期刊文献+
共找到20,560篇文章
< 1 2 250 >
每页显示 20 50 100
砂型铸造Mg-9Gd-3Y-0.5Zr合金的线收缩
1
作者 蒋锐 吴国华 +6 位作者 谢赫 童鑫 张亮 戚方舟 刘文才 耿莹晶 任广笑 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2024年第5期1441-1455,共15页
研究铸件几何特征对砂型铸造Mg-9Gd-3Y-0.5Zr(VW93)合金线收缩的影响。利用3D扫描仪精确提取自由收缩和受阻收缩砂铸件的尺寸,并用于计算收缩系数。引入砂芯体积与铸件包络体积之比(γ)量化砂芯对铸件收缩的约束程度。通过分析自由收缩... 研究铸件几何特征对砂型铸造Mg-9Gd-3Y-0.5Zr(VW93)合金线收缩的影响。利用3D扫描仪精确提取自由收缩和受阻收缩砂铸件的尺寸,并用于计算收缩系数。引入砂芯体积与铸件包络体积之比(γ)量化砂芯对铸件收缩的约束程度。通过分析自由收缩系数的统计分布和受阻收缩系数随γ的变化规律发现,VW93合金的自由收缩系数为1.96%,受阻收缩系数随γ的增大而线性减小,此关系为根据铸件几何结构预测VW93合金收缩率提供支持。 展开更多
关键词 自由收缩 受阻收缩 砂型铸造 Mg-9Gd-3y-0.5Zr合金
下载PDF
热处理对Mg-12Y-1Al合金组织及性能的影响
2
作者 聂敬敬 潘玥 +5 位作者 袁杏 夏先朝 孙京丽 李扬欣 应韬 肖旅 《材料工程》 EI CAS CSCD 北大核心 2024年第3期129-136,共8页
采用光学显微镜、X射线衍射仪及扫描电镜等研究固溶处理、时效处理后Mg-12Y-1Al合金的显微组织,利用拉伸实验分析热处理前后合金在室温及高温200℃下的力学性能,使用电化学方法测试热处理前后合金的耐腐蚀性能。结果表明:Mg-12Y-1Al合... 采用光学显微镜、X射线衍射仪及扫描电镜等研究固溶处理、时效处理后Mg-12Y-1Al合金的显微组织,利用拉伸实验分析热处理前后合金在室温及高温200℃下的力学性能,使用电化学方法测试热处理前后合金的耐腐蚀性能。结果表明:Mg-12Y-1Al合金的铸态组织由α-Mg基体、Mg_(24)Y_(5)相和Al_(2)Y相组成。Mg-12Y-1Al具有优异的高温热稳定性,在520℃×16 h(T4)固溶处理后,晶粒没有长大,产生新的长周期有序堆垛相(LPSO);225℃×30 h(T6)时效处理对组织的影响不大。与室温下的性能相比,T4态合金在200℃下的极限抗拉强度没有降低,而伸长率由室温的1.3%提高至12.5%。此外,Mg-12Y-1Al合金经固溶及时效处理后耐腐蚀性能得到提升,腐蚀电流密度由铸态的2.799×10^(-5)A/cm^(2)降低至1.551×10^(-5)A/cm^(2)。 展开更多
关键词 Mg-12y-1Al合金 热处理 显微组织 力学性能 腐蚀行为
下载PDF
Mg-9Gd-4Y-2Zn-0.5Zr合金连续降温压缩扭转组织演变
3
作者 朱明杰 王强 +5 位作者 杨勇彪 冯校泽 孙永海 胡博文 杨丽勤 段宇浩 《塑性工程学报》 CAS CSCD 北大核心 2024年第5期155-162,共8页
采用Gleeble-3500热力拟试验机对Mg-9Gd-4Y-2Zn-0.5Zr合金棒材进行了热压缩扭转实验,变形过程中采用连续降温,温度范围为420~480℃,降温速率为10℃·s^(-1)。分析了变形后试样微观组织的演化规律。结果表明,形成了梯度组织;随棒状... 采用Gleeble-3500热力拟试验机对Mg-9Gd-4Y-2Zn-0.5Zr合金棒材进行了热压缩扭转实验,变形过程中采用连续降温,温度范围为420~480℃,降温速率为10℃·s^(-1)。分析了变形后试样微观组织的演化规律。结果表明,形成了梯度组织;随棒状试样半径的增加,晶粒尺寸、LPSO相尺寸及ED//<0001>织构强度均减小。晶内LPSO相发生了机械破碎和扭折;块状LPSO相发生溶解,形成条纹状结构,部分条纹状结构在外力条件下发生扭折。变形过程中主要发生了连续动态再结晶及LPSO相激发的再结晶。连续降温有利于再结晶形核,产生大量细小的动态再结晶晶粒,抑制了再结晶晶粒长大和ED//<0001>织构强度增加。 展开更多
关键词 Mg-9Gd-4y-2Zn-0.5Zr合金 压缩扭转 降温 晶粒尺寸 织构
下载PDF
第二相体积分数对Mg-13Gd-4Y-2Zn-0.5Zr合金力学性能的影响
4
作者 易明 杨亚琴 张治民 《热加工工艺》 北大核心 2024年第10期68-71,77,共5页
采用万能拉伸试验机、SEM、EDS及XRD对固溶处理后的Mg-13Gd-4Y-2Zn-0.5Zr合金力学性能、第二相形态、化学成分进行了分析,并利用Image-Pro-Plus软件对第二相体积分数进行了统计。结果表明:固溶处理后,合金中仍有大量不同形态、成分的第... 采用万能拉伸试验机、SEM、EDS及XRD对固溶处理后的Mg-13Gd-4Y-2Zn-0.5Zr合金力学性能、第二相形态、化学成分进行了分析,并利用Image-Pro-Plus软件对第二相体积分数进行了统计。结果表明:固溶处理后,合金中仍有大量不同形态、成分的第二相,主要是灰色块状LPSO相、灰色棒状LPSO相和白色点状富稀土相。随着固溶时间的增加,Mg-13Gd-4Y-2Zn-0.5Zr合金的抗拉强度与伸长率表现出先降低后升高的变化规律。在510℃固溶16 h,合金的抗拉强度与伸长率达到最小值,分别为196.77 MPa、3.8%。510℃固溶10~16 h,LPSO相体积分数不变,富稀土相体积分数增加,富稀土相质地较脆,受力时容易破碎,成为裂纹萌发和扩展的源头,使合金抗拉强度、伸长率均降低。510℃固溶16~19 h,富稀土相体积分数减少,合金的力学性能增加。 展开更多
关键词 Mg-13Gd-4y-2Zn-0.5Zr合金 固溶时间 第二相 体积分数 力学性能
下载PDF
