Bring forward a new analytical method in order to evaluate the stability of the process of aluminum alloy pulsed MIG welding. The ratio of the first and the second peak in arc voltage signal probability density was se...Bring forward a new analytical method in order to evaluate the stability of the process of aluminum alloy pulsed MIG welding. The ratio of the first and the second peak in arc voltage signal probability density was selected to evaluate aluminum alloy pulse MIG welding stability. By calculating the arc voltage signal probability density from 80 sets of welding experiments, the ratio of the two peaks in arc voltage probability in every set was captured. And the evaluation system of aluminum alloy pulse MIG welding stability was established. The smaller the ratio of peaks in arc voltage signal probability density is, the better the stability of the welding will be;the bigger the ratio of peaks in arc voltage signal probability density is, the poorer the stability of the welding will be.展开更多
Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retr...Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retrospective planning study.Methods For a group of 9 patients diagnosed with left breast cancer,VMAT plan based on Agility MLC and beam modulator(BM) MLC were designed.The prescription dose was 50 Gy covering at least 95% of the planning target volume,2 Gy per fraction.TCPs were calculated according to dose-volume histogram(DVH) analysis.Results The TCP of the BM VMAT plan was slightly higher than that of the Agility VMAT plan(94.61% vs 94.23%) but was inferior with respect to delivery efficiency;the delivery time was reduced for Agility VMAT plan by 35% compared to BM VMAT plan.Conclusion For breast cancer radiation therapy after conservative surgery,BM VMAT plans provide slightly higher TCP while the delivery of Agility VMAT plans is significantly faster than the BM VMAT plans.展开更多
为提高500 k V线路绝缘子串并联间隙防雷的科学有效性,试制了500 k V线路5组不同结构参数绝缘子串并联间隙试品,在国网特高压交流试验基地对5组并联间隙试品的雷电冲击50%放电电压、伏秒特性及并联间隙疏导电弧有效性进行了研究,并分析...为提高500 k V线路绝缘子串并联间隙防雷的科学有效性,试制了500 k V线路5组不同结构参数绝缘子串并联间隙试品,在国网特高压交流试验基地对5组并联间隙试品的雷电冲击50%放电电压、伏秒特性及并联间隙疏导电弧有效性进行了研究,并分析了5组并联间隙试品电极和绝缘子串两端护套表面电场强度的最大值。结果表明:5组并联间隙试品雷电冲击50%放电电压及伏秒特性均能与绝缘子串形成良好绝缘配合;当绝缘子串高压、低压端并联间隙电极端部距绝缘子串中心线的横向伸出长度均为700 mm时,间隙雷电冲击失效起始电压最高,有效接闪导弧性能最好;五组绝缘子串并联间隙试品电极表面电场最大值均<26 k V/cm,绝缘子串两端护套表面电场最大值均<6 k V/cm,满足相关规程要求。因此,推荐500 k V线路绝缘子串高压、低压端并联间隙横向伸出长度均为700 mm为其优化的结构参数。展开更多
我国学者尝试在雷电活动强烈、污秽严重地区的110 k V架空线路应用复合材料绝缘杆,以提高相对地空气间隙距离和爬电距离。然而绝缘水平的提高,复合材料杆还是否需要架设避雷线以及避雷线接地引下线,是防雷面临的关键技术问题之一。针对...我国学者尝试在雷电活动强烈、污秽严重地区的110 k V架空线路应用复合材料绝缘杆,以提高相对地空气间隙距离和爬电距离。然而绝缘水平的提高,复合材料杆还是否需要架设避雷线以及避雷线接地引下线,是防雷面临的关键技术问题之一。针对典型110 k V复合材料杆,对比研究未架设避雷线的复合材料杆与架设避雷线的同电压等级、相同导线高度铁塔线路的雷电性能,考虑2种杆塔线路引雷能力、雷电冲击绝缘强度以及建弧率等因素的差异,发现:2种杆塔线路引雷能力间的差异可以忽略;未架设避雷线的复合材料杆雷电冲击绝缘强度是铁塔的3.5倍,建弧率为铁塔的53%,但是反击耐雷水平仅为24.5 k A,雷击跳闸率高达1.13次/(100 km?a),均明显劣于铁塔。据此,推荐110 k V复合材料杆架设避雷线。然后,对比估算避雷线不同接地方案下雷电性能的差异发现:避雷线若不经引下线接地,则复合材料杆雷电性能明显劣于铁塔,但若经引下线逐杆接地,则雷电性能显著优于铁塔。因此,提出避雷线应逐杆接地。综上所述,110 k V复合材料杆线路防雷接地方案应当采用架设避雷线,且通过金属引下线逐杆接地的设计。展开更多
文摘Bring forward a new analytical method in order to evaluate the stability of the process of aluminum alloy pulsed MIG welding. The ratio of the first and the second peak in arc voltage signal probability density was selected to evaluate aluminum alloy pulse MIG welding stability. By calculating the arc voltage signal probability density from 80 sets of welding experiments, the ratio of the two peaks in arc voltage probability in every set was captured. And the evaluation system of aluminum alloy pulse MIG welding stability was established. The smaller the ratio of peaks in arc voltage signal probability density is, the better the stability of the welding will be;the bigger the ratio of peaks in arc voltage signal probability density is, the poorer the stability of the welding will be.
