期刊文献+
共找到25,745篇文章
< 1 2 250 >
每页显示 20 50 100
Weld Seam Deviation Prediction of Gas Metal Arc Welding Based on Arc Sound Signal 认领
1
作者 Wang Zhao Jianfeng Yue +1 位作者 Wenji Liu Haihua Liu 《世界工程和技术(英文)》 2021年第1期51-59,共9页
Weld seam deviation prediction is the key to weld seam tracking control, which is of great significance for realizing welding automation and ensuring welding quality. Aiming at the problem of weld seam deviation predi... Weld seam deviation prediction is the key to weld seam tracking control, which is of great significance for realizing welding automation and ensuring welding quality. Aiming at the problem of weld seam deviation prediction in GMAW</span><span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">(gas metal arc welding), a method of weld seam deviation prediction based on arc sound signal is proposed. By analyzing the feature of the arc sound signal waveform, the time domain feature of the arc sound signal is extracted. The wavelet packet analysis method is used to analyze the time-fre</span><span style="font-family:Verdana;">- </span><span style="font-family:Verdana;">quency domain feature of the arc sound signal, and the wavelet packet energy feature </span><span style="font-family:Verdana;">is</span><span style="font-family:Verdana;"> extracted. The time domain feature and wavelet packet energy feature are used to establish the feature vector, and the BP (back propagation) neural network is used to realize the weld seam deviation prediction. The results show that the method proposed in this paper has a good weld seam deviation prediction effect, with a mean absolute error of 0.234</span><span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">mm, which provides a new method for GMAW weld seam recognition. 展开更多
关键词 Weld Seam Deviation GMAW Arc Sound BP Neural Network
在线阅读 免费下载
基于多重雷击防护的爆轰气流灭弧机理研究 认领
2
作者 王国锋 《电测与仪表》 北大核心 2021年第1期84-90,共7页
当多重雷击连续向输电线路放电时,将会对电网安全稳定运行造成严重打击,雷击跳闸事故会造成重大的安全隐患与经济损失。由于目前对多重雷击的防护存在空白,故提出了一种通过雷电诱导爆轰气流的灭弧防雷装置,实现对多重雷击重复建弧防护... 当多重雷击连续向输电线路放电时,将会对电网安全稳定运行造成严重打击,雷击跳闸事故会造成重大的安全隐患与经济损失。由于目前对多重雷击的防护存在空白,故提出了一种通过雷电诱导爆轰气流的灭弧防雷装置,实现对多重雷击重复建弧防护的全覆盖。先对灭弧原理进行了简单分析论证;建立了数学模型,对爆轰气流在灭弧筒内的作用效果进行分析计算;提出了多重雷击模型,并用fluent仿真软件对气流与电弧的耦合过程进行模拟;最后通过实验验证装置对多重雷击防护的可靠性。结果表明:爆轰气流能在0.5L的刚性空间内维持5.65 MPa的强气压2.64 ms;电弧能在气流正压作用时间内可靠熄灭,且未发生重燃,有效抑制了多重雷击下的重复建弧。 展开更多
关键词 多重雷击 爆轰气流 电弧 重复建弧 灭弧筒
在线阅读 免费下载
文章速递Effects of different atmospheres on the arc erosion behaviors of Ti_(3)SiC_(2)cathodes 认领
3
作者 ZHOU ZiJue FENG Yi +4 位作者 ZHAO Hao QIAN Gang ZHANG JingCheng ZHANG XueBin HUANG XiaoChen 《中国科学:技术科学英文版》 SCIE EI CAS CSCD 2021年第3期620-628,共9页
