汽车起重机变幅机构三铰点的合理确定

对汽车起重机变幅机构三铰点进行了运动分析和受力分析,合理确定了变幅机构三铰点的位置,得出起重特性曲线,并给出了三铰点各结构参数的调整方法。     

二维浮体大幅运动水动力物面非线性时域解

基于时域自由面格林函数，建立了线性自由面条件下计及物体大幅运动瞬时湿表面条件的非线性水动力理论计算模型，重点研究了时域分布源在水线上的特性，指出了传统分布源法在处理浮体与自由面外张斜交的计算失败的原因，并提出了新的时域分布源数值计算模型，对实船计算表明，这种新模型简便有效。     

Probabilistic fatigue crack growth analysis of spot‐welded joints

This paper presents a probabilistic fatigue crack growth life prediction methodology for spot‐welded joints under variable amplitude loading history. The loading is multi‐axial and is obtained from transient response analysis of a vehicle model using finite‐element analysis. A three‐dimensional (3D) finite element model of a simplified joint with four spot welds is developed, and the static stress analysis of this joint is performed. Then the fatigue crack inside the base material sheet is modelled as a surface crack. Probabilistic crack growth model is combined with the stress analysis result to develop a probabilistic fatigue crack growth life prediction methodology for spot welds. This new method is implemented with MSC/NASTRAN and MSC/FATIGUE and is useful for the reliability assessment of spot‐welded joints against fatigue crack growth.     

NH_2自由基~2A_1,~2B_1态振转能级的理论计算

采用大振幅弯曲振动哈密顿,同时考虑到Renner-Teller效应,理论上计算了NH2自由基A珟2A1,X珟2B1电子态振转能级,计算值与实验值符合较好。     

基于DDS芯片AD9854的信号产生器设计

介绍了一种采用2片DDs芯片AD9854和单片机芯片AT98LS52设计的信号产生器,该信号产生器能够实 现输出信号的频率、相位和幅度的调整。文中讨论了波形产生方法和参数调整方法,分析了使用一个同步信号控 制2片AD9854对输出相位的影响。实测结果表明,本文所研究的方法和研制的系统是可行的、有效的。     

强迫Duffing振子的增量谐波平衡格式

采用增量谐波平衡法导出强迫Duffing振子稳态响应的IHB计算格式，并作出特定系统参数下的周期响应极限环，其结果与Runge-Kutta方法进行对比，表明此法精度可以灵活控制，且收敛速度快。结果可靠，是强非线性问题动力学特性分析的有效方法，同时以外激励频率为参数进行跟踪延续获得系统主共振时的幅频响应特性。     

Diffusion-limited evaporation of thin polar liquid films

The stability of evaporating very thin films of a polar liquid is investigated. The microscopic interaction with the substrate and capillarity are taken into account in a lubrication equation. The stability of a flat interface is studied when evaporation is limited by the diffusion of the vapour in the gas phase. The evaporation rate is computed and evaporation is shown to be stabilizing. A stability phase diagram is obtained. A weakly nonlinear analysis leads to a film-thickness amplitude equation that is non local in space. Physical consequences of the results are eventually discussed.     

A new instrument for passive remote sensing: 2. Measurement of leaf and canopy reflectance changes at 531 nm and their relationship with photosynthesis and chlorophyll fluorescence

A previously described passive remote sensing fluorimeter (see companion paper) was modified to detect changes in the reflectance of vegetation. The utility of this remote sensing technique to measure the Physiological Reflectance Index (PRI) is shown at both leaf level under laboratory conditions and at the canopy level in the field. PRI, defined as the relative changes in reflectance at 531 nm with respect to those at 570 nm (PRI=R531−R570/R531+R570), is related to xanthophyll-related, dynamic changes of non-photochemical quenching of chlorophyll fluorescence. The robustness of this relationship by simultaneous remote sensing of PRI and chlorophyll fluorescence is strengthened. At the leaf level, the existence of two kinetically distinct components of PRI is shown. A fast (within seconds) component that is partly attributed to ΔpH induced chloroplast shrinkage, and a slow (within minutes), main component that is related to xanthophyll de-epoxidation, as demonstrated by its disappearance in the presence of DTT. Overall, PRI correlated better with non-photochemical quenching of chlorophyll fluorescence (NPQ) than with any other measured parameter, including the photochemical efficiency of PSII. Finally, at the canopy level and under field conditions, it is shown that PRI can be a useful tool for remote sensing of water stress in grapevines.     

Experimental study on the effect of nanosized carbon particles on fatigue resistance of asphalt binders

The present research study investigates the fatigue resistance of asphalt binders modified with carbon nanoparticles. Three different modified bitumens containing three different dosages of carbon nanoparticles were tested to capture fatigue properties under the concept of viscoelastic continuum damage mechanics through frequency sweep and linear amplitude sweep tests. Results show that adding carbon nanoparticles can enhance the fatigue life of neat asphalt binders.     

声波平面斜测法在拱坝混凝土构件质量检测中的应用

该文主要介绍了声波平面斜测法在拱坝混凝土构件质量检测中的应用。通过实例介绍了该方法的测线布置,成果分析,开挖验证,表明方法的有效性。同时,也阐述了实例中的不足和缺憾,分析了该方法的应用条件。该文可供同行们参考。