不同应力下的InxGa1-xAs薄膜表面形貌

利用分子束外延技术,通过反射式高能电子衍射仪实时监控InGaAs薄膜生长状况,在InAs(001)基片上生长In0.86Ga0.14As,在GaAs(001)基片上生长In0.14Ga0.86As(厚度均为20原子层)单晶薄膜。采用扫描隧道显微镜对原位退火后的InGaAs样品进行扫描,发现不同组分的InGaAs呈现不同的表面形貌。虽然生长的初始表面都是原子级平坦,但是由于晶格常数差异触发不同类型的表面应力,促使In0.14Ga0.86As/GaAs薄膜中台阶边缘平滑扭曲,而在In0.86Ga0.14As/InAs薄膜表面台阶却呈锯齿状;同时,由于不同类型表面应力的作用,低In组分薄膜形成更多的二维(2D)岛。     

An Input-Output Model with Stochastic Parameters for Economic Analysis

This paper presents an input-output model where the technology coefficients and the demand variables are random variables, rather than fixed quantities. The model is able to relate data acquisition costs to forecasted production levels and uncertainty, as the error in the estimate of distribution parameters is reduced. The nonlinearity of the resulting system of equations remains tractable and techniques such as the Newton-Raphson method can be applied advantageously. A numerical example is included.     

急件冲击下关键设备生产缓冲的GERT模型

为了降低非预期生产急件对关键设备正常生产活动的冲击,保证生产计划的稳定性,研究了关键设备的应急生产缓冲设计问题,为生产管理者合理地确定预留产能提供了理论依据。结合排队理论,分析了生产急件到达和处理活动,证明其属于一类负指数随机过程,揭示了生产状态的动态转移规律和实现条件;将关键设备组的急件加工过程描述为一类GERT（graphic evaluation and review technology）模型,测算状态转移过程的状态转移参数和矩母函数;结合梅森公式,设计系统状态稳态概率的求解方法,分析关键设备生产缓冲与稳态概率之间的关系,探寻其定量化表征。通过某研究院加工中心设备组的案例研究,发现关键设备组因急件冲突导致月生产计划变更的情况平均降低146%,较好地控制生产计划与调度工作的不良波动,从而验证了模型和方法的可行性和适用性。     

LRB隔震桥梁空间变异性地震随机响应分析

对装有铅芯橡胶支座（Lead—Rubber—Bearing，LRB）的隔震大跨连续梁桥进行了考虑地震动空间变异性的随机响应分析。地面运动加速度功率谱模型为零均值的平稳高斯过程，描述为过滤白噪声施加于支撑各点。地震动空间变异性综合考虑空间不相干效应、行波效应和局部场地土效应。推导了LRB隔震结构多点激励运动方程，并运用随机等价线性化方法以计入铅芯橡胶支座（LRB）的滞回非线性性能。对一大跨LRB隔震梁桥进行了一致激励和综合考虑地震动空间变异性的三种工况计算，得到了各工况下响应的拟静力项、动力项和总响应项的各自最大值的均值，并进行了对比分析。结果表明，对于带有铅芯橡胶支座的减隔震大跨连续梁桥，多点激励效应不容忽视，一致激励会对结构产生不安全的估计。     

A Modified Model for the Calculation of Fully Developed Heat Transfer and Drag in Tubes under Conditions of Turbulent Flow of Gases with Varying Physical Properties

It is demonstrated that the inclusion of the dependence of the tangential stress profile on thermal acceleration of gas flow and some other improvements enable one to significantly extend the capabilities of the classical model of fully developed turbulent flow and heat transfer in tubes and use this model as a simple and fairly reliable means of theoretical prediction of heat transfer and hydraulic drag of gases with varying physical properties.     