The effects of ambient atmospheres on the arc erosion behaviors of Ti_(3)SiC_(2)cathodes were investigated at 5.5 kV in argon,nitrogen,air,and oxygen.The mass loss of the cathodes increased in the order of argon,nitro... The effects of ambient atmospheres on the arc erosion behaviors of Ti_(3)SiC_(2)cathodes were investigated at 5.5 kV in argon,nitrogen,air,and oxygen.The mass loss of the cathodes increased in the order of argon,nitrogen,air,and oxygen and the morphologies were measured by 3D laser scanning confocal microscope with a gradual blooming phenomenon.Raman spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy were employed to detect the components of erosion regions.The erosion-chemical products mainly consisted of TiNx in nitrogen,TiN_(x),TiO_(2)and SiO_(2)in air,TiO_(2)and SiO_(2)in oxygen.The arc energy was responsible for the arc erosion characteristics in different atmospheres. 展开更多
关键词 Ti_(3)SiC_(2) atmosphere arc erosion
252 kV及以上断路器短路试验中SF_(6)气体分解产物特性研究 认领
4
作者 张长虹 王昊 +5 位作者 杨旭 黎卫国 黄忠康 刘广义 彭翔 袁明正 《高压电器》 CAS 北大核心 2021年第3期166-171,共6页
以SF_(6)气体为灭弧介质的高压交流断路器广泛应用于我国220 kV及以上电力系统中,开断短路电流后,灭弧室内SF_(6)会分解产生SO_(2)、CF_(4)、CS_(2)、SOF_(2)等气体,对断路器的开断性能产生影响。文中对多台高压交流断路器开展短路开断... 以SF_(6)气体为灭弧介质的高压交流断路器广泛应用于我国220 kV及以上电力系统中,开断短路电流后,灭弧室内SF_(6)会分解产生SO_(2)、CF_(4)、CS_(2)、SOF_(2)等气体,对断路器的开断性能产生影响。文中对多台高压交流断路器开展短路开断试验,对断路器内部气体进行检测,研究了不同电压等级断路器及不同短路试验方式与SF_(6)气体分解产物之间的关系。 展开更多
关键词 断路器 SF_(6)气体分解产物 短路开断试验 电弧
工艺参数对Al-Si合金CMT增材制造组织和力学性能的影响 认领
5
作者 王立伟 武子琴 +2 位作者 胡虎安 陈圣龙 朱晋良 《沈阳大学学报:自然科学版》 CAS 2021年第1期1-9,共9页
通过设置不同的层间停留时间、送丝速度和增材速度,对增材制造单道多层的直壁墙试样进行了金相、硬度和拉伸试验,在平行和垂直于增材2个方向上研究了工艺参数对Al-Si合金CMT增材制造组织和力学性能的影响.结果表明:在层间停留时间为60 s... 通过设置不同的层间停留时间、送丝速度和增材速度,对增材制造单道多层的直壁墙试样进行了金相、硬度和拉伸试验,在平行和垂直于增材2个方向上研究了工艺参数对Al-Si合金CMT增材制造组织和力学性能的影响.结果表明:在层间停留时间为60 s时,得到的微观组织最好,多为等轴晶;随送丝速度的增大,晶粒逐渐变大;随增材速度的增大,晶粒逐渐变小.送丝速度为3和4 m·min-1时,硬度较高,当送丝速度为4 m·min-1和增材速度为50 cm·min-1时,平行和垂直于增材2个方向上的抗拉强度和延伸率的差异最小,这时断口表面有很多深浅形状不一的韧窝,接头具有较好的塑性,断裂方式为韧性断裂.因此,Al-Si合金CMT增材制造较优的工艺参数为:层间停留时间为60 s,送丝速度为4 m·min-1,增材速度为50 cm·min-1. 展开更多
关键词 AL-SI合金 CMT增材制造 电弧 微观组织 力学性能
在线阅读 下载PDF
电弧等离子体干法除鳞的开放实验设计 认领
6
作者 汤中亮 张晓波 +2 位作者 李兵 高超 李强 《廊坊师范学院学报:自然科学版》 2021年第1期46-49,共4页
材料类专业开放实验可以将实践操作与所学的理论知识联系,强调学生的主导作用,充分调动他们的学习积极性。电弧等离子体干法除鳞的开放实验,通过改变实验参数研究电弧除鳞速率的变化;通过SEM、XRD对除鳞前后样品表面形貌及物相的表征,... 材料类专业开放实验可以将实践操作与所学的理论知识联系,强调学生的主导作用,充分调动他们的学习积极性。电弧等离子体干法除鳞的开放实验,通过改变实验参数研究电弧除鳞速率的变化;通过SEM、XRD对除鳞前后样品表面形貌及物相的表征,对电弧除鳞的效果进行评价。设计实验以及对结果的分析培养了学生的科学思维和独立思考的能力。在具体的实验操作中,学生的动手能力也得到充分的锻炼。 展开更多
关键词 材料类专业 开放实验 电弧 除鳞
在线阅读 下载PDF
Adakite-like granitoids of Songkultau:A relic of juvenile Cambrian arc in Kyrgyz Tien Shan 认领
7
作者 D.Konopelko R.Seltmann +4 位作者 A.Dolgopolova I.Safonova S.Glorie J.De Grave M.Sun 《地学前缘:英文版》 SCIE CAS 2021年第1期147-160,共14页
The early Paleozoic Terskey Suture zone,located in the southern part of the Northern Tien Shan domain in Kyrgyzstan,comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deepmarin... The early Paleozoic Terskey Suture zone,located in the southern part of the Northern Tien Shan domain in Kyrgyzstan,comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deepmarine sediments.In the Lake Songkul area,early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites(SiO2>56 wt.%,Al2O3>15 wt.%,Na2 O>3.5 wt.