Prediction of surface roughness profiles for milled surfaces using an artificial neural network and fractal geometry approach

Artificial neural networks (ANNs) models were developed for the analysis and prediction of the relationship between the cutting conditions and the corresponding fractal parameters of machined surfaces in face milling operation. These models can help manufacturers to determine the appropriate cutting conditions, in order to achieve specific surface roughness profile geometry, and hence achieve the desired tribological performance (e.g. friction and wear) between the contacting surfaces. The input parameters of the “ANNs” models are the cutting parameters: rotational speed, feed, depth of cut, pre-tool flank wear and vibration level. The output parameters of the model are the corresponding calculated fractal parameters: fractal dimension “D” and vertical scaling parameter “G”. The model consists of three-layered feed-forward back-propagation neural network. ANNs models were utilized successfully for modeling and predicting the fractal parameters “D” and “G” in face milling operations. Moreover, W–M fractal function was integrated with the developed ANNs models in order to generate an artificially fractal predicted profiles at different cutting conditions. The predicted profiles were found statistically similar to the actual measured profiles of test specimens.     

Theoretical approach to cell-impedance-controlled lithium transport through Li1 − δMn2O4 film electrode with partially inactive fractal surface by analyses of potentiostatic current transient and linear sweep voltammogram

Lithium transport through the partially inactive fractal Li_1 − δMn₂O₄ film electrode under the cell-impedance-controlled constraint was theoretically investigated by using the kinetic Monte Carlo method based upon random walk approach. Under the cell-impedance-controlled constraint, all the potentiostatic current transients calculated from the totally active and partially inactive fractal electrodes hardly exhibited the generalised Cottrell behaviour and they were significantly affected in shape by the interfacial charge-transfer kinetics. In the case of the linear sweep voltammogram determined from the totally active and partially inactive fractal electrodes, all the power dependence of the peak current on the scan rate above the characteristic scan rate deviated from the generalised Randles-Sev?ik behaviour. From the analyses of the current transients and the linear sweep voltammograms simulated with various values of the simulation parameters, it was further recognised that the cell-impedance-controlled lithium transport through the partially inactive fractal Li_1 − δMn₂O₄ film electrode strongly deviates from the generalised diffusion-controlled transport behaviour of the electrode with the totally active surface, which is attributed to the impeded interfacial charge-transfer kinetics governed by the surface inhomogeneities including the fractal dimension of the surface and the surface coverage by active sites and by the kinetic parameters including the internal cell resistance.     

The influence of frequency on fractal dimension of adsorbed layers

Alternating current (AC) voltammetry and electrochemical impedance spectroscopy are often the methods of choice for use in study of adsorption of organic molecules. The adsorption of organic molecules on interface may result in the formation of fractal structures, whose fractal dimension can be estimated using the method of scaling the hanging mercury drop electrode (HMDE). The aim of present study was to check whether the estimated fractal dimension, D (or for that matter the fractal ordering of the adsorbed layer) shows any correlation (dependence) with change of applied frequency, and second, to check the possibility to extend the method to broad frequency spectrum compatible with impedance spectroscopy. The investigation included two surfactants nonionic Triton-X-100 (T-X-100) and anionic sodium dodecyl sulfate (SDS) and alcohol tert-butanol. All measurements were performed on HMDE at thermodynamic equilibrium employing broad frequency spectrum. The validity of the approach was checked by measurements on pure electrolyte and by comparison with previously obtained results for fractal layers. The results of the investigations show that: (1) the method of scaling the HMDE to obtain the fractal dimension of adsorbed layer is compatible with impedance spectroscopy and the combination of these methods can be used as a powerful tool to investigate fractal aspect of adsorption of organic molecules; (2) fractal ordering of adsorbed layer and the value of fractal dimension is not influenced by the frequency of applied sinusoidal voltage perturbations.     

