Modeling of EDM responses by support vector machine regression with parameters selected by particle swarm optimization

Electrical discharge machining (EDM) is inherently a stochastic process. Predicting the output of such a process with reasonable accuracy is rather difficult. Modern learning based methodologies, being capable of reading the underlying unseen effect of control factors on responses, appear to be effective in this regard. In the present work, support vector machine (SVM), one of the supervised learning methods, is applied for developing the model of EDM process. Gaussian radial basis function and ε-insensitive loss function are used as kernel function and loss function respectively. Separate models of material removal rate (MRR) and average surface roughness parameter (Ra) are developed by minimizing the mean absolute percentage error (MAPE) of training data obtained for different set of SVM parameter combinations. Particle swarm optimization (PSO) is employed for the purpose of optimizing SVM parameter combinations. Models thus developed are then tested with disjoint testing data sets. Optimum parameter settings for maximum MRR and minimum Ra are further investigated applying PSO on the developed models.     

SiO_2/CH/Au复合黑腔诊断孔电火花加工技术

通过电火花加工技术,采用含碳较高的煤油作为电介质,利用导电性能及加工性能较好的紫铜作电极材料,实现了SiO2/CH/Au复合黑腔侧表面方形诊断孔的精密加工。采用OLYMPUS STM6测量显微镜对诊断孔尺寸,结果表明:孔的尺寸加工精度可控制在±10μm内,同一电极加工的诊断孔尺寸一致性可控制在±5μm内。采用扫描电镜能谱分析SiO2/CH/Au加工导电层的成分,结果表明:电火花加工过程中,由于电介质分解生成游离态的碳以及电极材料铜熔融后沉积在CH和SiO2层表面,形成辅助导电层。通过加工辅助导电层,产生的瞬时高温使SiO2和CH层熔融气化,从而实现对绝缘层的加工。     

一种聚合物分散液晶菲涅尔波带片

利用波长为800nm,脉宽130fs的飞秒激光在镀铝膜的玻璃基片上刻蚀出波带环图案,然后用溶致相分离法将其制备成聚合物分散液晶菲涅尔波带片.用波长为632nm的He-Ne激光对聚合物分散液晶菲涅尔波带片进行测试,结果表明:随着电压的增加该样品具有良好的光电可控性,可以实现对焦点光强的调控.在沿光轴方向上,测试到的主焦点位置与理论计算值相差小于5%,且聚合物分散液晶菲涅尔波带片在160V电压时衍射效率为10.4%,接近理论衍射效率12.1%,表明了该设计的可行性.     

Silicon nanowires as field-effect transducers for biosensor development: A review

The unique electronic properties and miniaturized dimensions of silicon nanowires (SiNWs) are attractive for label-free, real-time and sensitive detection of biomolecules. Sensors based on SiNWs operate as field effect transistors (FETs) and can be fabricated either by top–down or bottom–up approaches. Advances in fabrication methods have allowed for the control of physicochemical and electronic properties of SiNWs, providing opportunity for interfacing of SiNW-FET probes with intracellular environments. The Debye screening length is an important consideration that determines the performance and detection limits of SiNW-FET sensors, especially at physiologically relevant conditions of ionic strength (>100 mM). In this review, we discuss the construction and application of SiNW-FET sensors for detection of ions, nucleic acids and protein markers. Advantages and disadvantages of the top–down and bottom–up approaches for synthesis of SiNWs are discussed. An overview of various methods for surface functionalization of SiNWs for immobilization of selective chemistry is provided in the context of impact on the analytical performance of SiNW-FET sensors. In addition to in vitro examples, an overview of the progress of use of SiNW-FET sensors for ex vivo studies is also presented. This review concludes with a discussion of the future prospects of SiNW-FET sensors.     