%and high Sr/Y and La/Yb ratios).The Songkultau granitoids have positive initialεNd(+3.8 to+6.4)andεHf(+12.3 to+13.5)values indicating derivation from sources with MORB-like isotopic signature.Volcanic formations,surrounding the Songkultau intrusion,have geochemical affinities varying from ocean floor to island arc series.This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust.An age of 505 Ma,obtained for the Songkultau intrusion,shows that hot subduction under the Northern Tien Shan continued until middle Cambrian.The primitive arc complexes were obducted onto the Northern Tien Shan domain,where the Andean type continental magmatic arc developed in Cambrian and Ordovician.Formation of the Andean type arc was accompanied by uplift,erosion and deposition of coarse clastic sediments.A depositional age of ca.470 Ma,obtained for the gravellites in the Lake Songkul area,is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan,and corresponds to the main phase of the Andean type magmatism.The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan.On a regional scale this primitive arc can be compared with juvenile Cambrian 展开更多
关键词 Northern Tien Shan(Tianshan) Terskey suture ADAKITE Cambrian juvenile arc
在线阅读 下载PDF
Hermitian geometry on the resolvent set(Ⅱ) 认领
8
作者 Ronald G.Douglas Rongwei Yang 《中国科学:数学英文版》 SCIE 2021年第2期385-398,共14页
For an element A in a unital C^(*)-algebra B,the operator-valued 1-formωA(z)=(z-A)^(-1) dz is analytic on the resolvent setρ(A),which plays an important role in the functional calculus of A.This paper defines a clas... For an element A in a unital C^(*)-algebra B,the operator-valued 1-formωA(z)=(z-A)^(-1) dz is analytic on the resolvent setρ(A),which plays an important role in the functional calculus of A.This paper defines a class of Hermitian metrics onρ(A)through the coupling of the operator-valued(1,1)-formΩA=-ωA^(*)∧ωA with tracial and vector states.Its main goal is to study the connection between A and the properties of the metric concerning curvature,arc length,completeness and singularity.A particular example is when A is quasi-nilpotent,in which case the metric lives on the punctured complex plane C\{0}.The notion of the power set is defined to gauge the"blow-up"rate of the metric at 0,and examples are given to indicate a likely link with A’s hyper-invariant subspaces. 展开更多
关键词 C^(*)-algebra Hermitian metric CURVATURE arc length Fuglede-Kadison determinant quasi-nilpotent operator power set
受电弓通过分段绝缘器时电弧转移特性研究 认领
9
作者 陈少昆 景所立 +2 位作者 林光华 李成坤 段绪伟 《电器与能效管理技术》 2020年第3期14-22,共9页
受电弓通过分段绝缘器时,往往会产生电弧,且由于分段绝缘器两端数千伏高压,电弧往往难以熄灭,电弧转移时间过长将对分段绝缘器造成烧蚀损伤,影响铁路安全运营。分段绝缘器中电弧的转移以及弧根的演变对其燃弧、熄弧性能有重要影响。基... 受电弓通过分段绝缘器时,往往会产生电弧,且由于分段绝缘器两端数千伏高压,电弧往往难以熄灭,电弧转移时间过长将对分段绝缘器造成烧蚀损伤,影响铁路安全运营。分段绝缘器中电弧的转移以及弧根的演变对其燃弧、熄弧性能有重要影响。基于磁流体动力学理论(MHD),建立了受电弓过分段绝缘器空气电弧数学模型,研究了不同招弧角角度电弧转移过程,分析了转移过程气流场、电磁力、温度场以及电弧电压的变化,得到了受电弓过分段绝缘器弧根转移的根本原因。研究表明:随着招弧角增大,电弧转移速度呈现先增大后减小趋势;此外,角度增大使得电极间距变小,降低了电弧拉弧能力,最终得出60°为招弧角最优解。 展开更多
关键词 分段绝缘器 电弧 弧根运动 电弧演变 温度场
在线阅读 下载PDF
Numerical analysis of typical droplets transfer mode in wire and arc additive manufacture process 认领 被引量:1
10
作者 潘家敬 何锡鑫 +3 位作者 赵朋成 何燕 刘冰 郭怀志 《中国焊接:英文版》 EI CAS 2020年第3期44-53,共10页
