基于物元可拓法的轨道交通PPP项目风险评价研究

风险评价是风险控制的前提,风险控制对项目成功实施至关重要.文章通过文献查阅和专家访谈梳理了PPP(Public-Private-Partnership)项目风险,建立涵盖37条指标的轨道交通PPP项目风险指标体系,构建基于物元可拓法的风险评价模型,以呼和浩特轨道交通PPP项目为例,对其项目风险进行了评价,提供一种PPP项目风险事前事中评价的方法,给项目相关方的项目风险评价和管理提供参考.     

煤矸石充填复垦重构土壤重金属含量高光谱反演

为研究煤矸石充填复垦土壤重金属含量快速有效的监测方法,以淮南创大生态园煤矸石充填复垦田间试验小区为研究区域,首先采用化学方法监测土壤(0～20 cm)重金属(Cu, Cr, As)含量,然后采用ASD(analytical spectral devices) FiSpec4型高光谱仪测量土壤样品的反射光谱,提取光谱特征,并对光谱进行一阶微分变换、二阶微分变换及倒数对数变换;将变换后的各光谱特征参数与监测的土壤重金属含量进行相关性分析,并依据相关性分析结果选择显著相关的波段作为相关因子供建模使用。采用多元逐步回归(stepwise multiple liner regression,SMLR)分析、偏最小二乘回归(partial least squares regression, PLSR)及人工神经网络(artificial neural network, ANN)三种方法分别建立基于光谱反射率估算土壤重金属含量的预测模型,并采用回归模型进行精度评定,然后确定各重金属含量的最佳预测模型。实验结果表明,经过微分变换的光谱波段与土壤重金属含量达到了显著相关;重金属Cu和Cr的一阶微分光谱的人工神经网络模型为最佳预测模型,重金属元素As的二阶微分光谱的偏最小二乘回归模型为最佳预测模型。     

Equilibrium equations for 3D critical buckling of helical springs

In most cases,the research on the buckling of a helical spring is based on the column,the spring is equivalent to the column,and the torsion around the axial line is ignored.A three-dimensional(3D) helical spring model is considered in this paper.The equilibrium equations are established by introducing two coordinate systems,the Frenet and the principal axis coordinate systems,to describe the spatial deformation of the center line and the torsion of the cross section of the spring,respectively.By using a small deformation assumption,the variables of the deflection can be expanded into Taylor’s series,and the terms of high orders are ignored.Hence,the equations can be simplified to the functions of the twist angle and the arc length,which can be solved by a numerical method.The reaction loads of the spring caused by the axial load subjected to the center point are also discussed,giving the boundary conditions for the solution to the equilibrium equations.The present work is useful to the research on the behavior of the post-buckling of the compressed helical spring.     

Preservation potential of individual couplet and deposition rates on mudflats in the Changjiang Estuary

Non-barrier mudflats in the Changjiang Estuary is examined to obtain preservation potentials and deposition rates over different time scales. The preservation potential of couplet is ca. 46.6% within daily scale and decreases as the time-interval extending, with 9.2% on a semi-lunar scale and 3.7% on a seasonal scale. In the long term, only 1.6% of daily deposition can potentially be preserved in the tidal flat sequence and other 98.4% have been eroded and leave sedimentary discordances, discernable or un-discernable, in the mudflat deposits. A negative log-linear relationship is examined between sedimentation rates and the time spans. The length of sedimentary hiatuses on the mudflat deposition were estimated with considerable uncertainty, but it can provide from an actualistic base some further insights into the nature and origin of ancient mudflat deposits with emphasis on the sedimentary discordances.     

High Performance ZrNbAl Alloy with Low Thermal Expansion Coefficient

Thermal expansion is a common phenomenon in both metals and alloys, which is important for metallic material applications in modern industry, especially in nuclear and aerospace industries. A lower thermal expansion coefficient may cause lower thermal stress and higher accuracy. A new Zr-based alloy is developed and presented.The XRD diffraction results demonstrate that only a close-packed hexagonal phase(α or α' phase) exists in the microstructure. The thermal expansion and mechanical properties are studied. According to the experimental results, the new Zr-based alloy presents a low thermal expansion coefficient and good mechanical properties.Also,its thermal expansion coefficient is stable through solution treatment.     

电化学制氧及其氧气纯度影响因素的研究

研究了一种利用空气电极电化学制氧方法以及隔膜和阴阳极间距对氧气纯度的影响.试验中由KMnO4氧化法测定电解液中HO2-离子的浓度,铜氨溶液吸收法测定氧气纯度.实验表明,使用适当隔膜,在电流密度为80mA/cm2下,系统可连续运行500h以上,氧气纯度在99.8%以上,电化学反应包括4e历程和2e历程,其中2e历程约占31%～44%.     

Regional variation of sediment load of Asian rivers flowing into the ocean

Study of Asian major rivers discharge to the ocean reveals variations of their water discharges and sediment loads, and local characteristic of river sediment concentrations. On the basis of this, the Asian rivers can be divided into three regions: Eurasia Arctic, East Asia, Southeast and South Asia Region. The Eurasia Arctic Region is characteristic of the lowest sediment concentration and load, while the East Asia Region is of the highest sediment concentration and higher sediment load, and the Southeast and South Asia Region yields higher sediment concentration and highest sediment load.     

螺旋弹簧临界屈曲失稳的平衡方程

目前,针对螺旋弹簧失稳现象的研究主要基于当量柱模型,将弹簧等效为柱模型,忽略其绕轴线的转动．该文建立了三维螺旋弹簧模型,通过曲线Frenet坐标系和主轴坐标系,建立了描述弹簧螺旋中心线的空间变形和截面扭转变形的平衡方程．采用小变形假设,通过对弹簧挠度变量采用Taylor级数展开,并忽略其高阶小量,平衡方程可以被简化为扭转角和弧长的函数,使获得方程的数值解成为可能．同时,讨论了作用于弹簧圆心位置的轴向力引起的弹簧约束端反作用力,为平衡方程的求解确定了边界载荷条件．该文的研究工作为进一步研究受压螺旋弹簧的后屈曲性奠定了基础．     

大型冷却塔的风致振动响应数值分析

风荷载是大型冷却塔建筑设计的主要荷载之一,通过风振时域分析可以全面地了解塔身的风振响应特性。本文探讨了采用线性滤波法中的自回归模型(auto-regressive,AR)模拟大型冷却塔风致振动响应的数值方法。首先根据AR模型,基于随机模拟方法,计算冷却塔表面不同高度的随机脉动风压。通过将随机脉动风压和平均风压作为冷却塔表面的外载,采用有限元分析软件计算某冷却塔的风致振动响应。结果表明,基于随机脉动风荷载模拟的数值计算方法,能正确反映冷却塔塔身的风振响应。该方法特别适用于冷却塔高度超出规范要求的情况下,评估冷却塔的风振响应。