Advanced Materials Research Vols. 433-440

Abstract: The threading dislocation density (TDD) of thick G_aN films grown by hydride vapor phase epitaxy (HVPE) was estimated through counting etch pit density (EPD) and calculating full width at half maximum（FWHM）of double crystal X-Ray diffraction (DCXRD). TDD was about 108 through counting EPD, while it was about 109 through calculating the FWHMs of (0002) and (10¹2). The experiment results show that the two methods are both suited to estimating the TDD of the thick HVPE-G_aN films with 350um thickness. But they have some difference: EPD method is fitter in evaluating the dislocation density of the surface of thick GaN film, but FWHM method can gain the total dislocation density of thick G_aN film. The method calculating the FWHMs possesses more general statistical significance.

Abstract: Compound active clamping three-phase Boost PFC converter with soft-switch has a good potential application because of its high power factor, high efficiency and simple structure. The mathematical model of this converter is analyzed. A variable structure control method with the robustness item is proposed for the control of this converter, in order to overcome the shortcoming of the existing method, when the converter parameters changes. The time-varying boundary layer is used to smooth the control discontinuity. Simulation is performed using PSIM and MATLAB hybrid simulation method. The results indicate that the proposed method possesses not only better transient and steady state performance under the nominal parameters, but also better robustness under the parameter perturbations, compared with the traditional PI control and the former variable structure control without the robustness item.

Abstract: The difference signals, which between upper and lower shells of flange bolted joints structure, was applied to establish the autoregressive model for system condition identification. Firstly, an AR model is built by difference signals. The established AR model is used as a filter to process the difference signal in test state under the same condition and output residual series. Then the statistical parameters, such as Itakura distance, skewness, kurtosis and variance, are used to handle residual series. The results of experiment show that Itakura distance is a useful eigenvalue to identify the bolted joints condition.

Abstract: It is very crucial to find a suitable tracking method, because improving the efficiency of the maximum power point tracking will improve the efficiency of tracking improved solar energy utilization to the present generation system. Based on fuzzy logic control of recovery of maximum power point tracking is enough to a system for solar energy utilization. Based on MATLAB/simulink software, comparing the fuzzy logic controller of different dimensions and different simulation emulated, this article find each factor to influence the tracking accuracy and speed, and it will provide the basis for different systems.

Abstract: Based on ARM,multifuncttion GPS/GPRS automobile security system was designed,which focused on security and detectiong.The system combines with detection technology, sensor technology, GPS technology, GPRS technology and digital filtering technology.This system was discussed from software and hardware. Related math model was established. Corresponding test was been brought forward to improve system reliability. Average filtering method and median filtering algorithm have been used to inhibiting interference signals with variety of frequency in software. In this paper,the advantages of this system have been discussed.The embeded system realizes the function with characteristics of low cost, high performance, real-time and reliability ,it has high practical value.

Abstract: The productivity of whirlwind milling is 3-4 times more than that of ordinary milling and grinding. Considering that the tool numbers are always 6-12, the problems caused by tools wear are becoming the difficulties in whirlwind milling. According to the actual processing, the rotary surface equation of cutting tools is established by the space coordinates, and then the equations of tool processing angels are derived. By changing the parameters in the equations, the model lays good foundation for improving and compensating methods to achieve the high precision surface.

Abstract: A new quaternary amorphous alloy powder Ti₅₀Fe₂₂Ni₂₂Sn₆ are prepared by mechanical alloying. The milling was performed under an argon atmosphere in a high-energy planetary ball mill. After milled 70h, fully amorphous Ti₅₀Fe₂₂Ni₂₂Sn₆ powders can be obtained, with the condition of the milling speed, 300rpm, and the weighs ratio of ball to powder, 10:1. Crystal structure of the milled powders is investigated by XRD. Thermal analysis show that when the heating rate increasing from 10K/min to 40K/min, the super-cooled liquid region of milled amorphous alloy increased from 93K to 110K.

Abstract: In this research, we compared the performance of different processing chains resulting from combinations of spatial denoising filters, unsupervised feature transformation methods, and a support vector machine classifier. Two different training and test sample scenarios were investigated and conducted on an AVIRIS image over the Indian Pines region in Indiana, USA. The results showed that by using the process chain (adaptive enhanced Lee filter, maximum noise fraction, and support vector machine) the classification accuracies of the kappa coefficient were better than those of the best previously published techniques.

Abstract: This paper aims to compare the material removal rate, ν between a Dimensional Analysis (DA) model, an Artificial Neural Network (ANN) model and an experimental result for a low gap current of an Electrical Discharge Machining (EDM) process. The data analysis is based on a copper electrode and steel workpiece materials. The DA and ANN model that have been developed and reported earlier by authors are used to compare the material removal of EDM process. The result indicated that the ANN model provides better accuracy towards the experimental results.

Abstract: This paper presents a study on the influence of process parameters on the manufacturing and environmental aspects of die sinking electrical discharge machining process using graphite as the tool electrode. This investigation included peak current, pulse duration, dielectric level and flushing pressure as the input parameters and aerosol emission rate, material removal rate and tool wear rate as the output parameters. The experiments were planned according to the Taguchi L9 orthogonal array. The effects of process parameters on the output responses were analyzed using main effect plots. Peak current was the most significant process parameter. A discussion on the optimization of process parameters is also presented in this paper.