A two-dimensional model was established for the first time by coupling moving wire and arc in CMT-WAAM and GMAWWAAM process,revealing the temperature,potential and droplet transition behavior of droplet metal.The drop... A two-dimensional model was established for the first time by coupling moving wire and arc in CMT-WAAM and GMAWWAAM process,revealing the temperature,potential and droplet transition behavior of droplet metal.The droplet transition and the change of droplet transfer mode under different wire feeding speed were analyzed.The experiments and numerical simulation research found that droplet transition mode is projected transfer in GMAW-WAAM process under 150 A current,with a complete transition period is 14 ms.The droplet transition shows a short-circuit transition mode in CMT-WAAM process,with wire feeding speed of 5.5 m/min and a complete transition period is 20 ms.The droplet transition shows a mixture of droplet transfer and short-circuit transition mode in CMT-WAAM process,with wire feeding speed of 5.5 m/min and a complete transition period is 23 ms.Based on the theoretical research and experimental studies,the mechanism of droplet transfer mode in WAAM was studied,which can provide reference for optimizing parameters. 展开更多
关键词 gas metal arc welding cold metal transition droplet transfer arc temperature arc shape
在线阅读 下载PDF
Properties of intermediate-frequency vacuum arc in sinusoidal curved contact and butt contact 认领
11
作者 佟子昂 武建文 +1 位作者 金巍 陈均 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2020年第2期29-37,共9页
In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at ... In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at intermediate frequency(360-800 Hz)was conducted and the results were compared with a butt contact with the same contact diameter(41 mm)and the same material.By analyzing the arc behavior,arc voltage characteristics,arc energy,current interrupting capacity,ablation of the anode contact and condensation of the arc products at a 3 mm gap,the differences in their vacuum arc characteristics were determined.The correlations of their arc energy with the amplitude and the frequency of the current were also achieved.Analysis suggests that the ruled curved contact has strong application potentiality because of its low arc energy,low arc voltage noise and arc voltage peak,light ablation on the surface of the anode contact and high interrupting capacity. 展开更多
关键词 sinusoidal curved surface INTERMEDIATE FREQUENCY voltage characteristics ARC energy VACUUM ARC properties ARC behavior
电弧伤害机理及其防护服装测评技术研究现状 认领
12
作者 朱雯 唐虹 +1 位作者 张成蛟 薛霜 《棉纺织技术》 CAS 北大核心 2020年第7期75-78,共4页
探讨电弧伤害机理及防护服装测评技术的研究现状。介绍了电弧发生机理和电弧形式。重点阐述了电弧闪光测试技术研究现状和服装防护性能测试方法。指出:今后对于电弧入射能量模型的预测将应考虑电弧运动形式、实际作业设备等不可量化的因... 探讨电弧伤害机理及防护服装测评技术的研究现状。介绍了电弧发生机理和电弧形式。重点阐述了电弧闪光测试技术研究现状和服装防护性能测试方法。指出:今后对于电弧入射能量模型的预测将应考虑电弧运动形式、实际作业设备等不可量化的因素;同时,应针对各种电弧形式的服装防护性能测试方法进行研究。认为:建立多种电弧形式下的测试方法势在必行;服装整体系统以及人体动作姿势对防护服防护性能的影响将成为未来的研究方向。 展开更多
关键词 电弧 电弧形式 电弧防护服 电弧机理 电弧入射能量 电弧燃爆 测评技术
在线阅读 下载PDF
开关柜弧光短路引发机组停机故障分析及防范 认领
13
作者 张建军 关延伟 马其汉 《电工技术》 2020年第13期62-64,共3页
