Due to the covert nature of the listening process, English listening comprehension has become a demanding challenge for most EFL learners in China. Strategy-based listening instruction, with its more accurate insight ...Due to the covert nature of the listening process, English listening comprehension has become a demanding challenge for most EFL learners in China. Strategy-based listening instruction, with its more accurate insight into the listening process, could be one of the timely answers to the challenges facing Chinese EFL listeners. Starting with a comprehensive review of theories and studies on strategy-based listening instruction in recent Western academia, the current paper critically examined the possible advantages and the theoretical and practical limitations of strategy-based listening instruction.展开更多
An adaptive dynamic vibration absorber(ADVA)is designed for lowfrequency vibration suppression.The leaf springs are applied as the tuning stiffness elements.The principle of variable stiffness is analyzed to obtain th...An adaptive dynamic vibration absorber(ADVA)is designed for lowfrequency vibration suppression.The leaf springs are applied as the tuning stiffness elements.The principle of variable stiffness is analyzed to obtain the effective range of the first natural frequency variation.A classic simply supported manipulator is selected as the controlled system.The coupled dynamic model of the manipulator-ADVA system is built to obtain the maximum damping efficiency and the vibration absorption capacity of the designed ADVA.An experimental platform is set up to verify the theoretical results.It is revealed that the ADVA can adjust the first natural frequency on a large scale by changing the curvature of the leaf springs.The amplitude of the manipulator is reduced obviously with the installation of the designed ADVA.Finally,based on the short-time Fourier transformation(STFT),a stepwise optimization algorithm is proposed to achieve a quick tuning of the natural frequency of the ADVA so that it can always coincide with the frequency of the prime structure.Through the above steps,the intelligent frequency tuning of the ADVA is realized with high vibration absorption performance in a wide frequency range.展开更多
文摘Due to the covert nature of the listening process, English listening comprehension has become a demanding challenge for most EFL learners in China. Strategy-based listening instruction, with its more accurate insight into the listening process, could be one of the timely answers to the challenges facing Chinese EFL listeners. Starting with a comprehensive review of theories and studies on strategy-based listening instruction in recent Western academia, the current paper critically examined the possible advantages and the theoretical and practical limitations of strategy-based listening instruction.
基金supported by the National Natural Science Foundation of China(Nos.11772010 and 11832002)the State Key Laboratory of Mechanical System and Vibration of China(No.MSV202004)。
文摘An adaptive dynamic vibration absorber(ADVA)is designed for lowfrequency vibration suppression.The leaf springs are applied as the tuning stiffness elements.The principle of variable stiffness is analyzed to obtain the effective range of the first natural frequency variation.A classic simply supported manipulator is selected as the controlled system.The coupled dynamic model of the manipulator-ADVA system is built to obtain the maximum damping efficiency and the vibration absorption capacity of the designed ADVA.An experimental platform is set up to verify the theoretical results.It is revealed that the ADVA can adjust the first natural frequency on a large scale by changing the curvature of the leaf springs.The amplitude of the manipulator is reduced obviously with the installation of the designed ADVA.Finally,based on the short-time Fourier transformation(STFT),a stepwise optimization algorithm is proposed to achieve a quick tuning of the natural frequency of the ADVA so that it can always coincide with the frequency of the prime structure.Through the above steps,the intelligent frequency tuning of the ADVA is realized with high vibration absorption performance in a wide frequency range.
