Short fatigue cracks in austempered ductile cast iron (ADI)

The growth of short fatigue cracks was investigated in an austempered ductile cast iron (wt% 3.6C, 2.5Si, 0.6Mn, 0.15Mo, 0.3Cu), austenitized at 870 °C and then austempered at 375 °C for 2 h. At stress amplitudes close to the fatigue limit endurance limit of 10⁷ cycles, subcritical crack nuclei initiated at graphite nodules. The crack nucleus decelerated and arrested after propagating a short distance. The position of an arrested crack tip was characterized using an electron backscatter diffraction technique, demonstrating that short fatigue cracks in austempered ductile cast iron (ADI) can be arrested by boundaries such as those between ausferrite sheaves or packets and prior austenite grains. Refinement of the prior austenite grain size decreased the size of subcritical crack nuclei. It is proposed that the arrest and retardation of short crack nuclei are controlled by the austenite grain size and graphite nodule size. This determines the fatigue endurance limit.     

Contourlet变换和遗传算法相结合的沥青红外图像增强方法

沥青施工过程中,采集的红外图像容易受到周围环境噪声的影响,使图像变得模糊、信噪比低,从而导致后续图像处理分析的准确度降低。针对该噪声特性,提出了一种Contourlet变换和遗传算法相结合的红外图像增强方法。首先对原始红外图像进行Contourlet变换,得到带有多尺度、多方向信息的带通子带,然后对其进行模糊增强,并通过自适应遗传算法优化模糊增强参数,最后对增强后的带通子带进行Contourlet逆变换,得到效果增强的红外图像。实验结果表明,与其它几种常用的红外图像增强方法相比,此方法能更有效地抑制噪声,提高清晰度,取得了较好的增强效果。     

High‐Contrast SEM Imaging of Supported Few‐Layer Graphene for Differentiating Distinct Layers and Resolving Fine Features: There is Plenty of Room at the Bottom

For supported graphene, reliable differentiation and clear visualization of distinct graphene layers and fine features such as wrinkles are essential for revealing the structure–property relationships for graphene and graphene‐based devices. Scanning electron microscopy (SEM) has been frequently used for this purpose where high‐quality image contrast is critical. However, it is surprising that the effect of key imaging parameters on the image contrast has been seriously undermined by the graphene community. Here, superior image contrast of secondary electron (SE) images for few‐layer graphene supported on SiC and SiO₂/Si is realized through simultaneously tuning two key parameters—acceleration voltage (V_acc) and working distance (WD). The overlooked role of WD in characterizing graphene is highlighted and clearly demonstrated. A unified model of V_acc and WD dependence of three types of SE collected by the standard side‐attached Everhart‐Thornley (E‐T) SE detector is conceptually developed for mechanistically understanding the improved mass thickness contrast for supported few‐layer graphene. The findings reported here will have important implications for effective characterizations of atomically thick 2D materials and devices.     

基于遗传算法和梯度算法的桁架结构动力学形状优化

本文提出了一种基于遗传算法和梯度算法的桁架动力学形状优化方法 ,该方法综合了梯度算法的快速收敛与遗传算法的全局搜索能力。算例表明了本文方法的有效性和工程适应性。     

Color image denoising using evolutionary computation

Noise suppression in multichannel data sets, such as color images, has drawn much attention in the last few years. An issue of paramount importance in designing color image filters is the determination of the coefficients that should be used to weight the inputs to the filter. In this study, we propose an evolutionary computation‐based approach to select and optimize the coefficients in the class of weighted vector directional filters. Using a genetic algorithm, we were able to adapt the filter weights to match varying image and noise characteristics. Extended experimentation with realistic image processing applications, including television image enhancement and virtual restoration of artworks, indicates that the proposed filters are capable of removing noise while preserving chromaticity information, edges, and fine details, as well as structural image content. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 236–251, 2005     

Synthesis and characterisation of selenium nanowires using template synthesis

Selenium (Se) nanowires were grown in the pores of anodic alumina membrane as template. Facile electrodeposition technique was used for the synthesis of Se nanowires. Scanning electron microscopy was used for the morphological study of the nanowires. X-ray diffraction and Energy dispersive X-ray fluorescence were utilised for the structural characterisation. The optical properties of Se nanowires were investigated using optical absorption spectroscopy.     

