We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state...We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated.It is found that the cavity optomechanical system can be modulated to different topological Su–Schrieffer–Heeger(SSH)phases via designing the optomechanical couplings legitimately.Meanwhile,combining the effective optomechanical couplings and the probability distributions of gap states,we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields.Moreover,we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.展开更多
We theoretically investigate the periodically modulated interaction effect on the propagation properties of a traveling plane wave in a Bose–Einstein condensate(BEC) trapped in a deep annular lattice with local defec...We theoretically investigate the periodically modulated interaction effect on the propagation properties of a traveling plane wave in a Bose–Einstein condensate(BEC) trapped in a deep annular lattice with local defects both analytically and numerically. By using the two-mode ansatz and the tight-binding approximation, a critical condition for the system preserving the superfluidity is obtained analytically and confirmed numerically. We find that the coupled effects of periodic modulated atomic interactions, the quasi-momentum of the plane wave, and the defect can control the superfluidity of the system. Particularly, when we consider the periodic modulation in the system with single defect, the critical condition for the system entering the superfluid regime depends on both the defect and the momentum of the plane wave. This is different from the case for the system without the periodic modulation, where the critical condition is only determined by the defect. The modulation and quasi-momentum of the plane wave can enhance the system entering the superfluid regime. Interestingly, when the modulated amplitude/frequency, the defect strength, and the quasi-momentum of the plane wave satisfy a certain condition, the system will always be in the superfluid region. This engineering provides a possible means for studying the periodic modulation effect on propagation properties and the corresponding dynamics of BECs in disordered optical lattices.展开更多
We report polarization reversal periodically controlled by the electric field in multiferroic MnWO_(4) with a pulsed field up to 52 T.The electric polarization cannot be reversed by successive opposite electric fields...We report polarization reversal periodically controlled by the electric field in multiferroic MnWO_(4) with a pulsed field up to 52 T.The electric polarization cannot be reversed by successive opposite electric fields in low magnetic fields(<14 T)at 4.2 K,whereas polarization reversal is directly achieved by two opposite electric fields under high magnetic fields(<45 T).Interestingly,the polarization curve of rising and falling fields for H∥u(magnetic easy axis)is irreversible when the magnetic field is close to 52 T.In this case,the rising and falling polarization curves can be individually reversed by the electric field,and thus require five cycles to recover to the initial condition by the order of the applied electric fields(+E,-E,-E,+E,+E).In addition,we find that ferroelectric phaseⅣcan be tuned from parallel to antiparallel in relation to ferroelectric phase AF2 by applying a magnetic field approximated to the c axis.展开更多
To satisfy the requirement of developing a new generation of motorized treadmill for a famous domestic manufacturer, a brushless DC motor （BLDCM） driving and control system for motorized treadmill is developed. High...To satisfy the requirement of developing a new generation of motorized treadmill for a famous domestic manufacturer, a brushless DC motor （BLDCM） driving and control system for motorized treadmill is developed. High integration and reliability of this system are ensured under the condition that intelligent power module （IPM） is used and the protection module is included. Periodic current control method is applied to reduce the average current flowing through the armature winding of the motor when the treadmill is required to start with low speed while large load is added. Piecewise proportion-integration-differentiation （PID） control algorithm is applied to solve the problem of speed fluctuation when impulse load is added. The motorized treadmill of a new generation with the driving and control system has the advantages of high reliability, good speed stability, wide timing scope, low cost, and long life-span. And it is very promising for practical applications.展开更多
先进绝热压缩空气储能(advanced adiabatic compressed air energy storage,AA-CAES)具备天然的热电联供特性,能够有效缓解供热期出现的弃风问题。若能在规划阶段充分考虑运行需求,进而合理地配置储能容量,则能够在解决弃风问题的前提下...先进绝热压缩空气储能(advanced adiabatic compressed air energy storage,AA-CAES)具备天然的热电联供特性,能够有效缓解供热期出现的弃风问题。若能在规划阶段充分考虑运行需求,进而合理地配置储能容量,则能够在解决弃风问题的前提下,最大程度对燃煤机组进行清洁替代。为此,该文提出了多热源协同互补的AA-CAES系统容量配置模型。首先本模型在能量输入端引入电锅炉预热压缩机入口空气,以增大压缩机输气系数并提高机组产热量;其次在扩展热源端,通过太阳能反射镜场收集光热,以提高系统储热水平;并在计及储能系统各模块实际运行效率约束之余,以运行总成本最小为目标,计算储能容量配置最优解。再次,分析供热时长及环境温度等因素对投资成本回收年限的影响,并计算不同情况下本模型投资成本的回收年限,得出建设本模型可盈利的硬性条件;最后,基于东北某地区供热期及非供热期典型日负荷及气象数据在IEEE-39节点系统完成算例分析,验证所提模型有效性。展开更多
