The reentry trajectory planning for hypersonic vehicles is critical and challenging in the presence of numerous nonlinear equations of motion and path constraints, as well as guaranteed satisfaction of accuracy in meeting all the specified boundary conditions. In the last ten years, many researchers have investigated various strategies to generate a feasible or optimal constrained reentry trajectory for hypersonic vehicles. This paper briefly reviews the new research efforts to promote the capability of reentry trajectory planning. The progress of the onboard reentry trajectory planning, reentry trajectory optimization, and landing footprint is summarized. The main challenges of reentry trajectory planning for hypersonic vehicles are analyzed, focusing on the rapid reentry trajectory optimization, complex geographic constraints, and cooperative strategies.
Of the many direct numerical methods, the pseudospectral method serves as an effective tool to solve the reentry trajectory optimization for hypersonic vehicles. However, the traditional pseudospectral method is time-consuming due to large number of discretization points. For the purpose of autonomous and adaptive reentry guidance, the research herein presents a multistage trajectory control strategy based on the pseudospectral method, capable of dealing with the unexpected situations in reentry flight. The strategy typically includes two subproblems: the trajectory estimation and trajectory refining. In each processing stage, the proposed method generates a specified range of trajectory with the transition of the flight state. The full glide trajectory consists of several optimal trajectory sequences. The newly focused geographic constraints in actual flight are discussed thereafter. Numerical examples of free-space flight, target transition flight, and threat avoidance flight are used to show the feasible application of multistage pseudospectral method in reentry trajectory optimization.
We assessed the effectiveness and mechanism of action of Pecan oil on learning and memory and NF-κB levels in the hippocampus of rats after Morris water maze (MWM test). Pecan oil (200,400 or 800 mg/kg/d) were administered by intragavage once daily for 14 consecutive days. The Morris water maze test was used to evaluate the ability of Pecan oil to increase learning and memory impairment. The levels of NF-κB in hippocampus of rats were detected by Westernblot after MWM test. Compared to untreated controls (P<0.01), MWM could be prolonged after Pecan oil treatment (P<0.05 for low and intermediate dose groups). Westernblot analysis showed that the protein expression of NF-κB was decreased in different concentration Pecan oil(P<0.05 and P<0.01, respectively). The results suggest that Pecan oil is effective in improving the learning and memory in rats, the mechanism of which may be related NF-κB expression decreasing.
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