基金Supported by a grant from the Innovation Project of the PLA Army General Hospital of China(No.2015-LC-18)
文摘Objective To compute and compare the tumor control probability(TCP) of volumetric modulated arc therapy(VMAT) for breast cancer after conservative surgery based on two types of multileaf collimator(MLC) through a retrospective planning study.Methods For a group of 9 patients diagnosed with left breast cancer,VMAT plan based on Agility MLC and beam modulator(BM) MLC were designed.The prescription dose was 50 Gy covering at least 95% of the planning target volume,2 Gy per fraction.TCPs were calculated according to dose-volume histogram(DVH) analysis.Results The TCP of the BM VMAT plan was slightly higher than that of the Agility VMAT plan(94.61% vs 94.23%) but was inferior with respect to delivery efficiency;the delivery time was reduced for Agility VMAT plan by 35% compared to BM VMAT plan.Conclusion For breast cancer radiation therapy after conservative surgery,BM VMAT plans provide slightly higher TCP while the delivery of Agility VMAT plans is significantly faster than the BM VMAT plans.
文摘为提高500 k V线路绝缘子串并联间隙防雷的科学有效性,试制了500 k V线路5组不同结构参数绝缘子串并联间隙试品,在国网特高压交流试验基地对5组并联间隙试品的雷电冲击50%放电电压、伏秒特性及并联间隙疏导电弧有效性进行了研究,并分析了5组并联间隙试品电极和绝缘子串两端护套表面电场强度的最大值。结果表明:5组并联间隙试品雷电冲击50%放电电压及伏秒特性均能与绝缘子串形成良好绝缘配合;当绝缘子串高压、低压端并联间隙电极端部距绝缘子串中心线的横向伸出长度均为700 mm时,间隙雷电冲击失效起始电压最高,有效接闪导弧性能最好;五组绝缘子串并联间隙试品电极表面电场最大值均<26 k V/cm,绝缘子串两端护套表面电场最大值均<6 k V/cm,满足相关规程要求。因此,推荐500 k V线路绝缘子串高压、低压端并联间隙横向伸出长度均为700 mm为其优化的结构参数。
文摘我国学者尝试在雷电活动强烈、污秽严重地区的110 k V架空线路应用复合材料绝缘杆,以提高相对地空气间隙距离和爬电距离。然而绝缘水平的提高,复合材料杆还是否需要架设避雷线以及避雷线接地引下线,是防雷面临的关键技术问题之一。针对典型110 k V复合材料杆,对比研究未架设避雷线的复合材料杆与架设避雷线的同电压等级、相同导线高度铁塔线路的雷电性能,考虑2种杆塔线路引雷能力、雷电冲击绝缘强度以及建弧率等因素的差异,发现:2种杆塔线路引雷能力间的差异可以忽略;未架设避雷线的复合材料杆雷电冲击绝缘强度是铁塔的3.5倍,建弧率为铁塔的53%,但是反击耐雷水平仅为24.5 k A,雷击跳闸率高达1.13次/(100 km?a),均明显劣于铁塔。据此,推荐110 k V复合材料杆架设避雷线。然后,对比估算避雷线不同接地方案下雷电性能的差异发现:避雷线若不经引下线接地,则复合材料杆雷电性能明显劣于铁塔,但若经引下线逐杆接地,则雷电性能显著优于铁塔。因此,提出避雷线应逐杆接地。综上所述,110 k V复合材料杆线路防雷接地方案应当采用架设避雷线,且通过金属引下线逐杆接地的设计。
