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31.
针对边坡稳定性可靠度分析,当状态函数无法显式表达且传统计算方法求解复杂问题困难时,提出一种基于ABAQUS和粒子群优化径向基函数神经网络的可靠度分析方法。基于ABAQUS的强度折减方法计算所选随机变量对应的安全系数,利用径向基函数神经网络的数据拟合功能,建立模型并映射出安全系数和随机变量之间的关系,构造响应面功能函数;利用蒙特卡罗生成的大量随机样本代入功能函数得到相应的安全系数,进而计算边坡的失稳概率和可靠度指标来反映边坡稳定性。研究结果表明:相对于传统方法,本文方法计算效率更高、误差更小,适合实际工程应用。 相似文献
32.
Robert C. Lee James R. Fricke William E. Wright Walt Haerer 《Environmental geochemistry and health》1995,17(4):169-181
A partially probabilistic blood lead prediction model has been developed, based on the US Environmental Protection Agency integrated exposure-uptake-biokinetic blood lead model (IEUBK model). This study translated the IEUBK model into a spreadsheet format. The uptake submodel incorporates uncertainty distributions for exposure and bioavailability parameters. The biokinetic submodel is duplicated with a table incorporating partitioning and decay of lead levels in the body. As a case study, the probabilistic model is applied to a lead exposure scenario involving a former smelter site in Sandy, Utah. The probabilistic model produces less biased estimates of means and standard deviations than the deterministic model. Parameter uncertainty is propagated in the model by the use of Monte Carlo simulation. Thus, sensitivity analysis is possible, and driving variables can be determined. 相似文献
33.
Nonlinear state-space models have been increasingly applied to study population dynamics and data assimilation in environmental sciences. State-space models can account for process error and measurement error simultaneously to correct for the bias in the estimates of system state and model parameters. However, few studies have compared the performance of different nonlinear state-space models for reconstructing the state of population dynamics from noisy time series. This study compared the performance of the extended Kalman filter (EKF), unscented Kalman filter (UKF) and Bayesian nonlinear state-space models (BNSSM) through simulations. Synthetic population time series were generated using the theta logistic model with known parameters, and normally distributed process and measurement errors were introduced using the Monte Carlo simulations. At higher levels of nonlinearity, the UKF and BNSSM had lower root mean square error (RMSE) than the EKF. The BNSSM performed reliably across all levels of nonlinearity, whereas increased levels of nonlinearity resulted in higher RMSE of the EKF. The Metropolis–Hastings algorithm within the Gibbs algorithm was used to fit the theta logistic model to synthetic time series to estimate model parameters. The estimated posterior distribution of the parameter θ indicated that the 95% credible intervals included the true values of θ (=0.5 and 1.5), but did not include 1.0 and 0.0. Future studies need to incorporate the adaptive Metropolis algorithm to estimate unknown model parameters for broad applications of Bayesian nonlinear state-space models in ecological studies. 相似文献
34.
Ordered parameter problems arise in a wide variety of real world situations and are dealt with extensively in the literature. Traditional frequentist methods for dealing with these problems are rather complicated theoretically, especially when sample sizes are small. Bayesian methods are not widely used because high dimensional numerical integration is often required. However, Markov chain Monte Carlo methods provide alternatives to such numerical integration and also deal with ordered parameter problems in a straightforward manner. Little is known about the situation where functions of parameters are ordered. Such problems may seem to be of little practical concern initially, but one can readily see their importance in situations where ordering is placed on the means and variances of several normal or Gamma populations. For the Gamma distribution we will present real examples where we will analyze monthly precipitation data from San Francisco, California and Oakland Mills, Iowa. For the San Francisco data we will simultaneously order both monthly precipitation means and variances. For the Iowa data we will place ordering on seasonal average while still estimating monthly means. Our results show that we would obtain sharper, more accurate inference when order restrictions are employed. 相似文献
35.
Heather?R. Britt Bradley?P.?CarlinEmail author Traci?L.?Toomey Alexander?C.?Wagenaar 《Environmental and Ecological Statistics》2005,12(4):411-426
Misuse of alcohol is a significant public health problem, potentially resulting in unintentional injuries, motor vehicle crashes,
drownings, and, perhaps of greatest concern, serious acts of violence, including assaults, rapes, suicides, and homicides.
Although previous research establishes a link between alcohol consumption increased levels of violence, studies relating the
density of alcohol outlets (e.g., restaurants, bars, liquor stores) and the likelihood of violent crime have been less common.