Biological Profile of People Living with Human Immunodeficiency Virus Starting Treatment in Kinshasa, Democratic Republic of the Congo
5
作者 Berry Ikolango Bongenya Marie-Thérèse Ayanne Safi Sombo +5 位作者 Guy Makila Mabe Bumoko Benoit Obel Kabengele Fridolin Kule-Koto Kodondi Baudoin Bu-Tsumbu Buassa Richard Lunganza Kalala Erick Ntambwe Kamangu 《World Journal of AIDS》 2023年第1期1-10,共10页
Context: The biochemical assessment is a real-time indicator of the state and evolution of an infection. Among other things, it makes it possible to determine the right moment when it becomes necessary to start or cha... Context: The biochemical assessment is a real-time indicator of the state and evolution of an infection. Among other things, it makes it possible to determine the right moment when it becomes necessary to start or change a treatment. Objective: The objective of this study is to present the Biological profile of People Living with HIV starting AntiRetroViral treatment in Kinshasa in the era of Dolutegravir. Methods: The present study is a descriptive cross-sectional to determine the biological profile of People Living with HIV (PLHIV) starting AntiRetroViral Treatment (ART). The patient inclusion period was from October 4, 2021 to February 15, 2022. Sixteen centers were included. A sample of 5 ml of blood was taken in a tube with EDTA. Patients were randomly included consecutively in the centers during consultations. The population was made up of adults aged over 18, infected with HIV and starting ART. The parameters of interest retained for the present study were: sex, age, hemoglobin level, blood sugar, urea, creatinine, transaminases, total cholesterol, triglycerides, proteins total, as well as amylase. Results: 119 patients were included in this study in accordance with the inclusion criteria;67 (56.3%) are female, giving a sex ratio of 1.29 in favor of women. The average age of the patients is 39.87 ± 12.36 years. The most represented age group is that of 36 to 45 years with 37 patients (31.9%). The mean values of the biological parameters of the patients at the start of ART are as follows: 31.61 ± 20.71 IU/L for ALT/SGPT, 25.81 ± 19.96 IU/L for AST/SGOT, 79.35 ± 49.49 IU/L for Amylase, 108.13 ± 62.17 mg/dl for Total Cholesterol, 2.77 ± 1.27 mg/dl for Creatinine, 72.53 ±22.23 mg/dl for Glycaemia, 10.30 ± 2.33 g/dl for Hemoglobin, 7.91 ± 1.75 g/dl for Total Protein, 131.23 ± 68.80 mg/dl for Triglycerides, and 33.61 ± 26.27 mg/dl for Urea. Conclusion: Mean values of PLHIV are, for the most part, within the normal range. The average creatinine is higher than the normal average value while the average total cholesterol is below the limit values. 展开更多
