University of Science and Technology Beijing

About: University of Science and Technology Beijing is a education organization based out in Beijing, China. It is known for research contribution in the topics: Microstructure & Alloy. The organization has 41558 authors who have published 44473 publications receiving 623229 citations. The organization is also known as: Beijing Steel and Iron Institute.

Density-controlled hydrothermal growth of well-aligned ZnO nanorod arrays.

Abstract: Density-controlled ZnO nanorod arrays (ZNAs) were prepared on pre-treatment substrates by a hydrothermal approach under different conditions. The effect of substrate pre-treatment conditions on controlling the density of ZNAs was systematically studied by scanning electron microscopy and x-ray diffraction. It is demonstrated that the substrate pre-treatment conditions such as the concentration of the ZnO colloid, spin coating times, and substrate annealing treatment have their respective influence on controlling the density of the ZNAs. The introduction of a ZnO nanoparticle layer on the substrate not only helps to control the nanorod density but also has a strong impact on the orientation of the nanorod arrays. Although controlling the spin coating process has a similar mechanism to controlling the concentration of colloid, it offers a convenient method to prepare a series of ZNAs with variable density. An annealing treatment of the substrate can influence the microstructure of the ZnO seed layer and then influence the density of the ZNAs.

Off-Policy Actor-Critic Structure for Optimal Control of Unknown Systems With Disturbances

Abstract: An optimal control method is developed for unknown continuous-time systems with unknown disturbances in this paper. The integral reinforcement learning (IRL) algorithm is presented to obtain the iterative control. Off-policy learning is used to allow the dynamics to be completely unknown. Neural networks are used to construct critic and action networks. It is shown that if there are unknown disturbances, off-policy IRL may not converge or may be biased. For reducing the influence of unknown disturbances, a disturbances compensation controller is added. It is proven that the weight errors are uniformly ultimately bounded based on Lyapunov techniques. Convergence of the Hamiltonian function is also proven. The simulation study demonstrates the effectiveness of the proposed optimal control method for unknown systems with disturbances.

Microstructural stability and mechanical properties of a new nickel-based superalloy

Abstract: By means of thermodynamic calculation, OM, SEM, TEM and X-ray diffraction, microstructural stability was investigated on the new nickel-based superalloy, INCONEL alloy 740. Some mechanical properties of the new alloy were also studied. The results indicated that the microstructure of this alloy maintained good thermal stability to at least 750 °C. The major precipitates were MC, M23C6 and γ′ during prolonged aging at temperatures below 704 °C. Small amount of η precipitates formed at grain boundaries in sample aged at 750 °C in 1000 h and large amount of intragraunlar η precipitates formed a Widmanstatten pattern in sample aged at 849 °C for 1000 h. γ′ phases grew rapidly with increasing in temperature and partially resolutioned after 849 °C aging for 1000 h. Harmful phases, such as σ phase, have not been detected in these samples. The impact toughness of alloy declined and there was a ductile/brittle transition with increasing aging temperature and time. Room temperature microhardness of alloy decreased with an increase in temperature mainly due to the growth of γ′ phases. Elevated-temperature microhardness of alloy for standard heat-treated condition was higher than room temperature microhardness. In comparison to NIMONIC alloy 263, the new alloy exhibited higher ductility and higher tensile strength.