基于随机替代关系的单周期可替代品库存模型

基于确定型的可替代产品单周期库存模型已有研究,它假定替代数量关系是确定的。而事实上,替代过程中由于消费者需求的个性化因素影响,替代的数量关系往往是随机的。为此,假定替代数量关系符合随机分布条件下,提出了两类可替代产品的单周期库存模型,并设计了基于遗传算法的仿真优化算法。算例分析的结果表明,考虑随机替代关系可显著地提高决策者的收益;该算法是有效的。     

随机潜蚤病模型的动力学行为分析

潜蚤病是贫困地区的一种人畜共患病,其发病过程极易受到随机波动环境因素的影响。因此,建立并讨论了一类以正确卫生习惯为控制策略的随机潜蚤病模型。首先,通过构造恰当的Lyapunov函数并利用It$\hat{\rm o}$公式证明了随机系统全局正解的存在唯一性。其次,在一定的条件下证明了随机系统的正解围绕在确定性系统平衡点附近的振荡行为。最后,通过数值模拟验证了理论结果的正确性。数值结果表明,当随机干扰强度足够大时将会导致疾病灭绝。     

A Stochastic Multi-Scale Model for Prediction of the Autogenous Shrinkage Deformations of Early-age Concrete

Autogenous shrinkage is defined as the bulk deformation of a closed, isothermal, cement-based material system, which is not subjected to external forces. It is associated with the hydration process of the cement paste. From the viewpoint of engineering practice, autogenous shrinkage deformations result in an increase of tensile stresses, which may lead to cracking of early-age concrete. Since concrete is a multi-phase composite with different material compositions and microscopic configurations at different scales, autogenous shrinkage does not only depend on the hydration of the cement paste, but also on the mechanical properties of the constituents and of their distribution. In this paper, a stochastic multi-scale model for early-age concrete is presented, which focuses on the prediction of autogenous shrinkage deformations. In this model, concrete is divided into three different levels according to the requirement of separation of scales. These levels are the cement paste, the mortar, and the concrete. A specific representative volume element (RVE) for each scale is described by introducing stochastic parameters. Different scales are linked by means of the asymptotic expansion theory. A set of autogenous shrinkage experiments on the cement paste, the mortar, and the concrete is conducted and used for validation of the developed multi-scale model. Furthermore, the influence of the type and the volume fraction of the aggregate on autogenous shrinkage is studied. Besides, a combined optimum of fine and coarse aggregates is determined. The analysis results show that the proposed model can effectively estimate the autogenous shrinkage deformations of concrete at early-age by taking the influence of the material composition and configuration into consideration.     

A Stochastic EM Algorithm for Progressively Censored Data Analysis

Progressive censoring technique is useful in lifetime data analysis. Simple approaches to progressive data analysis are crucial for its widespread adoption by reliability engineers. This study develops an efficient yet easy‐to‐implement framework for analyzing progressively censored data by making use of the stochastic EM algorithm. On the basis of this framework, we develop specific stochastic EM procedures for several popular lifetime models. These procedures are shown to be very simple. We then demonstrate the applicability and efficiency of the stochastic EM algorithm by a fatigue life data set with proper modification and by a progressively censored data set from a life test on hard disk drives. Copyright © 2013 John Wiley & Sons, Ltd.     

结构随机响应分析的一种直接积分法

对结构随机响应分析的数值积分方法进行了深入的研究。首先，直接从控制方程出发计算加速度，其次，给出了位移和速度的一种近似计算公式，最后，推导出响应均方值的离散计算表达式。就两个算例进行了数值仿真，结果表明该方法对于结构的随机响应分析是有效的。     

理化分析测试实验室的矩阵式管理模型

理化分析测试实验室是承载综合分析测试功能的实验室或实验室群,在科学研究、疾病预防控制、食品安全和环境分析等领域都需要理化分析测试实验室作为其基本检测平台。从资源构成的角度看,理化分析测试实验室需要非常复杂的仪器设备;从应用领域角度看,它又承担着综合性的分析测试功能。以这两个管理分类角度作为矩阵维度,可以构建实验室管理矩阵。本文建立了这种管理矩阵的构建原理和模型,并通过实际案例介绍了矩阵式管理模型的使用方法。     