Fractal aggregate model of chain with mixed statistics

A fractal aggregate model is presented for chain molecules which are described by different statistics on different length scales. It describes the macromolecular chains as aggregates composed either of non-porous monomers or thermal blobs. The mass of non-porous monomer and the thermal blob mass are both dependent on the solvent quality. The blob mass can be calculated knowing the non-porous monomer mass in a solvent under consideration and that at the theta condition. Both the quantities can be deduced from the solution properties. The values of thermal blob mass normalized by that of monomer, deduced from intrinsic viscosity data for several polymers, form a dependence on Mark-Houvink-Sakurada exponent. This dependence is confirmed by the solvent quality dependence of the polymer mass at the onset of excluded volume behavior and some values obtained from sedimentation coefficients.     

基于分形的机械加工表面轮廓评价参数的计算方法

通过对机械加工表面轮廓特征的分析,说明了在表面轮廓参数测量中,消除各种误差影响的必要性。提出利用非倾向性振荡分析方法对机械加工表面轮廓稳定性问题进行了分析,以去除各种误差对表面轮廓参数的影响,并对表面轮廓评价参数提出了一种有效的计算方法。     

Fractal analysis of pressure fluctuations in a three phase bubble column reactor operating at low pressure

Pressure fluctuations in a three phase bubble column reactor operating at relatively low pressure (92 KPa) have been analyzed by adopting the spectral and fractal analyses to get the engineering informations for the on-line control and fault diagnosis of the reactors. The mean value, standard deviation, skewness and kurtosis of the pressure fluctuations have been obtained. The local fractal dimension has been determined from the Pox diagram obtained by means of the rescaled range analysis of the pressure fluctuations based on the fractional Brownian motion. The local fractal dimension of pressure fluctuations has increased and thus the pressure fluctuation signals have become less persistent and irregular, with increases in the gas flow rate reaction temperature, particle size and solid content in the slurry phase. The local fractal dimension has been well correlated in terms of the operating variables.     

基于微观结构分形表征的钼-氧化锆材料导电导热性能研究

金属陶瓷物理性能与材料组分和空间组织结构密切相关,其组成相的形态分布具有分形特征。基于渗流理论和分形理论,通过对材料微观结构图像的二值化处理进行导通相分形维数计算,建立分形维数与导通相微观形貌、渗流临界指数之间的定量表征,研究Mo-ZrO2金属陶瓷全组分范围内材料微观结构与电导率和热导率之间的关系。结果表明：导通相面积分形维数随着Mo体积分数的增加而增加,电导率与分形维数遵循渗流转变特征。采用通用有效介质(GEM)方程建立基于导通相分形维数的金属陶瓷电导率和热导率模型,实现材料微观组织定量分析结果与金属陶瓷的渗流模型相结合,有效预测材料宏观物理性质的梯度变化。     

不同级配粗骨料对橡胶混凝土构件力学性能的分形研究

基于材性试验研究了粗骨料级配对橡胶混凝土构件强度及弹性模量的影响;通过三根不同级配粗骨料橡胶混凝土梁探讨了粗骨料级配对试验梁受弯承载力、挠度等方面的影响,并研究了三根橡胶混凝土梁在集中荷载下损伤演化过程的分形行为。用分形几何学研究橡胶混凝土梁的损伤演化过程,为橡胶混凝土结构的健康检测和安全性评估提供新的方法。     

Programs as Paradigms

How might we synthesise two very different approaches in architecture? One based on programme and another on typology or paradigm. Pablo Miranda Carranza , a researcher at the Architecture School at the RoyalInstitute of Technology (KTH) in Stockholm, takes his cue from an approach suggested by Colin Rowe in the early 1980s to examine how computation formulates architectural thinking and presentation.     

分形Packing算法与建筑设计

Packing是一定数量的单元体以叠 合规则聚集在一起的一种算法。Packing算法 与分形迭代结合不仅在空间优化中具有重要 作用,在建筑设计中也具有一定的运用潜力。 本文分析了箱型Packing、圆形Packing等不同 种类的分形Packing算法的特性,并结合设计 案例探讨了分形Packing算法在建筑设计中的 运用方式。