A new insulation system with inorganic A-B-A insulators was proposed to improve the surface flashover performance in vacuum. Inorganic A-B-A insulator samples of Mo/Al2O3 cermet-Al2O3 ceramic-Mo/Al2O3 cermet were prep...A new insulation system with inorganic A-B-A insulators was proposed to improve the surface flashover performance in vacuum. Inorganic A-B-A insulator samples of Mo/Al2O3 cermet-Al2O3 ceramic-Mo/Al2O3 cermet were prepared, in which the conductivity and permittivity of the Mo/Al2O3 cermets were controlled through different amount of metallic molybdenum powder added. The effects of both conductivity and permittivity of Mo/Al2O3 cermets on the DC and impulse surface flashover voltage in vacuum were experimentally investigated. The result showed that the DC and impulse surface flashover voltage were improved by 52% and 95%, respectively. For the distribution of electric field, two triple junctions, i.e., vacuum-layer A-cathode （TJ1） and vacuum-layer A-layer B （TJ2） were prepared with the introduction of layer A into the A-B-A insulation system. Based on the electric field distribution obtained via electrostatic field simulation and Maxwell-Wagner three-layer model, the electric field of T J1 decreases while that of T J2 increases with the increase in conductivity and permittivity of layer A under applied DC and impulse voltage, respectively. Therefore, the improvement of surface flashover performance of A-B-A insulators has been reasonably explained.展开更多
The transition to flowering marks the initiation of reproductive compete nee in plants. After the floral transit! on, the shoot apical meristem (SAM) ceases to produce leaf primordia and starts to gen erate floral pri...The transition to flowering marks the initiation of reproductive compete nee in plants. After the floral transit! on, the shoot apical meristem (SAM) ceases to produce leaf primordia and starts to gen erate floral primordia, the reproductive organs of plants. To maximize reproductive success, the timing of this transition needs to be precisely aligned with the most favorable environmental conditions (Blackman, 2017). Day length and cold temperature variations usually act as predictable seasonal signals to initiate flowering. However, due to the complexity of natural conditions, plants must gage a much wider array of information before committing to reproductive development. A striking example of this developmental plasticity is the drought escape (DE) response, where drought conditions experieneed during vegetative growth cause an accelerated flowering time compared with optimal watering conditio ns (Figure 1A). Among the strategies to cope with drought stress, DE may provide ephemeral plants like Arabidopsis with a simple "exit strategy" to anticipate seed set before drought conditions become incompatible with their survival.展开更多
基金supported by National Science Fund for Outstanding Young Scholars of China (No. 50625721)
文摘A new insulation system with inorganic A-B-A insulators was proposed to improve the surface flashover performance in vacuum. Inorganic A-B-A insulator samples of Mo/Al2O3 cermet-Al2O3 ceramic-Mo/Al2O3 cermet were prepared, in which the conductivity and permittivity of the Mo/Al2O3 cermets were controlled through different amount of metallic molybdenum powder added. The effects of both conductivity and permittivity of Mo/Al2O3 cermets on the DC and impulse surface flashover voltage in vacuum were experimentally investigated. The result showed that the DC and impulse surface flashover voltage were improved by 52% and 95%, respectively. For the distribution of electric field, two triple junctions, i.e., vacuum-layer A-cathode （TJ1） and vacuum-layer A-layer B （TJ2） were prepared with the introduction of layer A into the A-B-A insulation system. Based on the electric field distribution obtained via electrostatic field simulation and Maxwell-Wagner three-layer model, the electric field of T J1 decreases while that of T J2 increases with the increase in conductivity and permittivity of layer A under applied DC and impulse voltage, respectively. Therefore, the improvement of surface flashover performance of A-B-A insulators has been reasonably explained.
文摘The transition to flowering marks the initiation of reproductive compete nee in plants. After the floral transit! on, the shoot apical meristem (SAM) ceases to produce leaf primordia and starts to gen erate floral primordia, the reproductive organs of plants. To maximize reproductive success, the timing of this transition needs to be precisely aligned with the most favorable environmental conditions (Blackman, 2017). Day length and cold temperature variations usually act as predictable seasonal signals to initiate flowering. However, due to the complexity of natural conditions, plants must gage a much wider array of information before committing to reproductive development. A striking example of this developmental plasticity is the drought escape (DE) response, where drought conditions experieneed during vegetative growth cause an accelerated flowering time compared with optimal watering conditio ns (Figure 1A). Among the strategies to cope with drought stress, DE may provide ephemeral plants like Arabidopsis with a simple "exit strategy" to anticipate seed set before drought conditions become incompatible with their survival.