关键词 Biological Profile PLHIV starting ART KINSHASA
下载PDF
Virological and Molecular Profile of People Living with the Human Immunodeficiency Virus Starting Dolutegravir Based Antiretroviral Treatment in Kinshasa, Democratic Republic of Congo
6
作者 Berry I. Bongenya Charlotte L. Tshinguta +4 位作者 Marie-Thérèse A. S. Sombo Guy M. M. Bumoko Benoit O. Kabengele Gauthier K. Mesia Erick N. Kamangu 《World Journal of AIDS》 2023年第3期83-94,共12页
Context: Despite the new recommendations “Test and Treat”, the virological and molecular parameters remain important information for Antiretroviral Treatment and adequate for monitoring of patients infected with HIV... Context: Despite the new recommendations “Test and Treat”, the virological and molecular parameters remain important information for Antiretroviral Treatment and adequate for monitoring of patients infected with HIV/AIDS. Objective: the Objective of this study is to present the virological and molecular profile of People Living with HIV starting Antiretroviral Therapy in Kinshasa in the era of the Dolutegravir. Methods: This was a transversal study to determine virological and molecular profile of People Living with HIV (PLHIV) starting an ARV Treatment. The patient’s inclusion period was from October 04, 2021 to February 15, 2022. A sample of 5 ml of blood was taken in a tube with EDTA anticoagulant for Molecular Biology analyzes (Viral Load and Sequencing) in all HIV patients, after reading and signing informed consent. The population was made up of adult patients over the age of 18, infected with HIV and starting ART. Results: 119 patients (56.3% of women) were included in this study, thus a sex-ratio of 1.29. The average age of patients included was 39.87 ± 12.36 years. The most represented age group is that of 36 to 45 with 37 patients (31.9%) followed by that from 26 to 35 years with 24 patients (20.7%). Out of 119 patients, 21 patients had an undetectable Viral Load (VL). The median value of VL was 4.16 log10 RNA copies/ml. 114 samples were successfully amplified. Subtype A was dominant with 23 cases (20.2%);followed by the subtype C and CRF02_AG each with 14.0%, and D (10.5 %). K65R (1.8%), T69P/N (4.4%), K70R (7.9%) and M184V (7.0%) mutations were listed as existing mutations for Nucleotide Transcriptase Inhibitors. Conclusion: 38 patients (31.93%) started the TARV with a positive virological prognosis. The subtype A remains dominant in Kinshasa with 23 cases (20.2%);followed by the subtype C and CRF02_AG each with 14.0%. For Inhibitors of Transcriptase Reverse Nucleotide;K65R, T69P/N, K70E/R and M184V mutations were found in patients’ naive of ARV Treatment. 展开更多
