle filtering, an improved extended Kalman filter （EKF） proposal distribution is presented. Evaluation of the weights is simplified and other improved techniques including the residual resampling step and Markov Chain Monte Carlo method are introduced for target tracking. Performances of the EKF, basic PF and the improved PF are compared in target tracking examples. The simulation results confirm that the improved particle filter outperforms the others. 相似文献
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《天津大学学报(英文版)》2017,(4)
Effectively and accurately modelling the spatial relation of fracture surfaces is crucial in the design and construction of large hydropower dams having a complex underlying geology. However, fracture surfaces are randomly formed and vary greatly with respect to their spatial distribution, which makes the construction of accurate 3-D models challenging. In this study, we use an optimal Monte Carlo simulation and dynamic conditioning to construct a fracture network model. We found the optimal Monte Carlo simulation to effectively reduce the error associated with the Monte Carlo method and use dynamic conditioning to ensure the consistency of the model with the actual distribution of fractures on the excavation faces and outcrops. We applied this novel approach to a hydropower station on the Jinshajiang River, China. The simulation results matched the real sampled values well, confirming that the model is capable of effectively and accurately simulating the spatial relations in a fracture network. 相似文献
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We present a Monte Carlo (MC) method to simulate the scattering for medium within randomly distributed particles,discuss the convergence of this method by varying the size parameter ka, volume parameter ηand calculation parameter Ni, then compare this method with the classical iteration method with the same parameters. The calculation results showed that this method has good convergence and accords with the iteration method while consuming less CPU time. At the end of this paper, this method is used to discuss the visual light scatter in the c-Si/α-Si films. 相似文献
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1 Introduction It is i mportant to study polymerization mechanisminpolymerization engineering. Obtaining kinetic data isthe key step for establishing polymerization mechanismand understanding elementary reactions . The kineticdata contains two groups of data ,i.e.,the rate andreaction order .The rate ,especially the rate constant ,is i mportant and to be esti mated assuming that the or-der of the reactionis known.Furthermore ,esti mationof rate constants for polymerization is an active anddif… 相似文献
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基于三级相互作用近似的旋转异构态模型,建立了一个蒙特卡洛模拟方法。使一个样本的产生按其在玻耳兹曼分布中的出现机率进行。然后以此方法计算了聚甲撑链的无扰均方末端距和均方回转半径,其结果和矩阵代数方法计算结果是一致的。 相似文献
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概述了蒙特卡罗方法的产生与发展，阐述了蒙特卡罗方法的基本特点，最后就蒙特卡罗方法在辐射剂量计算上的应用进行了讨论。 相似文献
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不同强度的规则运动对血小板功能的影响及其机理的探讨 总被引：2，自引：0，他引：2
陈英杰 《连云港职业技术学院学报》2003,16(2):60-62
本实验首次研究了同等条件下不同强度的规则运动对血小板内源性NOS的影响.实验将35个健康青年男子分为四组分别进行为期8周的不同强度的运动训练.结果如下:(1)中强度规则运动明显降低舒张压,增大脉压,小强度规则运动在增大肺活量上最为突出,而大强度规则运动在以上方面作用不明显;(2)中小强度规则运动后,血小板内NOS活性和血浆NO含量均明显升高,而大强度规则运动后NOS活性和NO含量没有明显升高.结果表明:中小强度规则运动在抑制血小板功能,减少血栓形成方面起重要作用. 相似文献
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Ithasbeenwellknownthatglobalilluminationsimu latesthelighttransportamongallthesurfacesandthelightsourcesinavirtualsceneconsideringdiffusereflection/refrac tionandspecularreflection/refraction .Duetosimplicity,generalityanddimensionalindependence,MonteCarlomethodorrandomwalkmethodisoneofthemostimportantmethodsforsolvingthedifficultglobalillumination .Inpartic ular,MonteCarloisthelastresortwhenallotheranalyticalornumericalmethodsfail[1 ] . Lighttransportormultiplelightinteractionsamongthesu… 相似文献
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计算机模拟晶粒生长所用的模型及模拟方法大体可分3种:蒙特卡罗(Monte Carlo)方法或改进的蒙特卡罗方法(简称MC法)、使用连续扩散界面场模型以及将细胞状的晶粒结构看作Laguere棋盘形布局来处理的Laguerre模型.特别是应用于模拟焊接热影响区(HAZ)晶粒长大的二维和三维过程取得了较好结果,但在生长模型的边界处理等方面有待继续完善,特别是晶粒生长与晶化温度、时间、气氛等参数密切相关,这种复杂工艺条件下的晶粒生长过程的模拟,是当前该领域正待解决的难题. 相似文献
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One challenge in mediation analysis is to generate a confidence interval (CI) with high coverage and power that maintains a nominal significance level for any well-defined function of indirect and direct effects in the general context of structural equation modeling (SEM). This study discusses a proposed Monte Carlo extension that finds the CIs for any well-defined function of the coefficients of SEM such as the product of k coefficients and the ratio of the contrasts of indirect effects, using the Monte Carlo method. Finally, we conduct a small-scale simulation study to compare CIs produced by the Monte Carlo, nonparametric bootstrap, and asymptotic-delta methods. Based on our simulation study, we recommend researchers use the Monte Carlo method to test a complex function of indirect effects. 相似文献