Iterative optimization for joint design of source and channel codes using genetic algorithms

Abstract

This paper presents a novel algorithm for the joint design of source and channel codes. In the algorithm, channel‐optimized vector quantization (COVQ) and rate‐punctured convolutional coding (RCPC) are used for design of the source code and the channel code, respectively. We employ the genetic algorithm (GA) to prevent the design of COVQ from falling into a poor local optimum. We also adopt the GA to reduce the computational time needed for realizing the unequal error protection scheme best matched to the COVQ. Both the GA‐based source coding and channel coding scheme are then iteratively combined to achieve a near global optimal solution for the joint design. Numerical results show that the algorithm can be an effective alternative for applications where high rate‐distortion performance and low computational complexity are desired.     

Optimal packetization scheme for embedded multimedia bitstreams using genetic algorithms

The problem of packetizing embedded multimedia bitstreams into fixed‐size packets is investigated and an optimal packetization scheme using a genetic algorithm is presented. In the proposed method, each individual packetization instance is represented by a decision sequence and mapped to a chromosome. A steady‐state genetic algorithm is applied to search for the optimal chromosome that minimizes the distortion between the original and the reconstructed media. In addition, we propose a fast method to calculate the fitness value based on the distortion associated with each chromosome to speed up the evolution process. The computer simulation results show that our proposed packetization scheme has high compression efficiency and provides error resiliency to packet losses with a relatively fast speed. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 77–84, 2006     

Camera calibration using a genetic algorithm

An autonomous robot will have to detect moving obstacles online before it can plan its collision-free path, while navigating in a dynamic environment. The robot collects information about the environment with the help of a camera and determines the inputs for its motion planner through image analysis. The present article deals with issues related to camera calibration and online image processing. The problem of camera calibration is treated as an optimization problem and solved using a genetic algorithm so as to achieve minimum distorted image plane error. The calibrated vision system is then utilized for the detection and identification of the objects by analysing the images collected at regular intervals. For image processing, five different operations, such as median filtering, thresholding, perimeter estimation, labelling and size filtering, have been carried out. To show the effectiveness of the developed camera-based vision system, inputs of the motion planner of a navigating robot are calculated for two different cases. It is observed that online detection of the shapes and configurations of the obstacles is possible by using the vision system developed.     

Going beyond histology. Synchrotron micro-computed tomography as a methodology for biological tissue characterization: from tissue morphology to individual cells

Current light microscopic methods such as serial sectioning, confocal microscopy or multiphoton microscopy are severely limited in their ability to analyse rather opaque biological structures in three dimensions, while electron optical methods offer either a good three-dimensional topographic visualization (scanning electron microscopy) or high-resolution imaging of very thin samples (transmission electron microscopy). However, sample preparation commonly results in a significant alteration and the destruction of the three-dimensional integrity of the specimen. Depending on the selected photon energy, the interaction between X-rays and biological matter provides semi-transparency of the specimen, allowing penetration of even large specimens. Based on the projection-slice theorem, angular projections can be used for tomographic imaging. This method is well developed in medical and materials science for structure sizes down to several micrometres and is considered as being non-destructive. Achieving a spatial and structural resolution that is sufficient for the imaging of cells inside biological tissues is difficult due to several experimental conditions. A major problem that cannot be resolved with conventional X-ray sources are the low differences in density and absorption contrast of cells and the surrounding tissue. Therefore, X-ray monochromatization coupled with a sufficiently high photon flux and coherent beam properties are key requirements and currently only possible with synchrotron-produced X-rays. In this study, we report on the three-dimensional morphological characterization of articular cartilage using synchrotron-generated X-rays demonstrating the spatial distribution of single cells inside the tissue and their quantification, while comparing our findings to conventional histological techniques.     