关键词 Virological Profile Molecular Profile PLHIV start of ART KINSHASA
下载PDF
时效温度对Mg-2.0Zn-1.0Y-0.5Zr合金组织与性能的影响
7
作者 郑向阳 贺俊光 +2 位作者 冯武云 龚圆 田培梧 《材料热处理学报》 CAS CSCD 北大核心 2024年第2期78-85,共8页
采用扫描电镜(SEM)、X射线衍射(XRD)、拉伸试验、浸泡试验和电化学试验等研究了固溶态Mg-2.0Zn-1.0Y-0.5Zr合金在180~220℃时效12 h后的微观组织、耐蚀性能和力学性能。结果表明:随着时效温度从180℃升高到220℃,合金中析出的颗粒状第... 采用扫描电镜(SEM)、X射线衍射(XRD)、拉伸试验、浸泡试验和电化学试验等研究了固溶态Mg-2.0Zn-1.0Y-0.5Zr合金在180~220℃时效12 h后的微观组织、耐蚀性能和力学性能。结果表明:随着时效温度从180℃升高到220℃,合金中析出的颗粒状第二相数量增多,第二相体积分数由0.03%(固溶态)升至0.36%(220℃时效12 h),力学性能明显提高,但耐蚀性能下降。当时效温度为200℃时,合金的综合性能较优,其抗拉强度、屈服强度、伸长率和腐蚀速率分别为(268.1±11.3) MPa、(170.4±8.5) MPa、(15.8±0.6)%和(0.575±0.039) mm/y。 展开更多
关键词 Mg-2.0Zn-1.0y-0.5Zr合金 时效温度 力学性能 耐蚀性能
下载PDF
Mg-9Gd-3.5Y-2Zn-0.5Zr合金材料喷丸强化工艺及摩擦磨损性能研究
8
作者 贺帅 张治民 《表面技术》 EI CAS CSCD 北大核心 2024年第7期96-106,共11页
目的提高Mg-9Gd-3.5Y-2Zn-0.5Zr合金的耐磨性能。方法通过喷丸强化工艺对Mg-9Gd-3.5Y-2Zn-0.5Zr合金表面进行处理,在合金表面制备出纳米强化层,随后进行干滑动摩擦磨损试验,探究其喷丸强化后耐磨性能的改变。利用OM、SEM研究合金表层至... 目的提高Mg-9Gd-3.5Y-2Zn-0.5Zr合金的耐磨性能。方法通过喷丸强化工艺对Mg-9Gd-3.5Y-2Zn-0.5Zr合金表面进行处理,在合金表面制备出纳米强化层,随后进行干滑动摩擦磨损试验,探究其喷丸强化后耐磨性能的改变。利用OM、SEM研究合金表层至内部晶粒尺寸及组织特征的变化。利用电子天平秤测量摩擦磨损试验前后质量的损失量。利用维氏显微硬度计测量合金强化层深度方向的硬度分布。利用SEM研究了合金摩擦磨损后的形貌特征,探究其磨损机制。结果对Mg-9Gd-3.5Y-2Zn-0.5Zr合金进行表面喷丸处理后,表面分别出现了200~370μm厚的晶粒细化层,其中喷丸气压为0.4 MPa、时间为40 s的试样的细晶强化层厚约为250μm,硬度约为155HV,较原始试样提高了50%左右。结论经喷丸强化后,镁合金表面发生塑性变形,获得纳米晶。晶粒尺寸从表层到内部逐渐变大,呈现梯度变化,喷丸处理后试样磨损质量普遍降低,耐磨性能得到提高,其中气压为0.4MPa、喷丸时间为40s的试样的耐磨性最好。铸态试样的摩擦磨损中,磨粒磨损和黏着磨损发挥主要作用,喷丸强化工艺后,磨损机制发生改变,喷丸时间为60 s时,氧化磨损起主导作用。另外,随着喷丸气压的增大,疲劳磨损由辅助作用逐渐变为主导作用。 展开更多
关键词 喷丸强化 耐磨性能 Mg-9Gd-3.5y-2Zn-0.5Zr合金 纳米晶
下载PDF
不同挤压温度下Mg-3Y-1.5Ce-0.5Zr合金的组织与力学性能
9
作者 刘鸿智 童景琳 《热加工工艺》 北大核心 2024年第8期104-106,112,共4页
对锻态Mg-3Y-1.5Ce-0.5Zr合金进行了不同温度的热挤压试验,通过金相显微镜、拉伸试验、断口形貌观察等手段研究了不同挤压温度(320~380℃)对该合金组织与力学性能的影响。结果表明:Mg-3Y-1.5Ce-0.5Zr合金经过不同温度挤压后,晶粒得到一... 对锻态Mg-3Y-1.5Ce-0.5Zr合金进行了不同温度的热挤压试验,通过金相显微镜、拉伸试验、断口形貌观察等手段研究了不同挤压温度(320~380℃)对该合金组织与力学性能的影响。结果表明:Mg-3Y-1.5Ce-0.5Zr合金经过不同温度挤压后,晶粒得到一定程度的细化。随着挤压温度的升高,合金晶粒尺寸先减小后增大,350℃下挤压的合金的晶粒平均尺寸最小,组织均匀性最佳。随着挤压温度的升高,合金的抗拉强度和伸长率均先升高后降低。350℃挤压的Mg-3Y-1.5Ce-0.5Zr合金的抗拉强度和伸长率均达到最大值,分别为276.3 MPa和17.6%。 展开更多
关键词 挤压温度 Mg-3y-1.5Ce-0.5Zr合金 显微组织 力学性能
下载PDF
变形条件对Mg-Gd-Y-Nd-Zr合金动态力学行为的影响
10
作者 田学锋 宋小春 《有色金属工程》 CAS 北大核心 2024年第4期24-31,共8页
采用金相观察、扫描电子显微镜、能谱分析、显微硬度计及分离式霍普金森压杆等手段,研究了峰值时效挤压态Mg-8Gd-3Y-0.5Nd-0.5Zr合金在变形温度及应变速率下的动态冲击力学变形行为。结果表明:合金在220℃/14 h到达峰值时效,其硬度约为1... 采用金相观察、扫描电子显微镜、能谱分析、显微硬度计及分离式霍普金森压杆等手段,研究了峰值时效挤压态Mg-8Gd-3Y-0.5Nd-0.5Zr合金在变形温度及应变速率下的动态冲击力学变形行为。结果表明:合金在220℃/14 h到达峰值时效,其硬度约为143.2 HV,提升了55%左右。在不同的变形温度下均表现出优异的抗冲击性能,在室温及应变速率为3000 s^(-1)条件下合金抗压强度可高达682 MPa;在100℃及应变速率为1500 s^(-1)条件下抗压强度为635 MPa;在400℃及应变速率为3000 s^(-1)条件下抗压强度为583 MPa。合金在不同温度下优异的抗冲击性能主要得益于时效强化相、稳定存在的块状富稀土粒子以及冲击过程中在晶界形成的动态析出相协同强化机制。随着应变速率和变形温度的增大,合金热软化效应增强,合金力学性能有所降低。 展开更多
