Development of calibration models for quality control in the production of ethylene/propylene copolymers by FTIR spectroscopy,multivariate statistical tools,and artificial neural networks

Principal component regression (PCR), partial least squares (PLS), StepWise ordinary least squares regression (OLS), and back‐propagation artificial neural network (BP‐ANN) are applied here for the determination of the propylene concentration of a set of 83 production samples of ethylene–propylene copolymers from their infrared spectra. The set of available samples was split into (a) a training set, for models calculation; (b) a test set, for selecting the correct number of latent variables in PCR and PLS and the end point of the training phase of BP‐ANN; (c) a production set, for evaluating the predictive ability of the models. The predictive ability of the models is thus evaluated by genuine predictions. The model obtained by StepWise OLS turned out to be the best one, both in fitting and prediction. The study of the breakdown number of samples to be included in the training set showed that at least 52 experiments are necessary to build a reliable and predictive calibration model. It can be concluded that FTIR spectroscopy and OLS can be properly employed for monitoring the synthesis or the final product of ethylene–propylene copolymers, by predicting the concentration of propylene directly along the process line. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

卸荷裂隙在水利水电工程建设中的危害

卸荷裂隙是对水工建筑物稳定最不利的软弱结构面之一。文中较系统地介绍了这种结构面的特点、分布规律、形成的力学机理、对工程的危害、勘查方法及处理措施。     

波导HCN激光器输出的EH_(11)模在自由空间中的传播

本文讨论了波导HCN激光器输出的EH_(11)模在自由空间中的传播模式,并与理论进行了比较。在近场,光强的分布明显受到激光器结构上不对称性的影响,其某些特征与Degnan的计算相符;在远场,EH_(11)模的传播近似于高斯光束。因此,对远场激光传播特性的测量是光学系统光路设计的基础。     

激光实际大气传输湍流效应相位校正一些实验结果

进行了近地面水平大气中激光传输湍流效应及其自适应光学相位校正实验，对光束振幅起伏、到达角起伏及其远场Strehl比进行了测量分析。实验结果表明，光束到达角起伏功率谱在低频段（f＜0．4υ／d）近似地满足-2/3次幂关系，而在高频段（f＞0．4υ／d）则近似满足-8／3次幂关系。在较弱湍流效应情况下时数振幅起伏方差小于0．3），相位补偿是有效的，而在较强湍流效应树数振福起伏饱和）时，自适应光学系统常常不能实现稳定闭环。由于传输场景地形复杂，湍流效应及其相位校正效果定量规律的描述还需进一步研究。     

根据波速计算多相土石地基压实度的理论模型

本文基于多相复合介质的波动传播特性，导出介质内纵、横波速的理论计算公式。通过对影响因素分析，建立了横波波速与土石复合介质的干密度之间的近似理论关系。在此基础上，推导出土石地基压实度的波速计算理论模型的近似表达式。最后进行了现场地基的波速测试和灌砂法测试，通过理论计算和灌砂法测试结果的对比分析，表明该近似模型是可行的，并且其在对非均匀土石复合地基的压实质量评价中优越于传统的密度法。     

Low-cycle fatigue behavior of Sn-Ag, Sn-Ag-Cu, and Sn-Ag-Cu-Bi lead-free solders

Low-cycle fatigue (LCF) tests on as-cast Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi, and Sn-3Ag-0.5Cu-3Bi solders was carried out using a noncontact strain-controlled system at 20°C with a constant frequency of 0.1 Hz. The addition of Cu does not significantly affect the fatigue life of eutectic Sn-Ag solder. However, the fatigue life was significantly reduced with the addition of Bi. The LCF behavior of all solders followed the Coffin-Manson relationship. The fatigue life of the present solders is dominated by the fracture ductility and can be described by the ductility-modified Coffin-Manson’s relationship. Steps at the boundaries of dendrite phases were the initiation sites for microcracks for Sn-3.5Ag, Sn-3Ag-0.5Cu, and Sn-3Ag-0.5Cu-1Bi solders, while for Sn-3Ag-0.5Cu-3Bi solder, cracks initiated along both the dendrite boundaries and subgrain boundaries in the dendrite phases. The linking of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through eutectic phases and intergranularly along dendrite boundaries or subgrain boundaries.     

A FETI-like domain decomposition method for coupling finite elements and boundary elements in large-size problems of acoustic scattering

Numerical simulations of acoustic scattering in the frequency domain based on hybrid methods coupling finite elements and boundary elements are the most suited for dealing with problems involving wave propagation in inhomogeneous media. Furthermore, it is necessary to resort to high performance computing to effectively solve the large size problems. However, the direct coupling yields a linear system with a matrix which is partly dense and partly sparse and thus not adapted to high performance computing. To avoid this difficulty, we present a new iterative method constructed from a non overlapping domain decomposition technique.     

Nondestructive evaluation of pavements using spectral analysis of surface waves in the frequency wave-number domain

The potential of using Spectral analysis of surface waves (SASW) for nondestructive testing of pavement and soil sites has been demonstrated in several publications. The usual SASW field testing and data analysis procedures and the assumption of a single propagation mode yield accurate results when there are no sharp changes in the stiffness of the site with depth. When this is not the case, however, difficulties arise in the interpretation of experimental data due to the participation of more than one mode in the wave field. In an earlier study, the multiple filter/crosscorrelation technique was suggested for analyzing multi-mode SASW signals. This technique, however, may not yield accurate results when propagation modes are closely spaced. A more general method using spectral analysis in the frequency wave-number domain is presented in this paper. Formulas are presented for determining a reasonably small number of surface measurements, and the accuracy of this method in resolving experimental dispersion curves is demonstrated for a pavement site.     

INITIAL FRACTURE MECHANISMS IN NICKEL ALLOYED PM STEEL

Abstract— Initial fatigue crack propagation mechanisms at near threshold conditions were studied for four nickel-alloyed, powder-metallurgy (PM) steels. Fatigue fracture surfaces were obtained by testing smooth rectangular specimens at 30 Hz and under constant amplitude and zero mean stress conditions. Materials based on Distaloy AE were used in two densities, namely 7.15 and 7.45 g/cm³.
All the fracture surfaces were composed of three morphological regions (i) a macrocrack initiation region Rl where cracks propagated preferentially through particles (ii) a macrocrack growth region R2 and (iii) an unstable crack growth region R3 where cracks propagated preferentially between particles. Initial fatigue crack growth, in region R1, was controlled by the propagation of short cracks whose dimensions were comparable to the material microstructure. The subsequent fatigue crack growth in regions R2 and R3 was controlled by ductile rupture between microvoids. Transparticle fracture in region R1 was independent of pore distribution, while interparticle fracture in regions R2 and R3 was dependent on pore distribution.     

PROPAGATION OF GASLESS COMBUSTION FRONTS: NONZERO REACTION RATE IN THE WHOLE DOMAIN

This paper deals with the gasless combustion problem in an infinite one-dimensional medium. The possibility of the existence of steadily propagating reaction waves is stated for system models with nonzero reaction rates everywhere but at the boundaries. Two forms for the chemical reaction rate dependence on the temperature are considered: the classical Arrhenius, and a modified Arrhenius incorporating and ignition temperature. The equations for the steadily propagating waves are studied in the phase-plane of the temperature and its derivative. The analysis first addresses the question of whether steadily propagating waves are admissible. Then bounds for the propagation velocity are sought and found. The results of the closed-form analysis are successfully tested against numerical experiments. Non-steady propagation regimes are also found, and regions in the parameter space associated with different asymptotic dynamical behaviour are identified.