In this paper we test for such a relationship at the small area level, using data from 79 neighborhoods in the city of Minneapolis,
Minnesota. We adopt a fully Bayesian point of view using Markov chain Monte Carlo (MCMC) computational methods as available
in the popular and freely available WinBUGS language. Our models control for important covariates (e.g., neighborhood racial
heterogeneity, age heterogeneity) and also account for spatial association in unexplained variability using conditionally
autoregressive (CAR) random effects. Our results indicate a significant positive relationship between alcohol outlet density
and violent crime, while also permitting easy mapping of neighborhood-level predicted and residual values, the former useful
for intervention in the most at-risk neighborhoods and the latter potentially useful in identifying covariates still missing
from the fixed effects portion of the model. 相似文献
36.
In this paper, we consider the use of a partition model to estimate regional disease rates and to detect spatial clusters.
Formal inference regarding the number of partitions (or clusters) can be obtained with a reversible jump Markov chain Monte
Carlo algorithm. As an alternative, we consider the ability of models with a fixed, but overly large, number of partitions
to estimate regional disease rates and to provide informal inferences about the number and locations of clusters using local
Bayes factors. We illustrate and compare these two approaches using data on leukemia incidence in upstate New York and data
on breast cancer incidence in Wisconsin. 相似文献
37.
简介了靠度与安全系数的区别;以混凝土结构为例,介绍了用Monte Carlo模拟来计算结构可靠度的方法。 相似文献
38.
钙基脱硫剂孔隙结构特性直接影响到脱硫效果及脱硫剂的利用率,对其空间网络特性的描述将有助于分析SO2的扩散及反应特性. 在石灰石分解动力学和烧结机理的基础上,结合固体分解的成核机理,运用Monte-Carlo 方法,建立了脱硫剂孔隙网络的动态生成模型,对钙基脱硫剂分解形成的孔隙结构进行了动态模拟,并对生成孔结构的分形特性进行研究.结果表明,运用动态生成模型,可以给出石灰石分解形成的CaO内部孔隙的微观空间结构,且模拟生成的孔隙网络的分形维数与实验测定值基本吻合. 相似文献
39.
D. Wendum 《Atmospheric environment (Oxford, England : 1994)》1998,32(24):6149
For operational or research purposes (dispersion computations of radioactive effluents during nuclear emergency situations, simulations of chemical pollution in the vicinity of thermal power plants), different models of passive dispersion in the atmosphere have been developed at the Environment Department of EDF’s R and D Division. This report presents the comparison of the performances of three such models: DIFTRA (lagrangian puff model, with operational goal), DIFEUL (three dimensional eulerian) and DIFPAR (Monte Carlo particle model) for the simulation of the first ETEX release, an international tracer campaign during which a passive tracer cloud has been followed over Europe. The results obtained in this study give model vs. experience differences of the same order as the model vs. experience differences observed during an international model comparison experiment using data of the Chernobyl release, the ATMES exercise. In addition to the standard statistical scores used in the evaluation of the performances of the transport models two asymmetric scores (in contradistinction with the Figure of Merit in Space) are proposed: “efficiency” and “power”. Their aim is to separate the two manners in which a model may be wrong: by predicting presence of pollutant while none is measured or conversely predicting absence when pollutant is actually detected. 相似文献
40.
By scoring the chromosome number of developing embryos, we show that the sex ratio bias of the African social spider Stegodyphus dumicola Pocock is the result of an overproduction of female embryos. Only 17% of 585 embryos sexed from 14 egg sacs were male, a
significant departure from a 1:1 sex ratio. We also explored the possibility of direct control of the sex of individual offspring
in this species by examining the variance in the number of males per sac and the spatial distribution of male and female embryos
within the sacs. We postulated that a variance in the number of males per sac lower than binomial (i.e., underdispersed or
precise sex ratios) or a non-random distribution of male embryos within the sacs would suggest direct control of the sex of
individual offspring. We found that the variance in the number of males per sac was indistinguishable from binomial and significantly
larger than expected under exact ratios. Likewise, the spatial distribution of male embryos within three sacs examined was
no more clustered than expected by chance. The sex ratio biasing mechanism in this species, therefore, apparently only allows
control of the mean sex ratio but not of its variance. We present randomization and Monte Carlo methods that can be applied
to test for departures from a random spatial arrangement of male and female embryos in an egg mass and for departures from
binomial or exact ratios when not all members of a clutch have been sexed.
Received: 21 October 1998 / Received in revised form: 23 March 1999 / Accepted: 26 April 1999 相似文献