针对一起中压开关柜弧光短路引发350 MW发电机组停机故障进行分析,认为开关柜手车B相动触头固定螺栓松动,导致手车推入时未对中,造成动静触头接触不良,在开关合闸过程中因启动电流较大,动静触头间产生电弧,同时相间绝缘距离不足导致三... 针对一起中压开关柜弧光短路引发350 MW发电机组停机故障进行分析,认为开关柜手车B相动触头固定螺栓松动,导致手车推入时未对中,造成动静触头接触不良,在开关合闸过程中因启动电流较大,动静触头间产生电弧,同时相间绝缘距离不足导致三相弧光短路,现有继电保护方式无法有效及时切断故障,6 kV段母线电压突降,最终导致机组停机故障,最后给出了相应的防范措施。 展开更多
关键词 开关柜 电弧 弧光短路
在线阅读 免费下载
探讨Arc GIS在计算区域水资源量中的应用 认领
14
作者 刘武 《水利科学与寒区工程》 2020年第4期153-154,共2页
本文主要通过Arc GIS自带Arc Toolbox中的分析工具,利用分割、联合功能,对计算单元的面积进行了快速批量计算,探讨结合面径流深进行区域水资源量计算。通过对区域资源量的快速计算,节省资源量量算工作时间,提高了工作效率及资源量计算... 本文主要通过Arc GIS自带Arc Toolbox中的分析工具,利用分割、联合功能,对计算单元的面积进行了快速批量计算,探讨结合面径流深进行区域水资源量计算。通过对区域资源量的快速计算,节省资源量量算工作时间,提高了工作效率及资源量计算精确度,为各级水行政主管部门重大决策提供了及时、有效的数据支撑。 展开更多
关键词 水资源量 Arc GIS Arc Toolbox分割 联合
在线阅读 下载PDF
基于MAXENT模型和Arc GIS预测蜡梅适生域在中国的潜在分布 认领
15
作者 秦思思 颜玉娟 欧阳晟 《生态科学》 CSCD 2020年第3期49-56,共8页
蜡梅(Chimonanthus praecox)是我国二级濒危珍稀植物,是重要的冬季传统观花植物。利用已报道的246个分布点和worldclim中提取的19个气候因子,基于最大熵(Maxent)模型和地理信息系统(Arc Gis)对蜡梅在中国的潜在适生区分布进行预测分析,... 蜡梅(Chimonanthus praecox)是我国二级濒危珍稀植物,是重要的冬季传统观花植物。利用已报道的246个分布点和worldclim中提取的19个气候因子,基于最大熵(Maxent)模型和地理信息系统(Arc Gis)对蜡梅在中国的潜在适生区分布进行预测分析,采用受试者工作特征(ROC)曲线对预测结果进行检验和评价。结果表明蜡梅的潜在适生范围相对集中,主要集中在西南的四川盆地、华中、华东及华北的中南部地区,其他地区则适应性较低。温度是影响蜡梅分布的决定性因子,其中,当最冷季度平均温度接近0℃,等温性范围为0—10℃,降雨量变异系数约为45时,蜡梅的分布概率最大。与原分布区相比较,蜡梅的适生区范围正向中国东部地区和北部地区迁移。ROC曲线检验评价结果表明,Maxent模型的ROC曲线分析法的面积(AUC)值为0.986,预测结果达到了极高精度。 展开更多
关键词 蜡梅 MAXENT Arc GIS 模型预测
在线阅读 下载PDF
Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area,South Eastern Desert,Egypt:constraints from their mineralogical and geochemical characteristics 认领
16
作者 Moustafa M・Mogahed Wlaa Mahmoud Saad 《中国地球化学学报:英文版》 EI CAS CSCD 2020年第6期887-910,共24页
Petrological and geochemical studies of Neo-proterozoic metagabbros were carried out in the Muiswirab area,South Eastern Desert of Egypt.The Muiswirab area comprises of ophiolitic metagabbroic rocks(MOM),which are tec... Petrological and geochemical studies of Neo-proterozoic metagabbros were carried out in the Muiswirab area,South Eastern Desert of Egypt.The Muiswirab area comprises of ophiolitic metagabbroic rocks(MOM),which are tectonically thrusted over a thick pile of metavolcanic rocks and intruded by syn-and post-tectonic granitoid rocks.The whole-rock geochemical variations coupled with chemical compositions of mineral constituents are used to attain the genesis and tectonic evolution of the studied metagabbros.The geothermobarometric investiga-tion of the analyzed amphiboles from(MOM)revealed that these metagabbros underwent regional metamorphism under lower to upper greenschist facies(biotite zone)conditions(at a temperature of 450 to 500℃and pressure of 1-3 kbar).Geochemically,the metagabbros(MOM)show tholeiitic affinity and cxhibiting both arc-and MORB-like characters as evidenced by their clinopyrox-ene compositions and the Ti/V ratios(11.84-31.65),which considered as prominent features of forearc tectonic regime.The geochemical features suggest a probable fractionation of olivine±clinopyroxene±plagioclase as well as insignificant crustal contamination.The parental magma of the investigated MOM rocks seems to be developed in a sub-arc