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语料库数据驱动的英语专业学生语义韵冲突研究 被引量:1
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作者 项名健 杨常新 《安徽工业大学学报(社会科学版)》 2011年第1期73-76,共4页
以happen和rather为关键词对我国学习者英语语料库英语专业子库进行检索,发现语义韵自身的特点、学习者词汇深度不够、语言输入不足以及母语的负迁移等,是产生语义韵冲突的主要原因。
关键词 英语专业 学生 语料库 语义韵 冲突
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Attitude Control Considering Variable Input Saturation Limit for a Spacecraft Equipped with Flywheels 被引量:6
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作者 TIAN Lin XU Shijie 《Chinese Journal of Aeronautics》 SCIE EI CSCD 2012年第3期437-445,共9页
A new attitude controller is proposed for spacecraft whose actuator has variable input saturation limit. There are three identical flywheels orthogonally mounted on board. Each rotor is driven by a brushless DC motor ... A new attitude controller is proposed for spacecraft whose actuator has variable input saturation limit. There are three identical flywheels orthogonally mounted on board. Each rotor is driven by a brushless DC motor (BLDCM). Models of spacecraft attitude dynamics and flywheel rotor driving motor electromechanics are discussed in detail. The controller design is similar to saturation limit linear assignment. An auxiliary parameter and a boundary coefficient are imported into the controller to guaran- tee system stability and improve control performance. A time-varying and state-dependent flywheel output torque saturation limit model is established. Stability of the closed-loop control system and asymptotic convergence of system states are proved via Lyapunov methods and LaSalle invariance principle. Boundedness of the auxiliary parameter ensures that the control objective can be achieved, while the boundary parameter's value makes a balance between system control performance and flywheel utilization efficiency. Compared with existing controllers, the newly developed controller with variable torque saturation limit can bring smoother control and faster system response. Numerical simulations validate the effectiveness of the controller. 展开更多
关键词 spacecraft attitude control variable input saturation limit Lyapunov methods flywheels brushless DC motor
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