Because of the obscurity of English preposition and the difficulties of acquisition of its abstract semantic knowledge,learners partly rely on frequently apperceived word co-occurrence(WCO)as collocational knowledge o...Because of the obscurity of English preposition and the difficulties of acquisition of its abstract semantic knowledge,learners partly rely on frequently apperceived word co-occurrence(WCO)as collocational knowledge of prepositions.This study will explore the role and scope of frequency-based learning and its relationship to L2 learners’performance on prepositions.The data suggest that,for all proficiency levels,frequency determines learners’ability to acquire preposition and show a growing dependence on collocational knowledge among lower English proficiency learners.The paper will further propose implications for instructing English prepositions to L2 learners at different levels.展开更多
Unit commitment (UC) is to determine the optimal unit status and generation level during each time interval of the scheduled period. The purpose of UC is to minimize the total generation cost while satisfying system d...Unit commitment (UC) is to determine the optimal unit status and generation level during each time interval of the scheduled period. The purpose of UC is to minimize the total generation cost while satisfying system demand, reserve requirements, and unit constraints. Among the UC constraints, an adequate provision of reserve is important to ensure the security of power system and the fast-response reserve is essential to bring system frequency back to acceptable level following the loss of an online unit within a few seconds. In this paper, the authors present and solve a UC problem including the frequency-based reserve constraints to determine the optimal FRR requirements and unit MW schedules. The UC problem is solved by using Lagrangian Relaxation-based approach and compared with the actual system schedules. It is observed that favorable reserve and unit MW schedules are obtained by the proposed method while the system security is maintained.展开更多
文摘Because of the obscurity of English preposition and the difficulties of acquisition of its abstract semantic knowledge,learners partly rely on frequently apperceived word co-occurrence(WCO)as collocational knowledge of prepositions.This study will explore the role and scope of frequency-based learning and its relationship to L2 learners’performance on prepositions.The data suggest that,for all proficiency levels,frequency determines learners’ability to acquire preposition and show a growing dependence on collocational knowledge among lower English proficiency learners.The paper will further propose implications for instructing English prepositions to L2 learners at different levels.
文摘Unit commitment (UC) is to determine the optimal unit status and generation level during each time interval of the scheduled period. The purpose of UC is to minimize the total generation cost while satisfying system demand, reserve requirements, and unit constraints. Among the UC constraints, an adequate provision of reserve is important to ensure the security of power system and the fast-response reserve is essential to bring system frequency back to acceptable level following the loss of an online unit within a few seconds. In this paper, the authors present and solve a UC problem including the frequency-based reserve constraints to determine the optimal FRR requirements and unit MW schedules. The UC problem is solved by using Lagrangian Relaxation-based approach and compared with the actual system schedules. It is observed that favorable reserve and unit MW schedules are obtained by the proposed method while the system security is maintained.