基于并行遗传算法的Otsu双阈值医学图像分割

传统遗传算法用于搜索某些函数极值时精确度较低且稳定性较差。针对该问题,提出了一种基于并行遗传算法的Otsu双阈值医学图像分割算法。在该算法中,进化在多个不同的子群中并行进行,避免单种群进化过程中出现的过早收敛现象,提高整个算法的收敛速度。100次阈值计算实验结果表明,提出的分割算法与传统遗传算法相比,不仅能够对图像进行准确的分割,而且具有更强的精确性和稳定性。其收敛速度明显优于基于单种群的遗传算法的Otsu双阈值医学图像分割。     

遗传算法加权中值滤波器的优化设计

当测试数据中随机干扰满足高斯分布时,可以采用线性滤波器进行信号处理得到所要求的有用信号.而当随机干扰为非高斯分布时,则必须采用非线性的信号处理方法才能获得所要求的有用信号.这里讨论一类非线性滤波器——加权中值滤波器的最优设计问题.取损失函数为绝对误差的数学期望值,采用实数值编码多子种群的标准遗传算法来极小化损失函数.由于遗传算法:是用点群进行寻优,而不是用一个单点进行寻优,具有隐含并行算法的特点;群体在每一代的进化过程中执行同样的复制、交叉、变异操作,仅使用问题本身所对应的适应度函数,而不需要任何其它先决条件或辅助信息;遗传算法使用随机转换规则,而不是确定性规则进行运算.遗传算法作为一类全局最优算法,它所得到的加权中值滤波器也是全局最优的.数值计算结果表明,采用遗传算法可以得到更小的绝对误差平均值,且优于LMA算法.     

SEM fractography and failure analysis of nonmetallic materials

This paper analyzes a collection of SEM fractographs compiled from 12 years of undergraduate and graduate level courses on fractography and failure analysis. Each nonmetallic material studied (glass, plastic, FRP, and wood) was fractured under controlled conditions so that the fracture was due mainly to one mode of loading such as tension, torsion, unidirectional bending, fatigue by reverse bending, and impact. With the aid of the stereomicroscope and the SEM, the fracture features of each sample were analyzed and fractographs obtained at a wide range of magnifications. The features and direction of crack propagation were correlated with the mode of loading which induced the fracture. From this study, correlations among the main fracture modes, micromechanisms, microfracture features, and loading conditions were compiled. Such correlations are invaluable for the proper interpretation of fracture features during failure analysis especially where little is known about the cause of the fracture. Reprinted from Microstructural Science, vol. 21, Metallographic Characterization of Materials Behavior, Proc. of the Twenty Sixth Annual Tech. Meeting of the International Metallographic Society, C.R. Brooks and M.R. Louthan, Jr., ed., The International Metallographic Society, Columbus, Ohio, and ASM International, 1994, pp. 121–134.     

Formulation and characterisation of nanosuspension of herbal extracts for enhanced antiradical potential

Nanotechnology is a promising technique to increase the bioavailability of herbal medicines. This paper presents the nanosuspension approach for increasing the aqueous solubility and thereby bioactivity of important herbal extracts. Nanosuspensions of the seeds of three plants extract (Silybum marianum, Elettaria cardamomum and Coriandrum sativum) were prepared by using polyvinyl alcohol (1.5% w/v) as a stabiliser. Prepared nanoparticles were characterised by scanning electron microscope. Activity of nanosuspension formulation was assessed by using four in vitro antioxidant assays. S. marianum, E. cardamomum and C. sativum particle size was observed to fall in range of 446.1 ± 112.6, 456.63 ± 339.2 and 432.1 ± 172.8 nm, respectively, most of the particles were having spherical shape and smooth topology. These synthesised nanoparticles were found to be more effective against quenching free radical than their crude extracts and standards [butylated hydroxyl toluene and ascorbic acid]. C. sativum nanosuspension showed most free radical scavenging potential against 2,2-diphenyl-1-picrylhdrazyl (DPPH) and superoxide free radical scavenging assays (IC₅₀ 0.59 ± 0.01 and 0.81 ± 0.11 mg/ml). S. marianum nanosuspension was found to be most effective against DPPH radicals scavenging (IC₅₀ 0.34 ± 0.02 mg/ml). It was concluded that nanosuspension of herbal medicines potentiates the antioxidant potential.     

