Enhancing optical properties of nanocrystalline silicon films with air exposure

We report the effect of air exposure and deposition temperatures, T_d, on the optical property of nanocrystalline silicon (nc-Si). The nc-Si thin films were investigated by photoluminescence (PL), optical absorption, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) absorption and Raman scattering. Experimental results show the structural change from an amorphous to a nanocrystalline phase at T_d=80 °C. In addition, it suggests that T_d low condition leads to the increase in the density of SiH-related bonds and a decrease in the average grain size, δ. The oxygen absorption peak increases with the air-exposure time. The PL exhibited two peaks at around 1.75–1.78 and 2.1–2.3 eV. The PL increases and blue shifts consistently with the decrease of δ and increase of oxygen content. The first peak may be related to nanocrystallites in nc-Si films and the origin of another one may be due to defect-related oxygen. Thus, by the plasma-enhanced chemical vapor deposition (PECVD) technique at low T_d, we can produce the nc-Si films with different grain sizes, causing the corresponding luminescent properties. The new method processes advantages of low deposition temperature and effective oxidation of nc-Si on inexpensive substrates, thus making it more suitable for developing low-cost array or flexible nc-Si optoelectronic devices.     

A Capacitor Voltage Clamped Dual Half-Bridge Series-Resonant Inverter for Home Cooking Applications

An induction heating appliance used for cooking includes more than one inductor, each being controlled by a separate inverter system. The main aim of this paper is to control each coil separately at a different frequency and power output by using the same inverter system. A working coil of two parts has been designed practically and a computer simulation has been carried out, using practical coil parameters. Each part of the coil has been operated at a different frequency and power output, which allows the use of vessels of two different diameters while obtaining a high coupling factor for both conditions. This also increases the efficiency of the system and improves power quality. The proposed topology can be applied to induction hotplates made up of several inductors in which the power and frequency must be separately regulated.     

RBF神经网络的梯度下降训练方法中的学习步长优化

梯度下降法是训练ＲＢＦ神经网络的一种有效方法。和其他基于下降法的算法一样,ＲＢＦ神经网络的梯度下降训练方法中也存在学习步长的取值问题。本文基于误差能量函数对学习步长的二阶Ｔａｙｌｏｒ展开,构造了一种优化学习步长的方法,进行了较详细的推导：实验表明,本方法可有效地加速梯度下降法的收敛速度、提高其性能。该方法的思想可以用于其他基于下降法的学习步长的优化中。     

应用新一代萃取剂Cyanex272进行钴镍分离的研究

Ｃｙａｎｅｘ２７２是新一代在硫酸盐溶液中分离钴、镍的萃取剂。本文研究了各种因素对Ｃｙａｎｅｘ２７２分离钴、镍的影响,探寻了Ｃｙａｎｅｘ２７２在镍电解净液钴渣处理工艺和高冰镍精炼新工艺中的应用前景。     

Amelioration of weld-crack resistance of the M951 superalloy by engineering grain boundaries

Fusion weld is a portable and economical joining and repairing method of metals.However,weld cracks often occur during the fusion weld of Ni-base superalloys,which hinder the applications of fusion weld on this kind of materials.In this work,the effects of microstructures of grain boundaries(GBs)of the prototype M951 superalloy on its weldability were investigated.The precipitated phases,the elemental segregations on GBs,and the morphologies of GBs can be largely altered by regulating the cooling rates of pre-weld heat treatments.With decreasing the cooling rate,chain-like M23X6 phase precipitates along the GBs,accompanying segregations of B,and GBs becomes more serrated in morphology.During fusion weld,the engineered GBs in the M951 superalloy with a low cooling rate favor the formation of the continuous liquid films on GBs,which together with the serrated GB morphology significantly prevents the formation of weld cracks.Our findings imply that the weld-crack resistance of the superalloys can be ameliorated by engineering GBs.     

Grain boundary optimization induced substantial squareness enhancement and high performance in iron-rich Sm-Co-Fe-Cu-Zr magnets

Increasing iron content has been witnessed an essential method to improve the remanence of 2:17-type Sm-Co-Fe-Cu-Zr magnets,however,the inferior squareness factor accompanied with the increased iron content turns into a neck sticking problem.In this work,the grain boundary optimization induced sub-stantial squareness enhancement from 63.4％to 91.4％,and consequently an excellent maximum energy product of 32.63 MGOe have been achieved in iron-rich Sm-Co-Fe-Cu-Zr magnets via tuning solution process.It is clearly revealed that the grain boundary(GB)phases as well as the micro-twins'density in grain interiors can be controlled and interprets the enhancement mechanism of squareness.     

The role of grain orientation in microstructure evolution of pure aluminum processed by equal channel angular pressing

A new approach describing the role of crystallographic orientation in the microstructural refinement of commercially pure aluminum during the successive passes of equal channel angular pressing (ECAP) is introduced. The study is based on analysis of X-ray diffraction texture data that is used to calculate the geometrical position of crystallographic slip planes with respect to the shearing plane of the ECAP die. The angular deviations of {111} slip planes from the macroscopic deformation plane for different processing routes were calculated and compared. The microstructure evolution was investigated using electron back-scattered diffraction (EBSD). The grain size and grain boundary character distribution obtained for each processing route are related to the angles between {111} planes and the shearing plane. It was shown that the more effective routes in grain refinement have higher angles between {111} slip planes and the shearing plane.     

Carbide size refinement by controlling the heating rate during induction tempering in a low alloy steel

The application of high heating rates in tempering treatments can provide a valuable tool for refining carbide sizes, mainly those located at high angle grain boundaries. This work analyses the influence of heating rates ranging from 1 to 300 °C/s during the tempering treatment of a 0.42%C low alloy steel. The results indicate that when high heating rates are combined with short holding times, predicting hardness will require the inclusion of the heating up and cooling down cycles in addition to the holding time and temperature used in the definition of the conventional Hollomon–Jaffe tempering parameter (TP). The effect of heating rate on carbide size distribution has been quantified, distinguishing between particles located at high (HAB) and low (LAB) misorientation angle boundaries. The former correspond to those carbides nucleated at prior γ grain, martensite block or packet boundaries whereas the latter refer to those nucleated within martensite laths and at lath boundaries. The refinement obtained has been evaluated from the point of view of hardness behaviour.