关键词 Mg-8Gd-3y-0.5Nd-0.5Zr合金 变形温度 应变速率 时效强化 动态析出
下载PDF
‘Y-1’苹果矮化砧木扦插繁殖关键技术
11
作者 王国平 陈秋芳 +2 位作者 樊新萍 刘伟 郭华 《现代园艺》 2024年第1期94-96,共3页
本研究从扦插前的准备、扦插中的注意事项、扦插后的管理,详细介绍了‘Y-1’苹果矮化砧木扦插育苗各个环节的关键技术,为给大规模繁育‘Y-1’苹果矮化砧木奠定技术基础,供参考。
关键词 y-1’苹果矮化砧木 扦插育苗 关键技术
下载PDF
《老年人潜在不适当处方筛查工具/处方遗漏筛查工具(STOPP/START)标准》第3版解读
12
作者 朱素燕 郑晓梦 +1 位作者 范苗 陈春燕 《中国全科医学》 CAS 北大核心 2024年第33期4097-4104,共8页
老年人潜在不适当处方筛查工具(STOPP)/处方遗漏筛查工具(START)由2008年爱尔兰Cork大学附属医院专家组首次发表并于2015年进行第2次更新。自发表以来,该标准在发现老年人潜在不适当用药、加强对老年人滥用药物的监管、减少老年人药品... 老年人潜在不适当处方筛查工具(STOPP)/处方遗漏筛查工具(START)由2008年爱尔兰Cork大学附属医院专家组首次发表并于2015年进行第2次更新。自发表以来,该标准在发现老年人潜在不适当用药、加强对老年人滥用药物的监管、减少老年人药品不良事件等方面发挥了积极作用。2023年第3版STOPP/START标准发布,在第2版基础上增加、修订和删减了一些标准,最终形成190条潜在不适当用药标准。新标准根据最新的老年人合理用药研究结果和临床证据,提供了更新、更实用的循证医学依据。本文对STOPP/START标准(第3版)进行了详细的解读,为我国潜在不适当用药标准更新和完善提供参考,并对未来该领域的研究方向提出思考和建议。 展开更多
关键词 潜在不当用药 老年人潜在不适当处方筛查工具 STOPP/start标准 老年人 多重用药 Beers标准
下载PDF
中国少年女子足球运动员功能性动作能力与下肢爆发力、Y-平衡的关系探究
13
作者 崔健华 张俊杰 叶俊 《四川体育科学》 2024年第1期35-41,共7页
目的:分析中国少年女子足球运动员(以下简称国少女足)功能性动作筛查评分结果与下肢爆发力、Y-平衡存在的内在联系,为提高国少女足运动员运动表现提供参考。方法:选取24名国少女足运动员进行功能性动作筛查测试、20m冲刺、立定跳远、下... 目的:分析中国少年女子足球运动员(以下简称国少女足)功能性动作筛查评分结果与下肢爆发力、Y-平衡存在的内在联系,为提高国少女足运动员运动表现提供参考。方法:选取24名国少女足运动员进行功能性动作筛查测试、20m冲刺、立定跳远、下蹲跳、Y-平衡测试,并对结果进行分析。位置间采用单因素方差分析,相关性研究采用Person分析。结果:(1)国少女足运动员功能性动作筛查测试平均分为16.20,最佳截断点为14.5分;(2)跨栏步、主动直膝抬腿与20m分段冲刺速度存在显著负相关(r=-0.466,P<0.05;r=-0.367,P<0.05),过顶深蹲动作模式与立定跳远存在显著正相关(r=0.181,P<0.05),Y-平衡临界值在各个位置之间存在统计学意义(P<0.01);(3)FMS总分对准确预测国少女足球员非接触性损伤具有较高的诊断价值,曲线下面积为0.903。结论:(1)我国优秀国少女足运动员髋关节主动灵活性和臀大肌-髂胫束联合等肌群的主动柔韧性较好,但存在膝关节、髋关节稳定性差、躯干核心区肌群控制能力不足等问题,训练应着重加强臀部肌群的激活与练习、核心区稳定与核心区力量训练。(2)FMS得分与20m分段冲刺速度存在显著负相关,与立定跳远存在显著正相关,与下蹲跳能力存在正相关,与Y-平衡得分存在负相关,FMS测试得分并不能全面反映球员下肢爆发力、Y-平衡能力的高低,测试评估与训练需要考虑球员个体差异性,强调针对性帮助球员提高运动表现,降低损伤风险。 展开更多
关键词 国少女足 功能动作筛查 下肢爆发力 y-平衡 ROC曲线
下载PDF
追求卓越的早期教育质量--OECD早期保教质量调查报告“Starting StrongⅢ”述评 被引量:2
14
作者 周玉娥 刘智成 《外国教育研究》 CSSCI 北大核心 2013年第6期11-16,共6页
早期教育质量的影响因素是多方面的,OECD成员国在提高早期教育质量方面作了许多积极探索,Starting StrongⅢ就是在广泛调研基础上形成的一份聚焦质量的报告。通过探讨Starting StrongⅢ的形成背景,进而分析其五个与早期教育质量密切相... 早期教育质量的影响因素是多方面的,OECD成员国在提高早期教育质量方面作了许多积极探索,Starting StrongⅢ就是在广泛调研基础上形成的一份聚焦质量的报告。通过探讨Starting StrongⅢ的形成背景,进而分析其五个与早期教育质量密切相关的重要政策杠杆,能为思考我国学前教育发展提供些许启示。 展开更多
关键词 早期教育和保育 质量 starting StrongⅢ
下载PDF
均匀化处理对铸态Mg-9Gd-3.5Y-2Zn-0.35Zr合金组织和力学性能的影响 被引量:1
15
作者 刘凯 陈伟 +5 位作者 谢家松 杨晓禹 王红杰 祁泽星 陈刚 张星 《热加工工艺》 北大核心 2023年第4期139-143,149,共6页