A Physical Model for the Prediction of Lateral Stress Exerted by Self-Compacting Concrete on Formwork

In this paper, a model is proposed to describe the evolutions of the lateral stress exerted by self compacting concrete (SCC) on a formwork during and after casting. The predictions of the model are compared to pressure drop measurements after the end of casting carried out on real formwork simultaneously with measurements of the evolution of the apparent yield stress of the cast concrete. Then, the predictions of the model during the casting phase are compared to results from the literature and show that the proposed model is able to explain and predict the experimental observations and the quantitative evolutions.     

非对称随机波动模型的参数估计及其实证

研究非对称随机波动模型参数的贝叶斯估计问题,提出一种计算参数贝叶斯估计量的MCMC (Markov Chain Monte Carlo)算法。并利用此算法对中国股市波动的非对称现象进行了实证分析。     

Artificial Neural Network for Creep Behaviour Predictions of a Parallel‐lay Aramid Rope Under Varying Stresses

Abstract: An improvement of the creep behaviour prediction of parallel‐lay aramid ropes under varying stresses is the scope of the following study in which application of artificial neural networks (ANNs) for the prediction of creep under varying stresses is presented. This qualitatively different approach assumes that the ANN can be trained to simulate time‐dependent response of the rope in the given load (stress) programme and time interval. The classic rheological constitutive equations are not needed in this case, because ANN acts as a constitutive operator trained by stresses and the corresponding creep strains from experimental data. Carried numerical experiments were divided into the following three parts: (i) searching the best ANN for a creep behaviour approximation under varying stresses, (ii) investigating the best topology of the selected neural network and (iii) investigating the best results for the creep function identification. Comparison between the experimentally observed creep strains of the parallel‐lay aramid rope under varying stresses, predicted creep strains when the linear creep constitutive equation is applied and predicted creep strains when the obtained Jordan neural network with the 3‐10‐1 topology is used confirmed that the Jordan neural network developed achieved less than half mean square error beside the existing creep constitutive analytical approach.     

A Total Operating Cost Model for Paced Lines with Stochastic Task Times

This paper presents a method for evaluating the often neglected component, the expected incompletion cost, of the operating cost of a paced line with stochastic task times. This incompletion cost is developed through a three stage process. First presented is a procedure for generating all possible combinations of incompleted tasks. Next is an evaluation of the probabilities and costs of their occurrence. Included are not only a mechanism for generating only those incompletion combinations with a significant probability of occurring, but also various techniques for reducing computer storage requirements and computation time. Finally, these make possible an evaluation of the operating cost of paced lines.     

不确定车数的随机车辆路径问题模型及算法

研究了一类有时间约束、车辆数量不确定的随机车辆路径问题;建立了该类问题的随机规划数学模型;设计了模型求解的遗传算法、禁忌搜索算法和遗传-禁忌混合算法.禁忌算法采用了对当前解的车辆-顾客分配结构和解的路径顺序分别禁忌的双层禁忌算法,使算法全局性更好,同时也降低了搜索时间.把禁忌算法作为变异算子应用于遗传算法形成了混合算法.最后给出了计算示例,对算法进行了比较分析.     

考虑运作风险的易腐产品生产配送随机规划模型

针对多层级易腐产品供应网络的特性,分析了风险因素对供应网络运作过程的影响,并针对5种关键风险因素,即质量风险、运输风险、生产风险、库存风险和需求风险进行量化分析;提出了生命周期固定的库存原材料的动态调度策略;结合运作风险及库存策略建立了多层级、多时段的易腐产品供应网络生产与配送过程的随机规划模型。在分析模型特点的基础上,用Ilog Cplex对模型进行求解。最后结合实际案例,分析了各种风险因子对供应链整体运作的影响,仿真结果表明了该方法的有效性和实用性。