Effects of a crack on the stability of a non-linear rotor system

The stability of a rotor system presenting a transverse breathing crack is studied by considering the effects of crack depth, crack location and the shaft's rotational speed. The harmonic balance method, in combination with a path-following continuation procedure, is used to calculate the periodic response of a non-linear model of a cracked rotor system. The stability of the rotor's periodic movements is studied in the frequency domain by introducing the effects of a perturbation on the periodic solution for the cracked rotor system.It is shown that the areas of instability increase considerably when the crack deepens, and that the crack's position and depth are the main factors affecting not only the non-linear behaviour of the rotor system but also the different zones of dynamic instability in the periodic solution for the cracked rotor. The effects of some other system parameters (including the disk position and the stiffness of the supports) on the dynamic stability of the non-linear periodic response of the cracked rotor system are also investigated.     

On certain bounds for the in-plane translational stiffness of a disc inclusion at a bi-material elastic interface

This paper presents a set of bounds that can be used to estimate the in-plane translational stiffness of a rigid circular disc inclusion that is embedded at the interface between two dissimilar elastic half-space regions.     

带长方形切口式样的冲击破坏数值模拟

简要介绍了光滑粒子动力学方法的基本思想和基本方程,利用该方法编制程序对带长方形切口式样的冲击破坏过程进行了数值模拟.给出了用这种方法模拟三维冲击破坏的一个算例,并对有关问题进行相关的讨论.     

两类时滞系统的鲁棒性分析

考虑了两类具有参数不确定性的时滞系统的鲁棒稳定性问题, 给出了系统具有鲁棒性能的几个充要条件. 这些结论对于研究具有时滞的反馈控制系统有重要的理论和实践价值.     

Further indication of a low quartz structure at the SiO2/Si interface from coincidence Doppler broadening spectroscopy

Results from coincidence Doppler broadening (CDB) measurements on various Si samples and Brazilian quartz having low quartz structure are presented with the aim to give further strong indication of the existence of a low quartz structure, but not of Si divacancies as frequently considered, at the SiO₂/Si interface.     

White-light digital image cross-correlation (DICC) analysis of the deformation of composite materials with random microstructure

A sophisticated image cross-correlation algorithm (J. Appl. Opt. 33 (1994) 6667) has been used to measure both components of in-plane displacement at the surface of a deforming composite material. The natural random pattern present on the surface of a polished polymer bonded explosive (PBX) sample is photographed using a high-resolution digital camera mounted on an optical microscope. Frames are taken as the sample deforms and small subimages from each frame are compared with a base-frame recorded before loading. The resulting displacement information reveals the average motion present from the centre of each of the small subimages used in the analysis, relative to the original position. Currently, there is considerable interest in monitoring the safety of PBXs over the medium to long term and in response to accidental stimuli. Knowledge of the ways in which cracks are created and propagate within the material is a key aspect of understanding. Experiment shows that the accuracy of this technique is 0.1 pixels corresponding to 50 nm in the experimental arrangement used. The technique has wide application to many small to medium strain experimental situations due to the ease of data recording. In the experiment presented here, the natural random microstructure of the sample is used to make measurements, however, any manufactured random pattern applied to a sample would enable the method to be successful.     

Nutraceutic Potential of Bioactive Compounds of Eugenia dysenterica DC in Metabolic Alterations

The fruit and leaves of Eugenia dysenterica DC., locally known as cagaita, are rich in antioxidant glycosylated quercetin derivatives and phenolic compounds that have beneficial effects on diabetes mellitus, hypertension and general inflammation. We conducted a literature search to investigate the nutraceutical potentials of these phenolic compounds for treating obesity, diabetes mellitus and intestinal inflammatory disease. The phenolic compounds in E. dysenterica have demonstrated effects on carbohydrate metabolism, which can prevent the development of these chronic diseases and reduce LDL (low-density lipoprotein) cholesterol and hypertension. E. dysenterica also improves intestinal motility and microbiota and protects gastric mucosa, thereby preventing inflammation. However, studies are necessary to identify the mechanism by which E. dysenterica nutraceutical compounds act on such pathological processes to support future research.     

Carbon nuclear magnetic resonance spectroscopic fingerprinting of commercial gasoline: Pattern-recognition analyses for screening quality control purposes

In this work, the combination of carbon nuclear magnetic resonance (¹³C NMR) fingerprinting with pattern-recognition analyses provides an original and alternative approach to screening commercial gasoline quality. Soft Independent Modelling of Class Analogy (SIMCA) was performed on spectroscopic fingerprints to classify representative commercial gasoline samples, which were selected by Hierarchical Cluster Analyses (HCA) over several months in retails services of gas stations, into previously quality-defined classes. Following optimized ¹³C NMR-SIMCA algorithm, sensitivity values were obtained in the training set (99.0%), with leave-one-out cross-validation, and external prediction set (92.0%). Governmental laboratories could employ this method as a rapid screening analysis to discourage adulteration practices.