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Ball milling induced the formation of nanocrystalline and amorphization phase in Fe–25.68% Dy2O3 powder mixtures (mass fraction, %). The microstructure was investigated by using X-ray diffraction and transmission electron microscopy. The transformation of Dy2O3 from cubic to monoclinic crystal structure and then to the amorphization was observed during ball milling. A few Dy atoms were dissolved into Fe crystal structure, which was discussed using mechanical kinetics. After 48 h of ball milling, the homogenous mixtures of supersaturated nanocrystalline solid solution of Fe (Dy, O) and Dy2O3 amorphization were formed and the elements of Fe, Dy, and O were distributed uniformly in the ball-milled particles. During the whole ball mining process, a rapid decrease in Fe grain size was observed over the initial time period, while a constant value was presented in later stage, resulting in a final size of about 20 nm. The mechanism of the microstructural evolution of powder mixtures was analyzed and discussed.
In this paper, a novel Predictive Variable Structure Filter (PVSF) and its adaptive deformation (APVSF) are presented for attitude synchronisation during Satellite Formation Flying (SFF). The PVSF is proposed based on the variable structure control concept and applied to any nonlinear system with model errors. The model errors in the PVSF need not satisfy the assumption of Gaussian white noise; therefore, it has advantages in dealing with various kinds of uncertainties, parameter variations or noises. Then, the APVSF is also presented to adjust the smoothing boundary layer of PVSF by minimising the Mean-Square Error (MSE). Simulations are performed to demonstrate the accuracy, robustness, and stability of the proposed methodologies for the attitude synchronisation estimation of the SFF system.
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