The high-voltage high-power press-packed IGBT(PPI)devices are the key component of the DC transmission apparatus.A PPI device is composed of several PPI submodules.In general,the PPI submodule works in a state of repe...The high-voltage high-power press-packed IGBT(PPI)devices are the key component of the DC transmission apparatus.A PPI device is composed of several PPI submodules.In general,the PPI submodule works in a state of repetitive turn-on and turn-off,and the corresponding working voltage is the positive periodic square waveform(PPSW)voltage,which is much different from the conventional AC or DC voltage.In addition,insulation capability is one of the most critical challenges in the design and fabrication of PPI devices.To improve the insulation capability of the device,composite insulation structures with multiple dielectrics are usually employed.Under the PPSW voltage,it is essential to analyze the transient electric field to solve the insulation challenge of the PPI devices.However,the electric field of the PPI is often calculated under the electrostatic field or DC field.Moreover,the transient characteristics of the electric field are ignored.Therefore,this paper focuses on the analysis of the transient characteristics of the electric field of the PPI submodule under the PPSW voltage.The influences of the waveform parameters of the PPSW voltage on the transient characteristics are demonstrated in detail.This study is significant for the insulation analysis and design of the PPIs.展开更多
In this paper, we prove the main result: Let both (K, S) and (K*, S*) be preordered fields, and let (K*, S*) be a finitely generated extension of (K, S). If K* is transcendental over K, then (K*, S*) has the weak Hilb...In this paper, we prove the main result: Let both (K, S) and (K*, S*) be preordered fields, and let (K*, S*) be a finitely generated extension of (K, S). If K* is transcendental over K, then (K*, S*) has the weak Hilbert property. This result answers negatively an open problem posed by the author in reference[1]. Moreover, some results on the weak Hilbert property are established. In this paper, we prove the main result: Let both (K, S) and (K*, S*) be preordered fields, and let (K*, S*) be a finitely generated extension of (K, S). If K* is transcendental over K, then (K*, S*) has the weak Hilbert property. This result answers negatively an open problem posed by the author in reference [1]. Moreover, some results on the weak Hilbert property are established.展开更多
The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data...The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered （CDO） state embedded with a few ferromagnetic （FM） metallic clusters to a charge-ordered （CO） state, corresponding to the transition from a high-temperature paramagnetic （PM） insulating state to a low-temperature antiferromagnetic （AF） insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.展开更多
基金This work was supported by the National Natural Science Foundation of China-State Grid Corporation Joint Fund for Smart Grid(No.U1766219)。
文摘The high-voltage high-power press-packed IGBT(PPI)devices are the key component of the DC transmission apparatus.A PPI device is composed of several PPI submodules.In general,the PPI submodule works in a state of repetitive turn-on and turn-off,and the corresponding working voltage is the positive periodic square waveform(PPSW)voltage,which is much different from the conventional AC or DC voltage.In addition,insulation capability is one of the most critical challenges in the design and fabrication of PPI devices.To improve the insulation capability of the device,composite insulation structures with multiple dielectrics are usually employed.Under the PPSW voltage,it is essential to analyze the transient electric field to solve the insulation challenge of the PPI devices.However,the electric field of the PPI is often calculated under the electrostatic field or DC field.Moreover,the transient characteristics of the electric field are ignored.Therefore,this paper focuses on the analysis of the transient characteristics of the electric field of the PPI submodule under the PPSW voltage.The influences of the waveform parameters of the PPSW voltage on the transient characteristics are demonstrated in detail.This study is significant for the insulation analysis and design of the PPIs.
基金Project supported by National Natural Science Foundation of China
文摘In this paper, we prove the main result: Let both (K, S) and (K*, S*) be preordered fields, and let (K*, S*) be a finitely generated extension of (K, S). If K* is transcendental over K, then (K*, S*) has the weak Hilbert property. This result answers negatively an open problem posed by the author in reference[1]. Moreover, some results on the weak Hilbert property are established. In this paper, we prove the main result: Let both (K, S) and (K*, S*) be preordered fields, and let (K*, S*) be a finitely generated extension of (K, S). If K* is transcendental over K, then (K*, S*) has the weak Hilbert property. This result answers negatively an open problem posed by the author in reference [1]. Moreover, some results on the weak Hilbert property are established.
基金Supported by the National Natural Science Foundation of China under Grant No 10334070. We would like to thank Professor Jin K. J. for her helpful discussion.
文摘The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered （CDO） state embedded with a few ferromagnetic （FM） metallic clusters to a charge-ordered （CO） state, corresponding to the transition from a high-temperature paramagnetic （PM） insulating state to a low-temperature antiferromagnetic （AF） insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.
