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[期刊论文] Xu XU
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CSTPCD SCI
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摘要:Risler & Trotman in 1997 proved that the multiplicity of an analytic function germ is left-right lipschitz invariant,which provided a partial answer to Zariski conjecture.In this note,based on the recent work of Comte,Milman & Trotman,we generalize the work of them to prove that the multiplicity of a C-∞ differentiable function germ is also left-right lipschitz invariant....
[期刊论文] Xu XU
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CSTPCD SCI
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摘要:In this paper, a criterion on the C0-sufficiency for a function germ with non-isolated singularity is obtained analogously to that of Kuiper-Kuo for the case of isolated singularities. Moreover,the Kuiper-Kuo condition and the Thom condition for an analytic function germ with non-isolated singularity are proved to be equivalent....
[期刊论文] 张运涛 徐栩
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北大核心 CSTPCD CSCD CBST SA
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摘要:本文研究曲率二次衰减的完备黎曼流形,证明了若它的直径增长满足小的线性增长条件,则其基本群是有限生成的....
摘要:The mixtures of two polymers, poly (N,N-dimethylacrylamide) (PDMA) and polyvinylpyrrolidone (PVP) were synthesized and used as the separation medium for double-stranded and single-stranded DNA fragments by capillary electrophoresis with UV detector. On optimal conditions, 2%w/v PDMA ( 2%w/v PVP can be used to separate the doublet 123/124bp in pBR322/Hae III Markers....
[期刊论文] 耿姗姗 许旭 顾林 赵晶
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北大核心 CSTPCD CSCD CA CBST
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摘要:目的:分析乳腺浸润性乳头状癌的临床病理特征及影响腋窝淋巴结转移和预后的相关因素.方法:收集2000年4月~2008年1月天津医科大学附属肿瘤医院乳腺科收治的72例乳腺浸润性乳头状癌患者的临床病理资料,分析影响浸润性乳头状癌腋窝淋巴结转移的临床病理因素.Kaplan-Meier法计算生存率,Log-rank检验进行生存率显著性检验,Cox比例风险模型用于单因素、多因素分析,评价各因素对预后的影响.结果:72例乳腺浸润性乳头状癌的3年、5年生存率分别为89.7%、83.7%.肿瘤大小及病程长短与浸润性乳头状癌腋窝淋巴结的转移存在相关性.单因素生存分析显示:ER、PR的表达状况及治疗方法的选择是影响乳腺浸润性乳头状癌预后的相关因素.Cox多因素分析则显示仅治疗方法的选择是影响预后的独立因素.结论:乳腺浸润性乳头状癌是一种多发生于绝经后妇女、预后较好的浸润性特殊型癌,其治疗方法的选择对患者的预后有重要影响,该类型乳腺癌应在个体耐受的情况下行手术联合其他治疗方法的综合治疗以提高患者的生存率....
摘要:To uncover the internal flow characteristics in an ethylene-fueled aeroramp injector/gaspilot (ARI/G-P) flame scramjet,a Reynolds-averaged Navier-Stokes (RANS) solver is constructed under a hybrid polyhedral cell finite volume frame.The shear stress transport (SST) k-o model is used to predict the turbulence,while the Overmann's compressibility corrected laminar flamelet model is adopted to simulate the turbulent combustion.Nonreactive computations for Case 1 (G-P jet on),Case 2 (ARI jets on),and Case 3 (both ARI and G-P jets on) were conducted to analyze the mixing mechanism,while reactive Cases 4-7 at equivalent ratios of 0.380,0.278,0.199 and 0.167 respectively were calculated to investigate the flame structure and combustion modes.The numerical results are compared well to those of the experiments.It is shown that the G-P jet plays significant role in both the fuel/air mixing and flame holding processes;the combustion for the four reactive cases takes place intensively in the regions downstream of the ARI/G-P unit;Cases 4 and 5 are under subsonic combustion mode,whereas Cases 6 and 7 are mode transition critical and supersonic combustion cases,respectively;the mode transition equivalent ratio is approximately 0.20....
摘要:Cryosection in plants is usually challenging because of the larger amounts of water contained in plant cell than animal cell.The formation of ice crystals within the plant cells easily destroys subcellular detail during freeze processing.And cell walls make freezing plant tissues hardly sliced and preserve the cell structure in subtle ways.In this study,the technique was improved on infusion,embedding and flatting sections with the winter wheat Variety Aikang58 as raw material....
摘要:An 89-year-old woman [body mass index (BMI) =20.27 kg/m2)] with hypertension underwent implantation of a dual-chamber pacemaker because of dizziness and syncope due to sick sinus syndrome.Pacemaker implantation via the left subclavian approach was performed on June 3,2017.A right ventricular active lead (TendrilTM STS 2088TC,St Jude Medical,Penang,Malaysia) and an atrial active lead (OptisenseTM 1999,St Jude Medical,Penang,Malaysia) were placed in the right ventricular apex and anterior wall of the right atrium,respectively.Atrial lead parameters were normal (Table 1)....