mantle wedge setting due to the enrichments of LILE(e.g..Rb,Ba,Sr,Pb)over HFSE(e.g,Ti,Nb,Y,Zr,Hf,Ta).The studied MOM rocks have lower values of Nb/U relative to MORB and OIB indicating that their geochemical variation produced due to the enrichment of a lithosphere mantle by OIB like components.The ratios of Zn/Fet,La/Sm,Sm/Yb,Th/Yb and Nb/Yb indicate that the MOM rocks represent a fragment of oceanic crust originated at a supra-subduction zone environment and their parental magma developed by 5-30%partial melting of a spinel lherzolite mantle rather than pyroxenite in an island arc setting and conformable with most of the Egyptian ophiolitic metagabbros. 展开更多
关键词 EGYPT Eastern Desert Muiswirab area Ophiolitic metagabbros N-MORB Arc tholeiites Foreare tectonic regime Volcanic-arc setting
Case Report: Anaplastic Astrocytoma Treated with Postoperative Radiotherapy Using Flattening Filter-Free Volumetric Arc Therapy (FFF-VMAT) during Pregnancy—Acceptable Fetal Dosimetry 认领
17
作者 Tomoyuki Noyama Wataru Takahashi +4 位作者 Yuki Nozawa Kanabu Nawa Hideomi Yamashita Osamu Abe Keiichi Nakagawa 《癌症治疗(英文)》 2020年第11期738-744,共7页
<strong>Background:</strong><span><span><span style="font-family:""><span style="font-family:Verdana;"> Postoperative irradiation for brain tumor in pregnan... <strong>Background:</strong><span><span><span style="font-family:""><span style="font-family:Verdana;"> Postoperative irradiation for brain tumor in pregnant women is a matter of concern. </span><b><span style="font-family:Verdana;">Aim:</span></b><span style="font-family:Verdana;"> We aimed to assess the safety of radiotherapy for brain tumors in pregnancy. We here report a successful treatment for anaplastic astrocytoma during pregnancy: surgery + postoperative irradiation. We wish to emphasize how we devised irradiation procedure to achieve both therapeutic effectiveness and safety to the fetus/infant. </span><b><span style="font-family:Verdana;">Case Presentation: </span></b><span style="font-family:Verdana;">A 34-year-old pregnant woman suffered with brain anaplastic astrocytoma. Tumor resection under craniotomy was performed with success. We decided to conduct postoperative radiotherapy at 25 weeks of gestation to reduce the risk of recurrence. We used a flattening filter-free volumetric arc therapy (FFF-VMAT) technique, which can achieve lower out-of-field dose than VMAT with a flattening filter or helical tomotherapy. We prescribed 60 Gy over 30 fractions. During actual beam delivery, surface and rectal dose to the patient (mother) were measured. The total fetal dose was estimated at 0.006 - 0.018 Gy, which is under the threshold set by the ICRP. A male healthy infant was born vaginally at the 37th week of pregnancy. The patient (mother) and the infant are healthy at the time of writing.</span><b><span style="font-family:Verdana;"> Conclusion: </span></b><span style="font-family:Verdana;">FFF-VMAT is a good choice for brain tumors during pregnancy</span></span></span></span><span style="font-family:Verdana;">.</span> 展开更多