Atomically Dispersed Nickel Anchored on a Nitrogen-Doped Carbon/TiO2 Composite for Efficient and Selective Photocatalytic CH4 Oxidation to Oxygenates

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO₂ composite (Ni−NC/TiO₂) as a highly active and selective catalyst for photooxidation of CH₄ to C1 oxygenates with O₂ as the only oxidant. Ni−NC/TiO₂ exhibits a yield of C1 oxygenates of 198 μmol for 4 h with a selectivity of 93 %, exceeding that of most reported high-performance photocatalysts. Experimental and theoretical investigations suggest that the single-atom Ni−NC sites not only enhance the transfer of photogenerated electrons from TiO₂ to isolated Ni atoms but also dominantly facilitate the activation of O₂ to form the key intermediate ⋅OOH radicals, which synergistically lead to a substantial enhancement in both activity and selectivity.     

Influence of the material removal mechanisms on hole integrity in ultrasonic machining of structural ceramics

Micro-chipping via micro-cracks, due to rapid mechanical indentations by abrasive grits, is the fundamental mechanism of material removal during ultrasonic machining (USM) of hard-brittle materials like ceramics and glass. This study aims mainly to investigate the adverse effects of this inherent removal phenomena on the hole integrity such as entrance chipping, wall roughness and subsurface damage. It also presents the material removal mechanism happens in the gap between the tool periphery and the hole wall (called ‘lateral gap’). To do so, experiments were conducted for drilling holes on three advanced structural ceramics, namely, silicon carbide, zirconia, and alumina. Earlier published basic studies on the initiation of different crack modes and their growth characteristics are employed to explain the experimental findings in this USM study. It is realized that the radial and the lateral cracks formed due to adjacent abrasives, which are under the tool face, extends towards radial direction of the hole resulting in entrance chipping. Additionally, the angle penetration and the rolling actions of the abrasives, which are at the periphery of the tool, contribute to the entrance chipping. Later on, in the ‘lateral gap’, the sliding (or abrasion) and the rolling mechanisms by the larger abrasives take part to material removal. However, they unfavorably produce micro-cracks in the radial direction resulting in surface and subsurface damages, which are ultimately responsible for higher wall-surface roughness. Since the size of micro-cracks in brittle materials is grit size dependent according to the earlier studied physics, it is realized that such nature of the hole integrity during USM can only be minimized by employing smaller grit size, but cannot fully be eliminated.     

干涉测量的误差分析与并联机床的准确度测量

对雷尼绍激光干涉仪的线性测量原理进行了详细探讨,分析了干涉仪在线性测量中的主要影响因素和误差诱因;作出了线性测量的准直误差特性曲线和阿贝误差特性曲面,并利用最小二乘法拟合得到了干涉仪准直测量误差的数学模型和沿u、v方向离散的阿贝误差特性曲线方程;给出了一种建立误差数学模型的方法.采用激光干涉仪检测了并联数控机床直线轴的运动准确度,并提出了一种适合于并联机床直线轴定位准确度测量的干涉测量方法.     

Modelling of micro-electrochemical machining parameters used for machining of holes on copper plate

The electrochemical machining is a non-conventional machining process based on the electrolysis principle. It is used to machine various features on conducting engineering materials with the required accuracy and precision. So an attempt has been made to machine micro-holes on a 300 μm thick copper plate as an anode and a hollow stainless steel tool electrode of 250 μm diameter as the cathode. The machining operation is performed on the in-house developed micro-ECM experimental setup with controlled machining parameters voltage, concentration, and duty factor varied in three levels. A full factorial experimental plan is used to study the output responses material removal rate (MRR), radial overcut (ROC), circularity, and taper angle (TA). Later an adaptive neuro-fuzzy inference system (ANFIS) model has been developed and shown the effectiveness of the developed model in the paper. The Sugeno fuzzy model has been used in ANFIS to generate the fuzzy rules required for the model. Out of 27 experiments, 22 machining data are used for training the model, and the remaining 5 machining data are used for testing the developed model. The average error observed between the ANFIS predicted values and experimental values of MRR is 12.56%, circularity is 43.09%, ROC is 13%, and TA is 27.53%, respectively.