关于海面无线传播模型的探讨

现有文献中一般都认为海面环境的无线传播模型近似于自由空间传播模型，但在实际测试中发现，自由空间模型预测值与实测值差别较大，不能很好地解释此类环境的信号传播。笔者根据多次海面覆盖测试的数据，分析并拟合出了新的海面传播模型。     

Thin hard coatings fracture propagation during the impact test

One of the most significant applications of the impact test is to investigate thin hard coatings fatigue properties. Herein the test conditions and duration up to the film damage initiation, are considered in order to determine the critical stresses associated with the coating fatigue strength. Moreover, the subsequent film damage propagation is a significant mechanism as well, since it refers to the ability of the coating to withstand loads after its fatigue damage initiation. In order to describe the film fracture propagation the failed area ratio was introduced and an algorithm to determine this magnitude developed, based on the analysis of imprint scanning electron microscopy graphs. The application of the coating failed area ratio will be demonstrated in various impact test film cases, also with superficial thin layers. The top layers do not affect, in general, the failure initiation of the basic coating. However, according to the obtained results, the superficial films influence the basic coating failure propagation rate during the impact test.     

Elastoplastic modelling of subsurface crack growth in rail/wheel contact problems

Propagation of small subsurface cracks subjected to shear under repeated rolling contact load is studied. An analytical crack model (Dugdale) with plastic strips at the two crack tips is employed. Compressive stresses promoting crack closure and friction between crack faces are considered. The triaxial stress state is used in the yield criterion. A damage criterion is suggested based on experimental LCF data. In a numerical study, critical crack lengths are found below which propagation of an existing crack should be effectively suppressed.     

Uncertainty analysis based on sensitivity applied to angle-ply composite structures

This article describes a finite element-based formulation for the statistical analysis of the response of stochastic structural composite systems whose material properties are described by random fields. A first-order technique is used to obtain the second-order statistics for the structural response considering means and variances of the displacement and stress fields of plate or shell composite structures. Propagation of uncertainties depends on sensitivities taken as measurement of variation effects. The adjoint variable method is used to obtain the sensitivity matrix. This method is appropriated for composite structures due to the large number of random input parameters. Dominant effects on the stochastic characteristics are studied analyzing the influence of different random parameters. In particular, a study of the anisotropy influence on uncertainties propagation of angle-ply composites is carried out based on the proposed approach.     

A fuzzy clustering algorithm enhancing local model interpretability

In this work, simple modifications on the cost index of particular local-model fuzzy clustering algorithms are proposed in order to improve the readability of the resulting models. The final goal is simultaneously providing local linear models (reasonably close to the plant’s Jacobian) and clustering in the input space so that desirable characteristics (regarding final model accuracy, and convexity and smoothness of the cluster membership functions) are improved with respect to other proposals in literature. Some examples illustrate the proposed approach.     

纳米SiO_2与有机物分子的亲和性和分散性

介绍纳米SiO2的合成和粒子表面的粗糙形貌以及纳米粒子链具有类似高分子链的弹性力学属性,研究纳米SiO2的亲合性,探讨亲合性对纳米SiO2的分散、改性、应用的影响。研究表明,在极性外加剂(如乙二胺、乙二醇、PEG、PDMS、PTHF、PMMA、PBMA等)存在的情况下,纳米SiO2的弹性粒子链和硅烷醇对SiO2的分散和改性具有显著的影响。带有大烷基侧链的高分子链与SiO2表面的亲合能较低,而带有官能团的高分子链与SiO2表面具有较高的亲合性。     

超短脉冲在远场的时空特性

将在时间和空间上为高斯型的超短脉冲分解成不同时间频率的高斯光束．详细地分析了其远场由于时空耦合引起的光谱频移、波前弯曲等复杂的时空特征。     

H原子对固态合金化颗粒表面成份分布影响的研究

本文研究了氢化物ＴｉＨ２对Ｆｅ＋Ｔｉ机械合金化非晶储氢合金的表面成份偏聚和性能的影响。应用Ｘ射线光电子谱（ＸＰＳ）和俄歇电子谱（ＡＥＳ）对样品表面由表及里逐层测量成份分布。同时应用热重分析方法研究了样品氧化性能和产物。研究结果表明，在机械合金化过程中，Ｈ原子不仅能使ＦｅＴｉ非晶化，同时促使表面产生明显的Ｆｅ原子偏聚。表面Ｆｅ／Ｔｉ原子比接近７。非晶ＦｅＴｉ（Ｈ）相的氧化分两个阶段进行，Ｔｉ原子首先氧化（８３３Ｋ），随后Ｆｅ原子氧化（８９０Ｋ）。