关键词 PREGNANCY Radiotherapy Flattening Filter-Free Volumetric Arc Therapy An-aplastic Astrocytoma Fetal Dose
在线阅读 免费下载
双TIG焊接电弧数值分析 认领
18
作者 王新鑫 罗怡 +1 位作者 李春天 迟露鑫 《热加工工艺》 北大核心 2020年第7期133-138,145共7页
针对双TIG电弧建立了包括钨极的双TIG焊接电弧数学模型。通过数值求解,得到了不同电流分配条件下双TIG焊接电弧的温度场、流场和电磁场等重要结果,并对等离子流剪切力和电弧压力进行分析。研究表明,在总电流不变的情况下,当钨极分配电... 针对双TIG电弧建立了包括钨极的双TIG焊接电弧数学模型。通过数值求解,得到了不同电流分配条件下双TIG焊接电弧的温度场、流场和电磁场等重要结果,并对等离子流剪切力和电弧压力进行分析。研究表明,在总电流不变的情况下,当钨极分配电流相同时,电弧温度场、流场和电弧压力等呈对称分布;当钨极分配电流不同时,电弧高温区域更靠近大电流钨极,但电弧整体上向小电流钨极一侧偏移。电流分配相同时,母材表面的电弧压力和等离子流拉力与相同条件下的单TIG电弧相比均显著下降,而钨极分配电流不同时,电弧压力和等离子流拉力峰值偏向于小电流钨极一侧。模拟结果与已有的研究结果吻合良好。 展开更多
关键词 双TIG 电弧 数值模拟 电弧压力 等离子流拉力
基于Arc GIS的不良地质三维建模及选线研究 认领
19
作者 杨宝荣 《粘接》 CAS 2020年第4期132-136,共5页
我国的地质环境较为复杂,在很多的工程项目中,尤其是铁路方面,会涉及到路线的选择问题。传统的选线方式不仅耗时耗力,而且精确度不高,对地质环境进行测量时往往存在的误差较大。随着科学技术的不断发展,现代科技在选线中发挥着重要作用... 我国的地质环境较为复杂,在很多的工程项目中,尤其是铁路方面,会涉及到路线的选择问题。传统的选线方式不仅耗时耗力,而且精确度不高,对地质环境进行测量时往往存在的误差较大。随着科学技术的不断发展,现代科技在选线中发挥着重要作用,大大提高了选线的质量。Arc GIS具有非常强大的数据分析和管理能力,将其运用于选线中将有助于提高选线质量,在进行选线分析之前需要建立不良地质三维模型,然后根据该模型和相关信息进行选线。文章首先对通过Arc GIS建立不良地质三维模型,其中主要包含三个程序,分别为建立三维地形环境、获取不良地质信息和表达不良地质信息三维模型。最后根据获得的不良地质三维模型和三维地形环境确定最优的选线方案。文章有助于提高选线方案的准确度和效率,具有实际的应用价值。 展开更多
关键词 Arc GIS 不良地质三维模型 选线
在线阅读 下载PDF
Design and characteristics of a new type laminar plasma torch for materials processing 认领
20
作者 曹修全 陈林 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2020年第1期24-32,共9页
Laminar plasma jet(LPJ)generated by laminar plasma torch(LPT)has a favorable temperature and velocity distribution.Thus,it is superior to the turbulent plasma jet in material processing.However,most of the reported LP... Laminar plasma jet(LPJ)generated by laminar plasma torch(LPT)has a favorable temperature and velocity distribution.Thus,it is superior to the turbulent plasma jet in material processing.However,most of the reported LPTs usually operate at a relatively low output power with a relatively low arc voltage and thermal efficiency,which limits its capabilities.In this context,this paper attempts to design a new type of high-power LPT with a relatively low arc current and a high thermal efficiency.In the first section,the design principle of the main components is studied and discussed in detail,and a new high-power LPT is proposed.Then,the experimental characteristics of the proposed high-power LPT are examined.Experimental results reveal the following characteristics of the proposed LPT.(1)The max jet length of the proposed LPT reaches at 540 mm.(2)Its mean arc voltage is higher than 290 V when the LPT works with arc currents lower than 200 A.leading to an output power greater than 50 kW.(3)The mean thermal efficiency is higher than 509f.Lastly,the proposed LPT has been applied to spheroidize the aluminum oxide powers.The experiment results for the production of spherical powders show that the proposed LPT hits a good characteristic for material processing. 展开更多
关键词 LAMINAR plasma TORCH DESIGN PRINCIPLES high ARC voltage with a low ARC current spheroidisation
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