Generally,the conjugated homo-macrocycles(CHMs)are synthesized by covalently linking the repeating subunits.However,large subunits are often difficult to conjugate together due to severe stereo-hindrance.Meanwhile,lar...Generally,the conjugated homo-macrocycles(CHMs)are synthesized by covalently linking the repeating subunits.However,large subunits are often difficult to conjugate together due to severe stereo-hindrance.Meanwhile,large polyaromatic blocks can not only incorporate its appealing electronic and optical properties into CHMs but also distort the CHMs from planar to three-dimensional(3D)molecular structure.Here we synthesized the 3D CHM composed of large polyaromatic units by post-π-extension.Specifically,cyclo-m-phenylenes,as the cyclic precursor,wereπ-extended by C-C coupling and then subjected to dehydrocyclization,affording cyclo-1,3-dibenzo[e,l]pyrenylenes(CMDP).The structures of CMDPs were unambiguously characterized by single crystal X-ray diffraction,showing a congested and strained 3D conformation,which was also confirmed by theoretical calculations.Compared with the monomer,CMDPs showed redshifted absorption and emission,as well as a ten-fold enhancement in photoluminescence quantum yield,which could be attributed to their 3D conformation.展开更多
When a high-speed train approaches the insulated phase-splitting section embedded between neighbouring power supply arms,the vacuum circuit breaker(VCB)installed on trains must be disconnected to maintain the traction...When a high-speed train approaches the insulated phase-splitting section embedded between neighbouring power supply arms,the vacuum circuit breaker(VCB)installed on trains must be disconnected to maintain the traction power supply system as a no-load condition for completing phase-switching action,as the train passes through the phase-splitting section depending on its inertia.However,when operating VCBs,the arc is easily triggered between the mobile contacts inside,accompanied by an overvoltage impulse.Herein,to explore the generating mechanism of inrush current and operational overvoltage,a model describing the‘substation-catenary-train’traction power supply system is launched based on an equivalent circuit modelling technique.Through the analysis of the transient VCB operational process,the phase of catenary voltage is directly related to the characteristics of the VCB switching-on overvoltage,as the traction cur-rent's phase angle is relevant to the amplitude-frequency characteristics of the VCB switching-off overvoltage.Inrush current as a noteworthy element is related to the traction transformer's remanence.The automatic phase-switching technique is utilised to suppress both operational overvoltage and inrush current,as the optimal combination of VCB switching-on and switching-off phases considering the balance between overvoltage and inrush current is achieved based on the particle swarm algorithm.展开更多
基金This work was supported by the Ministry of Science and Technology of China(2017YFA0204902,2018YFA0209500)the National Natural Science Foundation of China(21771155,21721001)the Fundamental Research Funds for the Central Universities(20720180035).
文摘Generally,the conjugated homo-macrocycles(CHMs)are synthesized by covalently linking the repeating subunits.However,large subunits are often difficult to conjugate together due to severe stereo-hindrance.Meanwhile,large polyaromatic blocks can not only incorporate its appealing electronic and optical properties into CHMs but also distort the CHMs from planar to three-dimensional(3D)molecular structure.Here we synthesized the 3D CHM composed of large polyaromatic units by post-π-extension.Specifically,cyclo-m-phenylenes,as the cyclic precursor,wereπ-extended by C-C coupling and then subjected to dehydrocyclization,affording cyclo-1,3-dibenzo[e,l]pyrenylenes(CMDP).The structures of CMDPs were unambiguously characterized by single crystal X-ray diffraction,showing a congested and strained 3D conformation,which was also confirmed by theoretical calculations.Compared with the monomer,CMDPs showed redshifted absorption and emission,as well as a ten-fold enhancement in photoluminescence quantum yield,which could be attributed to their 3D conformation.
基金National Natural Science Foundation of China,Grant/Award Numbers:52277166,51922090,51837009。
文摘When a high-speed train approaches the insulated phase-splitting section embedded between neighbouring power supply arms,the vacuum circuit breaker(VCB)installed on trains must be disconnected to maintain the traction power supply system as a no-load condition for completing phase-switching action,as the train passes through the phase-splitting section depending on its inertia.However,when operating VCBs,the arc is easily triggered between the mobile contacts inside,accompanied by an overvoltage impulse.Herein,to explore the generating mechanism of inrush current and operational overvoltage,a model describing the‘substation-catenary-train’traction power supply system is launched based on an equivalent circuit modelling technique.Through the analysis of the transient VCB operational process,the phase of catenary voltage is directly related to the characteristics of the VCB switching-on overvoltage,as the traction cur-rent's phase angle is relevant to the amplitude-frequency characteristics of the VCB switching-off overvoltage.Inrush current as a noteworthy element is related to the traction transformer's remanence.The automatic phase-switching technique is utilised to suppress both operational overvoltage and inrush current,as the optimal combination of VCB switching-on and switching-off phases considering the balance between overvoltage and inrush current is achieved based on the particle swarm algorithm.