均匀化热处理能够消除合金铸造缺陷,改善成分偏析提升变形能力。利用光学显微镜(OM)、差分扫描量热计(DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱分析(EDS)和万能拉伸实验机等手段,研究了不同均匀化时间(2、5、10、15、20 h)和温... 均匀化热处理能够消除合金铸造缺陷,改善成分偏析提升变形能力。利用光学显微镜(OM)、差分扫描量热计(DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱分析(EDS)和万能拉伸实验机等手段,研究了不同均匀化时间(2、5、10、15、20 h)和温度(480、500、520℃)对Mg-9Gd-3.5Y-2Zn-0.35Zr合金微观组织和力学性能的影响规律。结果表明,铸态Mg-Gd-Y-Zn-Zr合金主要包括沿晶界呈网状分布的块状Mg5(Gd,Y,Zn)相及片层状长周期堆垛有序结构相(LPSO),粗大的第二相容易引起局部应力集中而引发裂纹萌生,造成了铸态合金较低的力学性能;经均匀化处理后,大量第二相溶入基体,合金的力学性能得到了显著提升,断裂机制也由铸态的脆性断裂转变为塑性断裂,表明材料塑性得到显著提升;合金的最佳均匀化处理工艺为520℃/15 h,其抗拉强度、屈服强度和伸长率分别由铸态的166.2 MPa、130.2 MPa和3.3%提高到213.5 MPa、154.5 MPa和7.6%。 展开更多
关键词 Mg-9Gd-3.5y-2Zn-0.35Zr合金 均匀化处理 显微组织 力学性能
下载PDF
Reconstruction of the starting time series of rainy season in Yunnan and the evolvement of summer monsoon during 1711-1982 被引量:2
16
作者 YANG Yuda MAN Zhimin ZHENG Jingyun 《Journal of Geographical Sciences》 SCIE CSCD 2007年第2期212-220,共9页
According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yu... According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino's quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon. 展开更多
关键词 YUNNAN Qing Dynasty starting date of rainy season summer monsoon ENSO
下载PDF
Starting flow in a rotating parallel plate channel 被引量:1
17
作者 Chang Yi Wang 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2012年第5期1271-1276,共6页
The starting flow due to a suddenly applied pressure gradient in a parallel plate channel which is rotating as a system is studied. Exact analytic series solutions to the unsteady Navier-Stokes equations are found by ... The starting flow due to a suddenly applied pressure gradient in a parallel plate channel which is rotating as a system is studied. Exact analytic series solutions to the unsteady Navier-Stokes equations are found by both the Laplace transform method and the separation of parameters method, the latter is shown to be superior. Rotation not only induces a secondary transverse flow but also alters the character of the transient flow rate and velocity profiles. Back flow and inertial oscillations occur, especially at higher rota- tion rates. 展开更多
关键词 Rotating system Flow - starting
下载PDF
Simulation study on starting of dual clutch transmission for tracked vehicles 被引量:1
18
作者 张金乐 马彪 +1 位作者 张英锋 郑长松 《Journal of Beijing Institute of Technology》 EI CAS 2011年第1期77-83,共7页