基金the National Natural Science Foundation of China(Grant Nos.61822114,12074330,and 62071412)。
文摘We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated.It is found that the cavity optomechanical system can be modulated to different topological Su–Schrieffer–Heeger(SSH)phases via designing the optomechanical couplings legitimately.Meanwhile,combining the effective optomechanical couplings and the probability distributions of gap states,we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields.Moreover,we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11764039,11475027,11865014,11305132,and 11274255)the Natural Science Foundation of Gansu Province,China(Grant No.17JR5RA076)the Scientific Research Project of Gansu Higher Education,China(Grant No.2016A-005)
文摘We theoretically investigate the periodically modulated interaction effect on the propagation properties of a traveling plane wave in a Bose–Einstein condensate(BEC) trapped in a deep annular lattice with local defects both analytically and numerically. By using the two-mode ansatz and the tight-binding approximation, a critical condition for the system preserving the superfluidity is obtained analytically and confirmed numerically. We find that the coupled effects of periodic modulated atomic interactions, the quasi-momentum of the plane wave, and the defect can control the superfluidity of the system. Particularly, when we consider the periodic modulation in the system with single defect, the critical condition for the system entering the superfluid regime depends on both the defect and the momentum of the plane wave. This is different from the case for the system without the periodic modulation, where the critical condition is only determined by the defect. The modulation and quasi-momentum of the plane wave can enhance the system entering the superfluid regime. Interestingly, when the modulated amplitude/frequency, the defect strength, and the quasi-momentum of the plane wave satisfy a certain condition, the system will always be in the superfluid region. This engineering provides a possible means for studying the periodic modulation effect on propagation properties and the corresponding dynamics of BECs in disordered optical lattices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12074135,12104388,and 52272219)Nanyang Normal University,the Natural Science Foundation of Henan Province (Grant Nos.222300420255 and 232300421220)the Key Scientific and Technological Projiect of Technology Depeartment of Henan Province of China (Grant Nos.222102230105 and 212102210448)。
文摘We report polarization reversal periodically controlled by the electric field in multiferroic MnWO_(4) with a pulsed field up to 52 T.The electric polarization cannot be reversed by successive opposite electric fields in low magnetic fields(<14 T)at 4.2 K,whereas polarization reversal is directly achieved by two opposite electric fields under high magnetic fields(<45 T).Interestingly,the polarization curve of rising and falling fields for H∥u(magnetic easy axis)is irreversible when the magnetic field is close to 52 T.In this case,the rising and falling polarization curves can be individually reversed by the electric field,and thus require five cycles to recover to the initial condition by the order of the applied electric fields(+E,-E,-E,+E,+E).In addition,we find that ferroelectric phaseⅣcan be tuned from parallel to antiparallel in relation to ferroelectric phase AF2 by applying a magnetic field approximated to the c axis.
文摘To satisfy the requirement of developing a new generation of motorized treadmill for a famous domestic manufacturer, a brushless DC motor （BLDCM） driving and control system for motorized treadmill is developed. High integration and reliability of this system are ensured under the condition that intelligent power module （IPM） is used and the protection module is included. Periodic current control method is applied to reduce the average current flowing through the armature winding of the motor when the treadmill is required to start with low speed while large load is added. Piecewise proportion-integration-differentiation （PID） control algorithm is applied to solve the problem of speed fluctuation when impulse load is added. The motorized treadmill of a new generation with the driving and control system has the advantages of high reliability, good speed stability, wide timing scope, low cost, and long life-span. And it is very promising for practical applications.
文摘先进绝热压缩空气储能(advanced adiabatic compressed air energy storage,AA-CAES)具备天然的热电联供特性,能够有效缓解供热期出现的弃风问题。若能在规划阶段充分考虑运行需求,进而合理地配置储能容量,则能够在解决弃风问题的前提下,最大程度对燃煤机组进行清洁替代。为此,该文提出了多热源协同互补的AA-CAES系统容量配置模型。首先本模型在能量输入端引入电锅炉预热压缩机入口空气,以增大压缩机输气系数并提高机组产热量;其次在扩展热源端,通过太阳能反射镜场收集光热,以提高系统储热水平;并在计及储能系统各模块实际运行效率约束之余,以运行总成本最小为目标,计算储能容量配置最优解。再次,分析供热时长及环境温度等因素对投资成本回收年限的影响,并计算不同情况下本模型投资成本的回收年限,得出建设本模型可盈利的硬性条件;最后,基于东北某地区供热期及非供热期典型日负荷及气象数据在IEEE-39节点系统完成算例分析,验证所提模型有效性。
