客土喷播绿化技术在石质边坡防护中的应用

以长珲公路采用客土喷播技术对石质边坡绿化为例,介绍施工方案,发挥植物的生态防护及视觉诱导作用,符合"安全、舒适、环保、和谐"的建设要求,可供今后工程建设中参考。     

电动汽车驱动控制的PWM新技术

文章介绍了电动汽车交流驱动中采用确定脉宽调制(DPWM)技术和随机脉宽调制(RPWM)技术的比较研究结果.RPWM方法替代DPWM方法,采用Avant!公司先进的仿真软件SABER,其重点是降低电磁干扰(EMI).为了评估PWM技术对驱动性能的影响,同时对驱动效率,转矩脉动和电流控制系统动态响应进行了研究.文中考虑了逆变器开关频率随机变化定义的2种RPWM技术:一种技术是调制器的取样频率与开关频率同步变化;另一种技术是取样频率固定且等于平均开关频率.研究表明:在驱动性能几乎不受影响的同时,RPWM技术降低EMI的良好潜力,可使EMI下降10dB或更多.     

复合轻轨车体的多级优化法

以轻轨车辆为例,阐述了多级优化法的具体应用过程。本文首先根据标准载荷对轻轨车辆的车体进行全面有限元分析,从而找出临界板件,然后将临界板件划分为多个区域,优化了车窗的圆角半径和板件厚度。数值计算结果表明,多级优化法作为一种设计工具是切实可行的。     

Estimation of copepod production in a flooded savanna of Venezuela

This is the first contribution to the copepod production in Venezuelan tropical savannas. Total abundance, biomass, production and mean P/B ratio of nauplii, copepodids and adults were determined in interdaily samples from a flooded, embanked savanna during February and March (end of dry season), and May (beginning of rainy season). Highest values of biomass and total production were recorded during dry season (61.5 mg m⁻³, 153.8 mg m⁻³ day⁻¹, respectively), compared to the rainy season (5.6 mg m⁻³, 45.9 mg m⁻³ day⁻¹). The last values are related to a low population density found during rainy season. Highest production were observed in copepodids at the end of the dry season. Significant differences of production between nauplii and copepodid stages, as well as between nauplii and adults, were also found.     

Interactive flexural-torsional buckling behaviour of stiffened plating

Results from a series of studies on stiffened plates under axial compression are presented in this paper. The large-deflection elasto-plastic behaviour of each panel component is described by the von Karman equations, thus enabling the lateral-torsional buckling of the stiffener to be modelled in a rigorous manner. Material nonlinearity is represented using the von Mises yield criterion in conjunction with the Prandtl-Reuss flow rule. Results are presented in the form of average stress-strain curves which are used to generate maximum strength curves for the stiffener and plate.     

Prediction of ambient carbon monoxide concentration using nonlinear time series analysis technique

This study evaluates the potential of nonlinear time series analysis based methods in predicting the carbon monoxide concentration in an urban area. To establish the functional relationship between current and future observations, two models based on local approximations and neural network approximations are used. To compare the performance of the models, an autoregressive integrated moving average model is also applied. The multi-step forecasting capabilities of the models are evaluated.     

The Propagation of Waves in a Semi-Infinite Chain of Material Points and Springs Representing a Long Train

The dynamical behaviour of the longitudinal motion of a long train on which tractive or braking forces apply, often is investigated by representing the train by a model consisting of a continuous bar in which longitudinal vibrations can occur. In the present publication a model consisting of a chain of material points and springs is proposed. It can be investigated by means of difference equation methods and of Laplace transformations. In certain respects the discrepancies of the results with those obtained for a continuous model, are considerable and it may be concluded that a more complete investigation of the discrete model is necessary.     

Representing mental maps and cognitive learning in micro-simulation models of activity-travel choice dynamics

This paper develops a model, based on Bayesian beliefs networks, for representing mental maps and cognitive learning into micro-simulation models of activity-travel behavior. Mental maps can be used to address the problem that choice sets in models of travel demand are often ad hoc specified. The theory underlying the model is discussed, a specification is derived and numerical simulation is used to illustrate the properties of the model.