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An attitude controller with finite time convergence rate for satellite attitude tracking issue considering the flexible dynamic based on a finite time modal state observer is proposed in this paper. The deformation of flexible appendages is taken into consideration and a finite-time state observer with auxiliary state to offset the initial error is proposed to get the flexible vibration estimation. The modal state and its derivative could be estimated by a full dimensional feedback observer. A finite time sliding mode based on the fraction order feedback of MRP is constructed and the finite time controller is proposed. The modal estimation is implied in controller design hence the counteraction of flexible system could be offset. System global finite-time stability is proved by Lyapunov method and the superiority is demonstrated by simulation results.

In order to satisfy the rudder horn casting standards of the International Association of Classification Societies, the properties of ASTM A216 steel should be improved. Therefore, in this article the rudder horn casting and accompanying specimens were cast moulded by arc furnace smelting, external refining, and modification treatment of the molten steel by lanthanum. The samples were first underwent normalizing treatment at 900 °C for 10 hours, then air cooled, followed by tempering treatment at 600 °C for 7 hours and samples were air cooled again. The mechanical properties and microstructures of the samples were measured. The crystallography relationships between lanthanum compounds formed in the molten steel and primary δ-Fe were analysed. The nucleation effect of lanthanum compounds as a heterogeneous nucleation core of primary δ-Fe were calculated and discussed based on two-dimensional mismatch theory. The results indicated that the strip MnS inclusions in ASTM A216 steel became granular rare earth compound inclusions due to La. The refined microstructures were obtained by a synergistic effect of the enhanced condensate depression and the nucleation rate of melt and La compounds as the heterogeneous nucleation caused by La.

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