摘要:研究目的:通过实验方法定量研究在相变材料较为剧烈的熔化传热过程中散热器倾斜角度的改变对其瞬时性能所产生的影响。
  创新要点:定量研究在倾斜角度从水平到垂直时,储能式散热器在脉冲式热负荷作用下瞬时性能的变化规律,并在所研究的工况范围内给出了最优的倾斜角度参考值。
  研究方法:采用电加热方法模拟电子器件所产生的热源,通过调节电压改变脉冲式热负荷的强度和作用时间,并根据热电偶测量所得的加热表面温度变化来表征储能式散热器的瞬时性能。
  重要结论:在一定的倾斜角度下工作,可以有效提升基于相变材料的储能式散热器的瞬时性能。在加热功率为40 W、以75°C为目标时,其有效保护时间的相对增长可达约67%。...
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北大核心 CSTPCD CSCD AJ CA EI CBST
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摘要:叶面积指数(LAI,leaf area index)和地上部生物量是评价冬小麦长势的重要农学参数,其实时动态监测对冬小麦的长势诊断、产量预测和管理调控等具有重要意义.该研究通过分析叶面积指数、地上部生物量与冬小麦冠层光谱参数的相关性,筛选出冬小麦长势指标敏感波段及最佳带宽范围;基于敏感光谱波段下图像的彩色因子,构建冬小麦叶面积指数和地上部生物量监测模型.结果表明,叶面积指数、地上部生物量长势指标的敏感波段及最佳带宽范围为(560±6)和(810±10) nm.敏感波段560、810nm波段下获得的图像特征因子中,RGB颜色空间R810、G560、B810对叶面积指数的拟合效果最好,决定系数高达0.989;HSI颜色空间H810、S810、I560对地上部生物量的拟合效果最好,决定系数为0.937.试验数据检验表明,叶面积指数、地上部生物量监测模型的均方根误差RMSE分别为0.4515、3.3556,相对误差分别为15.7%、15.9%,所构建监测模型的精确度较高.因此,基于敏感光谱波段及相应图像特征构建的监测模型可有效对冬小麦叶面积指数、地上部生物量进行实时、快速、准确监测与诊断....
摘要:目的:明确在封闭腔内放置旋转柱体时,柱体尺寸及转速对不同浓度下纳米流体的流动传热的影响。创新点:1.数值模拟中采用的碳化硅-乙二醇(SiC-EG)纳米流体的重要热物性参数均为实验测量值;2.考虑封闭腔内柱体的动态旋转对腔内纳米流体流动传热的影响。方法:基于对SiC-EG 纳米流体导热系数与粘度的实验测量,采用数值模拟方法探究封闭腔内旋转柱体、纳米流体浓度以及瑞利数对SiC-EG 纳米流体流动传热性能的影响。结论:1.在柱体的旋转方向与由自然对流引起的纳米流体流动方向相同的情况下,置于腔内的旋转柱体可以起到强化传热的效果。2.二者旋转方向相反时情况较为复杂,当柱体尺寸较小且柱体转速较低时削弱传热效果;当柱体尺寸较大且转速较高而引发的强制对流占主导地位时,将对腔内传热起到一定的强化效果。...
摘要:Owing to adjustable thermal expansion performance,BaO-CaO-Al2O3-B2O3-SiO2 (BCABS)glass has a promising commercialization prospect for intermediate temperature-solid oxide fuel cells (IT-SOFCs) sealing.Herein,Al2O3 with two different contents was added into the same glass formulation,referred to as A and B glass,respectively.In terms of the non-isothermal crystallization kinetic behavior,the effect of Al2O3 as the unique intermediate was innovatively studied on the long-term performance of BCABS sealing glass.After the heat treatment at 1023 K for 100 h,the change of the network structure and the expansion coefficient of the glass were characterized.The results showed that the addition of Al2O3 as a network forming body could enhance the structure of glass,and increase the activation energy for glass transition,which could effectively inhibit the crystallization ability of sealing glass.Therefore,the B glass with the higher Al2O3 content showed the better long-term sealing ability,which was greatly beneficial for IT-SOFCs sealing....
摘要:目的:多孔结构植入体在骨科修复领域具有极大的应用前景.本研究提出了一种在结构与力学性能方面更贴近人体骨组织的多孔Ti6Al4V植入体.创新点:针对骨组织的结构特点,提出了"分层设计"理念,以期更好地模拟皮质骨和松质骨的结构.除了结构相似以外,这种植入体在力学性能和结构稳定性方面同样具有优势.方法:将传统多孔植入体三维晶胞设计方法转化为二维设计理念,设计出一种分层杆连接多孔结构,并利用选择性激光熔融(SLM)技术打印出样品;然后通过光学显微镜评测打印效果,利用单轴压缩试验研究分析样品的力学性能;最后利用有限元方法分析多孔结构的结构稳定性.结论:本研究所设计的新型分层杆连接结构可以通过SLM实现高质量的打印,且尺寸合理,力学性能与骨组织相接近,结构稳定性优于传统多孔结构.这种新型多孔结构植入体在骨缺损修复领域具有较好的潜在应用前景....
摘要:高真空条件下,绝热材料的放气速率会影响低温容器的真空性能,从而影响其绝热性能.根据GB/T31480-2015,搭建了绝热材料放气速率测试平台.通过本底放气速率的测定,验证了该测试平台的可靠性;利用静态法测试了某型号多层绝热材料的放气速率,给出了试验数据.本试验台将为绝热材料的应用及低温容器的设计提供数据支撑....
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