In order to study the application of dual clutch transmission (DCT) on tracked vehicles, a simulation moclel and two control methods were performed for starting analysis. Based on a certain transmission of an existi... In order to study the application of dual clutch transmission (DCT) on tracked vehicles, a simulation moclel and two control methods were performed for starting analysis. Based on a certain transmission of an existing tracked vehicle, a DCT structure was proposed. Matlab/Simulink was a dopted as a platform to develop the simulation model. The engine speed was controlled to follow the target speed as a launch strategy. Two control methods, a proportional integral derivative ( PID ) control method and a fuzzy control method, were proposed to control the engine throttle and oil pressure in order to track the target engine speed. Simulation results show that either the PID control or fuzzy control method can improve the starting performance compared with no loop control meth od. Fuzzy control method can lead a better starting quality compared with PID control method. 展开更多
关键词 starting control dual clutch transmission proportional integral derivative (PID) fuzz y tracked vehicle
下载PDF
Starting Characteristics of Motor in Inverter-Motor Drive System 被引量:1
19
作者 Xi-jun Yang Xiang-jun Zhang You-min Gong 《Advances in Manufacturing》 2000年第2期140-144,共5页
When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, base... When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, based on the steady state equivalent circuit of the induction motor.The corresponding expressions are derived, and the corresponding curves are also drawn, from which the initial starting frequency range can be determined properly and easily. The initial starting frequency range is the common range, in which the starting torque should be high enough and the starting current low enough.Some other useful formulas are also derived.These results are significant for electrical drive designers to make the starting schemes. The effects of the increase of the stator and the rotor resistances on the starting torque and the initial starting frequency range are also discussed, which is caused by the skin effects of the high order harmonics present in the PWM inverter output voltage. 展开更多
关键词 inverter motor drive system starting characteristics skin effect
下载PDF
Experimental study of the critical sand starting velocity of gas-watersand flow in an inclined pipe 被引量:2
20
作者 Rui-Yao Zhang Jun Li +3 位作者 Hong-Wei Yang Geng Zhang Xi-Ning Hao Peng-Lin Liu 《Petroleum Science》 SCIE CAS CSCD 2022年第6期2981-2994,共14页
The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment sy... The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering. 展开更多
关键词 Three-phase flow Critical sand starting velocity Flow pattern Sand migration Gas void fraction Hole deviation angles Sand concentration
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部