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蒙特卡洛方法数值研究大气颗粒物动力学效应和辐射传输性质 被引量:7
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作者 丁珏 李家骅 +1 位作者 邱骁 翁培奋 《力学学报》 EI CSCD 北大核心 2016年第3期557-565,共9页
爆发性增强的雾天,空气污染严重能见度低,这与大气边界层湍流性质、悬浮颗粒的动力学及散射性质密切相关.文中基于颗粒群平衡方程和Mie理论,采取加权蒙特卡洛方法,自行开发了Fortran程序.文中计算所得的颗粒尺度分布函数、颗粒散射性质... 爆发性增强的雾天,空气污染严重能见度低,这与大气边界层湍流性质、悬浮颗粒的动力学及散射性质密切相关.文中基于颗粒群平衡方程和Mie理论,采取加权蒙特卡洛方法,自行开发了Fortran程序.文中计算所得的颗粒尺度分布函数、颗粒散射性质与实验值、理论解一致,验证了数值模型和方法的正确性.此外,数值研究了雾爆发性增强阶段雾滴谱拓宽、能见度降低的机理,讨论湍流输运和颗粒局部聚集效应下颗粒间的碰并过程,并耦合颗粒散射性质,数值分析雾发展中湍流耗散率对颗粒对径向相对速度、系统透过率的影响;以及颗粒对径向相对速度与系统透过率、颗粒尺度的关系.研究结果表明:随着湍流耗散率的增大,颗粒的径向相对速度呈现先缓慢而后快速增大的变化趋势.1 000 s时刻,湍流的耗散率为1.0×10^(-2)m^2/s^3,颗粒径向相对速度(无量纲)为0.096 9;对于0.6μm的可见光,雾环境颗粒系统的透过率为0.47.此外,雾发展中雾滴易与气溶胶碰并,系统的散射性质与水组成的雾滴系统不同,天气的能见度明显降低. 展开更多
关键词 雾天 气溶胶 湍流耗散率 碰撞凝并 辐射传输 加权蒙特卡洛方法
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Jackknifed random weighting for Cox proportional hazards model
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作者 LI Xiao 1 ,WU YaoHua 2,& TU DongSheng 1 1 Cancer Research Institute,Queen’s University,Kingston,Ontario K 7L 3N6,Canada 2 Department of Finance and Statistics,University of Science and Technology of China,Hefei 230026,China 《Science China Mathematics》 SCIE 2012年第4期775-786,共12页
The Cox proportional hazards model is the most used statistical model in the analysis of survival time data.Recently,a random weighting method was proposed to approximate the distribution of the maximum partial likeli... The Cox proportional hazards model is the most used statistical model in the analysis of survival time data.Recently,a random weighting method was proposed to approximate the distribution of the maximum partial likelihood estimate for the regression coefficient in the Cox model.This method was shown not as sensitive to heavy censoring as the bootstrap method in simulation studies but it may not be second-order accurate as was shown for the bootstrap approximation.In this paper,we propose an alternative random weighting method based on one-step linear jackknife pseudo values and prove the second accuracy of the proposed method.Monte Carlo simulations are also performed to evaluate the proposed method for fixed sample sizes. 展开更多
关键词 Cox proportional hazards model JACKKNIFE random weighting second-order accuracy simulations survival data
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