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Latent basis curve models (LBCMs) have been popular in modeling change when the change trajectories are unknown or nonlinear. The estimated change trajectories from LBCMs are often viewed as optimal and used as reference points against which other change trajectories are tested. However, there is a proportionality assumption underlying LBCMs that has received little attention from researchers. This study uses a Monte Carlo simulation to show that violation of this assumption can potentially result in substantially biased estimates of the means and variances of changes and covariate effects on these changes, leading to incorrect statistical inference. The implications of the simulation study are discussed and alternatives to LBCMs are suggested for use when the proportionality assumption is likely to be violated. 相似文献
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INTRODUCTION Orthogonal frequency division multiplexing(OFDM) is generally known as an effective techniquefor high data rates and has been adopted by standardssuch as Digital Audio and Video Broadcasting (DABand DVB) (ETSI, 1994; 1997). OFDM is robustagainst frequency selectivity of a multipath channeland the single-tap equalization can be used to detectthe transmitted symbols if frequency-selective fadingchannels are known. Although, the use of pilot tonesis the most robust way … 相似文献
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《天津大学学报(英文版)》2015,(4)
Radio-frequency(RF) tomography is an emerging technology which derives targets location information by analyzing the changes of received signal strength(RSS) in wireless links. This paper presents and evaluates a novel RF tomography system which is capable of detecting and tracking a time-varying number of targets in a cluttered indoor environment. The system incorporates an observation model based on RSS attenuation histogram and a multi-target tracking-by-detection filtering approach based on probability hypothesis density(PHD) filter. In addition, the sequential Monte Carlo method is applied to implement the multi-target filtering. To evaluate the tracking system, the experiments involving up to 3 targets were performed within an obstructed indoor area of 70 m2. The experimental results indicate that the proposed tracking system is capable of tracking a time-varying number of targets. Keywords 相似文献
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Kenneth J. Levy 《Journal of Experimental Education》2013,81(3):188-191
The primary purpose of the present paper is to call attention to Hawkins’ (4) procedure for testing a sequence of observations for a shift in location. Such a procedure could have applicability for assessing change within a single subject. Monte Carlo results are provided which suggest that Hawkins’ procedure is robust with respect to moderate violations of its underlying assumptions of homogeneity of variance and normality. A hypothetical example is also discussed for illustrative purposes. 相似文献
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研究用内腔式He-Ne激光器做光源时,硅光电池实验中光电检流计读数不稳定的现象。利用硅光电池分别观测在不加偏振片、加上偏振片时内腔式He-Ne激光器输出的光强度,得到激光经偏振片后输出光强随时间而变。利用共焦扫描干涉仪扫描出激光束的各个纵模,实验表明,内腔式He-Ne激光器每个纵模的偏振方向随时间缓慢变化,引起了实验中输出的光强变化。 相似文献
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Margaret B. Mcfarland 《Journal of Experimental Education》2013,81(2):173-179
The jackknife and bootstrap methods are becoming increasingly popular in research. Although the two approaches have similar goals and use similar strategies, information is lacking with regard to the comparability of their results. In the present study, this issue was systematically investigated for a case of canonical correlation analysis. Bootstrap, jackknife, and Monte Carlo experiments were carried out for 4 sample sizes (n = 200, 100, 50, 20). The jackknife analyses were also varied as regards the number of jackknife observations deleted in each analysis. Some meaningful discrepancies were observed between the bootstrap and jackknife results, especially under small sample-size conditions. Based on the comparisons made with Monte Carlo estimates, the empirical results suggest that the bootstrap technique provides less biased and more consistent results than the jackknife technique does. 相似文献