Mg-5Zn-2Er-1.5Nd-xCa镁合金的显微组织和力学性能

利用光学显微镜、扫描电镜及其附带的能谱仪和电子万能试验机,研究了Mg-5Zn-2Er-1.5Nd-xCa(0.4相似文献   

Effect of weld microstructure on brittle fracture initiation in the thermally-aged boiling water reactor pressure vessel head weld metal

Effects of the weld microstructure and inclusions on brittle fracture initiation are investigated in a thermally aged ferritic high-nickel weld of a reactor pressure vessel head from a decommissioned nuclear power plant.As-welded and reheated regions mainly consist of acicular and polygonal ferrite,respectively.Fractographic examination of Charpy V-notch impact toughness specimens reveals large inclusions(0.5-2.5μm)at the brittle fracture primary initiation sites.High impact energies were measured for the specimens in which brittle fracture was initiated from a small inclusion or an inclusion away from the V-notch.The density,geometry,and chemical composition of the primary initiation inclusions were investigated.A brittle fracture crack initiates as a microcrack either within the multiphase oxide inclusions or from the debonded interfaces between the uncracked inclusions and weld metal matrix.Primary fracture sites can be determined in all the specimens tested in the lower part of the transition curve at and below the 41-J reference impact toughness energy but not above the mentioned value because of the changes in the fracture mechanism and resulting changes in the fracture appearance.     

SBS含量对沥青老化性能的影响

为了提高SBS改性沥青的路用性能,延长路面使用寿命,本文通过物理指标试验、流变测试、傅里叶红外光谱法（FTIR）和凝胶色谱法（GPC）对比分析了不同含量SBS改性沥青老化前后的性能差异,探究了SBS含量对沥青老化性能的影响。结果表明：短期老化后,随着SBS含量的增加,沥青粘度和复数模量增大,针入度减小,延度迅速下降,沥青显示出脆性;改性剂发生降解,GPC图谱中改性沥青SBS特征峰峰面积均有所减小;改性沥青的红外光谱图在1696 cm-1（C=O伸缩振动）处出现新的特征吸收峰。长期老化后,改性沥青中大分子物质几乎完全降解,SBS特征峰均消失;红外光谱图中1696 cm-1处吸收峰强度加强,BI指数减小一半;随着SBS含量的增加,CI指数和SI指数变化不大,而BI指数持续增加并与SBS含量呈现良好的线性关系。     

时效工艺对1．0％Ni—5．0％Sn铝合金组织和硬度的影响

本文对１．０％Ｎｉ—５．０％Ｓｎ铝合金进行了不同时效工艺的热处理试验，探讨了不同时效规范对铝合金的显微组织和布氏硬度的影响．结果表明：合理的时效规范可使１．０％Ｎｉ—５．０％Ｓｎ铝合金得到细密均匀的组织，使合金的硬度达到ＨＢ６０Ｋｇｆ／ｍｍ２以上，从而满足使用性能的要求     

人红细胞衰老过程抗氧化酶活性的研究

本文以新鲜及保存不同时间的献血员血液为研究材料,分别测定混匀、年老、年青三种状况 RBC 中的 GSH-PX、CAT 和 SOD 活性,获得了随血液保存期延长而三种酶活性皆显示逐周下降的结果。并且观察到年老 RBC 中三种酶活性比年青 RBC 中的酶活性更低、差别显著。我们的结果提示,RBC 衰老过程与这些抗氧化酶活性下降密切有关。     

低密度聚乙烯电树枝老化中氧的影响研究

作者采用了真空脱气后充六氟化硫(SF_6)气体的技术处理材料试样,能有效改进低密度聚乙烯(LDPE)的电树枝特性,把树枝起始电压和树枝起始时间提高到一个新的水平。与单一充SF_6气体的LDPE比较,两者分别提高及延长了一倍。试验表明LDPE中的氧和高能电子一样,都是促使电树枝发展的基本因素。     

基于检查点和Rejuvenation的软件可靠性建模分析

处于运行阶段的软件往往存在老化现象，即性能的逐渐下降或失效。为了避免软件老化造成的影响，人们提出了软件rejuvenation技术。这是一种预防性的软件容错策略，能有效的提高软件系统的可靠性和可用性。但由于rejuvenation操作过程的复杂性，它的成本也是不可忽略的。相对于rejuvenation来说，检查点是一种轻量级的软件容错策略，其成本远小于rejuvenation的成本。本文旨在结合rejuvenation和检查点技术，在rejuvenation周期间插入适当数目的检查点，以降低系统的宕机成本。丈中给出了系统的Detri网模型，并结合实例进行了分析。     

加强应收账款管理防范企业经营风险

分析了应收账款产生的原因及其影响,提出了应收账款的管理与控制对策。     

Aging effect of Co/C soft X-ray multilayer mirrors

Conclusion We have investigated the aging effect of Co/C soft X-ray multilayers prepared by dualfacing-target sputtering. It was found that phase-separation phenomena exist in the Co/C multilayers, which causes the reflectivity at grazing incidence to increase with time, and can be interpreted as positive enthalpy of Co-C mixing. It is evident that oxidation of the outermost layer of Co/C multilayers with Co deposited last is a potential problem in applications where the highest possible reflectivity is required.     

Differential changes in Cu,Zn and Mn superoxide dismutase activity in developing rat brain and liver

Summary The aim of our study was to assess the pattern of copper and zinc-containing superoxide dismutase (Cu, ZnSOD) and manganese-containing superoxide dismutase (MnSOD) activity from embryonic life to senescence in rat brain and liver. The two isoenzymes showed different profiles in the two organs examined. In particular, the cerebral MnSOD activity profile suggests a primary role during differentiation of this enzymatic form.