| 1 | Saturated coordinated control of multiple underactuated unmanned surface vehicles over a closed curve显示文摘This paper presents a design method for saturated coordinated control of multiple underactuated unmanned surface vehicles(USVs) on a closed curve, holding a symmetric formation pattern. Each vehicle is subject to unknown sideslip, uncertain vehicle kinetics, and limited control torques. First, the course angle and surge velocity are considered as immediate signals to stabilize the along-track and cross-track path following errors. In the vehicle kinematics, a reduced-order extended state observer is utilized to compensate for the effect of the unknown sideslip. Next, a bounded neural network control law is constructed at the kinetic level with the aid of the a saturated function, a projection operator, and a dynamic surface design method. Finally, a parameter cyclic pursuit approach is presented to guarantee that the vehicles are evenly spaced over the closed curve for achieving a symmetric formation pattern. The input-to-state stability of the closed-loop system is analyzed via cascade theory. Comparative studies are given to show the effectiveness of the proposed method. | Lu LIU Dan WANG Zhouhua PENG Hugh H.T.LIU | 2017 | Science China(Information Sciences)2017，60，7： | 5 |
| 2 | Role of grain boundary character on Bi segregation-induced embrittlement in ultrahigh-purity copper显示文摘Bismuth(Bi),as an impurity element in copper and copper-based alloys,usually has a strong tendency of grain boundary(GB)segregation,which depends on the GB characters.However,the influence of such a segregation on the properties of ultrahigh-purity copper has been rarely reported and the exact structural arrangements of Bi atoms at different GBs remain largely unclear.In this study,we investigated the influ-ence of trace amounts of Bi(50-300 wt ppm)on the ductility of an ultrahigh-purity copper(99.99999%)in the range of room temperature to 900°C.The tensile results show that the addition of Bi seriously damages the ductility of the ultrahigh-purity copper at temperatures of 450-900°C,which is due to the GB segregation of Bi.On this basis,such a segregation behavior at different types of GBs,including high and low angle GBs(HAGBs/LAGBs),and twin boundaries(TBs),via the scanning electron microscope-electron backscattered diffraction(SEM-EBSD)and aberration-corrected scanning transmission electron microscope(AC-STEM)investigations,combined with the first-principles calculations were systematically studied.The atomistic characterizations demonstrate an anisotropic Bi segregation,where severe enrich-ment of Bi atoms typically occurs at the HAGBs,while the absence of Bi adsorption prevails at LAGBs or TBs.In particular,the segregated Bi at random HAGBs exhibited the directional bilayer adsorption,while the special symmetrical7 HAGB presented a unique Bi-rich cluster superstructure.Our findings pro-vide a comprehensive experimental and computational understanding on the atomic-scale segregation of impurities in metallic materials. | Y.X.Hua K.X.Song H.T.Liu J.W.Wang C.M.Zhang Y.J.Zhou B.Pang J.T.Song J.L.He H.L.Zhao | 2023 | Journal of Materials Science & Technology2023，，28： | 0 |
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