结合遗传算法与方向图法的指纹图像分割

指纹作为人体的重要特征，由于其唯一性和终生不变性，越来越成为生物测定技术的重要手段，在自动指纹识别中，指纹图像分割是图像预处理中关键的一环，不仅能够对图像信息进行压缩，保留脊谷线的主要信息，同时能够去除大量的粘连，加速后续处理的速度和提高指纹特征提取和匹配的精度，将基于遗传算法的阈值分割方法和方向图法相结合对指纹图像进行分割。     

Reduced order model assisted evolutionary algorithms for multi-objective flow design optimization

Evolutionary algorithms (EAs) have been widely used for flow design optimization problems for their well-known robustness and derivative-free property as well as their advantages in dealing with multi-objective optimization problems and providing global optimal solutions. However, EAs usually involve a large number of function evaluations that are sometimes quite time consuming. In this article a reduced order modelling technique that combines proper orthogonal decomposition and radial basis function interpolation is developed to reduce the computational cost. These models provide an efficient way to simulate the whole flow region with varied geometry parameters instead of solving partial differential equations. As a test case, the design optimization of a heat exchanger is considered. Shape variation is conducted through a free form deformation technique, which deforms the computational grid employed by the flow solver. A comparison between the optimization results when using reduced order models and the exact flow solver is presented.     

On the determination of mechanical properties of composite laminates using genetic algorithms

This paper describes a method which combines finite element analysis and genetic algorithms (GAs) for identifying the elastic constants of composite laminates by using vibration test data. A procedure updates the elastic constants in a numerical model so that the output from the numerical code fits the results from vibration testing. In this approach, the elastic constants can be readily identified in a single test without damaging the structure. The GA, developed on a personal computer using the language MATLAB, applies the general-purpose numerical code MSC-NASTRAN to carry out the modal analysis.     

Determination of displacements around fatigue cracks using image analysis of in‐situ scanning electron microscope images

A technique to in‐situ measure the displacements in the vicinity of the crack tip during fatigue crack propagation has been developed. High‐resolution images of the crack tip were taken continuously throughout the fatigue load cycles with a scanning electron microscope (SEM), and an image analysis program was used to determine the displacements at different positions with respect to the crack tip. The displacements were then used to determine crack shapes and compliance curves. The measured crack shapes show a general √r dependence versus the distance to the crack tip. However, close to the crack tip the crack shape is clearly affected by plastic deformation, even in cases when small scale yielding prevails. The compliance curve measurements close to the crack tip can be used to determine the global stress level when the crack surfaces are separated, so that the exact opening and closure stresses can be determined.     

基于模拟退火并行遗传算法的Otsu双阈值医学图像分割

模拟退火和并行遗传算法是两种较好的改进进化算法性能的方法。将这两种思想有机地结合起来,利用遗传算法能全局寻优的优势和模拟退火算法的爬山性能,提出了一种基于模拟退火并行遗传算法的Otsu双阈值医学图像分割算法。在该算法中,进化在多个不同的子群中并行进行,利用模拟退火算法的爬山性能,避免单种群进化过程中出现的过早收敛现象,提高整个算法的收敛速度。实验证明,这种新的图像分割算法与并行遗传算法相比,不仅能够对图像进行准确的分割,而且具有更强的精确性和稳定性。其收敛速度明显比并行遗传算法的Otsu双阈值医学图像分割快。