二氯二硫脲合镉晶体的电子结构与光学性质的研究

采用基于平面波赝势方法（PWP）和局域密度近似（LDA）的第一性原理方法,研究了二氯二硫脲合镉（BTCC）晶体的电子结构,能态密度和线性光学性质。研究表明BTCC晶体属间接带隙晶体,带隙值为3.81 eV;电荷密度分析反映Cd和Cl原子,以及氢键对分子组合以及排列结构有重要影响。采用密度矩阵理论计算了介电常数和折射率,理论结果与实验符合甚佳。     

硫酸盐含量对盐渍土特性的影响

通过对某地区不同含量硫酸钠的盐渍土进行室内击实试验研究,并对该试验结果进行回归分析,从而了解盐渍化土壤中盐分、水分与最大干密度之间的联系,最后得到最大干密度与盐分之间、最佳含水量与盐分之间相互作用的规律。     

大城市中心区合理干道网密度研究

公交优先是提高城市中心区道路设施利用效率、改善交通环境的有效方法,确定中心区合理干道网密度是满足公交运行、提高运输效率的重要内容. 本文在分析城市中心区交通需求特征和公共交通发展要求的基础上,提出了从宏观系统层、设施、运输组织和交通管理四个方面分析中心区道路网密度影响因素,并探讨了公交优先下公共交通与道路网的关系,考虑公交线网布设和运行的要求,并以公交站点覆盖率和最佳公交线网密度两个主要指标为导向,研究并提出了中心区干道网合理密度和间距推荐值. 该研究提出的干道网密度能够较好地满足中心区公交运行,落实公交优先.     

城市轨道交通车站站台行人交通特性

为了确定城市轨道交通车站站台行人交通特性,以北京市地铁2号线西直门站站台视频资料为基础,观测站台区域行人交通行为,分析行人速度、候车位置分布、密度时空分布特性。分析结果表明：与街道环境相比,站台区域行人自由流速度均值偏高,且站台与楼梯邻接区域行人速度随密度的增大下降较快;车辆到达之前行人候车呈队列形式,车辆到达后呈扇形分布在车门两侧;站台区域行人密度时空分布受轨道交通车辆班次影响,表现出规律性波动变化。     

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利用多智能体模拟供应链中企业自动报价协商是智能商务得以实现的关键技术之一。本文对多主体的协商过程进行了形式化描述;在分析前人出价策略模型及相关参数确定的基础上,利用不同概率密度函数模拟各主体的不同出价策略,构造了一种新的出价策略协商报价模型;对概率密度函数中各参数的有关确定和实际意义进行了分析;主体在价格协商过程中,用自身的下一步期望出价和保留价格确定自身报价策略,同时还考虑了对手报价情况,使价格协商过程与现实中的“讨价还价”现象一致。最后通过实际算例对模型的实用性和合理性进行了分析和验证。     

Switching service types for multi-region bus systems

Conventional fixed-route bus services are generally preferred to flexible-route services at high demand densities, and vice versa. This paper formulates the problem of integrating conventional and flexible services that connect a main terminal to multiple local regions over multiple time periods. The system’s vehicle size, route spacing (for conventional services), service area (for flexible services), headways and fleet sizes are jointly optimized to minimize the sum of supplier costs and user costs. The route spacing for conventional bus services and service area for flexible bus services are also optimized for each region. The proposed solution method, which uses a genetic algorithm and analytic optimization, finds good solutions quickly. Numerical examples and sensitivity analyses confirm that the single fleet variable-type bus service may outperform either the single fleet conventional bus service or the single fleet flexible bus service when demand densities vary substantially among regions and time periods.     

A method for measuring accurate traffic density by aerial photography

Traffic density can be accurately measured by counting the number of vehicles within 1 km; however, it is often calculated between macroscopic traffic parameters using the fundamental equation because of difficulty of observing traffic density directly in the field. Measuring density in this way may be inaccurate and may bias the analysis because the relationship between these traffic parameters can vary across the study sites. The purpose of this study is to find a method for measuring traffic density from aerial photography that is easy and accurate, and for this purpose, we investigated whether the measuring length (i.e., the length of a section of roadway from which observations of traffic are simultaneously collected) can be shorter than 1 km and yet retain the same measured traffic density. We divided an aerial photograph into several 20‐m unit sections, counted the number of vehicles manually, and examined measured traffic density according to central limit theory. According to the results of this study, with the number of 20‐m unit sections for observing traffic density at 15 (the measuring length is 300 m), the measured traffic density was almost the same as the density of a representative section of 1 km. Copyright © 2014 John Wiley & Sons, Ltd.     

水下爆炸载荷的统计特性

为研究水下爆炸载荷的概率密度,选取炸药密度、水密度作为随机变量,基于乘同余组合发生器,利用Fortran语言编写随机数生成程序,产生100组随机变量的样本;采用有限元程序LS-DYNA对水下爆炸冲击波进行仿真计算,得到冲击波的峰值压力;并检验其是否服从正态分布,验证最大熵法程序的正确性,采用最大熵法拟合其概率密度函数,研究爆炸载荷的统计规律,得到不同爆距,不同时刻的冲击波峰值压力的概率密度.该方法可较好地解决爆炸载荷的随机数理统计模型,为进一步进行结构的可靠性分析提供理论依据.     

基于温度异重流模型的连续分层流数值模拟方法研究

文章基于温度异重流模型,通过指定流场中温度的分布及密度与温度的函数关系实现密度的连续分层,并假设流场中的热传导在数值过程中可以忽略不计以确保密度分层的稳定。分别采用RANS方法和LES方法对低傅汝德数和高傅汝德数情况下的圆柱绕流进行数值模拟,其尾流场中的lee波、葫芦状流线以及高傅汝德数情况下的波包与实验值相符,低傅汝德数情况下圆柱上下游速度剖面曲线的最小值与实验值仅存在2%的误差,且其分布规律相同。通过改变流体的导热系数,探讨了Peclet数对该方法收敛稳定性的影响,得到了收敛的数值条件。